WO2003056368A1

WO2003056368A1 - Circularly polarizing plate and liquid crystal display device

Info

Publication number: WO2003056368A1
Application number: PCT/JP2002/013539
Authority: WO
Inventors: Keiichi Taguchi; Hiromoto Kitakouji; Kentaro Shiratsuchi
Original assignee: Fuji Photo Film Co., Ltd.
Priority date: 2001-12-25
Filing date: 2002-12-25
Publication date: 2003-07-10
Also published as: AU2002360036A1; TW200301375A; KR100956534B1; KR20040078649A; TWI266084B

Abstract

A circularly polarizing plate in a continuous length comprising: a polarizing film having an absorption axis neither parallel nor perpendicular to the lengthwise direction, at least one optical film provided at: at least one surface of the polarizing film; and an adhesive layer provided at an outside of at least one of the polarizing film and the optical film, wherein an angle between the absorption axis and the slow axis of at least one of the optical films is no less than 10 degrees and less than 90 degrees, and the formulation (I) and (II) defined in the specification are satisfied.

Description

DESCRIPTION CIRCULARLY POLARIZING PLATE AND LIQUID CRYSTAL DISPLAY DEVICE

Technical Field

The present invention relates to a circularly polarizing plate which is excellent in durability and yield, and which can realize a circularly polarized light for any incident light of a visible region and to a liquid crystal display device of high display quality using the same.

Background Art

With the diffusion of liquid crystal display device (hereinafter abbreviated as "LCD"), a demand for polarizing plates has sharply increased. The polarizing plate is generally made by laminating, on both side or one side of a polarizing film (membrane) having a polarizing ability, a protective film, a surface protecting film, a phase retarder (λ/4 plate, λ/2 plate) or like optical film to use. Further, an adhesive layer is commonly provided on the outside of at least one of the optical film and the polarizing film for adhering the polarizing plate to other member such as a liquid crystal display device via the adhesive layer .

As a material for the polarizing film, polyvinyl alcohol (hereinafter abbreviated as "PVA") has mainly been used . The polarizing film is formed by uniaxially stretching a PVA film, then dyeing with iodine or a dichroic dye or, alternatively, by stretching after dyeing and, further, cross-linking with a boron compound. The polarizing film is commonly produced by stretching in the direction where a continuous film travels (lengthwise (longitudinal) direction) (lengthwise stretching) , and hence the absorption axis of the polarizing film becomes almost parallel to the lengthwise direction.

A protective film to be laminated on at least one side of the polarizing film is desired to have a low retardation because, in case where the protective film has a birefringence, it can change the state of polarization. However, there still arises a problem that retardation increases depending upon ambient temperature and humidity. Hence, as a countermeasure for this problem, the protective film has been laminated on the polarizing film so that a slow axis of the protective film becomes vertical to a transparent axis of the polarizing film (i.e., a slow axis of the protective film becomes parallel to an absorption axis of the polarizing film) . In this case, however, it has been found that, since the slow axis of the protective film is parallel to the absorption axis of the polarizing film, the resulting laminate has a poor dimensional stability and involves a problem particularly in the point of stability with time . That is , with the conventional ones , it has been found that the protective film shrinks in the same direction when the polarizing film shrinks and that, though it resists the force through the adhesive layer, it can not sufficiently depress shrinkage of the polarizing plate . Also, a λ/4 plate (quarter wave plate) has find many applications relating to anti-reflective films and liquid crystal display devices and has been laminated on the polarizing film so that the optical axis of the polarizing film crosses the optical axis of the λ/4 plate.

On the other hand, in conventional LCDs, the polarizing plate is disposed so that the transparent axis of the polarizing plate is inclined 45 degrees with respect to longitudinal or transverse direction of a screen. Hence, in the case where the polarizing film is produced by the lengthwise stretching or transverse stretching as described above, it has been necessary in a step of cutting out individual polarizing plates from a roll-form produced polarizing plate to blank in the direction 45 degrees inclined to the lengthwise direction of the roll. In this case, there has been involved the problem that the yield of the polarizing plates is lowered or that polarizing plates after lamination are difficult to re-use, resulting in an increase of the amount of waste. In order to solve this problem, it has been proposed to obtain a polarizing film by inclining the orientation axis of a polymer in a desired degree with respect to the film-conveying direction. For example, in Japanese Patent Laid-Open No. 9912/2000, it is proposed to uniaxially stretch in a transverse or longitudinal direction and, at the same time, tensile-stretching the left and the right sides of the film in the stretching direction at different speeds in the transverse or longitudinal direction different from the stretching direction to thereby inclining the orientation axis with respect to the uniaxially stretching direction. In this method, however, it is difficult to obtain a desirably inclined angle (45 degrees with respect to the polarizing plate) in the case of using, for example, a tenter system wherein conveying speeds on the left side and the right side must be made different from each other, which can cause wrinkles and film slippage. To decrease the difference in conveying speed between the left side and the right side requires to prolong the stretching step, leading to an enormous const on the equipment. Also, Japanese Patent Laid-Open No. 182701/1991 proposes a method for producing a film having a stretching axis any angle θto the film-traveling direction by means of the mechanism wherein a plurality of pairs of film-gripping points are provided on both edges of a continuous film in a direction at an angle of θ to the film-traveling direction and, as the film travels, each of the pair points can stretch the film in the direction of θ. However, in this method, too, there arises a difference in film-traveling speed between the left side and the right side of the film, and slipage or wrinkles of the film is generated. In order to reduce them, it is necessary to extremely prolong the stretching step, leading to an enormous cost on the equipment.

Further, Japanese Patent Laid-Open No. 113920/1990 proposes a production process wherein both edges of a film are gripped by two rows of chacks traveling on the rails disposed within a predetermined traveling region so that their traveling distances differ between the two edges to thereby stretch the film in a direction obliquely crossing the lengthwise direction of the film. However, in this process, too, slippage or wrinkles are formed upon the oblique stretching, thus the process being inconvenient for optical films .

Also, Korean Patent Laid-Open No. P2001-005184 proposes a polarizing plate whose transparent axis is inclined by rubbing treatment. However, it is generally known that orientation by rubbing is effective only on a nano order at the most from the film surface, and such technique fails to sufficiently orient a polarizing element containing iodine or a dichroic dye . As a result, it has the defect that there results a low polarizing ability.

Disclosure of the Invention

Therefore, an object of the invention is to solve the various problems with the above-mentioned prior art .

That is, an object of the invention is to provide an obliquely oriented circularly polarizing plate in a continuous length which has an excellent durability, which can realize a circularly polarized light in a wide wavelength region, and which can improve a yield.

Another object of the invention is to provide a circularly polarizing plate having a protective film which has an excellent durability and can realize a circularly polarized light in a wide wavelength region .

A further object of the invention is to provide a process for producing the above-described circularly polarizing plate.

A still further object of the invention is to provide a reflective liquid crystal display device using a circularly polarizing plate which can correct deviation of the circularly polarizing degree on the shorter wavelength side to provide a high display quality with no deviation of color.

It has been found that the above-described objects of the invention can be attained by the following constitutions . 1) A circularly polarizing plate in a continuous length comprising a polarizing film having an absorption axis neither parallel nor perpendicular to the lengthwise direction, with at least one surface of the polarizing film being covered by at least one optical film and an adhesive layer being provided on the outside of at least one of the polarizing film and the optical film, wherein the angle between the absorption axis of the polarizing film and the slow axis of at least one optical film is 10 degrees to less than 90 degrees, the ratio of the transmission of the circularly polarizing plate in the direction parallel to the transparent axis to the transmission thereof in the direction perpendicular to the transparent axis when a 450-nm light is incident into the circularly polarizing plate from the polarizing film side after durability test of the circularly polarizing plate satisfies the following formulation (I) , and the ratio of the transmission of the circularly polazising plate in the direction paralel to the transparent axis to the transmission thereof in the direction perpendicular to the transparent axis when a 590-nm light is incident into the circularly polarizing plate from the polarizing film side after durability test of the circularly polarizing plate satisfies the following formulation (II) :

(I) 0.95 < T//(450) / Tl(450) < 1.05

(II) 0.95 < T//(590) / Tl(590) < 1.05 wherein T//(450) represents a transmission of the circularly polarizing plate in the direction parallel to the transparent axis thereof when the 450-nm light is incident from the polarizing film side, T_L(450) represents a transmission of the circularly polarizing plate in the direction perpendicular to the transparent axis thereof when the 450-nm light is incident from the polarizing film side, T// (590) represents a transmission of the circularly polarizing plate in the direction parallel to the transparent axis thereof when the 590-nm light is incident from the polarizing film side, and T_(590) represents a transmission of the circularly polarizing plate in the direction perpendicular to the transparent axis thereof when the 590-nm light is incident from the polarizing film side . 2) A circularly polarizing plate comprising a polarizing film having an absorption axis neither parallel nor perpendicular to the lengthwise direction, with at least one surface of the polarizing film being covered by at least one optical film and an adhesive layer being provided on the outside of at least one of the polarizing film and the optical film, wherein the angle between the absorption axis of the polarizing film and the slow axis of at least one optical film is 10 degrees to less than 90 degrees, the ratio of the transmission of the circularly polarizing plate in the direction parallel to the transparent axis to the transmission thereof in the direction perpendicular to the transparent axis when a 450-nm light is incident into the circularly polarizing plate from the polarizing film side after durability test of the circularly polarizing plate satisfies the formulation (I) described in the above-described 1) , and the ratio of the transmission of the circularly polarizing plate in the direction parallel to the transparent axis to the transmission thereof in the direction perpendicular to the transparent axis when a 590-nm light is incident into the circularly polarizing plate from the polarizing film side after durability test of the circularly polarizing plate satisfies the formulation (II) described in the above-described 1) . 3) A process for producing the circularly polarizing plate described in the above (1) or 2) , which comprises stretching a continuously fed polymer film by gripping both edges of the film through a gripping means and migrating the means in the lengthwise direction of the film while imparting tension thereto, with a locus LI of the gripping means starting from a point on one side of the polymer film where gripping substantially initiates to a point on the same side where gripping is substantially released, a locus L2 of the gripping means starting from a point on the other side of the polymer film where gripping substantially initiates to a point on the same side where gripping is substantially released, and a distance W between the two points where the gripping is released satisfying the following formula (1) and difference in lengthwise conveying speed between the two film-gripping means being less than 1% :

Formula (1) | L2 - L2 | > 0.4W

4) The process for producing a circularly polarizing plate as described in the above 3) , wherein at least one sheet of optical film having a slow axis parallel to the lengthwise direction is continuously laminated on at least one side of the polarizing film. 5) A liquid crystal display device wherein a circularly polarizing plate obtained by cutting out from the circularly polarizing plate in a continuous length described in the above-described 1) or the circularly polarizing plate described in 2) is adhered to use as at least one of circularly polarizing plates disposed on both sides of a liquid crystal cell.

It has been found that, in the circularly polarizing plate of the invention, shrinkage of the circularly polarizing film caused in the direction along with the absorption axis of the polarizing film due to crossing of the absorption axis of the polarizing film and the slow axis of the optical film can effectively be depressed by the presence of an optical film having the crossing optical axis, and that even an adhesive layer having a comparatively weak shrinkage-loosening force can sufficiently depress the shrinkage owing to the presence of the adhesive layer. Further, since the absorption axis of the polarizing film in the circularly polarizing plate of the invention in a continuous length is neither parallel nor perpendicular to the lengthwise direction (hereinafter such polarizing plate in a continuous length being sometimes merely referred to as "obliquely oriented polarizing plate") , the yield in the blanking step can remarkably be improved.

The invention further contains the following constitution :

6) A circularly polarizing plate containing at least a polarizing film having a polarizing ability, wherein a polarizing plate cut out from a polarizing plate in a continuous length having an absorption axis neither parallel nor perpendicular to the lengthwise direction is laminated with a wide-band λ/4 plate in which a λ/4 plate giving a birefringent light of 1/4 wavelength in phase retardation is combined with a λ/2 plate giving a birefringent light of 1/2 wavelength in phase retardation so that their optical axes cross each other .

7) A circularly polarizing plate containing at least a polarizing ilm having a polarizing ability and having a protective film laminated on at leastone side thereof , wherein a polarizing plate having th protective layer and the polarizing film in such relation that the angle between the slow axis of the protective film and the absorption axis of the polarizing film is 10 degrees to less than 90 degrees is laminated with a wide-band λ/4 plate in which a λ/4 plate giving a birefringent light of 1/4 wavelength in phase retardation is combined with a λ/2 plate giving a birefringent light of 1/2 wavelength in phase retardation so that their optical axes cross each other.

8) A process for producing a circularly polarizing plate, which comprises laminating a polarizing plate cut out from a polarizing plate in a continuous length with a wide-band λ/4 plate in which a λ/4 plate giving a birefringent light of 1/4 wavelength in phase retardation is combined with a λ/2 plate giving a birefringent light of 1/2 wavelength in phase retardation so that their optical axes cross each other, said polarizing plate being prepared by stretching a continuously fed film so that a locus LI of a gripping means starting from a substantial grip-initiating point on one edge of the film to a substantial grip-releasing point, a locus L2 of another gripping means starting from another substantial grip-initiating point on another edge of the polymer film to a substantial grip-releasing point and a distance W between the two substantial grip-releasing points satisfying the following formula (1) and that self-supporting properties of the polymer film are maintained, with maintaining the volatile content at a level of 5% or more, then allowing to shrink while reducing the volatile content: Formula (1) | L2-L1 | >0.4W

9) A liquid crystal display device, wherein at least one of circularly polarizing plates disposed on a liquid crystal cell is the circularly polarizing plate described in 6) or 7) above.

As is described above, the circularly polarizing plate of the invention is a circularly polarizing plate , wherein a polarizing plate cut out from a polarizing plate in a continuous length having an absorption axis neither parallel nor perpendicular to the lengthwise direction (hereinafter such polarizing plate in a continuous length being called in some cases "obliquely oriented" polarizing plate) is laminated with the above-mentioned wide-band λ/4 plate, and can improve the yield in the step of cutting out individual polarizing plates. In addition, the resultant circularly polarizing plates have an excellent polarizing ability.

In the invention, as a semi-transparent liquid crystal display device, the following constitutions are preferred. 10) A semi-transparent liquid crystal display device having a backlight, a circularly polarizing plate and a liquid crystal display element usable for both reflective and transparent display devices, wherein:

(a) a polarizing film in the circularly polarizing plate is disposed between a 1/4 wavelength plate and a protective film of 20 nm or less in in-plane retardation value, so that the angle between the absorption axis of the polarizing film and the slow axis of the protective film and the angle between the absorption axis of the polarizing film and the slow axis of the 1/4 wavelength plate are 20 degrees to less than 70 degrees; and

(b) the thickness of the circularly polarizing plate is 80 μm to 250 μm . 11) Aprocess for producing the a circularly polarizing plate for the semi-transparent liquid crystal display device described in the above 10) , which comprises gripping a continuously fed polymer film for the polarizing film at its both edges by means of a gripping means, and imparting a tension while moving the gripping means in the lengthwise direction of the film, during which the stretching is conducted so that: (i) a locus LI of a gripping means starting from a substantial grip-initiating point on one edge of the film to a substantial grip-releasing point, a locus L2 of another gripping means starting from another substantial grip-initiating point on another edge of the polymer film to a substantial grip-releasing point and a distance W between the two substantial grip-releasing points satisfy the following formula (1) and

(ii) that self-supporting properties of the polymer film are maintained, with maintaining the volatile content at a level of 5% or more, then the film is allowed to shrink while reducing the volatile content, and the resultant polarizing film is laminated with a protective film and/or a λl4 plate while maintaining the water content of the polarizing film at a level of 5% or less to thereby form a circularly polarizing plate .

Formula (1) | L2-L1 | >0.4

Brief Description of the Drawings

Fig. 1 is a schematic perspective view showing the relation between the optical film and the polarizing ilm in the circularly polarizing plate of the inveiton . Fig. 2 is a schematic plane view showing the situation of blanking the circularly polarizing plates of the invention. Fig. 3 is a schematic plane view showing one example of the method of the invention for obliquely stretching a polymer film. Fig .4 is a schematic plane view showing one example of the method of the invention for obliquely stretching a polymer film.

Fig .5 is a schematic plane view showing one example of the method of the invention or obliquely stretching a polymer film.

Fig . 6 is a schematic plane view showing one example of the method of the invention for obliquely stretching a polymer film.

Fig .7 is a schematic plane view showing one example of the method of the invention for obliquely stretching a polymer film.

Fig . 8 is a schematic plane view showing one example of the method of the invention for obliquely stretching a polymer film. Fig. 9 is a schematic plane view showing the stratum structure of the liquid crystal display device of Example 3.

Fig. 10 (10A to 10D) is a schematic cross-sectional view showing one embodiment of the circularly polarizing plate of the invention.

Fig. 11 (11A and 11B) is an illustration showing def nition of the coordinate axes .

Fig .12 is a schematic plane view showing the manner of cutting out conventional polarizing plates. Fig. 13 is a schematic view showing the semi-transparent liquid crystal display device of the invention .

[Description of the Reference Numerals and Signs]

(1) Direction of introducing a film;

(2) Direction of conveying the film to the nest step ;

(a) Step of introducing the film; (b) Step of stretching the film; (c) Step of conveying the stretched film to a next step ;

Al A position at which gripping of the film by a gripping means starts and from which stretching of the film initiates

(substantial grip-initiating point; right side) ;

Bl A position at which gripping of the film by a gripping means starts (left side) ; CI A position from which stretching of the film initiates (substantial grip-initiating point; left side) ;

Cx A standard position at which the film is released and at which stretching of the film is completed (substantial grip-releasing point; left side) ;

Ay A standard position at which stretching of the film is completed (substantial grip-releasing point; right side); I L1-L2 I Difference in travel between the film-gripping means on the left side and the film-gripping means on the right side;

W Substantial width of the film at the end of the stretching step; θ An angle between the stretching direction and the film-traveling direction; Center line of the film on the film-introducing side ; center line of the film to be conveyed to the next step; Locus of the film-gripping means (left side) ; Locus of the film-gripping means (right side) ; Film on the film-introducing side; Film to be conveyed to the next step; , 17' Points from which gripping of film starts on the left and right sides; , 18' Points at which gripping of film is released ; Center line of the film on the film-introducing side; center line of the film to be conveyed to the next step; Locus of the film-gripping means (left side) ; Locus of the film-gripping means (right side) ; Film on the film-introducing side; Film to be conveyed to the next step; , 27 ' Points from which gripping of film starts on the left and right sides; , 28' Points at which gripping of film is released; , 43, 53, 63 Loci of the film-gripping means

(left side) , 44, 54, 64 Loci of the film-gripping means

(right side) , 45, 55,65 Film on the film-introducing side , 56, 66 Film to be conveyed to the next step; Optical film , 71' Slow axis of the optical film; Adhesive layer or self-adhesive layer; Polarizing film; Absorption axis of the polarizing film; Lengthwise direction ; Transverse direction; Circularly polarizing plate; Iodine-containing polarizing plate; Adhesive layer; Liquid cell; Backlight ; Lengthwise direction ; 0 Circularly polarizing plate; 0 Polarizing plate; 1 Adhesive layer; 2 λ/2 Plate; 3 Adhesive layer; 4 λ/4 Plate; 103 Front-side substrate;

104 Back-side substrate;

105 Liquid crystal portion;

106 Front electrode; 107 Rear electrode;

108 Front-side circularly polarizing plate; 1110 Back-side circularly polarizing electrode ;

112 Backlight;

113 Two-terminal element; 1122 Signal electrode ;

1124 Insulating layer; 125 Upper electrode within the two-terminal element ;

141 Semi-transparent liquid crystal display device;

142 Color filter

The invention is described in more detail below. The circularly polarizing plate of the invention contains a polarizing film having a polarizing ability , with at least one optical film being provided on both sides or one side of the polarizing film through an adhesive layer or a tacky layer. Here, the optical film of the invention means a film necessary for exhibiting performance as a circularly polarizing plate. Specifically, it means a surface protecting film, a protective film or a phase retardation film. The phase retardation film may be any one that can provide circularly polarizing properties when superimposed on a linear circularly polarizing plate, and is not particularly limited as to the number of the film sheets. Also, the surface protecting film includes a hard coat layer, an A6 layer, an AR layer and a CV layer , with two or more thereof being optionally used in combination. Additionally, it suffices that a slow axis of at least one of two or more optical films crosses the absorption axis of the polarizing film as mentioned hereinbefore . Apractical circularly polarizing plate is usually obtained by producing a circularly polarizing plate in a continuous length (usually in a roll shape) and cutting out depending upon the end-use thereof. The term "circularly polarizing plate" as used in the invention is used in the meaning of including both the circularly polarizing plate in a continuous length and a circularly polarizing plate obtained by cutting out therefrom unless otherwise specified. In the invention, the angle between the lengthwise direction of the circularly polarizing plate in a continuous length and the absorption axis of the polarizing film is freely set in the range of from 10 degrees to less than 90 degrees, and hence a proper angle can easily be selected upon using in combination with other optical member .

As is described hereinbefore, the circularly polarizing plate of the invention in a continuous length is characterized in that its absorption axis is neither parallel nor perpendicular to the lengthwise direction (i.e., obliquely oriented). Specifically, in a circularly polarizing plate 85 shown in Fig. 1 wherein an optical film 70 having a slow axis 71 is laminated on at least one side of a polarizing film 80 having an absorption axis 81 through, as needed, an adhesive layer 74, the circularly polarizing plate is characterized in that the angle θbetween the absorption axis 81 of the polarizing film and the stretching axis of the optical film (i.e., a dotted line 71') is in the range of from 10 degrees to less than 90 degrees. In this range, there is obtained an excellent durability . The angle between the lengthwise direction of the circularly polarizing plate in a continuous length and the absorption axis is preferably 20 degrees to 70 degrees, more preferably 40 degrees to 50 degrees, particularly preferably 44 to 46 degrees. This characteristic feature serves to permit to cut out the circularly polarizing plates as shown in Fig. 2, thus markedly improving the yield in the step of cutting out the circularly polarizing plates Here, the angle between the absorption axis of the polarizing film and the slow axis of the optical film can be estimated by separating the optical film and the polarizing film of the circularly polarizing plate from each other and measuring the absorption axis of the polarizing film and the slow axis of the optical film. Also, the absorption axis of the polarizing film is defined as an axis direction which gives the maximum transmission density when the polarizing plate is superimposed on a polarizing plate whose absorption axis is known in a cross-Nicol position. Also, the slow axis of the optical film is defined as an axis direction which gives the maximum birefringence when birefringence within the optical film plane is measured . The angle between the absorption axis of the polarizing film and the slow axis of the optical film means the angle between the two axis directions , and is preferably from 10 degrees to less than 90 degrees . The transmission density of the polarizing film can be measured by means of a transmission densitometer (for example, X Rite. 310TR fitted with a Status M filter) , and the refractive index of the protective film can be measured by a polarization analyzer (for example, a polarization analyzer AEP-10 made by Shimazu Seisakusho K.K.). Further, in the case where the optical film whose slow axis crosses with the absorption axis of the polarizing film, the slow axis 71 of the protective film 70 in Fig. 1 mentioned above is parallel to the lengthwise direction 82 or the transverse direction 83 of the polarizing plate, and the absorption axis 81 of the polarizing film 80 meets the lengthwise direction 82 or the transverse direction 83 at an angle of preferably 20 to 70 degrees, more preferably 40 degrees to 50 degrees, particularly preferably 44 to 46 degrees. It is most preferred to use a roll-formed polarizing plate wherein a protective film whose slow axis is parallel to the lengthwise direction is laminated on at least one side of a polarizing film whose absorption axis 81 meets the lengthwise direction 82 at an angle of about 45 degrees. Such polarizing plate roll enables to obtain polarizing plates in a good yield.

Also, the circularly polarizing plate of the invention preferably has a single plate transmission of 35% or more at 550 nm or more and a polarizing degree of 80% or more at 550 nm . The single plate transmission is preferably 40% or more, and the polarizing degree is preferably 95.0% or more, more preferably 99% or more, particularly preferably 99.9% or more. Additionally, in the invention , the transmission means the single plate transmission unless otherwise specified. The circularly polarizing plate of the invention has such an excellent single plate transmission and polarizing degree that, in the case of using it for a liquid crystal display device, it can enhance its contrast, thus being advantageous. The constitution of the circularly polarizing plate of the invention comprises at least one optical film and one polarizing film which are disposed so that the angle between the slow axis of the optical film and the absorption axis of the polarizing film becomes from 10 degrees to less than 90 degrees.

The ratio of the transmission of the circularly polarizing plate of the invention in a direction parallel to the transparent axis when a 450-nm light is incident from the polarizing film side of the circularly polarizing plate (T//(450)) to the transmission thereof in a direction perpendicular to the transparent axis (T_L(450)) satisfies the following formula :

(I) 0.95 <T// (450) /Tl(450)<1.05 Further, the formula of 0.98

<T// (450) /T_I_(450)<1.02 is more preferred. Also, the ratio of the transmission of the circularly polarizing plate of the invention in a direction parallel to the transparent axis when a 590-nm light is incident from the polarizing film side of the circularly polarizing plate (T// (590) ) to the transmission thereof in a direction perpendicular to the transparent axis (TJL(590)) satisfies the following formula :

(II) 0.95 <T// (590) /Tl(590)<1.05 Further, the formula of 0.98 <T// (590) /T±(590)<1.02 is more preferred.

In the case of using a single sheet of optical film as a λ/4 plate, it is preferred that the retardation value measured at a wavelength of 450 nm (Re (450)) is in the range of from 100 to 125 nm, the retardation value measured at a wavelength of 590 nm (Re (590)) is in the range of from 120 to 160 nm, and the relation between Re (590) and Re (450) is such that Re (590) - Re (450) >2 nm . The relation is more preferably such that Re(590) - Re(450)>5 nm, most preferably Re(590) - Re(450)>10 nm. It is preferred that the retardation value measured at a wavelength of 450 nm (Re (450)) is in the range of from 108 to 120 nm, the retardation value measured at a wavelength of 550 nm (Re (550)) is in the range of from 125 to 142 nm, the retardation value measured at a wavelength of 590 nm (Re (590)) is in the range of from 130 to 152 nm, and the relation between Re (590) and Re (550) is such that Re (590) - Re(550) >2 nm . The relation is more preferably such that Re (590) - Re (550) >5 nm, most preferably Re (590) - Re (550) >10 nm . It is also preferred that the relation between Re (450) and Re(550) is such that Re(550) - Re(450)>10 nm .

In the case of using a single sheet of optical film as a λ/2 plate, it is preferred that the retardation value measured at a wavelength of 450 nm (Re (450)) is in the range of from 200 to 250 nm, the retardation value measured at a wavelength of 590 nm (Re (590)) is in the range of from 240 to 320 nm, and the relation between Re (590) and Re (450) is such that Re (590) - Re (450) >4 nm . The relation is more preferably such that Re(590) - Re(450)>10 nm, most preferably Re(590)

- Re(450)>20 nm .

It is preferred that the retardation value measured at a wavelength of 450 nm (Re(450)) is in the range of from 216 to 240 nm, the retardation value measured at a wavelength of 550 nm (Re (550)) is in the range of from 250 to 284 nm, the retardation value measured at a wavelength of 590 nm (Re (590)) is in the range of from 260 to 304 nm, and the relation between Re (590) and Re (550) is such that Re (590) - Re (550) >4 nm . The relation is more preferably such that Re (590) - Re(550)>10 nm, most preferably Re(590) - Re(550)>20 nm . It is also preferred that the relation between Re(450) and Re(550) is such that Re(550) - Re(450)>20 nm .

The retardation value (Re) is calculated according to the following formula:

Retardation value (Re) = (nx-ny) x d wherein nx represents a refractive index in the slow axis direction within the plane of the phase retarder (maximum in-plane refractive index) , ny represents a refractive index in the direction vertical to the slow axis within the plane of the phase retardation plate, and d represents the thickness of the phase retardation plate (nm) .

The optical film preferably satisfies the following formula as a single film: l<(nx - nz)/(nx - ny)<2 wherein nx represents a refractive index in the slow axis direction within the plane of the phase retarder (maximum in-plane refractive index) , ny represents a refractive index in the direction vertical to the slow axis within the plane of the phase retarder, and nz represents a refractive index in the direction of thickness .

The optical film having the above-mentioned optical properties can be produced from the polymer by the process described below.

(Phase retardation film)

As a phase retardation film to be used in the invention, there is illustrated a phase retarder described in, for example, Japanese Patent Laid-Open Nos. 27118/1993 and 27119/1993 wherein a birefringent film having a larger retardation and a birefringent film having a smaller retardation are laminated so that their optical axes cross at right angles. With this film, if difference in retardation between the two films is λ/4 all over the visible light region , the retardation plate theoretically functions as a λ/4 plate all over the visible light region. Also, it is possible to use a phase retardation plate described in Japanese Patent Laid-Open No. 68816/1998 wherein a polymer film functioning as a λ/4 plate at a specific wavelength and a polymer film of the same material functioning as a λ/2 plate at the same wavelength are laminated on each other, and which functions as a λ/4 plate over a wide wavelength region , and a phase retarder described in Japanese Patent Laid-Open No. 90521/1998 wherein two polymer films are laminated so as to attain λ/4 over a wide wavelength region.

Further, in the invention, a phase retarder described in Japanese Patent Laid-Open No . 137116/2000 and WO00/26705 which shows, as a single polymer film, a smaller phase difference for a shorter wavelength for measurement. This technique of using one phase retardation film is preferred in that the production steps can be simplified, but it has also been found that the resulting circularly polarized light is insufficient. Therefore, in the invention , in the case where the phase retardation film to be laminated on both sides or one side of the polarizing film having a polarizing ability via an adhesive layer or a tacky layer comprises a single film, it is preferred that deviation of circularly polarizing degree on the shorter wavelength side to be caused when the phase retardation film is laminated on the polarizing film so that the angle between the slow axis of the phase retardation film and the absorption axis of the polarizing film becomes in the range of from 10 degrees to less than 90 degrees is corrected by using a retardation-increasing agent to thereby obtain a circularly polarizing plate having a wide wavelength region. This is based on the founding that an insufficient contrast level in a reflection type liquid crystal display using a conventional phase retarder is caused by deviation of circularly polarizing degree on the shorter wavelength side upon an incident light passing through the polarizing plate and the λ/4 film.

(Polymer film for phase retardation film)

It is preferred to use a polymer film having a light transmission of 80% or more.

As a polymer film to be used in the invention, those which difficultly exhibit birefringence by outer force are preferred, and examples thereof include cellulose-based polymers such as triacetyl cellulose and diacetyl cellulose ; norbornene-basedpolymers such as Artone and Zeonex , and polymethyl methacrylate . In particular, cellulose esters are preferred, with lower fatty acid esters of cellulose being more preferred. The term " lower faty acids" means fatty acids containing 6 or less carbon atoms. The number of carbon atoms is preferably 2 (cellulose acetate) , 3 (cellulose propionate) or 4 (cellulose butyrate) . Cellulose acetate is particularly preferred. It is also possible to use amixed fatty acid ester such as cellulose acetate propionate or cellulose acetate butyrate.

Also, even conventionally known polymers easily exhibiting birefringence such as polycarbonate or polysulfone may be used by reducing the birefringence-exhibiting properties through modification with molecules described in WOOO/26705. As a polymer film for the phase retardation film, it is preferred to use cellulose acetate having an acetylation degree of 57.0 to 61.5%.

The acetylation degree means the amount of bound acetic acid per unit weight of cellulose. The acetylation degree is in accordance with the measurement and calculation of acetylation degree in ASTM :D-817-91 (method for testing cellulose acetate or the like) . The viscosity-average polymerization degree (DP) of the cellulose ester is preferably 250 or more, more preferably 290 or more.

Also, the cellulose ester to be used in the invention has a narrow molecular weight distribution in terms of Mw/Mn (Mw : weight-average molecular weight ; Mn : number-average molecular weight) according to gel permeation chromatography. As a specific Mw/Mn value, a value of from 1.0 to 1.7 is preferred, with 1.3 to 1.65 being more preferred, and 1.4 to 1.6 being still more preferred.

In order to improve adhesion between the polymer film and a layer to be provided thereon (an adhesive layer, an orientation film or an optically anisotropic layer) , the polymer film may be subjected to surface treatment (for example, glow discharge treatment, corona discharge treatment, UV ray treatment or flame treatment) . These polymer films preferably contain a UV ray absorbent, and the like . Also , as is described in Japanese Patent Laid-Open No. 333433/1995, an adhesive layer (undercoating layer) may be provided on the polymer film. The thickness of the adhesive layer is preferably 0.1 μm to 2 μm, more preferably 0.2 μm to 1 μm .

(Control of retardation)

Amethod of giving an outer force such as stretching is generally conducted for adjusting retardation of a polymer film for a phase retardation film. It is also possible to use as a retardation-increasing agent an aromatic compound having at least two aromatic rings as described in European Patent No. 911656A2.

The aromatic compound is used in an amount of from 0.01 to 20 parts by weight per 100 parts by weight of cellulose acetate. It is preferred to use the aromatic compound in an amount of from 0.05 to 15 parts by weight per 100 parts by weight of cellulose acetate, with an amount of from 0.1 to 10 parts by weight being more preferred. It is possible to use two or more of the aromatic compounds in combination. Examples of the aromatic ring in the aromatic compound include aromatic hetero rings in addition to aromatic hydrocarbon rings. Particularly preferably, the aromatic hydrocarbon ring is a 6-membered ring (i.e. , benzene ring) . The aromatic hetero ring is generally an unsaturated hetero ring. The aromatic hetero ring is preferably a 5-, 6- or 7-membered ring, with a 5- or 6-membered ring being more preferred . The aromatic hetero ring generally contains maximum double bonds . As the hetero atoms, a nitrogen atom, an oxygen atom and a sulfur atom are preferred, with a nitrogen atom being particularly preferred. Examples of the aromatic hetero ring include a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, an isoxazole ring, a thiazole ring , an isothiazole ring , an imidazole ring, a pyrazole ring , a furazane ring , a triazole ring , a pyran ring, a pyridine ring, a pyridazine ring, a pyrimidine ring, a pyrazine ring and a 1 , 3 , 5-triazine ring .

As the aromatic ring, a benzene ring, a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, a thiazole ring, an imidazole ring, a triazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring and a 1 , 3 , 5-triazine ring are preferred.

The number of the aromatic rings the aromatic ring has is preferably 2 to 20, with 2 to 12 being more preferred, 2 to 8 being still more preferred, and 3 to 6 being most preferred. Also, it is preferred for the aromatic compound to have at least one 1 , 3 , 5-triazine ring as the aromatic ring. The relations between two aromatic rings can be classified into three cases: (a) a case where two aromatic rings form a fused ring; (b) a case where two aromatic rings are directly bound to each other through a single bond; and (c) a case where two aromatic rings are bound to each other through a linking group (spiro bond not being formed because they are aromatic rings) . The relation may be any of (a) to (c) .

Examples of the case (a) where a fused ring (a fused ring composed of two or more aromatic rings) is formed include an indene ring, a naphthalene ring, an azulene ring, a fluorene ring, a phenanthrene ring, an anthracene ring, an acenaphthylene ring, a naphthacene ring, a pyrene ring, an indole ring, an isoindole ring, a benzofuran ring , a benzothiophene ring , an indolizine ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, a benzotriazole ring , apurinering, an indazole ring, a chromene ring, a quinoline ring, an isoquinoline ring , a quinolizine ring , a quinazoline ring, a cinnoline ring, a quinoxaline ring, a phthalazine ring, pteridine ring, a carbazole ring, an acridine ring, a phenanthridine ring, a xanthene ring, a phenazine ring, a phenothiazine ring, a phenoxtine ring, a phenoxazine ring and a thianthrene ring. A naphthalene ring, an azulene ring, an indole ring, a benzoxazole ring, a benzothiazole ring, a benzimidazole ring, a benzotriazole ring and a quinoline ring are preferred.

The single bond in the case (b) is preferably a bond between carbon atoms of two aromatic rings. It is also possible to form an alicyclic ring or a non-aromatic hetero ring by binding two aromatic rings through two or more single bonds .

The linking group in the case (c) is preferably bound to the carbon atoms of two aromatic rings . The linking group is preferably an alkylene group, an alkenylene group , an alkynylene group , -CO-, -O- , -NH-, -S- or the combination thereof. Examples of the linking group composed of the combination are shown below. Additionally, the left-right relation of the following linking groups may be reversed.

cl : -CO-O- c2 : -CO-NH- c3 : alkylene-o- c4 : -NH-CO-NH- c5 : -NH-CO-O- c6 : -O-CO-O- c7 : -O-alkylene-O- c8 : -CO-alkenylene- c9: -CO-alkenylene-NH- clO: -CO-alkenylene-O- cll -alkylene-CO-O-alkylene-O-CO-alkylene^■ cl2 -O-alkylene-CO-O-alkylene-O-CO-alkylene-O- cl3 -O-CO-alkylene-CO-O- cl4 -NH-CO-alkenylene- cl5 -0-CO-alkenylene-

The aromatic group and the linking group may have a substituent or substituents .

Examples of the substituent include a halogen atom (F , CI , Br or I) , a hydroxyl group, a carboxyl group, a cyano group, an amino group, a nitro group, a sulfo group, a carbamoyl group, a sulfamoyl group, a ureido group, an alkyl group, an alkenyl group, an alkynyl group, an aliphatic acyl group, an aliphatic acyloxy group, an alkoxy group, an alkoxycarbonyl group, an alkoxycarbonylamino group, an alkylthio group, an alkylsulfonyl group, an aliphatic amido group, an aliphatic sulfonamido group, an aliphatic substituted amino group, an aliphatic substituted carbamoyl group, an aliphatic substituted sulfamoyl group, an aliphatic substituted ureido group and a non-aromatic heterocyclic group.

The number of carbon atoms of the alkyl group is preferably 1 to 8. Chained alkyl groups are more preferred than cyclic alkyl groups, with straight-chained alkyl groups being particularly preferred. The alkyl group may further have a substituent or substituents (e.g., a hydroxyl group, a carboxyl group, an alkoxy group or an alkyl-substituted amino group) . Examples of the alkyl group (including substituted group) include methyl, ethyl, n-butyl, n-hexyl, 2-hydroxyethyl , 4-carboxybutyl , 2-methoxyethyl and 2-diethylaminoethyl . The number of carbon atoms of the alkenyl group is preferably 2 to 8. Chained alkenyl groups are more preferred than cyclic alkenyl groups, with straight-chained alkenyl groups being particularly preferred. The alkenyl group may further have a substituent or substituents . Examples of the alkenyl group include vinyl, allyl and 1-hexenyl.

The number of carbon atoms of the alkynyl group is preferably 2 to 8. Chained alkenyl groups are more preferred than cyclic alkynyl groups , with straight-chained alkynyl groups being particularly preferred. The alkynyl group may further have a substituent or substituents. Examples of the alkenyl group include ethynyl , 1-butynyl and 1-hexynyl. The number of carbon atoms of the aliphatic acyl group is preferably 1 to 10. Examples of the aliphatic acyl group include acetyl, propanoyl and butanoyl .

The number of carbon atoms of the aliphatic acyloxy group is preferably 1 to 10. Examples of the aliphatic acyloxy group include acetoxy.

The number of carbon atoms of the alkoxy group is preferably 1 to 8. The alkoxy group may further have a substituent or substituents . Examples of the alkoxy group (including substituted alkoxy group) include methoxy, ethoxy, butoxy and methoxyethoxy . The number of carbon atoms of the alkoxycarbonyl group is preferably 2 to 10. Examples of the alkoxycarbonyl group include methoxycarbonyl and ethoxycarbonyl . The number of carbon atoms of the alkoxycarbonylamino group is preferably 2 to 10. Examples of the alkoxycarbonylamino group include methoxycarbonylamino and ethoxycarbonylamino .

The number of carbon atoms of the alkylthio group is preferably 1 to 12. Examples of the alkylthio group include methylthio, ethylthio and octylthio .

The number of carbon atoms of the alkylsulfonyl group is preferably 1 to 8. Examples of the alkylsulfonyl group include methanesul onyl and ethanesulfonyl . The number of carbon atoms of the aliphatic amido group is preferably 1 to 10. Examples of the aliphatic amido group include acetamido.

The number of carbon atoms of the aliphatic sulfonamido group is preferably 1 to 8. Examples of the aliphatic sulfonamido group include methanesulfonamido , butansulfonamido and n-octanesulfonamido .

The number of carbon atoms of the aliphatic substituted amino group is preferably 1 to 10. Examples of the aliphatic substituted amino group include dimethylamino , diethylamino and 2-carboxyethylamino .

The number of carbon atoms of the aliphatic substituted carbamoyl group is preferably 2 to 10. Examples of the aliphatic substituted carbamoyl group include methylcarbamoyl and diethylcarbamoyl .

The number of carbon atoms of the aliphatic substituted sulfamoyl group is preferably 1 to 8. Examples of the aliphatic substituted sulfamoyl group include methylsulfamoyl and diethylsulfamoyl .

The number of carbon atoms of the aliphatic substituted ureido group is preferably 2 to 10. Examples of the aliphatic substituted ureido group include ethylureido . Examlples of the non-aromatic heterocyclic group include piperidino and morpholino.

The molecular weight of the retardation-increasing agent is preferably 300 to 800. As to the retardation-increasing agent, description is also given in Japanese Patent Laid-Open Nos.

111914/2000 and 275434/2000 , and those compounds which are described in these publications may be used.

The phase retardation film of the invention is preferably a phase retardation film wherein a λ/4 plate (a birefringent film which gives a birefringent light of 1/4 wavelength in phase retardation) and a λ/2 plate (a birefringent film which gives a birefringent light of 1/2 wavelength in phase retardation) are combined so that their optical axes are crossed each other at a predesigned angle. In the invention, this phase retardation film is in some cases specifically referred to as "wide-band λ/4 plate" .

The wode-band λ/4 plate to be preferably used in the invention is described in detail below.

Coordinate axes are defined as shown in Fig. 11A, and an optical element is disposed within the yz plane and the light proceeds along with the x axis. Also, the direction of the axis of the optical element is measured in terms of an angle taking the clockwise direction from the y axis within the yz plane to be positive as shown in Fig. 11B. The same definitions apply in the following descriptions as well.

In Fig. 10A, 124 designates a λ/4 plate, 121 and

123 designate adhesive agents, 122 designates a λ/2 plate, and 110 designates a polarizing plate. As is shown in Fig. 10B, the stretching axis of the λ/4 plate

124 is disposed in a direction of 20 degrees and, as is shown in Fig. 10C, the stretching axis of the λ/2 plate 122 is disposed in a direction of 75 degrees. The polarizing plate 110 is disposed so that the transparent axis is in a horizontal direction as shown in Fig. 10D. This element is designed so that, when a light is incident into this element from the side of the λ/4 plate, a counter-clockwise circularly polarized light is absorbed by the polarizing plate and only a clockwise circularly polarized light transmits . The circularly polarizing plate 100 in a practical form shown in Fig. 10A to 10D is disposed so that wavelength dispersion properties of retardation of the λ/4 plate are canceled by the properties of the λ/2 plate 122, and hence it can show almost constant properties as a circularly polarizing plate in the visible light range (400 nm to 700 nm) . Also, proper characteristic properties can be selected by properly changing the angle between the λ/2 plate and the λ/4 plate depending upon demanded specification such as necessary wavelength region and, further, wavelength diffusion properties can be improved. As to the angle between the λ/2 plate 122 and the λ/4 plate 124 , it is preferred to properly select such angle that the ratio of retardation for the wavelength of an incident light becomes constant. Also, in the invention, when refractive indexes of at least one of the wavelength plates constituting the phase retardation film in the directions of rectangular axes within the plane of the wavelength plate and in the direction of the film thickness are respectively referred to as nx, ny and nz, they preferably satisfy the relations of nx > ny and (nx-ny) <1. The wavelength diffusion of retardation can be controlled by using a λ/4 plate which shows a retardation , defined by the product of the difference in refractive index of the birefringent light (Δn) and the thickness (d) ( Δnd) , of 1/4 of designed wavelength (λO) and a λ/2 plate which shows a retardation of 1/2 are laminated at a predesigned angle. In particular, it can make the ratio of retardation to wavelength (λ) of incident light (Δnd/λ) almost at a constant level , thus improving characteristic properties of an optical system using the phase retardation film.

The wavelength plate having such properties is characterized in that, when a light is incident not in the direction vertical to the wavelength plate but in an oblique direction, it shows less retardation. Therefore, when a phase retardation film (wide-band λ/4 plate) is prepared by using the wavelength plate having such properties, wavelength diffusion properties can be controlled in a wide incident angle region, thus advantages of the invention being more enhanced .

The λ/2 plate or the λ/4 plate of the invention can usually be prepared by stretching a high polymer film. In the invention, polycarbonate, triacetyl cellulose, polyolefin, etc. are preferred which are popularly used as materials for wavelength plates . The thickness is not particularly limited, but is preferably in the range of from 1 μm to 1000 μ . Lamination of the λ/2 plate and the v /4 plate and lamination of the wide-band λ/4 plate and the polarizing plate may be conducted by using a known contact-bonding type or hot-melt type tacky agent or adhesive. The angle of laminating the wide-band λ/4 plate and the polarizing plate is so properly selected that the resultant laminate may exhibit a certain performance as a circularly polarizing plate in a visible light region .

(Protective film)

The polarizing ilm of the invention is preferably used as a polarizing plate by laminating a protective film on both sides or one side thereof. Kind of the protective film is not particularly limited, and there maybe used cellulose acylates such as cellulose acetate and cellulose acetate butyrate, polycarbonate, polyolefin, polystyrene and polyester. The protective film for use in the polarizing plate is required to have such physical properties as transparency, proper moisture vapor permeability, low birefringence, and proper rigidity. From an overall point of view, cellulose acylates are preferred, with cellulose acetate being particularly preferred.

The protective film is usually fed in a roll form, and is preferably continuously laminated on a circularly polarizing plate in a continuous length so that lengthwise direction of the former coincides with that of the latter . Here, orientation axis (slow axis) of the protective film may be in any direction but, from the standpoint of convenience in operation, the orientation axis of the protective film is preferably in parallel with the lengthwise direction.

Also, the angle between the slow axis (orientation axis) of the protective film and the absorption axis (stretching axis) of the polarizing film is not particularly limited, either, and can properly be selected according to the end-use. Since the absorption axis of the circularly polarizing plate of the invention in a continuous length is not parallel to the lengthwise direction, there can be obtained a polarizing plate wherein the absorption axis of the polarizing ilm is not parallel to the orientation axis of the protective film, by continuously laminating the protective film whose orientation axis is parallel to the lengthwise direction on the circularly polarizing plate of the invention in a continuous length . An effective dimensional stability-improving effect can be exhibited when the angle between the slow axis of the protective film and the absorption axis of the polarizing film is in the range of 10 degrees to less than 90 degrees, more preferably 20 degrees to 80 degrees .

Physical properties of the protective film may be optional depending upon the end-use, but typical preferred values for use in a common transmissive LCD are shown below. The thickness of the film is preferably from 5 to 500 μm , more preferably from 20 to 200 μm, particularly preferably from 20 to 100 μm , in view of handling properties and durability. The retardation value is preferably from 0 to 150 nm , more preferably from 0 to 20, particularly preferably from

0 to 5 nm , at 632.8 nm . It is preferred that the slow axis of the protective film is substantially parallel or vertical to the absorption axis of the polarizing film in view of preventing a linearly polarized light from becoming ellipsoidally polarized. However, in the case of imparting the protective film the function of changing polarizing ability that a phase retardation plate has, this does not apply, and the angle between the absorption axis of the polarizing plate and the slow axis of the protective film may be any.

The visible light transmission of the protective film is preferably 60% or more , particularly pre erably 90% or more. The dimensional reduction after being treated at 90 C for 120 hours is preferably 0.3 to 0.01%, particularly preferably 0.15 to 0.01%. The anti-tension value measured by a tensile test of the film is preferably 50 to 1000 MPa , particularly preferably 100 to 300 MPa. The moisture vapor permeability of the film is preferably 100 to 800 g/m². day , particularly preferably 300 to 600 g/m². day . Needless to say, the application of the invention is not limited to the above-described values .

Cellulose acylates preferred as the protective film are described in detail below. Preferred cellulose acylates are those which satisfy all of the following formulae (I) to (IV) with respect to degree of substitution to the hydroxyl group of the cellulose: (I) 2.6<A+B<3.0 (II) 2.0<A<3.0 ( I I I ) O≤B≤O . 8

( IV) 1 . 9<A-B

In the above formulae, A and B represent a substitution degree of the acyl group substituted for the hydroxyl group of cellulose, and A represents a substitution degree of an acetyl group, andB represents a substitution degree of an acyl group having 3 to 5 carbon atoms . Cellulose has three hydroxyl groups per its glucose unit, and the above-described values represent substitution degrees based on the number of the hydroxyl groups of 3.0, thus the maximum value being 3.0. Cellulose triacetate generally has a substitution degree A of from 2.6 to 3.0 (in this case , the proportion of non-substituted hydroxyl groups is maximally 0.4) and a substitution degree B of 0. As the cellulose acylate for use in the protective film for the polarizing plate , cellulose triacetate wherein all of the acyl groups are acetyl groups and those wherein the proportion of the acetyl group is 2.0 or more, the substitution degree of the acyl group having 3 to 5 carbon atoms is 0.8 or less, and the degree of non-substituted hydroxyl groups is 0.4 or less are preferred. When an acyl group having 3 to 5 carbon atoms is used, its substitution degree is particularly preferably 0.3 or less from the point of physical properties. Additionally, the substitution degree is obtained by measuring binding degree of acetic acid and an aliphatic acid having 3 to 5 carbon atoms substituted for the hydroxyl groups of cellulose, followed by calculation. The measuring method may be conducted according to ASTM D-817-91.

The acyl group having 3 to 5 carbon atoms to be used as well as the acryl group are a propionyl group

(C₂H₅CO-) , a butyryl group (C₃H₇CO-) (n-, iso-) and a valeryl group (C₄H₉CO-) (n-, iso-, sec-, tert-) . Of these, n-type ones are preferred in view of mechanical strength when formed into a film and ease upon dissolution, with n-propionyl group being particularly preferred. In the case where the substitution degree of acetyl group is lowered, there results reduced mechanical strength and resistance to moist heat. In the case where the substitution degree of the acyl group having 3 to 5 carbon atoms is increased, there results an improved solubility in an organic solvent. Good properties can be obtained as long as the substitution degrees thereof are within the above-described ranges .

The polymerization degree of cellulose acylate (viscosity average) is preferably 200 to 700, particularly preferably 250 to 550. The viscosity average polymerization degree can be measured by means of an Ostwald' s viscometer , and conducting calculation according to the following formula using the measured intrinsic viscosity [η] of cellulose acylate: DP = [η]/Km wherein DP represents a viscosity average polymerization degree, and Km represents a constant of 6 x 10-⁴.

As the starting material for cellulose acylate, there are illustrated cotton fiber linter and woodpulp .

Cellulose acylate obtained from any starting cellulose may be used, and a mixture thereof may be used as well.

(Preparation of polymer film) The above-mentioned cellulose acylate is commonly produced by a solvent casting method. The solvent casting method is a method wherein cellulose acylate and various additives are dissolved in a solvent to prepare a thick solution (hereinafter referred to as "dope") , this is cast onto an endless support such as a drum or a band, and the solvent is evaporated to form a film. The dope is preferably adjusted so that the amount of solids becomes 10 to 40% by weight. The surface of the drum or band is preferably finished in a mirror state . As to the casting method and the drying method in the solvent casting method, descriptions are given in US Patent Nos .2,336,310, 2,367,603, 2,492,078, 2,492,977, 2,492,978, 2,607,704, 2,739,069 and 2,739,070, British Patent Nos. 640731 and 736892, Japanese Patent Publication Nos. 4554/1970 and

5614/1974, Japanese Patent Laid-Open Nos .176834/1985, 203430/1985 and 115035/1987.

A method of casting two or more dope layers is also preferably employed. In the case of casting a plurality of dopes, a film may be formed by casting dope-containing solutions respectively through a plurality of casting slits provided at intervals in the support-migrating direction to thereby form dope layers. For example, those methods may be applicable which are described in Japanese Patent Laid-Open Nos . 158414/1986, 122419/1989 and 198285/1999. Also, a film may be formed by casting the cellulose acylate solution through two casting slits. This may be conducted according to the methods described in, for example, Japanese Patent Publication No. 27562/1985, Japanese Patent Laid-Open Nos. 947245/1986, 104813/1986, 158413/1986 and 34933/1994. Also, a casting method of surrounding a high-viscosity dope flow by a low-density dope and extruding the high- and low-viscosity dopes at the same time, described in Japanese Patent Laid-Open No. 162617/1981 is preferably used as well.

Examples of the organic solvent for dissolving cellulose acylate include hydrocarbons (e.g. , benzene and toluene), halogenated hydrocarbons (e.g., methylene chloride and chlorobenzene) , alcohols (e.g. , ethanol and diethylene glycol) , ketones (e.g., acetone) , esters (e.g. , ethyl acetate and propyl acetate) and ethers (e.g., tetrahydrofuran and methyl cellosolve) . Halogenated hydrocarbons having 1 to 7 carbon atoms are preferably used, with methylene chloride being most preferably used. In view of physical properties such as cellulose acylate-dissolving properties, peeling properties from the support, mechanical strength of resultant films and optical properties, it is preferred to use one or several kinds of alcohols having 1 to 5 carbon atoms in combination with methylene chloride . The content of the alcohol is preferably 2 to 25% by weight, more preferably 5 to 20% by weight, based on the whole solvent. Specific examples of the alcohol include methanol, ethanol, n-propanol, isopropanol and n-butanol, with methanol, ethanol, n-butanol or a mixture thereof being preferably used. As components which become solid after drying other than cellulose acylate, there may optionally be contained a plasticizer, a UV absorbent, a heat stabilizer such as inorganic fine particles and a salt of an alkaline earth metal (e.g. , calcium or magnesium) , an antistatic agent, a fire retardant, a lubricant, an oil agent, an agent for accelerating peeling from the support, an agent for preventing hydrolysis of cellulose acylate, etc.

As the plasticizer to be preferably added, phosphoric acid esters or carboxylic acid esters are used. Examples of the phosphoric acid esters include triphenyl phosphate (TPP) , tricresyl phosphate (TCP) , cresyldiphenyl phosphate, octyldiphenyl phosphate, diphenylbiphenyl phosphate, trioctyl phosphate and- tributyl phosphate. As the carboxylic acid esters, phthalates and citrates are typical . Exmples of the phthalates include dimethyl phthalate (DMP) , diethyl phthalate (DEP) , dibutyl phthalate (DBP) , dioctyl phthalate (DOP) , diphenyl phthalate (DPP) and diethylhexyl phthalate (DEHP) . Examples of the citrates include O-acetyl triethyl citrate (OACTE) ,

O-acetyl tributyl citrate (OACTB) , acetyl triethyl citrate and acetyl tributyl citrate.

Examples of other carboxylic acid esters include butyl oleate, methyl acetyl ricinoleate, dibutyl sebacate and tri ellitates such as trimethyl trimellitate . Examples of glycollic acid esters include triacetin, tributyrin, butylphthalylbutyl glycollate, ethylphthalylethyl glycollate, methylphthalylethyl glycollate and butylphthalylbutyl glycollate.

Of the above-illustrated plasticizers , triphenyl phosphate, biphenyldiphenyl phosphate, tricresyl phosphate, cresyldiphenyl phosphate, tributyl phosphate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diethylhexyl phthalate, triacetin, ethylphthalylethyl glycollate and trimethyl trimalli ate are preferably used. Particularly, triphenyl phosphate, biphenyldiphenyl phosphate, diethyl phthalate, ethylphthalylethyl glycollate and trimethyl trimellitae are preferred. These plasticizers may be used alone or in combination of two or more of them. The amount of the plasticizer to be added is preferably 5 to 30% by weight, particularly preferably 8 to 16% by weight, based on cellulose acylate. These compounds may be added together with cellulose acylate and a solvent upon preparation of the cellulose acylate solution, or may be added during or after preparation of the solution. As the UV ray absorbent, any one may be selected depending upon the end-use, and there may be used absorbents of salicylate type, benzophenone type, benzotriazole type, benzoate type, cyano acrylate type and nickel complex salt type, with benzophenone type, benzotriazole type and salicylate type absorbents being preferred. Examples of the benzophenone type

UV ray absorbent include 2 , 4-dihydroxybenzophenone ,

2-hydroxy-4-acetoxybenzophenone ,

2-hydroxy-4-methoxybenzophenone , 2,2' -di-hydroxy-4-methoxybenzophenone ,

2,2' -di-hydroxy-4 , 4 ' -dimethoxybenzophenone ,

2-hydroxy-4-n-octoxybenzophenone ,

2-hydroxy-4-dodecyloxybenzophenone and

2-hydroxy-4- (2-hydroxy-3-methacryloxy) propoxybenzo " phenone. Examples of the benzotriazle type UV ray absorbent include

2 (2 ' -hydroxy-3 ' -tert-butyl-5 ' -methylphenyl) -5-chlo robenzotriazole ,

2(2' -hydroxy-5 ' -tert-butylphenyl) benzotriazole , 2(2' -hydroxy-3 ' , 5 ' -di-tert-amylphenyl) benzotriazol e,

2(2' -hydroxy-3 ' , 5 ' -di-tert-butylphenyl) -5-chloro- benzotriazole and

2(2' -hydroxy-5 ' -tert-octylphenyl) benzotriazole . Examples of the salicylate type include phenyl salicylate and p-octylphenyl salicylate, p-tert-butylphenyl salicylate. Of these illustrated UV ray absorbents, 2-hydroxy-4-methoxybenzophenone , 2,2' -di-hydroxy-4 , 4 ' -methoxybenzophenone , 2(2' -hydroxy-3 ' -tert-butyl-5 ' -methylphenyl) -5-chlo ro- benzotriazole,

2(2' -hydroxy-5 ' -tert-butylphenyl) benzotriazole , 2(2' -hydroxy-3 ' , 5 ' -di-tert-amylphenyl) benzotriazol e and 2(2' -hydroxy-3 ' , 5 ' -di-tert-butylphenyl) -5-chloro- benzotriazole are particularly preferred.

To use a plurality of absorbents different from each other in absorption wavelength enables to obtain a high barrier effect over a wide wavelength region, thus being particularly preferred. The amount of the UV ray absorbent is preferably 0.01 to 5% by weight, particularly preferably 0.1 to 3% by weight, based on cellulose acylate. The UV ray absorbent may be added simultaneously with dissolution of cellulose acylate, or may be added to a dope wherein cellulose acylate is dissolved. In particular, it is preferred to use a static mixer and add a UV ray absorbent solution to the dope immediately before casting.

As the inorganic fine particles to be added to cellulose acylate , silica, kaolin, talc, diatomaceous earth, quartz, calcium carbonate, barium sulfate, titanium oxide and alumina may freely be used according to the end-use. These fine particles are preferably dispersed in a binder solution by any means such as a high-speed mixer, a ball mill, an atritor or an ultrasonic wave disperser before being added to the dope. As the binder, cellulose acylate is preferred. It is also preferred to disperse together with other additives such as the UV ray absorbent. As the dispersing solvent, any solvent may be used, but a solvent having similar composition to that of the solvent for the dope is preferred. The dispersed particles have a number-average particle size of preferably 0.01 to 100 μm, particularly preferably 0.1 to 10 μm . The above-mentioned dispersion may be simultaneously added in the step of dissolving cellulose acylate or may be added to the dope in any step. However, as with the UV ray absorbent, the dispersion is preferably added immediately before casting using a static mixer or the like.

As the agent for accelerating peeling from the support, surfactants are effective, and any of phosphate-based surfactants, sulfonate-based surfactants, carboxylate-based surfactants , nonionic surfactants and cationic surfactants may be used with no particular limits. These are described in, for example, Japanese Patent Laid-Open No. 243837/1986. In the case of using the above-mentioned cellulose acylate film as the protective film, it is preferred to impart hydrophilicity to the surface of the film by such means as saponification , corona treatment, flame treatment or glow discharge treatment. Also, it is possible to disperse a hydrophilic resin in a solvent having some affinity with cellulose acylate and coat the dispersion on the film in a thin layer. Among the above-mentioned means, saponification treatment is particularly preferredd since it does not damage plane properties and physical properties of the film. The saponification treatment is conducted by, for example, immersing the film in an aqueous solution of alkali such as sodium hydroxide. After the treatment, it is preferred to neutralize with a low-concentration acid to remove excess alkali, followed by sufficient washing with water. The saponification treatment with an alkali , which is preferably employed as a surface-treating means for cellulose acylate film is specifically described below .

It is preferred to conduct the treatment as a cycle wherein the surface of the cellulose acylate film is immersed in an alkali solution, neutralization with an acidic solution is conducted, then washing with water and drying are conducted. As the alkali solution, there are illustrated a solution of potassium hydroxide and a solution of sodium hydroxide , with the equivalent concentration of hydroxide ion is preferably 0.1 N to 3.0 N , more preferably 0.5 N to 2.0 N . The temperature of the alkali solution is preferably room temperature to 90 °C, more preferably 40 °Cto70 °C. Subsequently, the film is generally washed with water and, after being passed through an acidic aqueous solution, washed with water to obtain a surface-treated cellulose acylate film. In this occasion , the acid is hydrochloric acid, nitric acid, sulfuric acid, acetic acid, formic acid, chloroacetic acid, oxalic acid or the like, and its concentration is preferably 0.01 N to 3.0 N, more preferably 0.05 N to 2.0 N. In the case of using the cellulose acylate film as a transparent protective film for the polarizing plate, it is particularly preferred to conduct the acid treatment and the alkali treatment, i.e., saponification treatment of cellulose acylate in view of adhesion to the polarizing film.

The surface energy of the solid thus obtained can be determined by a contact angle method, a wet heat method or an adsorption method as described in "Nure No Kiso To Oyo" (published by Riaraizu K . K . on 10, Dec. 1989) , with the contact angle method being preferred. The surface energy in terms of the contact angle is 5 to 90 degrees, preferably 5 to 70 degrees.

On the surface of the protective film of the circularly polarizing plate of the invention may be provided any of functional layers such as an optically anisotropic layer for compensation of a viewing angle of LCD described in Japanese Patent Laid-Open Nos . 229828/1992, 75115/1994 and 50206/1996 , an antidazzle layer or antireflective layer for improving viewing properties of a display, a layer having the function of PS wave separation by anisotropic diffusion or anisotropic optical interference for improving luminance brightness (e.g. , a high polymer-dispersed liquid crystal layer or a cholesteric liquid crystal layer) , a hard coat layer for enhancing scratch resistance of the polarizing plate, a gas barrier layer for depressing diffusion of moisture or oxygen, an easily adhesive layer for enhancing adhesion force to a polarizing film or an adhesive or self-adhesive, and a layer for imparting sliding properties .

The functional layer may be provided on the polarizing film side or on the side opposite to the polarizing film, which may properly be selected depending upon the end-use. On the polarizing film of the invention may be laminated directly on one side or on both sides thereof various functional films as the protective film. As such functional films , there may be illustrated a phase retardation film such as a λ/4 plate or a λ/2 plate, a light-diffusing film, a plastic cell having an electrically conductive layer on the opposite side to the polarizing plate , a luminance brightness-improving film having the function of anisotropic diffusion or anisotropic optical interference, a reflective plate and a semitransparent reflective plate.

As the protective film for the polarizing plate, a single sheet of the preferable protective film described above , or a plural sheets of them in a laminate may be used. The same protective films may be laminated on both sides of the polarizing film, or protective films different from each other in function andphysical properties maybe laminated on respective sides . Also , it is possible to laminate the protective film only on one side of the polarizing film, and an adhesive layer is directly provided on the other side for directly laminating a liquid crystal cell without laminating the protective film. In this case, a peelable separater film is preferably provided on the outer side of the adhesive layer. (Surface protective film)

As the surface protective film, there may be illustrated a hard coat layer, an AG layer, an AR layer and a CV layer. These layers may be constituted by a single layer or a plurality of layers but, from the viewpoint of production steps, the film is preferably constituted by a single film. The single layer may be formed by coating plural times as long as the layers have the same composition after coating and drying. On the other hand, the term "a plurality of layers" means that the layers are respectively formed from compositions different from each other in formulation . Also, these layers may be used in combination. The hard coat layer preferably contains a curable composition, particularly preferably a curable composition containing an ethylenically unsaturated group-containing compound and a compound containing three or more ring-opening polymerizable groups within the molecule. The contained components preferably undergo a crosslinking reaction upon curing reaction. The crosslinking reaction may be either of radical polymerization reaction and cationic polymerization reaction. In both cases, the polymerization reactions can be allowed to proceed by the action of heat and/or light. The polymerization reactions are generally allowed to proceed by adding a small amount of radical generating agent or a cation generating agent (or an acid generating agent) , called a polymerization initiator, and decomposing it by heat and/or light to generate radical or cation. The radical polymerization and the cationic polymerization may be conducted separately, but are preferably allowed to proceed simultaneously. As a method for allowing to proceed the cross-linking reaction without adding the radical generating agent, there is a method of merely heating the system, but a method of irradiating with actinic energy rays such as radiation , gamma rays , alpha rays, electronic beams and UV rays is preferably employed.

To the curable composition may be added, as needed, cross-linkable fine particles. Addition of the cross-linkable fine particles serves to improve adhesion to the substrate because it can reduce the cure shrinkage amount of the hard coat layer and, in the case where the substrate is a plastic film, it serves to reduce curling. As the cross-linkable fine particles, inorganic fine particles, any of organic fine particles and organic-inorganic composite fine particles may be used with no particular limitation. Examples of the inorganic fine particles include silicon dioxide particles , titanium dioxide particles , zirconium oxide particles and aluminum oxide particles . the inorganic fine particles are generally hard, and addition thereof to the hard coat layer serves to reduce shrinkage upon curing and, in addition, can raise hardness of the surface.

Generally, the inorganic fine particles have a low affinity for the organic components such as the polymer of the invention and a polyfunctional vinyl monomer, and hence mere mixing of them might cause in some cases formation of an aggregate or might cause cracking of the cured hard coat layer. Therefore, in order to increase affinity between the inorganic fine particles and the organic component, the surface of the inorganic fine particles may be treated with a surface-modifying agent containing an organic segment.

As the organic fine particles, there are illustrated those which are obtained by cross-linking general-purpose resins such as polyethylene, polypropylene, polytetrafluoroethylene , nylon, polyethylene terephthalte , polystyrene, poly (meth) acrylic acids and amides , polyvinyl chloride , acetyl cellulose, nitrocellulose and polydimethylsiloxane, and cross-linked rubber fine particles such as SBR and NBR.

The thickness of the hard coat layer also varies depending upon hardness of the substrate to be coated therewith, and the effect of providing an increased hardness and forming the hard coat layer difficultly cracked and peeled becomes remarkable by increasing the thickness of the hard coat layer. Such thickness is 1 to 200 μm, preferably 20 to 200 μm, more preferably 30 to 200 μm, still more preferably 40 to 200 μm, most preferably 50 to 200 μm.

The hardness of the surface of the hard coat layer formed from the curable composition also varies depending upon the kind of a substrate to be coated therewith but, the higher, the more preferred: The hardness of the surface to be used herein in the invention can be represented in terms of pencil strength defined in JIS K5400, and can be evaluated by directly scratching the surface of the hard coat layer by a pencil . The hardness of the surface of the hard coat layer is 3H to 9H, preferably 4H to 9H, more preferably 5H to 9H, in terms of the pencil hardness.

Also, both sides or one side of the substrate may be subjected to surface treatment by, for example, an oxidation method or a roughening method for the purpose of improving adhesion properties between the substrate and the hard coat layer. As the surface-treating method, there are illustrated, for example, treatment with a chemical, mechanical treatment, corona discharge treatment, glow discharge treatment, treatment with chromic acid (wet process) , flame treatment, high frequency treatment, hot air treatment, treatment with ozone, UV ray irradiation treatment, active plasma treatment and treatment with a mixed acid . Further, one or more undercoating layers may be provided. As materials for the undercoating layer, there are illustrated copolymers of vinyl chloride, vinylidene chloride, butadiene, (meth) acrylate , styrene, vinyl ester, etc. and a latex thereof, polyester, polyurethane , and water-soluble polymers such as gelatin .

Further, it is possible to provide on the hard coat layer a functional layer having various functions , such as an anti-reflective layer, a UV ray- and infrared ray-absorbing layer, a layer capable of absorbing a light of selected wavelength, an electromagnetic wave-shielding layer or a stain-proofing layer . These functional layers may be formed by conventionally known techniques. Also, in order to improve adhesion properties between the functional layer and the hard coat layer, the hard coat layer may be subjected to the surface treatment, or an adhesive layer may be provided thereon.

<Polarizing film> The obliquely oriented polarizing plate of the invention can easily be obtained by the method described below. That is, oblique orientation is attained by stretching the polymer film and, at the same time, the ratio of volatiles of the film upon stretching, shrinkage upon shrinking the film and elasticity modulus of the film before stretching are properly selected. Further, it is also preferred to adjust the amount of foreign matter adhering to the film before stretching. Thus, even when obliquely stretched, the stretched film does not suffer shrinkage, and there can be obtained a polarizing film having a small surface roughness and an excellent evenness. Also, since no shrinkage is formed, there are formed no deflection, and hence the stretching tension applied to the film is not reduced, which presumably serves to generate no streaky change in color.

A preferred stretching method for obtaining the polarizing plate of the invention (hereina ter in some cases referred to as "stretching method of the invention") is described in detail below. (Stretching method)

Figs . 3 and 4 are schematic plane view showing examples of obliquely stretching the polymer film. The stretching method of the invention includes : a step indicated by (a) wherein a raw film is introduced in the direction shown by an arrow (1) ; a step indicated by (b) wherein the film is stretched in the widthwise direction; and a step indicated by (c) wherein the stretched film is conveyed to the next step, i.e. , in the direction shown by an arrow (2) . Hereinafter, the term "stretching step" means the whole steps for conducting the stretching method of the invention including these steps (a) to (c) . The film is continuously introduced from the direction (1) , and is first gripped at a point Bl by a gripping means on the left side viewing from the upstream side. At this point, the other edge of the film is not gripped yet, thus no tension generating in the widthwise direction. That is, the point Bl is not a point at which substantial gripping initiates

(hereinafter referred to as "substantial grip-initiating point") .

In the invention, the substantial grip-initiating points are defined as points at which the film is gripped at both edges thereof. The substantial grip-initiating points are shown by two points: one being a grip-initiating point Al on the more downstream side; and the other being a point CI at which a straight line drawn from Al in an almost vertical direction to the center line 11 (Fig. 3) or 23 (Fig. 4) of the film crosses a locus 13 (Fig.3) or 23 (Fig. 4) of the gripping means on the opposite side.

When the gripping means on both edges are conveyed at a substantially equal speed starting from the substantial grip-initiating points , Al migrates to A2 , A3...An, whereas CI similarly migrates to C2 , C3... Cn every unit time. Namely, a straight line connecting An and Cn which the reference grip means pass at the same time shows the stretching direction at that point of time .

In the method of the invention , An gradually retards with respect to Cn as shown in Fig. 3 or Fig. 4, and hence the stretching direction gradually becomes inclined from the vertical direction to the conveying direction. Points of the invention at which substantial gripping is released (hereinafter referred to as "substantial grip-releasing point" ) are defined by two points: one being a grip-releasing point Cx on the more upstream side; and the other being a point Ay at which a straight line drawn from Cx in an almost vertical direction to the center line 12 (Fig. 3) or 22 (Fig. 4) of the film to be conveyed to the next step crosses a locus 14 (Fig.3) or 24 (Fig.4) of the gripping means on the opposite side.

The angle of the final film-stretching direction is determined by the ratio of difference in travel of the gripping means on the right side and the left side thereof at the points at which the stretching step is substantially finished (substantial grip-releasing points) , Ay-Ax (i.e., | L1-L2 | ) to a distance W between the substantial grip-releasing points (distance between Cx and Ay) . Therefore, an angle of inclination θ between the stretching angle and the next step-conveying direction is an angle satisfying the following formula: tanθ = W (Ay-Ax) that is, tanθ = W/ | L1-L2 |

Although the upper edge of the film shown in Figs . 3 and 4 is gripped till 18 (Fig. 3) or 28 (Fig. 4) after passing the point Ay, the other edge is not gripped, and hence widthwise stretching does not occur any more , and the points 18 and 28 are not the substantial grip-releasing points of the invention. As is described above, in the invention, the substantial grip-initiating points on both edges of the film are not simple points at which the film starts to be gripped by the gripping means on the left side and the right side of the film. To more strictly define the two substantial grip-initiating points of the invention, the substantial grip-initiating points are points at which a straight line connecting either left- or right-side griping point and the other-side gripping point meets the center line of the film to be introduced into the film-gripping step almost at right angles and which are positioned at the most upstream positions.

Similarly, in the invention, the two substantial grip-releasing points are defined as points at which a straight line connecting either left- or right-side griping point and the other-side gripping point meets the center line of the film to be conveyed to the next step almost at right angles and which are positioned at the most downstream positions. Here, the term "almost at right angles" means that the center line of the film meets a straight line connecting the left side substantial grip-initiating point and the right side substantial grip-initiating point or connecting the left side substantial grip-releasing point and the right side substantial grip-releasing point at an angle of 90 +- 0.5 degrees

(the term "+-" as used herein means "plus or minus ") .

In the case of producing a difference between the left travel and the right travel using a tenter type stretching machine, there often arises a serious gap between the point at which the film starts to be gripped by the gripping means and the substantial grip-initiating point or between a point at which the film starts to be released and the substantial grip-releasing point due to mechanical restrictions such as length of the rail. However, as long as the step between the above-defined substantial grip-initiating point and the substantial grip-releasing point satis ies the relation of formula (1) , the objects of the invention are attained.

In the above description, the angle of inclinaton of orientation axis of the resultant stretched film can be controlled and adjusted through the ratio of the outlet width W of the step (c) to the difference in travel of the two substantially gripping means | L1-L2 I .

With polarizing plates and phase retardation film, films oriented at an angle of 45 degrees to the lengthwise direction are often demanded . In this case , it is preferred to satisfy the following formula (2) in order to obtain an orientation angle near 45 degrees : formula (2) 0.9W< | L1-L2 | <1.1W with the following formula (3) being more preferred: formula (3) 0.97W< | L1-L2 | <1.03W. Specific structure of the stretching step can be designed freely as long as the relation of formula (1) is satisfied, as illustrated in Figs. 3 to 8 taking into consideration costs on equipment and productivity . The angle between the direction (1) wherein the film is introduced to the stretching step and the direction (2) wherein the film is conveyed to the next step may be any degree but, in view of minimizing the total area of the equipment including the steps before and after the stretching, the angle is preferably made smaller. The angle is preferably within 3 degrees, more preferably within 0.5 degree. This value can be attained in the structure as shown in, for example, Figs . 3 and 4. In such method wherein the film-proceeding direction does not substantially change, it is difficult to obtain an orientation angle of 45 degrees to the lengthwise direction, which angle is preferred as a polarizing plate or a phase retardation film, by merely enlarging the width between the gripping means . Therefore, as is shown in Fig. 3, | L1-L2 | can be increased by providing a shrinking step after once stretching the film.

The stretching ratio is desirably 1.1 to 10.0 , more desirably 2 to 10, and the subsequent shrinking ratio is desirably 10% or more. Also, as is shown in Fig. 6, to repeat stretching and shrinking is preferred because it serves to more increase | L1-L2 | .

Also, in view of minimizing costs on the equipment for the stretching step, bending times of the locus of the gripping means and the bending angle are preferably made smaller. From this point of view, it is preferred that the film-proceeding direction is bent so that the angle between the film-proceeding direction at the outlet of the step wherein both edges of the film are gripped and the direction wherein the film is substantially stretched is 20 to 70 degrees while gripping both edges of the film, as shown in Figs. 4, 5 and 7. In the invention, as an apparatus for stretching the film by gripping both edges thereof and imparting tension, a so-called tenter apparatus as shown in Figs. 3 to 7 are preferred. Also, in addition to the conventional two-dimensional tenter apparatuses, there may be employed a stretching step wherein edge-gripping means on both sides are provided spirally to produce a difference in travel between the two means as shown in Fig . 8.

With the tenter type stretching machine, there is often employed a structure wherein a clip-fixed chain migrates along a rail but, in the case of employing a left-right unbalanced stretching method as in the invention , the ends finally shift at the inlet and outlet of the step as shown in Figs. 3 and 4, and, in some cases, initial gripping and grip releasing do not take place at the same time. In such case, the substantial step lengths LI and L2 are not mere distances between initial gripping and grip-releasing but travel lengths of the portions where the film-gripping means grip both edges of the film as has already been stated.

In case where there exists a difference in traveling speed between the left side and the right side of the film at the outlet of the stretching step, there result wrinkles or slippage at the outlet of the stretching step, and hence the speed of conveying the film-gripping means on the left side and the speed of conveying the film-gripping means on the right side are substantially the same. The difference in conveying speed is preferably 1% or less, more preferably less than 0.5%, most preferably less than 0.05%. The speed as used herein means the length of locus of the gripping means on each of the right and the left sides per minute. In a general tenter stretching machine or the like, there is involved speed unevenness generated on the order of second or less depending upon the period of chain-driving sprocket blades, frequency of a driving motor , etc . , often an unevenness of several % . However , this unevenness does not correspond to the difference in speed stated in the invention.

(Shrinkage)

Shrinkage of the stretched polymer film may be conducted upon or after stretching. It suffices to conduct shrinkage so that wrinkles of the polymer film generated upon stretching in an oblique direction are removed. As means for shrinking the film, there are illustrated a method of applying heat to thereby remove volatile components , and the like . However, any means may be employed as long the film can be shrunk. As to preferred shrinking ratio of the film, it is preferred to shrink 1/sinθ or more using an orientation angle θin the lengthwise direction , or 10% or more as a value .

(Volatile content) Also, wrinkles and slippage are formed as difference in travel generates between the left side and the right side of the film. In the invention, in order to solve this problem, the supporting properties of the polymer film are maintained, and the polymer film is stretched with keeping the volatile content at 5% or more, followed by shrinking it with reducing the volatile content. The volatile content in the invention means the volume of volatile components contained in the unit volume of the film, and is a value obtained by dividing the volume of the volatile components by the volume of the film. As a method for incorporating volatile components, there are illustrated a method of casting the film to incorporate a solvent or water, a method of dipping, coating or spraying a solvent, water or the like before stretching , and a method of coating a solvent or water on the film during stretching. A film of a hydrophilic polymer such as polyvinyl alcohol which contains water under an atmosphere of a high temperature and a high humidity can be incorporated with volatile components by stretching after moisture conditioning under a high-humidity atmosphere or by stretching under high-humidity conditions. Any other means may be employed that can incorporate the polymer film with 5% or more volatile components.

Apreferred volatile content varies depending upon the kind of the polymer film. The maximum volatile content may be increased as long as the polymer film can maintain self-supporting properties. With polyvinyl alcohol, the volatile content is preferably 10% to 100%. With cellulose acylate, the volatile content is preferably 10% to 200%.

(Elastic modulus)

With respect to physical properties of unstretched polymer film, a too low elastic modulus results in a reduced shrinking ratio upon and after stretching, thus wrinkles being difficult to remove. Also, a too high elastic modulus requires a large tension to be applied upon stretching, and the strength of the portion for gripping the both edges of the film must be increased, leading to a large load for the machine. Therefore, the elastic modulus of the polymer ilm of the invention before stretching is 0.1 Mps to 500 Mpa, preferably 0.1 Mpa to 500 Mpa, in terms of Young's modulus.

(Distance between generation and removal of wrinkles) It suffices that wrinkles which generate upon orienting the polymer film in an oblique direction are removed till the substantial grip-releasing point of the invention. However, since unevenness in the stretching direction occurs in case where it takes time for the wrinkles to be removed from their generation, it is preferred that the wrinkles be removed in as short a distance as possible from the point at which the wrinkles generated. For realizing this, there is a method of increasing the speed of volatilization of the volatile components .

(Foreign matter)

In the invention, when foreign matter is adhered to the unstretched polymer film, the surface of the stretched film becomes coarse, and hence such foreign matter is preferably removed. Presence of such foreign matter can be the cause of unevenness in color and optical unevenness upon preparation of, particularly, a polarizing plate. It is also important for the foreign matter not to adhere before a protective film is laminated thereon . It is preferred to operate under an environment where floating dust is minimized. The amount of foreign matter in the invention means a value obtained by dividing the weight of foreign matter adhering to the surface of the film by the surface area, and is a gram number per square meter. The amount of the foreign matter is preferably 1 g/m or less, more preferably 0.5 g/m² or less and, the smaller the amount, the more preferred.

A method for removing the foreign matter is not particularly limited, and any method may be employed that can remove the foreign matter without exerting detrimental influences upon unstretched polymer film. For example, there are illustrated a method of removing foreign matter by spraying a water stream, a method of removing foreign matter by jetting a gas , and a method of removing foreign matter by wiping using cloth or a blade of, for example, rubber.

(Drying) Any drying condition may be employed under that generated wrinkles are removed. However, it is preferred to adjust so that the film can reach a drying point in as much a short travel distance as possible after being oriented to a desired angle. The drying point is a point at which the surface temperature of the film becomes the same as the ambient temperature.

From this viewpoint, the drying speed is preferably as large as possible.

(Drying temperature) Any drying temperature may be employed at that generated wrinkles are removed, thought it varies depending upon kind of the film to be stretched. In the case of preparing a polarizing plate by the invention using a polyvinyl alcohol film, the drying temperature is preferably 20 °C to 100 °C, more preferably 40 °C to 90 °C.

(Swelling ratio)

In the invention, when polyvinyl alcohol is used as a polymer film with using a curing agent , the swelling ratio of the ilm in water is preferably different before and after the stretching. Specifically, the swelling ratio before stretching is preferably higher than the swelling ratio after stretching and drying. More preferably, the swelling ratio of the film in water before stretching is more than 3%, and the swelling ratio after stretching is less than 3% .

(Definition of bending portion) Rails for defining the locus of the gripping means are often required to have a large bending ratio. For the purpose of avoiding interference between ilm-gripping means to each other or local stress concentration due to sharp bending, it is desirable for the locus of the gripping means to draw an arc. (Stretching rate)

The rate of stretching the film in the invention is 1.1 times/min or more, preferably 2 times/min or more, in terms of stretching ratio, and the more the rate, the better. Also, traveling speed in the lengthwise direction is 0.1 m/min, preferably 1 m/min . In view of productivity, the faster, the better. In every case, the upper limit varies depending upon the film to be stretched and the stretcher.

(Tension in the lengthwise direction)

In the invention, upon gripping the both edges of the film by the gripping means, the film is preferably in a pulled state so as to make the gripping operation easy. Specifically, there are illustrated, for example , a method of applying a tension in the lengthwise direction, and like methods. As to tension, a tension of a degree not to loosen the film is preferred, depending upon the state of film before stretching.

(Temperature upon stretching)

In the invention, the environmental temperature upon film stretching may be at least the solidifying point of volatile component contained in the film or higher. In the case where the film is polyvinyl alcohol film, the temperature is preferably 25 °C or higher. Also, in the case of stretching a polyvinyl alcohol film doped with iodine and boric acid for preparing a polarizing film, the temperature is preferably 25 °C to 90 °C.

(Humidity upon stretching]

In the case of stretching a film containing water as a volatile component such as a polyvinyl alcohol film or a cellulose acylate film, stretching may be conducted under a moisture-conditioned atmosphere.

With polyvinyl alcohol, the humidity is preferably 50% or more, more preferably 80% or more, still more preferably 90% or more.

(Polymer film for polarizing film)

There are no limitations as to polymer films to be stretched in the invention, and films composed of a proper thermoplastic polymer may be used. Examples of the polymer include PVA, polycarbonate, cellulose acylate and polysulfone .

The thickness of the unstretched film is not particularly limited but, in view of film-gripping stability and uniformity of stretching, the thickness is preferably 1 μm to 1 mm, particularly preferably 20 to 200 μm.

As a polymer for a film for polarizing film, PVA is preferably used. PVA is commonly a saponification product of polyvinyl acetate, and may contain a component copolymerizable with vinyl acetate, such as an unsaturated carboxylic acid, an unsaturated sulfonic acid, an olefin or a vinyl ether. Also, modified PVA containing acetoacetyl group, sulfonic acid group, carboxylic acid group or oxyalkylene group may be used.

The saponification degree of PVA is not particularly limited but, in view of solubility or the like, it is preferably 80 to 100 mol %, particularly preferably 90 to 100 mol % . The polymerization degree of PVA is not particularly limited, but is preferably 1000 to 10000, particularly preferably 1500 to 5000.

(Formulation and method for dyeing)

A polarizing film is obtained by dyeing PVA, and the dyeing step is conducted by gas-phase or liquid-phase adsorption. In an embodiment of the liquid-phase method using iodine, the dyeing is conducted by dipping the PVA film in an aqueous solution of iodine-potassium iodide. The content of iodine in the solution is preferably 0.1 to 20 g/1, the content of potassium iodide is preferably 1 to 200 g/1, and the ratio of iodine to potassium iodide is preferably 1 to 200. The dyeing period of time is preferably 10 to 5000 seconds, and the temperature of the solution is preferably 5 to 60 C. As the dyeing method, any means may be employed such as a method of coating or spraying iodine or a solution of a dye, as well as the dipping method. The dyeing step may be provided either before or after the stretching step of the invention but, since the film is suitably swollen to facilitate stretching, it is particularly preferred to dye in a gas phase prior to the stretching step.

(Addition of a curing agent (cross-linking agent or a metal salt)

In the step of producing a polarizing film by stretching PVA, it is preferred to use an additive capable of cross-linking PVA. Particularly in the case of employing the obliquely stretching method of the invention, the orientation direction of PVA may in some cases be deviated due to the tension in the step in case where PVA is not sufficiently cured at the outlet of the stretching step. Thus, it is preferred to dip the film in a cross-linking agent solution or coat the solution before or during the stretching step to thereby incorporate the cross-linking agent in the film. The means for imparting the cross-linking agent to the PVA film is not particularly limited, and any method may be employed such as a method of dipping the film in the solution, a method of coating or spraying the solution on or over the film, etc. , with the dipping method and the coating method being particularly preferred. As a coating means, any of commonly known means may be employed such as a roll coater , a die coater , a bar coater, a slide coater or a curtain coater . Also, a method of contacting the film with the solution-impregnated cloth, cotton or porous material is preferred. As the cross-linking agent , those which are described in US Reissued Patent No. 232897, with boric acid or borax being practically pre erred . Also, salts of metals such as zinc, cobalt, zirconium, iron, nickel and manganese may be used in combination with the cross-linking agent. It is possible to provide a washing or water-washing step after adding the curing agent.

Application of the cross-linking agent may be conducted before or after the grip initiation by the stretcher, and may be conducted in any of the steps till the terminal end of the step (b) in the embodiment shown in Fig .3 or 4 where the width direction stretching is substantially completed.

(Polarizing element)

It is preferred to dye with a dichroic dye as well as iodine. Specific examples of such dichroic dyes include dye compounds such as azo dyes, stylbene dyes, pyrazolone dyes , triphenylmethane dyes , quinoline dyes , oxazine dyes, thiazine dyes and quinone dyes. Water-soluble dyes are preferred, though not being limited thereto . It is also preferred that hydrophilic groups such as a sulfonic acid group, an amino group and a hydroxyl group are introduced into these dichroic molecules. Specific examples of the dichroic molecules include C.I. Direct Yellow 12 , C. I . Direct Orange 39, C.I. Direct Orange 72, C.I. Direct Red 39, C.I. Direct Red 79, CI. Direct Red 81, C.I. Direct Red 83, C.I. Direct Red 89, CI. Direct Violet 48, CI. Direct Blue 67, CI. Direct Blue 90, CI. Direct Green 59 and C.I. Acid Red 37 and further include those dyes which are described in Japanese Patent Laid-Open

Nos. 70802/1987, 161202/1989, 172906/1989,

172907/1989183602/1989, 248105/1989, 265205/1989 and

261024/1995. These dichroic molecules are used in the form of free acids or alkali metal salts , ammonium salts or amine salts. Polarizing elements having various colors may be produced by compounding two or more of these dichroic molecules. Those compounds (dyes) which appear black when polarizing axes of polarizing elements or polarizing plates containing them are made to cross at right angles or which contain various dichroic molecules in such combination that they appear black show both an excellent single plate transmission and an excellent polarizing ratio, thus being preferred. The stretching method of the invention is also preferably applicable to production of a so-called polyvinylene-based polarizing film whose polyene structure is made by dehydration or dechlorination of PVA or polyvinyl chloride to form conjugated double bonds serving to realize polarization.

The adhesive between the polarizing film and the protective film is not particularly limited, and there are illustrated PVA-based resins (including modified

PVA having acetoacetyl group, sulfonic acid group, carboxyl group or oxyalkylene group) and an aqueous solution of a boron compound, with PVA-based resins being particularly preferred. A boron compound or an aqueous solution of potassium iodide may be added to the PVA-based resins to use. The dry thickness of the adhesive layer is preferably 0.01 to 10 μm, particularly preferably 0.05 to 5 μm .

In the invention, the method preferably involves a drying step for shrinking the stretched film and reducing the volatile content thereof after stretching the film, and a post-heating step after laminating a protective film on at least one side of the film after or during drying. As a specific laminating method, there are illustrated a method wherein a protective film is laminated during drying on the film using an adhesive in a state of both edges of the film being gripped, followed by trimming the both edges, and a method wherein the film is released from the gripping means on both sides after drying and, after trimming, a protective layer is laminated on the film. As a trimming method, there may be employed common techniques such as a method of cutting by a cutter such as an edged tool and a method of using laser. Heating is preferably conducted after the lamination in order to dry the adhesive and improve polarizing ability.

As to heating conditions, heating temperature of 30 °C or higher is preferred with aqueous systems though depending upon kind of the additive , with 40 °Ctol00 °C being more preferred, and 50 °C to 80 °C being still more preferred. It is more preferred to conduct these steps in an integrated line in view of performance and productivity.

Fig. 2 shows an example of blanking the polarizing plates of the invention. While absorption axis 71 of polarization, i.e., stretching axis of conventional polarizing plates coincide with the lengthwise direction 72 , absorption axis 81 of polarization , i.e., stretching axis of the polarizing plates of the invention is inclined at 45 degrees to the lengthwise direction 82 as shown in Fig. 2. Since this angle coincides with the angle between the absorption axis of the polarizing plate and the longitudinal or transverse direction of the liquid crystal cell upon laminating the film onto the liquid crystal cell in LCD, oblique blanking is not necessary in the blanking step. In addition, as is seen from Fig. 2, the polarizing plates of the invention are cut in a straight line along with the lengthwise direction, and hence they can be produced not by blanking but by slitting along the lengthwise direction, thus their productivity being markedly excellent.

In the circularly polarizing plate of the invention , an adhesive layer for laminating onto other liquid crystal display member is provided on at least one side of the above-mentioned polarizing film or optical film . A release film is preferably provided on the surface of the adhesive layer . The adhesive layer is optically transparent and shows a proper viscoelasticity and adhesive properties . As the adhesive layer in the invention , a film is formed according to a drying method, a chemically curing method, a thermosetting method, a heat-melting method or a photo-curing method using an adhesive or a self-adhesive of a polymer such as acrylic copolymer , an epoxy-based resin , polyurethane , silicone-based polymer, polyether, butyral-based resin, polyamide-based resin , polyvinyl alcohol-based resin or a synthetic rubber , followed by curing . Above all, acrylic copolymer is most easy to control adhesive properties, and is excellent in transparency, weatherability and durability, thus being preferably used .

Also, the adhesive layer of the invention can be subjected to cross-linking treatment. In such cases, cross-linking treatment using an intermolecular cross-linking agent may be conducted according to a method of compounding a solution of the adhesive with the intermolecular cross-linking agent. As the intermolecular cross-linking agent, a proper one may be used with no limitations depending upon the kind of functional group in the adhesive polymer relating to the intermolecular cross-linking, thus any of known ones being usable. Further, in the invention , it is preferred to adjust elastic modulus at relaxation within a proper range, whereby troubles of curling of the polarizing plate due to shrinkage of the polarizing film when the liquid crystal display device is exposed for a long time to high-temperature and high-humidity conditions and, as a result, optical changes such as white unevenness can be avoided. Specifically, the elastic modulus at relaxation after a relaxation time of 105 seconds at a standard temperature of 23 ° C is preferably 15 x 10^s dym/cm² or less, more preferably 13 x 10⁵ dyn/cm², particularly preferably 10 x 10⁵ dyn/cm² or less. In case where the elastic modulus at relaxation is too small, cohesive failure of the adhesive layer proceeds and, in case where the elasticity modulus at relaxation is too large, it becomes impossible to sufficiently relax shrinkage of the polarizing film, leading to troubles of warp or the like of the liquid crystal display device.

A specific method for measuring the elasticity modulus at relaxation is described below. Storage elastic modulus G' of 1-mm thick adhesive layer (5 mm x 1.1 mm) at -100 to 200 °C is measured at a frequency of 1 Hz using a dynamic viscoelasticity-measuring apparatus (made by Seiko Denshi K.K.) , and the thus obtained datum is converted to a diffusion datum G' (ω) based on frequency ω using the time-temperature conversion rule of the following WLF formula at a standard temperature of 23 °C, then the elastic modulus at relaxation Gk and the relaxation time τk are estimated according to the generalized Maxwell model, thus determining the elastic modulus at relaxation at a standard temperature of 23 °C and a relaxation time of 10⁵ seconds. logaT = CI (T-Ts) / (C2+T-Ts) G' (ω) = Gk[ω.τk)2/{l+(ω.τk)2}] τk = ηk/Gk

In the above formulae, logTa represents a shift factor,

T represents a temperature, coefficient Cl = 8.86, coefficient C2 = 101.6, characteristic temperature Ts = glass transition temperature Tg + 45 °C, and ηk represents a relaxation viscosity.

The polarizing plate of the invention can find various applications but, because of its characteristics that the orientation axis is inclined with respect to the lengthwise direction, the polarizing film wherein the inclined angle of the orientation axis to the lengthwise direction is 40 to 50 degrees is particularly preferably used for polarizing plates for LCD (e.g., all liquid crystal modes including T , STN, OCB, ROCB, ECB, CPA, IPS and VA) and circularly polarizing plates for preventing reflection to be used in organic EL displays . It is also suitable in the case of using in combination with various members such as a phase retardation film (e.g. , a λ/4 plate and a λ/2 plate) , a viewing angle-enlarging film, an anti-dazzling film or a hard coat film. Fundamental structure of a reflective liquid crystal display device is described below.

For example, a reflective liquid crystal display device may comprise, in order from the bottom, a lower substrate, a reflective electrode , a lower orientation film, a liquid crystal layer , an upper orientation layer , a transparent electrode , an upper substrate , a λ/4 plate and a polarizing film.

The lower substrate and the reflective electrode constitute a reflective plate. The lower orientation film to the upper orientation film constitute a liquid cell. The λ/4 plate may be placed at any position between the reflective plate and the polarizing film. In the case of color display, a color filter layer is further provided. The color filter layer is preferably provided between the reflective electrode and the lower orientation film or between the upper orientation film and the transparent electrode. It is also possible to separately provide a reflective plate using a transparent electrode in place of the reflective electrode . As the reflective plate to be used in combination with the transparent electrode , a metal plate is preferred. In case where the surface of the reflective plate is plane and smooth, only a specular reflection component may be reflected in some cases, thus viewing angle being narrowed. Thus, it is preferred to introduce an uneven structure

(described in Japanese Patent No. 275620) onto the surface of the reflective plate. With a reflective plate having a flat surface, it may be possible to provide a light-diffusing film on one side of the polarizing film (on the cell side or outer side) (in place of introducing the uneven structure onto the surface) .

The liquid crystal cell is preferably of TN (twisted nematic) mode, STN (Super Twisted Nematic) mode or HAN (Hybrid Aligned Nematic) mode. The twist angle in the TN mode liquid crystal cell is preferably 40 to 100 degrees, more preferably 50 to 90 degrees, most preferably 60 to 80 degrees. The value of the product (Δnd) obtained by multiplying anisotropy of refractivity (Δn) of the liquid crystal layer by the thickness (d) of the liquid crystal layer is preferably 0.1 to 0.5 μm, more preferably 0.2 to 0.4 μm .

The twist angle in the STN mode liquid crystal cell is preferably 180 to 360 degrees, more preferably 220 to 270 degrees. The value of the product (Δnd) obtained by multiplying anisotropy of refractivity (Δn) of the liquid crystal layer by the thickness (d) of the liquid crystal layer is preferably 0.3 to 1.2 μm, more preferably 0.5 to 1.0 μm . With the HAN mode liquid crystal cell, it is preferred that liquid crystal molecules are substantially vertically oriented on the one substrate , and that the pretilt angle on the other substrate is

0 to 45 degrees. The value of the product (Δnd) obtained by multiplying anisotropy of refractivity (Δn) of the liquid crystal layer by the thickness (d) of the liquid crystal layer is preferably 0.1 to 1.0 μm , more preferably 0.3 to 0.8 μm . The substrate on which the liquid crystal molecules are vertically oriented may be the substrate on the reflective plate side or the substrate on the transparent electrode side . The reflective liquid crystal display device may be used in a normally white mode wherein portions to which a lower voltage is applied are displayed bright and portions to which a higher voltage is applied are displayed dark or in a normally black mode wherein portions to which a lower voltage is applied are displayed dark and portions to which a higher voltage is applied are displayed bright , with the normally white mode being preferred.

A typical example of the constitution of the semi-transparent liquid crystal display device is shown in Fig. 13 as a schematic cross-sectional view. Of course, it can be undertood by those skilled in the art that the semi-transparent liquid crystal display device of the invention is not limited to this example, and that there are various variations thereof.

The semi-transparent liquid crystal display device 141 shown in Fig. 13 includes a front-side substrate 103, a back-side substrate 104, a liquid crystal portion 105, a plurality of front electrodes 106, rear electrodes 107 corresponding to the front electrodes 106, , a front-side circularly polarizing plate 108, a back-side circularly polarizing plate 1110, and two or more color filters different from each other in wavelength of transmissible light.

The constitution of this semi-transparent liquid crystal display device 141 and a process for its production are described in detail below. A substrate comprising a glass material is used for the front-side substrate 103 and the back-side substrate 104. On one side of the back-s9de substrate 104 was formed a thin film of an electrically conductive material composed of tantalum (Ta) or the like according to a sputtering method, followed by patterning the thin film into a given shape. Thus, a signal electrode 125 within a two-terminal element 113 and a signal wiring connected to the signal electrode 125 are formed. Subsequently, in order to form an insulating layer 1124 within the two-terminal element, the surface of the signal electrode 125 and the surface of the signal wiring are anodically oxidized in an electrolyte of ammonium tartrate or the like. Then, in order to form an upper electrode 1122 within the two-terminal element, a thin film of an electrically conductive material such as titanium (Ti) is formed on one surface of the back-side substrate 104, followed by patterning the thin film into a given shape .

Subsequently, in order to form a back-side electrode 107 functioning as a pixel electrode, a semi-transparent thin film of aluminum (Al) was formed on the surface of the back-side substrate 104 on which surface the two-terminal element 113 has been formed, according to a vacuum deposition method or a suttering method using a photomask . Thus, rectangular portions of a plurality of semi-transparent thin films remain as the back-side electrode 107, and the rectangular back-side electrodes 107 are disposed in procession while in contact with the upper electrodes 125 of individual two-terminal elements. The back-side electrode 107 has a thickness of about 50 nm and, in a reflective mode , can reflect outer light having passed through the liquid crystal layer and, in a transparent mode, can transmit part of a light from a backlight 112.

A color filter 142 composed of a resin material capable of transmitting only a light component of a predetermined wavelength region is printed on one side of the front-side substrate 103 for each color. Then, a transparent thin film of ITO is formed on one side of the front-side substrate 103 , then patterned so that band-shaped portions disposed in a stripe remain on the front-side electrode 106.

The front-side substrate 103 and the back-side substrate 104, one surface of each of which parts have been formed, are registered so that the front electrode 106 faces the rear electrode 107 and that the signal wiring on the back-side substrate 104 is rectangular with the lengthwise direction of the stripe-formed front electrode 106 in viewing along with the normal direction of the substrate. Further, both substrates are laminated at the periphery thereof with a predetermined space being left. A liquid crystal material (e.g. , TN liquid crystal of 0.065 in refractive index anisotropy Δn) for forming a liquid crystal portion 105 is encapsulated in the internal space of the thus-obtained liquid crystal cell. After forming the liquid crystal portion 105 , a circularly polarizing plate is laminated onboth surfaces of the liquid crystal cell.

The semi-transparent liquid crystal display device 141 comprises a combination of the thus-prepared panel and a backlight 112.

Display of an image is conducted by utilizing disposition of the two circularly polarizing plates (in the case of reflective mode, polarized state of a light by the front-side circularly polarizing plate) and change in orientation state of the liquid crystal layer caused by application of voltage. The transparent axis of the polarizing film of the circularly polarizing plate laminated on the front-side substrate 103, the transparent axis of the polarizing film of the circularly polarizing plate laminated on the back-side substrate 104, and orientation alignment of liquid crystal molecules within the liquid crystal portion 105 and nearest the substrates 103 and 104 are usually registered so that the monochromatic liquid crystal display panel becomes normally white (displaying white when no voltage is applied to the liquid crystal portion 105) , though not being limited to this disposition.

EXAMPLES

The invention is described in detail by reference to Examples which, however, do not limit the invention in any way.

Example 1 [I] Preparation of λ/4 plate

100 g of 8-methyl-8-methoxycarbonyltetracyclo [4.4.0.12, 5.17 , 10] dodec-3-ene, 60 g of 1 , 2-dimethoxyethane , 240 g of cyclohexane and 3.4 ml of a toluene solution of 0.96 mol/liter of diethylaluminum chloride were added to an autoclave of 1 liter in internal volume . Separately, 20 ml of a 1 , 2-dimethoxyethane solution of 0.05 mol/liter of tungsten hexachloride and 10 ml of a 1 , 2-dimethoxyethane solution of 0.1 mol/liter of paraldehyde were mixed in a flask . 4.9 ml of this mixed solution was added to the above-described mixture in the autoclave. After tightly closing the autoclave, the mixture was heated to 80 °C for 3 hours under stirring . To the thus-obtained polymer solution was added a mixed solvent of 1 , 2-dimethoxyethane and cyclohexane (2/8 by weight ratio) to adjust the polymer/solvent ratio to 1/10 (by weight ratio) , followed by adding thereto 20 g of triethanolamine and stirring for 10 minutes. 500 g of methanol was added to this polymer solution, and stirred for 30 minutes, then allowed to stand. The upper layer of the formed two separate layers was discarded, and methanol was again added thereto, followed by stirring and allowing to stand, and discarding the upper layer. The same procedures were further repeated twice, and the resulting lower layer was properly diluted with cyclohexane and 1 , 2-dimethoxyethane to obtain a cyclohexane-1 , 2-dimethoxyethane solution of 10% in polymerization concentration. To this solution was added 20 g of palladium/silica magnesia (made by Nikki Kagaku K.K. ; palladium content=5%) , and hydrogenation reaction was conducted in an autoclave under a hydrogen pressure of 40 kg/cm2 at 165 °C for 4 hours, followed by removing the hydrogenating catalyst by filtration to obtain a hydrogenated (co) polymer solution.

Also, an antioxidant of pentaerythrityl-tetrakis [3- (3 , 5-di-t-butyl-4-hydro xyphenyl) propionate] was added to this hydrogenated (co) polymer solution in an amount of 0.1% based on the

(co) polymer, followed by removing the solvent at 380 °C under reduced pressure. Subsequently, the resin was molten and pelletized under nitrogen atmosphere using an extruder to obtain a thermoplastic resin A containing a fundamental skeleton of tricyclodecane .

A base film of 100 μm in thickness and 15 nm in retardation value was obtained from the thermoplastic resin A pellets by a solution-casting method using methylene chloride as a solvent. The resultant base film was uniaxially stretched with a stretching ratio of 125% to obtain a λ/4 plate A of 90 μm in thickness and 135 nm in retardation value. (Thickness of the film)

The thickness was measured by means of a laser focus displacement meter, LT-8010, made by Kience K.K.. Additionally, measurement of the retardation value was conducted by using KOBRA-21ADH made by Oji Keisoku Kiki K.K. Hereinafter, the same applies.

(2) Preparation of λ/4 plate

A film (λ/4 plate B) obtained by stretching a polycarbonate copolymer was prepared according to Example 3 of WOOO/26705.

The in-plane retardation value of the film at a wavelength of 450 nm was 148.5 nm, the in-plane retardation value at a wavelength of 550 nm was 161.1 nm , and the in-plane retardation value at a wavelength of 650 nm was 162.9 nm .

(3) Preparation of λ/4 plate C

100 parts by weight of cellulose acetate having an average acetylation degree of 59.5%, 7.8 parts by weight of triphenyl phosphate, 3.9 parts by weight of biphenyldiphenyl phosphate, 1.32 parts by weight of a retardation-controlling agent (41-trans), 587.69 parts by weight of methylene chloride and 50.85 parts by weight of methanol were mixed at room temperature to prepare a solution (dope) .

41-trans

The thus-obtained dope was cast onto a filmingband, dried at room temperature for 1 minute, and dried at 45 ° C for 5 minutes . The amount of the solvent remaining after drying was 30% by weight. The cellulose acetate film was released from the band, dried at 120 °C for 10 minutes, then stretched at 130 °C, 1.34 times in terms of actual stretching ratio in a direction parallel to the casting direction. The film was allowed to freely shrink in a direction vertical to the stretching direction. After stretching, the film was dried at 120 °C for 30 minutes, and the resultant film was used as a λ/4 plate C. The amount of the solvent remaining after stretching was 0.1% by weight.

The thickness of the resultant λ/4 plate C was 112.7 μm , and retardaton values at wavelengths of 450 nm , 550 nm and 590 nm measured by means of an ellipsometer (M-150 ; made by Nihon Bunko K.K. ) were 125.2 nm , 137.8 nm and 141.1 nm, respectively.

Further, the refractive index nx in the in-place slow axis direction at a wavelength of 550 nm , the refractive index ny in the vertical direction to the in-plane slow axis , and the refractive index nz in the thickness direction were determined by measuring refractive indexes using an Abbe reflactometer and measuring angle dependence of retardation, and a value of (nx-nz) / (nx-ny) was calculated to be 1.48. Additionally, (nx-nz) / (nx-ny) is a value called NZ parameter and, the larger is this value, the smaller is the change in display contrast due to viewing angle. Thus, the value is preferably larger.

(4) Preparation of λ/4 plate D

To

6-methyl-l ,4,5, 8-dimethano-l ,4, 4a, 5, 6, 7, 8, 8a- octahydronaphthalene were added 10 parts of a 15% cyclohexane solution of a catalyst of triethylaluminum ,

5 parts of triethyla ine and 10 parts of a 20% cyclohexane solution of titanium tetrachloride , followedby ring-opening polymerization in cyclohexane . The resultant ring-opening polymerization product was hydrogenated with the aid of a nickel catalyst to obtain a polymer solution. This polymer soslution was coagulated in isopropyl alcohol, and dried to obtain a powdery resin. This resin was 40,000 in the number average molecular weight , 99.8% in hydrogenation ratio , and 142 °C in Tg .

The above-mentioned powdery resin was molten at 250 °C, then pelletized. The pellets were melt-extruded through a T-die of 300 mm in width using a uniaxial extruder having a 40-mm full-flight type screw, wound up by three-roll cooling rolls of 300 mm in diameter to obtain a sheet. In these procedures, the resin temperature at the die portion was 275 °C, the temperatures of the three cooling rolls were 120 °C, 100 °C and 100 ° C in the order of the first roll, the second roll and the third roll .

Since this unstretched sheet was non-uniform in thickness at the edges thereof, the edge portions with a width of 20 cm from the edges were trimmed, and the surface was observed visually and under an optical microscope. No foaming, no streaks and no flaws were observed. Tg of the film was 139 °C, the average film thickness was 75 μm, with the thickness unevenness being +-2 μm or less. The light transmission was 91.5%, the average retardation value was 11 nm , with its in-plane variability being +-5 nm.

This unstretched sheet was controlled at 140 +-2 °C, and was uniaxially stretched with a stretching ratio of 1.25 times to obtain a λ/4 plate D. The /4 plate D had an average thickness of 50 μm, a thickness unevenness of +- 1.2 μm, and a retardation of 140 nm on the average with the in-plane variability being +-7 nm .

A λ/4 plate D was kept at 80 C for 2 hours, then allowed to cool to room temperature, followed by measuring the retardation value to be 136 nm on the average .

(5) Preparation of λ/2 plate A λ/2 plate was prepared in the same manner as in the λ/4 plate B . The average in-plane retardation value was 272 nm .

[II] Preparation of circularly polarizing plate (1) Preparation of a circularly polarizing plate A

Both surfaces of a PVA film of 2,400 in average polymerization degree and 75 μm in thickness were washed with ion-exchanged water having a temperature of from

15°C to 17°C for 60 seconds . Water was then scratched off the surfaces of the PVA film with a blade made of stainless steel. Then, the PVA film was dipped in an aqueous solution of 0.77 g/1 of iodine and 60.0 g/1 of potassium iodide at40°C for 55 seconds while concentration correction was being made to keep the concentration of the aqueous solution constant. The PVA film was then dipped in an aqueous solution of 42.5 g/1 of boric acid and 30 g/1 of potassium iodide at 40°C for 90 seconds while concentration correction was being made to keep the concentration of the aqueous solution constant. Then, excess water was scratched off the surfaces of the PVA film with a blade made of stainless steel to reduce the distribution of water content of the film to 2% or less. The PVA film thus processed was then introduced into a tenter stretcher shown in Fig. 1. The film was fed by 100 m at a conveying speed of 5 m/min, and was then stretched by a factor of 5.5 under the atmosphere of 50°C and 95%. The film was then dried under the atmosphere of 70°C while being shrunk with the tenter bent with respect to the stretching direction as shown in Fig. 2. The film was released from the tenter, and then trimmed 3cm from both edges using a cutter . The ilm was laminated with the above-prepared λ/4 plate on one side thereof and with Fuji Tack (cellulose triacetate having an in-plane retardation value of 3.0 nm and a thickness of 80 μm produced by Fuji Photo Film Co. , Ltd. ) which had been saponified, using a 3% aqueous solution of PVA (PVA-117H; produced by Kuraray Co., Ltd.), and then heated to 70°C for 10 minutes to obtain a polarizing plate A having an effective width of 650 mm and a length of 100m in a roll form. Since the polarizing plate is used in a roll form, the usable area of the polarizing plate was as high as 91.5% as calculated in terms of area efficiency as shown in Fig. 2. The drying point was located in the middle of the zone (c) , and the water content of the PVA film before drying was 40%, and the water content after stretching was 6.5%.

The difference in conveying speed between the left side tenter clips and the right side tenter clips was less than 0.05%, and the angle between the center line of the introduced film and the center line of the film to be fed to the next step was 0 degree. Here, | L1-L2

I was 0.7m, and W was 0.7m, with their relation being I L1-L2 I = W. No wrinkles or deformation of the film was observed at the outlet of the tenter.

The direction of the absorption axis of the resultant circularly polarizing plate A in a continuous length was inclined at 45 degrees to the slow axis of the protective film (Fuji Tack) and the slow axis of the λ/4 plate. The polarizing degree measured at 550 nm was 99.8%, and the transmission of the single polarizing plate was 41%. Also, the thickness of the circularly polarizing plate A was 200 μm .

(2) Preparation of circularly polarizing plates B, C, D and E

Circularly polarizing plates B, C and D were prepared in the same manner as mentioned above except that λ/4 plates B , C andD were used in the aforementioned process for the preparation of circularly polarizing plate, respectively, instead of the λ/4 plate A. Further, a polarizing plate was prepared in the same manner as mentioned above except that Fuji Tack (cellulose triacetate having an in-plane retardation value of 3.0 nm and a thickness of 80 μm produced by Fuji Photo Film Co., Ltd.) was used instead of the λ/4 plate A. The polarizing plate was laminated with a λ/4 plate B with an acrylic adhesive layer (20 μm) having a relaxation modulus of elasticity of 12 x 10⁴ dyn/cm interposed therebetween, and then subjected to aging at a temperature of 50°C to prepare a circularly polarizing plate E . Since the polarizing plate is used in a roll form, the usable area of the polarizing plate was as high as 91.5% as calculated in terms of area efficiency as shown in Fig. 2.

(3) Preparation of a circularly polarizing plate F As shown in Fig. 10, a λ/2 plate 122 and a λ/4 plate B 124 were laminated with an acrylic adhesive layer (20 μm) having a relaxation modulus of elasticity of 12 x 10⁴ dyn/cm interposed therebetween with its stretching axis being oriented at 75 degrees and 20 degrees, respectively. The polarizing plate thus prepared is designed to act as a λ/4 plate which exhibits an improved wavelength dispersibility when irradiated with a linear polarized light in the vertical direction (direction of zero degrees) on the λ/2 plate side thereof , making it possible to convert the linear polarized light to a substantially circularly polarized light regardless of wavelength in the range of visible light. This broad band λ/4 plate was then cut to a size of 310 x 233 nm along the vertical direction.

A circularly polarizing plate F was prepared in the same manner as in the process for the preparation of the circularly polarizing plate A except that a polarizing plate with a protective layer on one side thereof was prepared free of λ/4 plate A and the polarizing plate thus prepared was then laminated with the broad band λ/4 plate on the side thereof free of protective layer the longitudinal direction of the polarizing plate and the vertical direction of the broad band λ/4 plate coincide with each other. For the lamination of the two plates, the broad band λ/4 plate was coated with gelatin to a thickness of 0.5 μm, and the two plates were laminated with an aqueous solution of 3% of PVA (PVA-124H) as an adhesive. Since the polarizing plate is used in a roll form, the usable area of the polarizing plate was as high as 91.5% as calculated in terms of area efficiency as shown in Fig. 2.

(4) Preparation of comparative circularly polarizing plate G

A comparative polarizing plate G was prepared by using a commercially available iodine-basedpolarizing plate (HLC2-5618; width: 650 mm, produced by Sanritz Corporation) instead of polarizing plate, cutting the polarizing plate along the direction tilted at 45 degrees from the longitudinal direction into a sheet-like polarizing plate having a size of 310 x 233 nm, and then laminating the strip and the λ/4 plate

B. Since the polarizing plate is cut in the direction of 45 degrees, the usable area of the polarizing plate was as high as 64.7% as calculated in terms of area efficiency as shown in Fig. 12. <Properties evaluated> The polarizing degree and single plate transmission 550 nm and T | | (450) /TJ. (450) and T| I (590) /T± (590) before and after durability test of the various polarizing plates measured at 550 nm, the usable area of these polarizing plates and the visual evaporation of these polarizing plates are set forth in the table belo . <Visual evaluation method>

For the visual evaporation, the circularly polarizing plate portion was removed from Zaurus MI-Ll (produced by Sharp Corporation) . The aforementioned circularly polarizing plates were then each mounted on the device. The device was then visually evaluated for tint. <Durability evaporation method>

The durability evaporation method was conducted at a temperature of 60°C for 100 hours.

[III] Preparation of semi-transparent liquid crystal display devices A to E Semi-transparent liquid crystal display devices A to E shown in Fig. 13 were prepared according to the aforementioned procedures using the circularly polarizing plates A to E . Additionally, the semi-transparent liquid crystal display device E is for comparison .

[IV] Evaluation of the liquid crystal display devices The thus prepared semi-transparent liquid crystal display devices A to E were subjected to the following evaluation . (1) Display quality upon reflective mode

The reflectivity of each of the liquid crystal display device in the white display portion and the reflectivity thereof in the black display portion were measured using a spectrocolorimeter CM-2002 made by Minoruta K.K. , and the contrast ratios were calculated.

The results are shown in Table 3-1.

(2) Display quality upon transparent mode

The brightness of each of the liquid crystal display device in the white display portion and the brightness thereof in the black display portion upon turning on a backlight were measured using a brightness meter BM-5A made by TOPCOM K.K., and the contrast ratios were calculated. The results are shown in Table 3-1. Table 3-1

From the results shown in Table 3-1, it is apparent that, in comparison with the comparative liquid crystal display device E, the liquid crystal display devices A to E have a thinner thickness of the liquid crystal panel by about 100 μm without reducing contrast ratio in both the reactive mode and the transparent mode .

This application is based on Japanese Patent application JP 2001-391780 , filed December 25 , 2001, Japanese Patent application JP 2002-2477, filed January 9, 2002, and Japanese Patent application JP 2002-3778, filed January 10, 2002, the entire contents of those are hereby incorporated by reference, the same as if set forth at length.

Claims

1. A circularly polarizing plate in a continuous length comprising: a polarizing film having an absorption axis neither parallel nor perpendicular to the lengthwise direction, at least one optical film provided at: at least one surface of the polarizing film; and an adhesive layer provided at an outside of at least one of the polarizing film and the optical film, wherein an angle between the absorption axis and the slow axis of at least one of the optical films is no less than 10 degrees and less than 90 degrees, a ratio of a transmission of the circularly polarizing plate in a direction parallel to the transparent axis to a transmission thereof in a direction perpendicular to the transparent axis when a light of 450nm is incident into the circularly polarizing plate from the polarizing film side after a durability test of the circularly polarizing plate satisfies the following formulation (I) , and the ratio of a transmission of the circularly polarizing plate in a direction parallel to the transparent axis to a transmission thereof in a direction perpendicular to the transparent axis when a light of

590 nm is incident into the circularly polarizing plate from the polarizing film side after a durability test of the circularly polarizing plate satisfies the following formulation (II) :

(I) 0.95 < T//(450) / T±(450) < 1.05

(II) 0.95 < T//(590) / T±(590) < 1.05 wherein T// (450) represents a transmission of the circularly polarizing plate in the direction parallel to the transparent axis thereof when the light of 450 nm is incident from the polarizing film side, TJ_(450) represents a transmission of the circularly polarizing plate in the direction perpendicular to the transparent axis thereof when the light of 450 nm is incident from the polarizing film side, T// (590) represents a transmission of the circularly polarizing plate in the direction parallel to the transparent axis thereof when the light of 590 nm is incident from the polarizing film side, and TJ_(590) represents a transmission of the circularly polarizing plate in the direction perpendicular to the transparent axis thereof when the light of 590 nm is incident from the polarizing film side.

2. A circularly polarizing plate comprising: a polarizing film; at least one protective film provided at: at least one surface of the polarizing film; and an adhesive layer provided at an outside of at least one of the polarizing film and the protective film, wherein an angle between an absorption axis of the polarizing film and a slow axis of the protective film is no less than 10 degrees and less than 90 degrees, a ratio of a transmission of the circularly polarizing plate in a direction parallel to the transparent axis to a transmission thereof in a direction perpendicular to the transparent axis when a light of 450nm is incident into the circularly polarizing plate from the polarizing film side after a durability test of the circularly polarizing plate satisfies the following formulation (I) , and the ratio of a transmission of the circularly polarizing plate in a direction parallel to the transparent axis to a transmission thereof in a direction perpendicular to the transparent axis when a light of 590 nm is incident into the circularly polarizing plate from the polarizing film side after a durability test of the circularly polarizing plate satisfies the following formulation (II) :

(I) 0.95 < T//(450) / Tl(450) < 1.05

(II) 0.95 < T//(590) / T±(590) < 1.05 wherein T//(450) represents a transmission of the circularly polarizing plate in the direction parallel to the transparent axis thereof when the light of 450 nm is incident from the polarizing film side, TJ_(450) represents a transmission of the circularly polarizing plate in the direction perpendicular to the transparent axis thereof when the light of 450 nm is incident from the polarizing film side, T// (590) represents a transmission of the circularly polarizing plate in the direction parallel to the transparent axis thereof when the light of 590 nm is incident from the polarizing film side, and T (590) represents a transmission of the circularly polarizing plate in the direction perpendicular to the transparent axis thereof when the light of 590 nm is incident from the polarizing film side .

3. The circularly polarizing plate according to claim 1, further comprising a wide-band λ/4 plate which comprises a λ/4 plate giving a birefringent light of 1/4 wavelength in phase retardation and a λ/2 plate giving a birefringent light of 1/2 wavelength in phase retardation so that their optical axes cross each other.

4. The circularly polarizing plate according to claim 2, further comprising a wide-band λ/4 plate which comprises a λ/4 plate giving a birefringent light of 1/4 wavelength in phase retardation and a λ/2 plate giving a birefringent light of 1/2 wavelength in phase retardation so that their optical axes cross each other.

5. A liquid crystal display device which comprises a liquid crystal cell, a polarizing plate disposed on at least one side of the liquid crystal cell, and a circularly polarizing plate obtained by cutting out from the circularly polarizing plate according to claim 1.

6. A liquid crystal display device which comprises a liquid crystal cell, a polarizing plate disposed on at least one side of the liquid crystal cell, and a circularly polarizing plate obtained by cutting out from the circularly polarizing plate according to claim 2.

7. A liquid crystal display device which comprises a liquid crystal cell, a polarizing plate disposed on at least one side of the liquid crystal cell, and a circularly polarizing plate obtained by cutting out from the circularly polarizing plate according to claim 3.

8. A liquid crystal display device which comprises a liquid crystal cell, a polarizing plate disposed on at least one side of the liquid crystal cell, and a circularly polarizing plate obtained by cutting out from the circularly polarizing plate according to claim 4.

9. A process for producing a circularly polarizing plate, which comprises: preparing a polarizing plate having a continuous length by stretching a continuously fed film so that a locus LI of a gripping means starting from a substantial grip-initiating point on one edge of the film to a substantial grip-releasing point, a locus L2 of another gripping means starting from another substantial grip-initiating point on another edge of the polymer film to a substantial grip-releasing point and a distance W between the two substantial grip-releasing points satisfying the following formula (1) and that self-supporting properties of the polymer film are maintained, with maintaining a volatile content at a level of 5% or more , then allowing to shrink while reducing the volatile content; cutting out a polarizing plate from the polarizing plate having a continuous length; preparing a wide-band λ/4 plate by combining a λ/4 plate giving a birefringent light of 1/4 wavelength in phase retardation with a λ/2 plate giving a birefringent light of 1/2 wavelength in phase retardation so that their optical axes cross each other; and laminating the cut polarizing plate with the wide-band λ/4 plate:

I L2-L1 I >0.4W (1)