|Publication number||US3502494 A|
|Publication date||Mar 24, 1970|
|Filing date||Nov 4, 1966|
|Priority date||Nov 4, 1965|
|Also published as||DE1497488A1|
|Publication number||US 3502494 A, US 3502494A, US-A-3502494, US3502494 A, US3502494A|
|Inventors||Mamoru Ishiwata, Yosuke Uchida|
|Original Assignee||Fuji Photo Film Co Ltd|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (2), Referenced by (23), Classifications (19)|
|External Links: USPTO, USPTO Assignment, Espacenet|
March 24, 1970 MAMORU ISHIWATA ET AL 3,502,494
PROCESS AND AYPARATUS FOR CONTINUOUS FLUID COATING OF A TRAVELING WEB Filed Nov. 4, 1966 3 Sheets-Sheet 1 FIGI mvmons MAMORU ISHIWATA YOSUKE UCHIDA March 24, 1970 MAMORU ISHIWATA ETAL 3,502,494
PROCESS AND APPARATUS FOR CONTINUOUS FLUID COATING OF A TRAVELING WEB Filed Nov. '4 1966 3 Sheets- Sheec 2 4 9 i vT INVENTOR$ 4 Y MAMORU ISHIWATA YOSUKE UCHIDA BY I AM wm March 24, 1970 MAMORU ISHIWATA ETAL 3,502,494
- PROCESS AND APPARATUS FOR CONTINUOUS FLUID COATING OF A TRAVELING WEB Filed Nov. 4, 1966 3 Sheets-Sheet 3 P -P2 =00! Kg/cm t Flee (cc/ 200-- 0R Pl 'P2=0 100-- P -P2= -o.o|5 Kq/cm 0 I I I INVENTORS MAMORU ISHIWATA YOSUKE UCHIDA v d s United States Patent ()fice 3,502,494 Patented Mar. 24, 1970 3,502,494 PROCESS AND APPARATUS FOR CONTINUOUS FLUID COATING OF A TRAVELING WEB 1 Mamoru Ishiwata and Yosuke Uchida, Ashigara-Kamigun, Kanagawa, Japan, assignors to Fuji Shashin Film Kabushiki Kaisha, Kanagawa, Japan Filed Nov. 4, 1966, Ser. No. 592,096 Claims priority, application Japan, Nov. 4, 1965, 4 67,667 Int. 'Cl. B05c 3/12 U.S. Cl. 117-34 7 Claims ABSTRACT OF THE DISCLOSURE Process for coating a traveling web utilizing a doctor blade wherein improved results are obtained by reducing the pressure on the fluid coating composition in a fluid coating composition holding chamber, and simultaneously reducing the pressure on the backside and transverse sides of the composition as it is drawn from the doctor edge. A thinner coating is withdrawn than otherwise obtainable.
Apparatus for forming the above process comprising means to reduce the pressure on the fluid coating composition, a vacuum chamber surrounding the back and transverse sides of the coating composition is also disclosed. The means of reducing the pressure on the fluid coating composition comprises means for evacuating the space above the composition in the chamber containing the composition.
The present invention relates to a process for coating continuously a fluid coating composition or fiuid coating compositions in a layer or layers on the surface of a continuously traveling web and more particularly to an improved so-called doctor coating process or knife coating process by retaining a fluid coating composition in the chamber directly behind the doctor edge of a coating means placed with a slight interval from the surface of a continuously traveling web to be coated and withdrawing said coating composition therefrom by the traveling web in an amount defined by the clearance between the doctor edge and the surface of the web.
In doctor coating or knife coating, the thickness of the coated layer withdrawn by a traveling web may be generally represented by the following equation referring to the relations shown in FIG. 6 of the accompanying drawing:
wn-P2100 1 9 60S tc/2[1+ m t=thickness of the coated layer (cm), c=-clearance between doctor edge and web surface (cm.), l=length of doctor edge in the traveling direction of web (cm.), =viscosity of fluid coating composition (gr./crn. sec.), =density of coating composition (gr./cm. p =presSure of coating composition at the entrance side of doctor edge (Gr/sq. cm.), p =pressure of coating composition at the exit side of doctor edge (Gr./ sq. cm.), Li -velocity of support or web (cm./sec.), 0=degree of angle between the upwardly directing vertical line and the traveling direction of web, g=gravitational acceleration (=981) (cm./sec. and g =gravitational conversion factor (:981) (gr. cm./
In an ordinary doctor coating process, Equation A becomes wherein (I 1P2) clpg cos 020 and hence That is, the thickness of coating cannot be reduced to less than /2 of the clearance between the doctor edge and the support. Accordingly, in order to carry out thin layer coating by doctor coating, the clearance between the doctor edge and the support must be narrowed, which is accompanied by the following three difliculties.
One of the difliculties is that the clearance between the doctor edge and the support is locally narrowed when foreign solid matters deposited on or embedded in the back surface of the support or the surface of a roll pass through said clearance, which results in the formation of comets in the coated layer. The second difliculty is that accompanied with narrowing the clearance, the effect of errors in the accuracy of the doctor edge and the roll and in the thickness of the support are increased, which makes the thickness of the coated layer uneven. The third difficulty is that in the case where the joint portion of supports passes through the clearance betwen the doctor edge and the support, the coating means or roll must be moved so that the clearance is enlarged.
The inventors have found an improved coating process and apparatus not accompanied by the above-mentioned difficulties, which will be explained referring to the accompanying drawings, in which FIG. 1 is a side cross-sectional view showing an embodiment of the present invention,
FIG. 2 is a side cross-sectional view showing another embodiment of this invention,
FIG. 3 is a side cross-sectional view showing still another embodiment of the present invention in which the principle of the invention is applied to obtain multiple layers,
FIG. 4 is a side cross-sectional view showing another embodiment of multiple layer coating according to the present invention,
FIG. 5 is an enlarged sectional view showing a portion of a doctor edge, and
FIG. 6 is a graph showing the influence of the clearance between a doctor edge and the surface of a web on the amount of a fluid coating composition coated on the web surface.
Referring now to FIG. 1, there is shown a coating apparatus for carrying out one embodiment of the present invention. A web 1 to be coated is continuously moved and backed up by a roll 2. A coating means 3 having a doctor edge 4 and a chamber 5 for containing a coating composition, said chamber 5 being formed behind said doctor edge 4, is placed at a slight interval from the surface of the traveling web. The coating composition in the chamber is maintained at a definite level by means of a liquid level controlling means 6 and the pressure in the space 8 above the fluid composition in the chamber is reduced by means of a blower 7. Further, if necessary, a chamber 10, the pressure in which is suitably reduced by means of a blower 9, is provided to the back side and the transverse sides of the coating means to prevent the entrance of the ambient atmosphere into the chamber 5. A fluid coating composition, such as a photographic emulsion, is supplied into the chamber 5 by means of a pump 11 at a rate controlled by means of the aforesaid level controlling means 6, and is withdrawn from the chamber by the traveling web to provide the coated layer thereof on the surface of said web.
FIG. 2 shows another embodiment of the present invention, in which a coating means having a doctor edge 4 and a chamber 5 for a fluid coating composition and further equipped with, if necessary, a vacuum chamber 10 as in FIG. 1 is connected through a conduit 13 to a subsidiary chamber or tank 12. The tank 12 is equipped with a level controlling means 6 and has a space 8, the pressure of which is maintained at a proper reduced pressure by means of a blower 7. The fluid coating composition at the entrance of the doctor edge may be maintained at the value satisfying the following relation by leaving the space 8 and reducing the pressure in said space;
(P1P2) cpg cos 0 Accordingly, it follows;
Thus, the thickness of the coated layer can be reduced to less than A2 of the clearance between the doctor edge and the web surface. If the coating procedure is conducted by the following conditions:
p =1.013 kg./cm. (atmospheric pressure) 1.1.:50 cp.
The relation of the thickness of the coated layer and the clearance between the doctor edge and the web surface is illustrated in FIG. 6, which shows that the clearance for obtaining the thickness of the coated layer of, for example, 80 microns by an ordinary doctor coating method (p p ==0.01 kg./cm. is 0.15 mm., whereas that by the present invention (p -p =-0.0l5 kg./cm. is 0.47 mm.
Further, in the case of using the coating means of which the length of the doctor edge in the traveling direction of the web is 5 mm. and the clearance between the doctor edge and the web surface is 0.4-0.5 mm., the pressure diiference between the entrance and the exit of the doctor edge, that is, 11 -11 in FIG. 5 may be 80 to 250 mm. H O gauge for coating at a coating rate of 20-- 80 m./min. a coating composition having 30-100 cp. in viscosity and 1.0-1.1 gr./cc. in density in a thickness of 20-80 microns. Consequently, if the liquid level is maintained at 20-50 mm. H O, the pressure in the space 8 is usually from about l00 to about 300 mm. H O gauge.
As is clear from the above-mentioned example, according to the present invention, thin-layer coating can be conducted with a comparatively large clearance between the doctor edge and the web surface and not accompanied by such troubles as the formation of comets, unevenness of coating thickness, and the difiiculty encountered in passing the jointed portion of webs or supports through the clearance.
It will be understood from the above descriptions that an object of the present invention is to provide an improved coating process and apparatus by which thin coating of a good quality is obtained without narrowing the clearance between the doctor edge and the support. Further, the feature of the present invention is in the point that by providing a space having a reduced pressure above a fluid coating composition in a chamber of a coating means or in a subsidiary chamber connected to the coating means, a pressure gradient is applied to a fluid coating composition positioned between the doctor edge and a traveling support such that the pressure is gradually decreased in the direction opposite to the traveling direction of said support. Another feature of the present invention besides the above system, is providing a chamber having a reduced pressure at the back side and the transverse sides of said coating means, whereby the aforesaid pressure gradient can be increased remarkably.
Moreover, in the case of applying the present invention to the simultaneous coating of multiple layers, as illustrated in FIG. 3 and FIG. 4, a fluid coating composition or fluid coating compositions for forming a second or more layers on the coated layer on a support may be continuously supplied to the fore-wall of the doctor edge which is inclined toward the doctor edge and flow down in a layer or layers along the surface thereof. Also, an extrusion type hopper or extrusion type hoppers for forming a second layer or more thereon may be provided to the fore-wall of the doctor edge and said coating compositions may be applied to the coated surface on the support without leaving any air space between the layers.
The invention will be further explained by the following examples, although the invention shall not be limited to them.
EXAMPLE 1 By employing the coating apparatus illustrated in FIG. 1, a gelatino silver halide photographic emulsion for positive photographic cinefilm was applied to the surface of an undercoated cellulose triacetate film in accordance with the present invention. The operating conditions were as follows:
Coating composition: Viscosity 30 cp., density 1.05 g./cc.
Clearance between the doctor edge and the support: 0.5
Velocity of traveling support: 40 m./ min.
Liquid level of the coating composition in chamber 5:
Pressure in reduced-pressure chamber 8: 175 mm. H O
gauge Pressure in reduced-pressure chamber 10:
mm. H O gauge.
The thickness of the thus coated layer was about /5 of one obtained by a conventional doctor coating. After coating, the coated layer was immediately set and then dried, and the resulting film was subjected to quality tests, which showed that the layer had a uniform thickness and no comets were formed therein.
EXAMPLE 2 Three layers of gelatino silver halide photographic emulsions for positive color cinefilm were applied on an undercoated cellulose triacetate film using the coated apparatus illustrated in FIG. 4 in accordance with the present invention. The operating conditions were as follows:
First coated layerBlue-sensitive emulsion layer: Viscosity 50 cp., density 1.05 g./cc.,
Second coated layerRed-sensitive emulsion layer: Viscosity 50 cp., density 1.03 g./cc.,
Third coated layerGreen-sensitive layer: Viscosity 50 c.p. density 1.04 g./cc.,
Clearance between doctor edge and support: 0.4 mm.,
Flow rate of the second coating composition: 1.2 liter/ min./m.-width,
Flow rate of the third coating composition: 1.0 liter/ min./m.-width,
Velocity of traveling support: 20 m./min.,
Level of the first coating composition in subsidiary tank Pressure in reduced-pressure chamber 8: -225 mm.
H O gauge,
Pressure in reduced-pressure chamber 10: -l to 230 mm. H O gauge.
The thickness of the thus coated first layer was about one-fourth that of a layer obtained by a conventional doctor coating method. After coating, the coated layers were immediately set and dried, and the resulting film was subjected to quality tests, which showed that the layers have a uniform thickness, that no comets \were observed in the layers, and that no intermixing of coating compositions was observed between layers.
Although the invention was explained with reference to specific examples, it will be understood that it is not limited to the conditions for operating the coating procedure as well as the kind of coating compositions and the configuration of the coating means. Similarly, according to the present invention, the traveling direction of a support at the doctor edge of a forming means and a system for conducting multiple layer coating may be selected as desired.
What is claimed is:
1. In a process for coating 21 fluid coating composition on a continuously traveling web by placing a coating means, having a doctor edge and a chamber containing a fluid coating composition directly behind said doctor edge, at a slight interval from the surface of said web, retaining the fluid coating composition in the chamber, and withdrawing said coating composition from said chamber by the traveling web surface, the improvement which comprises reducing the pressure on the fluid coating composition in said chamber and simultaneously reducing the pressure on the back side and the transverse sides of said composition as it is drawn from said doctor edge by said web so that a thinner coating is withdrawn than \would otherwise be withdrawn onto said web at the same interval between the doctor edge and web.
2. The method of claim 1 wherein the pressure on the fluid coating composition in said chamber is reduced by reducing the pressure in a space above the composition in said chamber.
3. The method of claim 1 wherein the pressure on the fluid coating composition is reduced by reducing the pressure in a second chamber connected to the chamber containing said composition so that the pressure on said composition is reduced.
4. The method of claim 1 further comprising applying at least one additional layer of fluid coating composition to the surface of the first coated layer at the exit side of the doctor edge without permitting an a r space at the interface between the first coated layer and said additional layer.
5. The process of claim 1 wherein said fluid coating composition is a composition for the production of photographic, light-sensitive elements.
6. In an apparatus for applying a fluid coating composition to a web comprising a doctor edge and a chamber for supplying said composition to said doctor edge and means for advancing a web which is to be coated at a small interval from said doctor edge, so that said composition is withdrawn from said doctor edge at a layer on the surface of said web, the improvement which comprises:
means to reduce the pressure on said fluid coating composition being lwithdrawn from said doctor edge, means comprising means for evacuating a space above said composition in the chamber containing said composition, and vacuum means surrounding the back and transverse sides of said coating composition so that a thinner coating is withdrawn than would otherwise be withdrawn onto said web at the same interval between the doctor edge and said web.
7,. The apparatus of claim 6 wherein said means to reduce the pressure on said fluid coating composition comprises a second chamber so connected to the. chamber containing said composition that a reduction in pressure in said second chamber results in a reduction in the pressure on said composition and means to reduce the pressure in said second chamber.
References Cited UNITED STATES PATENTS 3,206,323 9/1965 Miller et al. 117-34 3,348,964 10/1967 Good 118-50 X ALFRED L. LEAVITT, Primary Examiner T. E. BOKAN, Assistant Examiner US. Cl. X.R.
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|U.S. Classification||427/358, 118/411, 430/935, 118/50|
|International Classification||B05C9/06, B05C1/12, B05C5/02, G03C1/74|
|Cooperative Classification||Y10S430/136, D21H23/40, G03C1/74, D21H5/0015, B05C9/06, B05C5/0254|
|European Classification||D21H23/40, B05C9/06, G03C1/74, B05C5/02F, D21H5/00C8B|