US 3653890 A
A charge induction electrophotographic imaging process wherein an insulating mesh is interposed between the photosensitive layer and the final record member.
Claims available in
Description (OCR text may contain errors)
United States Patent Seimiya et al.
SCREEN ELECTROPHOTOGRAPHIC CHARGE INDUCTION PROCESS Inventors: Ryubun Seimiya; Yuzo Ohmuro; Sigeru Hanaoka; Masaru Nakamura, all of Tokyo, Japan Assignee: Konishiroku Photo Industry Co., Ltd.
Filed: Oct. 21, 1968 Appl. No.: 769,255
Foreign Application Priority Data  References Cited UNITED STATES PATENTS 3,512,966 5/1970 Shatluck et al. ..96/l 2,833,648 5/1958 Walkup ....96/1 3,005,707 10/1961 Kallmann et al. ..96/1 3,011,473 12/1961 Gundlach.... ..1l8/637 3,268,331 8/1966 Harper ..96/] 3,306,160 2/1967 Dunhabel et a1 ..88/24 3,322,538 5/1967 Redington ...96/1.l 3,337,339 8/1967 Snelling ..96/l 3,363,552 1/1968 Rarey ..101/l29 3,394,002 7/1968 Bickmore ..96/l 3,449,568 6/1969 Vock ..250/49.5
Primary Examiner-George F. Lesmes Assistant Examiner-John C. Cooper, 111
Attorney-Harry C. Bierman, Jordan B. Bierman and Bierman and Bierman [5 7] ABSTRACT A charge induction electrophotographic imaging process wherein an insulating mesh is interposed between the photosensitive layer and the final record member.
11 Claims, 38 Drawing Figures .lllll l i Pa e! April 4, 1972 3,653,890
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mum/1v SEIMIYA, YUZO ofimum SIGERU HANAOKA \f- NASARU NAKAMURA A'r-reR-NEYS SCREEN ELECTROPHOTOGRAPHIC CHARGE INDUCTION PPOCESS The invention relates to improvements in or relating to an electrophotographic process, and more particularly, to novel means for preparation of an electrostatic latent image on a record member, and also to a radiation sensitive member which is subjected to imagewise exposure to an original to be reproduced and conveys image information to the final record member. The invention also relates to intermediate and final record members for use with such process.
The known electrophotographic process such as Xerography or Electrofax employs a layer of photoconductive material which is uniformly charged in darkness by corona discharge and then exposed imagewise to form an electrostatic latent image thereon. The latent image is developed by a toner, and the Electrofax process fixes the developed image on the photoconductive layer, while in the Xerography, the developed image is transferred onto an image receiving member to be fixed thereon. Usual photoconductive layer used in the Xerography comprises a deposited film of amorphous selenium and the residue of toner which remains unremoved on the selenium film during the transfer must be cleaned to ensure satisfactory operation of the film when used repeatedly. However, the film surface is susceptible to damage by the cleaning operation owing to abrasion by toner powder and cleaner brush, thereby causing a degradation in the image quality. There have been several proposals which avoid such disadvantage by transferring an electrostatic latent image on the selenium film directly onto an insulating record member before the image is developed, as disclosed in US. Pat. No. 2,982,647. Alternatively, an electrostatic latent image is formed on an insulating record member while holding it at a very small distance of air gap from a photoconductive member during imagewise exposure with a voltage being applied simultaneously across the both members, as disclosed in US. Pat. Nos. 2,825,214, 2,833,648 and 2,937,943 issued to LB. Walcup. However, these approaches involve technical difficulties in maintaining a constant and uniform air gap between the members and are dissatisfactory in their commercial utility.
Therefore, it is an object of the invention to provide an improved electrophotographic process and apparatus for preparation of an electrostatic latent image on a final record member which is technically readily feasible and lends itself to continuous recording with good image quality.
It is another object of the invention to provide a novel radiation sensitive member which serves to convey image information from an original to a final record member in the form of an electrostatic latent image.
Fundamentally, according to the invention, the electrophotographic process of forming an electrostatic latent image on an insulating record member held in contact with another member while a voltage is being applied thereacross is characterized in that one or the other of the members has a thin insulating layer of a mesh pattern on its surface, which abuts against the other or said one of the members.
In one aspect, the process according to the invention em ploys a radiation sensitive member comprising a radiation sensitive layer on which is formed an insulating layer of a mesh pattern. The term radiation sensitive layer is intended herein to mean a normally electrically insulating layer which obtains an increased electrical conductivity upon exposure to radiation of any suitable wavelength, including corpuscular ray and X-ray. Usually such layer may comprise a suitable known photoconductive material when light is chosen as a carrier of image information. Where X-ray is used as the image carrier, a deposited film of amorphous selenium may be used as such layer. A record member of an insulating material is held against the mesh layer of the radiation sensitive member and a voltage is applied across the both members for a short period during which the composite is exposed to radiation image of an original to be reproduced. This forms an electrostatic latent image of the original on the insulating record member, which image is developed and fixed subsequent to separation of the record member from the radiation sensitive member.
Alternatively, the radiation sensitive member may be initially formed with a latent image thereon by a separate process which may comprise any conventional means. The member is then placed in close contact with a final record member, and then a voltage is applied between the both members. Transfer of the latent image occurs from the radiation sensitive member to the record member by migration of electric charges through the spaces defined by the patterned dots of the mesh layer.
Preferably, the radiation sensitive member comprises a substrate having sufficient mechanical strength to withstand the pressure with which an insulating record member is pressed thereagainst. The substrate may be either insulative or conductive and when it is insulative, it should have a conductive surface commensurate in area with the radiation sensitive layer. The radiation sensitive layer may form an ohmic contact with the substrate, or a barrier which prevents injection of free charge carrier may be formed between the layer and the substrate. In the former case, the time constant, T, when charge is being supplied to the surface of the radiation sensitive layer by dark current is given by I 1- K, p, r 1 where K, denotes dielectric constant of the layer material, s permittivity in vacuum and p resistivity of the layer material when not exposed to radiation, which may be referred to hereinafter as dark resistivity. When both the radiation sensitive member and the insulating record member are exposed to imagewise radiation while in contact, the time period of voltage application required for the formation of the latent image must be at least equal to the exposure time, t thus 1' e t (2) The time t depends on the sensitivity of the radiation sensitive layer and the intensity of radiation used. For example, when a deposited film of amorphous selenium is used with a light source which comprises a tungsten incandescent lamp providing illumination of luxes on the surface of the selenium film, t will be 0.2 second. Thus, in this instance, p e 3 X 10 (2 cm. Amorphous selenium usually has a p-value of the order of 10 S cm. and hence is suitable for the purpose of the invention.
When a barrier is formed between the radiation sensitive layer and the conductive substrate which prevents injection of free charge carrier, the density of charge, 0, induced on the layer surface by application of the voltage will be given by s e (3) where n denotes the concentration of free charge carriers in the layer, 1,, the layer thickness and e the charge of a charge carrier. Assuming uniform distribution of donors or acceptors in the layer, the reverse electromotive force or polarization voltage caused by induced charges will be as follows:
where 1,, and K denote the thickness and dielectric constant of a record member, respectively, Z the length of air gap provided by the pattern dots between the both members and D is given by the following equation: D=l,/K,+l /K 5 The maximum permissible value of V, depends upon various factors, but for the purpose of illustration, it will be assumed here to be 100 v. and when other parameters assume the following values:
l /K,,= 3 microns l, /K,= 10 microns l, 63 microns Z 10 microns then the permissible concentration of charge carrier will have to be n e 3 X 10 cm. Using this figure, the dark resistivity, p, of a radiation sensitive layer having mobility p. of 1 cm. /v.sec. is calculated to be p 2 X 10 0. cm.,
which is nearly 10 times less than the necessary value in an ohmic contact system. In practice, however, there will be no contact which constitutes a potential barrier capable of completely suppressing injection of charge carrier. Thus the possibility of a small leakage current, I,,,, must be catered for which builds up a potential on the surface of the radiation sensitive layer. The charge accumulation is proportional to the time period of voltage application, and placing the resulting voltage equal to V, given by the equation (4), we have,
d s o/ s) P O) Assuming V, 100 v., K,/l,= 10 cm. and t 0.2 second,
I 5 5 X lo 8 A.
This is the value below which the leakage current of the radiation sensitive layer must be held.
When the radiation sensitive layer is formed with a latent image before it is held in pressed relationship with a record member, the time length from the formation of a latent image on the radiation sensitive layer until completion of transfer will be greater, that is, the factor t will be by about ten to hundred times greater than before, so that it is required that the dark resistivity be greater and the leakage current be smaller at corresponding proportions.
The process mentioned above depends for its operation upon the migration of electric change to the surface of a record member in those parts of the space defined by the dots of the mesh layer which correspond to irradiated parts of the radiation sensitive member. This requires the application of a sufficiently high voltage, which in turn necessitates to ensure good insulation of the mesh layer. Experiments have shown that the mesh layer should have a resistivity not less than 10 cm. and a surface resistance not less than 10 (I per square. The thickness of the mesh layer determines the length of the air gap between the radiation sensitive layer and the record member, and in order to ensure good image quality of the latent image, the thickness should be within a range from 0.5 to 100 microns, preferably from to 20 microns. Additional requirements imposed upon the material of the mesh layer are that it is highly adherent to the surface of the radiation sensitive layer, that it does not exhibit any aggressive behavior to the surface to cause degradation of its characteristics and that it has sufficient mechanical strength and durability to withstand repeated use.
Such mesh layer may be formed in various ways. In one example, a photopolymerizable material e.g. photoresist available from Eastman Kodak Company under the trademark of KPR or KMER is applied on a radiation sensitive layer to a thickness given above. After drying, it is exposed to ultraviolet ray through a mask of suitable pattern and unilluminated parts are removed by a developer principally comprising trichlene. After drying, the remaining photoresist is fixed. This provides a meshwork of very high resolution. Alternatively, conventional electrophotographic process proposed by Carlson may be used to form an electrostatic latent image of desired pattern on a radiation sensitive layer, and the latent image may be developed by an insulating toner and fixed. In this instance, the thickness can be controlled by the intensity of charge provided by corona discharge or by the intensity of exposure. Typical materials for the mesh layer includes polyethylene, polystyrene, polyester, polyamide, Teflon (trademark), vinyl chloride, vinyl acetate, phenol resin and co-polymers of these materials.
Where the mesh layer has a poor adherence to the underlying radiation sensitive layer or when it is desired to prevent any reaction with the latter, a substratum may be provided on the radiation sensitive layer. When the substratum has a thickness not less than 0.5 micron, and up to thick of the radiation sensitive layer, it is found that the provision of such substratum has no substantial influence upon the image quality. As known, such substratum may also serve to reduce mechanical abrasion of the radiation sensitive layer.
As mentioned previously, the dark resistivity required for a radiation sensitive layer can be reduced by several orders by providing a thin insulating layer, between the conductive substrate and the radiation sensitive layer, which prevents injection of charge carrier. The leakage current through such thin layer must be held below the value estimated by the equation (6) and its thickness should be chosen so as not to degrade the contrast of the image, which would be satisfied when the thickness is below about 10% of that of the radiation sensitive layer. In addition, the radiation sensitive layer may comprise more than one layers to increase the quantum efficiency during the formation of the latent image.
In another aspect, the process according to the invention employs a final record member which has on its insulating recording layer an insulating layer of a mesh pattern. The mesh layer may be similarly constructed as that of the radiation sensitive member described above. In addition, the insulating recording layer and the mesh layer may be formed integrally. The thickness and resistivities of the mesh layer are similar to those indicated previously. In this instance, the formation of an electrostatic latent image on the record member is effected by using a radiation sensitive member having a radiation sensitive layer supported on a substrate, the layer being pressed against the mesh layer of the record member. The major difference from the first mentioned process is that the radiation sensitive member used in this instance does not have a mesh layer, which is transposed onto the final record member.
Such mesh layer of the record member may be formed in various ways, and the techniques described above in connection with the preparation of the radiation sensitive member may be used. Alternatively, a copperplate of desired pattern and depth is prepared and is filled with a copperplate ink for printing on a recording layer. Such copperplate ink comprises a non-colored transparent solution which becomes electrically insulating upon drying and solidification, such for example as a transparent resin solution of relatively low viscosity. Excessive ink attaching to the surface of the copperplate is doctored off. When the recording layer and the mesh layer are formed as integral, a thermoplastic resin such as polystyrene is coated on a support or formed into a single-layered film as by extrusion or casting technique and pressed against a heated matrix which is previously formed on a metal roll in a desired pattern and with a desired depth. Upon removal of the resin film from the matrix, the resin film will have a mesh-shaped unevenness formed on its surface. In this operation, suitable choice of the roll temperature, pressing time or the relative speed between the roll and the film is important. To facilitate detachment of the film, it is preferred to shape the matrix so as to provide tapering dots in the form of truncated cone or pyramid. Application of higher fatty acids such as stearic acid, as a remover, on the matrix surface may be effectively used.
In a further aspect, the process according to the invention employs an intermediate record member which comprises an insulating recording layer on which is formed another insulating layer of a mesh pattern. The construction, material and sizes of the intermediate record member may be same as the record member described just above in connection with the second process. When preparing an electrostatic latent image on a final record member according to this process, the intermediate record member is held pressed against a radiation sensitive member in the first step, the radiation sensitive member used in this process comprising a radiation sensitive layer on which no mesh layer is formed. In the second step, the intermediate record member is held in close contact with a final record member. In each of the first and second steps, a high voltage is applied between the respective two members held in contact to effect transfer of a latent image from one to another. Imagewise exposure is effected in the first step simultaneously with the application of the voltage.
In all of the processes described above, it is essential for best results to ensure a close and uniform contact between mating members with proper spacing provided by patterned dots. Suitable means therefor will be described later with reference to various embodiments.
For better understanding of the invention, it will be described in more detail with reference to the drawings, in which FIG. I is a schematic section to an enlarged scale of a novel radiation sensitive member according to the invention,
FIG. 2 is a similar view of a modification of the member shown in FIG. 1,
FIG. 3 shows various patterns of the mesh layer,
FIG. 4 is a schematic view illustrating the process of the invention using a radiation sensitive member with a mesh layer,
FIG. 5 is a similar view where the radiation sensitive member is not, but the record member is transparent to radiation,
FIGS. 6a to 60 show the process in which a latent image is formed on the radiation sensitive member prior to its contact with the record member,
FIGS. 7a and 7b show the process in which a positive is obtained,
FIG. 8 is a schematic view of a copying machine in which the process shown in FIG. 4 is employed,
FIGS. 9a to 9d are sections of various forms of a record member used in the second manner of the process according to the invention,
FIG. 10 is a schematic view illustrating the process using the record member shown in FIG. 9,
FIG. 11 is a view schematically illustrating a preferred manner of ensuring good contact between a radiation sensitive member and a record member,
FIGS. 12a and 12b show the process using the record member of FIG. 9 in which a positive is obtained,
FIG. 13a to 13 show another manner of the process using the record member of F IG. 9 in which a positive is obtained,
FIG. 14a to 14d are schematic sections of an intermediate record member used in accordance with the third aspect of the process according to the invention,
FIGS. 15a and 15b show a manner of carrying out the process for formation of an electrostatic latent image on a final record member using the intermediate record member shown in FIG. M, I
FIGS. 16a to 16d show another manner of the process with the intermediate record member of FIG. 14, and
FIGS. 17 to 21 show various forms of a copying machine incorporating the intermediate record member of FIG. 14.
Referring first to FIGS. 1 to 8 inclusively, which show the radiation sensitive member proposed by the invention and processes and apparatus which use the member, this member is generally shown in FIG. 1 by reference numeral 1 and includes a conductive substrate 2, and a radiation sensitive layer 3 as defined above which is evaporated on the substrate or coated thereon in the form of a dispersion in resinous binder. On the layer 3 is secured an insulating layer 4 which has a mesh pattern as shown in FIG. 3. In FIG. 3, black portions may represent an insulating material and white portions spaces therebetween or vice versa, and the pattern may comprise any regular or irregular array of dots, lines, solid triangles, diamonds or the like which can represent a picture element. Usual halftone or crossline screen pattern widely used in the art of printing may be suitable for the pattern of the insulating layer 4. Preparation and useful thickness of such mesh layer has been mentioned previously. The radiation sensitive member shown in FIG. 2 is generally similar to that of FIG. 1 except that the substrate 2 is of an insulating material and has a conductive thin film 2' deposited thereon to provide an electrode.
Referring to FIG. 4, the process of forming an electrostatic latent image on a record member 5 with using the above radiation sensitive member 1 will be described. The record member 5 comprises an insulating recording layer 6 on a conductive base 7, but the record member may be a commercially available electrostatic recording sheet. As shown, both the members 1 and 5 are positioned on a counterelectrode 8, with the mesh layer 4 abutting against the insulating recording layer 6. Suitable pressure in the order of from 0.1 to l kg./cm. is applied between the substrate 2 and the electrode 8 to cause a close and uniform contact between the both members. The electrodes 2', 8 are connected to a DC source 9 through a switch 10 and are also interconnected by another switch 11. In the example shown, it is assumed that the substrate 2 and conductive film 2' are both transparent to radiation 12 which is used for the imagewise exposure. Such substrate and electrode can be formed with Nesa glass, for example.
Upon closure of the switch 10, a high tension is applied across the electrodes 2, 8, and as the assembly is exposed to radiation 12, free charge carriers, electrons or positive holes, created by irradiation move to the surface of the layer 3 under the influence of the electric field, so that there is produced a very strong field in the space between the layers 3 and 6. For this reason, there occurs migration of electric charge to the layer 6 through the air space left between the land or mesh material 4, so that there will be provided electric charge on the surface portions of the recording layer 6 which face the air space in the mesh layer 4 in the region exposed to radiation 12. Then switch 10 is opened followed by closure of switch 11, which short-circuits the members. Subsequently the record member 5 is separated from the member 1 and the latent image thereon is developed and fixed. The density of such surface charge on the recording layer 6 has a tendency to increase with an increasing amount of exposure, but saturates at a value which depends on the film thickness and dielectric constant of the layers, the characteristics of the radiation sensitive layer, the magnitude and polarity of the voltage applied and other factors. However, excessive exposure is objectionable because of spread or blur of a resulting image. The polarity of the voltage may be arbitrarily determined in most cases, but a particular polarity may be sometimes preferred depending upon the kind of the radiation sensitive material used. The optimum value of the voltage applied depends upon the thickness and dielectric constant of various layers, and an example will be given below.
Amorphous selenium was deposited on a Nesa glass to a film thickness of 50 microns and a mesh layer 10 microns thick of KPR was provided on the film. A record member comprised a film of Mylar 12.5 microns thick having a deposited aluminium film. These members were pressed together and to the surface of Nesa glass was applied a voltage of l,120 volts. After irradiation of a light image for one second with maximum illumination of 20 luxes on the image surface, the Nesa glass surface and the deposited aluminium film were short-circuited. Then the record member was separated from the Nesa glass and the latent image on the Mylar film surface was developed with a magnetic brush. The developed image had satisfactory image quality.
It is to be noted that synchronization of the exposure with the application of the voltage, though preferred, is not essential in the manner of operation shown in FIG. 4. It is sufficient to provide exposure during application of the voltage. However, the exposure time concurrent with the voltage application is the effective exposure period, which must be long enough to form an electrostatic latent image on the record member.
A suitable insulating record member 5 may be formed by providing an insulating recording layer on a flexible conductive support, such as a so-called electrostatic recording sheet which comprises a thin insulating recording layer applied on a paper which has been treated to be conductive. Also it may comprise a flexible insulating material provided with a thin conductive coating on one surface thereof, e.g. polyester film with deposited metal such as aluminium; a transparent insulating material with a transparent conductive layer which may comprise SnO TiO Cul or the like; or a film of insulating resin alone, whether transparent or opaque, which has resistivity and surface resistance sufficiently high to retain an electrostatic charge, for example, polyethylene, polystyrene, polyester, polyamide, Teflon (trademark), vinyl chloride, vinyl acetate, phenol resin or the like. Thus the record member 5 can be constituted by a single layer of an insulating material, which preferably is flexible to ensure good contact with the radiation sensitive member.
It will be appreciated that both the radiation sensitive member 1 (except mesh layer 4) and the record member 5 are not completely plane, but include surface roughness and undulations so that such unevenness causes irregularities in the degree of close contact between these member particularly when the electrode 8 comprises a rigid material such as metal, thereby resulting in the degradation of image quality. Such disadvantage can be eliminated by using the electrode 8 which is made from a soft, elastic material. Such soft, elastic electrode 8 should have sufficient thickness and deformability to compensate for the surface roughness and undulations. A conductive rubber sheet 1 cm. thick proved satisfactory for this purpose. When such soft, elastic electrode 8 is used, it is desirable to provide a support on the back of the electrode 8 for the convenience of applying pressure and such support can be formed from metals or plastics material of relatively high strength such as bakelite.
FIG. 5 shows another manner of the above process which is employed with a radiation sensitive member having an opaque conductive substrate. In this instance, a record member 5 consists of a transparent insulating film 6, e.g. a film of polyester resin, and a transparent conductive film 7 such as copper iodide. The electrode 8 is constituted by a transparent conductive material and is supported on a transparent substrate 8 which may be formed with Nesa glass. Radiation 12 is applied through the transparent layers 6 to 8 and 8. The operation of the process is the same as in FIG. 4.
The radiation sensitive member 1 may be previously formed with an electrostatic latent image before being placed in contact with the record member 5. An example of such manner of operation is illustrated in FIGS. 6a to 60, where like parts are designated by same reference numerals, but the electrode 8 is replaced by a roller and the switch 10 is a double pole-double throw switch rather than a single pole switch as in FIGS. 4 and 5. Also for the sake of brevity, the insulating mesh layer 4 is shown in continuous lines, but it should be noted that it is formed in a pattern as shown in FIG. 3. Initially the switch 10 is thrown to the position shown in FIG. 6a, and the roller 8 is moved from left to right while rolling, thereby providing a high negative potential to the conductive substrate 2 and providing a positive charge to the lower surface of the radiation sensitive layer 3 through the air space in the mesh layer 4. Then the member I is exposed to imagewise radiation 12 (FIG. 6b), thereby forming an electrostatic latent image thereon. Now the member I is superimposed on a record member 5. The switch 10 is thrown to the other position as shown in FIG. 6c, and the supply voltage is applied across the conductive substrate 2 and the roller electrode 8 with the substrate 2 positive (FIG. 6c). As the roller 8 is moved from left to right while pressing the record member 5 against the radiation sensitive member I, the latent image is transferred from the latter to the recording layer 6. Then the switch 11 is closed to remove charge from the member 5 and the two members 1, 5 are separated from each other.
Another manner of forming a latent image on the radiation sensitive member 1 prior to its contact with a record member is shown in FIGS. 7a and 7b. Here, the member 1 has a transparent substrate 2 and a transparent conductive layer 2, as shown in FIG. 2, and initially a negative potential is applied to the electrode layer 2 with respect to the roller electrode 8, which is moved from left to right, as shown. However, in this instance, there is provided a light shield 13 having a slit 14 above the member 1. The light shield is arranged to be slidable in a plane parallel to the member 1, and as the roller 8 moves to the right, the light shield 13 also moves in the same direction at the same speed. During such movement of the roller 8 and light shield 13, the member 1 is exposed imagewise to radiation 12 through the moving slit 14. Thus negative charges will be produced on the surface of the radiation sensitive layer 3 not covered by the patterned mesh layer 4. Then the radiation sensitive member 1 having a latent image thus formed thereon is superimposed on a record member 5 (FIG. 7b), and while applying the voltage, the roller 8 is again moved from left to right to urge the record member 5 against the radiation sensitive member 1, whereupon the latent image is transferred onto the insulating recording layer 6.
While in the above embodiments, charges are produced on the recording layer 6 at positions subjected to radiation 12 so that the image developed will be a negative, it is possible in FIG. 7b to reverse the poarity of the voltage applied to obtain a positive.
Several examples of the above process and radiation sensitive member will be given below, which however should not be construed as limitation to the invention.
EXAMPLE 1 v A substrate was prepared by using a hard glass 2 mm. thick to deposit thereon a thin film of tin oxide, which is usually called a Nesa film. On the Nesa film was applied an evaporated film of amorphous selenium to a thickness of 50 microns. An 8 micron thick layer of KPR was formed as a mesh layer on the selenium film. The meshwork comprised thin fiat discs of KPR having a diameter of about 50 microns which were arranged in a regular form with spacing of about 75 microns, providing 200 meshes. This constituted a radiation sensitive member. Such member was used together with a commercially available electrostatic recording sheet in the process generally similar to that illustrated in FIG. 4. The urging electrode used was a conductive rubber sheet having a thickness of 1 cm. and hardness of 30 (JIS), and pressure of about I kg./cm. was applied to press the radiation sensitive member and the record member together. Applying +750 volts to the conductive Nesa film and using an exposure of 20 lux-sec. from a photographic enlarger, a latent image of good image quality was obtained.
EXAMPLE 2 On the same Nesa glass substrate as used in Example I was applied a thin film, about 2 microns thick, of thermosetting epoxy resin and on the resin film was coated a mixture, in equal volume proportions, of fine powder of cadmium sulfide activated by copper and thermosetting silicone resin as binder. A mesh layer 10 microns thick was prepared on the coating in the similar manner as in Example 1, using Dycril, photopolymerizable resin available from Du Pont Company. Using a radiation sensitive member thus formed and a commercially available electrostatic recording sheet in the similar process as in Example 1, with the voltage of -l ,200 volts and exposure of 5 lux-sec., a latent image of good image quality was obtained.
EXAMPLE 3 On one surface of a 1 mm. thick alumium plate was formed an alumina film having a thickness of 500 A. by plasma oxidation technique. On the alumina film was provided the coating of cadmium sulfide-silicone resin dispersion, used in Example 1 2, to a thickness of 50 microns. After setting of the coating, a KPR mesh layer, 8 microns thick and 200 meshes, was applied thereon, thus completing a radiation sensitive member. This member was used in the process illustrated in FIGS. 6a to 6c. The voltage used in the step of FIG. 6a was --1 ,500 volts, the exposure in FIG. 6b was 5 lux'sec., and the voltage applied in the step of FIG. 60 was +900 volts. The roller speed was 20 cm./sec. and the urging force of 10 kg. weight was used. The latent image obtained showed good image quality.
EXAMPLE 4 On the same Nesa glass substrate as used in Example 2 was applied an epoxy resin layer about 2 microns thick on which was evaporated crystalline selenium to a thickness of 1 micron followed by further evaporation of amorphous selenium to a thickness of 50 microns. On the surface of the latter was applied a mesh layer of KPR, 8 microns thick and 200 meshes as in Example l. The radiation sensitive member thus formed was used in the similar process as in Example 1 and provided a latent image of good image quality, but the exposure required was lux-sec., showing that the present radiation sensitive member had four times as high a sensitivity as that of Example 1.
EXAMPLE 5 On an aluminium plate 1 mm. thick was evaporated a layer of amorphous selenium to a thickness of 100 microns and on the selenium layer was applied a mesh layer of KPR microns thick. This radiation sensitive member was used in the process illustrated in FIG. 4, but using the conductive rubber electrode as in Example 1. A pressure of l kg./cm. was ap plied to the electrode. The exposure to an X-ray image of maximum dosage rate 450 mr./sec. for one second during application of +1,200 volts produced an electrostatic latent image of good quality. The record member used in Examples 3 to 5 were commercially available electrostatic recording sheets, and the latent image was developed with a magnetic brush.
FIG. 8 shows a copying machine which is constructed to carry out the process illustrated above. The machine includes a stationary light source such as a lamp 20, which serves projection of the image of a transparent original 21 through an optical system 22 and a slit 23 in a fixed light shield 24 onto a radiation sensitive member 25. The member 25 includes a transparent conductive substrate which is earthed as shown and its radiation sensitive or photoconductive layer is disposed to face a continuous web of record member 26 as the latter is moved past a conductive rubber electrode 27, the record member 26 being supplied from a roll 28 through a pair of guide rollers 29. The member 25 is arranged slidable horizontally as indicated by a both-ended arrow, and the arrangement is such that as the original 21 is moved to the left, as viewed in this Figure, at a constant speed, the members 25, 26 are moved to the right at the same speed as the speed of the focussed image, so that the image of successive parts of the original 21 is focussed on the corresponding contiguous parts of the record member 26. The roller electrode 27 is made from conductive rubber and is rotatably carried on a vertically movable support 30. A DC source 31 has its one terminal connected with a finger 32 which contacts the roller surface for application of a suitable voltage, and the other terminal of the source is earthed. Suitable means is provided, though not shown, to maintain a tension in the record member 26 and to drive it, when necessary, past the roller 27, guide rollers 33, 34, a developer unit 35 and a fixing unit 36 to a take-up spool 37.
In operation, before the original is set in motion to move one frame of the original below the lamp 20, the support 30 is raised upward to cause the roller 27 to urge the record member 26 against the photoconductive layer or move precisely the mesh layer of the radiation sensitive member 25, and as the original starts to move, both the members 25 and 26 are fed to the right at the same speed as the original. The lamp and the source are turned on, and then an electrostatic latent image is formed on the record member 26. Upon termination of the motion of the original by a distance of one frame, the forward drive is interrupted for a period, and the support 30 is lowered to release the record member 26 from contact with the member 25, which is then allowed to return to its initial position. Then the machine is ready for another copying cycle. The latent image on the record member 26 is developed and fixed before the latter is taken up on the spool 37.
As mentioned previously, the process according to the invention is operable with a record member which includes on its insulating recording layer a mesh layer of the kind specified above. Such record member is shown in FIGS. 9a to 9d, and FIGS. 10 to 13 inclusively show the manners of the process using such record member.
Referring to FIG. 9a, such record member is generally shown at 50 and consists of an insulating layer 51 adapted for use as a record carrier and another insulating layer 52 of a mesh pattern as indicated in FIG. 3. The material for such mesh layer 52 as well as its thickness and electrical properties should be similar to those described with reference to the mesh layer of the radiation sensitive member shown in FIGS. 1 and 2. However, the layers 51 and 52 may be formed with same material and hence integrally as shown in FIG. 9b, where the record member 50 includes a conductive layer 53. The record member shown in FIG. 9c has a substrate 53 which may be electrically conductive or insulating. Numeral 54 denotes a substratum which prevents penetration of a solvent that is used when coating the insulating recording layer 51 on the substrate. Such substratum may be formed by using a water soluble resin such as polyvinyl alcohol or any other suitable material that is insoluble to the solvent used for the coating of the recording layer. Such substratum can be omitted in certain circumstances depending upon the nature of the substrate material and the coating technique used. FIG. 9d shows a modification of FIG. 9c where the layers 51 and 52 are integral. Suitable material for the recording layer 51 includes polyethylene, polystyrene, polyester, vinyl acetate, phenol resins or their copolymers, and the choice will be made from consideration of charge retention, film plasticity, flexibility, surface characteristics, compatibility with coating, economic factors or the like. The recording layers in FIGS. and 9d need not be transparent, but they may comprise a dispersion of fine white powder such as titanium or zinc oxide in any of above resins. However, the record member 50 having the mesh layer must have sufficient flexibility to ensure the forma tion of a uniform latent image. Flexibility found in commercially available electrostatic recording papers is satisfactory.
FIG. 10 shows a manner of the process of forming a latent image on a record member 50 of the type shown in FIG. 9c, and numerals 8 to 12 denote parts designated by corresponding numerals in FIGS. 4 and 5. For the convenience of description, it is assumed here that light is used as radiation 12. Then a photoconductive member 55 is used which comprises an integral lamination of a transparent substrate 56, a transparent conductive layer 57 and a photoconductive layer 58, which may be of similar material as used in Carlson process. The member 55 is placed on the member 50 with the photoconductive layer 58 abutting against the mesh layer 52, and the composite is positioned on an electrode 8. Suitable means (not shown) is used to press the both members together with a pressure of from 0.1 to 1 kg./cm. for example. The conductive layer 57 is connected through switch 10 to the positive terminal of a DC source 9, of which negative terminal is connected to the electrode 8. In addition, the electrode 8 and the layer 57 are interconnected through a switch 11. When the switch 10 is closed and radiation 12 is released imagewise, there will be produced positive charges on the surface of the photoconductive layer 58, opposite to the insulating recording layer 51, where subjected to the exposure. Such surface charges produce an electric field of sufficient strength to cause migration of charge to the layer 51, thereby forming an electrostatic latent image on the surface of the recording layer 51. Upon termination of the exposure, the switch 10 is opened and the switch 11 is closed to short-circuit the layer 57 and the electrode 8. Then the both members 50 and 55 are separated and the latent image on the recording layer 51 is developed.
The electrode 8 may be constituted by a soft, elastic material such as conductive rubber and a separate pressure plate may be urged against the back of the electrode in order to apply pressure, thereby ensuring close and uniform contact between the both members. The record member shown in FIGS. 9a and 9b may be equally employed in above process.
FIG. 11 shows a convenient method of assuring a close contact between the members. The record member 50 having a mesh layer and the photoconductive or radiation sensitive member 55 are disposed horizontally in superimposed relationship. The member 50 comprises transparent materials entirely and its conductive layer 53 is connected with one terminal of a DC source 9 through a switch 10. The member 55 has a conductive substrate 56 which is connected with the other terminal of the source. In this particular arrangement, the member 55 has a radiation sensitive layer 58 of such size and configuration that leaves a free marginal area of the conductive substrate 56 all around the radiation sensitive layer 58. The both members are covered by an air-tight and transparent film 60, such as Mylar film, which is sealed at its opposite ends and side edges with the conductive substrate 56 by suitable means indicated at 61. In an end part of the conductive substrate 56 is formed an opening 62, which is connected to a suction means such as vacuum pump. The space enclosed by the film 60 is partly evacuated, for example, to 0.8 atm.,
- and such sub-atmospheric pressure serves to achieve a close and uniform contact between the both members 50, 55. Then the switch is closed and radiation 12 is released. It is to be noted that while high vacuum is favourable to make the contact closer, it renders the charge migration through the air space between the both members difficult to occur, thereby requiring a higher voltage for the source 9.
In FIGS. 10 and 11, there will be an electric charge in the irradiated parts of the record member and therefore such charge provides a negative when developed. However, the process illustrated in FIGS. 12a and 12b provides a positive. In these Figures, the radiationsensitive member 55 totally comprises transparent materials and the electrode 8 is in the form of a roller. In addition, the switch 10 is a double-pole doublethrow switch. Initially, a negative potential is applied to the conductive layer 57 of the radiation sensitive member 55 from the DC source 9 and at the same time the assembly 50, 55 is exposed to uniform radiation from the side of the member 55. During such exposure, the roller 8 is moved from left to right while rolling to press together successive parts of the members 50, 55 (FIG. 12a). This step charges the record member 50 uniformly. Then the roller 8 is returned to the left, and a light shield 63 having a slit 64 is arranged above the assembly in parallel thereto (FIG. 12b). The switch 10 is thrown to the other position and thus a positive potential is applied to the conductive layer 57. Then the radiation 12 which is defined imagewise is released and the roller 8 is moved to the right as before. Simultaneously, the light shield 63 is moved to the right at the same speed as the roller 8 to scan the whole area of the member 55. The transfer of charge occurs again, which charge this time is positive and hence neutralize the charge which exists already on the record member. The neutralization occurs imagewise so that the remaining charge on the record member will conform in pattern to the original. In other words, the electrostatic latent image on the record member 50, when developed, provides a positive.
In the process using a record member having a mesh layer, the radiation sensitive member may also be formed with a latent image previously, that is, before it is placed in contact with the record member. Such manner of operation is schematically shown in FIGS. 13a to 13. Initially, a corona charger 65 is connected with a DC source 9' of high voltage and is moved over the radiation sensitive layer 58 of a radiation sensitive member 55 (FIG. 13a). The conductive substrate of the member is earthed as is the negative terminal of the source. The layer 58 is uniformly charged positive. Then, FIG. 13b, the member 55 is exposed imagewise to radiation 12, whereby the charge in the irradiated areas will disappear. Subsequently, the member 55 is superimposed with a record member 50 of the form shown in FIG. 9d and the both members are pressed together by using an electrode 8 of soft, elastic conductive material and a backing support 8'. When switch 10 is closed to apply a positive potential to the member 55 (FIG. 13c), the latent image thereon is transferred to the record member. Upon opening switch 10, switch 11 is closed and then the member 55 is removed. Development of the resulting latent image on the record member provides a positive.
Several examples of a record member shown in FIG. 9 and the process using such member will be given below.
12 EXAMPLE 6 On a 50 micron thick paper of high quality was coated a substratum of polyvinyl alcohol to a thickness of 5 microns and on the substratum was coated a film of polystyrene resin 10 microns thick. The resulting composite is equivalent to a commercially available electrostatic recording paper. On the resin film was applied an insulating mesh layer, 8 microns thick, of polyvinyl butyral resin, using the copperplate printing technique mentioned previously. The copperplate ink comprised a 20% resin solution in alcohol. On the other hand, a photosensitive member was prepared by coating a conductive film of tin oxide, or Nesa film, on one surface of a hard glass plate 2 mm. thick, and by evaporating a 50 micron thick film of amorphous selenium on the conductive film. The both members were used in the process shown in FIG. 10, using a voltage of +750 volts and an exposure for a quarter of a second to a light output from a photographic enlarging device providing maximum illumination of luxes on the image surface. The image on the record member was satisfactory.
EXAMPLE 7 On a paper of high quality, 50 microns thick, was coated a substratum of polyvinyl alcohol, 5 microns thick, and on the substratum was coated a 12 micron thick film of polystyrene resin. On the surface of the resin film was formed a mesh layer using the heated roll technique, thereby obtaining a record member of the form shown in FIG. 9d. The meshwork was 200 meshes and individual dots were in the form of a truncated cone having a heigh of 8 microns, top diameter of about 40 microns and bottom diameter of about 50 microns. This record member was used together with the photosensitive member described in Example 6 in the process shown in FIG. 10 with the alternative that the electrode 8 comprised a conductive rubber sheet of 1 cm. in thickness and having hardness of 30 (HS). Applying a pressure of 500 gr./cm. to the rubber sheet and using a voltage of +750 volts and exposure for one second to a photographic enlarging device which provides maximum illumination of 20 luxes on the image surface, an image of good quality was obtained.
EXAMPLE 8 On a 12.5 micron thick film of polyethylene terephtalate (Mylar) was coated photoresist KPR available from Eastman Kodak Company to a thickness of 8 microns. A meshwork of 200 meshes was held in contact with the photoresist layer and the latter was exposed to ultraviolet ray. A developer comprising principally trichlene was applied to the photoresist to dissolve those parts which had not been polymerized, thereby obtaining a record member of the form shown in FIG. 9a. The record member was used in the same process as in Example 7 and provided a latent image of good quality.
EXAMPLE 9 A polystyrene film of 30 microns in thickness was tensioned on a rubber-lined drum of 50 cm. in diameter, and a roller matrix made from copper and having a diameter of 10 cm. and heated to C. was held against the polystyrene film under pressure. Rotating the drum at a peripheral speed of 3 m./min., dots of 8 microns in height and 200 meshes were formed in the surface of the polystyrene film. The film was removed from the drum and on its back was applied a 1 micron thick layer of copper iodide, thereby forming a record member of the form shown in FIG. 9b. On the other hand, a photoconductive member was prepared by evaporating amorphous selenium to a thickness of 50 microns on an aluminium plate 2 mm. thick. The record member and radiation sensitive member thus prepared were used in the process illustrated in FIG. 11 with the inner space enclosed by the film 60 being evacuated to 0.8 atm. Applying +l,500 volts to the record member and using an exposure for one second to a photographic enlarging device providing maximum illumination of 20 luxes on the image surface, a satisfactory latent image was obtained.