JPS6289972A - Color electrophotography method - Google Patents

Abstract

PURPOSE:To improve image quality in a color electrophotography method by an EF method by using a specific substrate sheet for a photosensitive body sheet having a photosensitive titanium dioxide layer and grounding the rear surface of the photosensitive body sheet by a specific technique. CONSTITUTION:A conductive layer is laminated on the substrate sheet having high smoothness to form the conductive base and the photosensitive layer contg. the titanium dioxide as an essential photosensitive agent is laminated on the conductive layer to constitute the photosensitive body sheet. Conductor films are formed in the thickness direction part and rear surface part of such photosensitive body sheet and are grounded to a conductive conveyor. The high- smoothness substrate sheet to be used is preferably such a sheet which has preferably >=2,000sec Bekk smoothness, is usually about 80-130mu thick, is flexible, has the lower conductivity in the volume direction with usually 10<13>-10<15>OMEGAcm specific resistivity and obviates the ununiform conductivity distribution in the volume direction by the penetration of the conductive coating liquid into the substrate. Such sheet is exemplified by synthetic paper or the like.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to an electrophotographic method for forming a clear multicolor image on a titanium dioxide photoreceptor sheet using a highly smooth substrate sheet. .

[Technical background of the invention and its 1JlrJ points] A photoreceptor sheet in which a photosensitive layer made of a photoconductive substance dispersed in an insulating resin is laminated on a conductive support sheet is formed into a drum-shaped, belt-shaped, etc. conductive sheet. By sequentially repeating the image forming process of carrying the document on a conveyor, charging it by corona discharge, exposing it to light to form an electrostatic latent image corresponding to the document, and then developing it with toner, Color electrophotographic drawing in which color toner images are superimposed is well known as the so-called color electrofax method (hereinafter referred to as IEF method).

Incidentally, in the EF method, the photoreceptor sheet is usually a relatively porous base paper mainly composed of cellulose wL fibers and has a Beck smoothness of about 400 to 700 seconds, and the paper is conductive. A conductive support is obtained by coating or impregnating a substance, or by adding it to the base paper at the time of papermaking, and then oxidizing it as a photoconductive substance on this conductive support. The most commonly used one is one in which photosensitive layers made of zinc dispersed in insulating In resin are laminated.

However, with the conventional photosensitive paper using zinc oxide as described above, it has not been possible to produce a so-called Victorian high-quality copy image comparable to that of silver halide photography.

In recent years, there has been a strong desire for the electrophotographic method to be capable of copying and creating images with continuous gradation and sharpness comparable to that of silver halide photography. For some time, researchers have focused on using titanium dioxide as a photoconductive material, which has the characteristics of high whiteness and excellent continuous gradation performance. As a result of trying to do this, we found that the color E
In order to achieve high image quality in copying images by the F method, (1) it is necessary to use a highly smooth base sheet since the surface smoothness of the base sheet greatly affects the image quality;
and (2) even when such a highly smooth base sheet is used as a conductive support, sufficient uniform back grounding characteristics can be obtained in the thickness direction (volume direction) of the photoreceptor sheet. As a result of further studies based on this knowledge, we have completed the present invention.

[Summary of the invention]

Based on the above findings, the present invention utilizes a CF method by using a specific base sheet for a photoreceptor sheet having a titanium dioxide-based photosensitive layer and by grounding the back surface of the photoreceptor sheet by a specific method. In this method, a photoreceptor sheet is supported on a conductive carrier, and the photoreceptor sheet is charged and exposed to light to form an electrostatic latent image. In a color electrophotographic method in which a multicolor toner image is superimposed by sequentially repeating the steps of forming a toner image and then developing it with a liquid developer to form a toner image, a conductive layer is laminated on a highly smooth base sheet. A photoreceptor sheet is formed by laminating a photosensitive layer containing titanium dioxide as a main photosensitive agent on the conductive layer, and a conductive coating is applied to the thickness direction and back surface of the photoreceptor sheet. This is a color electrophotographic method characterized in that a conductive carrier is formed and grounded to the conductive carrier.

In the method of the present invention, the highly smooth base sheet used has a Beck smoothness of 1,000 seconds or more, preferably 2,000 seconds or more, and a thickness of usually 80 to 13 seconds.
It has flexibility at around 0 μ, and the specific resistance is usually IQ + 3
~1OIsΩ (conductivity in J+ and volume direction decreases slightly,
It is desirable that the conductive coating liquid does not penetrate into the substrate and make the conductivity distribution uneven in the volume direction.
For example, synthetic paper, resin film such as Mylar film,
Examples include non-porous tMa resin coated paper. Further, the conductive layer can be laminated on the base sheet by various methods, such as by vapor-depositing metals such as aluminum, gold, silver, or the like, or by laminating these metal foils. Furthermore, a conductive support can be formed by applying a conductive composition. Furthermore, the photosensitive layer containing titanium dioxide as the main photosensitive agent may be made of various resins with high electrical insulation properties, such as acrylic resins, alkyd resins, polyester resins, polyurethane resins, amino resins, vinyl resins, etc., either alone or in combination. By using titanium dioxide as a binder, sensitizing titanium dioxide in the binder with a sensitizing dye if necessary, dispersing this as a photosensitive main agent, and coating the dispersion composition on the conductive layer. can be formed.

In the method of the present invention, in order to ground the back surface of the photoreceptor sheet formed as described above with the conductive conveying member, it is necessary to ground the photoreceptor sheet in the 11th direction, that is, to This can be done by forming a conductive film on at least a portion of the back surface to provide electrical continuity.

In order to form the conductive film on the photoreceptor sheet, the conductive composition is applied to the relevant area by various methods such as spraying, roller coating, silk screen printing, and brush coating. In either case, at least a part or the entire surface of the side end surface and back surface of one side or both sides of the photoreceptor sheet in the conveying direction (lengthwise direction) of the photoreceptor sheet By applying the coating continuously or intermittently along the photoreceptor sheet surface, it is possible to form a film with a thickness of about 3 to 7μ and a surface resistance of about 101Ω or less, preferably 10”Ω or less. It is important to prevent the formation of a film of the conductive composition, and in particular, if the coating liquid of the conductive composition adheres to the peripheral edge of the surface of the photoreceptor sheet, image formation in that area will be inhibited, and the image will be damaged. The peripheral edges become extremely unclear, which is undesirable, especially in the case of Victorian color multicolor images, unlike in the case of so-called line copying, as the finishing properties are significantly impaired. In order to form a uniform film by selectively applying the conductive composition to the side end surfaces and the back surface while substantially avoiding adhesion to the surface, it can be done by various methods as described above. As in the example, for example, while a long roll-shaped photoreceptor sheet is running at a constant speed, a small [1] in the direction of running of the sheet, and in the J7 width direction part and the back side part of the sheet. For example, an airless type spray device may be installed so that a fan-shaped liquid film flow is formed on a part or all of the area, or the winding side end surface of a roll of a long photoreceptor sheet ( It is preferable to use, for example, a silk screen printing method or a brush coating method so that a conductive film is formed on the entire surface of the photoreceptor sheet (in the thickness direction) and at least a portion of the back surface of the photoreceptor sheet.

In the method of the present invention, the conductive composition for forming a conductive film for grounding the back surface of the photoreceptor sheet with the conductive carrier includes, for example, a conductivity-imparting substance, a water-soluble polymer binder, a conductive A conductivity imparting substance and a curable resin binder, a conductivity imparting substance, a soap-free emulsion, a water-soluble polymer binder, etc. may be used alone or in combination, but as the conductivity imparting substance, hydrochloric acid Inorganic salts such as salts and nitrates, organic hygroscopic substances such as glycerin and ethylene glycol, polyvinylbenzyltrimethylammonium 70lide,
Doping various different elements such as cationic, anionic, or amphoteric polymer electrolytes such as polystyrene sulfonate soda, metal fine powders such as gold, silver, and copper, carbon black such as carbon am, indium, and cadmium on the surface of metal oxides. The surface of titanium dioxide particles was treated with tin oxide,
Examples include those surface-treated with antimony oxide, low-order titanium oxide, conductive metal oxides such as copper iodide, or metal halides, and these may be used alone or in combination. Examples of the water-soluble polymer binder include cellulose derivatives such as methylcellulose and human axyethylcellulose, starch derivatives such as esterified starch and oxidized starch,
Natural animal and plant resins such as sodium alginate, casein, gelatin and gum arabic, polymers and copolymers such as acrylates and maleates, polyvinyl alcohol,
Polyacrylamide, polyethyleneimine, amino U (
Examples include synthetic polymers such as fats and water-soluble polyethylene, and these may be used alone or in combination. Further, if necessary, a polymer emulsion or copolymer emulsion, a crosslinking agent, an inorganic or organic pigment, etc. may be added within a range that does not adversely affect the conductivity. Examples of the curable resin binder include alkyd resin, reactive acrylic U (fat), phenol resin, polyurethane resin, polyamide resin, polyester resin, petroleum ? Add a catalyst or perform treatments such as heating, ultraviolet irradiation, or electron beam irradiation to suit the curing mechanism of The titanium dioxide particle surface treated with tin oxide or antimony oxide has a high degree of whiteness and does not color the photoreceptor sheet, and is of the so-called electron conductive type, making it conductive. It is even more desirable that it is stable against environmental humidity.

In the present invention, a photoreceptor sheet containing titanium dioxide as a main photosensitive material whose back surface has been grounded as described above is supported on an electrically conductive carrier, and is charged, exposed, and wetted with a toner of a complementary color to the color separation exposure. By developing and repeating this image forming process a predetermined number of times and superimposing each color toner of yellow, magenta, cyan, and black if necessary, a clear multicolor image with excellent continuous gradation is formed. be able to.

The present invention will be further explained below with reference to Examples.

In the example, synthetic paper (based on polypropylene, Yubo FPG manufactured by Tamago Yuka Co., Ltd., Beck smoothness 2.OS 0 seconds,
A conductive layer was formed by vapor depositing aluminum on the surface (thickness: 130 μm, +IJ: 297 mm, length: 100 m). A coating liquid in which a panchromatically sensitized titanium dioxide photoreceptor is dispersed in acrylic 4J4 resin paint (manufactured by Eclipse Arrow Co., Ltd., 707) is applied onto this conductive support by a reverse foot method to form a photosensitive layer. (dry film thickness 15μ) was formed. Next, conductive titanium oxide powder (titanium dioxide particles surface-treated with tin oxide, powder specific resistance is 2.7 Ωcm) was applied to the photoreceptor sheet. 3 Acrylic resin (manufactured by Soken Kagaku Co., Ltd., Elefund) Dispersed in (weight ratio: 1:
1) Coating liquid (p
vcso%, FORD CU P 94 viscosity 13 seconds) was applied to the side end surface (thickness direction of the photoreceptor sheet) of the photoreceptor sheet using an airless spray device (manufactured by Doson Co., Ltd.) as follows. Coated. That is, the coating liquid is sprayed so that the coating liquid is spread as a fan-shaped liquid film flow from one side end of the back surface (support side) of the photoreceptor sheet to the side surface (thickness direction of the photoreceptor sheet) extending to the conductive layer. A nozzle is disposed at an angle of 75 degrees to the support surface from the rear of the back surface of the sheet to discharge the coating liquid (50 cc/min).
I let it happen. At this time, the photoreceptor sheet was run at a speed of 50 m/min, and a suction/exhaust mechanism was installed to substantially avoid excess ejected liquid from depositing on the surface of the photoreceptor sheet. So I went.

On the surface of the thus obtained photoreceptor sheet containing titanium dioxide as the main photosensitive material and subjected to back-grounding treatment, substantially no conductive coating is formed on the surface of the photoreceptor sheet, which covers the entire side end surface of the sheet and the end portion of the back surface of the support. A conductive continuous film with a thickness of approximately 4 μm was formed over approximately 3 INI11. The surface resistance of the side end insertion portion was 104Ω. Furthermore, the electrophotographic properties and image properties of the photoreceptor sheet were evaluated as follows.

(1) Electrophotographic characteristics As shown in (a) to (c) below, the charging characteristics, dark retention rate, and photosensitivity are all excellent, and the grounding material can make the electrostatic latent image forming ability of the photoreceptor effective. It had excellent performance.

(a) Charging characteristics Surface potential after 20 seconds under corona charging (-6KV) (
Initial potential) is 1,000V, and (b)
Dark retention rate The surface potential value 20 seconds after reaching the initial potential value in (a) above is 75% as a percentage of the initial potential value, and (c) 25% when the light sensitivity exposure myoelectric potential is 200V. The time required for the surface potential to be reduced by half after irradiation with lux light was 0.5 seconds.

(2) Image characteristics The electrophotographic photoreceptor sheet having the electrophotographic characteristics described in (1) obtained in Example 1 was charged, exposed, and exposed in a conventional manner using Macbeth color batch as an image sample.
When developing with yellow, magenta, and cyan color-concentration developers and overlapping the colors to form a multicolor image, the color density of each toner image was the desired color density, that is, yellow 20.90, magenta: 1.23, cyan: 1.35.

Further, the electrophotographic photoreceptor sheet was supported on a drum-shaped conductive conveyor, and a corona discharge voltage of -6 KV was applied to uniformly charge the surface of the photosensitive layer negatively, and then the multicolor original was passed through a blue filter. An electrostatic latent image corresponding to the original image is formed by color separation exposure through a color filter, and then developed with a positively charged yellow toner wet developer to undergo the first image forming process, followed by a green filter. A multicolor image was formed by performing exposure using a red filter and a second image forming process using magenta toner, followed by exposure using a red filter and a third image forming process using cyan toner. The resulting image has no image noise such as fog, and there is no unevenness in density around the edges of the photoreceptor sheet, and it has a high density comparable to that of a silver halide photograph that corresponds to the original image, and is clear and has good gradation. It was in good condition.

In addition, in the above-mentioned airless spray coating film forming process, when the spray nozzle was discharged from a direction substantially horizontal to the surface of the support, the side edges of the surface of the photosensitive layer other than the side edges of the photoreceptor sheet Formation of a conductive film was also observed in the area, and as a result, image formation at the peripheral area was insufficient and uneven shading was observed.

Example 2 For the photoreceptor sheet used in Example 1, in which a photosensitive layer containing titanium dioxide as the main photosensitive agent was formed on the conductive support, carbon black powder was added to a polyester resin as a conductivity imparting substance. The coating liquid of the dispersed conductive coating composition (manufactured by Fujikura Kasei Co., Ltd., FC-404) was silk-screen printed using a screen (1.80 mesh, manufactured by New Long Seimitsu Kogyo Co., Ltd.) to form a roll of the photoreceptor sheet. A conductive film was formed by coating both sides of the end surface of the product and a part of the back surface of the photoreceptor sheet to form a conductive film.

The thus obtained photoreceptor sheet containing titanium dioxide as a main photosensitive material whose back surface has been grounded has substantially no conductive film formed on its surface, and covers the entire side end surface of the sheet and the back surface of the support. A conductive continuous coating having a thickness of approximately 5 μm was formed over approximately 0.5 mm at the end. The surface resistance of the side end insertion portion was 102Ω. Further, the electrophotographic properties and image properties of the photoreceptor sheet were good as in the case of nXjX Example 1.

Example 3 Carbon black powder was added to the roll of the long photoreceptor sheet used in Example 2 by adding 1j of aliphatic petroleum.
A conductive coating composition (manufactured by Fujikura Kasei Co., Ltd., X
C-32) is used to coat the entire roll of the photoreceptor sheet (1111) on both sides of the end face and a part of the back surface of the photoreceptor sheet using a brush coating method to form a conductive film. formed.

The thus obtained photoreceptor sheet containing titanium dioxide as a main photosensitive material whose back surface has been grounded has substantially no conductive film formed on its surface, and covers the entire side end surface of the sheet and the back surface of the support. A conductive continuous coating having a thickness of approximately 5 μm was formed over approximately 0.5 mm at the end. The surface resistance of the side end ground portion was 102Ω. Further, the electrophotographic properties and image properties of the photoreceptor sheet were good as in Example 1 above.

〔Effect of the invention〕

In the case of the method of the present invention, (1) the influence of image noise etc. due to the surface smoothness of the photoreceptor sheet can be substantially eliminated, and (2) the photoconductive properties of the titanium dioxide-based photosensitive layer can thereby be improved. (3) There is no need to provide a special grounding device as in the case of surface grounding, and Since a clear image can be formed over the entire surface of the photoreceptor sheet, excellent effects such as no special trimming of the ground portion at the periphery of the sheet are brought about.

Claims (1)

[Claims] A photoreceptor sheet is supported on a conductive carrier, and the photoreceptor sheet is charged and exposed to original light to form an electrostatic latent image,
In a color electrophotographic method in which multicolor toner images are superimposed by sequentially repeating the step of developing with a liquid developer to form a toner image, a conductive layer is laminated on a highly smooth base sheet to form a conductive support. A conductive film is formed on a thickness direction portion and a back surface portion of the photoreceptor sheet with respect to a photoreceptor sheet formed by laminating a photosensitive layer containing titanium dioxide as a photosensitive main ingredient on the conductive layer. A color electrophotographic method characterized in that the conductive carrier is grounded.