JPS604952A - Electrophotographic method and electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To stably reproduce a superior continuous gradation image by imagewise exposing the photoconductive layer of an electrophotographic sensitive body obtained by successively laminating a transparent electrically conductive layer and the photoconductive layer on a contact screen film, uniformly exposing said body from the nonscreen film side, developing it with a toner, then transferring the image and fixing it. CONSTITUTION:The surface of the photoconductive layer 5 of an electrophotographic sensitive body 1 is uniformly charged electrostatically by an ordinary method, and a light emitted from a light source 8 is transmitted through a light transmitting original 7 and projected through a lens 9 on the layer 5 from its side to imagewise expose it and form an electrostatic latent image. Then, the base 6 of a contact screen 2a of the body 7 is uniformly exposed from its side using a light source 11. The light transmitted through the screen 2 is converted into a light and dark pattern by this uniform exposure and reaches the layer 5, and converts the electrostatic latent image formed on the surface of the layer 5 into dots in such sizes corresponding to the height of the charged potential. After the double exposures, the image is developed by the electrophotographic developing method to form a toner image. It is transferred to a transfer sheet and fixed to form a permanent image.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an electrophotographic method with excellent gradation reproducibility and an electrophotographic photoreceptor suitable for use therein.

(Photographic technology) Photoreceptors for electrophotography generally have a structure in which a photoconductive layer is provided on a support whose surface at least has conductivity, and after charging, image exposure is performed from the photoconductive layer side. By this, an electrostatic layer image is formed. After being formed, the electrostatic latent image may be developed as it is using toner, or it may be transferred to another oil or the like and then developed. Incidentally, as a photoreceptor, there is also known a structure in which an insulating layer is further provided on the photoconductive layer and a latent image is formed on the insulating layer.

The quality of images obtained by such electrophotographic methods depends on factors such as the type of photoconductive layer, charging method, exposure method, development method, transfer method, fixing method, type of developer, and environmental conditions such as temperature and humidity. Although it is influenced by various factors, the factors that particularly affect continuous tone reproducibility include the particle size of the toner, the amount of charge of the toner, the surface potential of the photoreceptor, the development method, and the exposure method. .

Regarding the above factors, the surface potential of the photosensitive material differs depending on the type of photoconductive layer, but in general, the density range in which gradation can be reproduced is often narrow, and organic conductors such as polyvinylcarbazole, which are said to have a relatively wide density range, Even in an inorganic photosensitive material in which photoconductive powder such as cadmium sulfide, zinc oxide, etc. is dispersed in a grease-proofing material, or a photoconductor made of cadmium sulfide, etc., formed into a thin film of 1M by sputtering, etc., when compared with a silver salt photosensitive material, The density range in which gradations can be reproduced is insufficient.

Attempts to reproduce continuous gradations using an electrophotographic photoreceptor with a narrow gradation range can be broadly divided into studies on developing methods including toner materials and studies on exposure methods.

In terms of the former development method, it is known that a wet development method using a liquid developer exhibits excellent continuous tone reproduction. In a wet developer, since the toner particles are fine particles with a diameter of lμ or less, continuous tone reproducibility is excellent. However, since the wet developer contains an insulating solvent, it creates a bad working environment due to the odor (in addition, it requires a material with high solvent resistance as the transfer material, and it also has the disadvantage that it cannot be a completely dry system. ing.

In the dry development method that uses a powder developer, the toner particle size used is relatively large, approximately 2 to 35 microns, so continuous tone reproducibility is generally good (although not very good). Examples of dry developing methods with excellent continuous tone reproducibility include -pressure development method using component developers-?, powder cloud development method in which extremely fine powder toner is carried in a carrier air stream, and the like. However, in the pressure development method, corona charging is performed directly on the surface of the toner layer flattened by a blade, which causes severe toner deterioration, and has the drawback that toner particles tend to aggregate and become caked, and gradation reproducibility is poor. It is difficult to perform stable development because it is easy to change depending on the development voltage and negative voltage.In addition, the powder cloud development method has disadvantages such as difficulty in preventing scattering of toner particles and slow development speed. On the other hand, it is well known that continuous tone can be reproduced using the normal halftone decomposition method used in lithography. This method attempts to obtain excellent gradation by forming halftone dots with a width corresponding to the gradation of the original document by exposure through a screen or a glass screen.

However, when applying the method of exposing through a contact screen to an electrophotographic method, it is necessary to bring the contact screen into close contact with the electrophotographic photoreceptor. Because of the close contact, the hygroscopicity of gelatin has a strong influence on the electrical properties of the electrophotographic photoreceptor.Furthermore, exposure is performed with the contact screen in close contact with the charged electrophotographic photoreceptor. One drawback is that when the contact screen is peeled off from the photoreceptor after the contact screen is removed, the electrostatic latent image may be destroyed due to discharge destruction or the like.

Furthermore, there is a disadvantage that the apparatus for bringing the photoreceptor and the contact screen into sufficient contact with each other becomes complicated. or,
It is necessary to remove the contact screen before development, which has the disadvantage of tedious work.

On the other hand, when exposure is performed through a glass screen, the glass screen is usually fixed with a gap called the screen distance above the photoreceptor, and image exposure is performed using a lens system. The gradation characteristics change depending on the lens aperture, and the relationship between them must be determined through experience. Additionally, this method requires an expensive prepress camera;
It must be said that this method has major drawbacks in terms of simplicity and operability.

In addition, a common disadvantage of methods using contact screens and glass screens is that since the light transmitted through both screens is exposed to the electrophotographic photoreceptor, the amount of light is lost in both screens, resulting in an increase in exposure time and an increase in exposure time. This is accompanied by an increase in the intensity of the colored light, which poses severe economical and equipment constraints. More specifically, the increase in exposure time is
Due to the natural attenuation of the photoreceptor surface potential, the entire electrostatic latent image tends to disappear, which is a serious problem.

As mentioned above, the conventional process for reproducing continuous gradations using electrophotographic materials has the disadvantage of requiring special developers, development methods, and exposure methods that are different from those in general use. It has its drawbacks.

(Objective) The object of the present invention is to stably reproduce excellent continuous-level σ1 images by using an electrophotographic method and without using any special developer or developing method (by using a simple exposure method). It is in.

The present invention includes the steps of: preparing an electrophotographic photoreceptor in which a transparent conductive layer and a photoconductive layer are sequentially laminated on a film surface of a contact screen, and performing imagewise exposure from the photoconductive layer side of the electrophotographic photoreceptor; λ exposure steps of exposing the entire surface of the contact screen from the non-film side are performed, followed by development using toner, transfer, and then fixing.
The present invention relates to an electrophotographic method characterized by:

The present invention also relates to an electrophotographic photoreceptor in which a transparent conductive layer and a photoconductive layer are sequentially laminated on the film surface of a contact screen.

(composition) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a sectional view showing the structure of a 7:1 electrophotographic photoreceptor used in the present invention. In FIG. 1, the electrophotographic photoreceptor 1 has a structure in which a transparent conductive layer and a photoconductive layer 5 are sequentially laminated on a film surface 3 of a contact screen. Reference numeral 6 in FIG. 1 indicates the profiteering of the contact screen.

As the contact screen, all contact screens commonly used in printing plate making can be used. As the transparent conductive layer, metal, tin oxide,
It can be formed by vapor depositing indium oxide or silver iodide, or by applying a solution in which conductive particles are dispersed in a polymer to the membrane surface 3'' of a contact screen.

A photoconductive layer 5 is formed on the conductive layer. The photoconductive layer 5 may be made of an organic photoconductive material such as polyvinyl carbazole or a photoconductive powder (zinc oxide, zinc sulfide, titanium oxide, cadmium sulfide, copper phthalocyanine,
Resin-dispersed type in which selenium, etc.) is dispersed in transparent resin, inorganic photoconductive materials such as amorphous selenium and amorphous silicon,
They exhibit photoconductivity, such as functionally separated types with multilayer structures.
Any material used in known electrophotographic photoreceptors can be used, and the layer 5 may be provided by any known method. Here, a resin-dispersed photoconductive layer in which photoconductive powder such as zinc oxide is dispersed in a resin has lower transparency than an organic photoconductive layer such as polyvinyl carbazole, so it cannot be used as a basis for a contact screen.
It was thought that it would be impossible to form an electrostatic latent image on the surface of the photoconductive layer even if exposed to light, or even if it was possible, it would be accompanied by a decrease in photosensitivity. ,
It was confirmed that electrostatic latent image formation was possible without causing a decrease in photosensitivity.

As for the thickness of the photoconductive layer S! ;-100μ711 is preferred. In the present invention, since exposure is also performed from the contact screen 2 side of the electrophotographic photoreceptor, if the thickness of the photoconductive layer S is too large, exposure to light from the contact screen 2 side may cause light to appear on the surface of the photoconductive layer 50. This is because the location where carriers (charge carriers) are generated becomes blurred due to the diffusion of exposure light in the photoconductive layer S, impairing resolution. When the thickness of the photoconductive layer 5 exceeds 100 .mu.m, it becomes impossible to ensure the resolution of 100 lines/inch, which is the number of lines for ordinary printed matter.

The surface of the photoconductive layer S may be exposed as it is as shown in FIG. 1, but a protective layer or an easily peelable layer may be provided as necessary.

Next, an image forming method using the electrophotographic photoreceptor l described above will be described. For the sake of explanation, the charge polarity is shown as negative, but it goes without saying that this polarity is determined by the type of photoconductive material used.

FIG. 2 is a 1'' cross-sectional view showing the process of exposing an electrophotographic photoreceptor 1 to light using a transparent original 7 having gradations.

Exposure is performed by irradiating a transmission projection image from the transmission original 7 from the photoconductive layer 5 side through the lens 9 to form an electrostatic latent image. Here, methods for forming the electrostatic latent image include a method using a reflective light source g' and a reflective original 7f as shown in FIG. 3, a method using a fiber optical tube or a light emitting diode array, and a laser writing method. Any known electrostatic a-image forming method such as , etc. may be used.

Next, the entire surface of the contact screen 20 of the electrophotographic photoreceptor 7 is exposed to light using a light source. Due to this whole surface exposure, the light transmitted through the contact screen becomes a bright and dark pattern due to the action of the contact screen, and also reaches the photoconductive layer 5, causing an electrostatic latent image formed on the surface of the photoconductive layer. , the dots are converted into halftone dots whose size corresponds to the height of the charged potential.

In other words, the electrostatic latent image obtained is not only caused by changes in the degree of decrease in the surface potential of the electrophotographic photoreceptor l that is proportional to the density of the original (
By regulating the size of halftone dots, the gradation increases by 7.

Here, the amount of exposure for the entire surface exposure varies depending on the material 4F of the photoconductive layer 5 of the electrophotographic photoreceptor 1, but if the amount of exposure is too large, halftone dots may appear in the solid portion of the electrostatic latent image. The appropriate exposure amount is such that the solid portion of the electrostatic latent image does not become a halftone pattern, since this may cause a decrease in resolution.

In addition, the image exposure of the photoconductive layer and the contact screen 2
The order of both exposures of the entire surface from the base material 6 side may be carried out first as long as the electrophotographic photoreceptor is charged (although it is also possible to carry out both exposures at the same time).

The electrostatic latent image after both exposures can also be visualized by a known electrophotographic development method, such as a magnetic brush development method using dry toner or a powder cloud development method. , a pressure development method, and a liquid development method using a wet toner.

The image obtained after development shows excellent continuous gradation created by variations in toner coverage and the size of halftone dots.

A toner image visualized by development is transferred and fixed onto a transfer object to form a permanent image. Any known method can be used for transfer and fixing, and examples of transfer methods include electrostatic transfer, adhesive transfer, pressure transfer, etc., and fixing methods include fusion using force 1]Q. Examples include fusion using solvent vapor, fixing using transparent resin coating, and the like.

(effect〕 According to the present invention described above, there are the following effects.

(b) Gradation image [image exposure is performed through a contact screen, so the shading of the formed image is formed by changes in the size of halftone dots and the amount of toner adhesion, so the range of gradation reproducibility is narrow. Even if an electrophotographic photoreceptor is used, extremely excellent continuous tone reproducibility can be obtained.

Naka) The equipment and process for bringing the contact screen into close contact with the electrophotographic photoreceptor and the equipment and process for peeling the contact screen from the photosensitive material at the end of exposure can be omitted, simplifying the equipment and shortening processing time. can be achieved.

(・→Since the conventional contact screen film surface is a gelatin layer, it is susceptible to atmospheric influences such as moisture absorption.) JP causing latent image destruction
However, in the present invention, since the film surface is narrowed between the contact screen base and the photoconductive layer, there is no adverse effect caused by the gelatin layer.

b) Since there is no need to bring a contact screen or the like into close contact with the surface of the charged electrophotographic photoreceptor during exposure, problems such as discharge damage caused by contact and peeling operations are solved.

(e) The electrophotographic photoreceptor is made into a cylindrical or belt shape,
By providing the light source 7 inside, it can be applied to all currently popular electrophotographic devices, and it is possible to reproduce gradation images without increasing the size of the device by adding a special new mechanism.

(Since contact screen exposure and document exposure are performed in separate paths, if there is a halftone photograph on the document, moiré caused by interference between the contact screen of the photosensitive material and this halftone photograph can be selectively removed using the contact screen. This can be easily prevented by stopping the entire exposure from the base surface of the contact screen.Also, if there is no image with continuous gradation in the original, stop the full exposure from the base surface of the contact screen. This has the great advantage that operating time can be shortened.

Examples are given below to more specifically illustrate the present invention.

Example/ In203N (t o o o
X thickness) wo formation.

Next, Rose Bengal. A liquid having the following composition was prepared using ZnO powder adsorbed with 3% by weight.

(Contains θ3 rose bengal) ZnO...g
5 parts by weight silicone resin KR-,)O5<manufactured by Shin-Etsu Chemical Co., Ltd.)...Co. 〃Ethylseron rub acetate...
...0@・ss 〃Incyanate (Coronate Co. 3/.

2 parts by weight (manufactured by Nippon Polyurethane) were added and mixed.
It was applied over the O3 layer to a thickness of 1 SμηL by a spin coating method to form a photoconductive layer.

Thereafter, it was heated in an oven at a temperature of 100° C. for 2 hours to obtain an electrophotographic photoreceptor.

The electrophotographic method using the electrophotographic photoreceptor obtained above was carried out as follows. First, the surface of the photoconductive layer of the electrophotographic photoreceptor was negatively charged by a normal process. The surface potential of the electrophotographic photoreceptor after charging was -5oo. next,
Using this charge-stopping electrophotographic photoreceptor, a step tablet (manufactured by Fuji Photo Film Co., Ltd., Fuji Ps Step Projection exposure was performed using a guide).

Tungsten light was used as a light source for projection exposure, and the exposure amount of the portion corresponding to the base of the step tablet on the surface of the photoconductive layer was 50 lux for 2 seconds. after that,
The entire surface of the electrophotographic photoreceptor was exposed using a tungsten light beam from the substrate side so that the exposure amount on the substrate surface was /00 lux for 10 seconds. After exposure, the surface of the photoconductive layer of the electrophotographic photoreceptor was developed by a conventional magnetic brush development method, and then electrostatically transferred onto high-quality paper and fixed by heating in a thermal oven. At this time, a dry type l-ner manufactured by Tokyo Ink was used as a developer.

The J' image obtained here had halftone image quality with excellent continuous tone reproducibility, as shown by curve a in FIG. 9. use your body,
After the surface of the photoconductive layer was negatively charged in the same manner as in Example 2, tungsten light was first applied from the base material side of the electrophotographic photoreceptor using the method shown in FIG. 700
The entire surface was exposed to light for io seconds at lux. Thereafter, projection exposure was performed on the surface of the light guide 1a layer S using a step tablet in the same manner as in Example. After exposure, development, transfer, and fixing were carried out in the same manner as in Example 1, and the resulting image had excellent halftone image quality similar to that in Example.

Example 3 Using the same electrophotographic photoreceptor as used in Example 1,
After the surface of the photoconductive layer was negatively charged in the same manner as in Example 1, the surface of the photoconductive layer was exposed to a continuous gradation reflection IJj, a reflection projection image, as shown in FIG. As the reflective original, silver halide photographic paper obtained by reprinting the step tablet used in Example 1 was used. A fluorescent lamp was used as the exposure light source, and the exposure amount on the surface of the photoconductive layer was 501 ux for 2 seconds. Furthermore, after exposing the entire surface of the contact screen under the same conditions as in Example 1, development, transfer, and fixing were performed in the same manner as in Example 1. / showed excellent continuous tone reproducibility.

Example G A photoconductor was prepared in the same manner as in Example/, and after charging, the f-quadrant exposure from the photoconductive layer side and the entire surface exposure from the photoconductor substrate side were performed simultaneously at the same exposure amount as in Example/. A halftone image having the same gradation as in Example 1 was obtained.

Comparative example/Electron′! The process was carried out in the same manner as in Example 1, except that the entire surface exposure from the photoreceptor contact screen substrate side was omitted, and the obtained image quality was as shown by the curve in the diagram.
It was a high-contrast image with a narrow continuous tone reproduction density range.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of the electrophotographic photoreceptor used in the present invention, FIGS. 2 and 3 are schematic diagrams showing the exposure method in the electrophotographic method of the present invention, and FIG. The figure is a graph for explaining the gradation reproducibility of images obtained in Examples and Comparative Examples of the present invention. !・・・・・・・・・・・・Electrophotographic photoreceptor ・・・・
...Contact screen 3 ...Fist...
−Fist・−・Contact screen film surface・・・・・
...Transparent conductive layer S ...Photoconductive layer 6 ...
...Base material 7 of contact screen...
......Transparent manuscript 71...
...Reflection original g, gζI/----' light
Source 9・Sha...Fist...E Shinzu Spear 1 Illustration Fang 2 Fang 8 Illustration

Claims (2)

[Claims] (1) A step of preparing an electrophotographic photoreceptor in which a transparent conductive layer and a photoconductive layer are successively laminated on the film surface of a contact I/screen, and performing one-image exposure from the photoconductive layer side of the electrophotographic photoreceptor. The contact screen is characterized by performing two exposure steps: exposing the entire surface from the non-film side of the contact screen, then developing with toner, then transferring, and then fixing. electrophotographic method. (2) An electrophotographic photoreceptor in which a transparent conductive layer and a photoconductive layer are sequentially laminated on the film surface of a contact screen.