JPH03120559A - Liquid developing method for electrophotography - Google Patents

Abstract

PURPOSE:To prevent the contrast of an image from lowering and to prevent the occurrence of fogging by making pretreatment liquid adhere on a photosensitive body surface after forming an electrostatically charged latent image, then performing developing with liquid toner, and continously squeezing the liquid toner by a non-contact squeeze. CONSTITUTION:The pretreatment liquid is supplied through a supply pipe 1 and made to adhere on the image forming surface S of an electrophotographic photosensitive body T. And then, the liquid is conveyed to a toner developing processing part by conveying and squeezing rollers 2A and 2B while controlling the quantity of the preptreatment liquid adhering on the electrophotographic photosensitive body T. When the photosensitive body T enters in a toner developing part, the switch of a power source 8 in a reverse bias voltage impressing device 7 is closed and +40V reverse bias voltage is impressed on a back electrode 6 against a developing electrode 5. The photosensitive body T passing through the toner developing processing part is squeezed by an air knife 9 to eliminate surplus toner, then dry fixation is performed. Thus, the contrast of the image can be prevented from lowering and the occurrence of the fogging can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid developing method for electrophotography, and particularly to a method for liquid developing an electrophotographic photoreceptor suitable for printing plates.

[Conventional technology]

Conventionally, in the technology of developing an electrophotographic photoreceptor with a resin dispersion plate in which an inorganic photoconductive substance such as znO or CdS or an organic photoconductive substance such as a phthalocyanine pigment or an azo pigment is dispersed in a resin with a liquid toner. Tokikai, 1982-272760, as a technique for improving the drawbacks of toner adhering to non-image areas, reducing image contrast, and causing printing stains in non-image areas when used as a lithographic printing plate.
No. 61-272771 discloses a technique in which a pretreatment liquid is applied to the image forming surface of an electrophotographic photoreceptor, development is performed while applying a bias voltage, and excess toner developer is removed using a squeeze roller. It has been known.

However, the center line average roughness Ra (JIS standard BO6
For electrophotographic photoreceptors having a rough surface with 10) of 0.15 or more, the effect of preventing toner adhesion to non-image areas is insufficient, reducing image contrast, and when used as a lithographic printing plate. There is a problem of printing stains.

[Purpose of the invention]

The present invention aims to overcome the drawbacks of the above-mentioned known techniques, and an object of the present invention is to prevent toner from physically touching the surface of the photoreceptor when developing an electrophotographic photoreceptor having a rough surface as described above with liquid toner. It is an object of the present invention to provide a liquid developing method which can improve the occurrence of fog caused by adsorption to a liquid, particularly printing stains when applied to a lithographic printing plate.

[Structure of the invention]

The object of the present invention is to have a center line average roughness Ra of 0.15 to
In a method in which an electrophotographic photoreceptor having a surface of 0.70 μm is charged and exposed to form a charged latent image, and a toner image is formed by liquid development, a pretreatment liquid is attached to the surface of the photoreceptor after the charged latent image is formed. Then, liquid toner development is performed.
This is achieved by an electrophotographic liquid developing method characterized in that the liquid toner is subsequently squeezed by non-contact squeezing.

The present invention will be explained in detail below.

In the method of the present invention, the carrier liquid of the liquid toner developer used in the next processing step can be used as the pretreatment liquid to be applied to the surface of the photoreceptor after the charged latent image is formed. The amount of pretreatment liquid deposited on the surface of the photoreceptor at the start of liquid toner development is preferably 10 to 500 Q/a'', more preferably 20 to 200 Q/a.

Known means can be applied to deposit the pretreatment liquid on the surface of the photoreceptor in such an amount. For example, first,
For example, if an appropriate amount or more of the pretreatment liquid is supplied to the photoreceptor surface,
A method of dropping, spraying, or spraying the pretreatment liquid onto the photoreceptor surface using a shower pipe or nozzle, or sliding the photoreceptor surface with a porous or liquid-absorbing member such as a sponge or cloth. , by a method of coating through the member, etc.), and then passing through a squeezing roller having fine irregularities on the curved surface to regulate the amount of adhesion.

The preferred non-contact squeeze method following liquid toner development is air squeeze. As the air squeeze, the air doctor technique in the known air doctor coater technique can be applied. When using such an air doctor, a nozzle width of 0.5 to 5 mm, a distance of 1 to 100 a+m from the photoreceptor surface to the knife, and a setting angle of the knife of 45 to 135'' are appropriate. ” (written by Harasaki, published by Maki Shoten) can be referred to.

Examples of other preferable non-contact squeezes include corona squeeze, reverse squeezing roller squeeze, and the like. In the corona squeeze, after squeezing the amount of liquid on the photoconductor using a liquid amount regulating roller, a corotron of the same polarity as the toner is applied to further reduce the liquid film thickness. In the reverse aperture roller, the photoreceptor and 0.05
~(The liquid can be squeezed by providing a roller with a gap of Llmm and rotating the roller at high speed in a direction opposite to the direction of travel of the photoreceptor.

The present invention is particularly effective for electrophotographic photoreceptors having a photoreceptor surface having a centerline average roughness Ra of 0.15 to 0.70 μm, particularly 0.2 to 0.5 μm. The centerline average roughness Ra in the present invention is the centerline surface roughness Ra measured according to JIS standard BO610. The Ra is 0.1
If it is less than 5, the effect of using non-contact squeeze is not significant,
If it exceeds 0.70, it is difficult to remove fog sufficiently even using the method of the present invention.

The present invention applies when the support of the electrophotographic photoreceptor is a roughened metal support, when the photoconductor layer of the electrophotographic photoreceptor contains 10% by weight or more of a pigment, and when the pigment contains 7-talocyanine. When pigments are used, the surface of the photoreceptor tends to be rough and toner is easily adsorbed, so the effect of the present invention is large.

When the electrophotographic photoreceptor is used as a non-image area elution type printing plate, it is preferable to use a roughened metal support as the support. The roughened metal support has high hydrophilicity and, when used as a printing plate, has high oil insensitivity in non-image areas, and has good printability and printing durability. If the support is a metal support with a roughened surface in this way, even after the photoconductive layer is applied, the photoconductive layer will reflect the roughness of the support, and the surface of the photoreceptor will also tend to become rough. Therefore, the effect of the present invention is great.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 An electrophotographic photosensitive layer with a copper phthalocyanine pigment dispersed in a phenol resin was formed on a grained and hydrophilic aluminum plate to a thickness of 5 μm.
An electrophotographic photoreceptor was prepared with a thickness of . When the surface roughness of this photosensitive layer was measured using a belt meter 35P (manufactured by Perthan), the center line average roughness Ra was 0.30.
Met.

A latent image was formed on this photoreceptor by the same charging and image exposure as in a conventional electrophotographic plate-making machine, and then development was performed using the developing device shown in FIG. In Fig. 1, l is the front liquid supply pipe, 2A and 2B are conveyance/squeezing rollers, and 3
is the aperture pressure adjustment screw, 4 is the developer supply unit, 5 is the development electrode, 6 is the back electrode, 7 is the reverse bias voltage application device, 8
9 is a reverse bias power supply, 9 is an air knife, T is a photoreceptor, and S is its image forming surface.

As a pretreatment liquid, Isopar, an isoparaffinic solvent, is used.
G (manufactured by Exxon) was used. The pretreatment liquid is supplied from a liquid reservoir (not shown) to a pretreatment liquid supply pipe 1 using a pump (not shown), and is supplied to and adheres to the image forming surface S of the electrophotographic photoreceptor T.

An electrophotographic photoreceptor T whose image forming surface S is supplied with a pretreatment liquid
The pretreatment liquid is sent to the subsequent toner development processing section while the amount of pretreatment liquid adhering to the electrophotographic photoreceptor T is controlled by the conveyance/squeezing rollers 2A and 2B.

PPC100O (manufactured by Ricoh) was used as the toner developer supplied from the developer supply unit 4.

The supplied toner developer flows down while filling the space with a clearance of 2.0■■ between the developing electrode 5 and the back electrode 6, returns to the toner developer reservoir (not shown), and is circulated to the developer supply unit 4. Ru. The photoreceptor T sent to the toner developing section is immersed in a toner developer, and toner particles having a polarity opposite to that of the latent image are electrodeposited onto the electrostatic latent image on the photoreceptor T by Coulomb force, thereby forming an image.

When the photoconductor T enters the toner development section, the switch of the power supply 8 of the reverse bias voltage application device 7 is closed, and the voltage is applied to the development electrode 5.
A reverse bias voltage of +40V is applied to the back electrode 6.

The photoreceptor T that has passed through the toner development processing section is squeezed by an air knife 9, and excess toner is returned to the toner developer reservoir, whereupon the photoreceptor T is dried and fixed. When the fog density of the non-image area of the toner image thus obtained was measured, it was found to be 0.
．． 13, which was very good.

Comparative Example 1 A toner image was formed in the same manner as in Example 1 except that a metallic squeeze roller was used instead of the air knife 9 to squeeze the toner developer, and the fog density was 0.3.

Examples 2 to 6 In addition to the method of using an air knife in Example 1 (air squeeze) as a squeezing method after liquid toner development using conductive treated paper or grained aluminum plate as a support, comparative examples were also used. A toner image was formed in the same manner as in Example 1 except that a roller squeeze was used to measure the fog density. The results are shown in Cloth 1 below.

set Fogging can be significantly reduced.

〔Effect of the invention〕

According to the present invention, in the step of charging an electrophotographic photoreceptor having a rough photoreceptor surface and imagewise exposing it to form a charged latent image, and forming a toner image by liquid development, toner is adsorbed to the non-image area of the photoreceptor. This improves the disadvantages of image contrast deterioration and fogging when used as a printing plate.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a developing device for carrying out the method of the present invention. T...Photoreceptor■...Pre-treatment liquid supply device 4...Developer supply unit 9...Air knife

Claims (1)

[Claims] In a method of forming a charged latent image by charging and exposing an electrophotographic photoreceptor having a surface having a center line average roughness Ra of 0.15 to 0.70 μm, and forming a toner image by liquid development,
After forming a charged latent image, a pretreatment liquid is applied to the surface of the photoreceptor,
An electrophotographic liquid developing method characterized by subsequently performing liquid toner development and subsequently squeezing the liquid toner by non-contact squeezing.