JPH0833677B2 - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an electrophotographic photosensitive member, and more particularly to a lithographic printing original plate utilizing an electrophotographic system.

<Prior art and its problems> A method for preparing a printing plate having high printing durability using an electrophotographic process includes, for example, forming an organic photoconductive layer on an aluminum plate subjected to a hydrophilic treatment, After corona discharge, a desired printing original plate can be obtained by subjecting it to camera exposure or laser exposure, toner development and fixing steps, and eluting the non-image area with an alkaline solution. As a description of such a method, for example, JP-B-37-17162,
38-6961, 41-2426, 46-39405, JP-A-5
0-19509, 50-19510, 54-145538, 54-8
9801, 54-134632, 54-19803, 55-10525
No. 4, No. 57-161863, No. 58-76843, No. 58-76844
No. 58-118658, No. 60-244959, etc.

In recent years, inputting characters and image information by computer,
A method of creating, editing, sending such information as a digital signal to an output machine and making it into a hard copy is becoming established, but as this output method, a gas laser such as a helium-neon or argon laser is used and an AO modulator is used. Thus, it is possible to form an image (or latent image) by converting light of digital information into on-off and scanning exposure on the photoconductor. As a photoreceptor at this time, by using an electrophotographic method in which an organic photoconductive layer having sensitivity to the laser light wavelength used is formed on a conductive support such as a hydrophilized aluminum plate, An image can be formed, and a plate for printing can be obtained by elution of the non-image area with an alkaline solution.

However, when a photosensitive member having a large area such as a printing plate for newspaper printing is required, and when scanning exposure is often performed on the entire surface of the photosensitive member, the time required for scanning exposure ranges from several tens of seconds to several minutes. It takes a relatively long time, and the photoreceptor must keep a sufficient surface potential after the corona charging, through the exposure and toner development.

Many electrophotographic photoreceptors with higher sensitivity have been reported, but most of them are focused on application to printers such as PPC. In such applications, the time required from exposure to development is at most 1 second. Since the development of higher-speed copying machines is underway, the charge holding ability (dark decay characteristic) of the photoconductor after corona charging has been a problem only on a time scale of about 1 second at most.

However, when carrying out scanning exposure on a photoreceptor having a relatively large area for the purpose of producing a printing plate as described above, it is preferable to carry out planar scanning exposure, not on the drum, from the viewpoint of transportability. , It may be developed after the scanning exposure of the entire surface of the photoconductor is completed. Therefore, in such a case, the time required for exposure and development after corona charging is usually relatively long as described above, and even if an attempt is made to use a photoconductor that does not have sufficient charge retention, scanning During exposure, the surface potential drops below the permissible range, making image formation impossible. Therefore, the first important characteristics required for the photoconductor are sufficient charge retention ability and low dark decay, and no matter how sensitive the photoconductor is, it cannot be used if the potential decay is large. was there.

In addition to sensitivity, dark decay characteristics have been reported as the characteristics of various photoconductors that have been reported so far, but the dark decay measurement time is as short as about 10 seconds at the shortest. In most cases, it is unclear how the dark decay characteristics of the.

However, as a dark decay characteristic, for example, immediately after charging
It is easy to expect that the surface potential will decrease to about 60% after a long time, for example, 1 minute, if the surface potential of the photoreceptor decreases to about 80% after 10 seconds. We are checking the photoconductor of. The good dark decay characteristic referred to here is, for example, the characteristic that the surface potential 2 minutes after corona charging is about 60% or more of the initial value,
This corresponds to about 90% in terms of the value 10 seconds after corona charging.

In order to enhance the charge retention ability of the photoconductor, it is sufficient to increase the resistance of the photoconductor itself, but it often involves a significant decrease in sensitivity. The binder resin itself must be alkali-soluble in order to prepare the printing original plate, which is a factor that makes the binder resin itself not so highly resistant.

On the other hand, focusing on the photosensitivity of the photoconductor, aside from the dark decay characteristics, near infrared phthalocyanine photoconductors that have high sensitivity in the wavelength range of semiconductor lasers, which have been developing rapidly in recent years in addition to gas lasers, are attracting attention. . For example titanium,
A phthalocyanine compound having a central metal such as aluminum, indium, lead, and copper, a derivative thereof, or a metal-free phthalocyanine has attracted attention because of its ease of synthesis and high sensitivity in a wide wavelength range. Among them, titanyl phthalocyanine is known to be a near-infrared type photoreceptor which gives extremely high sensitivity (Japanese Patent Laid-Open No. 59-
49544, 59-166959, 61-109056, 61-171771,
61-217050, 61-239248, etc.). However, although titanyl phthalocyanine has the advantage of high sensitivity, it is significantly inferior to other photoconductors such as copper phthalocyanine and azo pigments in terms of dark decay characteristics as described above, and therefore, it is not suitable for scanning exposure. It could not be used for the original printing plate.

<Purpose of the Invention> The present invention has an object to overcome the above problems and to provide an electrophotographic photoreceptor having high sensitivity, stability, and high charge retention ability. Its main purpose is to apply it to the production of printing plates.

<Structure of the Invention> The present inventors have found that the dispersibility of the oxytitanyl phthalocyanine pigment is increased, and the dark resistance of the photoconductor itself is increased to some extent by hindering mutual contact due to aggregation of the pigments to some extent. At this time, in addition to the binder resin, by interposing other resin particles having a composition different from that of the binder resin as fine particles, the aggregation of the pigment itself can be effectively prevented, and further, the fine particles can be prevented. It has been found that by selecting a material that itself has high insulation properties, the resistance of the photoconductor itself can be increased, and excellent dark attenuation characteristics can be realized.

That is, the present invention provides an electrophotographic photoreceptor having a photosensitive layer formed by dispersing oxytitanyl phthalocyanine in a binder resin on a conductive support, wherein the photosensitive layer contains highly insulating resin fine particles. The electrophotographic photosensitive member is characterized in that it can be applied to a printing plate for printing by using an alkali-soluble resin as the binder resin.

Japanese Patent Application Laid-Open No. 62-217256 describes that the dissolution property can be improved by incorporating a polymer powder having a particle size of 10 μm or less in the photosensitive layer. It has not been shown that the drawbacks of oxytitanyl phthalocyanine, which are significantly worse, can be significantly improved.

The photoconductor according to the present invention has a chargeability of 60% or more of the initial value even after dark decay for 2 minutes after corona charging, and does not impair the development image quality after scanning exposure for a substantially long time. Can be given.

As a method of introducing the highly insulating resin fine particles into the photoreceptor, it is possible to mix such a resin in the form of a solution together with the alkali-soluble resin, but in many cases there is no common solvent with the alkali-soluble resin, Further, when the compatibility of both resins is low, it is often difficult to form a uniform film by causing phase separation in a solution or when forming a coating film. However, if the resin is a fine powder, it can be easily dispersed in the alkali-soluble resin, and the ratio of both resins can be changed at an arbitrary ratio. Therefore, the volume resistance value of the photoconductor can be increased by introducing the highly insulating resin fine particles for the purpose of increasing the resistance of the photoconductor, and good chargeability and dark decay characteristics can be exhibited. Furthermore, since such a highly insulating resin exists in the form of fine particles dispersed in the alkali-soluble resin, it does not interfere with the permeation of the alkaline solution even when eluting with the alkaline solution, and can elute the non-image area. There is no hindrance. In addition, the sensitivity of the photoconductor does not change significantly by the introduction of fine powder, and by blending the components that make up the photoconductor in an appropriate ratio, high charge retention while maintaining the high sensitivity of oxytitanyl phthalocyanine is achieved. It was possible to realize a photoconductor with high performance.

It does not matter whether the fine particles having a high insulating property are spherical or indefinite, but the size is preferably at most 10 μm or less. When a fine powder having a size larger than this is introduced, an image defect may occur, but if it is 10 microns or less, there is no trouble such as an image defect and practically no problem occurs.

The amount of the highly insulating resin fine particles contained in the photosensitive layer is preferably in the range of about 1 to about 30% by weight based on the binder resin.

The highly insulating resin fine particles referred to in the present invention have a resistance value of at least 10 ¹¹ ohms or more, and for example, polystyrene spherical particles, polymethylmethacrylate spherical particles, etc. are available, and fine particles having various particle diameters can be used. . Alternatively, resin powders such as polyacrylonitrile and the like can be used, and all of them can be easily dispersed in the photoreceptor coating liquid.

The presence of these fine powders imparts thixotropic properties to the coating liquid, improves the coating properties of the coating liquid, and prevents aggregation of the oxytitanyl phthalocyanine pigments, which is one of the great effects.

Various crystal types can be used as the oxytitanyl phthalocyanine used in the present invention.
Molds or mixtures thereof are preferred. The amount of titanyl phthalocyanine is preferably in the range of about 10 to about 40% by weight with respect to the binder resin.

The most basic layer structure of the photoconductor is a single layer type or a laminated type (separated function type), but in addition to this, an undercoat layer is provided between the photoconductor and the support. The protective layer may be provided on the surface of the photoconductor, or various layer constitutions such as providing an intermediate layer in the multi-layer photoconductor may be mentioned. A single-layer photoconductor using oxytitanyl phthalocyanine is a multi-layer photoconductor. It is possible to realize high sensitivity comparable to that of the function-separated type photoreceptor.

The present invention realizes high sensitivity and high resistance in a single-layer type photoreceptor using the oxytitanyl phthalocyanine compound as described above, and printing using an electrophotographic method by using an alkali-soluble resin as a binder. Made it possible to create a printing plate.

As the alkali-soluble resin, a resin containing a monomer having an acidic group such as acrylic acid, methacrylic acid or crotonic acid as at least one component of the polymer, for example, styrene-maleic anhydride copolymer, maleic acid monoester resin, vinyl acetate. Examples thereof include crotonic acid copolymer, vinyl acetate-maleic anhydride copolymer, phenol resin, (meth) acrylic acid ester- (meth) acrylic acid copolymer and the like.

Further, as the conductive support used in the printing original plate in the present invention, an aluminum plate, a zinc plate, an iron plate, or a like metal plate is preferable, and a graining treatment or a surface treatment such as anodization is particularly preferable. This is because when the printing plate is formed by elution of the image area, it can have hydrophilicity.

The method of preparing the printing original plate according to the present invention is carried out by removing (etching) the non-image area with an alkaline liquid after forming an image with a toner. As the alkaline liquid at this time, sodium hydroxide, hydroxide An inorganic alkaline aqueous solution such as potassium, sodium carbonate or sodium phosphate, or an alkanolamine aqueous solution such as monoethanolamine, and those obtained by adding a lower alcohol such as methanol, ethanol, propanol or benzyl alcohol, an aromatic alcohol or the like are used. To be It is necessary for the toner image to sufficiently prevent the liquid from penetrating into such an alkaline liquid and to remain as a strong image even after the etching treatment. Either a wet type toner or a dry type toner may be used as the toner having excellent etching resistance, but the wet type toner is preferable in order to obtain a printing original plate having excellent resolution.

<Example> An example is shown below.

Example 1 To 6 parts of α-type oxytitanyl phthalocyanine, 20 parts of butyl methacrylate / acrylic acid copolymer was added, and 1 part of polymethylmethacrylate fine powder having an average particle diameter of 3 μm, 40 parts of chloroform and 160 parts of isopropanol were added. And dispersed for 6 hours with a paint conditioner to obtain a photoreceptor coating liquid. This coating solution was applied onto an anodized aluminum plate so that the film thickness was 5 μm, and dried.

Example 2 A photoconductor was prepared in the same manner except that the fine powder of Example 1 was replaced with polystyrene fine powder having an average particle size of 2 μm.

Example 3 A photoreceptor was prepared in the same manner except that the fine powder of Example 1 was replaced with fine polyacrylonitrile powder having an average particle size of 3 μm.

Comparative Example 1. A photoconductor was prepared in the same manner except that the fine powder of Example 1 was not used.

The electrophotographic characteristics of these photoconductors were measured by Kawaguchi Denki's "Paper Analyzer SP-428" with a cosna applied voltage of + 6KV.
Irradiation with 2 lux of tungsten light, initial potential (V ₀ ), surface potential after 120 seconds (V ₁₂₀ ), half exposure (E1 /
2) The exposure dose (E ₅₀ ) required to reduce the surface potential to 50 V was determined. The results are shown in Table 1.

The photoconductors of Examples 1 to 3 were developed by a liquid developing device, and then the non-image area was eluted with an alkaline aqueous solution, washed with water and gummed to obtain a lithographic printing plate having a good image. These printing plates gave good printing results without smearing or image skipping even on 50,000 sheets or more.

<Effects of the Invention> According to the present invention, by using the highly insulating resin fine particles, it was possible to maintain the high sensitivity of titanyl phthalocyanine and significantly improve the long-term low dark decay retention. Therefore, a printing plate suitable for scanning exposure can be obtained.

Claims (1)

[Claims] 1. An electrophotographic photosensitive member having a photosensitive layer formed by dispersing oxytitanyl phthalocyanine in a binder resin on a conductive support, wherein the photosensitive layer contains fine particles of a highly insulating resin. An electrophotographic photoreceptor characterized by the above.