JPH04114166A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain the electrophotographi sensitive body freed of printing defect and superior in moisture resistance and adhesion by incorporating a specified component in an electric charge generating layer and an interlayer. CONSTITUTION:The electrophotographic sensitive body comprises a charge transfer layer 1, the charge generating layer 2, the interlayer 3, and a conductive substrate 4, and the layer 2 contains a copolymer of vinyl acetate, vinyl alcohol, and vinyl acetal, and the layer 3 contains at least one of cyanoethylated pullulan, cyanoethylated cellulose, and cyanoethylated polyvinylalcohol, thus permitting the obtained electrophotographic sensitive body to be freed of printing defect and superior in moisture resistance and adhesion.

Description

[Detailed Description of the Invention] [Summary] To provide an electrophotographic photoreceptor that is free from printing defects and has excellent moisture resistance and adhesion, with regard to electrophotographic photoreceptors that are widely used in copying machines, printers, etc. that apply an electrophotographic method. In an electrophotographic photoreceptor in which an intermediate layer, a charge generation layer, and a charge transport layer are sequentially laminated on a conductive support, the charge generation layer is a copolymer consisting of vinyl acetate, vinyl alcohol, and vinyl acetal. The intermediate layer contains one or more of cyanoethylated pullulan, cyanoethylated cellulose, and cyanoethylated polyvinyl alcohol.

[Industrial Application Field] The present invention relates to an electrophotographic photoreceptor that is widely used in copying machines, printers, etc. that apply an electrophotographic method.

As an example of electrophotography, a common method is to obtain printed matter by repeating the steps of charging, exposing, developing, transferring, and fixing.

The charging process applies a uniform positive or negative electrostatic charge to the surface of the photoconductive photoreceptor. In the subsequent exposure process, an electrostatic latent image corresponding to the image information is formed on the photoreceptor by irradiating it with laser light or the like to erase the surface charge on a specific portion. Next, this latent image is electrostatically developed with powder ink called toner, thereby forming a visible image of the toner on the photoreceptor. Finally, this toner image is electrostatically transferred onto recording paper and fused using heat, light, pressure, etc. to obtain a printed matter.

The quality of printed matter often depends on the photoreceptor.

Therefore, it is necessary to develop a photoreceptor that is free from printing defects and has excellent moisture resistance and adhesion.

[Prior Art] Inorganic photoreceptors typified by selenium-based photoreceptors have been widely used as photoreceptors having photoconductivity.

This inorganic photoreceptor is highly sensitive and resistant to mechanical abrasion, making it suitable for high-speed, large-scale machines. However, it must be manufactured using a vacuum evaporation method and must be collected because it is harmful to the human body. The problem is that the cost is high, and it is difficult to apply it to small, low-cost maintenance-free machines.

Organic photoreceptors were developed as an alternative to inorganic photoreceptors. This can be manufactured by a coating method, which makes it easy to reduce costs through mass production, and compared to inorganic photoreceptors that use inorganic substances such as selenium, there is a wide range of materials to choose from, so non-hazardous compounds can be selected, and users can dispose of them. It has the characteristics of being maintenance-free.

In particular, a functionally separated laminated photoreceptor in which a charge generation layer and a charge transport layer are laminated on a conductive support is attracting attention. Here, the charge generation layer has the function of absorbing incident light and generating electron-hole pairs (carrier pairs), and the charge transport layer retains a charge on its surface and carries carriers generated in the charge generation layer. It has the function of transporting one side of the photoreceptor to the surface of the photoreceptor to form an electrostatic latent image.

The charge generation layer is formed by dispersing a charge generation substance such as an azo pigment or a phthalocyanine pigment in a binder resin, applying this and drying it to have a film thickness of about 0.1 to 5 μm, particularly 1 μm or less. .

Further, the charge transport layer is formed by dissolving a charge transport material having a carrier transport ability in a binder resin, applying this and drying it to have a film thickness of 10 to 30 μm.

By separating the functions of the photoreceptor into two layers in this way, it is possible to select the optimal compound for each function almost independently, improving various properties such as sensitivity, spectral characteristics, and mechanical abrasion resistance. can be done.

[Problems to be Solved by the Invention] However, in such an organic photoreceptor, it is necessary to make the charge generation layer very thin, so the support may be non-uniform or the charge generation material If the dispersibility of
Easy to cause uneven coating. In addition, when charged due to corona discharge, etc., discharge breakdown often occurs, resulting in pinholes.
Another problem arises in that printing defects are likely to occur due to charge injection from the conductive support. As a countermeasure against this, it is natural to use a resin with good pigment dispersibility as much as possible for the binder of the charge generation layer, but this alone is not sufficient, and an intermediate layer made of a specific resin is added between the conductive support and the charge generation layer. It is known that a method of providing That is, this intermediate layer is intended to make the surface of the support uniform and to function as a barrier layer against charge injection. However, unless sufficient attention is paid to the characteristics of the resin used as the binder for the intermediate layer and the charge generation layer, the characteristics of the photoreceptor may be significantly deteriorated. For example, if the adhesion between the support and the intermediate layer or the charge generation layer and the intermediate layer or charge transport layer is poor, the problem arises that the photosensitive layer is likely to peel off, especially at the edges of the photoreceptor. . moreover,
If the moisture resistance is insufficient, care must also be taken to reduce adhesion upon moisture absorption. On the other hand, if a resin that is easily soluble in the solvent used to coat and form the charge generation layer is used for the intermediate layer, there may be problems such as mixing of the intermediate layer and the charge generation layer, resulting in deterioration of characteristics or uneven coating. Sign. Furthermore, if a resin with very good insulation properties is used for the intermediate layer, there is a drawback that the residual potential increases significantly and the printing density decreases.

The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an electronic photoreceptor that is free from printing defects and has excellent moisture resistance and adhesion.

In an electrophotographic photoreceptor in which an intermediate layer, a charge generation layer, and a charge transport layer are sequentially laminated on a support, the charge generation layer or
It contains a copolymer consisting of vinyl acetate, vinyl alcohol and vinyl acetal, and the intermediate layer contains one or more of cyanoethylated pullulan, cyanoethylated cellulose and cyanoethylated polyvinyl alcohol.

Hereinafter, the present invention will be explained in further detail with reference to FIG. 1 as necessary.

In FIG. 1, 1 is a charge transport layer, 2 is a charge generation layer, and 3 is a charge transport layer.
is an intermediate layer, and 4 is a conductive support.

First, the binder resin of the charge generation layer 2 is required to have pigment dispersibility, adhesion, moisture resistance, solubility in solvents, etc., or polyvinyl acetate is saponified and acetalized sequentially or simultaneously [to solve the problem]. [Means for achieving the above object] In order to achieve the above object, the present invention provides a conductive R-H or alkyl group, where the vinyl acetate content is preferably 60 mo 1% or less since heat resistance decreases if it is too large. In addition, moisture resistance,
In terms of solubility, the lower the vinyl alcohol content, the better.
Is it necessary to keep 4Qmo below 1%?

Note that known aldehydes can be used for the acetalization reaction, but formaldehyde, acetaldehyde, and butyraldehyde are particularly good, and in consideration of the balance of film strength, solubility, etc., it is recommended to mix two or more of these. It is better to use it as

The resins include alcohols such as methanol, ethanol, and isopropyl alcohol, cellosolves such as methyl cellosolve, ketones such as acetone and cyclohexanone, amides such as N,N-dimethylformamide, ethers such as dioxane and tetrahydrofuran, and methylene chloride. Since it is soluble in a number of single or mixed solvents such as chlorinated hydrocarbons such as chloroform, a solvent that does not dissolve the intermediate layer 3 can be easily selected.

Next, as the intermediate layer 3 that can realize excellent photoreceptor properties in combination with the above resin, one of cyanoethylated pullulan (A), cyanoethylated cellulose (B), and cyanoethylated polyvinyl alcohol (C) having the following structure is used. It is preferable to use at least two or more types.

(A) (B) (C) R: CH2CH2CN H These resins have a relatively low electrical resistance, which causes a decline in the photoreceptor properties, and they also have excellent moisture resistance because they do not dissolve in water. .

In addition, it is soluble in single or mixed solvents such as acetone, methyl cellosolve, NSN dimethylformamide, etc.
While the intermediate layer 3 can be easily formed by coating, it is difficult to dissolve in solvents such as ethanol, tetrahydrofuran, and chloroform, so the charge generation layer 2 can be formed by coating without causing mixing with the intermediate layer 3.

The resin group preferably has 60% or more substitution with cyanoethyl groups, and the preferable thickness of the intermediate layer 3 is 0.5%.
05-5 μm.

However, when combining the intermediate layer 3 and the charge generation layer 2, it is necessary to pay attention to the adhesion between the two, and in particular, when the vinyl acetate content is less than about 10 mo1%, the adhesion tends to deteriorate significantly. Therefore, it is necessary that the binder resin of the charge generation layer 2 has a vinyl acetate content of 10 to 5Qmo1%.

On the other hand, it has been found that even when the vinyl acetate content is low, good adhesion can be obtained by adding a compound having an isocyanate group to the intermediate layer 3 to introduce a crosslinked structure.

This is presumably because unreacted isocyanate groups also form a crosslinked structure between the intermediate layer 3 and the binder resin of the charge generation layer 2.

Note that the addition of the isocyanate compound also has the effect of increasing the solvent resistance of the intermediate layer 3, making the coating of the charge generation layer 2 easier. As the isocyanate compound, hexamethylene diisocyanate, tolylene diisocyanate, etc. having two or more isocyanate groups, or (cyclic) aliphatic or aromatic polymers having isocyanate groups can be used.Furthermore, caprolactam can be used to improve storage stability. It is effective to use a so-called block type (poly)isocyanate in which the isocyanate group is protected. The amount of isocyanate compound added is 0 to the resin.
．． It is 1 to 1Qvj%, preferably 1 to 3wj%.

The conductive support 4 may include various metal cylinders, resin cylinders imparted with conductivity, metals deposited or laminated on the surface of an insulating cylinder, insulating cylinders coated with a conductive organic thin film, and A film or the like having the same structure as above can be used.

Furthermore, if the material is an aluminum alloy or the like, a corrosion-resistant coating may be applied by electrolytic oxidation using oxalic acid, chromic acid, sulfuric acid, etc. in order to improve adhesion, storage stability, or photoreceptor characteristics.

As the charge generating substance contained in the charge generating layer 2, phthalocyan-based, azo-based, squarylium-based dyes and pigments can be used, and metal-free or metal phthalocyanine compounds are particularly preferred.

The charge transport layer 1 may be anything that can transport the charges generated in the charge generation layer 2. For example, a hole-transporting charge-transporting substance such as hydrazone, triarylamine, or stilbene, or an electron-transporting charge-transporting substance such as chloranil, promanil, or trinitrofluorenone dissolved in a binder resin can be used. Pore-transporting charge-transporting substances are preferred. Furthermore, it is also possible to use a photoconductive polymer that itself has charge transport ability, such as polyvinylcarbazole.

As the binder resin of the charge transport layer 1, polyester,
Known materials such as polycarbonate and epoxy can be used. As a solvent, depending on the binder resin used, tetrahydrofuran, toluene, dichloromethane,
Various organic solvents such as methyl cellosolve can be used alone or in combination.

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 1 part (by weight) of cyanoethylated pullulan with a degree of substitution of about 80% was dissolved in 9 parts of acetone, and this was dip coated onto an aluminum support and dried at 100°C for 1 hour to form a film with a thickness of 1 μm. An intermediate layer was formed.

Next, 1 part of metal-free phthalocyanine, 1 part of polyvinyl acetal resin synthesized using formaldehyde (vinyl acetate content: 15 mo1%, vinyl alcohol content: 10 mo1%, remainder vinyl acetal content), 20 mo of tetrahydrofuran.
24 parts using a hard glass hole and a hard glass pot.
The time-dispersed mixture was applied by dip coating on the intermediate layer, and 1
It was dried at 00° C. for 1 hour to form a charge generation layer with a thickness of 0.3 μm.

Furthermore, one part of a hydrazone derivative represented by the following structural formula,
1 part of polycarbonate was dissolved in 8 parts of dichloromethane, and the solution was dip-coated onto the charge generation layer and dried at 80° C. for 2 hours to form a charge transport layer having a thickness of 15 μm, thereby obtaining a photoreceptor of an example.

Example 2 5 parts mo1 of vinyl acetate in polyvinyl acetal resin
A photoreceptor of Example 2 was obtained in the same manner as Example 1 except that the photoreceptor was changed to %.

Example 3 Acetaldehyde and butyraldehyde (molar ratio 1.1)
Polyvinyl acetal resin synthesized using (vinyl acetate IQmo 1%, vinyl alcohol content 30ff101
%, remaining vinyl acetal), 1 part of aluminum chloride phthalocyanine, and 20 parts of chloroform were dispersed and mixed for 24 hours using a hard glass pole and a hard glass pot to prepare a charge generation layer coating solution. A photoreceptor of Example 3 was obtained in the same manner.

Comparative Example 1 A photoreceptor of Comparative Example 1 was obtained in exactly the same manner as in Example 1 except that the vinyl acetate content of the polyvinyl acetal resin was 5 m01% or less (vinyl alcohol content 20 mθ%, remaining vinyl acetal content).

Comparative Example 2 A photoreceptor of Comparative Example 2 was obtained in exactly the same manner except that a silicone resin (ES-1001N, Shin-Etsu Chemical) was used instead of the polyvinyl acetal resin of Example 1.

Comparative Example 3 A photoreceptor of Comparative Example 3 was obtained in exactly the same manner as in Example 1 except that no intermediate layer was formed.

Comparative Example 4 3 parts of hydroxypropyl methylcellulose (60SH5g Shin-Etsu Chemical) was dissolved in a mixture of 80 parts of pure water and 20 parts of methanol, and after coating this was dried at 110°C for 1 hour to form an intermediate layer with a film thickness of 0.5 μm. Example 1 except that
A photoreceptor of Comparative Example 4 was obtained in exactly the same manner as described above.

Comparative Example 5 1 part of the polyvinyl acetal resin used in Example 1 and 0.05 parts of hexamethylene 1,6-diisocyanate were dissolved in 10 parts of tetrahydrofuran, and the solution was coated at 180°C.
A photoreceptor of Comparative Example 5 was obtained in exactly the same manner as in Example 1, except that an intermediate layer having a thickness of 1 μm was formed by drying for 1 hour.

Example 4 2 parts of cyanoethylated cellulose (degree of substitution about 90%) and cyanoethylated polyhinyl alcohol (degree of substitution about 90%)
1 part hexamethylene and 1.6 parts diisocyanate 0.
05 parts with acetone and N.

Mixed solvent of N-dimethylformamide (volume ratio 31) 2
7 parts and dip-coated it onto an aluminum support.
It was dried at 80°C for 1 hour to form an intermediate layer with a thickness of about 1 μm.

Next, formaldehyde and butyraldehyde (molar ratio 1
2) Polyvinyl acetal resin synthesized using
%, remaining vinyl acecool), 1 part of oxotitanylphthalocyanine, and 20 parts of chloroform were dispersed and mixed for 24 hours using a hard glass pole and a hard glass pot to form a charge generation layer with a film thickness of 0.2 μm. was formed.

Further, a charge transport layer was formed thereon in exactly the same manner as in Example 1 to obtain a photoreceptor of Example 4.

Example 5 1 part of cyanoethylated pullulan with a degree of substitution of about 70% and 0.01 part of block polyisocyanate (IPDIB 1530. Daicel Yuzu) were added to 9 parts of a mixed solvent of acetone and methyl cellosolve (volume ratio 1:1). This was dissolved and coated on an aluminum support by dip coating, and dried at 180° C. for 1 hour to form an intermediate layer having a thickness of 1 μm.

A charge generation layer and a charge transport layer were formed thereon in the same manner as in Example 4 to obtain a photoreceptor of Example 5.

Comparative Example 6 A photoreceptor of Comparative Example 6 was obtained in exactly the same manner as in Example 5 except that no isocyanate compound was added to the undercoat layer.

Among the photoreceptors described above, in Comparative Example 2, phthalocyanine sedimentation was severe and uneven coating occurred in the charge generation layer.

Next, we conducted a printing test using our small laser printer prototype, and the results were as follows: Examples 1 to 5, Comparative Examples 1, 4.
Photoreceptor No. 6 had good characteristics, and Comparative Example 2 showed shading in the print corresponding to uneven coating of the charge generation layer.

Further, in the photoconductor of Comparative Example 3, significant staining occurred in the background area, and in the photoconductor of Comparative Example 5, a decrease in print density due to an increase in bright area potential was observed. Further, when the adhesion was evaluated by a substrate test, in Comparative Example 1.6, the undercoat charge generation layer was easily peeled off. Note that some peeling was observed in the photoreceptors of Example 3 and Comparative Example 4 as well. Further, as a result of being left in a high temperature and high humidity environment (50° C., 80%), only the photoreceptor of Comparative Example 4 showed a significant decrease in adhesion. The results are summarized in a table. Examples 1 to 5 showed no printing defects, moisture resistance,
A photoreceptor with excellent adhesion can be obtained.

[Effects of the Invention] As described above, according to the present invention, the charge generation layer contains a copolymer consisting of vinyl acetate, vinyl alcohol and bonyl acetal, and the intermediate layer contains cyanoethylated pullulan, cyanoethyl Since it contains one or more of compounded cellulose and cyanoethylated polyvinyl alcohol, a photoreceptor with no printing defects and excellent moisture resistance and adhesion can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the present invention. In the figure, 1... Charge transport layer, 2...charge generation layer, 3...middle class, 4... Conductive support.

Claims (3)

[Claims] (1) An electrophotographic photoreceptor in which an intermediate layer, a charge generation layer, and a charge transport layer are sequentially laminated on a conductive support, wherein the charge generation layer is a copolymer consisting of vinyl acetate, vinyl alcohol, and vinyl acetal. An electrophotographic photoreceptor comprising: and wherein the intermediate layer contains one or more of cyanoethylated pullulan, cyanoethylated cellulose, and cyanoethylated polyvinyl alcohol. (2) The electrophotographic photoreceptor according to claim 1, wherein the vinyl acetate content is 10 to 60 mol% of the binder resin of the charge generation layer. (3) The electrophotographic photoreceptor according to claim 1 or 2, wherein the intermediate layer contains a compound having an isocyanate group.