JPH02238459A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To obtain a photosensitive body superior in humidity resistance and adhesiveness by incorporating a specified alkylcyanocellulose in an interlayer and using a specified polyvinylacetal as the binder resin of an electric charge generating layer. CONSTITUTION:The interlayer 3 formed on a conductive substrate 1 contains the alkylcyanocellulose represented by the structural formula I in which R is a lower alkylcyano group, H, or alkyl. The charge generating layer 2 formed between the interlayer 3 and a charge transfer layer 4 contains as the binder resin the polyvinyl acetatal obtained by acetal forming reaction using at least 2 kinds of aldehydes and polyvinyl alcohol, thus permitting the obtained electrophotographic sensitive body 5 to be superior in adhesiveness, humidity resistance, printing characteristics, and the like.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems Actions Examples Effects of the Invention [Summary] Organic photosensitive material used in electrophotography, etc. The purpose is to obtain a photoreceptor with no printing defects, excellent moisture resistance and adhesion, and at least an intermediate layer on a conductive support. In a photoconductor of a functionally functional type formed by laminating a charge generation layer and a charge transport layer in this order, the intermediate layer contains an alkyl cyanated cellulose represented by the following formula (1), and the charge generation layer contains An electrophotographic photoconductor is constructed using polyvinyl acetal obtained by an acetalization reaction between at least two types of aldehydes and polyvinyl alcohol as a binder resin.

In 21, R represents a lower alkylcyano group, H or an alkyl group.

[Industrial application field]

The present invention relates to an electrophotographic photoreceptor in which the intermediate layer and the binder resin of the charge generation layer are improved.

Electrophotographic technology is widely used in copying machines, but it is also used in information devices such as printers and facsimiles.

The printing process of an electrophotographic printer is called the Carlson process.
Charging, exposure. Printed matter is obtained by repeating the steps of development, transfer, and fixing.

That is, charging applies a uniform positive or negative electrostatic charge to the surface of a photoreceptor having photoconductivity.

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 using a powder ink called toner, thereby forming a visible image using the toner on the photoreceptor.

After that, this toner image is electrostatically transferred onto a recording paper and is melted by heat, light, pressure, etc. to obtain a printed matter.

In some electrophotographic processes, organic photoreceptors are used in place of conventional inorganic photoreceptors as photoconductive insulators that form electrostatic latent images.

The present invention relates to improvements in such organic photoreceptors.

[Conventional technology]

Selenium (Se) is a typical photoconductive material, and it is formed into a film to a thickness of about 50 μm by vacuum evaporation on a conductive support made of aluminum (A!) alloy or the like. is used.

In addition, as an inorganic photosensitive material that is similarly used, S
Examples include e-Te (tellurium) and cadmium sulfide (CdS).

However, there is a problem in that these materials are generally highly toxic and must be recovered by the manufacturer.

On the other hand, as an alternative to this, there are organic photosensitive materials, which are less toxic than inorganic photosensitive materials. It has flexibility. It is lightweight. Rapid research and development is being carried out taking advantage of its low price.

Now, the photosensitive performance of organic photosensitive materials is generally inferior to that of inorganic photoreceptive materials, but the development of functionally separated photoreceptors that separate charge generation and charge transport has significantly improved the photoreceptivity. As a result, practical improvements are being made as electrophotographic photoreceptors.

In this case, the organic photoreceptor for electrophotography is aluminum (A
f) A charge generation layer on a conductive support made of an alloy or the like.
It is formed by laminating it with a charge transport layer.

In 21, the charge generation layer has the function of absorbing incident light and generating pairs of electrons and holes (carrier pairs), and the charge transport layer has the function of absorbing incident light and generating pairs of electrons and holes (carrier pairs), and the charge transport layer has the function of absorbing incident light and generating pairs of electrons and holes (carrier pairs). It has the function of holding holes or electrons generated in the charge generation layer 2 and transporting them to the surface by the electric field caused by the charged charges to neutralize them, thereby forming an electrostatic latent image.

In this case, the charge generation layer is formed by dispersing a charge generation substance in a binder resin, but as the charge generation substance that generates charges, dyes and pigments such as cyanine type, azo type, and squarylium type are used. Can be used.

On the other hand, various resins such as polyester, polyvinyl butyral, and silicone can be used as the binder resin, and these resins are selected in consideration of adhesion, dispersibility of the charge generating substance, and the like.

Solvents used for coating film formation include Te1-rahydrofuran, methanol, and ethanol, which are selected depending on the binder resin constituting the charge generation layer. Next, the charge transport layer is formed by dissolving a charge transport substance having carrier transport ability into a binder resin, and examples of the charge transport substance include trinitrofluorenone, chloranil 5-promanyl, etc., which have the property of transporting electrons. There are electron-transporting charge-transporting materials, and hole-transporting materials such as hydrazone derivatives, triphenylamine derivatives, and pyrazoline derivatives that have the property of transporting holes.As binder resins, known materials such as polycarbonate and styrene/acrylic are used. It is used. By separating the functions of the photoreceptor into two layers in this way, it is possible to independently select the optimal compound for each function, improving various properties such as sensitivity, spectral characteristics, and mechanical abrasion resistance. be able to.

[Problem to be solved by the invention]

However, from a practical standpoint, it is difficult to obtain satisfactory performance simply by directly forming a photosensitive layer consisting of a charge generation layer and a charge transport layer on a conductive support.

In other words, there are problems in that when charged by corona discharge, etc., discharge breakdown easily occurs, resulting in pinholes, and the conductive support is easily injected with charge, resulting in printing defects. Slight defects or dirt on the support can easily cause uneven thickness or uneven coating of the charge generation layer. As a countermeasure for this, as shown in FIG. 1, an intermediate layer 3 made of a specific resin is provided between the conductive support 1 and the charge generation layer 2, and a charge transport layer 4 is formed on the charge generation layer 2. A method of configuring the photoreceptor 5 in this manner is known.

However, if a resin that is easily soluble in the solvent used for forming the charge generation layer 2 is used as the resin for forming the intermediate layer 3, the intermediate layer 3 and the charge generation layer 2 may mix, resulting in deterioration of the characteristics.
This causes inconveniences such as uneven coating.

In addition, by using a thermosetting resin such as epoxy, acrylic, or phenolic resin, the poorly soluble intermediate layer 3 can be formed, but when a resin with excellent insulation properties is used, the residual potential increases significantly upon exposure. However, there is a problem that the print density decreases. On the other hand, methylcellulose. Casein, polyvinyl alcohol, etc. are difficult to dissolve in organic solvents and have excellent compatibility with the charge generation layer 2, which uses a phthalocyanine compound, but their moisture resistance is insufficient and adhesion deteriorates due to moisture absorption. The problem is that the sensitivity decreases. Next, the charge generation layer 2 may be formed by using a vapor-deposited film of a charge generation substance, but from the viewpoint of manufacturing cost, the binder resin and charge generation substance may be formed by ball milling. Atwriter. A coating solution is prepared by dispersing it in a solvent using a sand mill, etc., and this coating solution is applied by a dipping method, spray method, blade method, etc., and then solidified by heat treatment to form a charge generation layer. .

However, this coating solution has poor stability because the charge-generating substance is finely dispersed and suspended in the solvent. It settled, and it was necessary to add another dispersion process before use.

Further, some binder resins can improve stability by adjusting the concentration and viscosity of the coating liquid, but such binder resins have a problem of low sensitivity and are difficult to put to practical use.

It is possible to solve the above two problems individually, but the consistency between the intermediate layer and the charge generation layer is important, and solving only one of them will not satisfy both the sensitivity of the photoreceptor and the printing characteristics. I couldn't get any characteristics.

[Means to solve the problem]

The above problem can be solved in a functionally separated photoreceptor consisting of an intermediate layer, a charge generation layer, and a charge transport layer laminated in this order on a conductive support. The problem can be solved by using an electrophotographic photoreceptor containing cyanated cellulose and using polyvinyl acetal obtained by an acetalization reaction between at least two types of aldehydes and polyvinyl alcohol as a binder resin for the charge generation layer. can.

Here, P represents a lower alkylcyano group, H or an alkyl group. [Function] Requirements for the intermediate layer are: ■ Appropriate insulation resistance, ■ Excellent moisture resistance, ■ Excellent adhesion to the conductive support, ■ Charge generation layer. This means that there is good consistency with the In other words, use thermosetting resin such as epoxy resin or phenolic resin as the intermediate layer! ! When using resin with high edge resistance,
Although the adhesion to the conductive support is good, the charge generated in the charge generation layer does not escape, resulting in an increase in residual potential and a decrease in printing density. Also, ethyl cellulose. Membranes such as methylcellulose have good compatibility with the charge generation layer, but because of their high hygroscopicity, moisture absorption reduces adhesion to the conductive support and also causes a decrease in permeability.

Therefore, the present invention uses alkyl cyanated cellulose having the structural formula shown in formula (1) as a constituent material of the intermediate layer.

This resin is insoluble in solvents such as tetrahydrofuran and alcohols that are commonly used in coating and forming the charge generation layer, and does not mix with the charge generation layer.

In addition, it is particularly compatible with a photoreceptor using a capped cyanine compound as a charge generating material, and does not cause deterioration in characteristics such as a decrease in sensitivity or an increase in residual potential.

The excellent properties of this resin are thought to be due to its relatively low electrical resistance and the presence of cyano groups with excellent electron-attracting properties.

In addition, alkyl cyanated cellulose is not soluble in water and therefore has excellent moisture resistance.

It is preferable that the alkylcyano group in RM in 21 is 50% or more. Next, the preferred thickness of the intermediate layer formed using this material is 0.1 to 5 μm, and the coating film of alkyl cyanated cellulose is formed using N,N-dimethylformamide, acetone. Methyl acetoacetate. This can be carried out using an organic solvent such as N-methyl-2-pyrrolidone that dissolves this resin alone or in combination.

Also, the coating method is dip coating. Spray coating, doctor blade coating, etc. can be used.

Next, the polyvinyl acetal used in the present invention is obtained by an acetalization reaction between at least two types of aldehydes and polyvinyl alcohol, and has an average degree of polymerization of 30.
It is desirable that the degree of acetalization is 0 or more and the degree of acetalization is 50% or more by weight.

In 21, the anoledehyde used is an alkyl aldehyde such as honolem anoledehyde, acetaldehyde, propylaldehyde, butyraldehyde, isobutyraldehyde, and benzaldehyde. Examples include benzylaldehyde and benzylmethylaldehyde.

This structural formula is shown in Table 1.

This polyvinyl acetal has good dispersion stability when dispersed in a solvent together with a charge generating substance, especially a phthalocyanine compound, and the dispersibility of the coating liquid hardly changes even if it is left standing for a long period of time.

This is because the polyvinyl acetal of the present invention contains two different types of substituents as substituents on the acetal moiety, and these have a structure in which they are arranged irregularly, so the resin is highly amorphous, and the cap cyanine is highly amorphous. It seems that the dispersibility has improved.

Table 1 Furthermore, the vinyl acetate moiety and the vinyl alcohol moiety, which polyvinyl acetals have in common, are thought to work effectively to increase the affinity with the lid-opening cyanine fine particles.

Examples of the phthalocyanine compounds used as charge generating substances include metal-free phthalocyanine, w4 phthalocyanine, aluminum chloride phthalocyanine, titanyl phthalocyanine,
There are various futacyanine compounds such as vanadyl phthalocyanine and indium futacyanine.

The charge generation layer is formed by coating and drying a mixture of these charge generation substances and polyvinyl acetal dispersed in a solvent.

Any solvent may be used for coating as long as it dissolves the polyvinyl acetal of the present invention in an amount of about 1% by weight or more.
The solvent used for coating the intermediate layer (N,N-dimethylformamide, acetone, cyclohexanone, etc.) must be avoided.

Specifically, methanol and ethanol. Ethyl acetate, dichloromethane, tetrahydrofuran, dioxane, toluene. Various organic solvents such as xylene are used alone or in combination.

Ball mill and attritor are used for dispersion. Sand mills can be used, and coating methods include dip coating, spray coating, wire bar coating, and doctor blade coating. The thickness of the charge generation layer is 0. It is approximately 1 to 3μ, but preferably less than luII.

〔Example〕

Example 1: Cyanoethyl & (Cztls
Cyanoethylated cellulose 1 with about 90% of CN) introduced
Part by weight was dissolved in 1 part by weight of 20I of N,N-dimethylformamide, and this was applied by dip coating onto an Al support and heated at 100°C.
The mixture was dried for 1 hour to form an intermediate layer having a thickness of luIl.

Next, 1 part by weight of titanium oxide phthalocyanine and No. 1 shown in Table 1 as aldehyde were added. 2 and no. 1 part by weight of the polyvinyl acetal of the present invention synthesized using the aldehyde No. 4 (degree of polymerization approximately 2000, degree of acetalization 70%) and 35 parts by weight of tetrahydrofuran were dispersed for 24 hours using a hard glass pole and a hard glass pot. The mixture was mixed to form a coating solution for a charge generation layer.

This was applied by dip coating onto the intermediate layer described above, and heated to 100°C.
This was dried for 1 hour to form a charge generation layer of steel with a thickness of about 0.3 μm.

Next, 1 part by weight of a hydrazone derivative represented by the following structural formula and 1 part by weight of polycarbonate were dissolved in 9 parts by weight of tetrahydrofuran, and this was applied by dip coating onto the charge generation layer.
A photoreceptor was completed by drying at 0° C. for 2 hours to form a charge transport layer having a thickness of about 20 μm.

\ Example 2: After forming an intermediate layer on the A2 blank tube in the same manner as in Example 1, 1 part by weight of aluminum chloride phthalocyanine and No. 1 shown in Table 1 as aldehyde were added. 1 and no. 1 part by weight of the polyvinyl acetal of the present invention (polymerization degree of about 50 and acetalization degree of about 75%) synthesized using aldehyde No. 4 and 48 parts by weight of dichloromethane were dispersed for 24 hours using a hard glass pole and a hard glass pot. The mixture was mixed to form a coating solution for a charge generation layer.

This was coated by dip coating on the intermediate layer described above and dried at 100° C. for 1 hour to form a charge generating layer of steel with a thickness of about 0.3 μm.

Next, in the same manner as in Example 1, a charge transport layer was formed thereon to complete a photoreceptor. Example 3: 1 part by weight of cyanomethylated cellulose into which about 60% of cyanomethyl groups (CLCN) were introduced as alkylcyano groups was mixed with N.I. It was dissolved in 20 parts by weight of N-dimethylformamide, applied by dip coating onto an aluminum tube, and dried for 1 hour in a too-c oven to form an intermediate layer with a film thickness of about 1 μm. Next, 3 parts by weight of β-type cyanine and No. 1 in Table 1 were added as aldehyde. 1 and no. 2 and no.
2 parts by weight of the polyvinyl acetal according to the present invention synthesized using three types of aldehydes No. 9 (degree of polymerization: about 800; degree of acetalization: 70% by weight). Using a hard glass pole and a hard glass pot, add 100 parts by weight of tetrahydrofuran to 2.
The mixture was dispersed and mixed for 4 hours to obtain a coating solution for the charge generation layer.

This was dip-coated onto the intermediate layer and dried at 100°C for 1 hour to form a charge generation layer with a thickness of about 0.3 μm.

Next, in the same manner as in Example 1, a charge transport layer was formed thereon to complete a photoreceptor.

Comparative Example 1: (Characteristic of the intermediate layer, corresponding to Example 1) 1 part by weight of thermosetting acrylic resin (product name SE-5377, manufactured by Mitsubishi Rayon) was dissolved in 1 part by weight of tetrahydrofuran, and an A1 base tube was prepared. An intermediate layer of steel having a film thickness of about 1 μm was formed by dip coating on top.

Next, a charge generation layer and a charge transport layer were formed thereon in the same manner as in Example 1 to form an electrophotographic photoreceptor.

Comparative Example 2: (Characteristic of the intermediate layer, corresponding to Example 1) 1 part by weight of hydroxypropyl methyl cellulose (product name 60SH50, manufactured by Shin-Etsu Chemical) was dissolved in 10 parts by weight of pure water, and this was dip-coated onto an Al blank tube. Then, it was dried at 100°C for 1 hour to form an intermediate layer having a thickness of about 1 μm.

Next, a charge generation layer and a charge transport layer were formed thereon in the same manner as in Example 1 to obtain an electrophotographic photoconductor.

Comparative Example 3: (Features in charge generation layer, corresponds to Example 1)
An electrophotographic photoreceptor was obtained in the same manner as in Example 1 except that polyvinyl petyral (degree of polymerization of about 2000>) was used in place of the polyvinyl acetal according to the present invention in the charge generation layer of Example 1.

Comparative Example 4: (Characteristics of charge generation layer, corresponding to Example 1) In the charge generation layer of Example 941, silicone (product name: ES-100) was used instead of the polyvinyl acetal according to the present invention.
An electrophotographic photoreceptor was obtained in exactly the same manner except that 1N (manufactured by Shin-Etsu Chemical) was used.

Results; Of the seven types of electrophotographic photoreceptors mentioned above, the charge generation layer coating liquids used in Examples 1 to 3 and Comparative Examples 3 and 4, which are characterized by the binder resin of the charge generation layer, were coated with a diameter of 15 ann and a length of 15 ann. 300
When the coating solutions of Examples 1 to 3 and Comparative Example 3 were placed in a colorimeter tube and left to stand, no sedimentation occurred even after one month, but the coating solution of Comparative Example 4 showed no sedimentation after only one week. The liquid near the surface became transparent, and it was confirmed that the cyanine at the top of the lid had settled.

Next, when an adhesion test was conducted using a grid test for Examples 1 to 3 and Comparative Examples 1 and '2, it was found that the photoreceptors of Examples 1 to 3 and Comparative Example 1 showed good adhesion; In the photoreceptor of Comparative Example 2, there was a tendency for separation between the intermediate layer and the octane tube to occur easily.

Next, when we carried out a printing test using the seven types of photoreceptors mentioned above in our small laser printer, we found that the photoreceptors of Examples 1 to 3 and Comparative Examples 2 and 4 produced clear printing results. did it.

Furthermore, in the photoreceptor of Comparative Example 3, insufficient print density and fogging in the background occurred on the first 10 pages or so, but clear prints were obtained after that. Although good adhesion was maintained in the second photoreceptor, in the photoreceptor of Comparative Example 2, peeling occurred between the 82 support and the photosensitive layer due to moisture absorption in the intermediate layer.

Further, as a result of the printing test, the photoreceptor of Example showed no change from before wetting, but the photoreceptor of Comparative Example 2 showed a decrease in density and image blurring.

Table 2 summarizes these results, and the significant difference of the present invention is clear.

〔Effect of the invention〕

By carrying out the present invention, not only the characteristics of the photoreceptor but also the dispersion stability of the coating liquid for the charge generation layer and the A! Adhesion to raw pipe. It is possible to obtain an electrophotographic photoreceptor that is excellent in all respects such as moisture resistance and printing characteristics.

In the table, ○ marks are good, Δ marks have some problems. An x mark indicates that there is a problem.

Furthermore, regarding the photoreceptors of Examples 1 to 3 and Comparative Examples 1 and 2, 5
As a result of a moisture resistance test of leaving it for 5 days under the conditions of 0''C.90%RH, the results of Examples 1 to 3 and Comparative Example 1 were as follows.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional structural diagram of a functionally separated photoreceptor. In the figure, 1 is a conductive support, 2 is a charge generation layer, 3 is an intermediate layer, and 5 is a photoreceptor. 4 is a charge transport layer;

Claims (1)

[Scope of Claims] A functionally separated photoreceptor comprising at least an intermediate layer, a charge generation layer, and a charge transport layer laminated in this order on a conductive support, wherein the intermediate layer has the structural formula (1) below. Electrophotography, characterized in that it contains an alkyl cyanated cellulose represented by the formula, and uses polyvinyl acetal obtained by an acetalization reaction between at least two types of aldehydes and polyvinyl alcohol as a binder resin of the charge generation layer. Photoreceptor. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (1) Here, R represents a lower alkylcyano group, H, or an alkyl group.