JPH0715580B2 - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a function-separated electrophotographic photosensitive member, and more particularly, to improvement of a charge generation layer capable of improving electrophotographic characteristics.

[Prior Art] Inorganic conductive materials such as selenium, cadmium sulfide, and zinc oxide are conventionally known as photoconductive materials used in electrophotographic photoreceptors. While these photoconductive materials have many advantages, such as low dissipation of charges in the dark or rapid dissipation of charges by light irradiation, they have various drawbacks. . For example, selenium-based photoconductors easily crystallize due to factors such as temperature, humidity, dust, and pressure.In particular, when the ambient temperature exceeds 40 ° C, crystallization becomes remarkable, resulting in reduced chargeability and white spots on images. There is a drawback that Cadmium sulfide-based photoconductors cannot obtain stable sensitivity in a humid environment, and zinc oxide-based photoconductors require a sensitizing effect by a sensitizing dye represented by rose bengal. There is a drawback that a stable image cannot be provided for a long period of time because the photosensitive dye causes charge deterioration due to corona charging and photobleaching due to exposure light.

On the other hand, various organic photoconductive polymers such as polyvinylcarbazole have been proposed, but these polymers are superior to the above-mentioned inorganic photoconductive materials in terms of film forming property and light weight. Despite this, it has been difficult to put it into practical use until now, because it has not been able to obtain sufficient film-forming properties, and the inorganic photoconductivity is high in terms of sensitivity, durability and stability due to environmental changes. This is because it is inferior to the material. Further, hydrazone compounds disclosed in U.S. Pat.No. 4,150,987, triarylpyrazoline compounds described in U.S. Pat. No. 3,738,851, JP-A-51-94852, JP-A-51-94829, etc. Low molecular weight organic photoconductors such as 9-styrylanthracene compounds have been proposed. Such low molecular weight organic photoconductors have been able to eliminate the drawback of film-forming property, which has been a problem in the field of organic photoconductive polymers, by appropriately selecting the binder to be used. In terms of, it is not enough.

Under these circumstances, in recent years, a laminated structure has been proposed in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer. An electrophotographic photosensitive member having this laminated structure as a photosensitive layer can be improved in terms of sensitivity to visible light, charge retention, surface strength and the like.

Such an electrophotographic photoreceptor is disclosed in, for example, US Pat. No. 383785.
No. 1 and No. 3871882.

The function-separated type photoconductor is composed of at least two layers of a charge generation layer and a charge transport layer, and the charge carrier generated by light absorption of the charge generation layer is injected into the charge transport layer and moves to the surface to form a photoconductor. Neutralizes surface charges and creates electrostatic contrast.

The role of the charge generation layer in this process is extremely important. That is, how much and uniformly the charge carriers are generated, how efficiently the generated charge carriers are injected into the charge transport layer, and how the reverse charge carriers are smoothly flowed to the support. There are many places to bear

The charge generation layer is basically composed of an organic pigment which is a charge generation substance and a binder which is a binder. The weight ratio of the binder to the organic pigment is generally 25% of that of the organic pigment.
It's not as low as ~ 100Wt%. Therefore, the binder has a very important influence on the migration of the generated charge carrier in the charge generation layer. That is, the basic structure, functional group, molecular weight, purity and the like of the binder are largely related to the electrophotographic characteristics of the photoconductor such as sensitivity, potential characteristics and durability.

However, from the disclosure of literatures, patent documents, and the like, the viewpoint of the binder of the conventional charge generation layer is that it is an auxiliary agent of the organic pigment that is the charge generation substance, and it is sufficient that the dispersibility and the binding property can be imparted. It doesn't seem to come out.

As a result, in the conventional function-separated electrophotographic photoreceptor, many defects such as residual potential, potential fluctuation, and potential characteristic of photo memory are recognized. Also, the sensitivity is not sufficient.

[Problems to be Solved by the Invention] The present inventors have long considered that a binder is an electronic material which is another main material of the charge generation layer, and the binder is considered from the aspect of molecule such as structure, molecular weight and purity. The present invention has been studied and studied.

That is, an object of the present invention is to provide a novel binder for a charge generating layer, and to provide an electrophotographic photoreceptor having improved electrophotographic characteristics.

Another object is to provide an electrophotographic photoreceptor having practically high sensitivity characteristics and stable potential characteristics in repeated use.

[Means and Actions for Solving Problems] That is, according to the present invention, in an electrophotographic photoreceptor having at least a charge generation layer and a charge transport layer on a conductive support, polyvinyl alcohol and an aromatic ring are contained in the charge generation layer. An electrophotographic photoreceptor containing a polyvinyl ketal obtained by a ketalization reaction with a condensed 5- to 7-membered ring ketone compound.

The polyvinyl ketal used in the present invention is preferably a resin having a weight average molecular weight in the range of 10,000 to 400,000, and particularly preferably a resin in the range of 30,000 to 150,000.

The ketalization degree is effective if it is 30 mol% or more, but a range of 50 to 90 mol% is particularly preferable.

Further, it is contained in the raw material polyvinyl alcohol. The lower the content of the vinyl acetate component, the more effective it is, but it is sufficient if the saponification degree of polyvinyl alcohol is 85% or more.

Hereinafter, a representative example of the polyvinyl ketal used in the present invention will be described by describing the ketal structure portion.

Synthesis of Polyvinyl Ketal of Resin Example (2) 10 g of polyvinyl alcohol and 150 g of ketone compound having the following structural formula Pour into a mixed solvent of 200 g of benzene and 100 g of methanol, set the liquid temperature to 55 ° C., and stir strongly.

After 30 minutes, add 3 g of hydrochloric acid (Conc 35%) and let stand for 20 hours. After 20 hours, 150 g of acetone and 150 g of toluene are added, and the mixture is dropped into 3 l of methanol to reprecipitate the polymer.

After stirring for 3 hours, the polymer is filtered. Vacuum drying (760mmH
g, 50 ° C.) for 8 hours.

The yield was 11g.

In the present invention, the polyvinyl ketal is used as the binder of the charge generation layer of the function-separated photoreceptor.

The binder of the charge generation layer should be one that does not interfere with the movement of the charge carriers generated in the layer as much as possible.

Therefore, it is inevitably preferable that the content% by weight of the binder in the charge generation layer be low, but in practice, it imparts binding property,
Furthermore, in order to ensure stability when dispersing the pigment, 20
It is necessary to add it in an amount of not less than 20% by weight, and it is usually used in the range of 25 to 70% by weight, preferably 28 to 50% by weight.

The charge generation layer includes selenium, selenium-tellurium, amorphous silicon, pyrylium, thiapyrylium dye, phthalocyanine pigment, anthanthrone pigment, dibenzpyrenequinone pigment, pyranthrone pigment, trisazo pigment,
Inorganic pigments and organic dyes selected from charge generating substances such as disazo pigments, azo pigments, indigo pigments, quinacridone pigments, asymmetric quinocyanine dyes, and quinocyanine dyes can be used as the resin dispersion layer together with the binder.

Examples of the charge generating substance used in the electrophotographic photosensitive member of the present invention include inorganic compounds and organic compounds shown below.

Charge generation material (1) Amorphous silicon (2) Selenium-tellurium (3) Selenium-arsenic (4) Cadmium sulfide (63) Squaric acid methine dye (64) Indigo dye (CINo.78000) (65) Thioindigo dye (CINo.78800) (66) Copper phthalocyanine (67) Azurenium salt dye The charge-generating substance together with the specific binder in the present invention. The coating liquid is dispersed to form a coating liquid, in which case, as the organic solvent, acetone, methyl ethyl ketone, ketones such as cyclohexanone, N, N-dimethylformamide, amides such as N, N-dimethylacetamide, dimethyl sulfoxide, etc. Sulfoxides, tetrahydrofuran, dioxane, ethers such as ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, chloroform, methylene chloride, dichloroethylene,
Aliphatic halogenated hydrocarbons such as carbon tetrachloride and trichloroethylene, or benzene, toluene, xylene,
Aromatic compounds such as ligroin, monochlorobenzene, and cyclolbenzene can be used.

Dispersion is carried out by crushing and dispersing the above solvent, charge generating substance and binder using a sand mill, a ball mill, a roll mill, an attritor or the like until a predetermined particle size is obtained.
The particle size and the amount of the binder have a great influence on the stability of the dispersion and the characteristics of the photoconductor, and thus they need to be thoroughly examined.

Coating is dip coating method, spray coating method,
It can be carried out by using a coating method such as a spinner coating method, a bead coating method, a Meyer coating method, a blade coating method, a roller coating method and a curtain coating method.

Drying is preferably performed by drying by touching at room temperature and then drying by heating. The heat drying is performed at 30 to 200 ° C. for 5 minutes to 2 hours.

The charge generation layer contains as much of the above organic photoconductor as possible in order to obtain sufficient absorbance, and in order to shorten the range of the generated charge carrier, a thin film layer, for example, 5 μm or less, preferably 0.01 μm or less. It is preferable to use a thin film layer having a film thickness of ˜1 μm.

This means that most of the amount of incident light is absorbed by the charge generation layer to generate many charge carriers, and the generated charge carriers are injected into the charge transport layer without being deactivated by recombination or trapping. Is due to the need to.

The charge transport layer is electrically connected to the above-mentioned charge generation layer, and has a function of receiving the charge carriers injected from the charge generation layer in the presence of an electric field and transporting these charge carriers to the surface. ing.

In this case, the charge transport layer may be laminated on the charge generating layer or may be laminated thereunder.

However, the charge transport layer is preferably laminated on the charge generation layer.

Since the photoconductor generally has a function of transporting charge carriers, the charge transport layer can be formed by this photoconductor.

The substance that transports the charge carrier in the charge transport layer (hereinafter referred to as the charge transport substance) is preferably substantially insensitive to the wavelength range of the electromagnetic wave to which the above-mentioned charge generation layer is sensitive.

The term "electromagnetic wave" as used herein includes a broad definition including γ rays, X rays, ultraviolet rays, visible rays, near infrared rays, infrared rays, and far infrared rays.

The charge-transporting substances include electron-transporting substances and hole-transporting substances, and the electron-transporting substances include chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone. , 2,4,
Electron-withdrawing ability of 5,7-trinitro-9-fluorenone, 2,4,7-trinitro-9-dicyanomethylenefluorenone, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone There are substances and those obtained by polymerizing these electron-withdrawing substances.

Examples of the hole transport material include pyrene, N-ethylcarbazole, N-isopropylcarbazole, N-methyl-N-
Phenylhydrazino-3-methylidene-9-ethylcarbazole, N, N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N, N-diphenylhydrazino-3-methylidene-10-ethylphenothiazine, N,
N-diphenylhydrazino-3-methylidene-10-ethylphenoxazine, p-diethylaminobenzaldehyde-N, N-diphenylhydrazone, p-diethylaminobenzaldehyde-N-α-naphthyl-N-phenylhydrazone, p-pyrrodinobenzaldehyde- N, N-diphenylhydrazone, 1,3,3-trimethylindolenine-
hydrazones such as ω-aldehyde-N, N-diphenylhydrazone and p-diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrazone, 2,5-bis (p-diethylaminophenyl-1,3,4-oxa) Diazole, 1-phenyl-3- (p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [quinolyl (2)]-3- (p-diethylaminostyryl) -5- (p-diethylamino) Phenyl) pyrazoline, 1- [pyridyl (2)]-3- (p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [6-methoxypyridyl (2)]
-3- (p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1- [pyridyl (3)]-3- (p-diethylaminostyryl) -5-
(P-Diethylaminophenyl) pyrazoline, 1- [lepidyl (2)]-3- (p-diethylaminostyryl)
-5- (p-diethylaminophenyl) pyrazoline, 1
-[Pyridyl (2)]-3- (p-diethylaminostyryl) -4-methyl-5- (p-diethylaminophenyl) pyrazoline, 1- [pyridyl (2)]-3- (α-
Methyl-p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline, 1-phenyl-3
-(P-Diethylaminostyryl) -4-methyl-5-
Pyrazolines such as (p-diethylaminophenyl) pyrazoline, 1-phenyl-3- (α-benzyl-p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazoline and spiropyrazolin, 2- (p-
Diethylaminostyryl) -6-diethylaminobenzoxazole, 2- (p-diethylaminophenyl)-
Oxazole compounds such as 4- (p-diethylaminophenyl) -5- (2-chlorophenyl) oxazole, thiazole compounds such as 2- (p-diethylaminostyryl) -6-diethylaminobenzothiazole,
Triarylmethane compounds such as bis (4-diethylamino-2-methylphenyl) -phenylmethane, 1,1
-Bis (4-N, N-diethylamino-2-methylphenyl) heptane, polyarylalkanes such as 1,1,2,2-tetrakis (4-N, N-diethylamino-2-methylphenyl) ethane, triaryl Examples include phenylamine, poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinylacridine, poly-9-vinylphenylanthracene, pyrene-formaldehyde resin, and ethylcarbazolealdehyde resin. In addition to these organic charge transport materials, inorganic materials such as selenium, selenium-tellurium, amorphous silicon, and cadmium sulfide can also be used.

Moreover, these charge transport materials can be used alone or in combination of two or more.

When the charge transport material has no film-forming property, a film can be formed by selecting an appropriate binder. The resin that can be used as the binder is, for example, an acrylic resin,
Polyarylate, polyester, polycarbonate, polyethylene, acrylonitrile-styrene copolymer,
Insulating resins such as acrylonitrile-butadiene copolymer, polyvinyl butyral, polyvinyl formal, polysulfone, polyacrylamide, polyamide, and chlorinated rubber, or organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylpyrene are mentioned. it can.

Since the charge transport layer has a limit for transporting charge carriers, the film thickness cannot be increased more than necessary. Generally, it is 5 to 30 μ, but a preferable range is 8 to 20 μ. When the charge transport layer is formed by coating, an appropriate coating method as described above can be used.

The photosensitive layer having such a laminated structure of the charge generation layer and the charge transport layer is provided on the conductive support.

As the substrate having a conductive layer, it is possible to use, for example, aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold, platinum, etc., which support itself has conductivity. In other cases, for example, aluminum, aluminum alloy, indium oxide, tin oxide, plastic having a layer formed by vacuum deposition of indium oxide-tin oxide alloy and the like (for example, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate,
Acrylic resin, polyfluorinated ethylene, etc.), conductive particles (eg, carbon black, silver particles, etc.) coated on a plastic with a suitable binder, a support in which conductive particles are impregnated in plastic or paper, and a conductive material. It is possible to use a plastic having a hydrophilic polymer.

An undercoat layer having a barrier function and an adhesive function can be provided between the conductive support and the photosensitive layer.

The subbing layer can be formed of casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide (nylon 6, nylon 66, nylon 610, copolymer nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, aluminum oxide, etc. .

The thickness of the undercoat layer is 0.1 to 5 µ, preferably 0.5 to 3 µ.

When using a photoreceptor in which a conductive support, a charge generation layer and a charge transport layer are laminated in this order, the charge transport layer must be positively charged when the charge transport substance is an electron transport substance. When post-exposure is performed, in the exposed portion, electrons generated in the charge generation layer are injected into the charge transport layer, and then reach the surface to neutralize the positive charge, and the surface potential is attenuated.

A visible image can be obtained by developing the electrostatic latent image thus formed with a negatively chargeable toner. This can be fixed directly, or the toner image can be transferred to paper or a plastic film and then developed and fixed.

Further, a method of transferring the electrostatic latent image on the photoconductor onto the insulating layer of the transfer paper and then developing and fixing the latent image is also available.

The type of developer and the method of fixing the developing method may be selected from known methods and known methods, and are not limited to particular ones.

On the other hand, when the charge transport material is a hole transport material,
It is necessary to negatively charge the surface of the charge transport layer, and after exposure after charging, holes generated in the charge generation layer are injected into the charge transport layer in the exposed area and then reach the surface to neutralize the negative charge, The potential is attenuated, and an electrostatic contrast is generated with the unexposed portion. At the time of development, it is necessary to use a positively chargeable toner, contrary to the case where an electron transport substance is used. In both positive and negative charged electrophotographic photoreceptors, if light irradiation is performed before charging, electrophotographic characteristics of a portion irradiated with light may be different from characteristics of a portion not irradiated with light, that is, a so-called photomemory property may appear. In many cases, the present invention can improve this photomemory property.

[Examples] Example 1 4 parts of pigment of Example (13) of charge generation material and resin example (2)
2 parts of the above resin was put in 90 parts of cyclohexanone, and dispersed with a sand mill using 1φ glass beads for 20 hours.

A coating solution was prepared by adding 180 parts of 2-butanone to this dispersion.

This coating solution was applied on an aluminum sheet so that the coating amount was 0.2 g / m ² , and dried at 100 ° C. for 10 minutes to form a charge generation layer.

Next, 10 parts of 1- [pyridyl (2)]-3- (4-N, N-diethylaminostyryl) -5- (4-N, N-diethylaminophenyl) pyrazoline and a styrene-acrylic copolymer (trade name) 10 parts of MS200, manufactured by Iron Manufacturing Chemical Co., Ltd. was dissolved in 80 parts of toluene. This solution was applied on the charge generation layer and dried with hot air at 100 ° C. for 1 hour to form a 20 μ thick charge transport layer.

The electrophotographic photosensitive member thus formed was evaluated as follows.

The sensitivity of the photoconductor was measured using an electrostatic paper analyzer EPA8100 manufactured by Kawaguchi Electric Co., Ltd.

The conditions were such that the dynamic mode of the above tester was used, the surface of the photoconductor was charged to 700 ± 30 V, left in the dark for 1 second, and irradiated with 17.5 lux of light for 4.0 seconds to measure the light attenuation.

Let Vd (V) be the potential on the surface of the photoconductor after leaving it in the dark, and set Vd to 1 /
The exposure amount required to attenuate to 2 was E1 / 2 (lux · sec).

Also, the sample once measured was irradiated with 1500 lux light for 3 minutes and left in the dark for 2 minutes, and then the same measurement was performed, and the difference in the dark part potential at that time was used as a photo memory. The results are shown below.

Vd (V): -705, E1 / 2 (lux, sec): 2.85 Photo memory (V): 30 Examples 2 to 4 Resin Examples 3, Resin Examples 4 and Resins as resins used in the coating liquid for the charge generation layer Electrophotographic photoconductors were prepared in the same manner as in Example 1 except that the resin of Example 6 was used, and the photoconductors of Example 2, Example 3 and Example 4 were correspondingly prepared.

The results of the same evaluations as in Example 1 are shown below.

Vd (V) Example 2-720 Example 3-730 Example 4-700 E1 / 2 (lux, sec) Example 2 3.05 Example 3 3.10 Example 4 3.05 Photomemory (V) Example 2 40 Example 3 25 Example 4 35 Comparative Examples 1 to 3 For comparison, the resin used for the charge generation layer was polyvinyl butyral (degree of butyralization 60 mol%, molecular weight of synthetic product about 3).
60,000), acrylic resin (trade name Acrybase OM2-2)
0, Fujikura Kasei Co., Ltd., polyester (terephthalic acid)
1.00, isophthalic acid 1.15, ethylene glycol 1.00, neopentyl glycol 1.15 (molar ratio), molecular weight about 20,00
0) was used and other conditions were the same as in Example 1 to prepare electrophotographic photoconductors, and correspondingly, the photoconductors of Comparative Example 1, Comparative Example 2 and Comparative Example 3 were prepared. The results of evaluation performed in the same manner as in Example 1 are shown below.

Vd (V) Comparative Example 1-705 Comparative Example 2-700 Comparative Example 3-710 E1 / 2 (lux, sec) Comparative Example 1 3.85 Comparative Example 2 3.95 Comparative Example 3 3.75 Photo Memory (V) Comparative Example 1 75 Comparative Example 285 Comparative Example 3 100 Example 5 An electrophotographic photosensitive member was prepared in the same manner as in Example 1 except that ε-type copper phthalocyanine was used as the charge generating substance.

Comparative Example 4 An electrophotographic photosensitive member was prepared in the same manner as in Example 5 except that the polyvinyl butyral used in Comparative Example 1 was used as the binder used in the charge generation layer.

Example 6 An electrophotographic photoreceptor was prepared in the same manner as in Example 1 except that the pigment of the charge generating substance example (5) was used as the charge generating substance.

Comparative Example 5 An electrophotographic photosensitive member was prepared in the same manner as in Example 6 except that the polyvinyl butyral used in Comparative Example 1 was used as the binder used in the charge generation layer.

The above photoreceptor was evaluated in the same manner as in Example 1. The results are shown below.

Vd (V) Example 5-700 Example 6-710 Comparative Example 4-700 Comparative Example 5-700 E1 / 2 (lux, sec) Example 5 3.15 Example 6 3.50 Comparative Example 4 3.95 Comparative Example 5 4.45 Photo Memory (V) Example 5 10 Example 6 15 Comparative Example 4 55 Comparative Example 5 60 As is apparent from the above results, the electrophotographic photosensitive member of the present invention uses the specific polymer material in the charge generation layer. , Regardless of the type of charge generating material, compared to electrophotographic photoreceptors using polyvinyl butyral, polyester, acrylic resin, etc., which are generally used in the conventional charge generating layer,
The sensitivity can be increased to 20% or more, and the photo memory can be reduced to less than half.

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide an electrophotographic photosensitive member having a high sensitivity, and a fluctuation in the potential of the bright portion and the potential of the dark portion upon repeated charging and exposure is small, and moreover, a photo memory. It has an advantage that the sex can be effectively improved.

Claims (1)

[Claims] 1. An electrophotographic photoreceptor having at least a charge generating layer and a charge transporting layer on a conductive support, wherein polyvinyl alcohol and an aromatic ring are condensed in the charge generating layer.
An electrophotographic photoreceptor comprising a polyvinyl ketal obtained by a ketalization reaction with a membered ring ketone compound.