JPS62291663A - electrophotographic photoreceptor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] 3. Detailed description of the invention [Industrial application field] The present invention relates to a monofunctionally separated electrophotographic photoreceptor.

More specifically, the present invention relates to improvements in charge generation layers that improve electrophotographic properties.

[Prior Art] Conventionally, $99 photoconductive materials such as selenium, cadmium sulfide, and zinc oxide are known as photoconductive materials used in electrophotographic photoreceptors. These photoconductive materials have many advantages, such as being able to be charged to an appropriate potential in the dark, having little charge dissipation in the dark, or quickly dissipating the charge when irradiated with light. On the other hand, it has various drawbacks.For example, selenium-based photoreceptors easily crystallize due to factors such as temperature, humidity, dust, and pressure.
In particular, when the ambient temperature exceeds 40° C., crystallization becomes significant, resulting in drawbacks such as a decrease in chargeability and the appearance of white spots on images. Cadmium sulfide photoreceptors do not provide stable sensitivity in humid environments, and zinc oxide photoreceptors require the sensitizing effect of sensitizing dyes such as rose bengal. They have the disadvantage that they cannot provide stable images over a long period of time because the sensitive dyes undergo charging deterioration due to corona charging and photobleaching due to exposure light. On the other hand, various organic photoconductive polymers such as polyvinyl cartazoole have been proposed, but these polymers are superior to the above-mentioned inorganic photoconductive materials in terms of film formability and light weight. However, it has been difficult to put it into practical use to date because sufficient film formation properties have not yet been achieved, and inorganic photoconductive materials have been lacking in sensitivity, durability, and stability against environmental changes. This was because they were inferior in comparison. In addition, hydrazone compounds described in US Pat. No. 4,150,987, triarylpyranphosphorus compounds described in US Pat. No. 3,837,851, etc., JP-A-51-94828, JP-A-51-94829, etc. Low-molecular organic photoconductors such as the 9-styrylanthracene compound described in et al. solve the problem of film-forming properties in the field of organic photoconductive polymers by appropriately selecting the binder used. However, it cannot be said that the sensitivity is sufficient. For this reason, an fZt layer structure in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer has been proposed in recent years. Electrophotographic photoreceptors using this laminated structure as a photosensitive layer can now 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. 383
It is disclosed in the specification of No. 7851, the specification of Copper No. 3871882, etc. Such a functionally separated photoreceptor is composed of at least two layers: a charge generation layer and a charge transport layer.

Charge carriers generated by light absorption in the TrL charge generation layer are injected into the charge transport layer, move to the surface, neutralize the photoreceptor surface charge, and produce electrostatic contrast. The role played by the charge generation layer in this process is extremely important. In other words, electrophotographic characteristics depend on charge generation, how many charge carriers are generated uniformly, how efficiently the generated charge carriers are injected into the charge transport layer, and how smoothly opposite charge carriers flow into the support. The charge generation layer is basically composed of an organic pigment as a charge generation substance and a binder as a binding agent, but the weight ratio of the binder to the organic pigment is generally the same as that of the organic pigment. 25
The binder has a very significant influence on the movement of generated charge carriers within the charge generation layer.

That is, the basic structure, functional groups, molecular weight, purity, etc. of the binder greatly affect the electrophotographic properties of the photoreceptor, such as sensitivity, potential characteristics, and durability. However, as we know from literature and patent documents, the conventional view of the binder in the charge generation layer is that it is an auxiliary agent for the organic pigment, which is the charge generation substance, and that it is sufficient as long as it can impart dispersibility and grouping properties. It doesn't seem to be coming out. As a result, many defects in potential characteristics such as residual potential, potential fluctuation, and photomemory have been observed in the conventional functionally separated photoconductor E'(!,! photoconductor. Also, the sensitivity is not sufficient. .

[Problems to be solved by the invention] For many years, wood inventors have regarded binders as another main material of the charge generation layer and an electronic material, and have evaluated binders from molecular aspects such as structure, molecular weight, and purity. This study led to the present invention.

That is, the objects of the present invention are to provide a novel binder for a charge generation layer, an electrophotographic photoreceptor having improved electrophotographic properties, practical high sensitivity properties,
k′j! It is an object of the present invention to provide an electrophotographic photoreceptor having stable potential characteristics in repeated use, and to provide a coating material for producing an electrophotographic photoreceptor that has good dispersion stability with a charge generating material.

[Means and effects for solving the problems] The present invention provides an electrophotographic photoreceptor having at least a charge generation layer and a charge transport layer on a conductive support, in which a styrene monomer represented by the following general formula is polymerized. A device R3 composed of an electrophotographic photoreceptor characterized by containing the obtained resin (wherein R1, R2, R3, R4, R5 and R6 represent a hydrogen atom or a substituent, provided that R6 is a hydrogen atom In the case, R1-R5 are not all hydrogen atoms, and
When R6 is a substituent, R1-R5 may all be hydrogen atoms.) The styrenic resin used in the present invention suitably has a weight average molecular weight in the range of 10,000 to 200,000,
Especially 30,000~ao, oo.

Resins in the range of are preferred. However, this tends to be influenced by the atomic weight of the substituent, and in general, the degree of polymerization is 30.
Weight average molecular weight in the range of ~1500 10,000~2
Anything in the range of 00,000 is suitable for use.

Typical specific examples of styrenic resins that satisfy the requirements of the present invention are listed below.

Resin example Hs CHx CzHr
To explain the synthesis method of resin example (1) as an example of the synthesis of the above resin, 15 g of polystyrene (trade name Dick Elastyrene #200, manufactured by Dainippon Ink Co., Ltd.) and 300 m of carbon tetrachloride were placed in a 114-bottle flask. , dissolve with stirring. While maintaining the liquid temperature at 15° C., 30 g of anhydrous sulfuric acid was slowly added, followed by 100 ml of dioxane and stirred for 6 hours.

After 6 hours, the reaction solution was dropped into methanol 31 to precipitate the polymer. Yield was 18.5g.

The binder of the charge generation layer must be one that does not inhibit the movement of charge carriers generated within the layer as much as possible.

Therefore, it is naturally preferable that the content of the binder in the charge generation layer is lower in weight percent, but in practical terms, it is necessary to
Furthermore, in order to ensure stability during pigment dispersion, 20
It is necessary to use at least 25% by weight, usually 25 to 70% by weight, preferably 28 to 50% by weight.

The charge generating layer used in the present invention includes selenium, selenium-tellurium, amorphous silicon, pyrylium dyes, thiapyrylium dyes, phthalocyanine pigments, anthorone pigments, vilanthrone pigments, trisazo pigments, disazo pigments, heptanoazo pigments, indigo pigments, Inorganic pigments or organic dyes/pigments selected from charge generating substances such as quinacridone pigments, asymmetric quinocyanine pigments, and quinocyanine pigments can be used together with the binder as the resin dispersion layer.

Examples of the charge generating substance used in the electrophotographic photoreceptor of the present invention include the following inorganic compounds and organic compounds.

Charge generating substance (1) Amorphous silicon (2) Selenium-tellurium (3) Selenium-arsenic (4) Cadmium sulfide (1B) (3B) (3θ) (4?) CxHx
LiaHs (63) Methine squaric acid dye (64) Indigo dye (C, 1, No. 7
8000) (65) Thioindigo dye (C,1,N
o, 78800) (66) Copper phthalocyanine (67) Azlenium salt dye (68) The τ-type metal-free phthalocyanine charge-generating substance is dispersed together with the binder specified in the present invention to form a coating solution. The organic solvent used is ketones such as acetone, methylnityl ketone, and cyclohexanone.

Amides such as N,N-dimethylformamide and N,N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, chloroform , methylene chloride, dichloroethylene, carbon tetrachloride,
Aliphatic halogenated hydrocarbons such as trichlorethylene, benzene, toluene, xylene, ligroin,
Aromatic hydrocarbons such as monochlorobenzene and dichlorobenzene can be used.

Dispersion is carried out by crushing and dispersing the above solvent, charge generating substance, and binder using a sand mill, ball mill, roll mill, attritor, etc. until a predetermined particle size is obtained.

Particle size and binder amount are the stability of the dispersion.

It has a great influence on the characteristics of the photoreceptor and requires careful consideration.

Coating methods include dip coating, spray coating, spinner coating, bead coating,
This can be carried out using a coating method such as a Mayer bar coating method, a blade coach ink method, a roller coach ink method, or a curtain coating method.

Drying is preferably carried out by drying to the touch at room temperature and then heating. Drying by heating is carried out at 30 to 200° C. for 5 minutes to 2 hours.

The charge generation layer contains as much of the charge generation substance as possible in order to obtain sufficient absorbance and to shorten the range of the generated charge carriers.

A thin film layer, for example a thin film layer having a thickness of 5 l or less, preferably 0.01 to 1 l, is preferred.

This means that most of the incident light is absorbed by the charge generation layer, generating many charge carriers.

Furthermore, this is due to the fact that the generated charge carriers need to be injected into the charge transport layer without being deactivated by recombination or trapping.

The charge transport layer is electrically connected to the charge generation layer described above, and has the function of receiving 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, this charge transport layer may be laminated on top of the charge generation layer, or may be laminated below it.However, the charge transport layer may be laminated on the charge generation layer. is desirable.

The material that transports charge carriers in the charge transport layer (hereinafter referred to as charge transport material) is preferably substantially insensitive to the wavelength range of electromagnetic waves to which the charge generation layer is sensitive, and is not particularly sensitive to the electromagnetic waves referred to herein. are gamma rays, X-rays, ultraviolet rays,
Includes a broad definition of light that includes visible light, near-infrared light, infrared light, far-infrared light, etc.

When the photosensitive wavelength range of the charge transport layer coincides with or overlaps that of the charge generation layer, charge carriers generated in both layers trap each other, resulting in a decrease in sensitivity.

Charge-transporting substances include electron-transporting substances and hole-transporting substances. Examples of electron-transporting substances include chloro7nyl, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, and 2,4.7-dolinitro9- fluorenone,
2,4,5.7-tetranitro-9-fluorenone, 2
, 4.7-) Rinitro 9-dicyanomethylene fluorenone.

2.4,5.7-titranitroxanthone, 2°4.8
-) Electron-withdrawing substances such as linitrothioxanthone, and polymerized products of these electron-withdrawing substances.

Pyrene, N-ethylcarbazole, N-isopropylcarbazole, N-methyl-N-
Phenylhydrazino-3-methylten-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-10-ditylphenothiazine, N, N-diphenylhydrazino-3-methylidene-
10-Ethylphenoxazine, p-diethylaminobenzaldehyde-N, N-diphenylhydrazone, p-diethylaminobenzaldehyde-N-α-naphthyl-N
-Phenylhydrazone, p-pyrrolidinobenzaldehyde-N,N-diphenylhydrazone, 1,3.3-trimethylindolenine-ω-aldehyde-N,N-diphenylhydrazone, p-diethylbenzaldehyde-3-
Hydrazones such as methylbenzthiazolinone-2-hydrazone, 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, ■-phenyl-3
-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[quinolyl (2)
]-3-(p-diethylaminostyryl)-5-(p-
diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-3-(p-diethylaminostyryl)-5-
(p-diethylaminophenyl)pyrazoline, l-[6
-Medoxybilidyl(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-(p-diethylaminophenyl)hylazoline, l-phenyl-3-(α-benzyl-p-diethylaminostyryl)-5-(p -diethylaminophenyl)pyrazoline, spiropyrazoline and other pyrazolines, 2-(p-diethylaminostyryl)
-6-dinithylaminobenzoxazole, 2-(p-
Oxazoles such as diethylaminostyryl-4-(p-dimethylaminophenyl)-5-(2-chlorophenyl)oxazole, thiazoles such as 2-(p-diethylaminostyryl)-6-dinithylaminobenzothiazole, bis(4 Triarylmethane compounds such as -diethylamino-2-methylphenyl)-phenylmethane, 1,1-bis(4-N,N-diethylamino-2
-methylphenyl)hebutane, 1,1,2,2-tetrakis(4-N.

Polyarylalkanes such as N-dimethylamino-2-methylphenyl)ethane, triphenylamine, poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinylacridine, poly-9-
Examples include vinylphenylanthracene, pyrene-formaldehyde resin, and ethylcarbazole-formaldehyde 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.

When the charge transport material does not have any inherent properties, a film can be formed by selecting an appropriate binder. Examples of such binders include insulating resins such as acrylic resin, polyarylate, polyester, polycarbonate, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, polyvinyl butyral, polyvinyl formal, polysulfone, polyacrylamide, polyamide, and chlorinated rubber. Alternatively, organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylpyrene can be mentioned.

The thickness of the charge transport layer cannot be increased more than necessary because there is a limit to how much charge carriers can be transported.The thickness of the charge transport layer is generally s5-3o, but the preferred range is 8 to 20 JL.

When forming the charge transport layer by coating, an appropriate coating method as described above can be used.

A photosensitive layer having such a laminated structure of a charge generation layer and a charge transport layer is provided on a substrate having a conductive layer which is a conductive support.

Examples of the substrate having a conductive layer include those whose substrate itself is conductive, such as aluminum, aluminum alloy, copper, heavy chain, stainless steel, vanadium, and sled.

Budden, chromium, titanium, nickel, indium, gold, platinum, etc. can be used, and aluminum,
Plastics (e.g. polyethylene,
(polypropylene, polyvinyl chloride, polyethylene terephthalate, acrylic resin, polyfluoroethylene, etc.),
A substrate in which conductive particles (e.g. carbon black, silver particles, etc.) are coated on a plastic together with a suitable binder, a substrate in which plastic or paper is impregnated with conductive particles, a plastic having a conductive polymer, etc. can be used. .

A subbing layer having barrier and adhesive functions can be provided between the conductive layer and the photosensitive layer.

The subbing layer is casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide (nylon 6, nylon 66, nylon 610, copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin.

It can be formed from aluminum oxide, etc.

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

When using the electrophotographic photoreceptor of the present invention, when the charge transport material is an electron transport material, the surface of the charge transport layer must be positively charged.

When exposed to light after being charged, electrons generated in the charge generation layer are injected into the charge transport layer in the exposed area, and then reach the surface and neutralize the positive charge, resulting in attenuation of the surface potential and an electrostatic contrast between it and the unexposed area. occurs.

A visible image is obtained by developing the electrostatic latent image thus formed with a negatively charged toner. This can be directly fixed, or the toner image can be transferred to paper or plastic film, developed, and fixed. Alternatively, a method may be used in which the electrostatic latent image on the photoreceptor is transferred onto an insulating layer of transfer paper, and then visualized and fixed.

The type of developer, the developing method, and the fixing method can be any known method or agent, and are not limited to a specific method or agent.

On the other hand, when the charge transport material is made of a hole transport material, the surface of the charge transport layer must be negatively charged, and when exposed to light after charging, holes generated in the charge generation layer are injected into the charge transport layer in the exposed area. After that, it reaches the surface and neutralizes the negative charges, causing attenuation of the surface potential and creating an electrostatic contrast with the unexposed area. During development, it is necessary to use a positively charged toner, contrary to the case where an electron transporting substance is used.

When electrophotographic photoreceptors with either positive or negative charges are irradiated with light before being charged, the electrophotographic characteristics of the irradiated area are different from those of the area that is not irradiated with light, which often results in so-called photomemory properties. .

According to the present invention, it is possible to provide a highly sensitive electrophotographic photoreceptor, and the variation in bright area potential and dark area potential when repeatedly charged and exposed to light is small, and photomemory properties can be effectively improved. It has the advantage of being able to

[Example] Each of the resins in the resin examples above was synthesized from polystyrene.

In the synthesized resin, the percentage of one styrene monomer unit converted to one seven-unit unit shown in the resin example is shown below (one seven-unit unit is calculated as one molecule, and the ratio is a molar ratio). ) Synthetic resin example Resin example Resin component ratio (mol 2)
The following seven polymers were polymerized using 7zobisin butyronitrile as an initiator.

Synthetic resin example Monomer used Resin example Example 1 4 parts of the pigment of the charge generating substance example (13) and 2 parts of the resin of the synthetic resin example 3 were mixed with cyclihexanone/THF (1:1 weight ratio) 9
0 parts and milled with a sand mill using 1φ glass beads.
Dispersed for 0 hours. A coating solution was prepared by adding 180 parts of 2-butanone to this dispersion. This coating solution was applied onto an aluminum sheet in a coating weight of 0.2 g/m 2 and dried at 100'C for 10 minutes to form a charge generation layer.

Then, 1-[pyridyl(2)]-3-(4-N,N
10 parts of -diethylaminostyryl)-5-(4-N,N-diethylaminophenyl)pyrazoline and styrene-
Acrylic copolymer (product name MS 200. Steel Chemicals ■
Co., Ltd.) was dissolved in 80 parts of toluene. This liquid was applied onto the charge generation layer formed above and dried with hot air at 100''C for 1 hour to form a charge transport layer with a thickness of 20cm.

This electrophotographic photoreceptor is Kawaguchi type 4! Sensitivity was measured using an electrostatic paper analyzer EPA8100 manufactured by JB. The dark potential value (VD value) and sensitivity at this time are shown below. The primary charge during measurement was 100. A constant current method was used.

In addition, after irradiating the previously measured sample with 1500 lux light for 3 minutes and leaving it for 2 minutes, a similar measurement is performed, and the dark potential value measured initially is subtracted from the dark potential value at that time. was used as a photo memory.

Example V D El/2 Photomemory (V) (lux, 5ec) 1 -720 2.90 30 Examples 2 to 10 Synthetic resin example was used instead of synthetic resin example 3 as the resin used in the coating liquid for the charge generation layer 1.4.5.6.7.8゜10.11.1
An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that Example 4 was used.

The results measured in the same manner as in Example 1 are shown.

2 -720 2.95 30 3 -700 3.25 35 4 -735 2.75 405
-730 3.00 256
-680 3.40 157
-700 2.85 458
-695 2.75 109
-720 2.95 3510
-700 3.40 25 examples! ,
After the coating solution prepared in 2.3.4.5.6.8.9 was sealed in a glass container and left in the dark for one week, Example 1 was applied again.
When photoreceptors were prepared in the same manner as in Example 1, no spots or unevenness were observed on the coated surface, and the characteristics of these photoreceptors were measured in the same manner as in Example 1. The characteristics were shown.

Examples 11 to 14 Resin of synthetic resin example 2 and charge generating substance example (5) as pigment
, (32), (41), and (68), a coating solution was prepared in the same manner as in Example 1, and after being left for one week,
When it was coated on an aluminum sheet, a clean coated surface was obtained with no lumps or unevenness.

Comparative Examples 1 to 3 As comparative examples, the resin used in the coating liquid for forming the charge generation layer was (1) polyvinyl butyral resin (butyralization degree 60).
(mol%) (synthetic product molecular weight approximately 60,000), (2) Acrylic resin (trade name Acrybase 0M2-20, manufactured by Fujikura Kasei Co., Ltd.), (3) Polyester [terephthalic acid 1°OO, isophthalic acid 1.15, ethylene Molecular weight approximately 2, consisting of gelcol 1.00 and neopentyl glycol 1.15 (mole ratio)
A photoreceptor was prepared in the same manner as in Example 1, except that the photoreceptor was used, and its characteristics were measured. # Indicates results such as gender.

1 -720 3.75 55 2 -730 3.90 70 3 -700 3.65 150 The coating liquids used in Comparative Examples 1 to 3 showed that even if a standing experiment was conducted in the same manner as in the examples, the The particle size of the pigment component did not become larger than that at the start of standing.

Comparative Examples 4 to 6 The resin used in the coating solution for forming the charge generation layer was (4) polystyrene, (5) synthetic resin, and the resin of Example 3 had a styrene component of 55 mol%.
(6) Resin of synthetic resin example 6 with a styrene component of 70 mol%
A photoreceptor was prepared in the same manner as in Example 1, except that the photoreceptor was used, and its characteristics were measured.

4-7002 Bar 020 5 -710 2.95 35 6 -730 2.80 25 When this coating liquid was allowed to stand in a dark place, the coating liquid of Comparative Example 4 aggregated in 2 hours, and the coating was not completed. It's now possible. The coating solutions of Comparative Examples 5 and 6 started agglomerating in 1 day and 12 hours, respectively.
Painting has become impossible.

Based on this fact, styrenic resins with a large styrene component,
It turned out that the stability of the coating fluid was extremely poor.

[Effects of the Invention] The electrophotographic photoreceptor of the present invention has the advantage that it has high sensitivity, has small fluctuations in bright area potential and dark area potential when repeatedly charged and exposed, and can effectively improve photomemory properties. have.

Claims (3)

[Claims] (1) An electrophotographic photoreceptor having at least a charge generation layer and a charge transport layer on a conductive support, characterized by containing a resin obtained by polymerizing a styrene monomer represented by the following general formula. Electrophotographic photoreceptor. General formula ▲ There are mathematical formulas, chemical formulas, tables, etc. It is not a hydrogen atom, and when R_6 is a substituent, R_1 to R
All _5 may be hydrogen atoms. ) (2) The electrophotographic photosensitive material according to claim 1, wherein the resin obtained by polymerizing the styrene monomer represented by the general formula is a copolymer of the styrene monomer represented by the general formula and styrene. body. (3) The electrophotographic photoreceptor according to claim 1, wherein the styrene monomer represented by the general formula is contained in an amount of 50 mol % or more of the total styrene resin used.