JPS63250657A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To improve injection of carriers from an electric charge generating layer to a charge transfer layer and to enhance printing resistance by rendering the work function of the charge generating layer higher than that of the charge transfer layer and the difference of them a specified value or more. CONSTITUTION:The electrophotographic sensitive body is prepared by laminating a photosensitive layer composed of the charge generating layer and the charge transfer layer on a conductive supporting body, and the work function of the charge generating layer is made higher than that of the charge transfer layer and the difference of them is regulated to >=0.2eV. The work function of the charge generating layer is regulated by combining a charge generating material, such as azo pigments, with a binder, such as a vinylbutyral resin, and the work function of the charge transfer layer containing the charge transfer material, such as hydrazone derivatives, is allowed to match that of the generating layer, thus permitting rise of potential in the light to be lessened by specifying the work functions of the generating layer and the transfer layer, consequently, durability of a high-speed copying machine to be enhanced, and superior characteristics to be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electrophotographic photoreceptor, and more particularly to a laminated type electrophotographic photoreceptor.

[Conventional technology]

Electrophotographic photoreceptors using inorganic photoconductive materials such as selenium, cadmium sulfide, and zinc oxide as photosensitive components have been known so far.

On the other hand, since the discovery that certain organic compounds exhibit photoconductivity, many organic photoconductors have been developed. For example, organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, carbazole,
Low-molecular organic photoconductors such as anthracene, pyrazolines, oxadiazoles, hydrazones, polyaryl alkanes, phthalocyanine pigments, azo pigments, cyanine dyes, polycyclic quinone pigments, perylene pigments, indigo dyes, thio- Organic pigments and dyes such as indigo dyes and methine squaric acid dyes are known. In particular, organic pigments and dyes that have photoconductivity are easier to synthesize than inorganic materials, and the variety of compounds that exhibit photoconductivity in an appropriate wavelength range has been expanded.
A large number of photoconductive organic pigments and dyes have been proposed.

For example, US Pat. No. 4,123,270, US Pat. No. 42,476
No. 14, No. 4251613, No. 4251614, No. 4256821, No. 4260672, No. 4268596, No. 4278747, No. 429
As disclosed in Japanese Patent No. 3628, electrophotographic photoreceptors are known that use a disazo pigment exhibiting photoconductivity as a charge generation substance in a photosensitive layer that is functionally separated into a charge generation layer and a charge transport layer.

Electrophotographic photoreceptors using such organic photoconductors can be produced by coating by appropriately selecting a binder, so it is possible to provide photoreceptors with extremely high productivity and at low cost. It has the advantage of being able to freely control the sensitive wavelength range.

The electrostatic latent image forming mechanism of the photoreceptor described above is considered as follows. That is, excitons produced in the charge generation layer by light irradiation dissociate into electrons and holes within the charge generation layer or at the boundary between the charge generation layer and the charge transport layer to generate carriers (holes). The carrier is injected into the charge transport layer and forms an electrostatic latent image by neutralizing negative charges on the surface of the photoreceptor. On the other hand, electrons migrate to the conductive support.

In a photoreceptor in which the photosensitive layer is divided into a charge transport layer and a charge generation layer, carrier injection from the charge generation layer to the charge transport layer becomes a problem. In other words, even if the carrier generation efficiency in the charge generation layer and the carrier transport efficiency in the charge transport layer are good, if the carrier injection property at the boundary between the two layers is poor, residual frost, decreased sensitivity, and brightness due to an increase in the number of copies will occur. This causes harmful effects such as an increase in the partial potential (VL).

[Problem that the invention seeks to solve]

An object of the present invention is to solve the above-mentioned problems of conventionally known electrophotographic photoreceptors and to provide an electrophotographic photoreceptor with excellent carrier injection properties and high printing durability.

[Means for solving problems]

As a result of studies, the present inventors have discovered that the above object can be achieved by an electrophotographic photoreceptor that has a certain threshold value in the work function difference between the charge generation layer and the charge transport layer. .

That is, the present invention provides an electrophotographic photoreceptor having a photosensitive layer in which a charge generation layer and a charge transport layer are laminated on a conductive support, in which the work function of the charge generation layer is larger than that of the charge transport layer, and the charge The electrophotographic photoreceptor is characterized in that the work function difference between the generation layer and the charge transport layer is 0.2 eV or more.

In a photosensitive layer having such a laminated structure of a charge generation layer and a charge transport layer, the work function of the charge generation layer is required to be larger than that of the charge transport layer.

On the other hand, in order for a charge transport material to be stable against repeated characteristics such as charging and exposure, a larger work function is advantageous.

Therefore, in order to use the above-mentioned charge transport material, the work function difference between the charge generation layer and the charge transport layer must have a certain threshold value.
) will cause an increase in This is noticeable in high-speed copying machines that form images by rotating the photosensitive drum at a process speed of 2 seconds or less per rotation and performing at least the processes of charging, exposing, developing, and transferring. Therefore, by combining a binder with a charge-generating substance, the work function of the charge-generating layer can be controlled and matching with the charge-transporting layer can be achieved.

The electrophotographic photoreceptor of the present invention has a work function difference between the charge generation layer and the charge transport layer of 0.2 eV or more, preferably 0.3 eV.
The above characteristics make it possible to obtain good carrier injection from the charge generation layer to the charge transport layer.

Phthalocyanine pigments are used as charge generating substances.

Anthrone pigment, dibenzpyrene pigment, pyranthrone pigment, azo pigment, indigo pigment, quinacridone pigment pyrylium, thiapyrylium dye, xanthine dye, quinoneimine dye, triphenylmethane dye,
Examples include styryl dyes.

The charge generating substance is not limited to those described herein, and when used, one type or a mixture of two or more types of charge generating substances can be used.

The charge-generating layer can be formed by coating the above-mentioned charge-generating substance on a substrate together with a suitable binder (or without a binder), or can be obtained by forming a vapor-deposited film using a vacuum vapor tube apparatus. can.

The binder that can be used when forming the charge generating layer by coating can be selected from a wide variety of insulating resins, and can also be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylpyrene. Preferably, polyvinyl butyral, polyarylate (condensation polymer of bisphenol A and phthalic acid, etc.), polycarbonate, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide resin.

polyamide, polyvinylpyridine, cellulose resin,
Urethane resin, epoxy resin, casein.

Examples include insulating resins such as polyvinyl alcohol and polyvinylpyrrolidone.

Solvents that dissolve these resins vary depending on the type of resin, and specific organic solvents include alcohols such as methanol and ethanol isopropanol, ketones such as acetone, methyl ethyl ketone, and clohexanone, N,
Amides such as 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, and methylene chloride. , aliphatic halogenated hydrocarbons such as dichloroethylene, carbon tetrachloride, and trichlorethylene, or aromatics such as benzene, toluene, xylene, ligroin, monochlorobenzene, and dichlorobenzene.

Coating methods include dip coating, spray coating, spinner coating, bead coating,
Meyer bar coating method.

This can be carried out using a coating method such as a blade coating method, a roller coating method, or a curtain coating method. For drying, it is preferable to dry to the touch at room temperature and then heat dry. Heat drying at 30°C to 200°C
It can be carried out stationary or under ventilation for a time ranging from 5 minutes to 2 hours.

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

At this time, this charge transport layer may be laminated on or under the charge generation layer.

The substance that transports charge carriers in the charge transport layer (hereinafter simply referred to as charge transport layer material) is preferably substantially insensitive to the wavelength range of electromagnetic waves to which the charge generation layer is sensitive. The "electromagnetic waves" mentioned here include gamma rays, X-rays,
Includes a broad definition of "ray" that includes far-infrared rays. 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.

In order to have sufficient absorbance and shorten the range of generated charge carriers, the charge generation layer has a thickness of 5 μm or less, particularly 0.5 μm or less.
A thin film layer having a thickness of 0.01-1 μm is preferred. This means that most of the incident light is absorbed by the charge generation layer, generating many charge carriers, and that the generated charge carriers are not deactivated by recombination or trapping (injected into the charge transport layer). This is due to the need to do so.

The charge transport layer is electrically connected to the charge generation layer described above, and has the function of receiving and taking charge carriers injected from the charge generation layer in the presence of an electric field and transporting these charge carriers to the surface. ing. At this time, the charge transport layer is preferably laminated on the charge generation layer.

Charge transporting substances include electron transporting substances and hole transporting substances, and electron transporting substances include chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4.7-)dinitro-9- Fluorenone, 2,4,5.7-tetranitro-9-fluorenone,
2,4,7-dolinitro 9-dicyanomethylenefluorenone, 2,4,5,7-titranitroxanthone, 2
, 4.8-) There are electron-withdrawing substances such as linitrothioxanthone, and polymerization of these electron-withdrawing substances.

Examples of hole transporting substances include pyrene, N-ethylcarbazole, N-isopropylcarbazole, N-methyl-N
- Carbazoles such as phenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole,
N,N diphenylhydrazino-3-methylidene-10-
Hydrazones such as ethylphenothiazine, p-diethylaminobenzaldehyde-N, N-diphenylhydrazone, p-diethylaminobenzaldehyde-N-α-naphthyl-phenylhydrazone, p-diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrazone, 2.5-bis(p-diethylaminophenyl)-1
゜3.4-oxadiazole, 1-(pyridyl (2))
-3-(p-diethylaminostyryl)-5-(p-
diethylaminophenyl)pyrazoline, l-[pyridyl(3))-3-(p-diethylaminostyryl)-5-
(p-diethylaminophenyl)pyrazoline, 1-[lepidyl (2))-3-(p-diethylaminostyryl)
-5-(p-2 diethylaminophenyl)pyrazoline,
■-Phenyl-3-(p-diethylaminostyryl)-
Pyrazolines such as 4-methyl-5(p-diethylaminophenyl)pyrazoline and spiropyrazoline, 2-(p-diethylaminophenyl)pyrazoline,
-diethylaminostyryl)-6-ethylaminobenzoxazole, 2-(p-diethylaminophenyl)
Oxazole compounds such as -4-(p-dimethylaminophenyl)-5-(2-chlorophenyl)oxazole, thiazole compounds 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-detrakis (4-N, N
-Polyarylalkanes such as dimethylamino-2-methylphenyl)ethane, triphenylamine, poly-N
-Vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinylacridine, poly-9-vinylphenylanthracene, pyrene-formaldehyde resin, ethylcarbazole formaldehyde resin, and the like.

When the charge transport material does not have film-forming properties, a film can be formed by selecting an appropriate binder. Examples of resins that can be used as binders include acrylic resin, polyarylate, and polyester.

Polycarbonate, polystyrene, acrylonitrile
Styrene copolymer, acrylonitrile-butadiene copolymer, polyvinyl butyral.

Examples include insulating resins such as polyvinyl formal, polyacrylamide, polyamide, and chlorinated rubber, and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, and polyvinylpyrene.

The charge transport layer cannot be made thicker than necessary because there is a limit to its ability to transport charge carriers. Generally 5 to 30 μm, but the preferred range is 8 to 20 μm
It is. When forming the charge transport layer by coating, an appropriate coating method as described above can be used.

The photosensitive layer is provided on a support having electrical conductivity, that is, a conductive support. As the conductive support, the support itself is conductive, such as aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, and titanium.

Nickel, indium, gold, platinum, etc. can be used, and plastics (for example, carbon Titanium oxide (black, silver particles, etc.) is coated on plastic with a suitable binder.

A support provided with a resin layer in which conductive particles such as tin oxide are dispersed in a suitable binder, a plastic having a conductive polymer, etc. can be used.

A subbing layer having barrier and adhesive functions can be provided between the conductive support and the photosensitive layer. The subbing layer is casein, polyvinyl alcohol, nitrocellulose, and ethylene-acrylic acid copolymer.

Polyvinyl butyral, phenolic resin, polyamide (
It can be formed from nylon 6, nylon 66, nylon 610° copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, aluminum oxide, etc.

The thickness of the undercoat layer is 0.1 to 40 μm, preferably 0.1 to 40 μm.
3 μm is appropriate.

Next, the present invention will be explained in more detail with reference to Examples. In addition, all "parts" in the examples represent parts by weight.

Example 1 10 parts of an azo pigment (No, l) having the following structural formula, 6 parts of benzal resin (poly(vinyl acetate-corvinyl alcohol-corvinyl benzal)) having the following structure
Part and 1! :200 m:92 n:8 60 parts of cyclohexanone was dispersed for 20 hours using a sand mill device using 1φ glass beads. Add 100 parts of methyl ethyl ketone to this dispersion and add AI! Coat it on a sheet, heat dry at 1006C for 10 minutes, and get 0.1g/
% of the charge generation layer was formed.

Next, 10 parts of a hydrazone compound having the following structural formula and 10 parts of polycarbonate were dissolved in 100 parts of dichloromethane. This solution is applied onto the charge generation layer, and l 0
00C was dried with hot air for 1 hour to form a charge transport layer with a thickness of 20 μm.

Regarding this photoreceptor, the work function of each layer was measured using a low energy electron spectrometer (AC-1 manufactured by Kyuriken Keiki).

Next, this photoreceptor was tested using an electrostatic copying paper tester ((m
Using Nichiden, Wa Seisakusho: EPA-8100),
Negative corona charging is performed so that the dark area potential becomes 1700 V, and halogen light is irradiated so that the bright area potential becomes 1200 V. Charging and exposure are repeated 50,000 times at a cycle of 2 seconds/rotation, and the bright area is charged. The increase in potential (ΔVt) was measured.

At the same time, the exposure amount E% (I!ux-8eC) required for the surface potential after exposure to decrease to 1/2 of the initial surface potential was measured. The results are shown in Table-1.

This photoreceptor is also used as a corona charger and exposure optical system.

When the film was pasted on the cylinder of an electrophotographic copying machine equipped with a developing device, a transfer device, a static elimination exposure optical system, and a blade cleaning, an image with good contrast similar to the initial image was obtained even after 10,000 copies. Ta.

Example 2 10 parts of azo pigment No.1, 6 parts of butyral resin (trade name: BX-1, manufactured by Sekisui Chemical Co., Ltd.) and 60 parts of cyclohexanone were dispersed for 20 hours using a sand mill device using lφ glass beads. . Add 100 parts of methyl ethyl ketone to this dispersion and add AI! Apply on the sheet, 1
It was heated and dried at 00° C. for 10 minutes to form a charge generation layer with a coating weight of 0.1 g/rd.

Next, 10 parts of a benzidine compound having the following structural formula and 10 parts of polycarbohydrate were dissolved in 100 parts of dichloromethane. This solution was coated on the charge generation layer and 100'
A charge transport layer having a thickness of 20 μm was formed by drying with hot air for 1 hour.

Regarding this photoreceptor, the work function, ΔvL, and Ey2 of each layer were measured in the same manner as in Example 1. The results are shown in Table-1.

Comparative Example 1 An electrophotographic photoreceptor of the present invention was prepared in the same manner as in Example 1 except that a stilbene compound having the following structural formula was used as a charge transport material for the charge transport layer, and ΔVL and 8%
was measured.

The results are shown in Table-1.

Comparative Example 2 Acrylic resin (P
MMA: Dianal BR-85. Made by Mitsubishi Rayon)
An electrophotographic photoreceptor of the present invention was prepared in the same manner as in Example 2 except that ΔVL and 8% were measured.

The results are shown in Table-1.

Example 3 10 parts of an azo pigment (No. 2) having the following structural formula, 6 parts of an acrylic resin (PMMA: Dianal BR-85, manufactured by Mitsubishi Rayon), and 60 parts of cyclohexanone were used in lφ glass beads. Dispersion was carried out using a sand mill apparatus for 20 hours.

Add 100 parts of methyl ethyl ketone to this dispersion to
It was coated onto a sheet and dried by heating at 100°C for 10 minutes to form a charge generation layer with a coating weight of 0, 1 g, /i.

Next, 10 parts of a benzidine compound having the following structural formula and 10 parts of polycarbohydrate were dissolved in 100 parts of dichloromethane.

This solution was applied onto the charge generation layer and dried with hot air for 1 hour to form a charge transport layer with a thickness of 20 μm.

Regarding this photoreceptor, the work function, ΔVL, and EA of each layer were measured in the same manner as in Example 1. The results are shown in Table-1.

Example 4 Butyral resin (
The electrophotographic photoreceptor of the present invention was prepared in the same manner as in Example 1, except that Esrec B: BX-1 (manufactured by Miki Kagaku) was used and a hydrazone compound having the following structural formula was used as the charge transport material for the charge transport layer. Create △VL and EIA
was measured.

The results are shown in Table-1.

Comparative Example 3 An electrophotographic photoreceptor of the present invention was prepared in the same manner as in Example 3, except that a hydrazone compound having the following structural formula was used as the charge transport material for the charge transport layer, and ΔVL and 8% was measured.

The results are shown in Table-1.

Comparative Example 4 Polycarbon resin (
Bisphenol Z type car recarbonate, Mv, = 250
00. An electrophotographic photoreceptor of the present invention was prepared in the same manner as in Example 4, except that ΔVL and 8%
was measured. The results are shown in Table-1.

Example 5 10 parts of azo pigment (No, L), 6 parts of polycarpo resin (Bisphenol Z type car recarbonate MV25000, manufactured by Ondai Kagaku) and 60 parts of cyclohexanone were dispersed for 20 hours in a sand mill device using φ glass beads. did. 100 parts of methyl ethyl ketone was added to this dispersion, and Aj7
It was coated on a sheet and dried by heating at lOO'C for 10 minutes to form a charge generating layer with a coating weight of 0.1 g/rd.

Next, 10 parts of a hydrazone compound having the following structural formula and 10 parts of polycarbohydrate were dissolved in 100 parts of dichloromethane. This solution was applied onto the charge generation layer, and 100'C1
A charge transport layer having a thickness of 20 μm was formed by drying with hot air for a period of time.

Regarding this photoreceptor, the work function of each layer was measured using a low energy electron spectrometer (AC-t manufactured by Kyuriken Keiki).

Next, this photoreceptor was subjected to negative corona charging using an electrostatic copying paper tester ((Kikiyokuchi Denki Seisakusho: EPA-8100) so that the dark area potential became 1700V, and the bright area potential was Irradiate halogen light to -200V,
Charging and exposure were repeated 50,000 times each in cycles of 8 seconds/rotation, 4 seconds/rotation, 2 seconds/rotation, and 1 second/rotation.
The increase in light area potential (ΔvL) was measured. In addition, the exposure i! required for the surface potential after exposure to decrease to % of the initial surface potential. kE′A<lux·5ec) was measured.

The results are shown in Table-2.

Comparative Example 5 An electrophotographic photoreceptor of the present invention was prepared in the same manner as in Example 5, and ΔvL and E 'A was measured. The results are shown in Table-2.

Table-1 Table-2 [Effects of the Invention] The electrophotographic photoreceptor of the present invention has a bright area potential (VL
), the initial sensitivity is also excellent, and durability is particularly improved for high-speed copying machines.

Claims (1)

[Claims] In an electrophotographic photoreceptor having a photosensitive layer in which a charge generation layer and a charge transport layer are laminated on a conductive support, the work function of the charge generation layer is larger than that of the charge transport layer, and the charge generation layer and the charge transport An electrophotographic photoreceptor characterized in that the work function difference between the layers is 0.2 eV or more.