JPS59229563A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To prevent a reduction in the resolution in long-time continuous use and to obtain a stable copied image by using a charge transferring layer having a specified dielectric constant. CONSTITUTION:An electrically conductive layer, a charge generating layer contg. a charge generating org. pigment, and a charge transferring layer are laminated to manufacture a composite sensitive body. At this time, the dielectric constant of the charge transferring layer is regulated to <=3.8 at 25 deg.C and 1kHz. The charge transferring layer is formed by using a high molecular compound such as poly-N-vinylcarbazole as a charge transferring substance together with other additives. When a charge transferring substance having low mol.wt. is used, the substance is combined with a binder, and it is preferable that the dielectric constant of the substance and that of the binder are low. By regulating the dielectric constant of the whole charge transferring layer to <=3.8, the resolution of the resulting sensitive body is not reduced even in long-time continuous use, and a stable copied image can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic photoreceptor that exhibits little decrease in resolution even when used continuously.

Conventionally, inorganic conductive substances such as selenium, zinc oxide, titanium oxide, and cadmium sulfide have been mainly used in electrophotographic photoreceptors that utilize photoconductive substances as photosensitive materials.

However, many of these are highly toxic.

There are also problems with the method of disposal.

On the other hand, photoreceptors using organic photoconductive compounds.

Compared to the use of inorganic photoconductive materials, they are generally less toxic and have advantages in terms of transparency, flexibility, light weight, surface smoothness, and cost, and have recently been widely studied. Conventional composite photoreceptors separate the function of charge generation.

Rapid progress has been made in recent years because the sensitivity, which was a major drawback of photoreceptors using organic photoconductive compounds, can be greatly improved.

When these composite photoreceptors are applied to an electrophotographic device using the Carlson method, a latent electrostatic image is first formed on the surface of the photoreceptor, and then developed with a developer commonly called toner that is charged with the opposite sign. The image can be transferred and fixed onto another substrate, such as paper, to obtain a copy. However, it is charged like this.

When exposure is repeated and continuous copying is performed, there is a problem that the resolution of the copied image gradually decreases and the image becomes blurred.

As a result of intensive studies by the present inventors, we found that there is a correlation between the ease with which the resolution decreases and the dielectric constant of the charge transport layer.The lower the dielectric constant, the less the resolution decreases. It has been found that if the resolution is set to 8 or less (measured at 25° C., IKHzK), preferably 2.5 or less (measured at 25° C., IKHz), the decrease in resolution during continuous use will not become a practical waste.

That is, the present invention provides a Seiko photoreceptor having a conductive layer, a charge generation layer containing an organic pigment that generates charges, and a charge transport layer having charge retention and transport functions, in which the dielectric constant of the charge transport layer is 3.8. Below (measured at 25℃, IKHz)
This invention relates to an electrophotographic photoreceptor.

The materials used in the electrophotographic photoreceptor of the present invention will be described in detail below.

First, the charge-generating organic pigments contained in the charge generation layer include azobenzene-based, disazo-based, trisazo-based, benzimidazole-based, polycyclic quinone-based, indigoid-based, quinacridone-based, phthalocyanine-based, perylene-based, and methine-based pigments. Pigments known to generate electric charges, such as those based on pigments, can be used.

These pigments are disclosed in, for example, JP-A-47-37544, JP-A-47-18543, and JP-A-47-18.
544, JP 48-43942, JP 48-70538, JP 49-1231, JP 49-105536 2% JP 50-75
This method is disclosed in Japanese Patent Application Laid-Open No. 50-92738, etc. In addition to these, any organic pigment that generates a stain carrier upon irradiation with light can be used.

The charge transporting substances which are the main components of the charge transporting layer include polymer compounds such as BoIJ-N-vinylcarbasol,
Halogenated holy N-vinylcarbazole, polyvinylpyrene, polyvinylindoquinoxaline, polyvinylbenzothiophene, polyvinylanthracene, polyvinylacridine.

Polyvinylpyrazoly/etc. are low molecular compounds.
Fluorenone, 2,4.7-dolinitro-9-fluorenone, 4H-indeno(1,2,6)thiophene-4-
on, 3.7-sinitrocyhensothio 717-5-,
j-oxide, 1-bromopyrene, 2-phenylpyrene, carbazole, 3-phenylcarbazole, 2-phenylindole, 2-phenylnaphthalene, oxadiazole, triazole, 1-phenyl-a-(4-diethylaminostyryl)-5 -(4-diethylaminophenyl)hylasoline, 2-phenyl-4-(4-diethylaminophenyl)-5-phenyloxazole.

Triphenylamine, imidazole, chrysene.

Examples include tetrafen, acridine, and derivatives thereof.

Further, additives such as a binder, a plasticizer, a fluidity imparting agent, and a pinhole suppressing agent, which are commonly used in electrophotographic photoreceptors, can be used in the charge generation layer and the charge transport layer. Silicone resin is used as a binder.

Examples include polyamide, polyurethane, polyester, epoxy resin, polyketone, polycarbonate, polystyrene, polymethyl methacrylate, and polyacrylamide. Furthermore, thermosetting resins and photocurable resins that are crosslinked by heat and/or light can also be used. In any case, there are no particular limitations as long as the resin is insulative and has a film-forming ability in a normal state, or a resin that can be cured by heat and/or light to form a film. Examples of the plasticizer include non-loginated paraffin, dimethylnaphthalene, dibutyl phthalate, and the like. Examples of the fluidity imparting agent include Modaflow (manufactured by Monsanto Chemical Company) and Acronal 4F (manufactured by Pasuf Company), and examples of the pinhole inhibitor include benzoin and dimethyl terephthalate. These may be selected and used as appropriate, and the amount thereof may be determined as appropriate.

In the charge generation layer, components other than the organic pigments include the binders, plasticizers, additives, and the like.

The binder is used in an amount of 300% by weight or less based on the organic pigment. If the weight ratio exceeds 300, the electrophotographic properties will deteriorate. It is preferred that the plasticizer is used in an amount of less than 5% by weight based on the organic pigment. Other additives may be used in an amount of 3% by weight or less.

The charge transport layer may contain additives such as binders, plasticizers, flowability agents, pinhole inhibitors, etc. used in the charge generation layer described above, but the entire charge transport layer in combination with these additives may be used. The dielectric constant must be 3.8 or less when measured at 25°C and IKHz. Note that when a low molecular weight compound is used as the charge transporting substance, it is preferable to use the binder in an amount of 30% by weight or more in the charge transporting layer. To this end, the combination of charge transporting substance and binder that has the greatest effect on the dielectric constant of the charge transport layer is important.

In both cases, materials with low dielectric constants are desirable. However, it is often difficult to use a material with a low dielectric constant as the charge transporting material due to its relationship with the charge generating material described above, such as carrier injection efficiency, and other characteristics. In that case, it is necessary to adjust the dielectric constant of the entire layer using the binder. The dielectric constant of the binder alone depends on the type of resin.

Although it varies depending on the structure and concentration of functional groups, polystyrene, polymethyl methacrylate, etc. are generally low, and polyesters and polyamides are high. Therefore, it is desirable to use a single binder with a low dielectric constant.9 However, if a binder with a high dielectric constant must be used due to mechanical strength or other property constraints, some of the binders may have a dielectric constant. By mixing a binder with a low index, the dielectric constant of the entire charge transport layer is lower than 3.8, preferably 2.
Must be 5 or less. In addition, charge transporting substances generally have a higher dielectric constant than binders, so it is desirable to reduce the ratio of charge transporting substances and increase the ratio of binders as much as possible, preferably by increasing the ratio of charge transporting substance/binder. 171～1/
4 (weight ratio) is effective for lowering the dielectric constant of the charge transport layer.

In any case, if the dielectric constant of the entire charge transport layer is 3.8 or less, it is possible to sufficiently prevent a decrease in image resolution during continuous use. The lower limit of the dielectric constant is not particularly limited, but can be up to 1.1.

In the present invention, the conductive layer is a conductive material such as paper or plastic film subjected to conductivity treatment, a plastic film laminated with metal foil such as aluminum, or a metal plate.

The electrophotographic photoreceptor of the present invention preferably has a charge generation layer formed on a conductive layer and a charge transport layer formed thereon in terms of electrophotographic properties, but it is preferable that the charge generation layer and charge transport layer are reversed. It's okay. The thickness of the charge generation layer is 0.01 to lO
ttm, preferably 0.2 to 5 μm. 0.
If the thickness is less than 0.1 μm, it becomes difficult to uniformly form the charge generation layer, and if it exceeds 10 μm, the electrophotographic properties deteriorate. Further, the thickness of the charge transport layer is 5 to 50 .mu.In, preferably 8 to 20 .mu.In.

If the diameter is less than 5 .mu.m, the initial value will be low, and if it exceeds 50 .mu.m, the sensitivity will be low.

To form a charge generation layer and a charge transport layer.

This is done by uniformly dissolving or dispersing the components of each layer in a ketone solvent such as acetone or methyl ethyl ketone, an ether solvent such as tetrahydrofuran, or an aromatic solvent such as toluene or xylene, and then coating and drying it on the conductive layer. I can do it.

The photoreceptor of the present invention may further have a thin adhesive layer or barrier layer immediately above the conductive layer, or may have a protective layer of silicone or the like on one surface.

The copying method using the Naruko photographic photoreceptor according to the present invention can be carried out in the same way as in the conventional method by charging and exposing the surface of the photoreceptor, developing it, and transferring and fixing the image onto plain paper.

The electrophotographic photoreceptor of the present invention exhibits little decrease in resolution even when used continuously for a long period of time, and provides stable copied images.

Comparative examples and examples are shown below.

Each material used in the examples below is listed below.

(1) Phthalocyanine organic pigment that generates charge: Fastogln Blue F
GF [Dainippon Ink & Chemicals ■Product name] (2) Charge transporting substance 02-(1)-Schif'ropylaminophenyl)-4-(
p-dimethylaminophenyl)-5-(0-chlorophenyl)-1,3-oxazole (hereinafter abbreviated as OXZ) o 1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline (hereinafter abbreviated as pz) (3) Binder O silicone face: Niba-255 [Shin-Etsu Kagaku Kosu ■Product name] O polyester: Pylon 200 [Toyobo ■Product name] O Polybutyl methacrylate: Elvasite 2045
[Du Pont's product name] O polycarbonate: Panlite -1285 [Teijin Chemicals' product name] O acrylic resin: HA-310E [Hitachi Chemical's product name] 0 Polystyrene; Picotex 120 [ESSO's product name] Comparison Examples 1 to 3 and Examples 1 to 6 F (3F 2.5 g-, silicone face 5.0 p
(Solid content 50 to 1?, % 1) and tetrahydrofuran 92.51 i' were kneaded for 8 hours using a ball mill (3-inch pot mill manufactured by Nippon Kagaku Tome). (α conductor) and dried at 90℃ for 15 minutes to a thickness of 1 μIn.
A charge generation layer of 1 was formed.

Next, a tetrahydrofuran solution containing predetermined amounts of the charge transporting substance and binder shown in Table 1 was applied onto the charge generating layer using an applicator, and dried at 90°C for 20 minutes to form a 15 μm thick solution. A charge transport layer was formed.

The electrophotographic properties of the obtained photoreceptor were measured using an electrostatic recording paper tester (
The initial potential Vo (V) in Table 1 indicates the charged potential when a negative 5 Kv corona is discharged for 10 seconds, and the dark decay Vk (*) indicates the potential when the negative 5 Kv corona is discharged for 10 seconds. 30. This shows the potential attenuation when left for seconds.Vk=X 100. V
so: O potential after 30 seconds), half-decreased exposure (Eso) is 1011x
The amount of light until the potential is halved by irradiation with white light of
The measurement was carried out by forming a charge transport layer having the composition shown in Table 1 on an aluminum plate in advance to a thickness of 50 μm, and using a multi-frequency LCR meter 4274A (manufactured by Yokogawa Hewlett-Packard Co., Ltd.) at 25 μm. The measurement was carried out under the conditions of ℃ and 10ζ.

The results are also shown in Table 1.

Table 1 shows that the dielectric constant ε' of the charge transporting layer varies depending on the type of charge transporting substance and binder, the ratio of the charge transporting substance and binder, and the like. The dielectric constants of Comparative Examples 1 to 3 are 3.8 or more, and the dielectric constants of Examples 1 to 3 are less than 3.8. Also, comparative example 1~
The electrophotographic properties of the photoreceptors shown in Example 3 and Examples 1 to 6 show values that are not necessarily related to the dielectric constant of the charge transport layer.

Next, the photoreceptors obtained in Comparative Examples 1 to 3 and Examples 1 to 6 were applied to an electrophotographic apparatus using the Carlson method.

Table 2 shows the initial resolution and resolution after continuous copying of 7.500 sheets using a test chart.
It was shown to.

Table 2: Dielectric constant and resolution of charge transport layer As a result, photoreceptors whose charge transport layer has a high dielectric constant shown in comparison columns 1 to 3 show a significant decrease in resolution after continuous copying, resulting in blurred images. On the other hand, the photoreceptors whose charge transport layer has a low dielectric constant obtained in Examples 1 to 6 show little decrease in resolution, and
Photoreceptors having a C dielectric constant of 25 or less (Examples 1 and 5) have almost no decrease in resolution and can stably obtain good images. 'Thus, the electrophotographic photoreceptor of the present invention is
The present invention provides a practically stable copy image with little reduction in resolution even when used continuously for a long time.

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Claims (1)

[Claims] 1. In an electrophotographic photoreceptor having a conductive layer, a charge generation layer containing an organic pigment that generates a charge, and a charge transport layer having charge retention and transport functions, the dielectric constant of the charge transport layer is 3.
．． 8 or less (measured at 25°C and IKHz).