JP2814809B2 - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor having good photoresponsiveness and excellent repetition stability.

[0002]

2. Description of the Related Art In recent years, with the development of non-impact printer technology, research and development of electrophotographic printers using a laser light source have been actively conducted. In these devices, the miniaturization and speeding up of the device size are being promoted, and high sensitivity and high speed are also demanded for photosensitive materials. However, electrophotography using a conventional charge transfer material for the charge transfer layer is desired. The photoreceptor has not yet obtained sufficient characteristics such as a large residual potential and dark decay, and poor repetition characteristics.
Among them, improvement in characteristics has been demanded for high-speed operation by developing a new material for the charge transfer layer having high mobility and increasing the concentration of the charge transfer material in the charge transfer layer.
However, it is difficult to develop a new material, and increasing the concentration of the charge transfer material in the charge transfer layer is homogeneous in the three-dimensional direction when considered in a system uniformly dispersed in the binder resin. (Photoresponsiveness) is proportional to the cube of the average intermolecular distance (Leading Concept for Developing Better Chrage Tra
nsportable Organic Materials; R. Takahashi etal.,
Electrophotography Vol.25, No.3, 10 (1986)). Therefore, even if the concentration of the charge transfer material in the binder resin is increased, the mobility is only slightly improved, while there is a practical problem such as deterioration of the film strength. In view of the above problems, the present invention provides an electrophotographic photoreceptor that improves mobility without increasing the concentration of a charge transfer material in a charge transfer layer, suppresses a rise in residual potential, and has excellent repetition stability. The purpose is to:

[0003]

According to the present invention, there is provided an electrophotographic photosensitive member having at least an undercoat layer, a charge generating layer and a charge transfer layer on a conductive support, wherein the binder resin of the charge transfer layer is different. An electrophotographic photosensitive member comprising a polycarbonate resin having two or more kinds of molecular weights. Here, it is preferable that the polycarbonate resin has a bisphenol Z type structure. Also, the solvent of the coating liquid used to prepare the charge transfer layer is
It is preferable to be composed of a chlorinated solvent. Further, the charge transfer material constituting the charge transfer layer preferably contains at least one stilbene compound represented by the following general formula.

Embedded image (In the formula, R ^{1 to} R ⁴ represent an alkyl group and may be the same or different from each other.)

Generally, a binder resin for forming a photosensitive layer is
It is only necessary to assist the charge transfer material having no adhesive property and to have a property of sufficiently transmitting light at the time of exposure. In terms of electrical characteristics, the function of the charge transfer material is, of course, not hindered, but the resin itself is nonfunctional. Further, the solvent used for forming the photosensitive layer only needs to be such that the binder resin is easily dissolved and the stability as a solution is sufficient. In the process of conducting research in view of the conventional situation, the inventor has found that the properties of binders and solvents that have been considered to be electrically nonfunctional can be improved by manipulating the composition. I found it. That is, it was found that the mobility was improved only by increasing the molecular weight of the binder resin without changing the concentration of the charge transfer material (see FIG. 1).
From FIG. 1, it is found that the larger the molecular weight of the polycarbonate resin is about 1.46 times (the electric field strength is 4 × 1) as compared with the smaller one.
0 ⁵ V / cm) it can be seen that the higher mobility. However, when a substance having a large molecular weight is used, the residual potential becomes high in repeated use, which is not suitable for practical use. Therefore, by combining polycarbonate resins having two or more kinds of molecular weights, it is possible to produce a photoreceptor that can withstand repeated use while improving the mobility.

[0005] Further, it has been found that a solvent that is considered to be nonfunctional in terms of characteristics also contributes to the improvement of mobility by using a chlorine-based solvent (see FIG. 1). It can be seen that the mobility is higher by about 1.29 times (electric field intensity: 4 × 10 ⁵ V / cm) when a chlorine-based solvent is used than when it is not. Although the reason is not clear, it is because high-molecular-weight polycarbonate resin or chlorine-based solvent has some effect on the form of the charge transfer material in the charge transfer layer and works advantageously in hopping conduction. Seem. In addition, the use of high-molecular-weight resin significantly increases the viscosity of the coating solution compared to the use of low-molecular-weight resin. It becomes easy to aim at.

Hereinafter, the present invention will be described in detail. The charge transfer layer according to the present invention is selected from charge transfer materials such as hydrazone compounds, stilbene compounds, pyrazoline compounds, triphenylamine compounds, benzidine compounds, and oxazole compounds. In particular, stilbene-based compound materials are used. At times, the effect is remarkable due to its high crystallinity and high light responsiveness. Further, two or more kinds of other charge transfer materials may be mixed and used.

As the resin which can be used for forming the charge transfer layer by coating, it is desirable to use a polycarbonate resin, which has two or more distributions having different molecular weights. As the polycarbonate resin, for example, the following formula:

Embedded image 4,4'-dihydroxydiphenyl-1,1 represented by
-Cyclohexane (bisphenol Z type), and the following formula:

Embedded image 4,4'-dihydroxydiphenyl-2,2 represented by
-Propane (bisphenol A type).
Of these, bisphenol A type has poor solubility,
There is a drawback that it tends to gel when coated. Gelling is not as suitable for the present invention as it is high molecular weight.
Therefore, the Z type is preferable. The molecular weight of the Z-type polycarbonate resin ranges from 10,000 to 9.
Up to 0000, appropriate ones can be used in combination of those having a low molecular weight and those having a high molecular weight.

[0008] The content of the resin contained in the charge transfer layer is suitably 80% by weight or less. As a solvent for dissolving these resins, a chlorine-based solvent is desirable, and specifically, aliphatic halogenated hydrocarbons such as carbon tetrachloride, chloroform, dichloromethane, dichloroethane, and trichloroethylene are used. As a coating method for forming a coating film, there are a spin coater, an applicator, a spray coater, a bar coater, an immersion coater, a doctor blade, and a roller. The drying is performed at 30 to 160 ° C., preferably 60 to 1 ° C. using an apparatus such as a coater, a curtain coater, or a bead coater.
It can be performed at a temperature in the range of 20 ° C. for a time in the range of 30 to 90 minutes. The film thickness after drying is 5 to 40 μm, preferably about 10 to 20 μm. Various additives commonly used, such as an ultraviolet absorber and an electron absorbing material, can be added to the charge transfer layer as needed.

The charge generation layer is made of a known photoconductive material, for example, an inorganic material such as CdS, Se, ZnO, or an azo pigment, an indigo pigment, a pyrylium pigment, a thiapyrylium pigment, a phthalocyanine pigment, or a perylene pigment. It is selected from organic charge generation materials such as pigments, perinone pigments, polycyclic quinone pigments, squarium compounds, and cyanine dyes.

The resin which can be used when forming the charge generating layer by coating can be selected from a wide range of insulating resins, and can be selected from organic photoconductive polymers such as polyvinyl anthracene and polyvinyl pyrene. Also preferably, polyvinyl butyral, polyarylate, polycarbonate
Bonnet, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide resin, polyvinyl pyridine, cellulose resin, urethane resin, epoxy resin, silicone resin, polystyrene, polyketone,
Insulating resins such as polyvinyl chloride, polyvinyl acetal, phenol resin, melamine resin, casein, polyvinyl pyrrolidone and the like can be mentioned. The amount of the resin contained in the charge generation layer is 90% by weight or less, preferably 50% by weight or less. These resins may be used alone or in combination.
More than one kind may be combined.

The solvent for dissolving these resins differs depending on the type of the resin. Specifically, methanol, ethanol
Alcohols such as benzene, aromatic hydrocarbons such as benzene, xylene and dichlorobenzene, ketones such as acetone and methyl ethyl ketone, esters such as acetate and methyl cellosolve, chloroform, dichloromethane, dichloroethane, carbon tetrachloride, etc. Aliphatic halogenated hydrocarbons,
Ethers such as tetrahydrofuran and dioxane, N,
Amides such as N-dimethylformamide and N, N-dimethylacetamide and sulfoxides such as dimethylsulfoxide are used. As a coating method for forming a coating film, the same apparatus as used in forming the charge transfer layer described above is used, and drying is performed at 40 to 180 ° C., preferably 60 to 120 ° C.
It can be carried out at a temperature in the range of ° C. for a time in the range of 30 to 70 minutes. The film thickness after drying is 0.01 to 5 μm, preferably about 0.1 to 1 μm. Further, a plasticizer and the like can be used together with the resin as required.

The resin used for the undercoat layer is nylon 6, nylon 66, nylon 11, nylon 61.
0, alcohol-soluble polyamide resin such as copolymerized nylon, alkoxymethylated nylon, casein, polyvinyl alcohol resin, nitrocellulose resin, ethylene-
Acrylic acid copolymer, gelatin, polyurethane resin, polyvinyl butyral resin and the like are used. It is also effective to include conductive particles, a plasticizer, and the like in the resin.
The coating of the undercoat layer can be performed by the same method as that for the above-described charge transfer layer or charge generation layer.
5 to 10 μm, preferably about 0.1 to 1 μm is appropriate. Further, the electrophotographic photoreceptor of the present invention may have a structure in which an undercoat layer, a charge generation layer, and a charge transfer layer are laminated on a conductive substrate in this order, or a structure in which an undercoat layer, a charge transfer layer, and a charge generation layer are laminated in this order. Examples include: Further, these undercoat layers can be omitted as necessary.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but are not limited to the following embodiments without departing from the gist thereof. Parts in the examples mean parts by weight. Example 1 Nylon (T-8: manufactured by Unitika Ltd.) was coated on an aluminum substrate to obtain an undercoat layer having a dry film thickness of 0.5 μm. Next, using 5 parts of titanyl phthalocyanine having an X-ray diffraction image shown in FIG. A 0.3 μm thick charge generation layer was obtained.
Further, 8 parts of 1,1-bis- (p-diethylaminophenyl) -4,4-diphenyl-1,3-butadiene and a polycarbonate resin having an average molecular weight of 20,000 (Z
-200: manufactured by Mitsubishi Gas Chemical Company) 7 parts and average molecular weight 800
A solution prepared by dissolving 3 parts of a polycarbonate resin (Z-800: manufactured by Mitsubishi Gas Chemical Co., Ltd.) in 160 parts of dichloromethane was applied on the charge generation layer so that the dry film thickness became 15 μm. A moving bed was obtained. Thus, an electrophotographic photosensitive member having a laminated photosensitive layer was produced. The change of the drift mobility when the half-life exposure amount (E1 / 2) of the photoreceptor and the electric field intensity are changed is measured by an electrostatic copying paper test apparatus (EPA-
8100: manufactured by Kawaguchi Electric Works). Also,
The amount of change in the residual potential when the measurement was repeated 1000 times was obtained.

Example 2 An undercoat layer and a charge generation layer were formed on an aluminum substrate in the same manner as in Example 1, and o-methyl-p-dibenzylaminobenzaldehyde-diphenylhydrazone 4 was formed thereon as a charge transfer layer. 0.8 part, 3.2 parts of 1,1-bis- (p-diethylaminophenyl) -4,4-diphenyl-1,3-butadiene, and a polycarbonate resin having an average molecular weight of 30,000 (Z-200: Mitsubishi) 8 parts of a polycarbonate resin (Z-80) having an average molecular weight of 80000
(0: manufactured by Mitsubishi Gas Chemical Co., Ltd.), 2 parts of which was dissolved in 180 parts of dichloromethane, was applied onto the charge generation layer so that the dry film thickness became 15 μm, to obtain a charge transfer layer. Thus, an electrophotographic photosensitive member was manufactured.

Comparative Example 1 The procedure of Example 1 was repeated except that only 10 parts of a polycarbonate resin having an average molecular weight of 20,000 (Z-200: manufactured by Mitsubishi Gas Chemical Company) was used when forming the charge transfer layer. Example 1
An electrophotographic photoreceptor was produced in the same manner as described above. Comparative Example 2 Example 1 was repeated except that only 10 parts of a polycarbonate resin having an average molecular weight of 80,000 (Z-800: manufactured by Mitsubishi Gas Chemical Company) was used in forming the charge transfer layer.
An electrophotographic photoreceptor was produced in the same manner as described above. Comparative Example 3 An electrophotographic photosensitive member was produced in the same manner as in Comparative Example 1, except that the solvent was changed to tetrahydrofuran when forming the charge transfer layer. Embodiments 1 and 2 shown above
The results of evaluating various characteristics of the electrophotographic photosensitive members manufactured in Comparative Examples 1 to 3 are shown below.

[0016]

[Table 1] Static electricity characteristics ─────────────────────────────────── VO E1 / 2 Vr DDR RUNNING (- V) (Lux.sec) (-V) (%) (V) ───────────────────────────────── ── Example 1 710 0.5025 10 89.10 -32 Example 2 726 0.5120 12 94.75 -35 Comparative Example 1 712 0.5250 5 86.92 -28 Comparative Example 2 715 0.4920 10 84.46 -123 Comparative Example 3 736 0.6250 9 85.19 -32 ─── ──────────────────────────────── VO: Surface potential E1 / 2: Half exposure amount Vr: Residual potential DDR: Dark Attenuation rate RUNNING: Residual potential change after repeated measurement 1000 times (2nd-1000th)

FIG. 1 shows the relationship between the electric field strength (F) and the mobility (μ) of the charge transfer layer produced in each of the examples and comparative examples. From FIG. 1, it can be seen that the larger the molecular weight of the polycarbonate resin is, the higher the mobility is about 1.46 times (electric field intensity 4 × 10 ⁵ V / cm) as compared with the smaller one. In addition, it can be seen that the mobility is higher by about 1.29 times (electric field intensity: 4 × 10 ⁵ V / cm) when a chlorine-based solvent is used than when it is not.

[0018]

As described above, the mobility of the charge transfer layer material used in the electrophotographic photosensitive member of the present invention can be improved without increasing the concentration of the charge transfer material. As a result, an electrophotographic photoreceptor having good photoresponsiveness and excellent repetition stability is provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the mobility when the molecular weight of a polycarbonate resin having a Z-type structure used in the present invention is changed, and depending on the solvent type.

FIG. 2 is an X-ray diffraction diagram of titanyl phthalocyanine used in Example 1.

Claims (4)

(57) [Claims] 1. An electrophotographic photosensitive member having at least an undercoat layer, a charge generation layer and a charge transfer layer on a conductive support, wherein the binder resin of the charge transfer layer has an average molecular weight of 2
0000-30000 polycarbonate resin and average
Consists of a polycarbonate resin with a molecular weight of 80,000
An electrophotographic photoreceptor comprising a polycarbonate resin having two different molecular weights. 2. The electrophotographic photosensitive member according to claim 1, wherein the polycarbonate resin has a bisphenol Z type structure. 3. The electrophotographic photoreceptor according to claim 1, wherein the solvent of the coating solution used for producing the charge transfer layer is a chlorine-based solvent. 4. The electrophotographic photoreceptor according to claim 1, wherein the charge transfer layer comprises at least one stilbene compound represented by the following general formula. Embedded image (In the formula, R ^{1 to} R ⁴ represent an alkyl group and may be the same or different from each other.)