JPH08123045A - Production of dispersion liquid for electrophotographic photoreceptor and electrophotographic photoreceptor using same - Google Patents

Abstract

PURPOSE: To obtain a dispersion liq. free from dust of media due to wear and chips of media due to crushing and to obtain an electrophotographic photoreceptor having considerably improved electrophotographic characteristics and image characteristic using the dispersion liq. CONSTITUTION: When at least an org. pigment is dispersed to produce a dispersion liq. for an electrophotographic photoreceptor, the org. pigment is subjected to dispersion treatment in a solvent in the presence of crystalline glass media and the objective dispersion liq. is produced. A photosensitive layer is formed on an electrically conductive substrate by coating with this dispersion liq. to obtain the objective electrophotographic photoreceptor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrophotographic photosensitive member.

[0002]

2. Description of the Related Art Electrophotographic photoreceptors have a basic structure in which a photosensitive layer is formed on a conductive substrate. Conventionally, selenium is generally used as the photosensitive layer, and other inorganic photoconductive substances are used. Known as such are cadmium sulfide and zinc oxide. However, in recent years, electrophotographic photoreceptors using organic photoconductive substances have good film-forming properties and can be produced by coating, have extremely high productivity and are inexpensive, and increase the amount of organic pigments used. It has an advantage that color sensitivity can be freely controlled by selecting a sensitizer, and has been extensively studied. In particular, with the development of a function-separated type photoreceptor in which an organic photoconductive pigment is used as a charge generation layer and a charge transport layer made of a conductive polymer or a low molecular weight organic photoconductive substance is laminated, the range of material selection is greatly expanded. The sensitivity and durability, which are considered to be the drawbacks of the organic electrophotographic photoreceptor of, were remarkably improved.

Since such a function-separated type photoreceptor is composed of at least two layers of a charge generation layer and a charge transport layer,
Carriers generated by light in the charge generation layer are injected into the charge transport layer, and an electrostatic latent image is obtained by neutralizing the surface charge of the photoconductor.The role of the charge generation layer in this process is extremely important. is there. That is, the efficiency of carrier generation, the uniformity of generation, and the electrical characteristics such as how efficiently the generated carriers are injected into the charge transport layer, and electrophotographic characteristics such as image characteristics depend on the charge generation layer. However, it is big.

In the electrophotographic photosensitive member, the charge generation layer is
It is usually formed by dispersing the charge generating material in a polymer binder. As the charge generating substance, perylene-based, polycyclic quinone-based, phthalocyanine-based, bisazo-based, trisazo-based, squarylium dye, azurenium dye,
A thiapyrylium dye, ZnO or the like is used. Since these substances are generally hard and are unlikely to be fine particles, a medium is usually used for dispersion.

[0005]

Generally, inexpensive glass beads or ceramic beads such as zirconia having high abrasion resistance are used as media. However, when the glass beads are used, the foreign matter is mixed into the charge generation layer due to abrasion or crushing of the glass beads. It is known that such contamination of foreign matter adversely affects the electrophotographic characteristics of the photoconductor (for example, increase in residual potential, increase in dark decay, decrease in sensitivity, etc.). Also on the image, defects such as solid white areas due to the adhesion of these foreign matters or black spots on the background will occur.

On the other hand, when the ceramic beads having high abrasion resistance are used, a large impact force due to their large specific gravity and an excessive force to the organic pigment due to the extremely high hardness result in an electrophotographic characteristic of the photoconductor. Deterioration (overdispersion) and severe wear of the disperser container and stirring spring, resulting in
It is known to have the same adverse effect as when glass beads are used. Moreover, it is expensive.

[0007] In addition, in the organic pigments that are prone to crystal transition, the crystal form changes due to slight fluctuations in the dispersion conditions,
The temporal stability of the dispersion liquid differs, and the electrophotographic characteristics also vary depending on the dispersion batch. Further, when the dispersion treatment time is increased, coarse particles are reduced, but the particles that have been finely dispersed are excessively dispersed, so that the cohesiveness is increased, and the agglomerated particle size changes during or after the dispersion. Easy to do and significantly deteriorate the dispersion stability. Furthermore, requiring such a long dispersion treatment time is not preferable from the viewpoint of productivity.

That is, in the dispersion of the charge generation layer, in addition to the means for preventing the mixture of foreign matter, stable dispersion with a uniform particle size distribution, dispersion having a large tolerance with respect to the dispersion time and the like have been developed from the viewpoint of electrophotographic characteristics. We are also waiting for improvements in image quality.

[0009]

Therefore, as a result of intensive studies on the dispersion method and the medium, the present inventors have found that the use of crystalline glass as the medium solves the above-mentioned problems without changing the existing equipment. It was found to be effective and the present invention was reached.

That is, the gist of the present invention is to provide a method for producing a dispersion for an electrophotographic photosensitive member in which at least an organic pigment is dispersed, wherein the organic pigment is dispersed in a solvent in the presence of a crystalline glass medium. A method for producing a dispersion liquid for an electrophotographic photosensitive member, and a photosensitive material obtained by applying a dispersion liquid obtained by dispersing an organic pigment in a solvent in the presence of a crystalline glass medium on a conductive support. An electrophotographic photoreceptor characterized by having a layer.

The present invention will be described in detail below.

The organic pigment dispersed in the present invention is not particularly limited as long as it can be used as an organic photoconductive substance. For example, perylene pigments, azo pigments, phthalocyanine pigments, anthanthrone pigments, quinacridone pigments, cyanine pigments, pyrylium pigments, thiapyrylium pigments, indigo pigments, squaric acid pigments, polycyclic quinone pigments, etc. Is mentioned.

These pigments may be mixed with a suitable organic solvent such as an alcohol solvent such as methanol, ethanol or propanol, a ketone solvent such as acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone or cyclohexanone, benzene, toluene or xylene.
An aromatic solvent such as chlorobenzene, an ether solvent such as dioxane and tetrahydrofuran, and various solvents such as dimethylformamide and acetaldehyde are used as a dispersion medium to prepare a liquid to be dispersed. These solvents can be used alone or as a mixed solvent of two or more kinds. At this time, a binder resin may be added together as a binder, or the binder resin may be added after previously dispersing only the pigment and the dispersion medium. Examples of the binder resin include polyester resin, polyvinyl acetate, polyacrylic acid ester, polymethacrylic acid ester, polycarbonate, polyvinyl acetal, polyvinyl propional, polyvinyl butyral, phenoxy resin, epoxy resin, urethane resin, cellulose ester, and cellulose ether. Can be mentioned. The ratio of the organic pigment to the binder resin is not particularly limited, but the weight ratio of the organic pigment to the binder is preferably 100: 0 to 1000, and generally, an appropriate amount can be selected from this range. If the content ratio of the organic pigment is less than this range, the photosensitivity is low and the residual potential is increased, while if it is more than this range, the dark decay is increased and the charging potential is decreased. Further, the concentration of the organic pigment in this dispersion is preferably in the range of 0.1% by weight to 10% by weight, which is suitable for the coating method.

Further, the dispersion liquid of the present invention may contain a charge-transporting substance or other materials, if necessary.
When the charge transport substance is contained in the pigment dispersion, the weight ratio of the organic pigment and the organic transport substance is preferably 10: 0 to 1000, and particularly preferably 10: 0 to 100.

In the dispersion of the present invention, a known dispersing machine such as a ball mill, a sand grinder, an attritor or a kneader can be used.

The crystalline glass medium used in the present invention is obtained by precipitating fine crystalline particles in amorphous glass particles and has a coefficient of thermal expansion in the range of about 70 to 180 × 10 ^-7 / ° C. The Vickers hardness is about 750 to 1150 Kgf /
It is in the numerical range of mm ² , and the fine crystal grain size is about 0.02 to 20 μm, which is excellent in fineness. The detailed production method is described in JP-A-60-292646.

The composition of the crystalline glass is% by weight, SiO ₂ 30
~ 65%, Al ₂ O ₃ 5-25%, ZnO 10.5-40%, TiO ₂ and / or ZrO ₂ 2-15%, MgO 0-20%, one or more of CaO, SrO and BaO. Total amount 0-15%, B ₂ O ₃ 0
_{~5%, La 2 O 3,} Y 2 O 3, Gd 2 O 3, Ta 2 O 5, Mb 2 O 5 and WO ₃
1 or 2 or more of the total amount of 0-10%, P ₂ O ₅ 0-5
%, F 0 to 5%, SnO ₂ 0 to 2%, As ₂ O ₃ and / or Sb ₂ O ₃ 0 to 1%.

A preferable specific gravity is 3.0 to 3.4. When the specific gravity is lighter than this, the dispersion ability is decreased, the coarse particles remain and the particle size distribution is widened to increase the image defects, and when it is larger than 3.4, the width of the proper dispersion time is reduced. As the so-called latitude becomes narrower and some overdispersed particles are generated, the stability of the dispersion becomes a problem.

The abrasion loss rate of the beads is preferably 0.030% or less.

Here, the wear reduction rate was 400 g of beads and 200 g of methanol, and was 1500 rpm at 96 rpm with a sand grinder.
It is a value showing the amount of wear loss of beads after washing for a period of time as a percentage with respect to the initial weight.

The small wear reduction rate means that the bead fragments and the powder are not mixed in so much that the potential characteristics such as image defects and sensitivity are not deteriorated.

The amount of the crystalline glass medium is usually 0.3 to 5 times the volume of the non-dispersion liquid. The average particle size of crystalline glass media is 0.
It is possible to use those having a diameter of 4 to 1.0 mm, and in particular, spherical crystalline glass media having a sharp particle size distribution is effective for forming a dispersion liquid in which the dispersed particle size of the organic pigment is more uniform. The dispersion treatment time can be appropriately determined, but the average particle diameter of the organic pigment at the end of dispersion is preferably 1.0 μm or less, and more preferably 0.5 μm or less.

The photosensitive layer obtained by using the pigment dispersion prepared in this way is a photosensitive member in which a charge generating layer and a charge transport layer are laminated in this order on a conductive support to form a photosensitive layer,
Alternatively, it can be used for any photoreceptor such as a photoreceptor having a charge generation layer laminated on a charge transport layer, or a so-called dispersion type photoreceptor having a charge generation material dispersed in a charge transport medium. Usually, it is used for forming the above-mentioned laminated charge generation layer or photosensitive layer of a dispersion type photoreceptor. Further, in the present invention, an intermediate layer may be provided between the conductive support and the photosensitive layer. Further, a protective layer may be provided on the photosensitive layer, if necessary.

The pigment dispersion can be applied by a dip coating method, a spray coating method, a spin coating method, a bead coating method, a wire bar coating method, a blade coating method, a roller curtain coating method or the like. For drying, it is preferable to dry at room temperature and then heat. Heat drying is 30 ° C ~
It can be carried out at a temperature of 200 ° C. for 5 minutes to 2 hours while still or under blowing air.

The thickness of the charge generation layer is preferably in the range of 0.01 to 10 μm when it is laminated with the charge transport layer to form a photosensitive layer. The thickness of the dispersion type photoconductor is preferably 5 to 60 μm. When the charge transport layer is provided, the charge transport layer is formed of a charge transport material and a binder resin. The charge transporting substance used is not particularly limited, and examples thereof include oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds. , Hydrazone compounds, benzidine compounds, pyrazoline derivatives, stilbene compounds, amine derivatives, oxazolone derivatives, benzothiazole derivatives, benzimidazole derivatives, aminostilbene derivatives, poly-N-vinylcarbazole, poly-1-vinylpyrene, poly-9-vinylanthracene Etc.

The binder resin used in the charge transport layer can be appropriately selected from a wide range of insulating resins and used. Preferred binder resins include polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polycarbonate resin, polyvinyl acetate resin, styrene-butadiene copolymer, vinyl chloride-vinyl acetate-maleic anhydride. Examples thereof include insulating resins such as acid copolymers, silicone resins, silicone-alkyd resins, phenol-formaldehyde resins, poly-N-vinylcarbazole, and polysilane, but are not limited thereto. These binder resins may be used alone or 2
A mixture of two or more species can be used.

Further, as a solvent used for forming the charge transport layer, aromatic hydrocarbons such as benzene, xylene and chlorobenzene, ketones such as acetone and methyl ethyl ketone, halogenated methylene chloride, chloroform and ethylene chloride. Ordinary organic solvents such as aliphatic hydrocarbons, cyclic or linear ethers such as tetrahydrofuran and ethyl ether can be used alone or in admixture of two or more.

The ratio of the binder resin to the charge transport substance is 1:10 to 500, preferably 1:20 to 150.
The thickness of the charge transport layer is 1 to 50 μm, but further 5
-40 μm is preferred. As the coating method, the same method as that for the charge generation layer can be used.

The photosensitive layer may be mixed with various additives such as a leveling agent, an antioxidant and a sensitizer for improving the coating property, if necessary.

The photosensitive layer is provided on a conductive support, which may be aluminum, nickel,
A metal plate of stainless steel or the like, a metal drum, or a film or drum of plastic or the like having aluminum, copper, tin oxide, indium oxide or the like deposited on the surface thereof can be used.

In the present invention, an intermediate layer may be provided between the conductive support and the photosensitive layer, and the film thickness at that time is 0.01 to
The range of 15 μm is preferable, and the range of 0.05 to 10 μm is most effective. If it is less than 0.01 μm, the injection of charges from the support to the photosensitive layer cannot be prevented. In addition, pinholes are easily generated on the photoconductor due to the unevenness of the support. If it exceeds 15 μm, the residual potential of the photosensitive layer cannot be removed effectively.

Further, the binder used in the intermediate layer is selected in consideration of electrical resistance, environment resistance, adhesiveness to other layers, insolubility in solvents of other layers, and the like.

The binder resin selected for the intermediate layer, and the materials include metal oxides such as aluminum oxide and indium oxide, acrylic resins, methacrylic resins, vinyl chloride resins,
Vinyl acetate resin, epoxy resin, polyurethane resin, phenol resin, polyester resin, alkyd resin, polycarbonate resin, polyamide resin, silicone resin,
Melamine resin, vinyl chloride-vinyl acetate copolymer resin,
Polymeric substances such as vinyl chloride-vinyl acetate-maleic anhydride copolymer resin can be used.

As the solvent, n-butylamine, diethylamine, ethylenediamine, isopropanolamine,
Triethanolamine, triethylenediamine, N, N-dimethylformamide, acetone, methyl ethyl ketone,
Methyl isopropyl ketone, cyclohexanone, benzene, toluene, xylene, chloroform, dichloromethane, 1,2-dichloroethane, 1,2-dichloropropane, 1,1,
2-trichloroethane, 1,1,1-trichloroethane, trichloroethylene, tetrachloroethane, tetrahydrofuran, dioxane, methanol, ethanol, isopropanol, n-butanol, ethyl acetate, butyl acetate, dimethyl sulfoxide, methyl cellosolve, etc. The invention is not limited to these. These solvents can be used alone or as a mixed solvent of two or more kinds.

As a method for forming the intermediate layer, a method similar to that for the charge generation layer may be used by dissolving the resin in a solvent.

[0036]

EXAMPLES Examples of the present invention will be specifically described below, but the embodiments of the present invention are not limited thereto.

Pigment dispersion was carried out using crystalline glass beads A, B and C having the components and contents described in Table 1 according to the present invention. For comparison, pigment dispersion was also performed using glass beads Z in which the bead compact was not heat-treated and fine crystal particles were not precipitated in the amorphous glass particles.

Example 1 Crystalline glass beads A were placed in a sand mill, and an imidazole perylene compound (CGM-1) 7 was used as a charge generating substance.
g, polyvinyl butyral resin “BM-S” (manufactured by Sekisui Chemical Co., Ltd.) (1.5 g) and methyl ethyl ketone (250 ml) were added, and the mixture was dispersed for 20 hours to obtain a dispersion liquid. Next, the above charge generating substance dispersion liquid was applied onto a polyester base on which aluminum was vapor deposited using a wire bar to form a charge generating layer having a film thickness of 0.3 μm. Then charge transport material (CTM-1)
2 g and 1.5 g of polycarbonate "Z-200" (manufactured by Mitsubishi Gas Chemical Co., Inc.) dissolved in 10 ml of 1,2-dichloroethane were applied on the charge generation layer using a blade coater to form a film. A 25 μm-thick charge transport layer was formed to prepare a photoreceptor sheet sample.

[0039]

Embedded image

Example 2 A photoconductor sheet sample was prepared in the same manner as in Example 1 except that the crystalline glass beads A were replaced with the crystalline glass beads B.

Example 3 A photoconductor sheet sample was prepared in the same manner as in Example 1 except that the crystalline glass beads A were replaced with the crystalline glass beads C.

Comparative Example 1 A photoconductor sheet sample was prepared in the same manner as in Example 1 except that the glass beads A were used instead of the crystalline glass beads A.

[0043]

[Table 1]

The sensitivities of the respective photoreceptor sheet samples obtained as described above were measured with a paper analyzer "EPA-81".
00 "(manufactured by Kawaguchi Denki Co., Ltd.).

The measurement method is as follows. First, corona charging is performed for 5 seconds under the condition of -6 (KV), the surface potential Va (V) immediately after charging and the surface potential Vi (V) after standing for 5 seconds are obtained, and then, Exposure to obtain a surface illuminance of 2.0 (lux), and obtain the exposure amount E600 / 100 (lux · sec) required to reduce the surface potential from −600 (V) to −100 (V) And The results are shown in Table 2.

[0046]

[Table 2]

By using crystalline glass beads as shown in Table 2, a highly sensitive dispersion liquid for an electrophotographic photoreceptor can be obtained.

Example 4 30 g of polyamide resin CM-8000 (manufactured by Toray Industries, Inc.) was put into a mixed solution of 900 ml of methanol and 100 ml of 1-butanol, and the mixture was heated to 50 ° C.
It melted by heating. Outer diameter 80mm, total length 355.5m using this liquid
Four aluminum drums each having a 0.3 μm intermediate layer formed thereon were produced by dip coating on an aluminum drum substrate of m.

Next, cellulose-modified silicone resin KR
-5240 (manufactured by Sekisui Chemical Co., Ltd.) was dissolved in 1800 ml of methyl isopropyl ketone, 36 g of the exemplified compound (CGM-2) was mixed as a charge generating substance, and crystalline glass beads A, B, C and glass beads Z were added. Each of them was dispersed for 10 hours using a sand mill. This solution was used to dip-coat each of the above intermediate layers to form 0.5 μm CGL.

Next, the compound CTM-as a charge transport material.
2 150 g and 200 g of polycarbonate "Z-200" as a charge transport layer binder were dissolved in 1000 ml of 1,2-dichloroethane.

Using this solution, dip coating was performed on the CGL, followed by drying at 100 ° C. for 60 minutes to obtain a CT having an average film thickness of 21 μm.
L was formed to obtain photoconductors 1, 2, 3 and 4.

[0052]

Embedded image

The following characteristic evaluations were performed on the photoreceptor samples obtained as described above, and the results are shown in Table 3.

[Image Evaluation] Electrophotographic copying machine “U-Bix
4045 "(manufactured by Konica) was incorporated with each of the above photoconductor samples, and a white chart was photographed.

(1) Image Defects The number of white spots and the number of white spots were measured using an image analysis device “Omnicon 3000 type” (manufactured by Shimadzu Corporation), and the following evaluation was made with the number of white spots of φ (diameter) 0.5 mm or more / A4 paper. It was judged by the sign.

Judgment Number of white spots of 0.5 mm or more ○ 0 to 3 △ 4 to 10 × 11 or more (○ to △ is the practical range) [Durability evaluation] Modification of the above "U-Bix 4045" Then, a surface electrometer was installed, and the process of charging → exposure → static elimination was repeated 1000 times, and the potentials of the black and white papers and the residual potential Vr (−V) were measured at the first and 1000th times.

White paper potential; drum surface potential when copying a document surface having a density of 0.0, Vw (-V) Black paper potential: drum surface potential when copying a document surface having a density of 1.3, Vb (-V)

[0058]

[Table 3]

As shown in Table 3, in the preparation of the dispersion liquid for the electrophotographic photosensitive member, the use of the crystalline glass beads for the dispersion of the organic pigment causes less image defects and increases the residual potential during repeated copying. It is possible to obtain a small number of photoreceptors.

[0060]

Industrial Applicability According to the method of the present invention, the dispersion treatment of the organic pigment in the solvent in the presence of the crystalline glass medium can provide a dispersion liquid in which the abrasion powder of the medium and the broken pieces are not mixed. it can. Further, by obtaining a dispersion liquid which does not contain abrasion powder and crushed pieces of media, and by producing an electrophotographic photosensitive member using the dispersion liquid, electrophotographic characteristics and image characteristics are significantly improved as compared with the conventional photosensitive member. An electrophotographic photoreceptor can be obtained.

Claims (2)

[Claims] 1. A method for producing a dispersion liquid for an electrophotographic photosensitive member comprising at least an organic pigment dispersed therein, wherein the organic pigment is dispersed in a solvent in the presence of a crystalline glass medium. A method for producing a dispersion liquid for a photoreceptor. 2. An electrophotographic photoreceptor having a photosensitive layer formed by applying a dispersion liquid obtained by dispersing an organic pigment in a solvent in the presence of crystalline glass media on a conductive support. .