JP2000194148A - Electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high resolution without reducing the thickness of the photosensitive layer of an electrophotographic organic photoreceptor. SOLUTION: When an undercoat layer 3 is formed on an electrically conductive substrate 2 and a photosensitive layer 6 is formed on the undercoat layer 3 by laminating an electric charge generating layer 4 and an electric charge transferring layer 5 to obtain an electrophotographic photoreceptor 1, titanium dioxide is incorporated into the electric charge transferring layer 5 of the photosensitive layer 6 of the photoreceptor 1. High resolution is attained without reducing the thickness of the entire photosensitive layer 6 and an image having high image quality is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly, to an electrophotographic image forming apparatus having a photosensitive layer which is an image carrier for forming an electrostatic latent image and a toner image. It relates to a photoreceptor.

[0002]

2. Description of the Related Art In an image forming apparatus, for example, an image forming apparatus utilizing an electrophotographic system, a toner image is formed on an electrophotographic photosensitive member as an image carrier, and the toner image is transferred onto a sheet such as plain paper. Then, in order to hold the toner image on the sheet as a permanent image on the sheet, the toner is heated and fixed by, for example, passing through a heat fixing device, and then discharged outside the apparatus main body.

The electrophotographic photosensitive member used in such an image forming apparatus has a photosensitive layer formed on the surface of a conductive body, such as a cylindrical body or an endless belt made of metal, for example, aluminum.

[0004] Materials for the photosensitive layer can be broadly classified into inorganic materials and organic materials. Representative inorganic photoconductive materials include selenium such as amorphous selenium (a-Se) and amorphous selenium arsenide (a-As ₂ Se ₃ ), dye-sensitized zinc oxide (ZnO), and cadmium sulfide. (CdS) is dispersed in a binder, and amorphous silicon (a-Si) is used.

A typical organic photoconductive material is 2,4,7-trinitro-9-fluorenone (TN
E) and those using a charge transfer complex of poly-N-vinylcarbazole (PVD).

[0006] Photoreceptors having these photosensitive layers have many advantages as well as disadvantages. For example, a photoreceptor using a selenium-based or CdS-based photoconductor has problems in durability and storage stability, and has a limitation that it cannot be easily disposed of due to its toxicity and must be collected. Further, a photoreceptor using a ZnO resin dispersion system is hardly used at present because of low sensitivity and lack of durability.

In this regard, a photoreceptor formed with a-Si as a photoconductive layer has advantages of high sensitivity and high durability. However, there remain problems such as high manufacturing cost due to the complexity of the manufacturing process and image defects due to defects during film formation.

On the other hand, a photoreceptor having an organic photoconductive layer has a wide variety of organic materials and can be arranged in various ways by synthesis. Therefore, by appropriately selecting them, storage stability, toxicity, etc. Has been widely used because it can solve the problem described above and can be manufactured at low cost.

In particular, an electrophotographic photosensitive member using an organic photoconductive material has some problems in sensitivity, durability, environmental stability and the like, but uses the above-mentioned inorganic photoconductive material. Compared with the electrophotographic photoreceptor, there are great advantages in terms of toxicity, coct and freedom of material design. for that reason,
In recent years, in an electrophotographic photoreceptor, an organic photoconductive material has been used more frequently than an inorganic photoconductive material.

For this reason, various methods of sensitizing organic photoconductive materials have been proposed. Above all,
A charge-generating layer containing a charge-generating material that generates charge carriers when irradiated with light, and a charge-transporting layer mainly containing a charge-transporting material that receives and transports the charge carriers generated in the charge-generating layer. The function-separated type photoreceptor shows excellent sensitization, and the function-separated type photoreceptor occupies most of the organic photoreceptors currently in practical use. In addition, improvement of chargeability, prevention of unnecessary charge injection from the conductive substrate, covering of defects on the conductive substrate, and prevention of pinhole generation,
In order to improve the adhesiveness of the photosensitive layer and the durability, etc.
A structure in which an undercoat layer is provided on a substrate is mainly used.

The function-separated type photoreceptor as described above has a wide selection range of each substance, and has a charging characteristic, sensitivity, residual potential,
It has become possible to provide a high-performance photoreceptor by combining the best substances in electrophotographic characteristics such as repetition characteristics and printing durability. Also, the photosensitive layer
As described above, since it can be produced by coating, there is an advantage that the productivity is extremely high, an inexpensive photoreceptor can be provided, and the photosensitive wavelength range can be freely controlled by appropriately selecting the charge generation material. . for that reason,
At present, most copiers, printers, and image forming apparatuses that use the electrophotographic method such as facsimile,
A function-separated type photoreceptor (organic photoreceptor / OPC) has come to be used.

In recent years, the above-mentioned image forming apparatuses have been required to have high image quality, and the OPC photosensitive member has also been required to have a sensitivity or the like that can cope with high image quality. Was. In particular, there is a growing demand for higher resolution in order to improve image quality.

[0013]

One means for increasing the resolution of a photoreceptor, which is an electrophotographic image bearing member, is to increase the electrostatic capacity of the photosensitive layer of the photoreceptor to increase the surface charge density. I just need. It is widely accepted by those skilled in the art that the effect of increasing the S / N ratio at the stage of the electrostatic latent image and increasing the driving force of the toner on the developing body contributes to achieve higher resolution. It is a known fact.

However, although the organic photoreceptor has many advantages as described above, the dielectric constant is smaller than that of an inorganic photoconductive material such as selenium, so that the capacitance of the photosensitive layer is increased. It also has the disadvantage of being difficult to perform.

In order to increase the resolution of the photosensitive member by the electrophotographic method, the following two measures are taken at present.

First, an inorganic electrophotographic photosensitive member is used. Another is to increase the capacitance of an organic photoconductor. Therefore, Q = C · V
(Q: surface charge density, C: capacitance of photosensitive layer, V = photoconductor surface potential), C = ε · ε ₀ / d (ε: non-dielectric constant of photosensitive layer, ε ₀ : dielectric constant of vacuum, d: photosensitive layer thickness), there is a method of reducing the thickness of the photosensitive layer of the organic photosensitive member to increase the capacitance.

However, the use of inorganic photoconductors is limited due to the above-mentioned drawbacks. Further, in the case of an organic photoreceptor, by reducing the film thickness, the photosensitive layer is liable to be affected by a decrease in film thickness due to abrasion of the photosensitive layer when repeatedly used, which causes a deterioration in sensitivity and a decrease in charging potential, resulting in an extremely short life. .

An object of the present invention is to make it possible to increase the resolution of an electrophotographic photosensitive member in order to solve the above-mentioned disadvantages.

Another object of the present invention is to provide an electrophotographic photoreceptor capable of obtaining a desired resolution and achieving higher image quality without reducing the thickness of a photosensitive layer in an organic photoreceptor.

[0020]

According to the present invention, there is provided an electrophotographic photoreceptor for achieving the above-mentioned object by providing an inorganic pigment appropriately on a conductive support or in a photosensitive layer. , Enabling higher resolution.

In order to solve the drawbacks of the conventional organic photoreceptor, the photosensitive layer comprises a charge generation layer and a charge transport layer, and the charge transport layer contains the inorganic pigment, for example, titanium oxide. . As a result, it is possible to increase the resolution and provide a high-quality image.

In the electrophotographic photoreceptor used in the present invention, a great effect can be exhibited particularly when an organic material having a small dielectric constant is used. Thereby, the disadvantages of the inorganic system can be eliminated, and the advantages of the organic system can be maintained, and high resolution can be achieved without thinning the photosensitive layer as described above, so that problems such as life can be eliminated at the same time. .

As the above-mentioned inorganic material used in the present invention, titanium oxide is most suitable.
Tin oxide, indium oxide, zinc oxide, zinc white, lead white,
Examples include lithopone, zinc sulfide, zirconium oxide, silica, alumina, barium sulfate, and calcium carbonate. Basically, any material having a higher dielectric constant than an organic material can be used.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of the electrophotographic photosensitive member according to the present invention will be described. FIG. 1 is a cross-sectional view illustrating an example of a photoconductor for electrophotography according to the present invention, and in particular, illustrates an example of a stacked type photoconductor using function separation. The photoreceptor 1 is formed by forming, for example, an undercoat layer 3 on the surface of a cylindrical drum-shaped conductive support (substrate) 2, a charge generation layer 4 thereon, and a charge transport layer 5 on the top. It is constituted by providing a layer 6.

The conductive support 2 has a drum shape made of metal such as aluminum, aluminum alloy, copper, zinc, stainless steel and titanium. Alternatively, the conductive support 2 may be formed of a sheet, a seamless belt, or the like. Further, it may be constituted by a drum, a sheet, a seamless belt, or the like in which a metal material is laminated on a hard paper surface or a metal foil is applied to a polymer material such as polyethylene terephthalate, nylon, or polystyrene.

An undercoat layer 3 is formed on the surface (upper surface) of the conductive support 2 as shown in FIG. This undercoat layer 3
Is provided as needed between the conductive support 2 and the photosensitive layer 6 to improve the adhesiveness between the conductive support 2 and the photosensitive layer 6 or to adjust the photosensitive property from the support 2 side. It functions to prevent leakage of electric charge to the layer, and may not be provided depending on the case.

The undercoat layer 3 generally contains a resin as a main component, and these resins are coated with a general organic solvent in consideration of applying a photoconductive layer with a solvent to form the photosensitive layer 6 on the upper surface thereof. It is desired that the resin is highly resistant to solvents. Such resins include polyvinyl alcohol, casein, sodium polyacrylate, water-soluble resins such as polyvinyl acetal, copolymer-soluble nylon, alcohol-soluble resins such as methoxymethylated nylon, acrylic resin, polyurethane, melamine resin, phenol resin,
Curable resins that form a three-dimensional network structure, such as epoxy resins, may be used. The undercoat layer 3 has moiré prevention,
To reduce the residual potential, for example, titanium oxide, zinc oxide, silica, alumina, zirconium oxide, tin oxide,
A fine powder pigment of a metal oxide such as indium oxide can be added.

The thickness of the undercoat layer 3 is preferably in the range of 0.1 μm to 20 μm, and more preferably 0.1 μm to 20 μm.
It can be said that it is optimal if the thickness is in the range of 5 μm to 10 μm. In particular, when the thickness of the undercoat layer 3 is less than 0.1 μm, the function as the undercoat layer is not substantially achieved. For example, it is not possible to obtain uniform surface properties by covering defects of the conductive support 2 and it is not possible to prevent the carrier from being injected from the conductive support 2, thereby lowering the chargeability. Also,
When the thickness is more than 20 μm, when the undercoat layer 3 is applied by dip coating, it becomes extremely difficult to manufacture the photoreceptor 1, and the mechanical strength of the coating film decreases, which is not preferable.

The method of preparing the coating solution for the undercoat layer 3 includes stirring, a ball mill, a sand mill, an attritor,
Vibration mills, ultrasonic dispersers, etc. One of the methods for forming the undercoat layer 3 on the conductive support 2 is a coating method. This coating method includes an immersion method, a spray method,
A bead method, a nozzle method, and the like are applied as general methods.

As described above, the undercoat layer 3 also contains an inorganic pigment, which is well known in the art and is used to adjust the electric resistance of the undercoat layer 3, and is used in the present invention. The inorganic pigment for achieving the purpose is completely different from the purpose to be contained, and has no direct relation.

Next, the photosensitive layer 6 will be described. According to FIG. 1, the photosensitive layer 6 formed on the undercoat layer 3 is composed of a charge generation layer 4 and a charge transport layer 5 and has a function separated from each other.

Therefore, the charge generation layer 4 formed on the undercoat layer 3 contains a charge generation substance in a resin constituting the layer.

Examples of the charge generating material contained in the charge generating layer 4 include bisazo compounds such as chlorodiane blue;
Polycyclic quinone-based compounds such as dibromoansansthrone, perylene-based compounds, quinacridone-based compounds, phthalocyanine-based compounds, azurenium salt-based compounds and the like are known,
These may be used alone or in combination of two or more.

The charge generating layer 4 can be formed by a method of forming a charge generating material by vacuum deposition.
There is a method in which a film is formed by dispersing in a binder resin solution and applying the solution. Generally, the latter method is preferred. In the case of the coating method, the same method as that for the undercoat layer is used as a method of mixing and dispersing the charge generating substance in the binder resin solution and a method of applying.

As the binder resin, a melamine resin,
Epoxy resin, silicone resin, polyurethane resin, acrylic resin, polycarbonate resin, polyarylate resin, phenoxy resin, butyral resin, etc., and copolymer resins containing two or more repeating units, for example, vinyl chloride-vinyl acetate copolymer resin And an insulating resin such as acrylonitrile-styrene copolymer resin. Without being limited to these, all commonly used resins can be used alone or in combination of two or more.

Solvents for dissolving the resin include halogenated hydrocarbons such as methylene chloride and dichloroethane, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, tetrahydrofuran and dioxane. Ethers such as
Aromatic hydrocarbons such as benzene, toluene and xylene,
An aprotic polar solvent such as N, N-dimethylformamide and N, N-dimethylacetamide can be used.

The thickness of the charge generation layer 4 is preferably in the range of 0.05 μm to 5 μm, and more preferably in the range of 0.1 μm to 1 μm.

On the other hand, the charge transport layer 5 formed on the charge generation layer 4 constituting the photosensitive layer 6 contains the inorganic pigment according to the present invention together with a charge generation substance in the charge transport layer. .

As a method for forming the charge transport layer 5, a method for preparing a charge transport coating solution in which a charge transport material is dissolved in a binder resin solution, and applying this to form a film is generally used. is there.

The charge transport material contained in the charge transport layer 5 includes an enamine compound, a hydrazone compound,
Pyrazoline compounds, triphenylamine compounds, triphenylmethane compounds, stilbene compounds, oxadiazole compounds, butadiene compounds and the like are known. These may be used alone or in combination of two or more.

As the binder resin, polyester resin,
Polyurethane resin, acrylic resin, polycarbonate resin, polyarylate resin, styrene resin, phenoxy resin, butyral resin, and the like, and copolymer resins containing two or more repeating units, for example, vinyl chloride-vinyl acetate copolymer resin, acrylonitrile- An insulating resin such as a styrene copolymer resin can be used. Without being limited to these, all commonly used resins can be used alone or in combination of two or more.

Solvents for dissolving the resin include halogenated hydrocarbons such as methylene chloride and dichloroethane, ketones such as acetone, methyl ethyl ketone and cyclohexanone, esters such as ethyl acetate and butyl acetate, tetrahydrofuran, dioxane and the like. Ethers such as
Aromatic hydrocarbons such as benzene, toluene and xylene,
An aprotic polar solvent such as N, N-dimethylformamide and N, N-dimethylacetamide can be used.

According to the present invention, the inorganic pigment is contained in the charge transporting layer 5, and the method of dispersing the inorganic pigment in the charge transporting layer coating solution is the same as that of the undercoat layer 3 described above. A method can be used. The charge transport layer 5
If a resin with good mechanical properties and electrostatic properties is not suitable for dispersing inorganic pigments, first disperse it with a resin with good dispersibility for inorganic pigments, then charge transport material, mechanical properties
A method of preparing a coating liquid for the charge transport layer by dissolving a resin having good electrostatic properties is an effective means for obtaining good properties. The thickness of the charge transport layer 5 is preferably 5 μm to 5 μm.
Within a range of about 0 μm, more preferably 10 μm to
It can be said that it is preferable that the thickness be in the range of 40 μm.

As described above, in the photoconductor 1 for electrophotography having the structure shown in FIG.
An inorganic pigment such as titanium oxide is contained therein. This makes it possible to obtain a photoreceptor capable of achieving higher resolution by comparing the following example and a comparative example for comparison with this example, thereby providing an image capable of achieving high image quality. .

(Example 1) Diameter 65 mm, length 348 m
The following undercoat layer coating liquid was applied to an aluminum drum (2) having a thickness of m using a well-known dip coating apparatus, and dried at 110 ° C for 20 minutes. Thus, a subbing layer (3) having a thickness of 0.5 μm was formed on the aluminum drum (2).

[Coating solution for undercoat layer] Alcohol-soluble nylon resin (CM8000, manufactured by Toray Industries, Inc.) 4 parts by weight Methanol 35 parts by weight 1,2-dichloroethane 65 parts by weight The above components were stirred and dissolved with a stirrer. An undercoat layer coating solution was prepared.

Next, the following charge generation layer coating solution is applied onto the undercoat layer (3) formed as described above using a well-known dip coating apparatus, and dried at 120 ° C. for 10 minutes. Was. Thereby, a thickness of 0.3 μm is formed on the surface of the undercoat layer (3).
m of the charge generation layer (4) was formed.

[Charge Generating Layer Coating Solution] 4,10-dibromoanthranthrone (manufactured by Zeneca) 2 parts by weight Polyvinyl butyral resin (BX-1 manufactured by Sekisui Chemical Co., Ltd.) 1 part by weight Tetrahydrofuran 80 parts by weight The components were dispersed in a ball mill for 72 hours to prepare a charge generation layer coating solution.

Next, the following charge transport layer coating solution is applied onto the charge generation layer (4) formed as described above using a well-known dip coating apparatus, and dried at 120 ° C. for 20 minutes. Was. Thereby, the thickness of 30 μm is formed on the surface of the charge transport layer (4).
m of the charge transport layer (5) was formed to obtain an electrophotographic photoconductor (1) having a structure as shown in FIG. 1 according to the present invention.

[Coating solution for charge transport layer] Solution A Charge generating substance (hydrazone compound) having the following structural formula: 50 parts by weight

[0051]

Embedded image

Z-type polycarbonate resin (manufactured by Mitsubishi Gas Chemical Company: Z200): 47 parts by weight Silicon oil (KF-50 manufactured by Shin-Etsu Chemical Co., Ltd.): 0.01 parts by weight dichloromethane: 330 parts by weight The above components were stirred and dissolved. A liquid.

Liquid B Titanium oxide (TTO-55B manufactured by Ishihara Sangyo Co., Ltd.) 1 part by weight Vinyl chloride-vinyl acetate-maleic anhydride copolymer (SOLBIN M manufactured by Nissin Chemical Co., Ltd.) 2 parts by weight tetrahydrofuran 120 parts by weight The above components were dispersed in a paint shaker for 6 hours to obtain a liquid B.

Finally, the solution A and the solution B obtained as described above were mixed and stirred to prepare a charge transport layer coating solution.

(Example 2) The thickness of the charge transport layer (5) was set to 1
A photoconductor for electrophotography was produced in the same manner as in Example 1 except that the thickness was changed to 8 μm.

(Comparative Example 1) A photosensitive material for electrophotography was prepared in the same manner as in Example 1 except that the composition of Solution B for preparing the charge transport layer coating liquid of Example 1 was changed as follows. The body was made.

Liquid B Vinyl chloride-vinyl acetate-maleic anhydride copolymer (manufactured by Nissin Chemical Co., Ltd .: SOLBIN M): 2 parts by weight Tetrahydrofuran: 120 parts by weight The above components were dispersed for 6 hours using a paint shaker. Liquid.

Comparative Example 2 The charge transport layer had a thickness of 18 μm.
A photoreceptor for electrophotography was prepared in the same manner as described in Comparative Example 1, except for the following.

As described above, in Embodiments 1 and 2,
The charge transport layer (5) constituting the photosensitive layer (6) contained titanium oxide, and the film thickness was changed to obtain a photoconductor for electrophotography. On the other hand, in Comparative Examples 1 and 2, a photoconductor for electrophotography was obtained without adding titanium oxide to the charge transport layer (5).

Therefore, each photoconductor obtained as described above was mounted on a modified copy machine SF2022 manufactured by Sharp, and the resolution when each photoconductor was used was evaluated using a resolution chart. The evaluation results are shown in Table 1 below.

[0061]

[Table 1]

As shown in Table 1 above, a photosensitive member in which an inorganic compound, for example, titanium oxide was contained in the charge transporting layer constituting the photosensitive layer, was prepared in the same film thickness without using titanium oxide. It can be seen that the resolution is greatly improved as compared with the photoconductors 1 and 2. Therefore, a high-resolution photoconductor can be manufactured without reducing the thickness of the photosensitive layer 6. Therefore, the life of the high resolution photoconductor can be extended, and the problem of shortening the life can be solved.

In particular, according to the above-described embodiment, the electrophotographic photosensitive member in which the charge generation layer 4 and the charge transport layer 5 are laminated to form the photosensitive layer 6 of a type in which functions are separated has been described. Naturally, the resolution can be improved in the same manner even when the photosensitive layer in which the charge generation layer and the charge transport layer are the same layer contains titanium oxide as an inorganic material.

[0064]

According to the present invention, since the photosensitive layer of the electrophotographic photosensitive member according to the present invention contains an inorganic pigment, a high-resolution photosensitive member can be easily obtained without reducing the thickness of the photosensitive layer. . For this reason, it is possible to prevent a decrease in the life of the photosensitive layer due to a decrease in the film thickness.

In the case where the charge transport layer and the charge generation layer constituting the photosensitive layer are laminated, particularly, the charge transport layer contains titanium oxide, whereby high resolution can be achieved, and thus high image quality can be obtained. Can provide a perfect image.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an electrophotographic photosensitive member having a function-separated type laminated structure according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electrophotographic photoreceptor 2 conductive support 3 undercoat layer 4 charge generation layer 5 charge transport layer 6 photosensitive layer

Claims (2)

[Claims] 1. An electrophotographic photosensitive member having a photosensitive layer provided on a conductive support, wherein the photosensitive layer contains an inorganic pigment. 2. The electrophotographic device according to claim 1, wherein the photosensitive layer comprises a charge generation layer and a charge transport layer, wherein the charge transport layer contains an inorganic pigment, and the inorganic pigment is titanium oxide. Photoconductor.