JP2001075300A - Electrophotographic photoreceptor and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrophotographic photoreceptor capable of stably forming an image over a long period of time without lowering the characteristics of a photoreceptor with a middle layer consisting of titanium dioxide and a resin on the substrate and to obtain an image forming device using the electrophotographic photoreceptor. SOLUTION: At least a middle layer and a photosensitive layer are successively laminated on an electrically conductive substrate to obtain the objective electrophotographic photoreceptor. The middle layer consists essentially of titanium dioxide and a resin, and the crystal structure of the titanium dioxide includes 98-99.6% rutile type structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member, and more particularly, to an electrophotographic photosensitive member used in an electrophotographic copying machine, a printer, and the like.

[0002]

2. Description of the Related Art Conventionally, as a photoreceptor used in an electrophotographic system, an electroconductive support having a photosensitive layer mainly composed of selenium or a selenium alloy, inorganic light such as zinc oxide, cadmium sulfide or the like is used. Generally, a conductive material dispersed in a binder, an organic photoconductive material such as poly-N-vinylcarbazole and trinitrofluorenone or an azo pigment, and an amorphous silicon-based material are known. Have been.

[0003] Generally, the "electrophotographic method"
The photoconductive photoreceptor is first charged in a dark place by, for example, corona discharge, and then image-exposed to selectively dissipate the charge of only the exposed portions to obtain an electrostatic latent image. This is one of image forming methods in which an image is formed by developing and visualizing an image by using fine particles (toner) for detection composed of a coloring agent and a binder such as a polymer substance.

[0004] In such an electrophotographic method, the basic characteristics required of a photoreceptor are (1) that it can be charged to an appropriate potential in a dark place, (2) that there is little dissipation of electric charge in a dark place, and (3) And (3) electric charges can be quickly dissipated by light irradiation.

In recent years, as the speed, durability, and size of electrophotographic copying machines have been increasing, there has been a strong demand for the photoreceptors to have high image quality even when used repeatedly for a long period of time, in addition to the above characteristics. It is made like. In general, electrophotographic photoreceptors have various problems due to repeated use, such as deterioration of chargeability, deterioration of image characteristics, and deterioration of adhesion between a photosensitive layer and a substrate.

Further, in the case of a photoreceptor in which the photosensitive layer has a laminated structure of a charge generation layer and a charge transport layer, moire tends to occur between the substrate and the charge transport layer due to multiple reflections. In general, the charge transport layer has high light transmittance, and the charge generation layer also has high light transmittance because of its small thickness. Therefore, the light incident on the photosensitive layer is
Part of the light is transmitted through the photosensitive layer without being absorbed, and reaches the substrate surface. If the surface of the base is a mirror surface, the light transmitted through the photosensitive layer is reflected, rebounds on the photosensitive layer, and causes light interference with the incident light. This optical interference is not a problem in the case of a line image, but in the case of a solid image, interference fringe-like density unevenness (moire) occurs. This phenomenon is likely to occur in a process using monochromatic light such as laser light.

As means for solving the above problems,
It has been proposed to provide an intermediate layer between the photosensitive layer and the substrate, and among such intermediate layers, those in which titanium oxide is dispersed in a resin (JP-A-61-204642 and others) are known. Have been. Further, those in which the purity of these titanium oxides is specified (JP-A-2-67565, etc.) and those in which the crystal system is specified (JP-A-Hei.
-172361). At present, as the titanium oxide in the intermediate layer used for the photoconductor, titanium oxide having a rutile type crystal structure is used in consideration of various characteristics such as image characteristics, electrostatic characteristics, and environmental stability. There are many examples. It has been clarified that such rutile-type titanium oxide has a trace amount of titanium oxide having another crystal structure due to a problem in production and the like.

A photoreceptor provided with an intermediate layer in which a small amount of rutile-type titanium oxide having another crystal system is dispersed in such a resin does not cause any serious problem at the initial stage, but is used for a long time. In this case, a defect that defects (ground stains and white spots) on an image gradually become remarkable occurred.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and an object of the present invention is to provide a photoconductor having an intermediate layer composed of titanium oxide and a resin on a substrate. An object of the present invention is to provide an electrophotographic photoreceptor capable of performing stable image formation for a long period without deteriorating the characteristics of the electrophotographic photoreceptor and an image forming apparatus using the same.

[0010]

According to the present invention, there is provided an electrophotographic photosensitive member having a structure in which at least an intermediate layer and a photosensitive layer are sequentially laminated on a conductive support, wherein the intermediate layer comprises titanium oxide and a resin. The electrophotographic photoreceptor is characterized in that the crystal structure of the titanium oxide is a rutile structure having a content of 98% or more and 99.6% or less. By adopting the constitution of the electrophotographic photosensitive member of the present invention, the image characteristics of the photosensitive member due to long-term use can be improved.

Next, a description will be given of an abnormal image which is currently known. By using the photoreceptor for a long period of time, a portion where the chargeability is locally reduced occurs, resulting in an abnormal image such as background stain (in the case of negative-positive development) and white spots (in the case of positive-positive development) on the image, It becomes obvious. This local decrease in chargeability greatly changes depending on the state of the intermediate layer (material, film forming conditions, etc.). One of the conditions affecting the local decrease in chargeability is the crystal structure of titanium oxide. At present, titanium oxide having a rutile-type crystal structure is often used for the intermediate layer in consideration of various characteristics such as image characteristics, electrostatic characteristics, and environmental stability. Most of the titanium oxide used here has a rutile structure, but it is known that a small amount of titanium oxide having another crystal structure is included.

Abnormal images such as background stains and white spots generated during long-term use vary greatly depending on the content of the crystalline titanium oxide other than the rutile structure contained in the titanium oxide, and are different from those other than the rutile type structure. It has been found that the higher the content of crystalline titanium oxide, the more likely it is to generate. On the other hand, when the purity of the rutile type titanium oxide contained in the intermediate layer was increased, the effect on abnormal images was extremely large. It was also found that there was a tendency for the potential to rise.

As a result of extensive studies by the present inventors, as a means for achieving the above-described suppression of abnormal images and the stability of the exposed portion potential in the apparatus, the crystal structure of titanium oxide contained in the intermediate layer has a content of 98%. % Or less and 99.6% or less of a rutile structure was found to be effective. Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view of an electrophotographic photoreceptor of the present invention, in which an intermediate layer 25 and a photosensitive layer 2 are formed on a conductive substrate 21.
3 are sequentially provided. 2 and 3 each show a configuration example of another electrophotographic photoreceptor of the present invention.
2 is a function-separated type in which the photosensitive layer 23 is composed of a charge generation layer (CGL) 31 and a charge transport layer (CTL) 33. FIG. 3 is a CGL of the function-separated type photosensitive layer 23.
The CTL stacking order is reversed, respectively. The intermediate layer 25 is formed on the conductive support 21.
The above other layers and the type of the photosensitive layer may be arbitrarily combined as long as they have at least the photosensitive layer 23 and the photosensitive layer 23.

In the present invention, the conductive support used for the electrophotographic photoreceptor may be a conductor or an insulator subjected to a conductive treatment, for example, a metal such as Al, Fe, Cu, Au or an alloy thereof, Polyester, polycarbonate, polyimide, Al on an insulating substrate such as glass,
A thin film made of a metal such as Ag or Au, or a conductive material such as In ₂ O ₃ or SnO _2, or a paper subjected to a conductive treatment can be used. The shape of the conductive support is not particularly limited and is plate-like,
Any of a drum shape and a belt shape can be used.

Examples of the binder resin for the intermediate layer provided between the conductive support and the photosensitive layer include polyamide, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyvinyl methyl ether, polyvinyl pyrrolidone, poly-N-vinyl imidazole, Thermoplastic resins such as ethyl cellulose, nitrocellulose, ethylene-acrylic acid copolymer, casein and gelatin, and thermosetting resins such as phenol, urea resin, melamine, aniline, alkyd, unsaturated polyester and epoxy are used. As a method for forming the intermediate layer, a normal coating method is employed.

The photosensitive layer provided on the conductive support with an intermediate layer interposed therebetween may be any of the above-mentioned Se-based and OPC-based photosensitive layers, and may be of a single-layer type or a function-separated type. it can. Of these, the OPC system will be briefly described below.

Examples of the monolayer type organic photosensitive layer include dye-sensitized photoconductive powders of zinc oxide, titanium oxide, zinc sulfate, etc., amorphous silicon powder, squaric salt pigment, phthalocyanine pigment, azulhenium salt. Pigments, azo pigments and the like, if necessary, coated with a binder resin and / or an electron-donating compound as described below, or an eutectic complex formed from a bilillium-based dye and bisphenol A-based polycarbonate. Examples include a composition using a composition to which a donating compound is added. As the binder resin, the same resin as a function-separated type photoreceptor described later can be used. The thickness of the single-layer type photoreceptor is suitably 5 to 30 μm.

On the other hand, as an example of the function-separated type photosensitive layer, a layer in which a charge generation layer (CGL) and a charge transport layer (CTL) are laminated is exemplified. As a charge generation layer (CGL) for generating and separating latent image charges by image exposure, an inorganic photoconductive powder such as crystalline selenium or arsenic selenide or an organic dye or pigment is dispersed or dissolved in a binder resin. Is used.

Examples of the organic dyes and pigments as the charge generating substance include C.I. Pigment Blue 25 (Color Index (CI) 21180), C.I. Pigment Red 41 (CI2200), C.I. Acid Red 52 (CI45100), and C.I. (CI45210), a phthalocyanine-based pigment having a porphyrin skeleton, an azulhenium salt pigment, a squaric salt pigment, an azo pigment having a carbazole skeleton (described in JP-A-53-95033), and an azo pigment having a styrylstilbene skeleton ( 53-138229
Azo pigments having a triphenylamine skeleton (described in JP-A-53-132547), and azo pigments having a dibenzothiophene skeleton (described in JP-A-54-2).
1728), an azo pigment having an oxadiazole skeleton (described in JP-A-54-12742),
Azo pigments having a fluorenone skeleton (JP-A-54-22)
No. 834), an azo pigment having a bisstilbene skeleton (described in JP-A-54-17733), an azo pigment having a distyryloxadiazole skeleton (described in JP-A-54-2129), Azo pigments having a distyrylcarbazole skeleton (described in JP-A-54-17734), and triazo pigments having a carbazole skeleton (JP-A-57-195767, 57-1957)
Phthalocyanine pigments such as C.I. Pigment Blue 16 (CI74100);
Indigo pigments such as C-I Bad Brown 5 (CI73410) and C-I Bad Dye (CI73030);
Perylene-based pigments such as Argoscarlet B (manufactured by Violet) and Indance Scarlet R (manufactured by Bayer) can be used. These charge generating substances are used alone or in combination of two or more.

The binder resin is suitably used in an amount of 0 to 100 parts by weight, preferably 0 to 50 parts by weight, based on 100 parts by weight of the charge generating substance.

Examples of the binder resin used in combination with these organic dyes and pigments include condensation resins such as polyamide, polyurethane, polyester, epoxy resin, polycarbonate and polyether, and polystyrene, polyacrylate, polymethacrylate, poly-N-vinylcarbazole, Polymers such as polyvinyl butyral, styrene-butadiene copolymer, and styrene-acrylonitrile copolymer, and adhesive and insulating resins such as copolymers are exemplified.

The charge generating layer is prepared by dispersing a charge generating material together with a binder resin, if necessary, using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, or dichloroethane in a ball mill, an attritor, a sand mill, or the like, and appropriately diluting the dispersion. It can be formed by applying by applying. The coating can be performed by a dip coating method, a spray coating method, a bead coating method, or the like. The thickness of the charge generation layer is suitably about 0.01 to 5 μm, and preferably 0.1 to 2 μm.

Further, in the present invention, when particles such as crystalline selenium or arsenic selenide alloy are used as the charge generating substance, an electron donating adhesive and / or an electron donating organic compound are used in combination. Examples of such an electron donating substance include polyvinyl carbazole and derivatives thereof (for example, those having a carbazole skeleton having a halogen such as chlorine or bromine, a substituent such as a methyl group or an amino group), polyvinyl pyrene, oxadiazole, pyrazoline, and hydrazone. ,
There are nitrogen-containing compounds such as diarylmethane, α-phenylstilbene, and triphenylamine compounds, and diarylmethane compounds, and polyvinyl carbazole and its derivatives are particularly preferable. These substances can be used even if they are mixed. In this case, it is preferable to add another electron donating organic compound to polyvinyl carbazole and its derivative. The content of such an inorganic charge generating substance is suitably from 30 to 90% by weight of the whole layer. When an inorganic charge generating material is used, the thickness of the charge generating layer is suitably about 0.2 to 5 μm.

The charge transport layer (CTL) is a layer intended to hold the charged charges and to transfer the charges generated and separated in the charge generating layer by exposure to combine with the held charges. High electrical resistance is required to achieve the purpose of retaining the charged charge, and in order to achieve the purpose of obtaining a high surface potential with the retained charged charge,
It is required that the dielectric constant is small and the charge mobility is good.

The charge transport layer for satisfying these requirements is composed of a charge transport material and a binder resin used as required. That is, a charge transport layer can be formed by dissolving or dispersing the above substances in an appropriate solvent, and applying and drying the same.

The charge transport layer includes a hole transport material and an electron transport material. Examples of the hole transport material include poly-N-vinylcarbazole and its derivatives, poly-γ-carbazolylethylglutamate and its derivatives, pyrene-formaldehyde condensate and its derivatives, polyvinylpyrene, polyvinylphenanthrene, oxazole derivatives, and oxadiene. Azole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyryl) anthracene, 1,1-bis- (4-dibenzylaminophenyl) propane, styrylanthracene,
Electron-donating substances such as styrylpyrazolin, phenylhydrazones, and α-phenylstilbene derivatives are exemplified.

Examples of the electron transporting substance include chloranil, bromanil, tetracyanoethylene, tetracyanoquinonedimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorene. 2,4,5,7-tetranitroxanthone,
2,4,8-trinitrothioxanthone, 2,6,8-
Electron accepting substances such as trinitro-4H-indeno (1,2-b) thiophenone-4-one and 1,3,7-trinitrodibenzothiophenone-5,5-dioxide are exemplified. These charge transport materials are used alone or in combination of two or more.

As the binder resin used as required, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride Vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyacrylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-
Vinyl carbazole, acrylic resin, silicone resin,
Thermoplastic resins or thermosetting resins such as epoxy resins, melamine resins, urethane resins, phenolic resins, and alkyd resins.

As the solvent, tetrahydrofuran, dioxane, toluene, monochlorobenzene, dichloroethane, methylene chloride and the like are used.

The thickness of the charge transport layer is suitably about 5 to 100 μm. Further, a plasticizer or a leveling agent may be added to the charge transport layer. As the plasticizer, those used as general plasticizers for general resins such as dibutyl phthalate and dioctyl phthalate can be used as they are, and the amount of the plasticizer is suitably about 0 to 30% by weight based on the binder resin. As the leveling agent, silicone oils such as dimethyl silicone oil and methylphenyl silicone oil are used, and the amount of the silicone oil is suitably about 0 to 1% by weight based on the binder resin.

Even if these CGL and CTL are laminated on the support from the support side in the order of CGL and CTL, CTL, CTL
The layers may be laminated in the order of GL.

FIG. 4 is an example of a schematic cross-sectional view of an electrophotographic photosensitive member of the present invention and an electrophotographic process using the same.
In the figure, reference numeral 101 denotes an electrophotographic photosensitive member of the present invention, which is charged by a charging charger 102, then receives image exposure 103, contacts a developer via a developing roller 104, and forms a toner image. The toner image is transferred to a transfer member 105 such as paper by a transfer charger 106,
After passing through the fixing unit 109, a hard copy is formed. The residual toner on the electrophotographic photoreceptor 1 is removed by the cleaning unit 107, and the residual charge is removed from the charge removing lamp 108.
And move on to the next electrophotographic cycle.

Here, the image exposure 103 is analog image exposure for irradiating the reflected light of the copy original through a lens or a mirror, or an electric signal from a computer or the like, or an electric signal obtained by reading and converting the copy original with an image sensor such as a CCD. Any of digital image exposure for reproducing a signal or the like as an optical image by a laser beam, an LED array, or the like may be used.

The content of the crystal structure of titanium oxide used for the intermediate layer can be determined from the diffraction peak intensity by electron beam diffraction and X-ray diffraction.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1 A mixture having the following composition ratio was dispersed on an Al support (outer diameter: 30 mmΦ) by a ball mill for 72 hours, and the prepared intermediate layer forming liquid was dried so as to have a thickness of about 4.0 μm. Coating was performed by an immersion method to form an intermediate layer.

[Coating Liquid for Intermediate Layer] Alkyd Resin (Beccosol 1307-60-EL, manufactured by Dainippon Ink and Chemicals) 6 parts Melamine Resin (Super Beckamine G-821-60, manufactured by Dainippon Ink and Chemicals) 4 Part Titanium oxide (rutile-type titanium oxide content 98 wt%) 40 parts * The content mentioned here refers to the content of rutile-type titanium oxide in the total titanium oxide. Methyl ethyl ketone 200 parts On this intermediate layer, a charge generation layer coating solution containing a phthalocyanine pigment is applied by dip coating, dried at 70 ° C. for 10 minutes, and subjected to CGL.
Was formed.

[Coating Liquid for Charge Generating Layer] Oxotitanium phthalocyanine pigment 5 parts Polyvinyl butyral (UCC: XYHL) 2 parts Tetrahydrofuran 80 parts (Weight ratio) The diluted solvent is prepared with 500 parts by weight of the mixed solvent. Next, an organic photosensitive layer was prepared by dip coating the CGL with a charge transport layer coating solution having the following composition so that the film thickness after drying was about 30 μm.

[Coating solution for charge transport layer] Bisphenol A type polycarbonate (Teijin: Panlite C1400) 10 parts Low molecular charge transport material having the following structure 10 parts

[0041]

Embedded image 100 parts of dichloromethane

Example 2 Example 1 was repeated except that the content of rutile type titanium oxide in the titanium oxide used for the intermediate layer was 98.8 wt%.
In the same manner as in the above, a photoreceptor was produced.

Example 3 Example 1 was repeated except that the content of rutile titanium oxide in the titanium oxide used for the intermediate layer was 99.2 wt%.
In the same manner as in the above, a photoreceptor was produced.

Example 4 Example 1 was repeated except that the content of rutile type titanium oxide in the titanium oxide used for the intermediate layer was 99.6 wt%.
In the same manner as in the above, a photoreceptor was produced.

Comparative Example 1 A photoconductor was prepared in the same manner as in Example 1, except that the content of rutile-type titanium oxide in the titanium oxide used for the intermediate layer was 97.5 wt%.

Comparative Example 2 Example 1 was repeated except that the content of rutile type titanium oxide in the titanium oxide used for the intermediate layer was 96 wt%.
In the same manner as in the above, a photoreceptor was produced.

Comparative Example 3 Example 1 was repeated except that the content of rutile-type titanium oxide in the titanium oxide used for the intermediate layer was 90 wt%.
In the same manner as in the above, a photoreceptor was produced.

Comparative Example 4 A photoconductor was prepared in the same manner as in Example 1, except that the content of the rutile type titanium oxide in the titanium oxide used for the intermediate layer was 99.7 wt%.

Comparative Example 5 A photoconductor was prepared in the same manner as in Example 1, except that the content of rutile-type titanium oxide in the titanium oxide used for the intermediate layer was 99.9 wt%.

[Evaluation method of actual machine running characteristics] Each photoconductor was subjected to a paper-passing test of up to 80,000 sheets using a commercially available electrophotographic copying machine Imagio MF2200 (manufactured by Ricoh Co., Ltd.). The image quality characteristics of the photoreceptor at the initial stage and after the paper passing test, and the rise in the exposed portion potential in the machine were evaluated. It is shown in Table 1.

[0051]

[Table 1] * Ground dirt rank ... 1c of ground dirt (0.1 mm or more)
Number of generations per m ² 4 → → 0.2 / cm ² 3 → 0.2 / cm ² ~ 5.0 / cm ² 2 → 5.0 / cm ² 50.0 / cm ² 1 → 50.0 pieces / cm ^2- * △ VL (initial exposed portion potential) − (exposed portion potential after paper passing test)

As is clear from Table 1, the electrophotographic photoconductors of Examples 1 to 4 satisfying the claims of the present invention are:
It can be seen that there is little deterioration in image characteristics, and the exposure portion potential is very stable, and a high-quality hard copy can be stably obtained for a long period of time.

[0053]

As described above, according to the present invention, an electrophotographic photosensitive member having excellent image quality stability can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an electrophotographic photosensitive member of the present invention.

FIG. 2 is a cross-sectional view illustrating another configuration of the electrophotographic photosensitive member of the present invention.

FIG. 3 is a cross-sectional view showing still another configuration of the electrophotographic photosensitive member of the present invention.

FIG. 4 is a schematic view illustrating an example of an electrophotographic process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 ... Conductive support 23 ... Photosensitive layer 25 ... Intermediate layer 31 ... Charge generation layer 33 ... Charge transport layer 101 ... Photoconductor drum 102 ... Contact charging device 103 ..Image exposure 104: developing device 105: transfer member 106: contact transfer device 107: cleaning blade 108: static elimination lamp 109: fixing device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Satoshi Kurimoto 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H068 AA44 AA45 AA48 CA29 FA01 FA17 FB07

Claims (2)

[Claims] 1. An electrophotographic photosensitive member having a structure in which at least an intermediate layer and a photosensitive layer are sequentially laminated on a conductive support, wherein the intermediate layer is composed of at least titanium oxide and a resin, and the crystal structure of the titanium oxide is An electrophotographic photosensitive member having a rutile structure having a content of 98% or more and 99.6% or less. 2. An image forming apparatus comprising the electrophotographic photosensitive member according to claim 1.