JPH07191488A - Electrophotographic photoreceptor for liquid development - Google Patents

Abstract

PURPOSE:To obtain a picture image of extremely high quality by regular or reversal development of an electrophotographic photoreceptor for liquid development having an org. photoconductive layer on a conductive supporting body comprising aluminum or aluminum alloy, by forming an anodically oxidized film on the surface of the conductive supporting body and specifying the film thickness of the photoconductive layer. CONSTITUTION:The photoconductive layer is formed on a conductive supporting body which consists of aluminum or aluminum alloy, and an anodically oxidized film is formed on the surface of the supporting body. Before the anodically oxidized film is formed, the aluminum supporting body is degreased by various degreasing and cleaning methods. The anodically oxidized film is formed by anodic oxidation treatment in an acid bath, and the best result is obtd. by using a sulfuric acid bath. The average film thickness of the anodically oxidized film is preferably between <=15mum and >=5mum. The photoconductive layer consists of laminated layers of a charge producing layer and a charge transfer layer. The film thickness of the charge transfer layer is >=19mum, and preferably between >=22mum and <=45mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoreceptor for liquid development. More specifically, the present invention relates to an electrophotographic photosensitive member used in a copying machine, an optical printer or the like, which forms an image by an electrophotographic process utilizing a liquid developing method.

[0002]

2. Description of the Related Art Electrophotographic technology has been widely used and applied not only in the field of copying machines but also in the field of various printers in recent years because of its ability to obtain images of instant quality and high quality. Photoreceptors, which are the core of electrophotographic technology, have recently been formed as pollution-free inorganic photoconductors such as selenium, arsenic-selenium alloy, cadmium sulfide, and zinc oxide. A photoreceptor using an organic photoconductive material, which has advantages such as easy and easy manufacture, has been developed.

Among organic photoconductors, a so-called laminated type photoconductor in which a charge generation layer and a charge transport layer are laminated has been devised and is the mainstream of development. The multi-layered photoconductor is a high-sensitivity photoconductor obtained by combining a highly efficient charge-generating substance and a charge-transporting substance, and a photoconductor having a wide selection range of materials and high safety, Further, since the coating productivity is high and the cost is comparatively advantageous, the possibility of becoming the mainstream of the photoreceptor is high and the coating has been earnestly developed.

On the other hand, in recent years, with the aim of improving image quality such as resolution and halftone reproducibility, in terms of hardware, electrophotographic technology,
That is, although digitization of reading elements, writing elements, image processing devices, etc. is rapidly progressing, it is well known to use liquid development as a means for achieving higher image quality than before. In the liquid development, the toner particles can be made extremely fine as compared with the normal dry development, so that high resolution and good image reproducibility can be obtained. The liquid developer is usually one in which a dye / pigment and polymer particles are dispersed in a highly electrically insulating medium (solvent) for coloring, and a charge control agent is added to this to impart a predetermined charge. However, while high resolution can be obtained by performing liquid development, it becomes easier to reproduce a non-uniform portion due to defects in the photoconductor on the image more faithfully than in dry development. Therefore, a higher quality photoreceptor is required for the liquid development. In particular, when a laminated organic photoconductor, which is currently the mainstream as a photoconductor, is used, the charge generation layer is formed with a relatively thin film thickness, so that dirt or defects on the surface of the substrate, such as cutting scratches or impurities. It is easily affected by those derived from metals. In addition, the charge generation layer is generally formed by dispersing pigment particles in a binder in many cases, but in such a case, coating defects such as foreign matter, repellency, and agglomerates are likely to occur. It tends to appear as an image defect.

On the other hand, as an image forming method in an optical printer, for the purpose of effectively utilizing light or enhancing the resolution, a so-called reversal development method in which toner is attached to a portion irradiated with light to form an image is adopted. Many. In the reversal development process, the dark potential part becomes a white background and the bright potential part becomes a black background part (image area). However, in this system, if there is a local charging failure due to a defect on the photoconductor, When there are many black spots or a large number of them, a phenomenon called background fog occurs, which causes a remarkable image defect.

Such a local charging failure is likely to cause an image failure in reversal development even if it is at a level where there is no problem when used in regular development. There are various possible causes for this problem, namely, local charging failure. However, due to the local injection of charges between the conductive support that is an electrode and the photosensitive layer, the charging potential does not rise. It is thought that the main cause is.

As an organic photoreceptor which can be used for liquid development, a binder obtained by mixing an acrylic resin and a vinyl resin which are substantially insoluble in a paraffinic petroleum solvent has been used (Japanese Patent Publication No. 53-11856). An example of using an insoluble resin in a liquid developer as an overcoat layer (JP-A-52-89328) and an example of using a thermotropic liquid crystalline resin have been reported. Each of these is a type of photoreceptor formed by binding with a binder resin, and the binder resin causes softening, swelling, cracking, etc. of the photoreceptor due to contact or immersion in the solvent used for the liquid developer. Degradation (solvent resistance)
Nothing is said about images when these photoreceptors are used in a liquid development process.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic photoconductor that always obtains good image quality in a liquid development process in which a very high quality image is obtained in regular or reversal development. To provide.

[0009]

A blocking layer is provided between the photosensitive layer and the conductive support in order to reduce the coating defects of the photosensitive body and to suppress the injection of charges from the conductive support as described above. It is well known. Examples of such a blocking layer include inorganic layers such as aluminum oxide and aluminum hydroxide, polyvinyl alcohol, casein, sodium caseinate, polyvinylpyrrolidone, polyacrylic acid, celluloses, gelatin, starch, polyurethane, polyimide, polyamide and other organic resins. Layers are used. The present inventors have conducted various studies on the effects of such various blocking layers in the liquid development process. As a result, the one having an anodized film on the surface of a conductive support made of aluminum or an aluminum alloy is most effective. Found to give a very good image. In addition, the appearance of minute black spot defects on a white background image when such reversal development is performed also depends on the film thickness of the photosensitive layer, and the thicker the smaller the appearance of minute black spots is. I understood. In the case of ordinary dry development, such an image defect was hardly caused by only providing the anodic oxide coating, but this was not sufficient in the liquid development system. Therefore, as a result of detailed examination of the dependency on the film thickness of the photosensitive layer, it was found that a very good image can be obtained even in liquid development by setting the thickness to 19 μm or more, and the present invention was reached. This is considered to be because by increasing the thickness of the photosensitive layer, the electric field strength on the electrode surface is weakened and the charge injection from the electrode can be weakened when the surface potential of the photoconductor is the same. That is, the gist of the present invention is to provide a liquid developing electrophotographic photoreceptor having at least an organic photoconductive layer on a conductive support made of aluminum or an aluminum alloy, wherein the conductive support surface has an anodized film. And the photoconductive layer has a film thickness of 19 μm or more.

The present invention will be described in detail below. The photoconductive layer of the present invention is provided on a conductive support. Aluminum or an aluminum alloy is used as the conductive support. As a material of aluminum, for example, A105
0, A3003, A6063, etc. can be used.

Such an aluminum support is preferably subjected to degreasing treatment by various degreasing and washing methods such as acid, alkali, organic solvent, surfactant, emulsion and electrolysis before forming the anodized film according to the present invention. . The anodized film is usually formed by anodizing in an acidic bath of chromic acid, sulfuric acid, oxalic acid, boric acid, sulfamic acid, etc., but anodizing in sulfuric acid gives the best results. give.

In the case of anodization in sulfuric acid, the sulfuric acid concentration is 1
00-300g / l, dissolved aluminum concentration is 2-15g /
1, the liquid temperature is 10 to 30 ° C., the electrolysis voltage is 5 to 20 V, and the current density is preferably 0.5 to ² A / dm ² . The average thickness of the anodized film is usually 15 μm or less and preferably 5 μm or more. If the film thickness is too thin, the effect as a blocking layer decreases,
Fogging tends to occur particularly when used in the reversal liquid development process. On the other hand, if the thickness is too large, the cost for forming the anodic oxide coating becomes high, and the anodic oxide coating is prone to cracks, and the cracks are likely to appear on the image.

The anodic oxide coating thus formed is
For example, a low-temperature sealing treatment of immersing in an aqueous solution containing nickel fluoride as a main component or a high-temperature sealing treatment of immersing in an aqueous solution containing nickel acetate as a main component is performed. The concentration of the nickel fluoride aqueous solution used in the case of the low temperature sealing treatment can be appropriately selected, but it is 3 to 6 g / l.
It is most effective when used within the range.

In order to smoothly carry out the sealing treatment,
The treatment temperature is 25 to 50 ° C., preferably 30 to 35
And the pH of the nickel fluoride aqueous solution is 4.5 to 6.
5 It is good to treat in the range of 5.5 to 6.0. As the pH adjuster, oxalic acid, boric acid, formic acid, acetic acid, caustic soda, sodium acetate, aqueous ammonia, etc. can be used.

The treatment time is preferably within the range of 1 to 3 minutes per 1 μm of the average film thickness of the coating. In order to further improve the physical properties of the coating, nickel fluoride, cobalt acetate, nickel sulfate, a surfactant, etc. may be added to the nickel fluoride aqueous solution. As the sealing agent for the high temperature sealing treatment, an aqueous solution of a metal salt of nickel acetate, cobalt acetate, lead acetate, nickel acetate-cobalt, barium nitrate or the like can be used, but nickel acetate is particularly preferably used.

When using an aqueous solution of nickel acetate, the concentration is preferably within the range of 3 to 20 g / l.
Treatment temperature is 65 to 100 ° C, preferably 80 to 98 ° C
The pH of the aqueous nickel acetate solution is preferably in the range of 5.0 to 6.0. Here, as the pH adjusting agent,
Ammonia water, sodium acetate, etc. can be used. Also in this case, sodium acetate, an organic carboxylate, an anionic surfactant, a nonionic surfactant and the like may be added to the nickel acetate aqueous solution in order to improve the physical properties of the coating.

It is preferable that the sealing-processed anodized film formed as described above is subsequently thoroughly washed with water and dried. Further, various surface contaminations occur in the steps of anodic oxidation, sealing, and washing with water. Therefore, it is desirable to perform a physical contact rubbing washing treatment to finally obtain a clean surface. In this rubbing cleaning, it is preferable to use the following rubbing materials in a brush shape, a foam shape, or a cloth shape.

As the rubbing material, cotton, rayon, cellulose, natural fibers such as wool, polyester, nylon,
Synthetic fibers such as acrylic and acetate, thermoplastic foam such as polystyrene, polyethylene and polypropylene, and thermosetting plastic foam such as polyurethane and polyurea can be used. As the rubbing cleaning method, these rubbing materials are brought into contact with the anodized film, and while supplying a solvent such as water, methanol, isopropanol, etc., the rubbing material is mechanically or manually rotated while cleaning, or reciprocating. How to scrub and wash,
A method of reciprocating while rotating and cleaning can be used.

The photoconductive layer may be formed by stacking a charge generation layer and a charge transport layer in this order, or by stacking them in the opposite order, or by using a so-called dispersion type in which charge generation material particles are dispersed in a charge transport medium. You can In the case of a laminated photoconductive layer, the charge generating material used in the charge generating layer includes selenium and its alloys, arsenic-selenium, cadmium sulfide, zinc oxide, other inorganic photoconductive materials, phthalocyanines, azo dyes, quinacridones, and many other materials. Various organic pigments and dyes such as ring quinone, pyrylium salt, thiapyrylium salt, indigo, thioindigo, anthanthrone, pyranthrone and cyanine can be used. Among them, metal-free phthalocyanines, copper, indium chloride, gallium chloride, tin, oxytitanium, zinc, vanadium, and other metals or oxides thereof, chloride-coordinated phthalocyanines, monoazo, bisazo, trisazo, polyazo, etc. Azo pigments are preferred. In particular, oxytitanium phthalocyanine, for example, JP-A-63-218768, 62-134651, 2-
Those showing an X-ray diffraction pattern described in JP-A-2-111955 and the like, metal-free phthalocyanine of x type or τ type, bisazo pigments and the like are preferable. The charge generation layer contains fine particles of these substances, such as polyester resin,
Binding with various binder resins such as polyvinyl acetate, polyacrylic acid ester, polymethacrylic acid ester, polyester, polycarbonate, polyvinyl acetoacetal, polyvinyl propional, polyvinyl butyral, phenoxy resin, epoxy resin, urethane resin, cellulose ester, and cellulose ether. It may be used in the form of a dispersion layer. Among them, polyvinyl acetals such as polyvinyl acetoacetal and polyvinyl butyral, phenoxy resin, vinyl chloride resin and the like are particularly preferable. In this case, the usage ratio is usually 30 to 500 parts by weight with respect to 100 parts by weight of the binder resin, and the film thickness is usually 0.1 μm to 2 μm, preferably 0.15 μm to 0.8 μm. Is. Further, the charge generation layer may contain various additives such as a leveling agent, an antioxidant and a sensitizer for improving the coating property, if necessary. The charge generation layer may be a vapor deposition film of the above charge generation substance.

The charge transport layer may be of any type, such as a type in which a low molecular weight charge transport material is dispersed in a binder resin, a polymer type charge transport layer, or the like. As the low molecular weight charge transporting substance, there are known electron withdrawing substances such as 2,4,7-trinitrofluorenone and tetracyanoquinodimethane.
Heterocyclic compounds such as carbazole, indole, imidazole, oxazole, pyrazole, oxazoazole, pyrazoline, and thiadiazole, electron-donating substances such as aniline derivatives, hydrazone compounds, aromatic amine derivatives, and stilbene derivatives can be used as a polymer-type charge transport layer. It can be selected from electron-withdrawing substances or electron-donating substances such as polymers having groups consisting of these compounds in the main chain or side chains. Among them, hydrazone compounds having excellent sensitivity and responsiveness, such as the exemplified compound N shown below
o.1-16, stilbene compounds, such as No. 17-2
2. It is preferable to use aromatic amine compounds such as Nos. 23 to 30.

[0021]

[Chemical 1]

[0022]

[Chemical 2]

[0023]

[Chemical 3]

[0024]

[Chemical 4]

[0025]

[Chemical 5]

[0026]

[Chemical 6]

[0027]

[Chemical 7]

Among them, in order to have sufficient solvent resistance in liquid development, for example, a charge transporting substance having a relatively low solubility in a specific solvent, as described in Japanese Patent Application No. 5-70089, or a Japanese Patent Application. Flat 5-87380
Glass transition temperature as described in Japanese Patent Publication No.
It is preferable to use a charge transport material having a temperature of not less than ° C.

Examples of the binder resin used in the charge transport layer include vinyl polymers such as polymethylmethacrylate, polystyrene and polyvinyl chloride, and copolymers thereof, polycarbonate, polyester, polyester carbonate, polysulfone, polyimide, phenoxy,
Examples thereof include epoxy resins and silicone resins, and partially cross-linked cured products thereof can also be used.

The ratio of the binder resin to the charge transport material is usually 30 with respect to 100 parts by weight of the binder resin.
To 200 parts by weight, preferably 40 to 150 parts by weight. Further, the charge transport layer may contain various additives such as an antioxidant and a sensitizer, if necessary. The charge transport layer has a thickness of 19 μm or more, preferably 22 μm or more and 45 μm or less. As the outermost surface layer, a conventionally known overcoat layer mainly composed of a thermoplastic or thermosetting polymer may be provided. Usually, the charge transport layer is formed on the charge generation layer, but the reverse is also possible. As a method for forming each layer, a known method such as sequentially coating a coating solution obtained by dissolving or dispersing a substance contained in the layer in a solvent can be applied.

In the case of the dispersion type photoconductive layer, the above-mentioned charge generating substance is dispersed in the matrix containing the charge transporting substance having the above-mentioned compounding ratio as the main component. In that case, the particle size needs to be sufficiently small, and the particle size is preferably 1 μm or less, more preferably 0.5 μm or less. If the amount of the charge generating substance dispersed in the photosensitive layer is too small, sufficient sensitivity cannot be obtained, and if it is too large, there are adverse effects such as a decrease in charging property and a decrease in sensitivity. For example, preferably 0.5 to 50% by weight. %, More preferably 1-20% by weight. The thickness of the photosensitive layer is 20 μm or more, preferably 22 μm or more and 45 μm or less. Also in this case, known plasticizers for improving film-forming properties, flexibility, mechanical strength, etc., additives for suppressing residual potential, dispersion aids for improving dispersion stability, and coating properties are used. Leveling agents and surface active agents such as silicone oil, fluorine-based oil and other additives may be added for improvement.

[0032]

INDUSTRIAL APPLICABILITY An electrophotographic photosensitive member for liquid development, which uses aluminum or aluminum alloy having an anodized film according to the present invention as a conductive support and has a photoconductive layer having a film thickness of 19 μm or more, is regular or inverted. When used in any process of liquid development, a good image with very few image defects can be obtained.

Further, even when it is repeatedly used, the image quality hardly deteriorates, and a stable image can be always obtained. Therefore, it can be widely used in black and white and color copiers and printers using liquid development without any problem.

[0034]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the invention is not limited thereto.

Example 1 A 1 mm thick aluminum cylinder having a mirror-finished surface was used as a degreasing agent, NG- # 30 [made by Kizai Co., Ltd.].
Degreasing was performed for 5 minutes at 60 ° C. in a g / l aqueous solution.
Then, after washing with water, it was immersed in 7% nitric acid at 25 ° C. for 1 minute. After further washing with water, anodic oxidation was performed at a current density of 1.2 A / dm ² in a sulfuric acid electrolytic solution of 180 g / l (dissolved aluminum concentration 7 g / l) to form an anodic oxide coating having an average film thickness of 8 μm. Then, after washing with water, a sealing treatment was carried out by immersing in a 10 g / l aqueous solution of a high-temperature sealing agent Topseal DX-500 (manufactured by Okuno Chemical Industries Co., Ltd.) containing nickel acetate as a main component at 95 ° C. for 30 minutes. After washing with water,
Using a polyester sponge, the entire surface of the coating film was reciprocated three times for rubbing and cleaning. Then, it was washed with water and dried.

Next, the powder X by the line of CuX shown in FIG.
1,2 parts by weight of oxytitanium phthalocyanine having a line spectrum pattern and polyvinyl butyral (Sekisui Chemical Co., Ltd., S-REC BH-3) 5 parts by weight.
-Adding 500 parts by weight of dimethoxyethane, pulverizing and dispersing with a sand grind mill. An aluminum cylinder provided with an anodic oxide coating formed previously was applied by dip coating to this dispersion liquid, and a charge generation layer was provided so that the film thickness after drying was 0.4 μm. Next, this aluminum cylinder was mixed with 60 parts by weight of the following hydrazone compound,

[0037]

[Chemical 8] And 1.5 parts by weight of cyano compound

[0038]

[Chemical 9]

Also, 100 parts by weight of a polycarbonate resin [viscosity average molecular weight 30,000] shown below was immersed in a solution prepared by dissolving 1000 parts by weight of 1,4-dioxane,
The charge transport layer was provided so that the film thickness after drying was 20 μm. The drum thus obtained is referred to as a photoconductor A.

[0040]

[Chemical 10]

Example-2 A photoconductor B was prepared in the same manner as in Example-1, except that the thickness of the charge transport layer in Example-1 was 23 μm.

Example-3 A photoconductor C was prepared in the same manner as in Example-1 except that the thickness of the charge transport layer in Example-1 was changed to 25 μm.

Comparative Example-1 Comparative Photoreceptor D was prepared in the same manner as in Example-1 except that the thickness of the charge transport layer in Example-1 was 17 μm.

Comparative Example-2 A photoconductor E was prepared in the same manner as in Example-1, except that an aluminum cylinder having a mirror-finished surface and a thickness of 1 mm was used as the conductive support.

Each of the photoconductors prepared as described above is
It was mounted on a prototype laser printer consisting of an inversion liquid development process, and the development contrast potential was 400-600.
The image was evaluated by changing to V. Table 1 shows the evaluation results of the stains (fogging) on the obtained white background image portion.

[0046]

[Table 1] Explanation of symbols ◎: Very good image without any fog. ◯: Good image Δ: Fairly good image, although fogging is seen in only a part. ×: The whole is covered. XX: The entire surface is fogged and the contrast with the black background is very small.

As is clear from the above results, it is understood that a very good image can be obtained by the liquid developing photoreceptor of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hajime Kojima 1060 Narita, Odawara-shi, Kanagawa Mitsubishi Kasei Corporation Odawara Works

Claims (2)

[Claims] 1. A liquid developing electrophotographic photoreceptor having at least an organic photoconductive layer on a conductive support made of aluminum or an aluminum alloy, wherein the conductive support surface has an anodized film. And a photoconductive layer having a film thickness of 19 μm or more. 2. The electrophotographic photoreceptor for liquid development according to claim 1, wherein the organic photoconductive layer comprises a charge generation layer and a charge transport layer.