JPH0549233B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an electrophotographic photoreceptor, which is used in an electrophotographic system known as the Carlson process, and is formed by providing a photoconductive layer and a surface layer on a support.

(Prior art) Conventionally used electrophotographic photoreceptors include Se, Se-Te alloy, Se-As as a photosensitive layer on a conductive substrate.
Typical examples include those formed by vapor-depositing an alloy or the like, or those coated with an organic photoconductor such as polyvinylcarbazole or 2,4,7-trinitrofluorenone. However, when using these photoconductors repeatedly, they are easily damaged by peeling off the transfer paper or cleaning residual toner, and the photoconductor layer is also prone to wear, so the photoconductor may be used at a relatively early stage before its characteristics deteriorate. I had to replace it. In order to improve this point, it is known to provide a surface layer on the surface of the photoreceptor. One of the surface layers is an insulating layer made of a material with relatively high electrical insulation. This insulating layer has the advantage of being able to be made thick and having high mechanical strength. However, in order to use such a photoreceptor repeatedly, it is necessary to
A special latent image forming process is required, such as secondary charging → reverse polarity secondary charging → image exposure or primary charging → secondary charging simultaneous image exposure → uniform exposure, etc. In each copying process, two or more charging exposures are required, resulting in a complicated apparatus, resulting in unstable characteristics and increased costs. There is also a protective layer as a surface layer that does not require the above-mentioned special latent image forming process and can use the so-called Carlson process of charging→image exposure. This protective layer needs to have low insulation to prevent charge from accumulating on or inside the protective layer. The method that has been used so far is to add quaternary ammonium salts etc. to the protective layer, but the conductivity of these materials generally fluctuates widely due to moisture absorption, and the protective layer deteriorates when dry. As the conductivity decreases and charge accumulates,
Fog occurs on the image, and when the temperature is high, the conductivity increases more than necessary, causing charge to move in the lateral direction, causing blur in the image. Furthermore, in order to use the conventional protective layer in the Carlson process, it must be relatively thin, with a film thickness of several microns or less, which is difficult to satisfy in terms of mechanical strength, and requires low insulation. The protective layer is colored by the substances added for
This had an undesirable effect on the spectral sensitivity of the photoreceptor.

Attempts to obtain a protective layer by adjusting conductivity by dispersing conductive powder in a binder resin are known, for example, in JP-A-53-3338 and JP-A-53-44028.

(Problems to be Solved by the Invention) However, in the case described in the above publication, when carbon or metal is dispersed, light absorption is strong and it is difficult to increase conductivity while maintaining transparency. . Also, when particles such as zinc oxide or titanium oxide that do not absorb visible light are dispersed,
Although there is no absorption of light, due to the non-uniformity of the refractive index,
Light transmitted through the film is strongly dispersed and appears cloudy, and the film is not sufficiently conductive. On the other hand, when a fairly large amount of metal oxide fine powder is incorporated into a resin to improve conductivity, there is a drawback that permeability is impaired.

The present invention has been made in view of the above-mentioned problems in the conventional technology.

Therefore, the present invention relates to an electrophotographic photoreceptor having an improved surface layer for use in the Carlson process, which exhibits less charge accumulation even when used repeatedly, and which can withstand environmental conditions varying from low humidity to high humidity. The object of the present invention is to provide an electrophotographic photoreceptor that operates stably even under the following conditions. In particular, it is an object of the present invention to provide an electrophotographic photoreceptor having a surface layer with excellent light transmittance.

(Means and effects for solving the problems) The above-mentioned object of the present invention is to provide an electrophotographic photoreceptor having a photoconductive layer and a surface layer on a support, in which a metal oxide is contained in the binder resin of the surface layer. This can be achieved by dispersing metal oxide fine particles that are elliptical, columnar, or scale-like fine particles and have a ratio of the length of the long axis to the short axis in the range of 2.0 to 20.0.

In the present invention, the fine powder metal oxide to be dispersed in the binder resin is not particularly limited as long as it has conductivity, and non-magnetic metal oxides and magnetic metal oxides can be used. Either one can be used.

Examples of non-magnetic metal oxides include ZnO, _TiO2 ,
Examples include SnO ₂ , InO ₂ , BiO ₂ , etc., but tin oxide powder is preferred. An example of a tin oxide-based powder is a fine powder containing antimony oxide fused to tin oxide or as a solid solution. The amount of impurities contained in the tin oxide can be selected in the range of 0.001% to 30% and is chosen to lower the dark resistance of the fine powder.

Examples of magnetic metal oxides include γ-Fe ₂ O ₃ ,
Examples include CrO ₂ and Co-γ-Fe ₂ O ₃ .

In the present invention, these metal oxides are composed of fine particles having an ellipsoidal, columnar or scale-like shape, and have a long axis and a short axis, and the long axis is different from the short axis of the fine particles. The length ratio is in the range of 2.0 to 20.0. If the ratio of the length of the long axis to the short axis is greater than 20.0, it will be difficult to produce fine powder and the stability during coating will be poor; If it's small,
Since the above-mentioned object of the present invention cannot be achieved,
It is necessary that the ratio of the length of the long axis to the short axis is within the above range. In addition, if the length of the major axis is 0.3 μm or less, preferably 0.15 μm or less,
This is preferable because a surface layer with better light transmittance is formed.

The metal oxide fine particles can be directly dispersed in the binder resin, but may be surface-treated with a surfactant or a coupling agent to improve dispersibility.

The binder resin that can be used for the surface layer in the present invention is preferably one that is transparent to visible light and has excellent electrical insulation, mechanical strength, and adhesive properties, such as polyester resin, polycarbonate resin,
Examples include polyurethane resin, epoxy resin, acrylic resin, vinyl chloride-vinyl acetate copolymer, silicone resin, alkyd resin, polyvinyl chloride resin, cyclized butadiene rubber, and fluorine resin. Furthermore, when solvent resistance of the surface layer is required, it is desirable to use a curable resin.

The composition ratio of the binder resin and the metal oxide fine particles in the surface layer varies depending on the combination of materials, but usually the metal oxide is in the range of 5 to 100 parts by weight per 100 parts by weight of the binder resin. use

In the present invention, the thickness of the surface layer is suitably in the range of 1 to 30 μm. However, since the generation of charge carriers by light takes place in the photoconductive layer, the surface layer must be substantially transparent to the wavelength range of light to which the photoconductive layer is sensitive.

In the present invention, when magnetic fine powder is used as the metal oxide, it is recommended to apply a magnetic field during coating to orient the magnetic metal oxide fine powder so that its long axes are aligned perpendicularly in the surface layer. preferable. This orientation treatment makes it possible to vertically bias the electrical conduction of the surface layer, which not only improves potential stability during repeated use, but also reduces light scattering in the surface layer. It has excellent light transmittance.

As the support in the electrophotographic photoreceptor of the present invention, known supports can be used. For example, conductive supports such as aluminum, stainless steel, etc.
and insulating supports made of synthetic resins such as polyethylene terephthalate and polycarbonate. When using an insulating support, it is desirable to conduct a conductive treatment on the surface on which the photoconductive layer is provided.

As the photoconductive layer in the electrophotographic photoreceptor of the present invention, various known materials can be used, and photoconductors that have low mechanical strength and cannot be used in ordinary electrophotographic methods can also be used. for example,
Se, Se-Te alloy, Se-As alloy, Se-Sb alloy,
Vapor deposited film such as Se-Bi alloy, organic photoconductor layer such as polyvinylcarbazole-2,4,7-trinitrofluorenone, a-Si photoreceptor layer, ZnO, CdS
A photosensitive layer having an inorganic photoconductor dispersed in a binder resin, or a laminated layer of a charge generation layer and a charge transport layer can be used.

In the electrophotographic photoreceptor of the present invention, an intermediate layer may be provided between the surface layer and the photoconductive layer, if necessary, in order to improve adhesion or charge retention. The intermediate layer must have a higher resistance than the surface layer, which is at least a low insulating layer.
In addition to the role of the charge injection blocking layer, the intermediate layer can also function as an adhesive layer between the photoconductive layer and the surface layer. Materials suitable for the intermediate layer include those whose main component is a polymer compound or those whose main component is an inorganic compound. Examples of polymeric compounds include epoxy resin, polyester resin, polyamide resin, polyurethane resin, nitrified cotton, vinylidene chloride resin, silicone resin, and resin, and examples of inorganic compounds include zirconium oxide, silica, Se , S, As ₂ O ₃ and the like. The intermediate layer is formed by any method, such as painting, and its thickness is arbitrarily set, but is preferably 3 μm or less, particularly 1 μm or less.

The electrophotographic photoreceptor of the present invention is basically different from a photoreceptor known as a conventional laminated photoreceptor in which a photoconductive layer is provided on a conductive support and an insulating layer is provided thereon. different. That is, in the electrophotographic photoreceptor of the present invention, a charge pattern is formed between the conductive surface layer/photoconductive layer interface and the conductive support. In contrast, in a conventional photoreceptor having an insulating layer on its surface, charge patterns are formed above and below the insulating layer. Furthermore, in the surface layer of the present invention, electrical charges must be injected from the surface to the interface between the surface layer and the photoconductive layer, but in a laminated photoreceptor in which an insulating layer is present, the charges must remain on the surface. Furthermore, it must have a thinner film thickness than the photoconductive layer so that a sufficient potential difference is generated between the bright and dark areas, and therefore the function of the layer and the properties of the interface must be In this case, something different from that in the present invention is required.

(Example) Next, the present invention will be explained with reference to examples.

Example 1 100 parts by weight of polycarbonate resin (Teijin Kasei: Panlite), the major axis/minor axis ratio was 4, and the major axis was
Put 40 parts by weight of conductive powder (ELCOM, Catalysts & Chemicals Co., Ltd.) mainly composed of tin oxide with a size of 0.5 μm or less and 300 parts by weight of monochlorobenzene into an attritor.
The mixture was mixed and dispersed for 1 hour to obtain a dispersion liquid. On the other hand, 60 μm of As ₂ Se ₃ was deposited on an aluminum pipe with a smooth surface.
A photosensitive layer was formed by vapor deposition to a thickness of 0.2 μm, and a charge retention layer made of zirconium oxide and having a thickness of 0.2 μm was provided thereon by heating a zirconium oxide-butyl alcohol mixed system. The above dispersion was applied onto this charge retention layer and dried to form a surface layer with a thickness of 7 μm to obtain an electrophotographic photoreceptor. When an image was formed using this electrophotographic photoreceptor, a good copy image was obtained.

Comparative Example An electrophotographic photoreceptor having a surface layer with a thickness of 7 μm was prepared in the same manner as in Example 1, except that the conductive powder in Example 1 was replaced with a conductive powder containing tin oxide as a main component and having a particle size of 0.15 μm. I got it.

Example 2 An electrophotographic photoreceptor was obtained in the same manner as in Example 1, except that 40 parts by weight of the conductive powder in Example 1 was replaced with 35 parts by weight. When an image was formed using this electrophotographic photoreceptor, a good copy image was obtained.

In Examples 1 and 2, the electrophotographic photoreceptors of Comparative Examples were installed in an FX4370 copying machine (manufactured by Fuji Xerox Co., Ltd.), and the residual potential at the 500th cycle was measured, and the following results were obtained.

Residual potential Example 1 39V Example 2 46V Comparative example 53V From the above results, the electrophotographic photoreceptor of Example 1 has a significantly lower residual potential than that of the comparative example, and the amount of conductive powder It was found that the residual potential of Example 2, which was obtained by reducing the amount of the residual potential, was also lower than that of Comparative Example.

Example 3 100 parts by weight of polycarbonate resin, 50 parts by weight of γ-Fe ₂ O ₃ with a major axis/minor axis ratio of 5 and a major axis of 0.2 μm, and 200 parts by weight of monochlorobenzene were placed in a ball mill and dispersed for 40 hours. A dispersion was obtained. This dispersion was applied by dip coating onto the charge retention layer formed in the same manner as in Example 1, and after applying a magnetic field perpendicular to the surface layer to the drum surface, it was dried to form a film with a thickness of 5 μm. An electrophotographic photoreceptor having a surface layer was obtained. Although the residual potential of this electrophotographic photoreceptor was slightly higher than that of the above-mentioned comparative example, the light transmittance of the film was good, and the sensitivity increased by about 10%. When images were formed using this material, good copies were obtained.

(Effects of the Invention) As described above, in the electrophotographic photoreceptor of the present invention, the surface layer includes ellipsoidal, columnar, or scaly fine particles of metal oxide, and the length of the long axis of the fine particles is different from the short axis of the fine particles. Since we use particles with a ratio in the range of 2.0 to 20.0, we can increase the conductivity of the surface layer with less metal oxide content and have less residual potential compared to conventional spherical particles. This produces an excellent effect. Therefore, according to the present invention, not only is it possible to obtain an electrophotographic photoreceptor having a surface layer having a desirable volume resistivity value as a protective layer, but also it is possible to obtain a An electrophotographic photoreceptor with excellent potential stability can be obtained.

Furthermore, the electrophotographic photoreceptor of the present invention has the following advantages compared to conventionally known ones. That is, (1) a latent image can be formed without using any special process; (2) There is almost no accumulation or increase in residual charge even after repeated use. (3) Not easily affected by temperature and humidity. (4) The thickness of the surface layer can be made relatively thick. (5) It does not substantially affect the photosensitivity of the photoconductive layer.

Claims (1)

[Scope of Claims] 1. In an electrophotographic photoreceptor having a photoconductive layer and a surface layer on a support, the surface layer is made by dispersing elliptical, columnar, or scale-like fine particles of a metal oxide in a binder resin. An electrophotographic photoreceptor characterized in that the ratio of the length of the long axis to the short axis of the fine particles is in the range of 2.0 to 20.0. 2. The electrophotographic photoreceptor according to claim 1, wherein the metal oxide is a magnetic powder and is oriented in the direction of the magnetic field.