JPH04258963A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To provide an electrophotographic sensitive body having high mechanical strength and capable of forming high-quality stable images over a long period of time. CONSTITUTION:This electrophotographic sensitive body has a surface protecting layer contg. curable polyol polyurethane resin as binding resin and formed by dissolving fine metal or metal oxide powder in a polyol prepolymer having 20,000-50,000wt. average mol.wt., adding a polyisocyanate curing agent and carrying out coating, drying and curing.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoreceptor having a surface protective layer.

0002

[Prior Art] Conventionally, electrophotographic photoreceptors have been prepared by providing a photoconductive layer mainly made of selenium or a selenium alloy on a conductive support, or by using an inorganic photoconductive material such as zinc sulfide or cadmium oxide as a binder. dispersed in poly-
Those using organic photoconductive materials such as N-vinylcarbazole and trinitrofluorenone or azo pigments, and those using amorphous silicon are generally known.

[0003]Requirements for the reliability of these photoreceptors to maintain high image quality over a long period of time are increasing year by year. However, when the photoconductive layer is exposed, damage caused by corona discharge during the charging process and physical or chemical damage caused by contact with other members during the copying process shorten the life of the photoreceptor. As a method for eliminating such drawbacks, a technique is known in which a protective layer is provided on the surface of the photoreceptor. Specifically, a method of providing an organic film on the surface of a photosensitive layer (Japanese Patent Publication No. 38-154
46), Method of providing inorganic oxide (Japanese Patent Publication No. 43-145
17), a method of laminating an insulating layer after providing an adhesive layer (Japanese Patent Publication No. 43-27591), or a plasma CVD method
A method of laminating a-Si layer, a-Si:N:H layer, a-Si:O:H layer, etc. by photo-CVD method etc.
179859, Japanese Patent Application Laid-Open No. 59-58437).

However, if the protective layer has a high electrophotographic resistance (more than 10 14 Ω·cm), problems such as an increase in residual potential and accumulation during repeated use occur, which is not desirable in practice. As a technique to compensate for the above drawbacks, a method of using a photoconductive layer as a protective layer (Japanese Patent Publication No. 48-38427, Japanese Patent Publication No. 43-16198,
Special Publication No. 49-10258, USP-2901348),
A method of adding a transfer agent such as a dye or a Lewis acid to the protective layer (Japanese Patent Publication No. 44-834, Japanese Patent Application Laid-Open No. 53-13344)
4), or a method of controlling the resistance of the protective layer by adding metal or metal oxide fine particles (Japanese Unexamined Patent Publication No. 53-3338) has been proposed.

However, in such a case, light is absorbed by the protective layer and the amount of light reaching the photoconductive layer is reduced, resulting in a problem that the sensitivity of the electrophotographic photoreceptor is reduced. From this perspective, Japanese Patent Application Laid-Open No. 57-308
There is a method of making the surface substantially transparent to visible light by dispersing fine metal oxide particles having an average particle size of 0.3 μm or less as a resistance control agent in the surface protective layer as disclosed in Japanese Patent No. 46. An electrophotographic photoreceptor having this surface protective layer exhibits little decrease in sensitivity, and the surface protective layer has increased mechanical strength and improved durability. However, during long-term use, there is a problem in that the protective layer is scratched by the separation claw or the contact portion with paper dust, resulting in white streaks on the image.

[0006]

[Problems to be Solved by the Invention] In view of these circumstances, an object of the present invention is to provide an electrophotographic photoreceptor that has high mechanical strength and can stably form high-quality images over a long period of time. shall be.

[0007]

[Means for Solving the Problems] According to the present invention, a photoconductive layer and a surface protective layer in which a metal or metal oxide fine powder is dispersed in a binder resin are sequentially laminated on a conductive support. A photoreceptor for electrophotography, wherein the binder resin is made of a curable polyol polyurethane resin, and the weight average molecular weight of the polyol prepolymer, which is an active hydrogen component of the polyurethane resin, is 20,000 to 50,000. provided.

That is, as a result of extensive studies, the present inventors have found that in electrophotographic photoreceptors, an active hydrogen component is used as the binder resin of the surface protective layer in which metal or metal oxide fine powder is dispersed in the binder resin. A curable polyol polyurethane resin consisting of a polyol prepolymer and a polyvalent isocyanate curing agent, wherein the weight average molecular weight of the polyol prepolymer as an active hydrogen component is 20,000 to 50.
000, the surface protective layer obtained by drying and curing the curable polyol polyurethane resin has high surface hardness, mechanical strength, excellent abrasion resistance, and high quality over a long period of time. The intended purpose of the present invention, which is to be able to form images stably, can be achieved. On the other hand, if a polyol prepolymer with a weight average molecular weight of less than 20,000 is used, mechanical durability will deteriorate, and if a polyol prepolymer with a weight average molecular weight of more than 50,000 is used, cracks will occur in the surface protective layer. In addition, if something other than polyol is used as the active hydrogen component of polyurethane, for example, resins with amino groups as active hydrogens are reactive and have problems with liquid stability, while resins with carboxylic acid as active hydrogens are reactive. The disadvantage is that sufficient crosslinking density cannot be obtained due to insufficient crosslinking density, and the abrasion resistance deteriorates when a binder resin other than polyurethane resin is used.

The present invention will be explained in more detail below. The metal or metal oxide fine powder used in the present invention includes metals such as copper, tin, aluminum, indium, tin oxide, zinc oxide, titanium oxide, indium oxide, antimony oxide, bismuth oxide, antimony-doped tin oxide, Metal oxides such as tin-doped indium oxide can be used. Two or more of these metal or metal oxide fine powders may be mixed. The average particle size of these fine powders is 0.5 μm or less, preferably 0.
．． The thickness is preferably 2 μm or less from the viewpoint of transmittance of the protective layer.

The curable polyol polyurethane resin constituting the binder resin used in the present invention is a combination of a polyol prepolymer as an active hydrogen component and a polyvalent isocyanate as a curing agent. The polyol prepolymers used in the present invention include polyether polyols such as polyalkylene oxide, polyester polyols such as aliphatic polyesters having a hydroxyl group at the end, acrylic polymer polyols such as hydroxyalkyl methacrylate copolymers, and epoxy resins such as epoxy resins. Known polyols, fluorine-containing polyols, and the like can be used. Examples of the polyvalent isocyanate of the curing agent used in the present invention include aromatic isocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate, hexamethylene diisocyanate (HDI), HDI-trimethylolpropane adduct, HDI-isocyanurate, and HDI. - Known aliphatic isocyanates such as biuret isocyanates can be used.

To form the surface protective layer of the present invention, metal or metal oxide fine powder is dispersed in the polyol solution using a method such as a ball mill or bead mill, and then the curing agent is added to this dispersion. This may be applied onto the photoconductive layer by a method such as dip coating or spray coating, and then dried and cured.

The photoconductive layer used in the present invention is Se.
, Se-Te, Se alloys such as As2Se3, ZnO, C
Used are particles of II-VI group compounds such as dS and CdSe dispersed in resin, organic photoconductive materials such as polyvinylcarbazole, or a-Si. There are no particular restrictions on the structure of the photoconductive layer, and it may be a single layer or a stack of a charge generation layer and a charge transport layer. Furthermore, an adhesive layer for improving conductivity and an electrical barrier layer for preventing charge injection may be provided between the protective layer and the photoconductive layer.

[0013] As the conductive support, a conductor or an insulator treated for conductivity is used. For example, Al, Ni,
Metals such as Fe, Cu, Au, etc. or alloys, polyester, polycarbonate, polyimide, glass, etc. on insulating substrates such as Al, Ag, Au, etc. or In2O3
Examples include those formed with a thin film of a conductive material such as SnO2, and paper treated with conductive treatment. Further, there are no particular restrictions on the shape of the conductive support, and plate-like, drum-like, or belt-like ones may be used as required.

[0014]

[Examples] The present invention will be explained below with reference to Examples. Example 1 An 80 mmφ x 340 mm (length) Al drall support was set in a vacuum evaporation device, and As2Se3 alloy was placed in the evaporation source board of this device, and the vacuum degree was 3/106 Torr.
Vapor deposition was performed under the following conditions: r, support temperature 200° C., boat temperature 450° C., and a 60 μm thick photoconductive layer was formed on the support. Next, on top of this, a) a polysiloxane containing an alkoxy group, b) a polysiloxane containing a hydroxyl group, and c) at least one amino group, imino group, or nitrile group bonded to a carbon atom and 2 to 3 alkoxy groups bonded. Silicone resin A whose main component is an organic silicon compound having a silicon atom
(AY42-440 manufactured by Toray Silicone) and the above a)
A ligroin solution of an equal amount (by weight) mixture of silicone resin B (AY42-441 manufactured by Toray Silicone Co., Ltd.) having different component ratios of , b) and c) was spray applied, and the mixture was heated at 120°C.
to form a 0.15 μm thick electrical barrier layer (
intermediate layer) was formed. Next, the weight average molecular weight is 4000
20 wt% of St-MMA-2-HEMA copolymer of 0
2-ethoxyethyl acetate/methyl isobutyl ketone (7
/3 weight ratio) 30 parts by weight of solution and resistance control agent SnO214
parts by weight were dispersed in a ball mill for 120 hours, 3 parts by weight of hexamethylene diisocyanate was added, and this was spray coated onto the electrical barrier layer (intermediate layer), dried and cured at 130°C for 1 hour, and a 5 μm thick layer was formed. A surface protective layer was formed to produce an electrophotographic photoreceptor.

Example 2 An electrophotographic photoreceptor was prepared in the same manner as in Example 1 except that the prepolymer was replaced with a St-MMA-HEA copolymer.

Example 3 An electrophotographic photoreceptor was prepared in exactly the same manner as in Example 1, except that the weight average molecular weight of the prepolymer was changed to 20,000.

Example 4 Except for changing the molecular weight of the prepolymer to 50,000,
An electrophotographic photoreceptor was produced in exactly the same manner as in Example 1.

Comparative Example 1 An electrophotographic photoreceptor was prepared in exactly the same manner as in Example 1, except that the weight average molecular weight of the prepolymer was changed to 15,000.

Comparative Example 2 Except for changing the molecular weight of the prepolymer to 55,000,
An electrophotographic photoreceptor was produced in exactly the same manner as in Example 1.

The electrophotographic photoreceptor having the surface protective layer thus obtained was manufactured by Ricoh Co., Ltd., FT-6550.
The mechanical strength of the protective layer was evaluated by measuring the depth of scratches on the surface protective layer after 100,000 sheets were attached. The results are shown in Table 1.

[0021]

[Table 1]

As is clear from Table 1, when the weight average molecular weight of the prepolymer of the curable polyol polyurethane resin is in the range of 20,000 to 50,000, the depth of the scratches on the protective layer after 100,000 sheets is shallow and good images are obtained. Obtained. On the other hand, when the molecular weight was less than 20,000, the protective layer had deep scratches and many white streaks appeared on the image. Also, the molecular weight is 500
When it was larger than 00, many cracks occurred in the protective film, and their marks appeared on the image. From these results, it can be seen that the present invention is a photoreceptor with high mechanical strength during long-term use.

[0023]

According to the present invention, an electrophotographic photoreceptor having a surface protective layer with high surface hardness and abrasion resistance can be obtained, and the photoreceptor can stably produce high-quality images over a long period of time. Can be formed.

Claims (1)

[Claims] 1. An electrophotographic photoreceptor in which a photoconductive layer and a surface protective layer in which fine metal or metal oxide powder is dispersed in a binder resin are sequentially laminated on a conductive support, wherein the binder resin is cured. Made of polyol polyurethane resin,
The weight average molecular weight of the polyol prepolymer which is the active hydrogen component of the polyurethane resin is 20,000 to 50,000.
An electrophotographic photoreceptor characterized by: