JPH0448213B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a functionally separated electrophotographic photoreceptor, and more particularly to an improvement in a charge generation layer capable of improving electrophotographic characteristics. [Prior Art] In recent years, electrophotographic photoreceptors have been proposed that have a laminated structure in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer. These have been improved in terms of sensitivity to visible light, charge retention, and surface strength (for example, US Pat. Nos. 3,837,851 and 3,871,882). Such a functionally separated photoreceptor is composed of at least two layers: a charge generation layer and a charge transport layer. Charge carriers generated by light absorption in the charge generation layer are injected into the charge transport layer and migrate to the surface, neutralizing the photoreceptor surface charge and creating electrostatic contrast. The role played by the charge generation layer in this process is extremely important. In other words, electrophotographic properties depend on the charge generation layer, such as how to uniformly generate a large number of charge carriers, how efficiently to inject the generated charge carriers into the charge transport layer, and how smoothly to flow opposite charge carriers to the support. There is a lot to be owed.
The charge generation layer is basically composed of an organic pigment as a charge generation substance and a binder as a binder, and the weight ratio of the binder to the organic pigment is generally 25 to 100 wt%, which is not low. The binder therefore has a very important influence on the movement of generated charge carriers within the charge generation layer. That is, the basic structure, functional groups, molecular weight, purity, etc. of the binder greatly affect the electrophotographic properties of the photoreceptor, such as sensitivity, potential characteristics, durability, etc. However, as discussed in literature, patents, etc., the conventional view of the binder in the charge generation layer is that it is an auxiliary agent for the organic pigment, which is a charge generation substance.
It seems that they do not think that it is sufficient if dispersibility and binding properties can be imparted. As a result, many defects in potential characteristics such as residual potential, potential fluctuation, and photomemory are observed in conventional functionally separated electrophotographic photoreceptors. Also, the photosensitivity is not sufficient. [Problems to be Solved by the Invention] The present inventors understood the binder as an electronic material that is another main component of the charge generation layer, and as a result of researching the binder from molecular aspects such as structure, molecular weight, and purity, the present inventors discovered that the present invention This invention has been achieved. It is an object of the present invention to provide a new binder for a charge generating layer and to provide an electrophotographic photoreceptor with improved charging characteristics. Another object of the present invention is to provide an electrophotographic photoreceptor having practical high sensitivity characteristics and stable potential characteristics during repeated use. [Means for Solving the Problems] According to the present invention, in an electrophotographic photoreceptor in which at least a charge generation layer and a charge transport layer are provided on a conductive support, polyvinyl alcohol is added to the charge generation layer as a binder. An electrophotographic photoreceptor containing a polyvinyl acetal resin obtained by an acetalization reaction with an aldehyde compound (the butyl group may be substituted with a halogen) of the following structural formula (1) or (2): is provided. The butyl group of the present invention is a halogen (fluorine, chlorine,
(bromine, iodine) may be substituted. The weight average molecular weight of the polyvinyl acetal resin used in the present invention is suitably in the range of 10,000 to 200,000, particularly preferably in the range of 30,000 to 80,000. The degree of acetalization is suitably 50 mol% or more, particularly preferably 65 to 90 mol%. Furthermore, the lower the content of residual vinyl acetate components derived from polyvinyl alcohol as a raw material, the more effective it is, but it is preferable to use polyvinyl alcohol with a saponification degree of 85% or more as a raw material. The reason why the potential characteristics of an electrophotographic photoreceptor having a charge generation layer containing the polyvinyl acetal resin is improved is not clear, but when the carrier moves between the pigment particles, the binder that fills the spaces between the particles is This is thought to be because the barrier it forms is weak due to its structure, and therefore does not hinder carrier movement much. That is, it is considered that the three-dimensional structure of the alkyl group of the acetal makes it difficult for the binder molecules to take a densely packed form. Representative examples of the polyvinyl acetal resin used in the present invention are illustrated below. Next, a synthesis example of the resin will be shown. Synthesis example 1 Method for synthesizing polyvinyl butyral resin No. 1: In an Erlenmeyer flask, add 5.0 g of polyvinyl alcohol with a degree of polymerization of 600 (degree of saponification 98.5%) and 35 ml of isobutyraldehyde, then add 50 ml of ethanol and 5 ml of purified water, and add 1 ml of concentrated hydrochloric acid. was added, and the mixture was reacted for 18 hours at 40°C with stirring. After the reaction, the reaction solution was added to a large amount of water containing sodium hydroxide to recover the polymer. The obtained polymer was purified by reprecipitation with acetone-hydrogen for 2
After spinning, it was dried under reduced pressure. As a result of molecular weight measurement by GPC, the synthesized butyral resin had a weight average molecular weight of 115,000. In addition, the degree of butyralization was measured by JIS (K-6728) method and was 75
It was in mol%. Synthesis Example 2 Method of Synthesizing Polyvinyl Butyral Resin No. 2: A butyral resin was synthesized in exactly the same manner as in Synthesis Example 1 except that 35 ml of tert-butyraldehyde was used instead of isobutyraldehyde. Weight average molecular weight was 120,000; degree of butyralization was 65 mol%. The binder in the charge generation layer must be one that does not inhibit the movement of carriers generated within the layer as much as possible. Therefore, it is naturally preferable that the binder content in the charge generation layer be low, but in practice it is necessary to have a binder content of 20% by weight or more in order to provide binding properties and ensure stability during pigment dispersion. It is usually used in a range of 25 to 90% by weight, more preferably 28 to 50% by weight. Furthermore, the binder of the present invention may be used in combination with other known binders. The charge generation layer used in the present invention is selenium, selenium-
Tellurium, amorphous silicon, pyrylium, thiopyrylium azulenium dyes, phthalocyanine pigments, anthanthrone pigments, dibenzpyrenequinone pigments, pyranthrone pigments, trisazo pigments, disazo pigments, azo pigments, indigo pigments, quinacridone pigments, asymmetric quinocyanine dye,
Inorganic pigments or organic pigments selected from charge-generating substances such as quinocyanine dyes are dispersed in the binder. Specific examples of such charge generating substances are as follows. (1) Amorphous silicon, (2) Selenium-tellurium,
(3) Selenium-arsenic, (4) Cadmium sulfate, (63) Methine squaritate dye (64) Indigo (CI No. 78000) (65) Thioindigo dye (CI No. 78800) (66) Copper phthalocyanine (67) Azulenium salt dye The charge generating substance is dispersed together with the binder of the present invention. At this time, organic solvents include ketones such as acetone, methyl ethyl ketone and cyclohexanone, amides such as N,N-dimethylformamide and N,N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, Ethers such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, esters such as methyl acetate, ethyl acetate, aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, trichloroethylene, or benzene, Aromatics such as toluene, xylene, ligroin, monochlorobenzene, dichlorobenzene, etc. can be used. Fractionation is carried out by crushing the above-mentioned solvent, charge-generating substance, and binder using a sand mill, ball mill, roll mill, attritor, or the like until a predetermined particle size is obtained. Particle size and binder amount have a great influence on the stability of the dispersion liquid and the properties of the photoreceptor, and must be carefully examined. Coating can be performed using a coating method such as a dip coating method, a spray coating method, a spinner coating method, a pea coating method, a Mayer coating method, a blade coating method, a roller coating method, a curtain coating method, or the like. The coating film after coating is preferably dried to the touch at room temperature and then heated and dried. Heat drying is from 30°
It is preferable to carry out the reaction at 200°C for 5 minutes to 2 hours. The charge generation layer contains as much of the charge generation substance as possible in order to obtain sufficient absorbance and to shorten the range of the generated charge carriers.
A thin film layer having a thickness of 0.01 micron to 1 micron is preferable. This means that most of the incident light is absorbed by the charge generation layer and generates a large number of charge carriers, and that the generated charge carriers are not deactivated by recombination or trapping, and the charge transport layer This is due to the need to inject. The charge transport layer is electrically connected to the charge generation layer described above, and has the function of receiving charge carriers injected from the charge generation layer in the presence of an electric field and transporting these charge carriers to the surface. ing. At this time, this charge transport layer may be laminated on or under the charge generation layer. However, it is desirable that the charge transport layer is laminated on the charge generation layer. Since the photoconductor generally has the function of transporting charge carriers, the charge transport layer can be formed by the photoconductor. The substance that transports charge carriers in the charge transport layer (hereinafter simply referred to as charge transport substance) is preferably substantially insensitive to the wavelength range of electromagnetic waves to which the charge generation layer is sensitive. The term "electromagnetic waves" used herein includes a broad definition of "light rays" that includes gamma rays, X-rays, ultraviolet rays, visible light, near infrared rays, infrared rays, far infrared rays, and the like. When the photosensitive wavelength range of the charge transport layer coincides with or overlaps that of the charge generation layer, charge carriers generated in both layers capture each other, resulting in a decrease in sensitivity. Charge transport substances include electron transport substances and hole transport substances, and electron transport substances include chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, and 2,4,7-trinitro-9-fluorenone. , 2, 4, 5, 7-
Tetranitro-9-fluorenone, 2,4,7-
trinitro-9-dicyanomethylenefluorenone, 2,4,5,7-tetranitroxanthone,
Examples include electron-withdrawing substances such as 2,4,8-trinitrothioxanthone, and polymerized versions of these electron-withdrawing substances. Examples of hole-transporting substances include pyrene, N-ethylcarbazole, N-isopropylcarbazole,
N-Methyl-N-phenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-
3-methylidene-10-ethylphenothiazine,
N,N-diphenylhydrazino-3-methylidene-10-ethylphenoxazine, P-diethylaminobenzaldehyde-N,N-diphenylhydrazone, P-diethylaminobenzaldehyde-N
-α-Naphthyl-N-phenylhydrazone, P-
Pyrrolidinobenz-aldehyde-N,N-diphenylhydrazone, 1,3,3-trimethylindolenine-ω-aldehyde-N,N-diphenylhydrazone, P-diethylbenzaldehyde-3-
Hydrazones such as methylbenzthiazolinone-2-hydrazone, 2,5-bis(P-diethylaminophenyl)-1,3,4-oxadiazole,
1-phenyl-3-(P-diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, 1-[quinolyl(2)]-3-(P-diethylaminostyryl)-5-(P-diethylaminophenyl) ) Pyrazoline, 1-[pyridyl(2)]-3-(P-
diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, 1-[6-methoxy-pyridyl(2)]-3-(P-diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, 1- [Pyridyl(3)]-3-(P-diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, 1-[Lepidyl(2)]-3-(P-
diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-
3-(P-diethylaminostyryl)-4-methyl-5-(P-diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-3-(α-methyl-P-
diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, 1-phenyl-3-
(P-diethylaminostyryl)-4-methyl-5
-(P-diethylaminophenyl)pyrazoline,
1-Phenyl-3-(α-benzyl-P-diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, spiropyrazoline and other pyrazolines, 2-(P-diethylaminostyryl)
-6-diethylaminobenzoxazole, 2-
Oxazole compounds such as (P-diethylaminophenyl)-4-(P-diethylaminophenyl)-5-(2-chlorophenyl)oxazole, 2
Thiazole compounds such as -(P-diethylaminostyryl)-6-diethylaminobenzothiazole, triarylmethane compounds such as bis(4-diethylamino-2-methylphenyl)-phenylmethane, 1,1-bis(4-N,N -diethylamino-2-methylphenyl)heptane, 1,
Polyarylalkanes such as 1,2,2-tetrakis(4-N,N-dimethylamino-2-methylphenyl)ethane, triphenylamine, poly-
N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinylacridine,
Examples include poly-9-vinylphenylanthracene, pyrene-formaldehyde resin, and ethylcarbazole formaldehyde resin. In addition to these organic charge transport materials, inorganic materials such as selenium, selenium-tellurium amorphous silicon, and cadmium sulfide can also be used. In addition, these charge transport substances may be one or two types.
More than one species can be used in combination. When the charge transport material does not have film-forming properties,
A film can be formed by selecting an appropriate binder. Resins that can be used as binders are:
For example, insulating resins such as acrylic resin, polyarylate, polyester, polycarbonate, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, polyvinyl butyral, polyvinyl formal, polysulfone polyacrylamide, polyamide, chlorinated rubber, or poly-N-vinyl Mention may be made of organic photoconductive polymers such as carbazole, polyvinylanthracene, polyvinylpyrene. Since the charge transport layer has a limit in its ability to transport charge carriers, it cannot be made thicker than necessary. Typically it is between 5 microns and 30 microns, with a preferred range between 8 microns and 20 microns. When forming the charge transport layer by coating, an appropriate coating method as described above can be used. A photosensitive layer having such a laminated structure of a charge generation layer and a charge transport layer is provided on a substrate having a conductive layer. As the base material of the conductive layer, materials whose base material itself is conductive, such as aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold, and platinum, can be used. In addition, plastics (e.g., polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, acrylic resin, polyethylene fluoride, etc.), or conductive particles (e.g. carbon black, silver particles, etc.) coated on plastic with a suitable binder; substrates made of plastic or paper impregnated with conductive particles; For example, plastics containing polymers having a high molecular weight can be used. A subbing layer having barrier and adhesive functions can also be provided between the conductive layer and the photosensitive layer. The subbing layer is made of casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide (nylon 6, nylon 66, nylon
610, copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, aluminum oxide, etc. The thickness of the undercoat layer is 0.1 micron to 5 micron.
Preferably, 0.5 micron to 3 micron is appropriate. When using a photoreceptor in which a conductive layer, a charge generation layer, and a charge transport layer are laminated in this order, and the charge transport material is an electron transport material, the surface of the charge transport layer must be positively charged, and after charging, When exposed to light, electrons generated in the charge generation layer are injected into the charge transport layer in the exposed area, and then reach the surface and neutralize the positive charge, resulting in attenuation of the surface potential and an electrostatic contrast between it and the unexposed area. arise. A visible image can be obtained by developing the electrostatic latent image thus formed with a negatively charged toner. This can be directly fixed, or the toner image can be transferred to paper, plastic film, etc. and then developed and fixed. Alternatively, a method may be used in which the electrostatic latent image on the photoreceptor is transferred onto an insulating layer of transfer paper, then developed and fixed. The type of developer, the developing method, and the fixing method may be any known ones or known methods, and are not limited to specific ones. On the other hand, when the charge transport material consists of a hole transport material, the surface of the charge transport layer must be negatively charged.
After charging, when exposed to light, holes generated in the charge generation layer in the exposed area are injected into the charge transport layer, and then reach the surface and neutralize the negative charge, causing a decrease in the surface potential and static electricity between the exposed area and the unexposed area. Electrocontrast occurs. During development, it is necessary to use a positively charged toner, contrary to the case where an electron transport material is used. When an electrophotographic photoreceptor with either a positive or negative charge is exposed to light before being charged, the electrophotographic characteristics of the area irradiated with light are different from those of the area that is not irradiated with light, which often results in so-called photomemory properties. . According to the present invention, it is possible to provide a highly sensitive electrophotographic photoreceptor, and the variation in bright area potential and dark area potential when repeatedly charging and exposing is small, and photomemory properties can be effectively improved. It has advantages. Hereinafter, the present invention will be explained according to examples. Example 1 An ammonia aqueous solution of casein (11.2 g of casein, 1 g of 28% ammonia water and 222 ml of water) was placed on an aluminum plate.
(dissolved in) was applied using a wire round bur so that the dry thickness was 1.0 microns and dried. Next, a disazo pigment with the following structure (see published patent publication 56-116039 for the manufacturing method) Add 5 g to a solution of 3 g of the resin example No. 1 dissolved in 90 ml of methyl ethyl ketone, and add 2 g with an attritor.
Spread out time. This dispersion was applied onto the previously formed casein layer using a wire round bar so that the film thickness after drying would be 0.3 microns, and dried at 70°C to form a charge generation layer. Next, a hydrazone compound with the following structure (see published patent publication 57-101844 for the manufacturing method) Dissolve 5 g of polymethyl methacrylate resin (number average molecular weight 100,000) in 70 ml of toluene, apply this onto the charge generation layer using a wire round bar to a dry film thickness of 15 microns, dry and charge. A transport layer was formed and a sample of Example 1 was prepared. Next, as a comparative example, a comparative sample of an electrophotographic photoreceptor was prepared in exactly the same manner as described above, using butyral resin Esrec BM-2 manufactured by Sekisui Chemical Co., Ltd. in place of the above-mentioned synthetic polyvinyl butyral resin No. 1. The electrophotographic photoreceptor thus prepared was statically charged with a corona at -5kV using an electrostatic copying paper tester Model SP-428 manufactured by Kawaguchi Electric Co., Ltd., and after being held in a dark place for 10 seconds, the illuminance was The charging characteristics were investigated by exposure at 5 lux. The charging characteristics are surface potential (V ₀ ) and 10 in the dark.
The exposure amount (E _1/2 ) required to attenuate the potential to 1/2 when the potential is attenuated in seconds was measured. Furthermore, after exposing the electrophotographic photoreceptor for 3 minutes at an illuminance of 600 lux,
After a minute has passed, check the charging characteristics again, and check the surface potential at that time.
The photomemory property was evaluated based on the difference between V ₀ ′ and the initial V ₀ , that is, V ₀ −V ₀ ′. The results are shown in Table 1.

[Table] As is clear from Table 1, the sample of Example 1 had a lower
Both sensitivity and photo memory are good. Furthermore, in order to evaluate the stability during repeated use, the photoconductor prepared in this example was attached to the photoconductor drum cylinder of a PPC copier NP-150Z manufactured by Canon Inc., and 10,000 copies were made with the same machine. Early and
Fluctuations in the bright area potential (V _L ) and dark area potential (V _D ) after copying 10,000 sheets were measured. Similar operations were performed on comparative samples. The results are shown in Table 2.

[Table] It is clear from Table 2 that the sample of Example 1 is also superior in durability stability compared to the sample of Comparative Example. Examples 2-5 Phthalic anhydride 148g, urea 180g, anhydrous chloride 1
25 g of copper, 0.3 g of ammonium molybutate, and 370 g of benzoic acid were reacted at 190° C. for 3.5 hours with stirring. After the reaction was completed, benzoic acid was distilled under reduced pressure, followed by washing with water, washing with acid, and washing with water in order to obtain 130 g of crude copper phthalocyanine. This crude phthalocyanine was dissolved in 1,300 g of concentrated sulfuric acid, stirred at room temperature for 2 hours, poured into a large amount of ice water, and the precipitated pigment was separated and washed with water until it became neutral. Next, stir 6 times with DMF2.6, and then
After stirring twice with MEK2.6, 2 times with water 2.6.
The mixture was stirred twice and dried under vacuum to obtain 115 g of purified copper phthalocyanine. The above synthetic polyvinyl butyral resin No. 2 was dissolved in a mixed solvent of 54 g of THF and 25 g of cyclohexanone in varying amounts, and 5 g of the above copper phthalocyanine was added to form a charge generation layer in the same manner as in Example 1. Next, a pyrazoline compound having the following structure was used in place of the hydrazone compound of Example 1, and a charge transport layer of 15 microns was laminated to prepare an electrophotographic photoreceptor. The charging characteristics and durability of each photoreceptor were measured in the same manner as in Example 1. These results are summarized in Table 3.

[Table] Example 6 A charge generation layer was prepared in exactly the same manner as in Example 1, except that 5 g of chlorodiambre was used in place of the disazo pigment used in Example 1, and 2.5 g of synthetic polyvinyl butyral resin No. 1 was used. On the charge generating layer, 5 g of 2,4,7-trinitro-9-fluorenone and poly-4,4'-dioxydiphenyl-2,
2'-propane carbonate (molecular weight 300000) 5g
A coating solution prepared by dissolving the above in 70 ml of tetrahydrofuran was applied so that the coating amount after drying was 10 g/m ² and dried. The electrostatic charge of the electrophotographic photoreceptor thus prepared was measured in the same manner as in Example 1. At this time, the settings of the electrostatic copying paper tester were changed so that the charging polarity was as follows, and the NP-150Z was modified. The results are shown in Table 4.

【table】

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor comprising at least a charge generation layer and a charge transport layer on a conductive support, wherein the charge generation layer contains polyvinyl alcohol as a binder and the following structural formula (1) or (2). ) An electrophotographic photoreceptor containing a polyvinyl acetal resin obtained by an acetalization reaction with an aldehyde compound (the butyl group may be substituted with a halogen):