JPH0448214B2 - - 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, surface strength, etc. (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. How many charge carriers are available immediately?
Electrophotographic characteristics, such as how to uniformly generate charge carriers, how efficiently the generated charge carriers are injected into the charge transport layer, and how smoothly reverse charge carriers flow to the support, are largely dependent on the charge generation layer. The charge generation layer is basically composed of an organic pigment as a charge generation substance and a binder as a binder, but 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 the charge generation substance.
They do not seem to have come up with the idea that it is sufficient if dispersibility and stability 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 sensitivity 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 of the following general formula: RCHO (wherein R represents an alkyl group having 1 to 3 carbon atoms, the alkyl group is substituted with a halogen) may be done)
is provided. In the above general formula, the alkyl group may be substituted with halogen (fluorine, chlorine, bromine, iodine). 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.
It is preferable to use polyvinyl alcohol having 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 barrier formed is small because the alkyl group of the acetal is small. It is also believed that because the alkyl group of the acetal is small, dispersibility is improved, a good coating film is obtained, and the properties are improved. Typical examples of the polyvinyl acetal resin used in the present invention are illustrated below with respect to their acetal structure portions. Next, a synthesis example of the polyvinyl acetal resin used in the present invention will be shown. Synthesis Example 1 Synthesis method for Resin Example No. 1: Add 5.0 g of polyvinyl alcohol with a degree of polymerization of 600 (degree of saponification 98.5%) and 35 ml of acetaldehyde into an Erlenmeyer flask, add 50 ml of ethanol, and 5 ml of purified water, and add 1 ml of concentrated acid. was added and 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 twice in an acetone-water system and then dried under reduced pressure. This synthesized polyvinyl acetal resin has a weight average molecular weight determined by GPC.
It was 99,000. Also, the degree of acetalization is JIS
(K-6728) method, it was found to be 72 mol%. Other polyvinyl acetal resins used in the present invention are also synthesized in the same manner as above. 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 content of the binder in the charge generation layer is low, but in practical terms it should not exceed 20% by weight in order to provide binding properties and ensure stability during pigment dispersion. necessary, usually 25 to 90% by weight, more preferably 28 to 50% by weight
Used within the range of. 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,
An inorganic or organic pigment selected from charge generating substances such as quinacridone pigments, asymmetric quinocyanine dyes, and quinocyanine dyes is 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 sulfide, (63) Methyl squarate dye (64) Indigo dye (CI No. 78000) (65) Thioindigo dye (CI No. 78800) (66) Copper phthalocyanine (67) Azulenium salt dye Charge generating substance is dispersed 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, and sulfoxides such as dimethyl sulfoxide. , ethers such as tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethyln, carbon tetrachloride, and trichloroethylene, or benzene and toluene. , xylene, ligroin, monochlorobenzene, dichlorobenzene, and other aromatic compounds can be used. Dispersion 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 carried out using coating methods such as dip coating, spray coating, spinner coating, bead coating, Meyer bar coating, blade coating, roller coating, and curtain coating. The coating film after application is preferably dried to the touch at room temperature and then dried by heating. 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 jump 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 in electrical contact with 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. There is. 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" including r-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, promoanil, 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-
Pyrrolidinobenzaldehyde-N,N-diphenylhydrazone, 1,3,3-trimethylindolenine-ω-aldehyde-N,N-diphenylhydrazone, p-diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrazone hydrazones such as 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-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-dimethylaminophenyl)-5-(2-chlorophenyl)oxazole, 2
-(p-diethylaminostyryl)-6-diethylaminobenzothiazole compounds, triarylmethane compounds such as bis(4-diethylamino-2-methylphenyl)-phenylmethane, 1,1
-bis(4-N,N-diethylamino-2-methylphenyl)heptane, 1,1,2,2-tetrakis(4-N,N-dimethylamino-2-methylphenyl (polyarylalkane such as ethane,
Examples include triphenylamine, poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinylacridine, 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. Moreover, 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 carbazole. , polyvinylanthracene, polyvinylpyrene, and the like. 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 substrate having the conductive layer, materials that are themselves conductive can be used, such as aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold, and platinum. 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; Plastics with polymers, etc. can be used. A subbing layer having barrier and adhesive functions can also be provided between the conductive layer and the photosensitive layer. The undercoat layer is made of casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide (nylon 6, nylon 66, nylon
610, copolymer 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 exposure after charging is required. Then, in the exposed area, electrons generated in the charge generation layer are injected into the charge transport layer, and then reach the surface and neutralize the positive charge, causing a decrease in surface potential and creating an electrostatic contrast with the unexposed area. . A visible image can be obtained by treating 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 and then 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. At the time of this phenomenon, 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 bar so that the dry film 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) 5 g was added to a solution in which 3 g of Resin Example No. 1 was dissolved in 90 ml of methyl ethyl ketone, and the mixture was dispersed using an attritor for 2 hours. This dispersion was applied onto the previously formed casein layer using a wire round bar so that the film thickness after drying was 0.3 microns, and dried at 70°C to form a charge generation layer. Next, a hydranone 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 so that the dry film thickness is 15 microns, and dry. A charge transport layer was formed and a sample of Example 1 was prepared. Next, as a comparative example, an electrophotographic photoreceptor comparison sample-1 was prepared in exactly the same manner as above, using butyral resin Esrec BM-2 manufactured by Sekisui Chemical Co., Ltd. in place of the above-mentioned polyvinyl acetal resin No. 1.
It was created. 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 _O ) 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 few minutes have elapsed, check the charging characteristics again, and check the surface potential at that time.
The photomemory property was evaluated based on the difference between V′ _O and the initial V _O , that is, V _O −V′ _O. 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 using 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 for comparison materials. 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
2.5 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. Using 5g of the above copper phthalocyanine pigment,
First, a charge generation layer was prepared in the same manner as in Example 1 using 1.7 g of the resin shown in the table as a binder.
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 chlorodiane blue was used in place of the diasazo pigment used in Example 1, and 2.5 g of polyvinyl acetal resin Example No. was used. On top of 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)
A coating solution prepared by dissolving 5 g 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. In an electrophotographic photoreceptor having at least a charge generation layer and a charge transport layer provided on a conductive support, the charge generation layer is acetalized with polyvinyl alcohol and an aldehyde of the following general formula as a binder. Electrophotographic photoreceptor containing polyvinyl acetal resin obtained by reaction: RCHO (wherein R represents an alkyl group having 1 to 3 carbon atoms,
Alkyl groups may be substituted with halogen).