JPS61149964A - Electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To improve sensitivity and to suppress the fluctuation of the potential in bright and dark parts in the stage of repetitive electrostatic charge and exposing and the appearance of a photomemory characteristic by incorporating a PVAL and specific polyvinyl acetal as a binder into the electric charge generating layer of a separated-function type photosensitive body. CONSTITUTION:The polyvinyl acetal resin obtd. by the acetal forming reaction of the PVAL and the aldehyde expressed by the formula RCHO (R is a substd. or unsubstd. alkyl of 5-9C) is incorporated as the binder into the charge generating layer of the photosensitive body provided with the charge generating layer and charge transfer layer on a conductive substrate. The substituent of the alkyl of R is the above-mentioned formula is preferably a halogen, alkoxy, aryl, hydroxyl group, nitro or amino, and the content of the polyvinyl acetal in the charge generating layer is made about 20-90wt% Such polyvinyl acetal is incorporated into the charge generating layer and the molecules of the binder assume hardly the densely aggregated state owing to the adequate length and stereo structure of the alkyl group possessed by the same and therefore the good potential characteristic is obtd. without spoiling the movement of the carrier.

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 properties.

[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, U.S. Pat. No. 3,837
, No. 851, No. 3,871,882, etc.).

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, the electrophotographic properties of the charge generation layer include how many charge carriers are generated uniformly, how efficiently the generated charge carriers are injected into the charge transport layer, and how smoothly opposite charge carriers flow into the support. I owe a lot to

The charge generation layer is basically composed of an organic pigment as a charge generation substance and a binder as a binding agent, and the weight ratio of the binder to the organic pigment is generally 25 to 100.
The wt% is by no means low. Therefore, the binder has a very important influence on the movement of generated charge carriers within the charge generation layer. That is, the basic structure of the binder,
Functional group 1 molecular weight.

Purity etc. have a large impact on 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 that is the charge generation substance, and it is sufficient if it can impart dispersibility and binding properties. It seems that he has not come up with this idea.

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.

[Problem that the invention seeks to solve]

The present inventors understood the binder as another main electronic material 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 invention was 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 problems]

According to the present invention, in an electrophotographic photoreceptor comprising at least a charge generation layer and a charge transport layer provided on a conductive support, the charge generation layer is provided with polyvinyl alcohol as a binder and the following general 2RCHO, (wherein R is substituted). Provided is an electrophotographic photoreceptor containing a polyvinyl acetal resin obtained by an acetalization reaction with an aldehyde represented by the above-mentioned or unsubstituted alkyl group having 5 to 9 carbon atoms.

In the above general formula, substituents for R (alkyl group) include, for example, halogeno (fluorine, chlorine, bromine, iodine), alkoxy groups (eg, methoxy, ethoxy, !ropoxy, butoxy, etc.), and aryl groups (phenyl).

naphthyl, etc.), hydroxyl group, nitro group, amino group, etc.

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 in the range of 30,000 to so, o o o.
A range of is preferred. Further, the degree of acetalization is suitably 50 molar or more, and particularly preferably 65 to 90 molar.

Furthermore, the lower the content of residual vinegar dust vinyl 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 32 libinyl 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 not clear. This is thought to be because the barrier formed by the above-mentioned specific structure is weak and therefore does not inhibit the movement of carriers much. That is, it is believed that the binder molecules maintain a densely packed form due to the appropriate length and three-dimensional structure of the alkyl group of the acetal. However, when the alkyl group in the above general formula has 10 or more carbon atoms, the size of the alkyl group acts as a barrier and inhibits the migration of the cycarrier. In addition, the dispersibility is poor, making it impossible to obtain a good coating film, resulting in deterioration of photographic properties.

Typical examples of the polyvinyl acetal resin used in the present invention are illustrated below with respect to their acetal structure portions.

H3 F CH.

Ct 0M313 H Acetal structure part CH.

Resin example shop Acetal structure part NO□ Next, a synthesis example of the polyvinyl acetal resin according to the present invention will be shown.

Synthesis Example 1 Synthesis method of Resin Example 41: Polyvinyl alcohol with a degree of polymerization of 600 (saponification degree of 9B, 5T) in an Erlenmeyer flask was placed in a 5.0. f and C3H15-CH
o 35 m, further ethanol 59 mJ and purified water 5
- was added, concentrated hydrochloric acid 1- was added, and the mixture was reacted at 40°C for 18 hours 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 privinyl acetal resin is GP
The weight average molecular weight according to e was 115,000. The degree of acetalization was 76 molti based on the JIS (K-6728) method.

Ya1. Other polyvinyl acetal resins used in the above are also synthesized in the same manner as above.

-'--The binder of the raw layer is the carrier generated within the layer-
It must be something that does not interfere with 7V movement as much as possible.

Therefore, it is naturally preferable that the content of Nonon inder in the charge generation layer is lower in weight percent, but in practical terms, it is necessary to provide binding properties.
Furthermore, in order to ensure stability during pigment dispersion, it is necessary to use at least 20% by weight, and it is usually used in the range of 25 to 90% by weight, more preferably 28 to 50% by weight.

Further, 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,
Azurenium dyes, phthalocyanine pigments, anthoanthrone pigments, dipenzpyrenginone pigments, pyranthrone pigments, trisazo pigments, disazo pigments, azo pigments, indigo pigments.

Quinacridone pigments, asymmetric quinocyanine dyes.

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 sulfide.

翰C=0 0-C C-00=C C west ni west (
wealth).

B) Squaric acid methine dye (C) Indigo dye (C, 1, 78000)) Thioindigo 9 dye (C, 1, A2B2O7)) Copper 7 talocyanine (B) Azulenium salt dye The charge generating substance is used in the present invention. The organic solvent used is acetone, ketones such as methyl ethyl ketone and cyclohexanone, and amides such as N,N-trimethylformamide and N,N-dimethylacetamide. sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, and fats such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, and trichloroethylene. Group halodanized hydrocarbons or aromatics such as benzene, toluene, xylene, refloin, monochlorobenzene, dichlorobenzene, etc. can be used.

Dispersion is carried out by crushing the above-mentioned solvent, charge generating substance, and binder using a sand mill, Gale 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 methods include dip coating method, spray coach ink method, spinner coating method, bead coating method,
This can be carried out using a coating method such as a Mayer coating method, a blade coating method, a roller coating method, or a curtain coating method.

The coating film after application is preferably dried to the touch at room temperature and then dried by heating. Heat drying at 30°C to 200°C
Preferably, the heating time is from 1 minute to 2 hours.

The charge generation layer contains as much of the charge generation substance as possible in order to obtain sufficient absorbance, and in order to shorten the range of the generated charge carriers, the charge generation layer is a thin film layer, for example, 5 microns or less, preferably. 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, generating many charge carriers, and that the generated charge carriers are not deactivated by recombination or trapping, but are transferred to the charge transport layer. This is due to the need for injection.

The charge transport layer is electrically connected to the charge generation layer described above, and has the function of receiving and taking charge carriers injected from the charge generation layer in the presence of an electric field, and transporting these charge carriers to the surface. have. 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 the broad definition of "light rays" that includes gamma rays, When the area coincides with or over doubles that of the charge generation layer, charge carriers generated in both of them trap each other, resulting in a decrease in sensitivity.

Charge transporting substances include electron transporting substances and hole transporting substances, and electron transporting substances include chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4.7-)dinitro-9- Fluorenone, 2,4.5.7-tetranitro-9-fluorenone,
2,4.7-dolinitro 9-dicyanomethylenefluorenone, 2,4.5.7-ketone nitroxanthone, 2
, 4.8-) There are electron-withdrawing substances such as linitrothioxanthone, and polymerization of these electron-withdrawing substances.

Examples of hole-transporting substances include pyrene, N-ethylcarbazole, N-ingrovir carhasol, N-methyl-N
-7enylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-10-ethylphenothianone, N,N-diphenylhydrazino 3-methylidene-10-ditylphenoxazine, p--,zethylaminobe/dualdehyde N,N-diphenylhydrazone,
P-diethylaminobenzaldehyde-N-α-su7teru-N-phenylhydrazone, P-pyrrolidinobenzaldehyde-N,N-diphenylhydrazone, 11313
-) IJ,)' f Ruindolenine-ω-aldehyde-N, N-2 phenylhydrazone, p-x Ethylbenzaldehyde-3-methylbenzthiazolinone-2-
Hydrazones such as human 2sin, 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-dimethylaminophene/I/
) pyrazoline, 1-[pyridyl (2) ) -3-(P
-diethylaminostyryl)-5-(P-diethylaminophenyl]pyrazoline, 1-(6-medoxypyridyl(2))-3-(P-diethylaminostyryl)-5
-(p-diethylaminophenyl)virason+)one, 1-
[Pyridyl (3)] -3-(P-diethylaminostyryl)-5-(P-diethylaminophenyl)pyrazoline, 1-[Lepidyl (2)) -3-(P-diethylaminostyryl)-5-(P-diethylaminostyryl) phenyl)pyrazoline, 1-[pyridyl(2))-3-(P
-diethylaminostyryl)-4-methyl-5-(P-
diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-3-(α-methyl-P-diethylaminostyryl)-s-(p-diethylaminophenyl)pyrazoline, 1-phenyl-3-(P-diethylaminostyryl) Pyrazolines such as -4-methyl-5-(P-diethylaminophenyl)pyrazoline, 1-phenyl-3-(α-benzyl-P-diethylaminostyryl)-s-(p-diethylaminophenyl)pyrazoline, spiropyrazoline, z - (p-diethylaminostyryl)
-6-dinithylaminopenzoxasol, 2-(P-
Oxazole compounds such as diethylaminophenyl)-4-(P-dimethylaminophenyl)-5-(2-chlorophenyl)oxazole, thiazole compounds such as 2-(P-diethylaminosteryl)-6-noethylaminopenzothiazole Compound, bis(4-diethylamino-2-
triarylmethane compounds such as (methylphenyl)-phenylmethane, 1,1-bis(4-N,N --/ethelamino-2-methylphenyl)hebutane, 1,1,2
．． 2-tetrakis(4-N,N-dimethylamino-2-
Ilyaryl alkali such as methylphenyl)ethane,
triphenylamine, poly-N-vinylcarbazole,
Examples include teribinylpyrene, polyvinylanthracene, polyvinylacridine, /IJ-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.

Further, these charge transport substances can be used alone or in combination of two or more.

When the charge transport material does not have film-forming properties, a film can be formed by selecting an appropriate binder. Examples of resins that can be used as binders include acrylic resin,
? Realylate, I-lyester, I-recarbonate, ?
Listyrene, acrylonitrile-styrene copolymer,
Insulating resins such as acrylonitrile-citadiene copolymer, polyvinyl polymer, polyvinyl formal, polysulfone, polyacrylamide, polyamide, chlorinated copolymer, or organic resins such as polyvinylcarbazole, polyvinylanthracene, polyvinylpyrene, etc. Mention may be made of photoconductive polymers.

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 5 microns to 30 microns, with a preferred range of 8 microns to 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. Examples of substrates having a conductive layer include those in which the substrate itself is conductive;
For example, aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium,
Nickel, indium, gold, platinum, etc. can be used, and in addition, plastics having a layer formed by vacuum evaporation of aluminum, aluminum alloy, indium oxide, tin oxide, indium oxide-tin oxide alloy, etc. (for example, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, acrylic resin, polyfluorinated ethylene, etc.), or conductive particles (e.g. carboxylic resin, silver particles, etc.) are coated on the plastic together with a suitable binder. The substrate may be a substrate made of gelastec or paper impregnated with conductive particles, a plastic containing a conductive polymer, or the like.

A subbing layer having barrier and adhesive functions can also be provided between the conductive layer and the photosensitive layer. Subbing layer, casein,
Polyvinyl alcohol, nitrocellulose, ethylene-
Acrylic acid copolymer, I-lyamide (nylon 6, nylon 66, nylon 61O1 copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin,
It can be formed from aluminum oxide, etc.

The thickness of the undercoat layer is suitably 0.1 micron to 5 micron, preferably 0.5 micron to 3 micron.

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 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, and then visually imaged 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, it is necessary to negatively charge the surface of the charge transport layer, and when exposed to light after charging, holes generated in the charge generation layer are injected into the charge transport layer in the exposed area. , which then reaches the surface and neutralizes the negative charges, resulting in attenuation of the surface potential and an electrostatic contrast between the surface potential and the unexposed area.

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 properties 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 charged and exposed to light is small, and the photomemory property can be effectively improved. have.

Hereinafter, the present invention will be explained according to examples.

Example 1 Ammonia aqueous solution of casein (casein 1
Dissolve 1.2 g of 28% ammonia water and 1 g of 28% ammonia water in 222 g of water) using a wire round parr until the film thickness after drying is 1.
, 0 microns and dried. Next, a disazo pigment with the following structure (the manufacturing method is disclosed in Published Patent Publication No. 56-11)
6039) syt-1 3 g of the polyvinyl acetal resin of Resin Example &1 above was added to a solution dissolved in methyl ethyl ketone 9Qd, and dispersed with an attritor for 2 hours. This dispersion is applied onto the previously formed casein layer so that the film thickness after drying is 0.
．． It was coated with a wire round parr to a thickness of 3 microns and dried at 70°C to form a charge generation layer. Next, a hydrazone compound with the following structure (M method is published patent publication 57-
101844) 5y and I trimethyl methacrylate resin (number average molecular weight ioo, ooo) sg to toluene 70
m, and apply it on the charge generation layer so that the film thickness after drying is 15
It was coated with a wire round parr so as to have a micron thickness and dried to form a charge transport layer, which was used as a sample of Example-1.

Next, as a comparative example, the above polyvinyl acetal resin A1
As a substitute, an electrophotographic photoreceptor comparison sample-1 was prepared using a butyral resin (S-LEC BM-2) manufactured by Sekisui Chemical Co., Ltd. and the same treatment as above.

The electrophotographic photoreceptor produced in this way was manufactured by Kawaguchi Electric Co., Ltd.
Corona charging was carried out statically at 15kV using Seiden Copying Paper Testing Equipment Model 5P-428, and 1kV was charged in the dark.
After holding for 0 seconds, it was exposed to light at an illuminance of 5 Lux to examine the charging characteristics.

The charging characteristics include the surface potential (Vo) and the amount of light exposure (E) required to attenuate the potential to A when attenuated for 10 seconds in the dark.
1/' was measured. Furthermore, the electrophotographic photoreceptor is illuminated at an illuminance of 600.
After 3 minutes of exposure with Aux, the charging characteristics were checked again after 1 minute in the dark, and the surface potential V at that time. ' and early V. , that is, V. -yot was used to evaluate photomemory properties. The results are shown in Table 1.

Table 1 As is clear from Table 1, the sample of Example 1 has better sensitivity and photomemory than the comparative sample using a commercially available binder.

Furthermore, in order to evaluate the stability during repeated use, the photoreceptor prepared in this example was used in a PPC copier NP manufactured by Canon Co., Ltd.
-150z photosensitive drum cylinder, 10,000 copies were made using the same machine, and fluctuations in bright area potential (vL) and dark area potential (V, ) were measured at the initial stage and after 100 copies were copied. Similar operations were performed on comparative samples. The results are shown in Table 2.

Table 2 It is clear from Table 2 that the sample of Example-1 is superior in durability and stability compared to the sample of Comparative Example.

Examples 2-5 Phthalic anhydride 148 p, urea 180 g, anhydrous 1st chloride
25 g of copper, 0.3 g of ammonium molybutate, and 3701 benzoic acid were reacted at 190° C. for 3.5 hours with stirring. After completion of the reaction, benzoic acid was distilled under reduced pressure, and then water washing, filtration, pickling, washing and filtration were sequentially carried out to obtain crude steel phthalocyanine 1301.

This crude 7-tasecyanin was dissolved in concentrated sulfuric acid at 1300 ml. After stirring at room temperature for 2 hours, the pigment was poured into a large amount of ice water, and the precipitated pigment was separated and washed with water until it became neutral.

Next, iCDMF was stirred and filtered 2.6 times, then stirred and filtered twice with MEK 2.6, and then water was added 2.6J.
Purified copper phthalocyanine 11 by stirring twice and vacuum drying.
5g was obtained.

Using the above steel phthalocyanine pigment 5y and using 1.7 g of the resin shown in Table 3 as a binder, a charge generation layer was first prepared in the same manner as in Example 1.

Next, a 15 micron charge transport layer was laminated using a pyrazoline compound having the following structure in place of the hydrazone compound of Example 1 to prepare an electrophotographic photoreceptor.

Polyvinyl acetal resin 4 according to the present invention as a comparative example
Electrophotographic photoreceptor comparative sample 2 was prepared in exactly the same manner as described above, using a polyvinyl acetal resin having an alkyl group of 12 carbon atoms in place of No. 2 to A5.

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.

Example-6 Chlorodian Blue 5 was used instead of the disazo pigment used in Example-1! Using I, I ribinyl acetal resin Example 1
A charge generation layer was prepared in the same manner except that 2.5 g of No. 4 was used. On top of the charge generation layer, 2.4.7-)
Dinitro-9-fluorenone 5J and Iso 4,4'-dioxydiphenyl-2,2'-prono-linker? 5 g of Nate (molecular weight 300,000) in 7 g of tetrahydrofuran
A coating solution prepared by dissolving 01111 was applied so that the coating amount after drying was 1097 m'', 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 became ■, and the NP-1
502 has been modified. The results are shown in Table 4.

Table 4 1・

Claims (3)

[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 provided with polyvinyl alcohol as a binder and the following general formula RCHO, (wherein R is substituted 1. An electrophotographic photoreceptor comprising a polyvinyl acetal resin obtained by an acetalization reaction with an aldehyde represented by (or an unsubstituted alkyl group having 5 to 9 carbon atoms). (2) The electrophotographic photoreceptor according to claim 1, wherein the alkyl substituent of R in the above general formula is a halogen, an alkoxy group, an aryl group, a hydroxyl group, a nitro group, or an amino group. (3) The electrophotographic photoreceptor according to claim 1, wherein the content of polyvinyl acetal resin in the charge generation layer is 20 to 90% by weight.