JPH052983B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor having a low molecular weight organic photoconductor that provides improved electrophotographic properties. [Prior Art] Various organic photoconductive polymers, including polyvinylcarbazole, have been proposed as photoconductive materials for use in electrophotographic photoreceptors, but these polymers have poor performance compared to inorganic photoconductive materials. Although it has excellent film formability and light weight, it has been difficult to put it into practical use until now because sufficient film formability has not yet been obtained, and sensitivity, durability, and environmental This is because they are inferior to inorganic photoconductive materials in terms of stability due to changes. In addition, hydrazone compounds disclosed in U.S. Patent No. 4150987, triarylpyrazoline compounds disclosed in U.S. Patent No. 3837851, and JP-A-51-94828
No. 9 described in Japanese Patent Application Laid-open No. 51-94829, etc.
- Low molecular weight organic photoconductors such as styryl anthracene compounds have been proposed. By appropriately selecting the binder used, such low-molecular-weight organic photoconductors can overcome the film-forming problems that had been a problem in the field of organic photoconductive polymers. However, it cannot be said to be sufficient in terms of sensitivity. For these reasons, a laminated structure in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer has been proposed in recent years. Electrophotographic photoreceptors using this laminated structure as a photosensitive layer can now be improved in terms of sensitivity to visible light, charge retention, surface strength, and the like. Such an electrophotographic photoreceptor is disclosed in, for example, US Pat. No. 3,837,851.
No. 3871882, etc. However, in electrophotographic photoreceptors that use conventional low-molecular organic photoconductors in the charge transport layer, even if the sensitivity and characteristics have reached a practical level, bright areas deteriorate when repeatedly charged and exposed. The drawback of large fluctuations in potential and dark potential has not been fully resolved. In order to suppress the potential fluctuation during repeated use, for example, JP-A-57-122444, JP-A-62
-39863 discloses a method of mixing an antioxidant in a charge transport layer, and there is also a method published in JP-A-53
−26128, JP-A-60-164745, JP-A-62-
No. 105151 etc. describes a method of stabilizing by adding additives. However, the current situation is that these methods are not sufficiently effective, especially when repeatedly used over a long period of time. [Problems to be Solved by the Invention] An object of the present invention is to provide an electrophotographic photoreceptor that eliminates the above-mentioned drawbacks or disadvantages. Another object of the invention is to provide a new organic photoconductor. Another object of the present invention is to provide a novel charge transport material in a laminated photosensitive layer in which a charge transport layer and a charge transport layer are functionally separated. [Means for Solving the Problems] The present invention provides an electrophotographic photoreceptor having a photosensitive layer on a conductive support, wherein the photosensitive layer has the general formula ()
This is an electrophotographic photoreceptor characterized by containing a thioether compound represented by: general formula In the formula, R ₁ and R ₂ are methyl, ethyl, propyl,
Alkyl groups such as butyl, benzyl, phenethyl,
It represents an aralkyl group such as naphthylmethyl or an aryl group such as phenyl, naphthyl, anthryl, biphenyl. Also, R ₁ and R ₂ are combined to 5
Residues necessary to form a 6-membered ring are shown.
Further, the alkyl group, aralkyl group, and aryl group described above may have a substituent. These substituents include methyl, ethyl, propyl,
Alkyl groups such as butyl, alkoxy groups such as methoxy, ethoxy, propoxy, butoxy, alkyl groups such as benzyl, phenethyl, naphthylmethyl,
Halogen atoms such as fluorine, chlorine, bromine, and iodine, alkylthio groups such as methylthio, ethylthio, and butylthio, aralkylthio groups such as benzylethio, phenethylthio, or phenylthio, naphthylthio,
Examples include arylthio groups such as biphenylthio. Ar is an arylene group such as phenylene, naphthylene, anthrylene, biphenylene, and phenanthrylene, which may have a substituent, or pyridine, quinoline, indole, carbazole, thiophene, benzothiophene, acridine, phenothiazine,
Phenoxazine, phenazine, benzofuran,
Indicates a divalent heterocyclic group derived from dibenzofuran, benzoxazole, benzothiazole, benzotriazole, oxadiazole, oxathiadiazole, etc. These substituents include
Groups similar to those used for R ₁ and R ₂ can be mentioned. Further, n represents an integer of 0 or 1. X
is S-R ₃ or

[Formula], Y represents S-R ₃ , an alkyl group, an aralkyl group, or an aryl group which may have a substituent, and either or both of X and Y has a thioether structure. R ₃ and R ₄ have the same meanings as R ₁ and R ₂ described above. Specific examples of alkyl groups, aralkyl groups, and aryl groups that may have substituents are listed above.
Synonymous with R ₁ and R ₂ . Furthermore, X and Y are combined

【formula】

【formula】

【formula】

The residues necessary to form a thioether ring as shown in the formula are shown (m is an integer of 2, 3 or 4, and Z is a fused aromatic ring). An electrophotographic photoreceptor containing the novel compound represented by the general formula [] in its photosensitive layer has high sensitivity, and particularly, potential fluctuations caused by repeated charging and exposure over a long period of time are significantly reduced. The reason for this is not clear, but ozone, NOx,
Against environmental deterioration factors such as nitric acid that occur inside copying machines,

It is thought that the basicity of N in [Formula] and the d-orbital effect of the sulfur atom in the thioether structure work synergistically to prevent internal penetration of environmental deterioration factors. However, when one of X and Y is a hydrogen atom, the effect is small. The compounds of the invention are particularly represented by the general formula []
Ar is phenylene, and both X and Y are S-
This effect is particularly effective when there are two or more thioether structures, such as the thioether structure represented by R ₃ , or the residues necessary to combine to form a thioether ring having two thioether structures. Significant. Representative examples of compounds represented by the general formula [] are listed below. <Compound example> Next, a synthesis example of the above compound will be shown. (Synthesis method of compound No. 17) Trimethyl phosphite 23g (187mmol) and trithiocarbonate with the following structure

[Formula] Trithiocarbonate 3.4g (22mmol) is heated to 55℃ under a nitrogen stream 3
Stir for an hour to react. Next, P-diphenylaminobenzaldehyde dissolved in 35 g of methylene chloride
Add 5.4 g (20 mmol) and continue the reaction at 55°C for 15 hours. Next, the reaction solution was once dried to dryness under reduced pressure, and in the case of methylene chloride-petroleum ether, recrystallization was performed twice with a solvent to obtain 5.3 g of the target product as charged white crystals. Yield 71%, melting point 132-133℃ Elemental analysis value Theoretical value Measured value C 73.56 73.59 H 5.64 5.60 N 3.73 3.76 Compounds other than the synthesis examples are generally prepared using similar methods or with the corresponding aldehyde.

It is synthesized by a method such as dehydration condensation with a dithioether having an active methylene group as shown in the formula. In a preferred embodiment of the present invention, a compound represented by the above general formula can be used as a charge transport material in an electrophotographic photoreceptor in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer. The charge transport layer according to the present invention is preferably formed by applying a solution prepared by dissolving the compound represented by the above general formula and a binder in an appropriate solvent and drying the solution. Examples of the binder used here include polyacrylate resin, polysulfone resin, polyamide resin, acrylic resin, acrylonitrile resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, phenol resin, epoxy resin, polyester resin, alkyd resin, and polycarbonate. , polyurethane or copolymer resins such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, and the like.
In addition to such insulating polymers, organic photoconductive polymers such as polyvinylcarbazole, polyvinylanthracene, and polyvinylpyrene can also be used. The blending ratio of this binder and the charge transport substance of the present invention is 10 to 10 parts by weight of the charge transport substance per 100 parts by weight of the binder.
It is preferable to set it as 500 weight. The charge transport layer is electrically connected to the charge generation layer described below, 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. are doing. 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 this charge transport layer has a limit in its ability to transport charge carriers, it cannot be made thicker than necessary. Generally, it is 5 μm to 40 μm, but
The preferred range is 10 μm to 30 μm. The organic solvent used when forming such a charge transport layer varies depending on the type of binder used.
Alternatively, it is preferable to select a material that does not dissolve the charge generation layer or the subbing layer described below. Specific organic solvents include alcohols such as methanol, ethanol, and isopropanol; 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, and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, chloroform, Aliphatic halogenated hydrocarbons such as methylene chloride, dichloroethylene, carbon tetrachloride, trichlorethylene, etc., or aromatics such as benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, etc. can be used. Coating can be carried out using a coating method such as a dip coating method, a spray coating method, a Meyer bar coating method, or a curtain coating method. For drying, it is preferable to dry to the touch at room temperature and then heat dry. Heat drying is generally preferably carried out at a temperature of 30° C. to 200° C. for a period of 5 minutes to 2 hours, either stationary or under ventilation. The charge transport layer of the present invention may contain various additives. For example, plasticizers such as diphenyl, m-terphenyl, and dibutyl phthalate, silicone oil, grafted silicone polymers, surface lubricants such as various fluorocarbons, dicyanovinyl compounds, potential stabilizers such as carbazole derivatives, β-carotene, and Ni complexes. ，
Examples include antioxidants such as 1,4-diazabicyclo[2,2,2]octane. The charge generating layer used in the present invention includes inorganic charge generating substances such as selenium, selenium-tellurium, amorphous silicon, pyrylium dyes, thiapyrylium dyes, azulenium dyes, thiacyanine dyes, quinocyanine dyes, azulenium dyes, etc. cationic dyes, squbarium salt dyes, phthalocyanine pigments, anthorone pigments, dibenzpyrenequinone pigments, polycyclic quinone pigments such as pyranthrone pigments, indigo pigments, quinacridone pigments, azo pigments, etc. Materials selected from the generated substances can be used alone or in combination as a vapor deposited layer or a coating layer. Among the charge generating substances used in the present invention,
There are a wide variety of azo pigments in particular, but typical structural examples of particularly effective azo pigments are shown below. As a general formula of an azo pigment, if we express the central skeleton as A and A(-N=N-Cp)n as the coupler part as Cp as shown below (where n
=2, or3), first, the following are specific examples of A:

【table】

【table】

【table】

[Table] etc. These central skeletons A and couplers
Cp forms a pigment that becomes a charge-generating substance by appropriate combination. The charge-generating layer can be formed by dispersing the charge-generating substance described above in a suitable binder and coating it on a support, or by forming a vapor-deposited film using a vacuum evaporation device. You can get it by twisting it. The binder can be selected from a wide range of insulating resins, including poly-N-vinylcarbazole,
It can be selected from organic photoconductive polymers such as polyvinylanthracene and polyvinylpyrene. Preferably, polyvinyl butyral, polyacrylate (condensation polymer of bisphenol A and phthalic acid, etc.),
Examples include insulating resins such as polycarbonate, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, polyacrylamide resin, polyamide, polyvinylpyridine, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol, and polyvinylpyrrolidone. . The resin contained in the charge generation layer is suitably 80% by weight or less, preferably 40% by weight or less. Organic solvents used during coating include alcohols such as methanol, ethanol and isopropanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, amides such as N,N-dimethylformamide and N,N-dimethylacetamide, dimethyl Sulfoxides such as 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, dichloroethylene, carbon tetrachloride, trichloroethylene, etc., or aromatics such as benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, etc. can be used. The charge generation layer may contain the thioether compound of the present invention. The charge generation layer contains as much of said organic photoconductor as possible in order to obtain sufficient absorbance and in order to inject carriers into the charge transport layer during the lifetime of the generated charge carriers, a thin film layer, e.g. It is preferable to form a thin film layer having a thickness of 5 μm or less, preferably 0.01 μm to 1 μm. 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. A photosensitive layer having such a laminated structure of a charge generation layer and a charge transport layer is provided on a conductive support. As the conductive support, materials that have conductivity themselves, such as aluminum, aluminum alloy, stainless steel, titanium, nickel, and indium, can be used. In addition, aluminum, aluminum alloy, indium oxide, tin oxide, Plastic conductive particles having a layer formed by vacuum deposition of indium oxide-tin oxide alloy, etc. (e.g., aluminum powder, titanium oxide, tin oxide, zinc oxide, carbon black, etc.)
A support obtained by coating plastic or the above-mentioned conductive support with silver particles (silver particles, etc.) together with a suitable binder, a support obtained by impregnating plastic or paper with conductive particles, a plastic containing a conductive polymer, etc. can be used. A subbing layer having barrier and adhesive functions can also be provided between the conductive support and the photosensitive layer.
The undercoat layer can be 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. It can be formed by twisting it. The thickness of the undercoat layer is 0.1 μm to 5 μm, preferably
0.5 μm to 3 μm is suitable. In another embodiment of the present invention, the disazo pigments described above, or U.S. Pat.
Pigments having photoconductivity such as pyrylium dyes, thiapyrylium dyes, selenapyrylium dyes, benzopyrylium dyes, benzothiapyryllium dyes, naphthopyryllium dyes, and naphthothiapyrylium dyes disclosed in the same publication No. 3586500, etc. Dyes can also be used as sensitizers. In another specific example, a eutectic complex of a pyrylium dye and an electrically insulating polymer having an alkylidene diarylene moiety, as disclosed in US Pat. No. 3,684,502, can also be used as a sensitizer. This eutectic complex is composed of, for example, 4-[4-bis-(2-chloroethyl)aminophenyl]-2,6-diphenylthiapyrylium perchlorate and poly(4,4'-
isopropylidene diphenylene carbonate) in a halogenated hydrocarbon solvent (e.g. dichloromethane, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichlorolethane, 1,
1,2-trichloroethane, chlorobenzene, bromobenzene, 1,2-dichlorobenzene) and then dissolved in a non-polar solvent (e.g. hexane,
It is obtained as a particulate eutectic complex by adding octane, decane, 2,2,4-trimethylbenzene, ligroin). The electrophotographic photoreceptor in this specific example includes styrene-butadiene copolymer, silicone resin, vinyl resin, vinylidene chloride-acrylonitrile copolymer, styrene-acrylonitrile copolymer, and vinyl acetate-copolymer.
vinyl chloride copolymer, polyvinyl butyral,
Polymethyl methacrylate, poly-N-butyl methacrylate, polyesters, cellulose esters, etc. can be contained as a binder. The electrophotographic photoreceptor of the present invention can be used not only for electrophotographic copying machines, but also for laser printers,
It can also be widely used in electrophotographic applications such as CRT printers and electrophotographic plate making systems. According to the present invention, it is possible to provide an electrophotographic photoreceptor that is highly sensitive and exhibits little potential fluctuation even after repeated charging and exposure over a long period of time. Hereinafter, the present invention will be explained according to examples. Example 1 and Comparative Examples 1 to 2 A coating solution was prepared by dispersing 5 g of a disazo pigment represented by the following structural formula in a sand mill for 24 hours with a solution of 2 g of butyral resin (degree of butyralization 70 mol%) dissolved in 100 ml of cyclohexanone. . Apply this coating solution on an aluminum sheet until the dry film thickness is
A charge generation layer was formed by coating with a Mayer bar to a thickness of 0.2 μm. Next, as a charge transport material, the above-mentioned exemplified compound No. (13) 10
g and polycarbonate resin (average molecular weight 20000)
10 g of the monochlorobenzene was dissolved in 70 g of monochlorobenzene, and this solution was applied onto the charge generation layer using a Mayer bar to form a charge transport layer having a dry thickness of 20 μm, thereby producing a two-layer electrophotographic photoreceptor. The electrophotographic photoreceptor thus prepared was statically charged with corona at -5 KV using an electrostatic copying paper tester Model-SP-428 manufactured by Kawaguchi Electric Co., Ltd.
After holding it in a dark place for 1 second, it was exposed to light at an illuminance of 20 lux to examine the charging characteristics. As for the charging characteristics, the surface potential (Vo) and the exposure amount (E1/2) required to attenuate the potential ( _V1 ) by 1/2 when dark decayed for 1 second were measured. Furthermore, in order to measure the fluctuations in bright area potential and dark area potential during repeated use, the photoreceptor prepared in this example was attached to the photosensitive drum cylinder of a PPC copier NP-3525 manufactured by Canon Inc. , on the same plane
50,000 sheets were copied, and the fluctuations in the bright area potential (V _L ) and the dark area potential (V _D ) at the initial stage, after 5,000 copies, and after 50,000 copies were measured. Note that the initial V _D and V _L were set to -700V and -200V, respectively. For comparison, similar photoreceptors were manufactured using compounds (A) and (B) represented by the following structural formulas in place of the above-mentioned exemplified compounds as charge transport materials, and measurements were performed in the same manner. (Compound described in JP-A-62-134652) The results are shown in Table 1.

[Table] As is clear from Table 1, the photoreceptor using the compound of the present invention is highly sensitive and stable with little potential fluctuation even after a durability test of 50,000 sheets. Incidentally, after the photoconductors of Example 1 and Comparative Examples 1 and 2 were used for 50,000 sheets, the above-mentioned copying machine NP
-3525 under the same conditions as the initial stage, almost no fogging was observed in the examples, but quite severe background fogging was observed in the comparative examples. Examples 2 to 15 and Comparative Examples 3 to 12 In each of these Examples, Exemplified Compound No. (1) (4) (5) was used instead of Exemplified Compound (13) as the charge transport material used in Example 1. (8)(11)(16)(18)(21)(25)(28
) (29)
An electrophotographic photoreceptor was produced in the same manner as in Example 1, except that (34), (35), and (38) were used, and a pigment having the structure shown below was used as the charge generating substance. The electrophotographic properties of each photoreceptor were measured in the same manner as in Example 1. The results are shown in Table 2 below. In addition, as comparative examples, photoreceptors manufactured in the same manner using several compounds known as charge transport materials, and photoreceptors manufactured by adding 10% by weight of a known stabilizer to the compound of Comparative Example 2 were also similarly prepared. We carried out measurements. The results are shown in Table 3.

【table】

【table】

【table】

【table】

【table】

〔Effect of the invention〕

As explained above, the electrophotographic photoreceptor containing a thioether compound according to the present invention has high sensitivity, and has excellent durability with small fluctuations in bright area potential and dark area potential during continuous image formation by repeated charging and exposure. It is possible to provide an electrophotographic photoreceptor.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor having a photosensitive layer on a conductive support, wherein the photosensitive layer has the general formula () [In the formula, R ₁ and R ₂ are an alkyl group, an aralkyl group, an aryl group, which may have a substituent, or
Residues necessary for bonding R ₁ and R ₂ to form a 5- to 6-membered ring are shown. Ar represents an arylene group or a divalent heterocyclic group which may have a substituent,
n represents an integer of 0 or 1. X represents S-R ₃ or [Formula], Y represents S-R ₃ , an alkyl group, an aralkyl group, or an aryl group that may have a substituent, or X and Y combine to form a thioether ring. The residues necessary to form are shown. _R3
and R ₄ is synonymous with R ₁ and R ₂ . ] An electrophotographic photoreceptor comprising a thioether compound represented by the following. 2 In the general formula (), Ar represents a phenylene group, and X and Y both have a thioether structure represented by S-R ₃ or combine to form a thioether ring having two thioether structures. The electrophotographic photoreceptor according to claim 1, which is a residue necessary for.