JPH0441338B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic photoreceptor having at least two layers, a charge generation layer and a charge transport layer, further comprising at least 10% of the total pigment contained in the charge generation layer in the electrophotography photoreceptor. This invention relates to an electrophotographic photoreceptor characterized by being an organic pigment. As electrophotographic photoreceptors using organic photoconductive substances, poly-9-vinylcarbazole, poly-9-
Those using photoconductive polymers such as vinyl anthracene, poly-9-vinylphenyl anthracene, 2,5-bis(1-diethylaminophenyl)-1,3,4-oxadiazole, P- Those using low-molecular organic photoconductive substances such as diethylaminobenzaldehyde-N,N-diphenylhydrazone, P-phenyl-3-P-diethylaminostyryl-5-P-diethylaminophenylpyrazoline, and furthermore, such organic light Combinations of conductive substances and various dyes and pigments are known. An electrophotographic photoreceptor using an organic photoconductive substance has good film forming properties and can be produced by coating, so it is possible to provide an extremely highly productive and inexpensive photoreceptor. In addition, it has the advantage that color sensitivity can be freely controlled by selecting the sensitizers such as dyes and pigments used.
A wide range of studies have been carried out so far. In particular, recently, with the development of functionally separated photoreceptors, which have an organic photoconductive pigment as a charge generation layer and a so-called charge transport layer laminated with the aforementioned photoconductive polymer or low-molecular organic photoconductive substance, Improvements are being made in the sensitivity and durability, which were considered to be shortcomings of electrophotographic photoreceptors. Furthermore, various compounds and pigments that are suitable for functionally separated photoreceptors have also been discovered. On the other hand, since the function-separated photoreceptor has at least a two-layer structure of 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, causing a charge on the surface of the photoreceptor. disappears, producing electrostatic contrast. In order to put such a laminated electrophotographic photoreceptor into practical use, it is currently desired to further improve the sensitivity and potential stability during long-term use. By the way, by making the particle shape of the organic pigment used in the charge generation layer of the laminated electrophotographic photoreceptor into a flaky shape according to the present invention, it has become possible to significantly improve the characteristics with respect to the above-mentioned problems. The reason why the use of flaky pigments in the charge generation layer significantly improves sensitivity and improves potential stability during long-term use is that in the case of flaky pigments, pigment particles are formed inside the charge generation layer. Because the flat surfaces face each other and are densely stacked, the hiding power is high, and the quantum efficiency of carriers generated by light is high. ), and as a result, the efficiency of carrier injection into the charge transport layer increases, which is presumed to have led to a marked improvement in sensitivity. Regarding potential stability during long-term use, since pigment particles are densely packed inside the charge generation layer, carriers generated by light are easily injected into the charge transport layer without being trapped. It is assumed that problems such as an increase in residual potential are becoming less likely to occur. The electrophotographic photoreceptor of the present invention will be explained in more detail. Examples of photoconductive organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, cyanine pigments, pyrylium pigments, thiopyrylium pigments, indigo pigments, scalic acid pigments,
Polycyclic quinone pigments and the like can be used as charge-generating materials for electrophotographic photoreceptors. At least 10 of the total pigments contained in the charge generating layer
%, preferably 30% or more is flaky organic pigment. Pigment dispersants include alcohol solvents such as methanol, ethanol, and isopropyl alcohol, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, aromatic solvents such as benzene, toluene, xylene, and chlorobenzene, and DMF. Various solvents such as , DMAC, etc. can be used. As the dispersion means, methods such as a sand mill, colloid mill, attritor, and ball mill can be used. Binder resins include polyvinyl butyral, formal resin, polyamide resin, polyurethane resin, cellulose resin, polyester resin, polysulfone resin, polycarbonate resin,
Acrylic resin, styrene resin, etc. are used. The charge generation layer can be formed by coating the above-mentioned dispersion directly on the conductive support or on the adhesive layer. It may also be coated on top of the charge transport layer. The thickness of the charge generation layer is 5μ or less, preferably
A thin film layer having a thickness of 0.01 to 1 μm is desirable. Most of the incident light is absorbed by the charge generation layer to generate a large amount of charge, and the generated charge carriers must be injected into the charge transport layer without being deactivated by recombination or trapping. Thickness is preferred. Coating methods include dip coating method, spray coating method, spinner coating method, bead coating method, Meyer bar coating method, blade coating method, roller coating method,
This can be done using a coating method such as a curtain coating method. For drying, it is preferable to dry to the touch at room temperature and then heat dry. Heat drying can be performed at a temperature of 30° C. to 200° C. for a period of time ranging from 5 minutes to 2 hours, either stationary or under ventilation. 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 trap 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-
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-(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-dimethylaminophenyl)-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,
Examples include 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 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 base having a conductive layer. As the substrate having the conductive layer, materials that are conductive themselves 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.), conductive particles (e.g. carbon black,
A substrate made of plastic coated with silver particles (silver particles, etc.) together with a suitable binder, a substrate made of plastic or paper impregnated 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 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, 0.3 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 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 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. Another specific example of the present invention is an electrophotographic photoreceptor in which the photoconductive organic pigment described above is contained in the same layer as a charge transport material. At this time, a charge transfer complex compound consisting of poly-N-vinylcarbazole and trinitrofluorenone can be used in addition to the above-mentioned charge transport substance. The electrophotographic photoreceptor of this example can be prepared by dispersing the aforementioned organic photoconductor and charge transfer complex compound in a polyester solution dissolved in tetrahydrofuran, and then forming a film thereon. All photoreceptors contain at least one type of pigment, and if necessary, pigments can be added to increase the sensitivity of the photoreceptor by combining pigments with different light absorption, or to obtain a panchromatic photoreceptor. It is also possible to use two or more types. The electrophotographic photoreceptor of the present invention can be used not only for electrophotographic copying machines, but also for laser printers and CRTs.
It can also be widely used in electrophotographic applications such as printers. Furthermore, the organic photoconductor of the present invention can be used not only in the above-mentioned electrophotographic photoreceptor but also in solar cells and optical sensors. Solar cells can be prepared, for example, by sandwiching the aforementioned organic photoconductors with indium oxide and aluminum. Hereinafter, the present invention will be explained according to examples. Example 1 In a 500ml beaker, 80ml of water and 16.6ml of concentrated hydrochloric acid (0.19
mole),

[Formula] 6.94g (0.029mol) of (C ₁₄ H ₁₃ N ₃ O, MW239.30)
and stir while cooling in an ice water bath to bring the liquid temperature to 3.
℃. Next, 4.2g (0.061mol) of sodium nitrite
was dissolved in 7 ml of water and added dropwise over 10 minutes while controlling the temperature within the range of 3 to 10°C, and after the dropwise addition was completed, the mixture was stirred for an additional 30 minutes at the same temperature. Carbon was added to the reaction solution to obtain a tetrazonation solution. next,
2 Put 700ml of water in a beaker and add 21g of caustic soda.
16.2 g of naphthol AS (3-hydroxy-2-naphthoic acid anilide) after dissolving (0.53 mol)
(0.016 mol) was added and dissolved. This coupler solution was cooled to 6°C, and while controlling the liquid temperature at 6 to 10°C, the above-mentioned tetrazotized solution was added dropwise over 30 minutes with stirring.Then, the solution was stirred at room temperature for 2 hours, and further left overnight. After filtering the reaction solution, wash with water and remove the crude pigment.
19.03g was obtained. Washing was then repeated five times with 400 ml each of N,N-dimethylformamide. Then each
Repeat washing 3 times with 500ml of MEK to remove purified pigment.
71.47 g of MEK paste was obtained. The solid content was 25% and the yield was 78%. The resulting pigment has the following structure. Aqueous solution of casein in ammonia (11.2 g of casein, 1 g of 28% ammonia water, 222 ml of water) on an aluminum plate.
was applied with a Mayer bar so that the film thickness after drying was 1.0μ, and dried. Next, the above disazo pigment 1
20g of MEK paste (solid content 5g) to 95ml of MEK
butyral resin (butyralization degree 63 mol%) 2
g was added to the dissolved liquid and dispersed in a sand mill for 40 hours. When this dispersion was observed under an electron microscope, it was found to be flaky. This dispersion was applied onto the previously formed casein layer using a Mayer bar so that the film thickness after drying was 0.5 μm, and dried to form a charge generation layer. Then the structural formula 5 g of hydrazone compound and 5 g of polymethyl methacrylate resin (number average molecular weight 100,000) were added to benzene.
Dissolve it in 70ml and apply it on the charge generation layer using a Mayer bar so that the film thickness after drying is 12μ.
It was dried to form a charge transport layer. On the other hand, in order to create a comparative sample, the crude pigment was synthesized in exactly the same manner, and then DMF, MEK
Soxhlet purification was carried out for 15 hours each. Pigment MEK
A photoreceptor was prepared in exactly the same manner as in Example 1, except that the paste was used, and was used as a comparative sample. As a result of electron microscopic observation of the pigment dispersion, the pigment was found to be columnar crystals. 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 5 lux, and the charging characteristics were examined. As for the charging characteristics, the surface potential (V _p ) and the exposure amount (E1/2) required to attenuate the potential to 1/2 when dark decayed for 1 second were measured. The results are shown below. V _p (-v) E1/2(lux.sec) Sample 1 580 3.2 Comparative sample 1 590 8.6 Furthermore, in order to measure the fluctuations in the bright area potential and dark area potential during repeated use, the sample prepared in this example was The photoreceptor was attached to the cylinder of an electrophotographic copying machine equipped with a -5.6 KV corona charger, an exposure optical system with an exposure amount of 10 lux.sec, a developer, a transfer charger, a static elimination exposure optical system, and a cleaner. This copying machine is configured to produce an image on transfer paper as a cylinder is driven. Using this copying machine, the initial bright area potential (V _L ), dark area potential (V _D ) and
The bright area potential and dark area potential were measured after 5000 uses, and the results are shown below.

[Table] From the above results, it is known that the electrophotographic photoreceptor of the present invention is extremely excellent in sensitivity and stability of V _D and V _L during long-term use. Example 2 In the same manner as in Example 1, a pigment represented by the following structural formula was prepared.
MEK pastes were prepared for Sample 2 and Comparative Sample 2, respectively. Same as Example 1 except that each paste was used and the charge transport material used in the charge transport layer was replaced with 1-(2)-pyridyl-3-P-diethylaminostyryl-5-P-diethylaminophenylpyrazoline. Photoreceptors were prepared using the same method as Sample 2 and Comparative Sample 2. The electron micrograph of the pigment dispersion used in the sample is
The crystals for Sample 2 and Comparative Sample 2 were flaky and columnar crystals, respectively. Charging characteristics were investigated in exactly the same manner as in Example 1. V _p (-v) E1/2(lux.sec) Sample 2 570 3.6 Comparative sample 2 580 9.5

[Table] Example 3 The flaky pigment used in Example 2 was added to 10%, 30%,
50% and correspondingly 90% columnar crystal pigment.
A photoreceptor was produced in exactly the same manner as in Example 2 except that %, 70%, and 50% were used. The charging characteristics of each photoreceptor are shown below.

[Table] All samples of the present invention containing flaky pigments had high sensitivity.

Claims (1)

[Claims] 1. An electrophotographic photoreceptor having at least two layers, a charge generation layer and a charge transport layer, characterized in that at least 10% of the total pigment contained in the charge generation layer is a flaky organic pigment. Photoreceptor.