JPH11149165A - Electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic photoreceptor using potential barrier through pn junction free from image defect and deterioration of sensitivity and high in quality and hardly being affected by printing circumstances and the surface conditions of a conductive substrate even in the case of enhancing carrier mobility in an n-type semiconductor layer and the film thickness of the n-type semiconductor layer, and even in a circumstance of low temperature or after repeating charging and exposure. SOLUTION: The electrophotographic photoreceptor is provided with a charge generating layer and a charge transfer layer laminated on the conductive substrate, and the charge generating layer contains a p-type semiconductor pigment dispersed into a resin, and an n-type semiconductor layer formed between the conductive substrate and the charge generating layer contains an n-type semiconductor pigment dispersed into a resin exhibiting an electrically nonrectifying conjunction state to the substrate, and the n-type semiconductor layer contains a triphenylmethane compound represented by the formula in which each of R<1> -R<4> is an H atom or an optionally substituted alkyl or aryl group; each of R<5> -R<7> is an H or halogen atom or an optionally substituted alkyl or aryl or amino group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoreceptor, and more particularly, to an n-type semiconductor layer having a pn junction with a charge generation layer, which is a p-type semiconductor layer, comprising a charge generation layer and a conductive support. The present invention relates to an electrophotographic photoreceptor having greatly improved electrophotographic characteristics by being provided between the photoconductors.

[0002]

2. Description of the Related Art In general, an electrophotographic photosensitive member is formed by forming a photosensitive layer on a conductive support. In particular, the photosensitive layer is of a function-separated type comprising a charge generation layer and a charge transport layer. Laminated electrophotographic photoconductors are often used. It is known that the characteristics of such an electrophotographic photoreceptor greatly change depending on the electrical bonding state between the conductive support and the charge generation layer.

For example, in the case of a non-rectifying type (a so-called ohmic type) in which a normal current and an electric field are in a proportional relationship, a charge is always injected from a conductive support during charging, so that a surface potential is reduced. And the chargeability of the electrophotographic photosensitive member is significantly reduced. In this case, it is known that by providing an electrical barrier layer between the photosensitive layer and the conductive support to prevent the injection of charges from the conductive support, the chargeability can be increased.

On the other hand, for example, a so-called Schottky type junction is used, as seen in a combination in which a metal having a small work function such as aluminum is used as a conductive support and a phthalocyanine compound is used as a charge generation material. When it has, it is known that its rectifying action restricts the injection of electric charge from the conductive support, and shows relatively excellent charging ability even without providing a barrier layer.

However, even in this case, a local drop in potential occurs due to defects scattered on the conductive support, crystallization of impurities, impurities in the coating film, and the like. It is known that it appears as a defect above, and it is common to provide an additional barrier layer as a countermeasure.

In the prior art, in an electrophotographic photoreceptor in which the function is improved by utilizing a barrier layer, for example, when an electrically insulating high molecular polymer is used for the barrier layer, an appropriate barrier property is obtained. Materials that can be used as a barrier layer are considerably limited due to the need to satisfy conditions such as adhesiveness and not dissolving when coating the upper layer. Injection of electric charge into the photosensitive layer is hindered, resulting in a decrease in sensitivity and an increase in residual potential, deterioration of electrophotographic properties due to a change in barrier properties due to water absorption, and insufficient adhesion with the photosensitive layer.

In the case where an insulating inorganic compound film such as Al ₂ O ₃ or SiO ₂ is used for the barrier layer, chemical treatment or means such as vacuum evaporation and sputtering are required, so that it takes a long time to form the film. However, there are problems such as cost and increase in cost, and the problems such as a decrease in sensitivity and an increase in residual potential as in the case of the resin coating type barrier layer have not been solved.

Further, there is also known a technique using a layer in which a white inorganic powder such as TiO ₂ or ZnO is dispersed in a resin as a barrier layer. However, this method basically has the same problems as the resin coating type. In order to obtain practical electrophotographic photosensitive characteristics, it was very troublesome to adjust the purity of the material, the particle size, the surface state, and the mixing ratio with the resin.

Therefore, as a means for solving these problems, a method of utilizing a potential barrier of a pn junction to prevent charge injection from a conductive support during charging and to increase the charging ability of a photoreceptor has been proposed. And JP-A-7-160010.

That is, phthalocyanine pigments such as titanyl phthalocyanine and metal-free phthalocyanine, which are often used in the charge generation layer of an electrophotographic photoreceptor, have the property of a p-type semiconductor. Between the dispersed charge generation layer and the conductive support, there is provided a layer in which an n-type semiconductor pigment that exhibits a non-rectifying bonding state with the conductive support is dispersed in a resin.

In this case, when the photoreceptor is negatively charged, a reverse bias electric field is applied to the formed pn junction, and the rectification of the pn junction prevents injection of charges (holes) from the conductive support. As a result, the charging ability is improved.

Here, when light of a wavelength having absorption in the charge generation layer is irradiated on the pn junction type photoreceptor, pairs of holes and electrons are generated in the charge generation layer, and the holes are p-type. It is injected and transported from the charge generation layer to the charge transport layer to neutralize the surface charge. On the other hand, electrons are injected into the conductive support through the n-type semiconductor layer.

In a conventional electrophotographic photosensitive member,
Since charge injection is prevented by a rectifying junction typified by a Schottky junction between the conductive support and the charge generation layer, or by the electric resistance of an independent barrier layer, the conductive support and the photosensitive layer Substantial contact between them can cause a large change in characteristics.

For example, when there is a stain or a defect on the conductive support, effective barrier formation is hindered, and the probability of appearing as a defect on an image becomes extremely large.

On the other hand, in the electrophotographic photoreceptor using the pn junction described above, the n-type semiconductor layer in contact with the conductive support and the support are in ohmic contact with each other. It is not necessary to set various conditions, and charge injection is prevented at a portion of the interface between the n-type semiconductor layer and the charge-generating layer, which is a p-type semiconductor layer, away from the surface of the conductive support. , And high quality image characteristics can be obtained.

However, in the n-type semiconductor layer in which the pigment is dispersed in the resin, the carrier trap density in the layer is large, and the structure in which the pigment is dispersed in the resin having a high electric resistance causes the carrier hopping conduction. However, there is a problem that the mobility of carriers is small due to the low density of hopping sites required for the above.

For this reason, when the thickness of the n-type semiconductor layer is large, or in a low-temperature environment, or when charging and exposure are repeated, the carrier mobility of the n-type semiconductor layer decreases and space charge due to carrier trapping occurs. In some cases, degradation of electrophotographic characteristics such as a decrease in sensitivity, an increase in residual potential, and an increase in dark decay may occur.

As a result, in the case of a drum-shaped photosensitive member that performs printing while rotating, the image pattern of the previous circumference appears again as an image or an inverted image even though no exposure is performed, which is called a memory phenomenon. Image defects.

[0019]

SUMMARY OF THE INVENTION The present invention solves these problems in an electrophotographic photoreceptor using a pn junction, and has excellent image characteristics and does not change its characteristics even when used repeatedly. Is to provide.

[0020]

As a result of diligent studies, the present inventor has found that the above-mentioned problems can be solved by the following means.

That is, according to the present invention, there is provided an electrophotographic photoreceptor having a photosensitive layer obtained by laminating a charge generation layer and a charge transport layer on a conductive support, wherein the charge generation layer is p-type.
A semiconductor pigment is dispersed in a resin, and an n-type semiconductor pigment is dispersed in a resin between the conductive support and the charge generating layer, so that the conductive support is electrically non-rectifying with the conductive support. An n-type semiconductor layer exhibiting an excellent junction state, and the n-type semiconductor layer contains a triphenylmethane compound represented by the following general formula.

[0022]

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(Wherein R ¹ , R ² , R ³ and R ⁴ represent a hydrogen atom or an alkyl group which may have a substituent,
Represents an aryl group, and R ⁵ , R ⁶ , and R ⁷ are a hydrogen atom, a halogen atom, or an alkyl group which may have a substituent,
Represents an aryl group, an alkoxy group, or an amino group. )

Preferably, in the triphenylmethane compound represented by the above general formula, R ¹ , R ² , R ³ , R ⁴ , R
^5, R ⁷ is a hydrogen atom or a methyl group, an electrophotographic photoreceptor which R ⁶ is an amino group which may have a hydrogen atom or a methyl substituent.

Preferably, the n-type semiconductor pigment is a perylene pigment, and more preferably, the p-type semiconductor pigment is a pigment selected from the group consisting of titanyl phthalocyanine pigments and metal-free phthalocyanine pigments. It is a photoconductor.

According to the present invention, the sensitivity decreases, the residual potential increases, and the dark decay increases when used in a low temperature environment or when charging and exposure are repeated, which are problems in the pn junction type electrophotographic photoreceptor. Thus, it is possible to provide an electrophotographic photoreceptor capable of obtaining a stable and high-quality image without being affected by the environment and use conditions.

N obtained by dispersing an n-type semiconductor pigment in a resin
It is observed by transient photocurrent (TOF) measurement that the drift mobility of photocarriers in the n-type semiconductor layer is increased by adding the above triphenylmethane compound to the n-type semiconductor layer. It is considered that this improves the carrier transport efficiency in the n-type semiconductor layer and suppresses the generation of space charges in the photosensitive layer, thereby solving the above problem.

Among these triphenylmethane compounds, leuco compounds, in particular, have a high electron transporting property, and when added to the n-type semiconductor layer, the carrier transporting efficiency is significantly increased. Examples of these leuco compounds include leuco bases of triphenylmethane dyes such as magenta, methyl violet, crystal violet and malachite green. Among them, leucomalachite green has a particularly large effect on improving carrier transport efficiency, and is particularly preferable.

In the present invention, the amount of the triphenylmethane compound added to the n-type semiconductor layer is particularly preferably in the range of 1 to 25% by weight based on the pigment of the n-type semiconductor layer. The effect on the improvement is particularly remarkable.

Further, the thickness of the n-type semiconductor layer is 0.5 μm
As described above, a sufficient rectifying property by the pn junction can be obtained. In particular, when the film thickness is in the range of 5 to 20 μm,
Defects on an image due to defects, contamination, and the like on the surface of the conductive support can be effectively improved.

Examples of the pigment which can be used in the n-type semiconductor layer in the present invention include organic pigments such as disazo pigments, perylene pigments, anzanthrone pigments and perinone pigments, and inorganic pigments such as cadmium sulfide and zinc sulfide. Pigments. Of these, perylene pigments in particular have a large electron transporting ability, and the addition of the triphenylmethane compound in the present invention further improves the electron transport efficiency,
A good pn junction type photoconductor can be obtained.

On the other hand, examples of pigments that can be used in the p-type charge generation layer include organic pigments such as phthalocyanine pigments and merocyanine pigments, and inorganic pigments such as hexagonal selenium. Of these, phthalocyanine-based pigments, particularly titanyl phthalocyanine-based pigments and metal-free phthalocyanine-based pigments, have a large quantum yield, provide a highly sensitive photoreceptor, and have a better pn junction with the n-type semiconductor layer than the perylene-based pigment. It is particularly preferred to form

The p-type and n-type semiconductor materials used in the electrophotographic photoreceptor of the present invention are not limited to those described above, and two or more p-type or n-type semiconductor materials may be used. Can be used in combination.

The charge generation layer and the n-type semiconductor layer are generally formed with p-type and n-type semiconductor pigments dispersed in a suitable binder resin, respectively. As the binder resin for dispersing these p-type and n-type semiconductor pigments, a polymer capable of forming a film is preferable.

Examples of such high-molecular polymers include polycarbonate, polyester, methacrylic resin, acrylic resin, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, and styrene.
Butadiene copolymer, vinylidene chloride-acrylonitrile polymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, silicone resin, silicone-alkyd resin, phenol-formaldehyde resin, styrene-alkyd resin , Poly-N-
Vinyl carbazole, polyvinyl butyral, polyvinyl formal, polysulfone, casein, gelatin,
Examples include, but are not limited to, polyvinyl alcohol, ethyl cellulose, phenolic resin, polyamide, carboxy-methyl cellulose, vinylidene chloride-based polymer latex, polyurethane, and the like.

These binder resins are used alone or in combination of two or more. In particular, the pn junction state between the charge generation layer and the n-type semiconductor layer and the carrier mobility in the n-type semiconductor layer change depending on the magnitude of the electric resistance of these resins, and the chargeability, sensitivity, image characteristics, etc. Therefore, it is more preferable to select a resin that can obtain an appropriate resistance value and has a small change in electric resistance due to moisture absorption.

As the conductive support in the electrophotographic photosensitive member of the present invention, for example, a metal or alloy such as aluminum, copper, zinc, stainless steel, chromium, nickel, molybdenum, vanadium, indium, gold, platinum and the like was used. Metal plate, metal drum, belt, or conductive polymer, conductive compound such as indium oxide or aluminum,
Paper, plastic films, plates, drums, belts, etc. coated, vapor-deposited or laminated with a metal or alloy such as palladium or gold, or conductive carbon, etc.

It is necessary for these conductive supports to exhibit a non-rectifying junction with the n-type semiconductor layer. The conditions for non-rectifying joining are based on the material of the conductive support and the conductivity. It is determined by the combination of the pigment used for the semiconductor layer in contact with the support.

For example, when a perylene-based pigment is used for the n-type semiconductor layer, by using a material having a small work function such as aluminum for the conductive support, a non-conductive material is provided between the n-type semiconductor layer and the conductive support. Rectifying junctions are realized and are particularly preferred.

The charge transport layer in the invention is preferably of a hole transport type. Examples of the hole transport material include low molecular weight compounds such as pyrene compounds, carbazole compounds, hydrazone compounds, stilbene compounds, pyrazoline compounds, triphenylamine compounds, triphenylmethane compounds, benzidine compounds, and butadiene. And the like.

Examples of the high molecular compound include poly-N-vinyl carbazole, halogenated poly-N-vinyl carbazole, polyvinyl pyrene, polyvinyl anthracene, polyvinyl acridine, pyrene-formaldehyde resin, ethyl carbazole-formaldehyde resin, Triphenylmethane polymer, polysilane and the like. These charge transport materials are not limited to those listed here, and can be used alone or as a mixture of two or more.

FIG. 1 shows an example of the structure of the electrophotographic photosensitive member according to the present invention. An n-type semiconductor layer 2 is formed on a conductive support 1, and a charge generation layer 3 and a charge transport layer 4 are sequentially formed. After dissolving a binder resin in a solvent, an n-type semiconductor substance In general, each layer is formed by applying a coating material in which a p-type semiconductor material and a charge transport material are dispersed or dissolved.

Examples of the application method include dip coating, roll coating, spray coating, and the like, but are not limited thereto.

For the n-type semiconductor layer and the charge generation layer, a physical film forming method such as vapor deposition can be selected.

[0045]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In the examples, “parts” means “parts by weight”.

Example 1 4 parts of butyral resin (trade name "ESREC BH-3" manufactured by Sekisui Chemical Co., Ltd.) and 1 part of polyamide resin (trade name "CM-8000" manufactured by Toray Industries, Inc.) were mixed. Solvent (methylene chloride 50%, methanol 50
%) Dissolved in 100 parts. The following structural formula, which is an n-type semiconductor pigment,

[0047]

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A perylene pigment represented by the following formula (trade name "PALIOG"
EN Maroon L3820 (manufactured by BASF) was added and dispersed using a sand grinder to prepare a paint.
This paint has the following structural formula

[0049]

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Leucomalachite green (p,
0.5 part of p'-Benzylidenebis (N, N-dimethylaniline), manufactured by Kanto Chemical Co., Ltd.) was added to obtain a paint for an n-type semiconductor layer.

Next, 1 part of butyral resin was dissolved in 100 parts of methylene chloride, and 2 parts of α-type titanyl phthalocyanine as a p-type semiconductor pigment was added and dispersed using a vibration mill to obtain a paint for a charge generation layer. Was.

Further, the following structural formula which is a hole transport material

[0053]

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4 parts of a hydrazone compound represented by the following formula and a polycarbonate resin (trade name “PANLITE C-140”)
5 "(manufactured by Teijin Chemicals Ltd.) was dissolved in 40 parts of methylene chloride to obtain a paint for a charge transport layer.

Next, an aluminum plate having a film thickness after drying of 5
The prepared coating for the n-type semiconductor layer was applied using a bar coater to a thickness of μm, and dried. Next, similarly, a coating for a charge generation layer is applied on the n-type semiconductor layer so that the film thickness after drying is 0.4 μm, and after drying, the charge is further adjusted so that the film thickness after drying is 25 μm. A photoreceptor was prepared by applying a paint for the transport layer.

(Example 2) 2 parts of butyral resin and 3 parts of polyamide resin similar to those in Example 1 were dissolved in 100 parts of a mixed solvent.

[0057]

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A perylene pigment represented by the following formula (trade name "PALIOG"
EN Red L3910 (manufactured by BASF) was added and dispersed using a sand grinder, and 1 part of leucomalachite green was added thereto. This was used as a paint for an n-type semiconductor layer, applied in the same manner as in Example 1, and a charge generation layer and a charge transport layer similar to those in Example 1 were sequentially laminated thereon to produce a photoreceptor.

Example 3 An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that X-type non-metallic phthalocyanine was used as the p-type semiconductor pigment used in the charge generation layer.

Comparative Example A paint for an n-type semiconductor layer was prepared in the same manner as in Example 1 except that leucomalachite green was not added, and was applied in the same manner as in Example 1. A photoreceptor was prepared by sequentially laminating the same charge generation layer and electron transport layer.

(Electrical Characteristics) In order to evaluate the electrophotographic characteristics of the photoreceptors obtained in the respective Examples and Comparative Examples, electrophotography was performed using an electrostatic charging tester Model EPA-8100 (manufactured by Kawaguchi Electric Works). The properties were measured.

The measurement was carried out at 23 ° C. First, the electrophotographic photosensitive member was charged in a dark place by corona discharge at an applied voltage of −6 kV, and the surface potential immediately after this was set as an initial potential V _{0 to determine} the charging ability of the electrophotographic photosensitive member. Used for evaluation. Then 10 seconds, and measuring the potential after leaving in a dark place, and the V _10. Where the ratio V
It was to evaluate the potential retention capacity by ₁₀ / V _0.

Next, the light of a tungsten lamp passed through an interference filter of 780 nm was set so that the intensity became 1 μW / cm ² , and the photosensitive layer was irradiated with light for 15 seconds, and the decay curve of the surface potential was recorded. Here by measuring the surface potential after 15 seconds, was it a residual potential V _R. The calculated amount of exposure until the surface potential by light irradiation is reduced to 1/2 of V _10, were evaluated sensitivity as half-decay exposure ^{_{E 1/2 (mJ / m 2)}} . Thereafter, white light of 3000 lux was irradiated for 0.1 second to eliminate static electricity. Further, a change in characteristics after repeating the steps of charging, exposing, and removing electricity 100 times was measured. The results are shown in Table 1.

[0064]

[Table 1]

As is clear from Table 1, the electrophotographic photoreceptors of Examples 1 to 4 are compared with the electrophotographic photoreceptors of Comparative Examples in which the n-type semiconductor layer does not contain the triphenylmethane compound of the present invention. The residual potential was small, and the deterioration of dark decay due to repeated charging and exposure was small.

(Image characteristics) Outer diameter 30 mm, surface roughness 0.
The electrophotographic photosensitive members of Examples 1 to 4 and Comparative Example were coated on a 3 μm aluminum drum by a dip coating method so as to have the same film thickness condition, and dried to prepare an on-drum electrophotographic photosensitive member. To evaluate the image characteristics, a commercially available laser printer (trade name “Laser Jet 4” manufactured by Hewlett Packard) was used, and the prepared drum-shaped electrophotographic photoreceptor was mounted.
° C, 20% RH, 23 ° C, 50% RH, 35 ° C, 85%
A printing test was performed under three types of temperature and humidity environment conditions of RH, and the evaluation was performed.

As a result, the electrophotographic photoreceptors of Examples 1 to 4 can obtain clear images without background dirt under any environmental conditions, and even after printing 10,000 sheets continuously. Early quality was retained.

On the other hand, in the electrophotographic photosensitive member of the comparative example, 1
When a printing test was performed in an environment of 0 ° C. and 20% RH, a memory phenomenon was observed in which an image pattern on the front circumference of the drum appeared as an inverted image despite no exposure.

In the early stage of the printing test in an environment of 23 ° C. and 50% RH, such a memory phenomenon was not observed. However, when continuous printing was repeated about 1500 times, the image pattern of the front circumference of the drum was obtained. Was observed as a normal rotation image.

[0070]

The triphenylmethane compound of the present invention is contained in the n-type semiconductor layer of the pn junction type electrophotographic photoreceptor, whereby the carrier mobility in the n-type semiconductor layer is increased, and Even when the film thickness is increased, it is possible to prevent image defects such as a decrease in sensitivity in low-temperature environments and repeated charging / exposure and memory phenomena, and to improve the printing environment and the surface state of the conductive support. It is possible to provide a high-quality electrophotographic photoreceptor which is hardly affected and whose characteristics do not change even after repeated use.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating an example of a layer configuration of an electrophotographic photoconductor of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conductive support 2 n-type semiconductor layer 3 charge generation layer 4 charge transport layer

Claims (4)

[Claims] Claims: 1. An electrophotographic photoreceptor having a photosensitive layer comprising at least a charge generation layer and a charge transport layer laminated on a conductive support, wherein the charge generation layer is formed by dispersing a p-type semiconductor pigment in a resin. And an n-type semiconductor layer in which an n-type semiconductor pigment is dispersed in a resin between the conductive support and the charge generation layer, and which exhibits an electrically non-rectifying junction with the conductive support. And the n-type semiconductor layer contains a triphenylmethane compound represented by the following general formula. Embedded image (Wherein, R ¹ , R ² , R ³ , and R ⁴ represent a hydrogen atom, or
Represents an alkyl group or an aryl group which may have a substituent, and R ⁵ , R ⁶ and R ⁷ are a hydrogen atom, a halogen atom, or an alkyl group, an aryl group or an alkoxy group which may have a substituent. Represents an amino group. ) 2. R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁷ are each a hydrogen atom or a methyl group, and R ⁶ is a hydrogen atom or an amino group optionally having a methyl substituent. The electrophotographic photoreceptor according to claim 1, wherein: 3. The electrophotographic photoconductor according to claim 1, wherein the n-type semiconductor pigment comprises a perylene pigment. 4. The electrophotographic device according to claim 1, wherein the p-type semiconductor pigment is a pigment selected from the group consisting of titanyl phthalocyanine pigments and metal-free phthalocyanine pigments. Photoconductor.