JP2637495B2 - Electrophotographic photoreceptor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrophotographic photoreceptor, and more particularly, to an electrophotographic photoreceptor in which a surface layer contains a fluororesin powder and a photosensitive layer thereunder contains an antioxidant. It relates to a photoreceptor.

[Conventional technology]

The electrophotographic photoreceptor is required to have predetermined sensitivity, electrical physical properties, and optical characteristics according to the applied electrophotographic process. The surface layer of the photoreceptor, that is, the layer most distant from the support, is subjected to direct electrical and mechanical external forces such as corona charging, toner development, transfer to paper, and cleaning, so that durability against them is required. Is done. Specifically, there is a demand for durability against abrasion and scratches on the surface due to sliding contact, and deterioration on the surface due to ozone generated during corona charging under high humidity. In addition, there is a problem that toner adheres to the surface layer due to repeated development and cleaning of the toner. For this purpose, it is required to improve the cleaning property of the surface layer. Various methods have been studied to satisfy the various properties required for the surface layer as described above, and among them, it is possible to provide a resin layer in which a fluororesin powder is dispersed on the surface of the electrophotographic photosensitive member. Especially effective.

By providing a resin layer in which a fluorine-containing resin powder is dispersed on the surface of the electrophotographic photoreceptor, the durability of the surface of the electrophotographic photoreceptor is improved in terms of scratches, surface cleaning properties, abrasion, etc. It is also effective in preventing surface deterioration under high humidity because the property is improved.

On the other hand, when the electrophotographic photoreceptor is used in accordance with the applied electrophotographic process, in addition to the physical impact received from the process, the electrophotographic photoreceptor receives fatigue due to repeated exposure, or is generated by corona discharge. Exposed to ozone and nitrogen oxides. In particular, ozone and nitrogen oxides directly chemically act on the charge transport material on the surface of the electrophotographic photosensitive member, reduce the surface resistance, and affect the image. In order to prevent this, it is effective to use a charge transporting material having a high oxidation potential so that it does not easily react with the above-mentioned ozone or nitrogen oxide.

However, especially with respect to nitrogen oxides, in addition to acting on the electrophotographic photoreceptor in a gaseous state, it acts on the electrophotographic photoreceptor in the form of nitric acid by combining with moisture in the air.

Particularly near the corona charger, a large amount of nitric acid is generated, which adheres to the corona charger, moves onto the electrophotographic photosensitive member while the machine is idle for a long time, and further enters the inside of the electrophotographic photosensitive member. However, since the charge reaches the support, the portion under the charger lowers in charging ability and changes in sensitivity, causing a phenomenon that the portion has characteristics different from those of the other portions.

In order to prevent these phenomena from occurring, studies have been made to add an antioxidant to the surface layer to inactivate ozone or nitric acid and the like that enter the inside of the electrophotographic photosensitive member. It has worked well.

[Problems to be solved by the invention]

If the above two techniques are combined, an electrophotographic photosensitive member excellent in mechanical properties, surface lubricity, and moisture resistance should be completed. However, in reality, good things are not always possible. This is because the fluororesin powder taken up here has extremely poor dispersibility when dispersed in a binder resin, and it is almost indispensable to use a surfactant or the like as a dispersing aid for uniform dispersion. It can be said that.

However, when both the surfactant and the antioxidant coexist in the same layer of the electrophotographic photoreceptor, their interaction adversely affects the electrophotographic characteristics of the electrophotographic photoreceptor. This causes a decrease, an increase in residual potential, an increase in potential fluctuation due to durability, and the like.

An object of the present invention is to overcome the above-mentioned drawbacks, to have durability against the occurrence of surface abrasions and scratches caused by repeated rubbing during repeated use, to have moisture resistance, and to partially charge due to nitric acid and the like. An object of the present invention is to provide an electrophotographic photosensitive member that does not cause image unevenness due to non-uniformity and sensitivity unevenness.

Another object of the present invention is to provide an electrophotographic photoreceptor having high quality in a repetitive electrophotographic process, particularly high sensitivity.

[Means for solving the problem]

In the present invention, as a result of repeated studies according to such an object, a surface layer containing a fluorine-containing resin powder but not containing an antioxidant, and a next layer containing a phenolic antioxidant, The problem has been solved by providing an electrophotographic photosensitive member having a laminated structure.

That is, the present invention is an electrophotographic photosensitive member having a conductive support, a photosensitive layer and a surface layer, wherein the surface layer contains a binder and a fluorine-containing resin powder dispersed therein but does not contain an antioxidant, The electrophotographic photoreceptor in which the layer on the side in contact with the surface layer of the laminated photosensitive layer or the single-layered photosensitive layer contains a phenolic antioxidant.

In the present invention, as the fluorine-containing resin powder, ethylene tetrafluoride, ethylene trifluoride chloride, ethylene hexafluoropropylene, vinyl fluoride, vinylidene fluoride, ethylene dichloride diethylene chloride, trifluoropropylmethyldichlorosilane And the like, or a copolymer thereof, or a resin powder of a copolymer of these with vinyl chloride can be used as appropriate. In particular, an ethylene tetrafluoride resin and a vinylidene fluoride resin are preferable. The molecular weight of the resin and the particle size of the powder
It is selected within a range that does not affect the uniformity of the coating film to be formed. Specifically, the average particle size is 2 μm or less, preferably 1
μ or less.

The content of the dispersed fluororesin powder is suitably 1 to 50% by weight based on the total solid content of the surface layer. 1% content
If the amount is less than 50%, no sufficient effect can be obtained, and if it exceeds 50%, the electrophotographic properties are adversely affected.

The binder resin used for dispersion may be any polymer as long as it is a film-forming polymer, but from the viewpoint of having a certain degree of hardness even if used alone and not hindering carrier transport, polymethacrylic acid ester , Polycarbonate, polyarylate, polyester, polysulfone,
Vinyl chloride / vinyl acetate copolymer, polystyrene and the like are preferred.

The surface layer in which the fluororesin powder is dispersed in the binder does not necessarily need to be treated only as a protective layer. That is, the surface layer can contain the charge transporting material and function as a part of the charge transporting layer or contain the charge generating material and function as a part of the charge generating layer. The charge transport material / binder ratio or the charge generation material / binder ratio may be the same as that of the charge transport layer or the charge generation layer. The amount of the charge transporting material or the charge generating material to be contained can be appropriately selected depending on the performance of the electrophotographic photosensitive member. Even when the surface layer contains a charge transport material or a charge generation material, the effect of the fluororesin powder is sufficiently exhibited.

In the electrophotographic photoreceptor of the present invention, the photosensitive layer may be of a single-layer type, or may be of a laminated type in which a charge generation layer and a charge transport layer are functionally separated. In the case of a laminate type, the conductive support, the charge generation layer, the charge transport layer and the surface layer may be laminated in this order, or the order of the charge generation layer and the charge transport layer may be reversed. .

In the present invention, the phenolic antioxidant is contained in the entire photosensitive layer when the photosensitive layer is of a single layer type, and in the case of a laminated type, a layer in contact with the surface layer, for example, a conductive support, When the layers are stacked in the order of a layer, a charge transport layer, and a surface layer, they are contained in the charge transport layer. However, it may be contained in both the charge transport layer and the charge generation layer.

The added amount of the phenolic antioxidant is preferably 0.1 to 10 mol% based on the charge transporting material in the layer to be added. If the amount is less than 0.1 mol%, a sufficient effect cannot be obtained, and if it exceeds 10 mol%, the electrophotographic properties are adversely affected.

The phenolic antioxidants that can be used in the present invention include the following: When producing the electrophotographic photoreceptor of the present invention, the conductive support may be any as long as it has conductivity, for example, aluminum, metal such as stainless steel,
Alternatively, a cylindrical cylinder or film such as plastic or paper provided with a conductive layer by applying a conductive substance alone or with an appropriate binder resin is used. An undercoat layer (adhesive layer) having a barrier function and an undercoat function can be provided on these conductive supports. The undercoat layer is formed for the purpose of improving the adhesion of the photosensitive layer, improving the coatability, protecting the support, covering defects on the support, improving the charge injection property from the substrate, and protecting the photosensitive layer against electrical breakdown. be able to.

Known materials for the undercoat layer include polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, methyl cellulose, ethylene / acrylic acid copolymer, casein, polyamide, copolymerized nylon, glue, gelatin, and the like. These are dissolved in a suitable solvent and applied on a support.
Its film thickness is about 0.2 to 2.0 μm.

Examples of the charge generating material include pyrylium-based, thiapyrylium-based dyes, phthalocyanine-based pigments, anthantrone pigments, dibenzopyrenequinone pigments, pyranthrone pigments, trisazo pigments, disazo pigments, azo pigments, indigo pigments, quinacridone-based pigments, asymmetric quinocyanines, quinocyanines, and the like. Can be used.

As the charge transport material, pyrene, N-ethylcarbazole, N-isopropylcarbazole; N-methyl-N-
Phenylhydrazino-3-methylian-9-ethylcarbazole, N, N-diphenylhydrazino-3-methylian-9-ethylcarbazole, N, N-diphenylhydrazino-3-methylian-10-ethylphenothiazine, N,
N-diphenylhydrazino-3-methylian-10-ethylphenoxazine, p-diethylaminobenzaldehyde-N, N-diphenylhydrazone, p-diethylaminobenzaldehyde-N-α-naphthyl-N-phenylhydrazone, p-pyrrolidinobenzaldehyde- N, N-diphenylhydrazone, 1,3,3-trimethylindolenine-α-aldehyde-N, N-diphenylhydrazone, p-
Hydrazones such as diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrazone; 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) pyrazolin, 1- [pyridyl (3)]-3- (p-diethylaminostyryl) -5-
(P-diethylaminophenyl) pyrazolin, 1- [lepidyl (2)]-3- (p-diethylaminostyryl)
-5- (p-diethylaminophenyl) pyrazoline, 1
-[Pyridyl (2)]-3- (p-diethylaminostyryl) -4-methyl-5- (p-diethylaminophenyl) pyrazolin, 1- [pyridyl (2)]-3- (α-
Methyl-p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazolin, 1-phenyl-3
-(P-diethylaminostyryl) -4-methyl-5-
Pyrazolines such as (p-diethylaminophenyl) pyrazolin, 1-phenyl-3- (α-benzyl-p-diethylaminostyryl) -5- (p-diethylaminophenyl) pyrazolin, and spiropyrazolin; 2- (p-diethylaminostyryl)- 6-diethylaminobenzoxazole, 2- (p-diethylaminophenyl) -4-
Oxazole compounds such as (p-dimethylaminophenyl) -5- (2-chlorophenyl) oxazole; 2-
Thiazole compounds such as (p-diethylaminostyryl) -6-diethylaminobenzothiazole; bis (4-
Triarylmethane compounds such as diethylamino-2-methylphenyl) -phenylmethane; 1,1-bis (4-N,
N-diethylamino-2-methylphenyl) heptane,
1,1,2,2-tetrakis (4-N, N-dimethylamino-2-
Polyarylalkanes such as methylphenyl) ethane can be used.

In the present invention, as a method of dispersing the fluororesin powder in the resin solution, a method such as a homogenizer, a ball mill, a vibrating ball mill, a sand mill, an attritor, and a roll mill can be used. As a procedure, a binder resin is dissolved in an organic solvent, a fluororesin powder and a dispersing aid are mixed in necessary amounts, and the mixture is dispersed by the above-described dispersion method. Just mix them. When the charge generation material is a pigment, a dispersion of the charge generation material alone may be separately prepared according to the dispersion conditions of the charge generation material, and then mixed with the dispersion of the fluorine-containing resin powder, and the conditions allow. In this case, the charge generation material may be dispersed simultaneously with the fluorine-containing resin powder.

When manufacturing the electrophotographic photoreceptor of the present invention, as a method for applying each layer, for example, a coating method such as a dip coating method, a spray coating method, a spinner coating method, a bead coating method, a blade coating method, and a curtain coating method is used. be able to.
Here, especially when coating the surface layer in which the fluororesin powder is dispersed, the solvent used for one of the lower layer and the binder dissolves the other if the binder and the binder are the same type of resin or not the same type. In such a case, the dip coating method or the like may not be used, and in that case, the spray coating method or the like is suitable.

The thickness of the surface layer after coating and drying can be set to an appropriate thickness depending on the purpose. Particularly in a system containing a charge transporting material or a charge generating material, the surface layer also functions as a charge transporting layer or a charge generating layer. It does not deteriorate.

 Examples will be described below.

Example 1 A 5% methanol solution of 6-6,6-6,10-1,2 quaternary polyamide copolymer resin was applied by dipping on an aluminum cylinder support having a diameter of 80 mm and a length of 360 mm. 0.5
An μ undercoat layer was provided.

Next, the structural formula Was dispersed for 20 hours by a sand mill using 12 parts of a charge generation material, 6 parts of a polyvinyl benzal resin, 60 parts of cyclohexanone, and 1 mmφ glass beads. To this dispersion, 120 parts of tetrahydrofuran was added and mixed, and the mixed solution was applied on an undercoat layer to form a 0.2 μm charge generation layer.

Then the formula Is dissolved in 70 parts of a mixed solvent of monochlorobenzene and dichloromethane, and further charged with the phenolic antioxidant of No. 35 in the above table. 1 mol% was added and dissolved based on the transport material. This solution is applied on the charge generation layer by dip coating, dried with hot air at 120 ° C.
A μ-thick charge transport layer was formed.

Next, 5 parts of a low molecular weight polytetrafluoroethylene powder having an average primary particle diameter of 0.3 μm, and a fluorine-based comb-type graft polymer 0.5 having a fluoroalkylate in a side chain as a dispersing aid.
And 5 parts of bisphenol Z-type polycarbonate having a number average molecular weight of about 20,000 as a binder were mixed with 35 parts of monochlorobenzene, and dispersed in a ball mill for 50 hours.
To this dispersion, 52 parts of the above-described charge transporting material, 50 parts of polycarbonate, 700 parts of monochlorobenzene and 100 parts of dichloromethane are added, and the resulting liquid is applied on the charge transporting layer with an air spray coating device, and then heated at 120 ° C. It was dried to form a 5 μm surface layer. This electrophotographic photosensitive member is designated as Sample 1.

In addition, when preparing the coating solution for the surface layer of the sample 2 and the surface layer coating solution of the sample 1, the amount of the solvent to be added later was 300 parts of monochlorobenzene and 50 parts of dichloromethane. The phenolic antioxidant of No. 35 in the above table was added and dissolved in an amount of 1 mol% of the added charge transporting material, and the resulting dispersion was applied on the charge generation layer. Sample 3 was dried at 120 ° C. to form a charge transport layer having a thickness of 22 μm. Sample 3 was obtained by adding no antioxidant to the charge transport layer.

These samples 1 to 4 were set in a dry-type plain paper copier, and conditions were set so that the dark part potential was 650 V and the light part potential was 130 V.
An electrophotographic process including corona charging, image exposure, dry toner development, toner transfer to plain paper, and cleaning with a rubber blade was performed, and the image after 30,000 sheets of durability was evaluated. The results were as follows.

Next, these electrophotographic photoreceptors after endurance use were left in a copying machine for 24 hours, and the images were evaluated again. With respect to samples 1 to 3, images similar to those before leaving were obtained. In Sample 4, the sensitivity of the portion facing the corona charger was apparently improved, and when a halftone image was displayed, the portion became white as a band. Ie
Only Sample 1 did not show any scratches, white background fog, or strip-like white drop after 30,000 sheets were run.

Example 2 In the method of Example 1, polyvinylidene fluoride powder was used as the fluorine-containing resin powder, a fluorine-based bunlock polymer composed of a perfluoroalkyl group portion and an acrylic resin was used as a dispersing aid, and an antioxidant was used. The same result was obtained when No. 26 phenolic antioxidant in the above table was used.

Example 3 An 80 mmφ × 360 mm aluminum cylinder was used as a support, and a 5% methanol solution of the polyamide resin used in Example 1 was dip-coated thereon to form a 1 μm undercoat layer.

Next, the structural formula 1 part of the charge generating material and 10 parts of bisphenol Z-type polycarbonate are added to 60 parts of monochlorobenzene,
This mixture was dispersed in a stainless steel ball mill for 72 hours, and 6 parts of the charge transporting material used in Example 1 was further added and dissolved. Further, 1.5 mol% of the phenolic antioxidant No. 37 in the above table was added to this solution based on the charge transport material. This solution was applied onto the undercoat layer by dip coating to form a 15 μm photosensitive layer.

Next, except that the antioxidant was not added, the same method and the same components as in the method for preparing this photosensitive layer coating liquid were used, and when dispersed by a stainless steel ball mill, 4 parts of polytetrafluoroethylene resin powder was further dispersed. And, as a dispersing aid, 0.4 part of a fluorine-based chestnut-type graft polymer composed of a perfluoroalkyl group and a styrene resin was simultaneously added and dispersed to prepare a dispersion containing a charge transporting material. Monochlorobenzene was further added to this dispersion to form a solution having a solid fraction of 10%.
This is applied on the photosensitive layer with a spray coating device, and
To form a 5μ surface layer. The electrophotographic photoreceptor thus prepared is referred to as Sample 5.

In addition, when the photosensitive layer was provided, the thickness was set to 20 μm, and a sample without the surface layer was designated as Sample 6, and a sample 5 in which no antioxidant was added to the photosensitive layer was designated as Sample 7. Further, when the photosensitive layer was provided, both the polytetrafluoroethylene resin powder and the antioxidant were contained in the photosensitive layer.

The electrophotographic photoreceptors of Samples 5 to 8 were set in a plain paper copying machine in the same manner as in Example 1, and were subjected to corona charging, image exposure, dry toner development, transfer to plain paper, and cleaning strong exposure with a rubber blade. An image output durability test was performed by the process of removing the surface potential by the above method. The image evaluation after 30,000 copies is shown below.

The residual potential of these photosensitive members after strong exposure was measured and was as follows.

Further, in the same manner as in Example 1, these electrophotographic photosensitive members were
After leaving the machine in the machine for a time, the same image was obtained for Samples 5, 6, and 8 as before, but for Sample 7, the portion corresponding to the corona charger was found in the halftone image. It was a white band.

Example 4 A 5% methanol solution of a 6-6,6-6,10-1,2 quaternary polyamide copolymer resin was applied on an 80 mmφ, 360 mm long aluminum cylinder support by an immersion method to form a 0.5 μm A thick undercoat layer was provided.

Then the formula 12 parts of a charge transport material, 10 parts of a bisphenol Z-type polycarbonate and 1.5 mol% based on the charge transport material
Was dissolved in monochlorobenzene and dip-coated on the undercoat layer to form a charge transport layer having a thickness of 18 μm.

Then the formula Was added to 100 parts of a mixed solvent of tetrahydrofuran / cyclohexanone = 1/1, and dispersed by a sand mill until the average dispersed particle diameter of the charge generating material became 0.1 μm or less. did. 5 parts of the charge transport material and 1.5 mol% of the antioxidant No. 10 in the above table based on the charge transport material are dissolved in the dispersion, and after dissolution, the charge transport layer is spray-coated. It was applied on top to form a charge generating layer having a thickness of 3 μm. Further, 2 parts of polytetrafluoroethylene powder, 0.2 part of the fluorine-based graft polymer used in Example 1 and 8 parts of bisphenol Z-type polycarbonate were mixed with 100 parts of a mixed solvent of monochlorobenzene / dichloromethane = 7/3, and the mixture was mixed with a ball mill. 50
Time dispersed. This dispersion was applied onto the charge generation layer by a spray coating method to form a protective layer having a thickness of 3 μm. The photoreceptor thus prepared is referred to as Sample 9. Sample 9
Samples 10 and 9 having no protective layer were designated as sample 11 and those having no antioxidant in the charge transport layer and sample 9 in Sample 9. Electrons consisting of corona charging, latent image formation by image exposure, development with dry toner, transfer of toner to plain paper, cleaning process with urethane rubber blade, and removal of residual potential by strong exposure are applied to these samples 9 to 11. Image output durability of 10,000 sheets was performed by a photographic process, and the image after the durability and the evaluation of the potential were evaluated.

Further, after the samples 9 to 11 after 10,000 sheets durability were left in the machine for 24 hours, an image was again taken out, and a comparison of the halftone images was performed. The corresponding portion was in the form of a white band with almost the same width as the charger. This is considered to be because the nitric acid adhering to the charger moved to the photoreceptor while it was left and reached the support, and became a white band.

From this result, it was found that the durability of Sample 9 was excellent.

〔The invention's effect〕

Since the electrophotographic photoreceptor of the present invention is configured as described above, mechanical properties, surface lubricity, moisture resistance,
Has excellent durability.

Claims (1)

(57) [Claims] 1. An electrophotographic photosensitive member having a conductive support, a photosensitive layer and a surface layer, wherein the surface layer contains a binder and a fluorine-containing resin powder dispersed therein but does not contain an antioxidant. An electrophotographic photoreceptor wherein the layer on the side of the laminated photosensitive layer which is in contact with the surface layer or the single-layered photosensitive layer contains a phenolic antioxidant.