JPH0534956A - Production of electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To enhance the sensitivity, durability and productivity of a sensitive body by carrying out heat treatment at the glass transition temp. of the electric charge transferring layer or above after coating with the electric charge transferring layer in place of conventional aging. CONSTITUTION:An electric charge generating layer formed on an electric conductive substrate is coated with an electric charge transferring layer and heat treatment is carried out at the glass transition temp. of the electric charge transferring layer or above to produce an electrophotographic sensitive body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrophotographic photosensitive member. More specifically, the present invention relates to a method for producing a highly sensitive and highly durable electrophotographic photoreceptor having a heat treatment step at a temperature not lower than the glass transition point of the charge transport layer.

[0002]

2. Description of the Related Art In recent years, electrophotographic copying machines and printers have been remarkably developed, and various types of models having various forms, types, and functions have been developed according to their uses, and correspondingly, photoconductors used for them have also been developed. A wide variety of things are being developed. Conventionally, inorganic compounds have been mainly used as electrophotographic photoreceptors from the viewpoint of sensitivity and durability. For example, zinc oxide, cadmium sulfide, selenium, etc. can be mentioned. However, these often use harmful substances, and their disposal poses a problem and causes pollution. When using selenium, which has good sensitivity,
It is necessary to form a thin film on the conductive substrate by a vapor deposition method or the like, which is inferior in productivity and causes a cost increase.

In recent years, amorphous silicon has attracted attention as a non-polluting inorganic photoconductor, and research and development thereof have been advanced. However, although these are also excellent in sensitivity, the productivity is extremely poor because the plasma CVD method is mainly used when forming a thin film, and the photoreceptor cost and the running cost are large.

On the other hand, the organic photoreceptor can be incinerated,
It has the advantage of being pollution-free, and many of them can be formed into thin films by coating and are easy to mass-produce. Therefore, it has an advantage that the cost can be significantly reduced and that various shapes can be processed according to the application. However, with respect to the organic photoconductor, problems remain in its sensitivity and durability, and it is strongly desired to develop an organic photoconductor with high sensitivity and high durability. Various methods have been proposed as means for improving the sensitivity of the organic photoconductor, but at present, a function-separated photoconductor mainly having a two-layer structure in which the functions are separated into a charge generation layer and a charge transport layer has become mainstream. There is. For example, the charge generated in the charge generation layer by exposure is injected into the charge transport layer, transported through the charge transport layer to the surface, and the surface charge is neutralized to form an electrostatic latent image on the surface of the photoreceptor. To be done. Compared to the single-layer type, the function-separated type has a smaller possibility of trapping the generated charges, and each layer can efficiently transport the charges to the surface of the photoconductor without hindering the function of each layer (US Patent No. 2803541).

As the organic charge generating material used in the charge generating layer, a compound which absorbs the energy of irradiated light and efficiently generates charges is selected and used.
Azo pigments (JP-A-54-14967), metal-free phthalocyanine pigments (JP-A-60-19146), metal phthalocyanine pigments (JP-A-57-146255), and squarium salts (JP-A-63). -113462 gazette) etc. can be mentioned. As the charge transport material used in the charge transport layer, it is necessary to select a compound having a high charge injection efficiency from the charge generation layer and a high charge mobility in the charge transport layer. For that purpose, a compound having a small ionization potential and a compound which easily generates a cation radical are selected. For example, a triarylamine derivative (JP-A-58-123542) and a hydrazone derivative (JP-A-57-101844) are selected. , Oxadiazole derivatives (JP-B-34-5466), pyrazoline derivatives (JP-B-52-4188), stilbene derivatives (JP-A-58-198043), triphenylmethane derivatives (JP-B-45-555). Gazette), 1, 3-
Butadiene derivatives (JP-A-62-287257) and the like have been proposed.

[0006]

However, the above-mentioned organic photoreceptor is still not satisfactory in terms of sensitivity as compared with the inorganic photoreceptor. In addition, charging, exposure,
In a series of electrophotographic processes such as development, transfer, and charge removal, the photoreceptor is placed under extremely severe conditions and required to have durability, but a satisfactory one has not yet been obtained. For these reasons, various organic photoconductors have been developed in the art to improve them.

It is known that the sensitivity of an electrophotographic photoreceptor is generally governed by the charge generation efficiency in the charge generation layer, the charge injection efficiency from the charge generation layer to the charge transport layer, and the charge mobility in the charge transport layer. Has been. For the purpose of improving the sensitivity of the electrophotographic photosensitive member, a charge generating material having a high charge generating efficiency and a charge transporting material having a large charge mobility have been actively developed. In fact, the charge injection efficiency from the charge generation layer to the charge transport layer has not been studied or improved.

This injection efficiency is as high as 50 in the high electric field region.
%, 10% or less in the low electric field region, and it is considered that the sensitivity can be further increased by increasing this.
Generally, in order to efficiently inject charges from the charge generation layer into the charge transport layer, it is necessary to make the ionization potential of the charge transport material smaller than that of the charge generation material to eliminate the energy barrier. However, even if this condition is satisfied, the injection efficiency is often low. It is considered that one of the causes is that partial microcrystals of the charge transport material or the binder used in the charge transport layer serve as a barrier. The other is a barrier due to an interface defect between the charge generation layer and the charge transport layer. These are the adhesion between the charge generation layer and the charge transport layer, poor adhesion, morphological defects that occur during drying after coating, physical irritation during use (contact with toner, paper, cleaning blade), It is thought that the cause is crystallization due to stimulation by an electric field.

As a method for solving these problems, use of a charge transport material having a lower crystallinity and excellent compatibility, use of a binder, and selection of a charge transport material having excellent adhesiveness and adhesion and a binder can be considered. However, materials developed to date for such purposes, except for the special polycarbonate binder,
Hardly considered. Further, the same cause can be considered for the problem of durability. That is, if any barrier is present at the interface between the charge generation layer and the charge transport layer, space charges will accumulate there, causing an increase in residual potential and destabilization of the photoreceptor surface potential. Further, the accumulation of the space charge causes deterioration of the charge transport material, which makes it impossible to withstand continuous use.

For the purpose of solving such problems of sensitivity and durability and obtaining a stable photoconductor, an aging process for one week or longer at room temperature is usually adopted after the photoconductor is manufactured. It is said that by carrying out this operation, the familiarity between the charge generation layer and the charge transport layer and the dispersibility of the charge transport material are improved, and an electrophotographic photoreceptor having stable performance can be obtained. However, this method is still insufficient in terms of improving sensitivity and durability, and requires aging for one week or longer, resulting in extremely poor productivity. Therefore, it is the actual situation that a method replacing the aging method is strongly desired in this field.

The object of the present invention is exactly at this point, and as a solution to this problem, after coating the charge transport layer,
By having a heat treatment step at a temperature not lower than the glass transition point of the charge transport layer, while obtaining the same effect as the above-mentioned aging operation in a short time, further, morphologically such as generation of fine crystals in the charge transport layer and interface defects. Another object of the present invention is to provide a method for producing an electrophotographic photosensitive member which is particularly effective for improving the sensitivity and durability of the photosensitive member and improving the productivity by improving various defects.

[0012]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, the present invention comprises (1) a step of applying a charge transport layer on a charge generating layer provided on a conductive support, and then performing a heat treatment step at a temperature not lower than the glass transition point of the charge transport layer. (2) A method for producing an electrophotographic photoreceptor, which comprises a step (2) of applying a charge transport layer and then previously drying the charge transport layer. 3) The method for producing an electrophotographic photosensitive member according to the above (1) or (2), wherein the heat treatment temperature does not exceed a temperature 20 ° C. higher than the glass transition point of the charge transport layer, and (4) The present invention relates to the method for producing an electrophotographic photosensitive member according to (1) or (2) above, wherein the heat treatment time is 10 minutes or more and 3 hours or less.

Examples of the base material of the conductive support in the present invention include metals such as aluminum and nickel, metal evaporated polymer films, metal laminated polymer films, and the like, and the shape thereof is, for example, a drum shape or a sheet. Shapes, belt shapes, etc. may be used, and any of them may be used. The charge generation layer in the present invention is composed of a charge generation material, a binder, an additive added as necessary, and the like. Examples of the manufacturing method thereof include a coating method, a vapor deposition method, a CVD method and the like.

The charge generating material is not particularly limited as long as it absorbs light of a specific wavelength and efficiently generates charges, and either an organic material or an inorganic material can be used. .. Examples of organic materials include perylene pigments, polycyclic quinone pigments, metal-free phthalocyanines, metal phthalocyanines, bisazo pigments, trisazo pigments, thiapyrylium salts, squarium salts, and azurenium pigments, which are mainly dispersed in a binder. Used. Examples of the inorganic material include selenium, selenium alloy, cadmium sulfide, zinc oxide, amorphous silicon, amorphous silicon carbide and the like.

The binder is not particularly limited, and examples thereof include condensation polymers such as polycarbonate, polyarylate, polyester and polyamide; polyethylene,
Polystyrene, polyacrylate, polymethacrylate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal, polyvinyl alcohol, polyacrylonitrile, polyacrylamide, styrene-acrylic copolymer, styrene-maleic anhydride copolymer, acrylonitrile-butadiene copolymer, etc. Addition polymer; polysulfone, polyether sulfone, silicone resin, phenoxy resin and the like are used, and of these, one kind or two or more kinds may be used. The amount of the binder used is 0.1% by weight to 80% by weight of the charge generation layer. 80% by weight
If the amount is larger, the sensitivity of the photoconductor is sharply reduced.

Additives used as required include
Examples thereof include antioxidants, ultraviolet absorbers, dispersants, pressure sensitive adhesives, sensitizers and the like. The film thickness of the charge generation layer manufactured using the above materials is 0.1 μm to 2.0 μm, preferably 0.1 μm to 1.0 μm. 0.1
If it is smaller than μm, the sensitivity is lowered, and if it is larger than 2.0 μm, the charging property is deteriorated. The charge transport layer in the present invention is formed in a thin film on the above charge generation layer. Specifically, the charge transport material, a binder and, if necessary, an additive are dissolved in a solvent to generate a charge. After coating on the layer, it is dried by heat treatment. At this time, before the heat treatment, the charge transport layer may be dried in advance at an arbitrary temperature below the glass transition point of the charge transport layer.

The solvent used is not particularly limited as long as it dissolves the charge transport material, the binder and the additive, and for example, an aromatic solvent such as benzene, toluene, xylene, tetralin, chlorobenzene; dichloromethane; Halogen solvents such as chloroform, dichloroethane, trichloroethylene, tetrachloroethylene, carbon tetrachloride; ester solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl formate, ethyl formate; diethyl ether, dipropyl ether, dioxane, tetrahydrofuran, etc. Ether-based solvents; alcohol-based solvents such as methanol, ethanol, isopropyl alcohol, n-butanol; dimethylformamide, dimethylacetamide, dimethylsulfoxide, etc., among which alone or 2 It may be mixed and used more.

The charge transport material used is not particularly limited as long as it is a known charge transport material, and examples thereof include hydrazone compounds, stilbene compounds, butadiene compounds, triarylamine compounds, bistriarylamine compounds and carbazole. Examples thereof include compounds, polyvinylcarbazole compounds, oxadiazole compounds, oxazole compounds, pyrazoline compounds, triphenylmethane compounds, and the like, and these may be used alone or in combination of two or more.

The binder is not particularly limited as long as it is an insulating material, and examples thereof include condensation polymers such as polycarbonate, polyarylate, polyester and polyamide; polyethylene, polystyrene, polyacrylate, polymethacrylate, polyvinyl butyral, polyacrylonitrile, Addition polymers such as polyacrylamide, styrene-acryl copolymer, styrene-maleic anhydride copolymer, acrylonitrile-butadiene copolymer, and the like; polysulfone, polyether sulfone, silicone resin, etc., among which alone or 2 You may mix and use 1 or more types.

Additives used as necessary include
Examples thereof include antioxidants, ultraviolet absorbers, quenchers, dispersants, lubricants and the like. The amount of the binder used in the present invention is 0.1 to 3% by weight, preferably 0.1 to 2% by weight, based on the charge transport material. If it is less than 0.1 weight ratio, the wear resistance is lowered, and if it is more than 3 weight ratio, the sensitivity is lowered. As the coating means of the charge transport layer in the present invention,
Without being particularly limited, for example, dip coater, bar coater, calendar coater, gravure coater,
The method of using a spin coater etc. is mentioned.

In the method for producing an electrophotographic photoreceptor of the present invention, after the above charge transport layer is coated on the charge generation layer, a heat treatment step is performed at a temperature not lower than the glass transition point of the charge transport layer. The heat treatment in the present invention means a heat drying step or a heat aging step after previously drying at an arbitrary temperature. The heat treatment temperature in the method for producing an electrophotographic photosensitive member of the present invention is not lower than the glass transition point of the charge transport layer, preferably not higher than 20 ° C. higher than the glass transition point. If the heat treatment temperature is lower than the glass transition point, the above-mentioned morphological factors are not improved, and the sensitivity and durability of the photoreceptor become insufficient, and if the temperature exceeds 20 ° C. higher than the glass transition point, morphological change is caused. Remarkably, the sensitivity is lowered. Here, for the glass transition point of the charge transport layer, a thin film of the charge transport layer is separately prepared and subjected to differential thermal analysis (for example, DS
C210, manufactured by Seiko Denshi KK) or a viscoelasticity test (for example, Rheovibron, manufactured by Rheometrics) can be known in advance. In general, the glass transition point of the charge transport layer is 50 to 200 ° C., and the temperature above this temperature is the temperature at which the heat treatment is actually performed.

The heat treatment time in the method for producing an electrophotographic photosensitive member of the present invention is usually 10 minutes to 3 hours, preferably 10 minutes to 2 hours. If the time is shorter than 10 minutes, sufficient drying cannot be performed unless the drying step is performed, and even if it is, the improvement of the above-mentioned morphological factors becomes insufficient, and the sensitivity and durability of the photoreceptor are reduced. I can't get enough sex. Further, if it is 3 hours or more, the charge transport layer is deteriorated, resulting in a decrease in sensitivity. The method for performing heat treatment under these conditions is not particularly limited, for example, leaving it in a general-purpose oven,
Alternatively, a method of heating by irradiating infrared rays or the like can be mentioned.

On the other hand, in the method of previously providing the step of drying the charge transport layer before the heat treatment step, the drying temperature and the drying time are not particularly limited as long as the solvent is evaporated and a thin film can be formed. Also, the drying method is not particularly limited, and examples thereof include a method of leaving it in a general-purpose oven and heating it by applying warm air, heating with a heater, or infrared rays. The film thickness of the charge transport layer thus produced is 10 μm to 50 μm, preferably 10 μm to 30 μm. If the film thickness is larger than 50 μm, the sensitivity is lowered, and if it is smaller than 10 μm,
Decrease in mechanical strength and durability occurs.

In the present invention, if necessary, an intermediate layer such as an adhesive layer or a barrier layer may be provided between the electrically conductive support and the charge generating layer. For example, polyamide,
Use either an insulating resin such as polyvinyl butyral, a conductive inorganic fine powder dispersed in an insulating resin, or a conductive polymer ion-doped into a conjugated polymer such as polypyrrole. You can Also,
A protective layer may be provided on the surface of the photoconductor.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 4.1 g of X-type metal-free phthalocyanine, polyvinyl butyral (S-REC BM-2, manufactured by Sekisui Chemical Co., Ltd.) 4.1
g, cyclohexanone 200 g, glass beads (diameter 1
650 g (mm) was put in a sand mill and dissolved and dispersed for 4 hours to prepare a charge generation layer coating material. An aluminum cylinder with a mirror-finished surface (diameter 4
(0 mm) was applied by dip coating so that the film thickness after drying would be 0.15 μm, and dried. Next, equation (1)

[0027]

[Chemical 1]

80 g of the hydrazone compound represented by and 80 g of a polycarbonate resin (Lexan 131-111, manufactured by Engineering Plastics Co., Ltd.) were dissolved in 450 g of dioxane to prepare a coating material for the charge transport layer. The charge generation layer previously coated with the coating material was coated so that the film thickness after drying would be 25 μm, and the coating was dried in an oven at 110 ° C. for 1 hour.
Heat treatment was also performed for time drying. The glass transition point (Tg) of the charge transport layer separately prepared by the same method was measured by a differential thermal analysis method (DSC210, manufactured by Seiko Denshi KK), and was 101.3 ° C.

The electrophotographic characteristics of the drum-shaped electrophotographic photosensitive member produced as described above were evaluated by a drum xerographic tester. First, it was charged at a corona voltage of −5.5 kV and the initial surface potential V ₀ was measured. Next, the surface potential V ₂ after standing for 2 seconds in a dark place was measured.
Next, a semiconductor laser with an oscillation wavelength of 790 nm (1 μW)
Was irradiated, and the half-exposure amount E _1/2 and the residual potential V _R were measured. As a result, -790V, -780V,
It was 0.35 μJ / cm ² and −0.6V. further,
After repeating the above operation 50,000 times, V ₀ , V ₂ , E _1/2 ,
Measurement of the V _R, respectively, respectively, -770
V, -760 V, 0.35 μJ / cm ² , and -3.7 V, which showed high sensitivity and high durability.

Further, as an actual machine test, an electrophotographic photosensitive member manufactured by the same method as described above was mounted on a commercially available laser beam printer of a reversal development system by a blade cleaning system, and a print test was conducted. As a result, there was no change in the image density after printing 50,000 sheets, and the high density of 1.4 (using a Macbeth densitometer) was maintained, and no blurring of characters or memory phenomenon was observed.

Examples 2 to 5 As charge transport materials, compounds shown in Table 1 (the following formulas (2) to (5)) were used.

[0032]

[Chemical 2]

[0033]

[Chemical 3]

[0034]

[Chemical 4]

[0035]

[Chemical 5]

The procedure was repeated until the charge transport layer was coated in the same manner as in Example 1 except that was used, and then heat treatment was carried out at the temperature shown in Table 1 for 30 minutes also as drying. With respect to the electrophotographic photosensitive member produced in this manner, Tg, V ₀ , V ₂ , E _{1/2 at} the initial stage and after 50,000 times were measured in the same manner as in Example 1.
V _R was measured.

Example 6 As a binder for the charge transport layer, a polyarylate resin (L1
003, manufactured by Unitika Ltd., except that Example 1 is used.
The same procedure as above was performed until the charge transport layer was coated, and then a heat treatment was performed at 120 ° C. for 30 minutes also as drying. With respect to the electrophotographic photosensitive member produced in this manner, Tg, V ₀ at the initial stage and after 50,000 times, by the same method as in Example 1,
V ₂ , E _1/2 and V _R were measured, and then a real machine test was conducted.

Example 7 The same procedure as in Example 1 was repeated until the charge transport layer was coated, followed by drying at 80 ° C. for 1 hour and further heat treatment in an oven at 110 ° C. for 1 hour. With respect to the electrophotographic photosensitive member thus produced, Tg, V ₀ , V ₂ , E _1/2 and V after the initial and 50,000 cycles were measured in the same manner as in Example 1.
_R was measured and then a real machine test was performed.

Comparative Example 1 The charge transport layer was coated and dried in exactly the same manner as in Example 7, and then aged at 25 ° C. for 1 week. Regarding the electrophotographic photosensitive member produced in this way,
In the same manner as in Example 1, Tg, V ₀ , V ₂ , E _1/2 and V _R at the initial stage and after 50,000 cycles were measured, and then the actual machine test was conducted.

Examples 8 to 11 As the charge transport material, the compounds shown in Table 2 (above, respectively,
The procedure is carried out in the same manner as in Example 1 except that the formulas (2) to (5) are used, until the charge transport layer is coated, followed by drying at 80 ° C. for 1 hour and further heat treatment at the temperature shown in Table 2 for 1 hour. Was done. With respect to the electrophotographic photosensitive member thus produced, Tg and V ₀ , V ₂ , E _1/2 and V _R at the initial stage and after 50,000 cycles were measured in the same manner as in Example 1.

Comparative Examples 2 to 5 As the charge transport material, the compounds shown in Table 2 (above,
The procedure was repeated until the charge transport layer was coated in the same manner as in Example 1 except that the formulas (2) to (5) were used, followed by drying at 80 ° C. for 1 hour and further aging at 25 ° C. for 1 week. .. With respect to the electrophotographic photosensitive member thus produced, Tg and V ₀ , V ₂ , E _1/2 and V _R at the initial stage and after 50,000 cycles were measured in the same manner as in Example 1.

Example 12 As a binder for the charge transport layer, polyarylate resin (L1
No. 003, manufactured by Unitika Ltd.) is performed until the charge transport layer is coated in the same manner as in Example 1, and then 8
It was dried at 0 ° C. for 1 hour and further heat-treated at 120 ° C. for 1 hour. With respect to the electrophotographic photosensitive member thus produced, Tg, V ₀ , V ₂ , E _1/2 and V _R at the initial stage and after 50,000 cycles were measured by the same method as in Example 1, and then the actual machine test was conducted. I did.

Comparative Example 6 In the same manner as in Example 12, the charge transport layer was coated and dried, and then aged at 25 ° C. for 1 week. Regarding the electrophotographic photosensitive member produced in this way,
In the same manner as in Example 1, Tg, V ₀ , V ₂ , E _1/2 and V _R at the initial stage and after 50,000 cycles were measured, and then the actual machine test was conducted.

Regarding the above results, Examples 1 to 6 are shown in Table 1.
In addition, Examples 7 to 12 and Comparative Examples 1 to 6 are shown in Table 2, and the actual machine test is shown in Table 3.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

As shown in the results of Tables 1 and 2, in any of the examples, the residual potential V _R and the half-exposure amount E _1/2 were initially 50,000 times regardless of which charge transport material or binder was used. An electrophotographic photoreceptor having high sensitivity and high durability, in which the surface potentials V ₀ and V ₂ were small after the repetition and showed little change after the initial and 50,000 times repetition, was obtained. On the other hand, as shown in the comparative example in Table 2, when the heat treatment temperature is lower than the glass transition point, the residual potential V _R and the half-exposure amount E _1/2 are initially 50,000 even after aging at low temperature for a long time. It was found that the electrophotographic photosensitive member was large both after repeated times and had large changes in surface potentials V ₀ and V ₂ after the initial and 50,000 times repeated, and was inferior in sensitivity and durability.

Further, in the actual machine test shown in Table 3, in the embodiment, there is almost no difference between the initial image density and the image density after printing 50,000 sheets, and there is no character blurring or memory phenomenon. It turned out to be a high-performance photoconductor. On the other hand, in each of the comparative examples, a decrease in image density was observed after printing several thousand sheets, and the image density after printing 50,000 sheets was low, indicating that the performance was poor.

[0050]

EFFECT OF THE INVENTION In the method for producing an electrophotographic photosensitive member of the present invention, it is conventionally used because it has a heat treatment step at a temperature not lower than the glass transition point of the charge transport layer after coating the charge transport layer. Unlike the aging operation, it is possible to improve the sensitivity and durability of the photoconductor and the productivity.

Claims (4)

[Claims] 1. An electron characterized by comprising a step of applying a charge transport layer on a charge generating layer provided on a conductive support and then performing a heat treatment step at a temperature not lower than the glass transition point of the charge transport layer. Manufacturing method of photographic photoreceptor. 2. The method for producing an electrophotographic photosensitive member according to claim 1, which further comprises a step of drying the charge transport layer after coating the charge transport layer. 3. The method for producing an electrophotographic photosensitive member according to claim 1, wherein the heat treatment temperature is within a range of 20 ° C. higher than the glass transition point of the charge transport layer. 4. The method for producing an electrophotographic photosensitive member according to claim 1, wherein the heat treatment time is 10 minutes or more and 3 hours or less.