JPH09258463A - Formation of charge generating layer by dip coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ameliorate unequal coating (striped unequal steps) by adjusting the flow rate of the coating liquid fed into a coating vessel so as to satisfy a certain specified relation. SOLUTION: The coating liquid in a tank 1 is sucked by a pump 2 and is sent through a filter 3 to the bottom of the coating vessel 4. The coating liquid flows over from the top end of the coating vessel 4 and returns to the tank 1. The circulation of the coating liquid is thus established. A conductive substrate is used as the material to be coated and the coating liquid for an electrification generating layer is used as the coating liquid in this dip coating device. The amt. of the coating liquid for forming the electrification generating layer to be fed into the coating vessel 4 is required to satisfy the conditions expressed by equation as the dip coating conditions of this case. In the equation, R-(D/2)<2> πv>0, R denotes the flow rate (mm<3> /s) of the coating liquid, S denotes the coating liquid surface area (mm<2> ) at the top end of the coating vessel 4, D denotes the diameter (mm) of the material to be coated and V denotes a coating speed (mm/s).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrophotographic photosensitive member by a dip coating method, and more particularly to a coating method for uniformly coating a charge generating layer of a function-separated electrophotographic photosensitive member.

[0002]

2. Description of the Related Art Conventionally, a dip coating method has been widely practiced as a method for manufacturing an electrophotographic photosensitive member. The dip coating method is considered to be advantageous in terms of productivity and film thickness uniformity as a method for manufacturing a photoreceptor. In this method, the article to be coated is immersed in the coating solution, and coating is performed by moving the coating vessel containing the coating solution and the article to be coated. Due to the vertical movement of the coating liquid surface due to this relative movement, the coating liquid adheres to the inner wall of the coating tank and is dried, and it is mixed as a dry solid in the coating liquid, which may cause a coating film defect.

In order to improve this problem, an overflow type is known. This method keeps the height of the coating liquid level constant by supplying the coating liquid into the coating tank by a pump from a tank containing the coating liquid and continuously overflowing the coating liquid from the upper end of the coating tank. Is. However, even in this method, the liquid level of the coating liquid vibrates due to the influence of the pulsation of the pump, the vibration caused by the relative movement of the coating tank and the coating object, and the coating unevenness (streak step unevenness) is generated. May occur. In particular, when the photoreceptor is a function-separated type and a thin film (about 0.1 to 1 μm) of the charge generation layer is formed by coating, coating unevenness is likely to occur as a coating film defect. The coating unevenness of the charge generation layer affects the charging property, sensitivity, etc., and causes image density unevenness on the image as it is. Therefore, improvement thereof has been conventionally desired.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to improve charge generation (streaky step unevenness) when forming a charge generation layer of an electrophotographic photosensitive member by an overflow type dip coating method. It is to provide a layer forming method.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have examined the uniformity of the coating film of the charge generation layer formed by the overflow type dip coating in the electrophotographic photoreceptor having at least the charge generation layer and the charge transport layer. However, it was found that coating unevenness (streak step unevenness) can be improved by adjusting the flow rate of the coating liquid fed into the coating tank so as to satisfy a certain relationship, and the present invention was completed. It was

That is, the present invention relates to a method for forming a charge generating layer of an electrophotographic photosensitive member by a dip coating method, in which a charge generating layer is formed by immersing an article to be coated in a coating liquid in a coating tank. In doing so, the coating liquid is circulated so that the flow rate of the coating liquid fed into the coating tank satisfies the following formula (1).

[Equation 2] Here, R = flow rate of the coating liquid (mm ³ / s) S = surface area of the coating liquid (mm ² ) at the upper end of the coating tank D = diameter of object (mm) V = coating speed (mm / s)

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a dip coating device used in the present invention. The coating liquid in the tank 1 is sucked by the pump 2, passes through the filtration filter 3,
It is sent to the bottom of the coating tank 4. The coating liquid overflows from the upper end of the coating tank, returns to the tank 1, and the circulation of the coating liquid is established. In addition, 5 is a coating tank lid.

In the present invention, a conductive support is used as the article to be coated and a charge generation layer forming coating solution is used as the coating solution by the above dip coating apparatus. It is necessary that the flow rate of the charge generation layer forming coating liquid (hereinafter, simply referred to as the coating liquid) fed into the coating tank 4 satisfies the above formula (1).

Here, the surface area of the liquid level of the coating liquid in the coating tank when the object to be coated is not immersed in the coating tank is S (m
m ² ) and the diameter of the object to be coated (electrophotographic photoreceptor) is D (m
m), coating speed (relative speed of coating tank and object to be coated) is V
If it is (mm / s), the change in volume in the coating tank during coating of the object to be coated is (D / 2) ² πV. The amount of the coating liquid overflowing from the upper end of the coating tank during coating is (S- (D / 2) ² π) · a per unit time. Here, a is the rising speed of the coating liquid with respect to the coating tank in the vicinity of the upper end of the coating tank during coating of the object to be coated. When the flow rate of the coating liquid sent from the pump to the coating tank per unit time is R (mm ³ / s), R = (S− (D / 2) ² π) · a + (D / 2) ² πV, Therefore,

(Equation 3) Becomes Also, since the coating liquid always overflows,
a> 0. FIG. 2 is an explanatory diagram for explaining the relationship between the coating speed V of the object to be coated 6 and the rising speed a of the coating liquid.

In the overflow dip coating method, the relationship between the coating speed V and the ascending speed a of the coating liquid with respect to the coating tank in the vicinity of the upper end of the coating tank during coating of the object to be coated is 4 (mm / s). ) ≧ V−a ≧ −0.5 (mm / s) (where a> 0), the uniformity of the coating film of the charge generation layer formed is improved. That is, the coating liquid flow rate R per unit time sent from the pump to the coating tank is
The coating film of the charge generation layer to be formed becomes uniform by adjusting the following formula (1) and circulating the coating solution.

[0011]

(Equation 4)

The electrophotographic photosensitive member produced by the present invention may be any known one having a charge generating layer and a charge transporting layer as a photosensitive layer. As the charge generation layer forming coating liquid for forming the charge generation layer, a charge generation material and a binder resin added to an appropriate solvent are used. For example, as a charge generation material,
Amorphous selenium, crystalline selenium-tellurium alloy, selenium-arsenic alloy and other selenium compounds, zinc oxide, inorganic photoconductive materials such as titanium oxide, phthalocyanine series, squarylium series, anthanthrone series, perylene series, azo series, Organic pigments and dyes such as anthraquinone type, pyrene type, pyrylium salt and thiapyrylium salt can be used. As the binder resin, for example, polyvinyl butyral resin, polyvinyl acetal resin such as polyvinyl formal resin, polyamide resin, polyester resin, polycarbonate resin, acrylic resin, polyvinyl chloride resin,
Polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate copolymer,
Examples thereof include silicone resin, phenol resin, phenoxy resin, melamine resin, urea resin and polyurethane resin. The charge generating material and the binder resin are preferably mixed in a weight ratio of 5: 1 to 1: 2. Further, as the solvent used when preparing the coating solution, methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, chlorobenzene, toluene, xylene, methyl acetate , N-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform and the like, or a mixture of two or more thereof.

[0013]

Next, the present invention will be described in detail with reference to Examples and Comparative Examples. Example 1 An aluminum pipe having a diameter of 84 mm and a length of 340 mm was prepared as a substrate, and the surface was rounded by honing.
The surface was roughened to a = 0.18. On this substrate, 100 parts of a 50% toluene solution of tributoxyzirconium acetylacetonate (ZC540, manufactured by Matsumoto Kosho Co., Ltd.), 10 parts of γ-aminopropyltriethoxysilane (A1100, manufactured by Nippon Unicar Co., Ltd.), and n-butanol 130. The coating solution obtained by mixing the above parts was applied by dip coating and heated at 140 ° C. for 10 minutes to form a cured undercoat layer having a thickness of 0.1 μm. Next, as the coating liquid for forming the charge generation layer, the same amount of X-type metal-free phthalocyanine pigment and polyvinyl butyral resin (B
X-1 (manufactured by Sekisui Chemical Co., Ltd.) was dispersed in cyclohexanone at a solid content of 3.5% by weight to prepare a coating solution, which was placed in the dip coating apparatus shown in FIG. A coating tank having a cylindrical shape with an inner diameter of 110 mm is used. When coating at a coating speed of 4.5 mm / s, the flow rate R of the coating liquid per unit time sent from the pump to the coating tank should satisfy the above formula (1). At 30c
The coating liquid was circulated after adjusting to m ³ / s for coating.
After coating, dry at 100 ° C for 10 minutes to obtain a film thickness of 0.25
A μm coating film was formed. As a result, a charge generation layer having a uniform appearance was formed. Further, as a charge transport layer forming coating liquid, N, N-bis (3,4-dimethylphenyl) biphenyl-4-amine in the same amount and a polycarbonate resin were solidified in a mixed solvent of monochlorobenzene: tetrahydrofuran (1: 3). Prepare a liquid dispersed in an amount of 22% by weight, dip-coat it on the one already coated up to the charge generation layer by the above method, and use an oven dryer at 125 ° C. for 40
Drying was performed for a minute to form a coating film having a film thickness of 24 μm. A printer (GW116
When a copying operation was carried out using a 0 remodeling machine, manufactured by Fuji Xerox Co., Ltd., a good image was obtained.

Comparative Example 1 In a dip coating apparatus containing a coating liquid for forming a charge generating layer, the flow rate R of the coating liquid per unit time sent from a pump to a coating tank was 25 cm ³ / s (at this time, the formula (1)). The electrophotographic photosensitive member was manufactured in the same manner as in Example 1 except that the coating was carried out under the condition (1) was not satisfied. From the appearance, coating unevenness (streak-shaped step unevenness) was observed in the charge generation layer. When a copying operation was performed using a printer (GW1160 remodeling machine, manufactured by Fuji Xerox Co., Ltd.) using the manufactured electrophotographic photosensitive member, the gray image showed a portion corresponding to coating unevenness (streak step unevenness) of the charge generation layer. There was streak-like density unevenness on the surface.

Examples 2-5, Comparative Examples 2-3 Except that the coating speed V of the charge generation layer and the coating liquid flow rate R per unit time sent from the pump to the coating tank were changed.
Application was carried out in the same manner as in Example 1. Table 1 shows the results.
Shown in

[0016]

[Table 1]

As can be seen from Examples and Comparative Examples, when the flow rate R of the coating liquid per unit time fed from the pump to the coating tank was adjusted according to the present invention, the charge generation layer could be formed uniformly. On the other hand, when coating is carried out at a coating liquid flow rate outside the above range of the present invention, coating unevenness (streak step unevenness) occurs. That is, when the relationship of the coating speed V and the rising speed a of the coating liquid with respect to the coating tank in the vicinity of the upper end of the coating tank during application of the coating object is in an appropriate state, the state of the coating liquid surface near the coating object Is stable on dip coating,
A uniform coating film can be obtained.

[0018]

In the dip coating method according to the present invention, the flow rate of the coating liquid fed into the coating tank is adjusted so as to satisfy the above formula (1). Therefore, the charge generating layer forming coating liquid is used. In the case of forming a charge generation layer, it is possible to form a uniform charge generation layer without causing unevenness (streak-like step unevenness). Therefore, the electrophotographic photosensitive member manufactured according to the present invention can form an image without density unevenness.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a dip coating device used in the present invention.

FIG. 2 is an explanatory diagram for explaining a relationship between a coating speed of an object to be coated and a rising speed of a coating liquid.

[Explanation of symbols]

1 ... Tank, 2 ... Pump, 3 ... Filtration filter, 4 ... Coating tank, 5 ... Coating tank lid, 6 ... Object to be coated.

Claims (1)

[Claims] 1. When forming a charge generation layer of an electrophotographic photosensitive member by immersing an object to be coated in a coating liquid in a coating tank, the flow rate of the coating liquid fed into the coating tank is represented by the following formula (1). A method for forming a charge generation layer by a dip coating method, which comprises circulating the coating liquid so as to fill the coating liquid. [Equation 1] Here, R = flow rate of the coating liquid (mm ³ / s) S = surface area of the coating liquid (mm ² ) at the upper end of the coating tank D = diameter of object (mm) V = coating speed (mm / s)