JP3216347B2 - Immersion coating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dip-coating a coating on the surface of a cylindrical substrate, for example, by dipping a coating solution containing a photosensitive material on the outer peripheral surface of a cylindrical substrate for an electrophotographic photosensitive member. The present invention relates to a method for forming a uniform coating film by coating.

[0002]

2. Description of the Related Art A dip coating method is conventionally suitable as a method for forming a uniform coating film on the outer peripheral surface of a cylindrical substrate, and is widely used in the production of electrophotographic photosensitive drums. In such a dip coating method, a gripping device that grips a base using an expandable and contractible rubber member or the like is inserted into the base while the rubber member or the like is contracted, and then the rubber member or the like is press-fitted with air or the like. It is common practice to expand and press-contact and closely contact the inner wall of the cylindrical substrate to grip the substrate and apply dip coating. However, when the cylindrical substrate is immersed in a coating solution, the lower end opening of the cylindrical substrate is opened. It was necessary to prevent the coating liquid from entering the inside of the base from the portion and adhering to the inner peripheral surface of the base.

[0003] For this reason, it has been practiced to fit a gripping device airtightly into a cylindrical base, and to keep the lower part inside the cylindrical base airtight except for the lower end opening. On the other hand, a volatile solvent having a relatively low boiling point is usually used as the solvent of the coating solution, and the pressure of the space in the lower portion of the cylindrical substrate increases due to the solvent vapor, so that the lower end of the cylindrical substrate during the dip coating is applied. Bubbles were generated in the coating solution, and such bubbles sometimes impaired the uniformity of the coating film formed on the outer peripheral surface of the cylindrical substrate.

[0004] In order to prevent the generation of such bubbles, a method of adjusting the pressure in the lower space inside the cylindrical substrate by a gripping mechanism having a pressure adjusting function is disclosed in JP-A-60-132678 and JP-A-60-255164. Gazette, JP-A-63-
No. 315167.

[0005]

However, in such a method of adjusting the pressure in the lower space in the cylindrical substrate, it is necessary to delicately control the pressure, and further requires a special gas suction mechanism and a gripping mechanism. Also had the disadvantage of becoming complicated.
An object of the present invention is to prevent the generation of bubbles and to easily form a uniform coating film on the outer peripheral surface of a cylindrical substrate without requiring a delicate control of a pressure in a lower space in the cylindrical substrate and a complicated gripping mechanism. It is another object of the present invention to provide a dip coating method which can be formed on a substrate.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and the gist of the present invention is to dip and coat a cylindrical substrate in a coating solution to coat the outer peripheral surface of the cylindrical substrate. In the method of forming a film, there is provided a dip coating method characterized in that the lower end of the cylindrical substrate is immersed in the coating liquid, then pulled up once on the liquid surface of the coating liquid, then immersed in the coating liquid, and pulled up. .

Hereinafter, the present invention will be described in detail. FIG. 1 shows the outline of the steps in the dip coating method of the present invention.
This shows that a coating film is formed on the outer peripheral surface of the cylindrical substrate by following the steps of B → C → D → E → F → G.
As shown in FIG. 1A, the cylindrical substrate 2 is gripped by the gripping device 1 and moved to a position above the coating liquid 4, and is held relative to the surface of the coating liquid 4 while being gripped by the gripping device. And then dipped into the coating liquid from the lower end. FIG. 1B shows the cylindrical substrate 2 whose lower end is immersed in the coating liquid 4, and the axis of the cylindrical substrate is preferably perpendicular or substantially perpendicular to the surface of the coating liquid, and the lower end opening of the cylindrical substrate is preferable. Part 5
Is present in the coating solution. Here, by creating such a state, the solvent evaporates in the lower space inside the cylindrical substrate, and the air in this space is filled with the solvent vapor of the coating liquid.

FIG. 1C shows that the lower space has become the atmosphere of the coating liquid solvent vapor 3 due to the evaporation of the solvent, and
The gas volume in the lower space increases due to the evaporation vapor,
This shows a state in which the gas lower surface 6 has protruded from the lower end opening 5 of the base. After that, the lower end of the cylindrical substrate is once pulled up on the surface of the coating solution and then immersed in the coating solution, whereby the increased gas volume is released into the atmosphere, and the lower space is again sealed with the coating solution. It will be in the state of being caught.

As a result, most of the air in the lower portion of the cylindrical substrate is replaced by the solvent vapor of the coating solution.
Intrusion into the lower space inside the substrate is suppressed, so that bubbles can be prevented from being generated in the coating liquid from the lower end of the cylindrical substrate during dip coating, and a uniform coating film is formed on the outer peripheral surface of the cylindrical substrate. It is formed.

In the present invention, the state in which the lower end of the cylindrical base is once immersed in the coating liquid before being pulled up onto the coating liquid level means that the lower end opening of the cylindrical base is below the coating liquid level. Good, but the distance between the lower end opening of the cylindrical substrate and the liquid surface of the coating liquid is larger than 0 and smaller than 5 cm from the viewpoint that a factor that impairs the film thickness uniformity of the coating film is not left on the cylindrical substrate. It is preferably in a range larger than 0 and smaller than 2 cm.

In the present invention, the time during which the lower end of the cylindrical substrate is immersed in the coating solution after the lower end of the cylindrical substrate is immersed in the coating solution and once pulled up on the surface of the coating solution depends on the type of the solvent of the coating solution. The preferred time varies depending on the volume of the lower portion of the inside of the cylindrical substrate, the temperature of the coating solution and the atmosphere, the time from the start of immersion for actually applying to the end of the withdrawal, and the like. It is preferable that the relative speed between the cylindrical substrate and the surface of the coating liquid is substantially zero for a period from when the substrate is immersed in the coating liquid to when the lifting is started to once raise the surface of the coating liquid. Here, the substantial time is not limited as long as the substantial amount of air in the lower portion of the cylindrical substrate is at least equal to the time required for replacing the solvent vapor of the coating liquid with the amount capable of preventing the generation of bubbles, but the productivity is not limited. Considering the point, it is preferably 60 seconds or less, more preferably 1 second to 30 seconds.
Seconds.

Further, in the present invention, the state in which the lower end of the cylindrical substrate is once pulled up on the coating liquid surface and the time until the lower end is immersed in the coating liquid again, are as follows. The distance between the lower end opening of the cylindrical substrate and the liquid surface of the coating liquid is larger than 0 and smaller than 3 cm, more preferably larger than 0 and smaller than 1 cm, and the time, Due to the same point as above, it is preferably 3 seconds or less, more preferably 0.5 second to 2 seconds.
Seconds.

In FIG. 1E, the lower end of the cylindrical substrate is immersed in the coating solution and then pulled up once again on the surface of the coating solution to raise the relative speed between the cylindrical substrate and the surface of the coating solution again to a predetermined value larger than zero. FIG. 1 shows a state in which immersion in the coating solution is started.
F shows a state where the cylindrical substrate is immersed in the coating solution. This predetermined value may be the same as or different from the relative speed between the cylindrical substrate and the liquid surface of the coating solution in A.

FIG. 1G shows a state in which the outer peripheral coating film of the cylindrical substrate is being pulled up from the coating solution. At the start of immersion, the axis of the cylindrical substrate being immersed or pulled up is preferably perpendicular to the liquid surface of the coating solution. FIG.
FIG. 4 shows an example of the relationship between the relative speed between the cylindrical substrate and the coating solution level and the passage of time in each of the above steps. In this case, the lower end of the cylindrical substrate in the step shown in FIG. After immersion in the liquid, the relative speed between the cylindrical substrate and the coating liquid level is zero until the lifting is started to once raise the coating liquid level, and the process shown in FIG. , The relative velocity between the cylindrical substrate and the coating liquid surface during immersion in the step shown in FIG. 1B, and the relative speed between the coating liquid surface and the coating liquid surface before immersion in FIG. The case where the relative velocity between the cylindrical substrate and the coating liquid level before immersion in the step and the relative velocity between the cylindrical substrate and the coating liquid level during immersion in the step shown in FIG. I have.

FIG. 3 shows an example of a conventional case in which the lower end of a cylindrical substrate is immersed in a coating solution and is not once pulled up on the surface of the coating solution. As the cylindrical substrate in the present invention,
For example, in the case of a cylindrical substrate for an electrophotographic photoreceptor, any of those used for known electrophotographic photoreceptors can be used. Specifically, for example, a metal drum of aluminum, stainless steel, copper, or the like, or a laminate or a vapor-deposit of these metal foils can be used. Further, plastic drums, paper tubes, and the like, which have been subjected to a conductive treatment by applying a conductive substance such as metal powder, carbon black, copper iodide, and a polymer electrolyte together with a suitable binder, may be mentioned. Further, a plastic drum which contains a conductive substance such as metal powder, carbon black, and carbon fiber and is made conductive may be used. Further, a charge generation layer, an undercoat layer and the like may be provided on these cylindrical substrates.

As the coating solution in the present invention, for example, in the case of a coating solution for an electrophotographic photoreceptor, one or two selected from charge transporting materials, charge generating materials, dyes, electron-withdrawing compounds and the like. A coating solution in which the above and a binder are dissolved or dispersed in a solvent is used. The coating liquid may contain known additives such as a lubricant, a leveling agent, and an antioxidant.

Well-known materials can be used as the charge transporting material, the charge generating material, the dye, the electron withdrawing compound, the binder and the like. As the binder, for example, styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, polymers and copolymers of vinyl compounds such as butadiene, polyvinyl acetal, polycarbonate, polyester, polysulfone, polyphenylene oxide, polyurethane, cellulose Various polymers such as esters, cellulose ethers, phenoxy resins, silicon resins, and epoxy resins are exemplified.

As the charge transporting material, for example, 2, 4, 6
-Trinitrofluorenone, tetracyano methane,
Electron-withdrawing substances such as diphenoquinone derivatives, carbazole, indole, imidazole, oxazole, pyrazole, oxadiazole, heterocyclic compounds such as pyrazoline and thiadiazole, aniline derivatives, hydrazone compounds, aromatic amine derivatives, stilbene derivatives, or these And an electron-donating substance such as a polymer having a group consisting of the compound in the main chain or the side chain.

Examples of charge generation materials that generate charge carriers with extremely high efficiency when absorbing light include, for example, selenium,
Inorganic photoconductive particles such as selenium-tellurium alloy, selenium-arsenic alloy, cadmium sulfide, amorphous silicon; phthalocyanine pigments, perinone pigments, thioindigo, quinacridone, perylene pigments, anthraquinone pigments,
Organic photoconductive particles such as azo pigments, bisazo pigments, trisazo pigments, tetrakisazo pigments, and cyanine pigments are exemplified. Examples of the dye include a triphenylmethane dye, a thiazine dye, a quinone dye, a cyanine dye, a pyrylium salt, a thiapyrylium salt, and a benzopyrylium salt. Examples of the electron-withdrawing compound that forms a charge-transfer complex with the charge-transfer material include electron-withdrawing compounds such as quinones, aldehydes, ketones, acid anhydrides, cyano compounds, and phthalides.

Examples of the solvent contained in the coating solution in the present invention include ethers such as tetrahydrofuran and 1,4-dioxane; ketones such as methyl ethyl ketone and cyclohexanone; aromatic hydrocarbons such as toluene and xylene; Dimethylformamide, acetonitrile,
Aprotic polar solvents such as N-methylpyrrolidone and dimethylsulfoxide; esters such as ethyl acetate, methyl formate and methyl cellosolve acetate; dichloroethane;
Solvents such as chlorinated hydrocarbons such as chloroform.

The solid content in the coating solution is determined mainly according to the thickness of the coating film of the layer to be formed. In the case of forming a laminate type charge generating layer, the solid content concentration is 10% by weight. Hereinafter, the content is more preferably 0.5 to 5% by weight. In the case of forming a stacked type charge transport layer or a single layer type photosensitive layer containing a charge generation material and a charge transport material, it is necessary to form a thicker photosensitive layer, so the solid content concentration is 50% by weight or less. And more preferably 10 to 40% by weight.

The layer thickness of the coating film of the charge generating layer is usually 0.05 μm to 5 μm, preferably 0.1 μm to 2 μm.
μm is preferred. The layer thickness of the coating film of the charge transport layer is usually 5 μm to 80 μm, preferably 10 μm to 60 μm.
μm is preferred. The thickness of the coating film of the single-layer type photosensitive layer is usually 5 μm to 80 μm, preferably 10 μm to 60 μm.
m is preferred.

In the case of forming a polymer layer or a polymer layer in which conductive fine powder is dispersed, the solid concentration is preferably 45% by weight or less, more preferably 1 to 35% by weight. The thickness of the coating film of the polymer layer or the polymer layer in which the conductive fine powder is dispersed is usually 0.1 μm to 100 μm, preferably 0.2 μm to 80 μm.

[0024]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 A coating solution for a charge transport layer for an electrophotographic photoreceptor having the following formulation was prepared, and at room temperature and a liquid temperature of 25 ° C, an outer diameter of 4 cm and a length of 40.
cm, a wall thickness of 1 mm, the lower end portion of which is open, the lower inner volume of the substrate is about 80 cm ³ , and the aluminum cylindrical substrate coated with the charge generation layer is immersed in the coating solution at a speed of 1 m / min. When the opening at the bottom of the substrate reaches a distance of 1 cm below the liquid surface of the coating solution, the speed is set to zero. After maintaining the state for 10 seconds, the substrate is pulled up at a speed of 50 cm / min. As soon as the distance on the liquid surface of the coating liquid became 5 mm, the entire area to be coated was immersed in the coating liquid at a speed of 1 m / min, and the cylindrical substrate was pulled up at a speed of 30 cm / min. No good coating was obtained.

[0025]

(Formulation of coating liquid) 110 parts of hydrazone compound represented by Structural Formula (1) 100 parts of polycarbonate resin represented by Structural Formula (2) 1.5 parts of acceptor represented by Structural Formula (3) 1.5 parts Structural Formula (4) ) 2 parts Antioxidant represented by structural formula (5) 0.03 parts Charge control agent represented by structural formula (6) 0.2 part 1,4 dioxane 290 parts Tetrahydrofuran 540 parts

[0026]

Embedded image

COMPARATIVE EXAMPLE 1 In Example 1, even when the lower end opening of the aluminum cylindrical substrate was at a distance of 1 cm below the surface of the coating solution, the entire area to be coated was maintained at a relative speed of 1 m / min. When the cylindrical substrate was pulled up in the same manner as in Example 1 except that it was immersed in air, bubbles were generated from the opening at the lower end of the cylindrical substrate during the lifting, and the liquid surface of the coating liquid was disturbed. The coating film formed on the surface was remarkably uneven, and was unsuitable for use as an electrophotographic photoreceptor.

[0028]

According to the method of the present invention, generation of air bubbles during dip coating is prevented, and a uniform coating film having no unevenness on the surface of the cylindrical substrate can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic view of a step in a dip coating method of the present invention.

FIG. 2 is a schematic diagram showing a relationship between a relative speed between a cylindrical substrate and a coating liquid level and an elapsed time in a dip coating step in the dip coating method of the present invention.

FIG. 3 is a schematic diagram showing a relationship between a relative speed between a cylindrical substrate and a liquid surface of a coating solution and an elapsed time in a dip coating process in a conventional dip coating method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gripping device 2 Cylindrical base 3 Solvent vapor atmosphere of coating liquid 4 Coating liquid 5 Lower end opening of cylindrical base 6 Lower surface of gas in lower space inside cylindrical base

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B05D 1/18 G03G 5/05 102 B05C 3/09

Claims (1)

(57) [Claims] 1. A method for forming a coating film on the outer peripheral surface of a cylindrical substrate by dip-coating a cylindrical substrate in a coating solution, wherein the lower end of the cylindrical substrate is immersed in the coating solution and then temporarily coated. A dip-coating method, wherein the dip-coating method is carried out by pulling up on a liquid surface and subsequently immersing in a coating solution and pulling up.