JPH07136576A - Dip coating method - Google Patents

Abstract

PURPOSE:To form a uniform coating film at the time of dipping a cylindrical substrate in a coating soln. to form a coating film on the periphery of the substrate by blowing the vapor of solvent into the space in the substrate immediately before the lower opening of the substrate is dipped into the soln. CONSTITUTION:A cylindrical substrate 2 is dipped in a coating soln. 4 to form a coating film on the periphery of the substrate 2. In this case, the substrate 2 is firstly held by a holder 1 in the stage A and arranged above the soln. 4. The lower opening 5 of the substrate 2 is placed directly above the soln. 4 in the stage B. A gas 3 contg. the vapor of solvent is blown into the space in the substrate 2 from a blowing pipe 7 through a check valve 8 in the stage C. Namely, the solvent vapor of the soln. 4 does not enter into the substrate 2 from the lower opening 5, and bubbles are not produced in dip coating. The substrate 2 is dipped into the soln. 4 in the stage D, and the substrate 2 is pulled up in the stage E.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a dip coating method is suitable as a method for forming a uniform coating film on the outer peripheral surface of a cylindrical substrate, and it is widely used in the manufacture of electrophotographic photosensitive drums. In such a dip coating method, when the cylindrical substrate is dipped in the coating liquid, the coating liquid enters the substrate through the lower end opening of the cylindrical substrate and adheres to the inner peripheral surface of the substrate. To prevent this, a gripping device that grips the base with a rubber member that can expand and contract is inserted into the base while the rubber member is contracted, and then the rubber member is expanded by press-fitting air or the like into a cylindrical shape. It is customary to hold the substrate in pressure contact with and closely contact it with the inner wall of the substrate, and to apply by dipping.

For this reason, it has been practiced to fit the gripping device into the cylindrical base body in an airtight manner and to keep the inner and lower parts of the cylindrical base body in an airtight state except for the lower end opening. On the other hand, as the solvent of the coating liquid, a volatile solvent having a relatively low boiling point is usually used, and during dip coating, the solvent evaporates from the lower end of the cylindrical substrate to the space inside and below the cylindrical substrate, and then from the lower end. Air bubbles are generated in the coating liquid. Then, the air bubbles may impair the uniformity of the coating film formed on the outer peripheral surface of the cylindrical substrate.

Various methods have been proposed to prevent the generation of such bubbles. If you raise the representative one,
First, there is a method of extracting a part of the gas in the lower space inside the cylindrical substrate or changing the volume of the lower space inside the cylindrical substrate during dipping, as disclosed in JP-A-58-74170. -21960, JP-A-2-21961,
It is described in JP-A-2-21962. Second, there is a method of replacing the gas in the lower space inside the cylindrical substrate with a gas containing the solvent vapor of the coating solution before dipping, as disclosed in Japanese Utility Model Laid-Open Nos. 63-201672 and 63-201673.
It is described in Japanese Patent Publication No. Third, a method of covering the lower end of the cylindrical substrate or reducing the evaporation area of the gas lower surface of the lower space inside the cylindrical substrate is disclosed in Japanese Utility Model Laid-Open No. 63-201674 and Japanese Patent Laid-Open No. 64-47470. Japanese Patent Laid-Open No. 2-14
No. 769 and Japanese Patent Laid-Open No. 277577/1990. In addition, the volume of the lower space inside the cylindrical substrate is specified to be small (Japanese Patent Laid-Open No. 63-315171), and the gas in the lower space inside the cylindrical substrate is preheated before immersion or cooled after immersion. (JP-A-2-31853
Japanese Patent Laid-Open Publication No. Hei 1-148359), a method of placing a projecting object in the coating liquid tank (Japanese Laid-Open Patent Publication No. 62-24157).
No. 7), a method of simultaneously immersing an object for gas outflow, which communicates with the lower space inside the cylindrical substrate (Japanese Patent Laid-Open No. 5-66583).
Issue gazette) etc.

[0005]

However, such a method has the following drawbacks. The method of extracting part of the gas in the lower space inside the cylindrical substrate or changing the volume of the lower space inside the cylindrical substrate during the first immersion is a delicate control of the pressure in the lower space inside the cylindrical substrate. In each case, it is necessary to set the gas extraction volume in consideration of conditions such as the diameter and length of the cylindrical substrate, the immersion time, the temperature of the atmosphere and the solvent (ratio).

Next, also in the second method in which the gas in the lower space inside the cylindrical substrate is replaced with the gas containing the solvent vapor of the coating liquid before dipping, the lower end opening of the cylindrical substrate is coated. The method of sucking the gas in the upper part of the coating liquid into the space inside and below the cylindrical substrate before dipping in the liquid is a gas containing solvent vapor in the upper part of the coating liquid depending on the constant overflow method of the coating liquid often used in dip coating. However, the method of holding the volatile component in the lower space inside the cylindrical substrate had the adverse effect that solvent vapor was generated from this portion even after the immersion.

Further, in other methods as well, in view of certainty of prevention of bubble generation, derived coating quality problems, complexity of equipment, operability, etc., all of them have disadvantages. An object of the present invention is to provide a dip coating method capable of preventing the generation of bubbles and easily forming a uniform coating film on the outer peripheral surface of a cylindrical substrate without requiring a complicated mechanism or complicated condition setting. To provide.

[0008]

The present invention has been made to solve the above-mentioned problems, and the gas in the lower space inside the cylindrical substrate is replaced with a gas containing the solvent vapor of the coating solution before immersion. The method is a method of forming a coating film on the outer peripheral surface of the cylindrical substrate by immersing the cylindrical substrate in a coating solution, and the method is to apply the coating to the lower end opening of the cylindrical substrate. A method of immersion coating is characterized in that the solvent vapor of the coating solution is blown into the lower space inside the cylindrical substrate before the immersion in the solution. The present invention will be described in detail below.

FIG. 1 shows an outline of the steps in the dip coating method of the present invention, showing that a coating film is formed on the outer peripheral surface of a cylindrical substrate by following the steps A → B → C → D → E. ing. As shown in A of FIG. 1, the cylindrical substrate 2 is gripped by the gripping device 1, moved to a position above the coating liquid 4, and is held relative to the liquid surface of the coating liquid 4 by the gripping device. Approach.

FIG. 1B shows the cylindrical substrate 2 immediately before its lower end is immersed in the coating liquid 4, and the axis of the cylindrical substrate is preferably perpendicular or nearly perpendicular to the liquid surface of the coating liquid. The lower end opening 5 of the cylindrical substrate is located slightly above the surface of the coating liquid. In FIG. 1C, the gas containing the solvent vapor of the coating liquid is blown into the lower space inside the cylindrical substrate at this position, and the lower space inside the cylindrical substrate is filled with the gas containing the solvent vapor of the coating liquid. . The lower space in the figure shows a state where the solvent vapor atmosphere 3 of the coating liquid is set. After the blowing, the check valve 8 in the middle of the blowing pipe 7
Therefore, the gas in the lower space does not flow out of the blowing pipe.

In this way, most of the gas in the lower space inside the cylindrical substrate is replaced by the gas saturated with the solvent vapor of the coating liquid, and in a subsequent step, the solvent vapor is radiated from the lower end opening 5 of the cylindrical substrate. Invasion into the space below the body is suppressed, and as a result, 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

In the present invention, the position immediately before the lower end portion of the cylindrical substrate is immersed in the coating liquid means that the amount of the gas containing the solvent vapor blown into the coating liquid is re-replaced with the outside air, so that the lower end of the cylindrical substrate is reduced. The distance between the opening and the surface of the coating liquid is greater than 0 and less than 3 cm, more preferably greater than 0 and less than 1 cm, and further preferably greater than 0 and less than 0.5 cm.

Similarly, in order to prevent the gas containing the blown solvent vapor from rushing out of the space in the lower part of the substrate, an air flow control member, for example, a collision, is applied to the end of the blowing pipe 7 on the space side. Non-woven boards and non-woven fabrics for dust, mesh,
It is preferable to install a porous material such as a sponge so as to diffuse the gas into the space. It is preferable that the volume of the gas blown in is larger than one time the volume of the lower space in the cylindrical substrate, but if the length of the cylindrical substrate is short or the coating speed is high, this is the case. The amount is not limited and may be smaller. Further, even if the blowing amount is set below the above-mentioned minimum amount, there is no problem in terms of quality, and it is sufficient that the blowing amount accuracy is low.

The relative velocity of the cylindrical substrate and the coating liquid when the gas containing the solvent vapor of the coating liquid is blown into the lower space of the cylindrical substrate makes the cylindrical substrate of A relatively close to the liquid surface. Although the speed may be the same as it is, if the wind speed becomes too high to blow a predetermined amount of gas within the above range, it is preferable to lower the value than the value of A or temporarily stop.

FIG. 1D shows the cylindrical substrate immersed in the coating solution. The value of the relative velocity between the cylindrical substrate and the liquid surface of the coating liquid may be the same as or different from the value in A above. E in FIG. 1 shows a state where the cylindrical substrate is pulled up from the coating liquid and the outer peripheral coating film is formed. It is preferable that the axis of the cylindrical substrate at the start of immersion, during immersion, and during withdrawing is perpendicular to the liquid surface of the coating liquid.

FIG. 2 is a schematic view of an example of a gas generator including a solvent vapor of a coating liquid in the dip coating method of the present invention.
FIG. 2 is a schematic view of two examples of the device for generating the gas shown in FIG. 1C, and is not limited to the device shown here as long as the object of the present invention is achieved. 2A is an example of an apparatus for sucking a gas containing a solvent vapor from a solvent vapor generation tank 9 by a syringe 12 and sending the gas into the lower space inside the cylindrical substrate, and FIG. 2B is a solvent vapor generation tank. 9
An example of an apparatus for injecting a gas into a cylinder and feeding a gas containing the generated solvent vapor into the lower space inside the cylindrical substrate by utilizing the pressure is shown.

The concentration of the solvent vapor of the gas containing the solvent vapor is preferably close to its saturation temperature, and this is why the diffuser pipe 11 provided in the solvent vapor generation tank is provided. Although the solvent of the coating liquid is used as the solvent 10, when the coating liquid is a mixed solvent system, a mixed solvent having the ratio may be used, or a low boiling point solvent therein is used to facilitate generation of vapor. May be.
The gas supplied into the solvent vapor generation tank may be air,
Nitrogen or the like may be used if more safety considerations are required.

As the cylindrical substrate in the present invention, for example, a cylindrical substrate for an electrophotographic photosensitive member which is adopted in a well-known electrophotographic photosensitive member can be used.
Specifically, for example, a metal drum of aluminum, stainless steel, copper or the like, or a laminate or vapor deposition of these metal foils can be used. Furthermore, a metal drum, carbon black, copper iodide, a polymer drum or other conductive substance is applied together with an appropriate binder to conduct a conductive treatment, and a plastic drum, a paper tube and the like can be mentioned. Further, a conductive plastic drum containing a conductive substance such as metal powder, carbon black, or carbon fiber can be used. Further, a charge generation layer, an undercoat layer, etc. may be provided on these cylindrical substrates.

As the coating liquid in the present invention, for example, in the case of a coating liquid for an electrophotographic photoreceptor, one or two kinds selected from charge transport materials, charge generating materials, dye pigments, electron withdrawing compounds and the like. A coating liquid prepared by dissolving or dispersing the above and a binder in a solvent is used. The coating liquid may contain known additives such as a lubricant, a leveling agent and an antioxidant.

As the charge transport material, charge generating material, dye pigment, electron withdrawing compound, binder and the like, known materials can be used. Examples of the binder include polymers and copolymers of vinyl compounds such as styrene, vinyl acetate, vinyl chloride, acrylic acid ester, methacrylic acid ester, and butadiene, polyvinyl acetal, polycarbonate, polyester, polysulfone, polyphenylene oxide, polyurethane, and cellulose. Examples thereof include various polymers such as esters, cellulose ethers, phenoxy resins, silicon resins and epoxy resins.

Examples of the charge transport material include 2, 4, 6
-Trinitrofluorenone, tetracyanokidimethane,
Electron withdrawing substances such as diphenoquinone derivatives, carbazole, indole, imidazole, oxazole, pyrazole, oxadiazole, pyrazoline, thiadiazole, and other complex compounds, aniline derivatives, hydrazone compounds, aromatic amine derivatives, stilbene derivatives, or these An electron-donating substance such as a polymer having a group consisting of the above compound in its main chain or side chain can be mentioned.

Charge generating materials that generate charge carriers with extremely high efficiency when absorbing light include selenium and the like.
Inorganic photoconductive particles such as selenium-tellurium alloy, selenium-arsenic alloy, cadmium sulfide, and amorphous silicon; phthalocyanine pigment, perinone pigment, thioindigo, quinacridone, perylene pigment, anthraquinone pigment,
Examples thereof include organic photoconductive particles such as azo pigments, bisazo pigments, trisazo pigments, tetrakisazo pigments, and cyanine pigments. Examples of the dye include triphenylmethane dye, thiazine dye, quinone dye, cyanine dye, pyrylium salt, thiapyrylium salt, and 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 liquid 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; N, N- Dimethylformamide, acetonitrile,
Aprotic polar solvents such as N-methylpyrrolidone and dimethyl sulfoxide; Esters such as ethyl acetate, methyl formate and methyl cellosolve acetate; Dichloroethane,
Examples include solvents such as chlorinated hydrocarbons such as chloroform.

The content of the solid content in the coating liquid is determined mainly according to the thickness of the coating film of the layer to be formed, but in the case of forming a laminated charge generating layer, the solid content concentration is 10% by weight. Below, it is more preferable to set it to 0.5 to 5% by weight. When forming a laminated type charge transport layer or a single layer type photosensitive layer containing a charge generating 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 film thickness of the coating film of the laminated type charge generation layer is usually 0.05 μm to 5 μm, preferably 0.1 μm to 2
μm is preferred. The thickness of the coating film of the laminated 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 8 μm, preferably 10 μm to 60 μm.
Is preferred.

When forming a polymer layer or a polymer layer in which conductive fine powder is dispersed, the solid content 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 conductive fine powder is dispersed is usually 0.1 μm to 100 μm, preferably 0.2 μm to 80 μm.

[0027]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 A charge transport layer coating liquid for an electrophotographic photoreceptor having the following formulation was prepared.

[Table 1] Solid content Charge transport material (hydrazone compound) 100 parts Binder (polycarbonate resin) 100 parts Solid content concentration 20 wt% Solvent 1,4-dioxane / tetrahydrofuran 4/6 (wt ratio)

Outside diameter 10c at room temperature and liquid temperature of 25 ° C
m, a length of 98 cm, a thickness of 3 mm, a lower end opened, and a volume of the lower space inside the substrate of about 940 cm ³ , in which a cylindrical aluminum substrate coated with a charge generation layer is constantly overflowed Of the above coating solution at a speed of 1 m / min. When the opening at the lower end of the substrate reached 2 mm above the surface of the coating solution, the speed was set to zero, and the state was maintained for 3 seconds, during which tetrahydrofuran vapor was included. About 1450 cm ³ of air was blown into the lower space of the substrate through a tube incorporated in the gripping device. Immediately, then, at a speed of 1 m / min, immerse the entire coating area in the coating solution and
When the cylindrical substrate was pulled up at a speed of cm / min, no bubbles were generated and a good coating film was obtained.

[0029] Incidentally, the generation of air containing tetrahydrofuran vapors, what was injected air from the compressor to the pressure tank volume of about 4880cm ³ containing the tetrahydrofuran about 1000 cm ^3, as air containing tetrahydrofuran steam It was released and used. The volume of the released gas at 1 atm was calculated and calculated from the value of the pressure gauge attached to the pressure tank. Further, a dust-free non-woven fabric was applied to the tip of the blow-in tube in the space below the substrate to diffuse the blown-in gas.

Comparative Example 1 In Example 1, even if the opening at the lower end of the aluminum cylindrical substrate was 2 mm above the liquid surface of the coating liquid, the relative speed was 1 m /
Immerse all the areas to be applied in the coating solution while keeping the
When the cylindrical substrate was pulled up in the same manner as in Example 1 except that the air containing tetrahydrofuran vapor was not blown in, bubbles were generated from the lower end of the cylindrical substrate immediately after the start of the pulling process and during the pulling process. Due to the disturbance of the liquid surface of the coating liquid, the coating film formed on the outer peripheral surface of the cylindrical substrate was markedly uneven, and it could not be used as an electrophotographic photoreceptor.

Comparative Example 2 In Example 1, the velocity was set to zero at the time when the lower end opening of the aluminum-made cylindrical substrate reached 2 mm above the liquid level of the coating liquid, and the state was maintained for 25 seconds. When the cylindrical substrate was pulled up in the same manner as in Example 1 except that about 800 cm ³ of the gas above the coating liquid was sucked into the space below the substrate without blowing air containing steam, About 2/3
When the coating liquid was applied, air bubbles were generated from the lower end of the cylindrical substrate and the liquid surface of the coating liquid was disturbed, resulting in remarkable unevenness in the coating film formed on the outer peripheral surface of the cylindrical substrate, and its use as an electrophotographic photoreceptor. Was unbearable.

[0032]

By using the method of the present invention, generation of 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 drawings]

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

FIG. 2 is a schematic diagram of an example of a gas generator including a solvent vapor of a coating liquid in the dip coating method of the present invention.

[Explanation of symbols]

 1 Gripping Device 2 Cylindrical Substrate 3 Solvent Vapor Atmosphere of Coating Liquid 4 Coating Liquid 5 Lower End Opening of Cylindrical Substrate 6 Gas Lower Surface in Lower Space of Cylindrical Substrate 7 Gas Injection Tube with Solvent Vapor 8 Check Valve 9 Solvent Vapor generation tank 10 Solvent for coating liquid 11 Air diffuser 12 Syringe 13 Compressor 14 Air filter 15 Control valve 16 Pressure gauge

Claims (1)

[Claims] 1. A method of forming a coating film on the outer peripheral surface of a cylindrical substrate by immersing the cylindrical substrate in a coating solution, wherein the lower end opening of the cylindrical substrate is immersed in the coating solution. A dip coating method, characterized in that a solvent vapor of a coating liquid is blown into the lower space inside the cylindrical substrate.