JP3223667B2 - 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, when the cylindrical substrate is immersed in the coating liquid, the coating liquid enters the substrate from 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 using a rubber member that can expand and contract is inserted into the base with the rubber member and the like contracted, and then the rubber member and the like are expanded by press-fitting air or the like into a cylindrical shape. It is common practice to hold the substrate in pressure contact or close contact with the inner wall of the substrate and apply dip coating.

[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, as a solvent for 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 base to a space below the cylindrical base, and then the solvent evaporates from the lower end. Bubbles are generated in the coating solution. As a result, 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,
One method is to extract a part of the gas in the lower space inside the cylindrical substrate during immersion or to change the volume of the lower space in the cylindrical substrate, as disclosed in JP-A-58-74170 and JP-A-58-74170. JP-A-21960, JP-A-2-21961,
It is described in, for example, JP-A-2-21962. Secondly, a method of replacing the gas in the lower space inside the cylindrical substrate with a gas containing the solvent vapor of the coating liquid before immersion is disclosed in Japanese Utility Model Laid-Open No. 63-201672 and Japanese Utility Model Laid-Open No. 63-201673.
No., etc. Thirdly, a method of closing the lower end of the cylindrical base or reducing the evaporation area of the gas lower surface in the lower space in the cylindrical base is disclosed in Japanese Utility Model Laid-Open No. 63-201674, Japanese Patent Laid-Open No. 47470/1988, JP-A No. 2-14
769 and JP-A-2-277577. In addition, those in which the volume of the lower space in the cylindrical substrate is specified to be small (Japanese Patent Laid-Open No. 63-315171), those in which the gas in the lower space in the cylindrical substrate is heated before immersion or cooled after immersion (JP-A-2-31853)
Japanese Patent Application Laid-Open No. Hei 1-148359) and a method in which a protruding object is placed in a coating liquid tank (Japanese Patent Application Laid-Open No. 62-24157).
No. 7), a method of simultaneously immersing an object for gas outflow communicating with a lower space in a cylindrical substrate (Japanese Patent Laid-Open No. 5-66583).
Publication).

[0005]

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

Next, in the second method, in which the gas in the lower space inside the cylindrical substrate is replaced with a gas containing the solvent vapor of the coating liquid before immersion, the lower end opening of the cylindrical substrate is coated. Prior to immersion in the liquid, the gas above the coating liquid is sucked into the lower space inside the cylindrical substrate by a method of constantly overflowing the coating liquid, which is often used in dip coating. And the method of retaining volatile components in the lower space inside the cylindrical substrate has the opposite effect because even after immersion, solvent vapor is generated from this portion.

Still other methods have disadvantages in view of the certainty of preventing the generation of bubbles, the problem of the quality of the resulting coating film, the complexity of the apparatus, the operability, and the like. 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]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problem, and replaces a gas in a lower space in a cylindrical substrate with a gas containing a solvent vapor of a coating solution before immersion. The gist of the method is to form a coating film on the outer peripheral surface of a cylindrical substrate by immersing the cylindrical substrate in a coating solution. A dip coating method characterized in that a solvent vapor of a coating liquid is blown into a lower space in the cylindrical substrate before being immersed in the liquid. 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, and shows that a coating film is formed on the outer peripheral surface of a cylindrical substrate by following the steps of A → B → C → D → E. ing. 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. 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 almost perpendicular to the liquid surface of the coating liquid. The lower end opening 5 of the cylindrical substrate is located slightly above the coating liquid level. In FIG. 1C, at this position, a gas containing the solvent vapor of the coating liquid is blown into the lower space inside the cylindrical substrate, and the lower space inside the cylindrical substrate is filled with the gas containing the solvent vapor of the coating liquid. . The lower space of the figure shows a state in which the solvent vapor atmosphere 3 of the coating liquid has been reached. After blowing, a check valve 8 in the middle of the blowing pipe 7 is used.
Thus, 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 in the cylindrical substrate is replaced by the gas which has saturated the solvent vapor of the coating liquid, and the solvent vapor is released from the lower end opening 5 of the cylindrical substrate in the subsequent step. Intrusion into the lower space in the body is suppressed, and as a result, bubbles can be prevented from being generated in the coating solution 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. You.

In the present invention, the position immediately before the lower end of the cylindrical substrate is immersed in the coating liquid is defined as the lower end of the cylindrical substrate in order to reduce the amount of the gas containing the solvent vapor that has been blown in to the outside air. The distance between the opening and the surface of the coating solution is more than 0 and less than 3 cm, more preferably more than 0 and less than 1 cm, and still more preferably more than 0 and less than 0.5 cm.

Similarly, in order to prevent the gas containing the injected solvent vapor from vigorously exiting the lower space inside the base, an air flow control member, for example, an impingement member, is provided at the front end of the blowing pipe 7 on the space side. Plates and dust-free non-woven fabrics, mesh,
It is preferable to install a porous substance such as a sponge so as to diffuse the gas into the space. The volume of the gas to be blown in is preferably larger than one time the volume of the lower space in the cylindrical substrate. However, when the length of the cylindrical substrate is short or the coating speed is high, and when the immersion time is short, this is preferable. The amount is not limited and may be smaller. Even if the blowing amount is larger than the required minimum amount, there is no problem in quality, and a low blowing amount accuracy is sufficient.

When the gas containing the solvent vapor of the coating liquid is blown into the lower space in the cylindrical substrate, the relative speed between the cylindrical substrate and the coating liquid is such that the cylindrical substrate of A is relatively close to the liquid surface. However, when the wind speed is too high to blow a predetermined amount of gas within the above range, it is preferable to lower the value of A or to temporarily stop.

FIG. 1D shows a state in which the cylindrical substrate is immersed in a coating solution. The value of the relative speed between the cylindrical substrate and the liquid surface of the coating liquid may be the same as or different from that in the above A. FIG. 1E shows a state in which the cylindrical substrate is pulled up from the coating liquid and the outer peripheral coating film is formed. 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. 2 is a schematic view showing an example of an apparatus for generating a gas containing a solvent vapor of a coating solution in the dip coating method of the present invention.
FIG. 2 is a schematic view of two examples of the gas generating device shown in FIG. 1C, and is not limited to the device shown here if the object of the present invention is achieved. 2A shows 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 a lower space in a cylindrical base. FIG. 9
1 shows an example of an apparatus for injecting a gas into a cylindrical substrate and feeding a gas containing a generated solvent vapor into a lower space in a cylindrical base body using the pressure.

The solvent vapor concentration of the gas containing the solvent vapor is preferably close to its saturation temperature, and the diffusion tube 11 provided in the solvent vapor generation tank is for this purpose. As the solvent 10, the solvent of the coating solution is used. When the coating solution is a mixed solvent system, a mixed solvent having the same ratio may be used. May be.
The gas supplied into the solvent vapor generation tank may be air,
If more safety considerations are required, nitrogen or the like may be used.

As the cylindrical substrate in the present invention, for example, in the case of a cylindrical substrate for an electrophotographic photosensitive member, any of those used 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 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 a charge transporting material, a charge generating material, a dye, an electron withdrawing compound 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.

As the charge transporting material, charge generating material, dye / dye, electron-withdrawing compound, binder and the like, well-known materials can be used. 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, pyrazoline, thiadiazole, etc., heterocyclic compounds, 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. When a charge generation layer of a laminate type is formed, the solid content 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 thickness of the coating film of the charge generating layer of the laminated type 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 8 μm, preferably 10 μm to 60 μm.
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.

[0027]

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 charge transport layer coating solution for an electrophotographic photosensitive member 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)

At room temperature and a liquid temperature of 25 ° C., an outer diameter of 10 c
m, a length of 98 cm, a thickness of 3 mm, an open bottom end, a volume of lower space in the base body of about 940 cm ³ , and a coating liquid tank in which an aluminum cylindrical base body coated with a charge generating layer is always overflowed. At a speed of 1 m / min., When the lower end opening of the substrate became 2 mm above the surface of the coating liquid, the speed was set to zero, and the state was maintained for 3 seconds, and tetrahydrofuran vapor was contained during that time. About 1450 cm ³ of air was blown into the lower space of the substrate through a tube incorporated in a gripping device. Then, immediately at a speed of 1 m / min, the entire area to be coated was immersed in the coating solution,
When the cylindrical substrate was pulled up at a speed of cm / min, no good air bubble was 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 Released and used. The volume of the released gas at 1 atm was calculated from the value of the pressure gauge attached to the pressurized tank. Further, a dust-free nonwoven fabric was applied to the tip of the blowing tube in the space below the base to diffuse the gas to be blown.

Comparative Example 1 In Example 1, even when the lower end opening of the aluminum cylindrical base was 2 mm above the coating liquid level, the relative speed was 1 m / m.
Immerse the entire area to be coated in the coating solution
When the cylindrical substrate was pulled up in the same manner as in Example 1 except that air containing tetrahydrofuran vapor was not blown, bubbles were generated from the lower end of the cylindrical substrate immediately after the start of the pulling and during the pulling. Due to the disorder of the liquid surface of the coating solution, the coating film formed on the outer peripheral surface of the cylindrical substrate was remarkably uneven, and could not be used as an electrophotographic photoreceptor.

Comparative Example 2 In Example 1, when the lower end opening of the aluminum cylindrical substrate reached 2 mm above the liquid surface of the coating liquid, the speed was set to zero, and the state was maintained for 25 seconds. The cylindrical substrate was pulled up in the same manner as in Example 1 except that the air containing steam was not blown in but the gas above the coating solution of about 800 cm ³ was sucked into the lower space of the substrate. About 2/3 of the way
At the time of coating, bubbles are generated from the lower end of the cylindrical substrate and the liquid surface of the coating liquid is disturbed, resulting in significant unevenness of the coating film formed on the outer peripheral surface of the cylindrical substrate. Was unbearable.

[0032]

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 view of an example of a gas generating apparatus including a solvent vapor of a coating liquid in the dip coating method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gripping device 2 Cylindrical base 3 Solvent vapor atmosphere of coating liquid 4 Coating liquid 5 Lower opening of cylindrical base 6 Gas lower surface in lower space inside cylindrical base 7 Gas blowing pipe containing solvent vapor 8 Check valve 9 Solvent Vapor generation tank 10 Solvent of coating liquid 11 Air diffuser 12 Syringe 13 Compressor 14 Air filter 15 Control valve 16 Pressure gauge

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-154672 (JP, A) Fully open 1988-201672 (JP, U) Fully open 1988-201673 (JP, U) (58) Investigation Field (Int.Cl. ⁷ , DB name) B05D 1/18 B05C 3/09 G03G 5/05 102

Claims (1)

(57) [Claims] 1. A method for 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 before the coating. A dip coating method, wherein a solvent vapor of a coating liquid is blown into a lower space in the cylindrical substrate.