JPH05111656A - Dip coating device - Google Patents

Abstract

PURPOSE:To provide a dip coating device capable of minimizing the occurrence of unevenness in film thickness and sagging. CONSTITUTION:In a dip coating device with a dip coating tank 6 and a substrate holding means 2 to hold a substrate 1 to be coated so that it can be moved up and down, a cover 3 is put on the dip coating tank 6 and a sucking mechanism capable of sucking gas from the entire peripheral direction of the substrate 1, e.g. a porous plate 4 for regulating inflow air is disposed under the cover 3 so that it is positioned relatively under the surface of a coating soln. in the dip coating tank 6.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a dip coating apparatus for forming a coating film on a substrate to be coated. For more details,
The present invention relates to a dip coating device that improves the uniformity of a coating film.

[0002]

2. Description of the Related Art Conventionally, a method of immersing a substrate to be coated in a coating liquid and pulling it up in a direction perpendicular to the liquid surface for coating is known as a dip coating method. The dip coating method is
Since a desired coating film can be easily formed on the surface of a cylindrical substrate to be coated, it is widely used for manufacturing, for example, electrophotographic photoreceptors. In the dip coating method as described above, the coating liquid coated on the surface of the substrate to be coated may drips before it is dried, or the formed coating film may have uneven film thickness. When such a coated substrate is used as, for example, an electrophotographic photosensitive member, image unevenness, white spots or background stains due to toner adhesion occur, and a clear image cannot be supplied. In general, it is known that the sagging and the film thickness unevenness are in an integrated relationship, and it is difficult to suppress both the sagging and the film thickness unevenness. In order to suppress the sagging, a method of accelerating the touch-sensitive film drying by evaporation of an organic solvent is used. However, if the coating film is dried too quickly to the touch by evaporation of the organic solvent, the leveling of the coating film cannot be caught up and the unevenness of the film thickness becomes large. Further, if there is uneven distribution of the solvent vapor concentration in the coating substrate circumferential direction in the finger-drying area of the coating film, the finger-drying speed will vary depending on the location, resulting in uneven film thickness. As described above, many attempts have been proposed to suppress sag and film thickness unevenness that are difficult to control at the same time. In order to suppress the sagging and the film thickness unevenness at the same time, the solvent vapor concentration in the circumferential direction of the coating substrate in the finger-drying area should be made uniform and the finger-drying speed should be controlled. It was difficult to control the touch dry speed.

Most of the conventional dip coating apparatuses cover the upper part of the dip coating tank, that is, the touch-drying area, and generate an air flow during touch-drying to control the touch-drying speed. .. For example, the one disclosed in Japanese Unexamined Patent Publication No. 62-225266 causes an upward flow of solvent vapor air during touch-drying. Further, Japanese Patent Application Laid-Open No. 63-7873 discloses a method for making the solvent vapor concentration uniform in the circumferential direction of the substrate by a descending air flow.

[0004]

However, in the apparatus disclosed in Japanese Patent Laid-Open No. 62-225266, since the nozzle is used in the ascending airflow generating portion, the solvent vapor concentration in the circumferential direction of the substrate is made uniform. Is difficult. Further, the apparatus disclosed in Japanese Patent Laid-Open No. 63-7873 has a problem that the downflow causes disturbance of the coating liquid surface in the dip coating tank, which causes unevenness of the coating film.
The present invention has been made for the purpose of ameliorating the above-mentioned drawbacks of the prior art. That is,
An object of the present invention is to provide a dip coating device that can minimize the occurrence of sagging and film thickness unevenness.

[0005]

The above object of the present invention is to provide a cover on the upper part of a dip coating tank which constitutes a dip coating device,
The solvent vapor concentration control means achieves this by creating an ascending air stream such that the solvent concentration in the circumferential direction is uniform during touch dry of the coating. That is, the present invention is a dip coating tank, in a dip coating apparatus provided with a substrate supporting means for movably supporting the substrate to be coated in the vertical direction, a cover is provided on the dip coating tank, and a lower part of the cover is provided. It is characterized in that a suction mechanism, which is located relatively below the surface of the coating liquid in the dip coating tank, is capable of sucking gas from the entire circumferential direction of the substrate to be coated.

In the dip coating apparatus of the present invention, the dip coating tank contains, for example, a coating liquid for forming an undercoat layer, a coating liquid for forming a photosensitive layer, or a coating liquid for forming a protective layer, which constitutes an electrophotographic photoreceptor. Injected. These coating liquids contain a resin component for forming a coating film and an organic solvent as main components, and the coating liquid for forming a photosensitive layer further contains photosensitive components such as cadmium sulfide, zinc oxide and disazo. A pigment, a pyrazoline compound, a hydrazone compound, polyvinylcarbazole, or the like is contained in a dispersed or dissolved state.
As the organic solvent, for example, methanol, ethanol,
Alcohols such as isopropanol, ketones such as acetone and methyl ethyl ketone, amides such as N, N-dimethylacetamide, ethers such as tetrahydrofuran and dioxane, esters such as methyl acetate and ethyl acetate, chloroform, methylene chloride and dichloro. ethylene,
Halogenated hydrocarbons such as carbon tetrachloride, trichloroethylene and monochlorobenzene, and hydrocarbons such as hexane, cyclohexane, benzene, toluene and ligroin are used. Further, the coating liquid is a cellulose resin, a vinyl resin, an acrylic acid resin, a phenol resin, an epoxy resin, or an organic photoconductive polymer such as polyvinylcarbazole or polyvinylanthracene, which has It can be prepared by dissolving a fast organic solvent alone or in combination of two or more kinds, or in combination with an organic solvent having a slow evaporation rate.

[0007]

In the dip coating apparatus of the present invention, the substrate to be coated is supported by the substrate supporting means and moved downward, the substrate to be coated is dipped in the coating liquid in the dip coating tank, and then pulled up. A coating layer is formed on the upper surface of the dip coating tank by the solvent vapor concentration control means attached to the upper cover of the dip coating tank. Updrafts come into contact with each other uniformly. That is, since the gas is sucked over the entire circumferential direction of the substrate to be pulled up by the suction mechanism provided below the surface of the coating liquid in the dip coating tank in the lower part of the cover, the gas is sucked in the circumferential direction of the substrate to be coated. Eliminates uneven distribution in solvent vapor concentration. Therefore, the occurrence of sagging and uneven film thickness is suppressed.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are cross-sectional views of essential parts of the dip coating device of the present invention. FIG. 1 schematically shows a state before dipping, FIG. 2 shows a state during dipping, and FIG. 3 shows a state during pulling up. .. In the figure, reference numeral 1 denotes a substrate to be coated, which is supported by a substrate supporting means 2. Reference numeral 3 denotes a cover, which is provided with an inflow air amount adjusting porous plate 4 at a lower portion thereof, and is attached to an upper portion of the dip coating tank 6 by a cover attachment jig 5. The dip coating tank 6 is filled with a coating liquid 7. It should be noted that, in the drawing, the relative moving means of the substrate to be coated with respect to the dip coating tank is omitted.

The dip coating operation is started from the state shown in FIG. 1. First, the substrate 1 to be coated is moved downward to be substantially airtight to the cover 3 in the coating liquid 7 in the dip coating tank 6. Soak while maintaining the condition. At this time, as shown by the arrow in FIG. 2, the air containing the same amount of solvent vapor as the outer volume of the base of the cover 3 is passed through the inflow air amount adjusting porous plate 4 to cover the cover 3
Is discharged to the outside.

Next, the substrate 1 to be coated is pulled up while maintaining a substantially airtight state with respect to the cover 3. At this time, as shown by the arrow in FIG. 3, outside air in an amount corresponding to the outer volume of the substrate 1 to be coated is sucked from the entire periphery of the dip coating tank 6 through the inflow air adjusting porous plate 4. In this way, the outside air is sucked from the entire periphery of the dip coating tank 6, so that a uniform upward flow of gas is generated around the coating surface. In this case, the gap between the base support 2 and the cover 3 is preferably as narrow as possible in order to generate an upward flow. The solvent concentration around the undried coating film after coating can be controlled by appropriately changing the pore diameter of the inflow air regulating porous plate 4 to change the inflow air amount. The material for the inflow air regulating perforated plate 4 is preferably solvent resistant and has a uniform pore distribution. Further, in order to prevent the coating liquid surface from being disturbed by the inflowing air and to suppress the rapid evaporation of the solvent from the coating film immediately after the substrate to be coated comes out of the dip coating tank 6, the cover mounting jig 5 has a structure shown in FIG. It is desirable that the inclination angle A as shown in FIG.

The dip coating apparatus of the present invention is the same as that shown in FIGS.
However, the means is not limited to the one shown in (2), and any means may be used as long as it can generate a uniform upward flow of gas around the surface to be coated. FIG. 4 is a cross-sectional view of the essential part of another embodiment of the dip coating device of the present invention, in which a forced gas supply device 8 is provided below the inflow air regulating porous plate 4 to force the gas to flow. It is configured to be supplied. In this dip coating device, the gas to be supplied may be only dry air or a mixed gas of solvent vapor and air, and the mixing ratio may be the kind of solvent used in the coating liquid, the viscosity of the coating liquid and the coating liquid. Varies with speed. According to the above dip coating apparatus of the present invention, it is possible to make the solvent vapor concentration in the circumferential direction around the non-coated surface uniform and simultaneously control sagging and film thickness unevenness. Next, a specific example of the case where the dip coating operation is performed using the dip coating device of the present invention will be shown.

(Example 1) As a substrate to be coated, 84 mmφ ×
A 340 mm aluminum drum was dip coated using the dip coating device shown in FIGS. As the coating liquid, a mixture of the following materials was used. Polycarbonate 9 parts by weight Charge transfer agent (note) 6 parts by weight Methylene chloride 85 parts by weight (note) N, N'-diphenyl-N, N'-bis (3-
Methylphenyl) -4,4′-diamine First, as shown in FIG. 1, an aluminum drum is immersed in the coating solution 7 in a dipping coating tank 6 to form an inflow air regulating porous plate 4 provided below the cover 3. Air containing solvent vapor was discharged from the coating solution control filter having a pore size of 0.5 μm. Next, the substrate 1 to be coated was pulled up at a speed of 150 mm / min. The coating environment at this time was an air temperature of 24 ° C. and a relative humidity of 50%. After the above operation, the dry area for touch is passed at a speed of 150 mm / min, and then 100
It heat-dried at the temperature of 40 degreeC for 40 minutes. After drying, the film thickness of the coated substrate was measured using a dial gauge. The result is shown in FIG. From FIG. 5, it can be seen that when the dip coating device of the present invention is used, the film thickness distribution has small unevenness. In this case, the difference between the maximum value and the minimum value in the vertical direction of the coating film 2 cm or less from the upper end of the coating film could be suppressed to 1.5 μm.

Example 2 (Comparative Example) For comparison, dip coating was performed in the same manner as in Example 1 except that the cover 3 was not attached. The result is shown in FIG. From FIG. 5, when the cover is not attached, the film thickness is not stable,
It can be seen that the coating film becomes thicker as it gets closer to the lower end.
In this case, the difference between the maximum value and the minimum value in the vertical direction of the coating film 2 cm or less from the upper end of the coating film was 3.5 μm. Also, whitening occurred at the bottom of the coated substrate.

[0014]

Since the dip coating apparatus of the present invention has the above-mentioned constitution, the concentration of the solvent vapor around the substrate to be coated after coating the coating composition is controlled to make the coating film in a uniform upward flow of solvent. It is possible to obtain a coating film having uniform thickness without sagging and having a small thickness unevenness.

[Brief description of drawings]

FIG. 1 is a sectional view showing a state before dipping of an embodiment of the dip coating device of the present invention.

FIG. 2 is a cross-sectional view showing a state during immersion of an embodiment of the dip coating device of the present invention.

FIG. 3 is a cross-sectional view showing a state at the time of pulling up of one embodiment of the dip coating device of the present invention.

FIG. 4 is a sectional view of another embodiment of the dip coating device of the present invention.

FIG. 5 is a graph showing a film thickness distribution of a coating film formed by dip coating.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate to be coated, 2 ... Substrate supporting means, 3 ... Cover, 4 ... Inflow air control porous plate, 5 ... Cover mounting jig, 6 ... Immersion coating tank, 7 ... Coating liquid, 8 ... Forced gas supply device.

Claims (2)

[Claims] 1. A dip coating apparatus comprising a dip coating tank and a substrate supporting means for movably supporting a substrate to be coated in a vertical direction, wherein a cover is provided on the dip coating tank, and a lower part of the cover is provided. An immersion coating apparatus, which is provided below an application liquid surface of an immersion coating tank and is provided with a suction mechanism capable of sucking gas from the entire circumferential direction of a substrate to be coated. 2. The dip coating device according to claim 1, wherein the suction mechanism is a perforated plate.