JPH0651155B2 - Immersion coating method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dip coating method for coating only the outer surface of a cylinder.

2. Description of the Related Art Conventionally, various methods have been known for applying a coating material or the like on the surface of a cylindrical body, but a dip coating method is used particularly when importance is attached to the smoothness of a coating film.

Generally, in the dip coating method, the tubular body is dipped in the coating material and then pulled up at an appropriate speed to perform coating. However, in this case, in the case of a cylindrical body that is open in both the upper and lower directions, the coating material also enters the interior of the cylindrical body, so that the coating is also applied to the inner surface.
When the coating material is applied to the inner surface of the cylindrical body, not only the coating material is wasted, but also the inner surface becomes difficult to dry, or a problem of contamination occurs.

In order to solve this problem, a method has also been proposed in which a lid is attached to the lower portion of the cylinder to prevent the paint from adhering to the inner surface of the cylinder. (For example, JP-A-59-142869) On the contrary, by closing the upper part of the cylinder, air is confined inside the cylinder when the cylinder is immersed in the paint.
A method is also known in which air pressure inside the cylinder prevents the paint from entering. To close the upper part of the cylinder, there is a method of using a cylinder whose top is closed or a method of closing the top of the cylinder whose both ends are open by a sealing mechanism.

In this way, when a cylinder whose upper part is closed is immersed in the paint and pulled up, the pressure of the air trapped inside the cylinder rises as the solvent of the paint evaporates, and the volume of the air remains unchanged. When the volume is larger than the enclosed volume, a phenomenon occurs in which bubbles are generated from the lower part of the cylinder. The bubbles burst at the surface of the paint and disturb the liquid surface of the paint, causing serious coating defects. Therefore, it is necessary to prevent the bubbles from being generated.

As a method for preventing the generation of bubbles, Japanese Patent Laid-Open No. 58-18
Japanese Patent No. 6472 describes that the generation of bubbles is prevented by operating an electromagnetic valve according to the internal pressure to maintain the internal pressure at a required value.

In addition, JP-A-59-4467 and JP-A-60-13.
Japanese Patent No. 2678 describes a method of attaching a pressure adjusting mechanism to a closing device that closes the upper part of a cylindrical body to prevent the generation of bubbles.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention By the way, in the coating method described in JP-A-58-186472, a thin tube for detecting the internal pressure has to be introduced into the cylinder, which is inconvenient. . Further, there is a drawback that an auxiliary device such as a pressure sensor, a solenoid valve and an electric circuit for controlling these is required.

On the other hand, JP-A-59-4467 and JP-A-60-1
In the method described in Japanese Patent No. 32678, a valve is provided in the upper closing device as a pressure adjusting mechanism, and when the tubular body is pulled up,
The air pressure inside the cylinder is adjusted by opening the valve just before the liquid level of the paint that has entered the cylinder reaches the lower end of the cylinder.
Although the generation of bubbles is prevented, these methods have a difficulty in adjusting the timing of opening the valve when the cylinder is pulled up.
Furthermore, there is a problem in that it cannot be applied to a cylinder whose upper part is closed, and the type of cylinder that can be used is limited.

Further, since the pressure in the cylinder changes depending on the type of solvent or the weather conditions such as temperature and humidity, it is necessary to change the adjustment conditions in accordance with various coating conditions in any of the methods described in the above publications. There is a problem in that the adjustment becomes complicated, and since there are many movable parts for pressure adjustment, the device becomes complicated and maintenance work is required.

The present invention has been made to solve the above-mentioned problems in the conventional technique, and its object is a method of dip-coating only on the outer surface of a cylinder whose upper end is closed, which is a very simple means. Accordingly, it is an object of the present invention to provide a dip coating method that prevents the generation of bubbles when the cylinder is pulled up.

Means for Solving the Problems The dip coating method of the present invention has an outer diameter smaller than the inner diameter of the cylindrical body when the cylindrical body having the upper end closed and the lower end opened is vertically dipped in the coating material. The float having the above is floated on the liquid surface of the coating material, and the cylindrical body is immersed in the coating material so that the float enters the inside of the cylindrical body.

Next, the dip coating method of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a coating apparatus used to carry out the present invention, and 1 indicates a cylinder. The cylindrical body 1 has a shape in which the upper part is closed, and is attached to the support member 7,
It moves up and down by the lifting member 8. When the tubular body has a shape in which both ends are open, the upper end is closed and attached to the support member. The coating tank 3 is filled with the paint 2, and the paint is circulated through the filter 5 by the pump 6. The float 4 is floated on the liquid surface of the paint.
This float has an outer diameter smaller than the inner diameter of the cylinder so that it can freely move in and out of the inner surface of the cylinder.
However, it is desirable to make the outer diameter as large as possible within a range in which it can freely move in and out of the inner surface of the cylindrical body. When the cylinder is immersed in the paint, the float is immersed in the inner surface of the cylinder. FIG. 2 shows a state in which the tubular body is immersed to the bottom. From this state, the cylinder is pulled up to form a coating film on the outer surface of the cylinder. FIG. 3 shows a state in which the tubular body is pulled up to form the coating film 9 on the surface of the tubular body.

Note that, in FIG. 2, the paint is slightly intruded into the lower portion inside the cylindrical body, but this is because the paint slightly enters the inside due to the pressure of the paint. for that reason,
A part of the inner surface of the cylindrical body to which the paint is applied is generated, but there is no problem in the application work.

The float used in the present invention has a maximum outer diameter portion with a maximum outer diameter within a range where it can freely move in and out of the cylinder body, and if the shape floats on the liquid surface, the shape is not particularly limited. It is not something that will be done. In that case, in order to effectively prevent the evaporation of the paint solvent, the float
The shape is preferably such that the maximum outer diameter portion is located above the coating liquid surface. As an example of such a float, for example, a float 41 having a dish shape shown in FIG. 4 or a float 42 having a bowl shape having a weight at the bottom shown in FIG. 5 is exemplified. it can.

Further, in order to allow these floats to be properly taken into the inside of the cylinder, it is more preferable to provide a wedge-shaped slope on the upper part of the float. FIG. 6 shows an example of such a case, where a surface is formed and the upper part of the float has a conical shape. Further, in FIG. 7, in another example, the float 44 has an oval shape having a weight at the bottom. The top of this oval float may be sealed or perforated.

Further, in order to prevent each float from moving to the peripheral portion at the liquid level in the coating tank, as shown in FIG.
The foot 10 may be provided.

The material of these floats may be any as long as it is durable against the solvent of the paint, and examples thereof include metals such as aluminum, stainless steel, brass, copper, tinplate, galvanized iron, polyethylene, polypropylene and poly. It can be made of plastic such as fluoroethylene. Also, when the foot 10 is provided as shown in FIG.
The foot can be made of a plate material or wire.

Function In the present invention, when the cylinder is immersed in the paint as shown in FIG. 2, the float enters the inside of the cylinder, so that the liquid surface formed inside the cylinder is floated by the float. Will be covered with a slight gap between the outer diameter of the cylinder and the inner diameter of the cylinder. Therefore, since the area of the liquid surface where the solvent of the paint evaporates becomes very small, the evaporation rate of the solvent becomes extremely slow, and there is almost no phenomenon that the solvent evaporates inside the cylinder and the air pressure inside the cylinder rises. . Therefore, a drawback as in the prior art, that is, the solvent of the paint evaporates to increase the air pressure inside the cylinder,
When pulling up the tubular body, the air inside the tubular body does not form bubbles and go out of the tubular body.

Example An example of applying the present invention to the formation of the undercoat layer of an electrophotographic photoreceptor will be described.

An aluminum pipe having an outer diameter of 84 mm, an inner diameter of 82 mm, and a length of 310 mm was prepared as a cylindrical body.

As the coating material, one prepared by dissolving 8 parts (part by weight, the same hereinafter) of copolymerized nylon resin (trade name: CM8000, manufactured by Toray) in 60 parts of methanol and 40 parts of butanol was used.
Methanol has a vapor pressure of about 100 mmHg at 20 ° C. and is a solvent that easily evaporates.

This coating material was put into the dip coating device shown in FIG. As the float, the shape shown in FIG. 8 has a maximum outer diameter of 70 mm,
0.5m so that the height of the maximum outer diameter from the liquid surface is 20mm
It was made of aluminum with a thickness of m, and at the bottom,
The one with the legs attached by three wires so that the outer diameter was 2 mm smaller than the inner diameter of the coating tank was used.

With the float floating on the liquid surface, the cylinder was immersed at 800 mm / min and then pulled up at 100 mm / min. No bubbles were generated during the pulling. After pulling up, it was dried at 100 ° C. for 5 minutes to form a 1.0 μ thick undercoat layer. In this case, no foam was generated.

Also, by processing polyethylene, the shape as shown in Fig. 7 has a maximum outer diameter of 80 mm, a maximum outer diameter of 30 mm above the liquid surface,
When a float having a total height of 90 mm was prepared and the float was applied in the same manner, generation of bubbles could be prevented.
In the case of this float, since it appropriately rolls and enters the inside of the cylindrical body, it is not necessary to have the feet as in the case of the float.

For comparison, when coating was performed in the same process without using a float, when the cylinder was pulled up by about 200 mm, bubbles were generated from the lower part of the cylinder, the bubbles burst at the liquid surface, and the liquid surface fluctuated The film thickness is uneven.

EFFECTS OF THE INVENTION According to the present invention, when the coating film is formed only on the surface of the cylinder whose upper end is closed and whose lower end is opened by the dip coating method, bubbles are generated from the lower part of the cylinder during the coating process. As a result, the coating film formed is of clean quality with no defects. Therefore, the present invention is extremely suitable for a technique for forming a uniform and smooth coating film on the surface of a cylinder, for example, for manufacturing an electrophotographic photoreceptor. Moreover, the present invention can perform dip coating by an extremely simple means of only floating the float on the liquid surface, and therefore, as in the conventional technique,
There is an advantage that a complicated mechanism for pressure adjustment and auxiliary equipment therefor are not required, maintenance and inspection are easy, and coating cost is low.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a dip coating device used in the present invention, FIGS. 2 and 3 are explanatory diagrams for explaining a coating step, and FIGS. 4 to 8 are respectively, It is sectional drawing of the float used for this invention. 1 ... Cylindrical body, 2 ... Paint, 3 ... Coating tank, 4, 41, 42, 4
3, 44 ... Float, 5 ... Filter, 6 ... Pump, 7
... Support member, 8 ... Elevating member, 9 ... Coating film.

Claims (3)

[Claims] 1. A method of vertically dipping a cylinder whose upper end is closed and whose lower end is opened into a coating material to apply the float having an outer diameter smaller than the inner diameter of the cylindrical body to the coating liquid surface. And a coating method in which the cylindrical body is immersed in paint so that the float can enter the inside of the cylindrical body. 2. The dip coating method according to claim 1, wherein the maximum outer diameter portion of the float is above the coating liquid surface. 3. The dip coating method according to claim 1, wherein an upper part of the float is constituted by an inclined surface.