JP2521972B2 - 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 cylinder is immersed in the paint,
Next, the coating is applied by pulling it up at an appropriate speed. 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, by closing the upper part of the cylinder, air is trapped inside the cylinder when the cylinder is immersed in the paint, and the air pressure inside the cylinder prevents the paint from entering. It has been known. To close the top of the barrel,
There is a method of using the cylinder itself whose upper part is closed, or a method of closing the upper part of the cylinder whose both ends are open by a sealing mechanism.

In this way, when a cylinder whose top is closed is immersed in paint and pulled up, the pressure of the air trapped inside the cylinder rises as the solvent of the paint evaporates, and the original volume of air is 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. 58-1864
Japanese Patent Laid-Open No. 72-72 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.

Further, JP-A-59-4467 and JP-A-60-132678 describe a method for preventing bubbles from being generated by attaching a pressure adjusting mechanism to a closing device that closes the upper part of the cylindrical body.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the coating method described in JP-A-58-186472, however, 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, in the methods described in JP-A-59-4467 and JP-A-60-132678, a valve was provided in the upper closing device as a pressure adjusting mechanism, and the valve was inserted into the cylinder when the cylinder was pulled up. The air pressure inside the cylinder is adjusted by opening the valve just before the liquid surface of the paint reaches the lower end of the cylinder to prevent the generation of bubbles.However, in these methods, the timing of opening the valve when pulling up the cylinder is adjusted. There was a difficulty in adjusting. 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 in order to solve the above-mentioned problems in the prior art, and its object is a method of dipping and coating only on the outer surface of a cylindrical body having an upper end 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.

As a means for solving the above-mentioned problems, a method is proposed in which a space portion communicating with the inside of the cylindrical body and closed is formed in the upper portion of the cylindrical body to reduce the pressure of air rising due to evaporation of the solvent. (Japanese Patent Application No. 61-84743). Fifth
The figure illustrates the case, in which reference numeral 1 denotes a cylindrical body, which is held by a columnar supporting member 4, a gripping member 3, an O-ring 5, and a cylindrical supporting member 2. A space S is formed in the cylindrical support member 2, and this serves as a pressure relief function. In addition, 6 is a coating tank and 7 is a coating material.
However, this method has a problem in that a supporting member having a complicated structure has to be used as a supporting device for a cylindrical body, and cannot be used for a cylindrical body having an upper portion closed.

On the other hand, a float having an outer diameter smaller than the inner diameter of the cylinder is floated on the liquid surface of the paint, and the cylinder is immersed in the paint so that the float enters the cylinder to suppress the evaporation of the solvent. A method of preventing the pressure rise inside the cylinder has also been proposed (Japanese Patent Application No. 62-137784). FIG. 6 illustrates the case, in which the float 8 floats on the liquid surface of the coating material 7 in the coating tank 6 and enters the inside of the cylindrical body 1 supported by the columnar supporting member 4. The area where the solvent evaporates is practically only a small gap between the inner diameter of the cylindrical body and the outer diameter of the float, which suppresses the evaporation of the solvent.

However, in this method, since there is a slight gap between the inner diameter of the cylinder and the outer diameter of the float, the solvent evaporates little by little. As a result, when the evaporation rate of the solvent is extremely high, or when the pulling rate is extremely slow during coating, the pressure increase inside the cylinder cannot be suppressed and bubbles may occur.

Means for Solving the Problems As a result of further studies, the present inventors have found that the combination of the two proposed methods can more effectively prevent the occurrence of bubbles, and have completed the present invention. Came to do.

The dip coating method of the present invention, when the cylindrical body with the upper end closed and the lower end opened is vertically dipped in the coating material,
A float having an outer diameter smaller than the inner diameter of the cylindrical body, a space portion inside, and a shape in which most of the space portion exists below the liquid surface of the coating material is applied to the liquid surface of the coating material. Float in a state in which most of the
It is characterized in that 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, is attached to the columnar support member 4, and moves up and down by the elevating member 10 and the screw screw 11. When the both ends of the cylindrical body are open, the upper end is closed and attached to the columnar support member. The coating tank 6 is filled with paint 7, which is circulated through a filter 13 by a pump 12. It should be noted that this paint circulation system may not be present if it is not desired. A cylindrical float 9 having a space S formed therein is floated above the liquid surface of the paint. The tubular float has an outer diameter smaller than the inner diameter of the tubular body so that it can freely move in and out of the inner surface of the tubular body. 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. In that case, in order to effectively prevent the evaporation of the paint solvent, the tubular float preferably has a shape such that the maximum outer diameter portion thereof is located above the liquid surface of the paint.

Further, since the space portion S of the cylindrical float 9 is intended to increase the volume of air contained in the cylinder body, most of the space portion of the cylindrical float 9 exists below the coating liquid surface. It is necessary to keep it floating. The volume of the space portion is selected to be an appropriate size so that the paint does not properly enter the inside of the cylinder and bubbles do not occur when the coating is actually performed. However, if the volume of the space is too large, the bottom of the cylindrical float comes into contact with the bottom of the coating tank when the cylinder is immersed, so the volume of the space is Select a size that does not exist.

When immersing the tubular body in the paint, the tubular float 9 is immersed in the state of being taken into the inner surface of the tubular body. FIG. 2 shows a state where the tubular body 1 is immersed to the lowermost portion. From this state, the cylinder is pulled up to form a coating film on the outer surface of the cylinder.

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. Therefore, 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.

In the present invention, it is more preferable to provide a wedge-shaped slope on the upper part of the float in order to allow the float to be taken into the tubular body well. FIG. 3 shows an example of such a case, in which the upper part of the cylindrical float 9 forms a conical portion 14 having a conical shape. Of course, a part of the conical part 14
A hole through which air flows is provided.

Further, the float may be provided with feet 15 as shown in FIG. 4 so as not to move to the peripheral portion on the liquid surface in the coating tank.

The material of these floats is durable against the solvent of the paint, and when the float is floated on the liquid surface of the paint, most of the space inside the float exists below the liquid surface of the paint. Anything will do as long as it does. For example, a metal such as aluminum, stainless steel, brass, copper, tin plate, galvanized iron, or a plastic such as polyethylene, polypropylene, or polyfluoroethylene can be used. When the foot 15 is provided as shown in FIG. 4, 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 even if there is a solvent that evaporates little by little, the space inside the float alleviates the pressure increase. Therefore, the phenomenon that the air pressure inside the cylinder rises is almost eliminated. Therefore, there is a drawback as in the prior art, that is, when the paint solvent evaporates and the air pressure inside the cylinder rises, and when the cylinder is pulled up, the air inside the cylinder becomes bubbles to the outside of the cylinder. There is no going out.

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.

Copolymer nylon resin (trade name: CM8000,
Toray) 8 parts (part by weight, the same applies hereinafter) to 55 parts of methanol,
And that prepared by dissolving in 40 parts of butanol were used. Methanol has a vapor pressure of about 100 mmHg at 20 ° C.
It is a solvent that easily evaporates.

This coating material was put into the dip coating device shown in FIG. As the float, it has the shape shown in Fig. 4 and the maximum outer diameter is 70 m.
m, inner diameter is 69 mm, cylinder depth is 60 mm, and the outer diameter of the maximum outer diameter portion is 20 mm, made of brass with a thickness of 0.5 mm. The one with legs attached with three wires so that the outer diameter was smaller by 2 mm was used.

With the float floating on the liquid surface, the cylinder was immersed at 800 mm / min and then pulled up at 80 mm / min. No bubbles were generated during the pulling. After pulling up, it was dried at 100 ° C. for 5 minutes to form a uniform undercoating layer having a thickness of 1.0 μm.

For comparison, when coating was performed in the same process without using a float, when the cylinder was pulled up by about 180 mm, bubbles were generated from the lower part of the cylinder, the bubbles burst at the liquid surface and the liquid surface fluctuated,
Terrible film thickness unevenness has occurred.

Also, as shown in Fig. 6, it is a float that does not have a space inside, and is made of aluminum with a thickness of 0.5 mm so that the maximum outer diameter is 70 mm and the height from the liquid surface of the maximum outer diameter is 20 mm. In the case of using the produced one, bubbles were generated from the lower part of the cylinder when the cylinder was pulled up by about 250 mm.

EFFECTS OF THE INVENTION The present invention has the above-described structure, and in particular, floats a float having a space portion formed therein, on the liquid surface of the coating material, with most of the space portion existing below the liquid surface of the coating material. Therefore, even if there is a solvent that evaporates little by little, the pressure increase is mitigated by the space part of the float, so bubbles do not occur from the lower part of the cylinder during the coating process, and the coating film formed is free of defects. There will be no clean quality. 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, since the present invention can perform dip coating by an extremely simple means of only floating the float on the liquid surface, a complicated mechanism for pressure adjustment and auxiliary equipment therefor are required as in the prior art. In addition, maintenance and inspection are easy and the 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, FIG. 2 is an explanatory diagram explaining a coating step, and FIG.
FIG. 4 and FIG. 4 are sectional views of the float used in the present invention, and FIG. 5 and FIG. 6 are explanatory views showing the structure of the dip coating device for comparison. 1 ... Cylinder body, 2 ... Cylinder support member, 3 ... Gripping member, 4
…… Column support member, 5 …… O-ring, 6 …… Coating tank, 7
…… Paint, 8 …… Float, 9 …… Cylindrical float, 10…
Lifting member, 11 …… Screw screw, 12 …… Pump, 13…
... filter, 14 ... conical part, 15 ... foot, S ... space part.

Claims (3)

(57) [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 have an outer diameter smaller than the inner diameter of the cylinder and having a space portion inside. A float having a shape in which most of the space portion is below the coating liquid surface is floated on the coating liquid surface in a state where most of the space portion is below the coating liquid surface, An immersion coating method, which comprises applying the coating by immersing the tubular body in paint so that the float enters the inside of the tubular 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.