JPH027709B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for coating the inner surface of cans such as drum cans and pail cans, including the seamed parts, with a synthetic resin film by electrostatic coating. It is something.

Prior art and its problems Empty containers such as open drum cans and pail cans are used to store or transport a fixed amount of goods. However, since these cans are made of iron, they have the drawback that if they are directly filled with powders or fluids of medicines, chemicals, etc., they will rust, or in the case of acidic products, pinholes or other problems will form in the can. Also, direct contact with metals may cause the chemical to deteriorate. In order to prevent this drawback, an inner bag made of a synthetic resin such as polyethylene having properties corresponding to the properties of the filling material is inserted into the can, or the inner surface of the can is coated with epoxy resin. However, when using an inner bag, it takes time to insert the inner bag into the can, and there is a risk of the bag being damaged.Epoxy coating is hard and brittle, so pinholes form after one use, making it impossible to reuse it. Not only is it impossible, but epoxy coating is only applicable to new cans and is not suitable for recycled cans.
It has the disadvantage of being expensive. To improve this, Japanese Patent Publication No. 59-26354 proposes a method of electrostatically coating the inner surface of the can with polyethylene resin powder and then melting it in a heating furnace to obtain a coating film.
However, in this method, in order to completely form a coating film even on the tightened portion of the drum can, the tightened portion of the can is first coated with a resin with a low melting point, and then a polyethylene resin with a higher melting point is applied. It is electrostatically painted and then heat treated. Therefore, there is the inconvenience of using two different types of synthetic resin materials.

Means for Solving Problems In view of the above-mentioned drawbacks, the present invention aims to form a synthetic resin film of uniform thickness on the entire inner surface of the can, including the seamed portion, by using the same type of synthetic resin powder material. The inner surfaces of open drum cans, pail cans, etc. are brought into a state suitable for resin coating, and the tightened portion of the can is coated with polyethylene resin powder using an electrostatic coating method. The amount of powder exceeding the electrostatic coating limit was sprayed with a nozzle having the required angle to the inner circumferential surface of the can, and the entire inner circumferential surface of the can, including the tightened part, was coated, and the electrostatic powder coating limit was exceeded. After coating the inner circumferential surface and inner bottom of the can so that the excess powder adheres to the bottom of the can, the can is heated so that the air contained in the powder coating and/or the air in the tightened portion becomes bubbles when the paint melts. The powder coating is melted by heat treatment to such an extent that no pinholes are formed, and is applied to the entire inner peripheral surface of the can to form a resin coating.

EXAMPLES The present invention will be described below based on examples. Cans applied to the present invention are not limited to open drum cans, pail cans, or any can with at least one side open, and are not limited to new cans or recycled cans. In the embodiment, a recycled can that has been used at least once will be described.

First, the recovered open drum can 1 undergoes a cleaning process in which the inner circumferential surface and outer circumferential surface of the can are cleaned to remove any adhering substances.
This includes cleaning with water or cleaning fluids, or incinerating the deposits. Furthermore, if necessary, it is shaped, polished with shotplast, and inspected for the presence of pinholes.

In this way, the recyclable open drum can 1 is brought into a state suitable for resin coating at least its inner peripheral surface and inner bottom surface, and polyethylene resin powder is first applied to the inner bottom peripheral surface of the open drum can, that is, the tightened portion. 2. Paint 8 using an electrostatic powder coating gun.

At this time, the operator may hold the gun and apply the coating almost uniformly to the tightened part of the drum can, or the worker may face the gun towards the tightened part of the drum can and rotate the drum can side. It's okay.

Next, electrostatic coating 5 is performed by spraying the same polyethylene resin powder that was coated 3 on the tightened portion in the previous process using an electrostatic coating gun 4 that is opposed to the inner peripheral surface of the drum can at a certain angle. The gun 4 is slowly raised from the inner bottom of the drum can toward the opening of the drum can while rotating the drum can side. Of course, at this time, polyethylene resin powder is injected from the gun 4 to perform electrostatic coating. However, in electrostatic powder coating, the maximum film thickness is 300 microns. In the present invention, a powder coating material that exceeds the limits of electrostatic powder coating is sprayed.

As a result, as the gun moves up, the paint is applied to the inner peripheral surface of the drum can within the limit, that is, at a thickness of 300 microns, but the excess paint that exceeds this limit falls and adheres to the unpainted inner bottom of the drum can. be.

Therefore, the amount of powder paint injected from the gun 4 is determined by the rotational speed of the drum can and the rising speed of the gun so that the paint adheres to the inner peripheral surface of the drum can at a thickness of 300 microns and the gun reaches the highest point at the opening end of the drum can. The entire amount of excess paint is spread over the entire bottom of the drum can.
It is economical if the coating is determined to be 300 microns thick.

The drum can whose inner peripheral surface and inner bottom surface have been electrostatically coated in this manner is then placed into a heating furnace. At this time, when the powder paint enters the furnace, it is merely attached to the drum can due to electrostatic action, so it is necessary to heat the paint in a manner that prevents it from being blown away. Finally, the paint is electrostatically adhered to the drum can and melted to ensure resin coating. During this heat treatment, the heating is stopped just before or before the air sealed in the seamed part and/or the air contained in the powder paint melts and escapes as bubbles. This is to adjust the heating time.

The purpose of coating the drum can with resin is to prevent the articles contained in the drum can from coming into direct contact with the metal drum can. If pinholes are formed in the resin coating due to degassing, etc., the contents may come into contact with the metal parts of the drum can through the pinholes, corroding the can or causing deterioration of the contents; Even if the metal surface is sealed within the coating, the purpose can be fully achieved as long as there are no pinholes on the surface of the coating and the metal surface is completely covered.

Effects of the Invention According to the present invention, the inner circumferential surface of the drum can and the tightening part are electrostatically coated using the same paint, so the method is simple, and the powder paint is used economically to maximize the effect. There is an advantage that you can get Further, the method of the present invention has the advantage that it can be applied regardless of whether it is a new can or a recycled can.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the open drum can, Figure 2 is an enlarged cross-sectional view of the sealed portion with electrostatic coating, Figure 3 is an explanatory diagram of electrostatic coating on the inner surface of the can, and Figure 4
The figure is an enlarged cross-sectional explanatory view after coating. 1 is the drum can, 2 is the tightening part, 3 is the first electrostatic coating, 4 is the gun, and 5 is the second electrostatic coating.

Claims (1)

[Claims] 1. Bring the inner surface of an open drum can, pail can, etc. into a state suitable for resin coating, apply polyethylene resin powder to the wrapped portion of the can by electrostatic coating, and then apply the polyethylene resin powder to the sealed part of the can by electrostatic coating. Spray an amount of powder in excess of the coating limit using a nozzle having a required angle to the inner circumferential surface of the can to coat the entire inner circumferential surface of the can, including the tightened portion, and remove any excess powder that exceeds the electrostatic powder coating limit. After coating the inner periphery and inner bottom of the can by attaching it to the inner bottom of the can, the air contained in the powder paint and/or the air in the tightened part becomes bubbles when the paint melts, causing pinholes. A method for coating an inner surface of a drum can with a resin film, characterized in that the powder coating material is melted by heat treatment to such an extent that no formation occurs, and the resin coating is applied to the entire inner peripheral surface of the can.