JPH027710B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of coating the inner surface of a can such as a drum can or a pail can with a synthetic resin film, including the wrapped portion thereof.

Prior art and its problems Containers such as open drum cans and pail cans are used to store or transport a fixed amount of goods. However, since this can is made of iron, it has the disadvantage that if it is directly filled with powder or fluid products such as medicinal chemicals, it will rust, and if acidic products are used, pinholes or the like will form in the can. In addition, direct contact with metal may cause deterioration of the stored article. In order to prevent this drawback, an inner bag made of 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 and effort to insert the inner bag into the can, and there is a risk of the bag being damaged.Also, the epoxy coating is hard and brittle, so pinholes form after one use, making it impossible to reuse it. It is not possible to do so, and epoxy coating is only applicable to new cans and is not suitable for recycled cans, which has the disadvantage of being expensive.
To improve this problem, 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 drum 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 coated and then heat treated. Therefore, there is the inconvenience of using two different types of synthetic resin materials, and there is also the disadvantage that the previously applied paint is blown off during the second application.

Solution to the Problems In view of the above-mentioned drawbacks, the present invention uses the same type of synthetic resin material to form a synthetic resin film with a uniform thickness over the entire inner surface of the can, including the seamed portion. Then, the inner surfaces of open drum cans, pail cans, etc. are brought into a state suitable for resin coating.
After melting polyethylene resin into the tightly wound part of the can and filling it with it, powder the same material as the polyethylene resin, and in an amount exceeding the electrostatic coating limit, at the required angle to the inner peripheral surface of the can. Spray with a paint gun to coat the entire inner circumferential surface of the can, including the tightened part, and also deposit excess powder exceeding the electrostatic powder coating limit on the inner bottom of the can to coat the inner circumferential surface of the can. After coating the inner bottom surface of the can, the can is heat-treated to melt the powder coating and applied to the entire inner circumferential surface of the can to form a resin coating.

EXAMPLES The present invention will be described below based on examples. Cans applicable 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 so-called old open drum can, which 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 on its inner peripheral surface and inner bottom surface, and then polyethylene resin is first heated and melted, and the molten resin 3 is then opened. The inner bottom circumferential surface of the drum can, that is, the seamed portion 2 is filled with the injection nozzle 6. At this time, the operator may hold the injection nozzle 6 and inject and fill the wound portion of the drum can almost uniformly, or the operator may face the gun toward the tightened portion of the drum can and place the gun on the side of the drum can. may be rotated.

Next, electrostatic coating is performed by spraying the same polyethylene resin powder that was injected into the tightened portion in the previous process using an electrostatic coating gun 4 that faces 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 a gun 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 rises, the paint is applied to the inner peripheral surface of the drum can within the limit, that is, 300 ml.
The paint is applied to a micron thickness, but excess paint that exceeds this limit falls off and adheres to the unpainted inner bottom of the drum can. Therefore, the amount of powder paint injected from the gun 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. It would be economical if the entire amount of paint that becomes surplus during the movement of the drum is determined so that it is coated on the entire inner bottom of the drum to a thickness of about 300 microns.

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 5.

Effects of the Invention The purpose of coating the drum can with resin is to prevent articles stored 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 in the resin coating, corroding the can or causing deterioration of the contents. After injecting and filling pre-molten polyethylene resin into the tightened parts where pinholes are likely to occur due to air, to ensure that air is removed from these areas, the entire inside of the can is coated with electrostatic powder coating. Therefore, there is an advantage that pinholes etc. do not occur, and the powder coating can be used economically to obtain the maximum effect. Furthermore, 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 molten resin injected into the tightened part, Figure 3 is an illustration of electrostatic coating on the inner surface of the can, and Figure 4 is the coating. It is a later enlarged sectional explanatory view. 1 is a drum can, 2 is a tightening part, 3 is a molten resin, 4 is a painting gun, 5 is a resin coating, and 6 is an injection nozzle.

Claims (1)

[Claims] 1. After bringing the inner surface of an open drum can, a pail can, etc. into a state suitable for resin coating, and filling the wrapped portion of the can with pre-molten polyethylene resin, the same material as the polyethylene resin is powdered, and Spray an amount of powder that exceeds the electrostatic coating limit with a painting gun that has 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 at the same time exceed the electrostatic powder coating limit. After coating the inner periphery and inner bottom of the can so that the excess powder is attached to the inner bottom of the can, the can is heat-treated to melt the powder coating and adhere to the entire inner periphery of the can to form a resin coating. A method for coating the inner surface of a drum can with a resin film.