JPH05138125A - Powder coating method for inside surface of vessel body - Google Patents

Abstract

PURPOSE:To form coatings film without pollution and without adopting intricate stages by including a stage for heating a powder coating material to the temp. above its melting temp. and applying the powder coating material on the bottom of a vessel body rotating at 20 to 1000 revolutions per minute around the central axis of the vessel body as the axis of rotation and a stage for sticking the powder coating material to the barrel part of the vessel body rotating at 2000 to 30000 revolutions per minute and subjecting the coating to a heating treatment to form the coating. CONSTITUTION:The bottom of the vessel body 1 is heated to the temp. at which the powder coating material can be melted and applied. The vessel body is fixed by a rotatable gripping means in such a manner that the vessel body is placed to face upward or sideways. The vessel body is then rotated at 20 to 1000 revolutions per minute around the central axis of the vessel body as the axis of rotation and the powder coating material of the amt. enough to coat the bottom part is ejected from a nozzle 2 into the vessel body. The vessel body 1 is then horizontal held and is rotated at 2000 to 30000 revolutions per minute and the powder coating material is supplied by the nozzle. The powder coating material is uniformly dispersed and stuck to the barrel part by the air flow generated in the vessel body at the high speed revolutions. The powder coating material sticking to the inside surface is pressed to the wall surface in the vessel body by centrifugal force. The powder coating material uniformly stuck to the barrel part forms the uniform coating film by a heating treatment of the vessel body including the vessel body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating an inner surface of a can with a powder coating material.

[0002]

2. Description of the Related Art A two-piece can whose bottom is integrally formed is used to protect the material of the can, such as steel and aluminum, from corrosion by the contents, and to preserve the flavor of the drink, etc. Therefore, the inner surface of the can is painted and used.

For coating the inner surface of a two-piece can, a coating method of two coats and two bake is employed, in which a base coat is baked and then a top coat is baked. The paint used is a liquid paint in which a resin such as an epoxy resin or a vinyl chloride resin is dissolved in a solvent. In recent years, since organic solvents contained in these liquid paints are volatilized into the air during coating and cause air pollution, the shift to pollution-free paints has been rapidly promoted.

Further, the two-coat, two-bake coating system is complicated in process and wasteful in terms of energy, so that a new coating system has been desired to be developed.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the problems of using a liquid paint for the inner surface coating of a two-piece can and the problems of the two-coat two-bake coating system.

[0006]

According to the present invention, in a state where at least the bottom of the can body is heated to a temperature higher than the melting temperature of the powder coating material, the central axis of the can body is set as a rotation axis to 20 to 100 per minute.
Rotating at 0 revolutions, a step (A) of coating the bottom of the can by supplying a powder coating in an amount sufficient to coat the bottom of the can, and the can at 2000 to 30000 revolutions per minute. The powder coating is supplied to the inside of the can in an amount sufficient to cover the barrel of the can, and the powder coating is adhered to or coated on the barrel of the can. For example, the present invention relates to a powder coating method for an inner surface of a can, which includes a step (B) of performing heat treatment to melt-coat the powder coating adhered to the body.

The can body used in the present invention is preferably a two-piece can having an integrally molded bottom obtained by forming a can metal material such as a tin-plated steel plate or an aluminum plate by a forming process such as drone and ioning. It may be a three-piece can in which the can body and the can bottom are fitted together.

The powder coating used in the present invention comprises polyester resin, acrylic resin, epoxy resin, nylon resin, polyolefin resin and the like having an average particle size of 1 to 50.
μm, preferably 1 to 20 μm. The melting point of the powder coating material may be 100 ° C. or higher.

The step (A) of the present invention is the coating of the bottom of the can body, which includes the step of heating the bottom part of the can body and the step of imparting rotational motion to the can body. After the can body is heated, the rotary motion may be applied, or the can body may be heated together with the rotary motion of the can body.

For heating the can body, known methods such as oven heating, induction heating and high frequency heating can be employed. The heating part of the can is the bottom including the boundary between the bottom and the body,
The entire can may be heated. The heating temperature is a temperature at which the powder coating material can be melt-coated, that is, 200 to 300 ° C.

In step (A), the can body is turned upward, that is,
The bottom is held downward or the can is set sideways, and the can is fixed with a rotatable gripping tool, and the central axis of the can is rotated about 20 to 1,000 revolutions per minute, preferably Rotate at 100 to 700 rotations. If the number of revolutions is higher than the above value, the powder paint will adhere to the body rather than the bottom, resulting in insufficient coating of the bottom. Non-uniform coverage on the boundary area. The powder coating material may be supplied by jetting a sufficient amount to cover the bottom portion into the can body by means of a nozzle or the like while the can body is rotating. The coating thickness of powder coating is about 5-1
The thickness is 00 μm, preferably 5 to 60 μm. The nozzle preferably has a single nozzle opening so that the powder coating can only cover the bottom and the boundary area between the bottom and the barrel.

In the step (B) of the present invention, the body of the can is coated. In this step, the can body is preferably horizontally oriented at 2000 to 30000 rpm, preferably 5000.
Rotate at ~ 15,000 revolutions. The powder paint is uniformly diffused and adhered to the body part by the action of the air flow and gravity generated inside the can body by the high speed rotation. The attached powder coating is pressed against the inner wall surface of the can by centrifugal force. Therefore, the lower limit of the rotation speed is limited by the uniform coating property of the powder coating material.

Another important factor in the step (B) is to supply the powder coating material while the can body is rotated. Even if the powder coating is supplied with the rotation stopped and the rotation is given, a uniform coating cannot be obtained. In the present invention, the powder coating material can be applied after applying an electrostatic charge by a known charging treatment, but can be applied without electrostatic treatment at a high rotation speed of 5000 rpm or more.

The powder coating material may be supplied from the nozzle as in the step (A). As described above, since the powder coating material can be diffused over the entire body portion as the can body rotates, even if the powder coating material is supplied only to a part of the body portion of the can, it is possible to uniformly coat the entire body portion. For efficient coating, it is preferable to provide a plurality of nozzle openings corresponding to the body of the can.

In the step (B), the coating of the powder coating material is not necessarily accompanied by heating of the body portion, but may be carried out in some cases. When the entire can is heated in the step (A), the heating in the step (B) can be omitted. The powder coating uniformly attached to the body forms a uniform coating film by heating the can body including the body of the can.

According to the present invention, it is preferable to coat the can body with the powder coating material in the step (A) and then the step (B), but the step (B) and the step (A) may be performed in this order. it can.

[0017]

EXAMPLE An aluminum DI can body (can height 122 mm, 65.8 mm) horizontally mounted on the apparatus shown in FIG. 1 is 500 RP.
It was rotated at M and the can body portion in the bottom and a region of about 1 cm from the bottom was heated to 130 ° C. by high frequency heating. Then, from the coating nozzle, an epoxy-ester type powder coating material (trade name: EPPN FINE BI, manufactured by Vanicolor Co .;
m) was supplied in 100 mg over 10 seconds, and the bottom of the can and a part of the barrel were coated. Next, remove the heating device, replace the painting nozzle with that shown in FIG. 2, and change the rotation speed to 1000 RP.
Rotate the can body with M and apply the above powder coating from the coating nozzle 1
It took 400 seconds to supply 400 mg and uniformly adhered to the inner surface of the can body. The can body subjected to the above treatment was detached from the apparatus, and the whole can was baked at 160 ° C. for 5 minutes to obtain a can body with an inner surface coated. The coating thickness of the obtained coated can was in the range of 10 to 15 μm for both the bottom and the body.

[0018]

According to the powder coating method for the inner surface of the can of the present invention, the bottom portion of the can which cannot be covered in the step (B) can be covered in the step (A). In particular, the bottom and can body boundary areas, where a relatively thick coating is required, can be coated by step (A). Further, in the step (B), a relatively thin and defect-free coating can be formed on the body of the can. Therefore, according to the coating method of the present invention, a coating film having an excellent function of protecting the can material from corrosion can be formed without pollution and without employing complicated steps such as liquid coating.

[0019]

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a step (A)

FIG. 2 is a cross-sectional view illustrating step (B).

[Explanation of symbols]

 1 can body 2 nozzle 3 heating device 4 rotation drive source 5 can pressing device

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Fujio Fujio 86-9 Miyakooka-cho, Asahi-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Hirotoshi Suzuki 441 Ogura, Kokura-ku, Kawasaki-shi, Kanagawa Shin-Kawasaki Corpus B-205

Claims (1)

[Claims] 1. A can body is rotated at 20 to 1000 revolutions per minute with a central axis of the can body as a rotation axis in a state where at least a bottom portion of the can body is heated to a temperature higher than a melting temperature of the powder coating material. A step (A) of supplying a powder coating material in an amount sufficient to cover the bottom portion to cover the bottom portion, and a step of rotating the can body at 2000 to 30,000 rpm. The powder coating material is supplied to the inside of the can in an amount sufficient to cover the body of the can, and the powder coating is attached to or coated on the body of the can.
A powder coating method for the inner surface of the can, which includes a step (B) of performing heat treatment to melt-coat the powder coating adhered to the body, if necessary.