JPH03217279A - Method for coating inner surface of beverage can - Google Patents

Abstract

PURPOSE:To uniformize the thickness of a coating film by injecting a water paint on the inner surface of the beverage can to coat the surface and then repeatedly inverting the can. CONSTITUTION:The beverage can K is introduced into a spraying machine 1, and a water paint is injected on the inner surface of the can K from a spray gun G to coat the surface. The can K is then discharged from the machine 1 and vertically placed, hot air is blown into an oven H from the upper part, and the recess 5 is filled with the paint S. The can K is then discharged from the oven H, reversed and inverted on a conveyor belt 2. As a result, an excess of the paint S in the recess 5 mostly flows along the barrel 4, and an excess of the paint S at the bottom 3 also flows along the barrel 4. Consequently, the paint S is uniformly spread over the bottom 3, barrel 4, recess 5 and bottom wall 6. The foaming of the coating film is prevented in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" This invention relates to a coating method for coating the inner surface of a beverage can with a water-based paint.

"Prior Art" Generally, the inner surface of a beverage can is coated with paint in order to prevent corrosion of the inner surface of the can due to contact with beverages or the like. As shown in FIG. 6, this coating is carried out by spraying the paint onto the inner surface of the can K using a spray gun G, and then heating and drying it in an oven.

As shown in Figure 7, solvent-based paints are currently used as the above-mentioned paints because they increase viscosity faster and have better coating properties than water-based paints. It is.

However, when using the above-mentioned solvent-based paints, there are problems such as work environment and air pollution, and in some regions, local ordinances require the use of paints with low solvent content. The use of water-based paints as paints for painting the inside surfaces of beverage cans is being considered.

``Problems to be Solved by the Invention'' However, since the viscosity of water-based paints increases more slowly than that of solvent-based paints, the paint film tends to foam when heated and dried in an oven.

Also, when using water-based paints with a small amount of paint, it is difficult to
Conversely, when the amount of coating increases, the flow increases in proportion to the square of the amount of coating, which tends to cause large irregularities in the coating distribution (distribution of coating film thickness) on the inner surface of the beverage can, as shown in Figure 2. When a water-based paint is applied to the inner surface of the can K using the spray gun G, the paint is excessively distributed particularly at the bottom (bottom part 3) of the can, and the paint film in this area is likely to foam.

``Object of the Invention'' This invention has been made in view of the above circumstances, and provides a method for coating the inner surface of a beverage can that can uniformly coat the inner surface of a beverage can with a water-based paint to a predetermined film thickness. It is an object.

[Means for Solving the Problems] In order to achieve the above object, the method for coating the inner surface of a beverage can of the present invention involves spraying and coating the inner surface of a cylindrical beverage can with a water-based paint, and then applying the water-based paint to the inner surface of a cylindrical beverage can. A step of placing the beverage can upright so that its axis is perpendicular to a horizontal plane, and a step of inverting the beverage can so that the bottom is upside down from the upright position. This is repeated more than once.

"Function" In the method of painting the inside surface of a beverage can of the present invention, by repeating the upright and upside down cans one or more times, the paint flows along the inside surface of the can, and the paint can be applied uniformly. especially,
Even in bottom coatings where paint tends to accumulate, the coating film does not become excessively thick, so the coating film does not foam during heating and drying in an oven.

Embodiment An embodiment of the method for coating the inner surface of a beverage can of the present invention will be described below with reference to FIGS. 1 to 4.

In FIG. 1, reference numeral 1 indicates a spray machine.

Beverage cans K are carried into this spray machine 1 from the previous process, and a water-based paint S is sprayed and applied to the inner surface of the can K by a spray gun G shown in FIG.

At this time, the coating distribution on the inner surface of the can K is such that the paint S accumulates in the bottom part 3 and the film thickness in this part is thicker (thickness: 28μ1 or more) than in the body part 4, as shown in FIG. At the same time, the paint S is not completely spread over the groove 5 at the bottom.

Thereafter, the can K is taken out of the spray machine I, placed on the conveyor belt 2 with its axis perpendicular to the horizontal plane, and conveyed by the conveyor belt 2 into an oven H for pre-drying. , hot air is blown into the oven H from above. At this time, the paint S accumulated in the bottom 3 flows into the recess 5 along the inner surface of the can K due to gravity, as shown in FIG. This results in
The paint S completely spreads over the recess 5, and a small amount of the paint S on the bottom wall 6 of the can K also flows into the recess 5. Note that at this time, the paint S has flowed into the recess 5 in a slightly excessive amount.

Next, the can K taken out from the oven H is turned over and placed upside down on the conveyor belt 2. Then, as shown in FIG. 4, the paint S that had accumulated slightly excessively in the recess 5
most of it flows along the trunk 4, and the bottom part 3
The paint S, which remained slightly excessively, also flows along the body 4. As a result, the paint S is distributed almost uniformly over the bottom 3, top 4, recess 5, and bottom wall 6 of the can K.

Furthermore, the can K is again reversed and placed upright on the conveyor belt 2. As a result, the paint S remaining slightly but excessively in the bottom part 3 and body part 4 of the can K flows, and as a result, the paint S is distributed more evenly.

Thereafter, the can K is further conveyed by a conveyor belt and carried into a main drying oven (not shown), where it is completely heated and dried to complete the coating.

In addition, as a result of investigating the coating distribution on the inner surface of the can painted through such a process, it was found that the coating was applied almost uniformly on the barrel 4, recess 5, and bottom wall 6, while the bottom section 3 was slightly more coated than these. Although the coating was thick, the film thickness at the bottom was less than 28 μl, and it was confirmed that no foaming occurred.

According to the method for painting the inside surface of a beverage can, the slow increase in viscosity of the water-based paint S is used to spray the paint S onto the inside surface of the can K using a spray gun G, and then apply the paint S to the inside surface of the can K. By repeatedly placing the can K upright and upside down and allowing the paint S to flow along the inner surface of the can, the paint S can be applied uniformly, so that the paint film does not foam during heating and drying in the oven. There's nothing to do.

Further, by repeatedly placing the can K upright and upside down, even in the phototom part 3 where paint S tends to accumulate, the thickness of the coating film does not become excessively thick, thereby preventing foaming in this part where foaming is likely to occur. I can do it.

In the above example, the can K whose inner surface was coated with the paint S by the spray gun G was placed in the upright position, inverted position, and upright position in this order; Well, furthermore,
The number of times of upright and inverted positions may be increased.

Further, for example, the paint S is not spread over the part indicated by the reference numeral 8 on the inner surface of a can with a bottom shape as shown in FIG. 5 when sprayed by the spray gun G. It can also be distributed along the inner surface of the can bottom to the area shown by the reference numeral 8 above.

"Effects of the Invention" As explained above, according to the method for coating the inner surface of a beverage can of the present invention, the slow increase in viscosity of water-based paint is utilized to inject the water-based paint onto the inner surface of the can. After coating, the paint can be applied evenly by repeating placing the can upright and upside down once or more to flow the paint along the inner surface of the can, so that the paint film will not fade during heating drying in the oven. does not foam.

Further, by repeatedly placing the can upright and upside down, the coating film does not become excessively thick even in the bottom part where paint tends to accumulate, and it is possible to prevent foaming in this part where foaming tends to occur.

[Brief explanation of drawings]

1 to 4 are for explaining one embodiment of the present invention, and FIG. 1 is a schematic configuration diagram of a coating device, and FIG.
Figures 4 to 4 are cross-sectional views of the bottom of cans in each painting process, and Figure 5 is a cross-sectional view of the main parts of cans with different bottom shapes.
FIG. 6 is a cross-sectional view showing the state in which the inner surface of a can is coated with a spray gun, and FIG. 7 is a graph showing the viscosity increase curves of water-based paint and solvent-based paint. S...Water-based paint, K...Beverage can, 3.
...Bottom part, 4...Torso part, 5...
... recess, 6... bottom wall.

Claims (1)

[Claims] A step of spraying and coating the inner surface of a cylindrical beverage can with a bottom and then placing the beverage can upright with its axis perpendicular to a horizontal plane; A method for coating the inner surface of a beverage can, comprising repeating the steps of placing the bottom in the upright position and inverting the can upside down, one or more times.