JPS61227177A - Surface treatment for painting of aluminum alloy plate for food can - Google Patents

Abstract

PURPOSE:To increase the adhesive power of a coated film by etching an aluminum alloy plate with an alkaline soln. then cleaning the surface with rolls flocked on the outside circumference, forming a chemical conversion film on such surface and painting the surface. CONSTITUTION:The deteriorated layer by rolling of the aluminum alloy plate for a food can is etched away by the alkaline soln. The aluminum alloy plate 12 after the above-mentioned treatment is passed in the arrow A direction opposite from the rotating directions of a pair of rolls 10, 11 rotating in the opposite directions through a cleaning device 9 consisting of the rolls 10, 11 flocked with nylon hair 10a, 11a on the surface; at the same time the alkaline cleaning liquid consisting of approximately the same components as the components of the etching soln. is sprayed from a spray nozzle 15. The smut on the plate 12 is thereby effectively removed and thereafter the chemical conversion film is uniformly formed on the surface to make the formation of the coated film having the good adhesive power possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for treating the coating surface of aluminum alloy plates for food cans, which improves the so-called degreasing process in the surface treatment of aluminum alloy plates for food cans. .

[Prior Art] Conventionally, aluminum alloy plates used for beverage cans and food cans are coated with paints such as vinyl organosol paints to improve corrosion resistance.

In this application, degreasing is performed as a pretreatment, and the surface of the alloy plate is etched by dipping or spraying using an alkaline solution, an acid solution, or a combination thereof.

For etching, there is a non-etching method in which the alloy surface is etched by 5 mg/m2 or less using a treatment solution with a pH of 9 to 7;
Weak etching with 0 mg/m2 etching and l)H
is 12 or more, 50 m(]/m2 or more, or etching).

[Problems to be Solved by the Invention] However, there is a problem in that the non-etching and weak etching described above cannot sufficiently remove the rolled-processed deteriorated layer of the alloy plate.

On the other hand, with strong etching, the rolled-processed deteriorated layer is removed, but after the treatment, lump-like impurities (smut) 2 with a size of 0.1 to several microns are left on the Au alloy plate 1, as shown in FIG. There was a problem in that bacteria remained and the subsequent uniform formation of the chemical conversion coating 3 was hindered, resulting in a decrease in the adhesion of the coating film 4.

The present invention was made in order to solve the problems of the above-mentioned conventional technology, and it is possible to sufficiently remove the deteriorated layer due to rolling of an aluminum alloy plate, reduce the residual smut, and uniformly apply the chemical conversion coating. An object of the present invention is to provide a method for treating a coating base of an aluminum alloy plate for food cans, which is formed to increase the adhesion of a coating film.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and after removing the rolled-processed deteriorated layer of an aluminum alloy plate for food cans by etching with an alkaline solution, flocking is performed on the outer periphery. The method is characterized in that the alloy plate is passed between a pair of rotating rolls to clean the surface of the alloy plate, and then a chemical conversion film is formed on the aluminum alloy plate.

[Function] When forming a coating film on an aluminum alloy plate for food cans, first, the aluminum alloy plate after rolling is etched with an alkaline solution to remove a layer affected by rolling. At this time, smut of compounds such as AΩ, M(], Zn, etc. remains on the alloy plate, but the alloy remains between a pair of rotating rolls that rotate in opposite directions and have hair flocked on the outer periphery. The smut is removed by passing it through the plate.

Next, a chemical conversion film such as a phosphate film and a coating film are formed on the alloy plate, but since the smut has been sufficiently removed by the above degreasing treatment, the chemical conversion film is uniformly formed on the alloy plate. and the paint film will adhere.

[Example code] An embodiment of the present invention will be described below.

First of all, the plate is made of Ω alloy (AA50B2>) with a thickness of 0°3 mm.
After forming a nail stand alloy plate with a width of 900 mm by rolling processing, degreasing processing is performed. As this treatment solution, a mixed solution of sodium hydroxide and chromium phosphate was adjusted to pH 12, and the mixed solution was heated to 60°C and applied to the surface of the AΩ alloy plate.
Spray for 5 seconds.

As a result, the surface of the 71 alloy plate is etched by 50 mg/m2 or more, and the rolled deteriorated layer is removed.

Next, the AΩ alloy plate 12 is cleaned using a cleaning device 9 as shown in FIGS. 1 and 2. In Figure 1,
10.11 is a pair of rolls, these rolls 10.1
1, there are 82 gaps through which the Ω alloy plate 12 passes. In addition, on the surface of the above-mentioned Rho/l/10.11, nylon fimbriae 1 with a wire diameter of 0.02 to 0.2 mm are attached.
0a and 11a are planted.

During processing by the cleaning device 9, the roll 10.1
1 are driven to rotate in opposite directions by motors (not shown), and the rotation direction is set to be opposite to the traveling direction A of the AΩ alloy plate 12.

At this time, when the first alloy plate 12 passes between the rolls 10 and 11, an alkaline cleaning solution having almost the same composition as the etching solution is poured from the spray nozzle 15 to remove the nail stand alloy plate 1.
2 is cleaned by the fimbriae 10a, 11a of the roll 10.11, and the smut on the AΩ alloy plate 12 is removed.

In addition, water injection from the nozzle 15 also has the effect of cleaning smut adhering to the roll surface.

Then, after washing with hot water, a chemical conversion film forming treatment is performed. That is, a mixed solution of 3% by weight of chromium phosphate and 0.5% by weight of hydrofluoric acid is sprayed onto an AΩ alloy plate at a temperature of 40'C to form a chromium phosphate film of 100 to 15OA on the surface thereof.

Next, paint such as vinyl organosol is applied onto the AQ alloy plate by spraying, and 5 to 1
A coating film with a thickness of 0μ is formed.

The results of the above examples are shown in Table 1 along with a comparative example that does not use the cleaning device shown in FIG.

Table 1 As shown in Table 1, the amount of AΩ and MO smut remaining on the AQ alloy plate after etching treatment was reduced by cleaning using the cleaning device 9. As a result, the adhesion between the AQ alloy plate and the paint film was improved through the mediation of a uniform chemical conversion film, and the enamel feathering properties were improved.

Now, to explain the enamel feathering properties,
As shown in FIG. 3, the top plate 21 of the food can 20 is provided with a score 22, and by pulling the tab 27a, it is broken from the cut 23 shown in FIG. 4 to form a predetermined opening. . Then, by visual inspection of the broken state of the coating film 24 based on the score 22, as shown in FIG.
．． The enamel feathering property is expressed by a number from 5 to 5. Here, 26 is the coating film that protrudes from the opening 27 when the opening is opened, and the opening area is 20Qmm2 in parentheses.
The approximate area of the broken coating is shown.

That is, as shown in Table 1, AΩ was formed during the etching process due to cleaning by the cleaning device 9.

Since the smut of compounds such as Mg and Zn is sufficiently removed, a chemical conversion film is uniformly formed on the AQ alloy plate, and the coating film adheres closely, improving the enamel feathering properties.

Further, the cleaning work for degreasing can be done in a short time because it is only necessary to pass the AQ alloy plate 12 between the rolls 10 and 11.

Note that when the chemical conversion coating treatment is performed by dipping in a chemical bath instead of spraying, the chemical bath will not be contaminated because smut has been sufficiently removed by the previous degreasing treatment.

[Effects of the Invention] As explained above, according to the present invention, bulk impurities can be sufficiently removed from the alloy plate by degreasing treatment, so that a chemical conversion film can be formed uniformly and the adhesion of the paint film can be increased. can be done.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams showing a cleaning device used in a method according to an embodiment of the present invention, FIG. 3 is a perspective view showing a food can, and FIG. 4 is a cross-sectional view showing the main parts of FIG. 3. FIG. 5 is an explanatory diagram showing enamel feathering properties, and FIG. 6 is an explanatory diagram explaining problems caused by the prior art. 9...Cleaning device 10.11...Rolls 10a, 11 a-...Cilia 12...AQ alloy plate

Claims (1)

[Claims] After removing the rolled-processed deteriorated layer of an aluminum alloy plate for food cans by etching with an alkaline solution, the surface of the alloy plate is washed by passing the alloy plate between a pair of rotating rolls whose outer periphery is flocked with hair. A method for treating an aluminum alloy plate for food cans as a base for painting, the method comprising: thereafter forming a chemical conversion film on the aluminum alloy plate.