JPS6216711B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum plate for food cans, particularly a sheet or coil-shaped aluminum plate used as a material for can lids formed by subjecting the plate material to severe plastic deformation processing or for opening tabs fixed to can lids. This article relates to a surface treatment method for aluminum plates. Opening tabs that are formed by applying severe plastic deformation to sheets or coiled aluminum plates that have been degreased or otherwise treated with water and then washed and dried may develop white rust for unknown reasons on their surfaces. Further, black discoloration may occur after sterilization under heated steam and cooling treatment with cooling water. (Note that white rust and black discoloration also occur when making can lids, but the degree of occurrence is lower than in the case of tabs, so we will focus on tabs here.) Conventionally, as a countermeasure for this, mild white rust, black discoloration, etc. If the occurrence of rust is expected to occur, use a tab made from an aluminum plate that has been subjected to chromate treatment after degreasing to prevent them.If severe white rust or black discoloration is expected to occur, This problem has been avoided by using a tab made from an aluminum plate that has been subjected to the chromate treatment and further coated with a synthetic resin paint. However, when tabs are made from chromate-treated aluminum plates, the chromate film cracks or peels off due to severe plastic deformation during tab manufacturing, and as a result, rust may not be sufficiently prevented. Moreover, when forming a tab at high speed, it takes a long time to separate from the punch, which hinders processing work and reduces production efficiency. The latter tab, i.e., a tab made from a chromate-treated and painted aluminum plate,
The above drawbacks (insufficient rust prevention, reduced production efficiency)
However, since it requires a process of chromate treatment, drying, painting, and drying baking, it has other drawbacks such as increased equipment costs, increased equipment space, and increased number of steps. In general, the food can manufacturing industry produces large quantities of several hundred cans per minute, and therefore there is a strong desire to always improve production efficiency and reduce work processes, so it is impossible to be satisfied with these shortcomings. It cannot be done. The present inventors have endeavored to develop a technology capable of resolving the above-mentioned drawbacks, but in doing so, the surface treatment liquid was used to improve production efficiency since the target material of the method of the present invention is a can-making material. Thermosetting resins, which require high-temperature and long-term heating, are not suitable for this purpose, so they are excluded, and solvent-based processing solutions are also excluded in consideration of air pollution. The research was limited to salt. The present invention was obtained as a result, and according to this, the surface of an aluminum plate for food cans is degreased and washed with water, and then α-olefin and α,β unsaturated carboxylic acid are added to the treated surface. A surface treatment solution in which a water-soluble thermoplastic polymer resin consisting of an ammonium salt of a copolymer of
Apply an amount in a range exceeding 1.0 g/m ² and below 1.0 g/m ² .
A method for surface treatment of aluminum plates for food cans, which is characterized by drying, is obtained. The method of the present invention has the following effects. First, an explanation will be given of comparative experimental examples of an aluminum plate subjected to the surface treatment according to the method of the present invention, an aluminum plate subjected only to degreasing and water washing, and an aluminum plate subjected to chromate treatment after degreasing and water washing. Experimental examples 1 to 5 Ethylene-acrylic acid copolymer resin 220g, 28
% ammonia water/43g, deionized water 73.7g to 4.5
Kg/cm ² , maintained at 130℃, stirred for about 1 hour, cooled and then adjusted to pH 9.5 ± 0.5 with 28% ammonia water. Make this resin solution at 0.2%, 1%, 2.5
Degreased and water-detergent sheet aluminum tab material (A 5082, 0.35 mm thick, H19) was added to an aqueous solution diluted with deionized water to a concentration of 10% and 10% at 25℃ for 5 minutes.
After soaking for seconds, squeeze with a rubber roll to reduce the amount of application to 5
g/m ² and then dried in a hot air atmosphere (140℃) for 5 seconds to remove moisture and give a dry film amount of 0.01, 0.05,
Test plates of 0.1, 0.25 and 0.5 g/m ² were prepared. Table 1 shows the boiling tap water test results for these test plates. Comparative Examples 1 to 3 The same degreased and water-washed aluminum tab material as in Examples 1 to 5 was subjected to chromate treatment, which is conventionally done on some tab materials, and the dry chromium adhesion amount was 0.01 and 0.02, respectively. A boiling tap water test was conducted in the same manner as in Experimental Examples 1 to 5 on a test plate having a chromate film of 0.03 g/m ² and 0.03 g/m 2 . The results are also shown in Table 1. Comparative Example 4 The same performance tests as in Experimental Examples 1 to 5 were conducted on the same degreased and washed aluminum tab materials used in Experimental Examples 1 to 5 and Comparative Examples 1 to 3 without any treatment. These results are also listed in Table 1.

【table】

[Table] As is clear from the results of the boiling tap water test in Experimental Examples 1 to 5 and Comparative Examples 1 to 4 above, even in the seam folded part, which was subjected to a more severe bending process than in the case of tab material processing, the experimental examples It is known that the material has better corrosion resistance than the comparative example, in other words, there is no cracking or peeling of the film, and it has excellent water resistance and no rust. Furthermore, even in the same experimental example, it is clear that one example is inferior to another. In addition, the treatment steps in Experimental Example 1-5 include degreasing, water washing,
After draining, a surface treatment solution is applied immediately, and five steps are omitted compared to the case of coated aluminum plates, whose surface is treated through the steps of degreasing, washing, drying, chromate treatment, drying, painting, and drying. This can be said to be the most simplified process. Furthermore, in the present invention, since an aqueous solution of a water-soluble thermoplastic polymer resin in the form of an ammonium salt is used as the surface treatment liquid, as exemplified in the above experimental example, heating conditions can be applied at a relatively low temperature and for a short time. A resin film with excellent water solubility resistance can be formed. Next, the results of measuring the friction coefficients of the surfaces of the aluminum plates of Experimental Example 2, Comparative Example 2, and Comparative Example 4 will be shown. The load was 0.6Kg. Experimental Example 2 0.081 Comparative Example 2 0.173 〃 4 0.357 The friction coefficient of the aluminum plate (Experimental Example 2) that had been surface-treated by the method of the present invention was lower than that of the others (Comparative Examples 2 and 4). It can be seen that the stickiness is extremely low and that the stickiness is good. When a tab was formed using the aluminum material of Experimental Examples 1-5, it was easily separated from the processing punch and did not cause any problems during processing. Using the same method as in Experimental Example 1-5, the film weight was set to 1.0 g/ ^m2 .
When tabs were made from aluminum plates with a coating of 1.5 g/m ² , the tabs coated with 1.0 g/m ² did not cause problems in processing, but the tabs coated with 1.5 g/m ² had difficulty separating from the processing punch. It was hot. Next, a comparative test with other resins will be explained. For comparison with resins other than those used in the method of the present invention, an aluminum plate of the same degreasing agent used in Experimental Example 1-5 was used, and an acrylic resin made of a copolymer of methyl methacrylate-butyl acrylate-acrylic acid was used. Acid ester emulsion (Comparative Example 5), alkyd resin emulsion (Comparative Example 6), and methyl vinyl ether-maleic acid copolymer resin aqueous solution (Comparative Example 7) were deionized to concentrations of 1.0, 2.0, and 10% by weight, respectively. Resin solution obtained by diluting with water (9 types of solutions in total)
The above aluminum plates were immersed in a bath at a temperature of 25°C for 5 seconds, and then squeezed with a rubber roll to give each plate 5
g/m ² of the resin solution remained, and dried it in a hot air atmosphere at 140°C for 30 seconds to prepare test pieces with dried resin films of 0.05, 0.1, and 0.5 g/m ² , respectively. A corrosion resistance test was conducted using the same test method as in Experimental Example 1-5. The results are shown in Table 2.

[Table] From Table 2, when compared with the resins used in Comparative Examples 5 to 7, the water-soluble thermoplastic polymer resin used in the method of the present invention has a film thickness that is sufficiently thinner than that of the resins of these comparative examples. It can be seen that the resin exhibits superior corrosion resistance to the resin of the comparative example. As the α-olefin in the method of the present invention,
In addition to those shown in the above experimental examples, there are propylene, etc., and as α,β unsaturated carboxylic acids, in addition to those shown in the above experimental examples, there are methacrylic acid, maleic acid, etc. The water-soluble thermoplastic polymer resin used in the method of the present invention preferably has an acid value of 30 to 300.
This is because if the acid value is less than 30, dispersion or solubility in water is poor and it becomes difficult to obtain a uniform film, and if the acid value is more than 300, the dried film is easily dissolved in water and has difficulty in corrosion resistance. Also, those with a low molecular weight do not have sufficient corrosion resistance. The aluminum plate treated by the method of the present invention can be easily separated from the processing punch when processed into can lids and tabs, which improves production efficiency during processing.
Products molded from this plate have no cracks or peeling in the surface treatment film, and the film is water resistant.Furthermore, it is a continuous film with a uniform thickness, so it is good even though it is a thin film. It shows excellent corrosion resistance. In addition, since the surface treatment solution is water-soluble, it can be applied to the surface of an aluminum plate by simply degreasing, washing, and draining the surface without drying. This method requires the least number of steps and therefore contributes to a reduction in equipment space. Further, the tab formed from the aluminum plate that has undergone the surface treatment according to the method of the present invention is riveted to the can lid, and then when it is tightened to the can body,
It also showed the effect of preventing the tab from rotating with respect to the can lid.

Claims (1)

[Claims] 1 The surface of an aluminum plate for food cans is degreased and washed with water, and then a water-soluble thermoplastic polymer resin consisting of an ammonium salt of a copolymer of α-olefin and α,β unsaturated carboxylic acid is dissolved in water. The surface ^treatment liquid used ⁱⁿ
A method for surface treatment of aluminum plates for food cans, characterized by applying the coating in the following amount and drying it.