JPH0347151B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF INDUSTRIAL APPLICATION This invention relates to an aluminum material for caps for forming the caps of containers for drinks, whiskey, seasonings, and other food/beverage products, and particularly to an aluminum material for caps having a base film for resin coating. In this specification, the term aluminum is used to include aluminum alloys. BACKGROUND TECHNOLOGY AND PROBLEMS Generally, aluminum material coated with resin is used for the caps of food and drink containers as described above. This resin coating is applied to improve the appearance of the cap or to prevent aluminum from being corroded by the contents of the container. However, such caps have conventionally been formed by applying an undercoat called a size coat to the surface of an aluminum base material and then applying a topcoat on top of the undercoat, which has the following drawbacks. In other words, although the undercoat is applied to improve the adhesion of the topcoat, the coating may peel off during molding or may be damaged by the contents of the container during long-term storage. There were drawbacks such as peeling and corrosion of the aluminum base material. On the other hand, in order to eliminate the above-mentioned drawbacks and improve the adhesion of the paint film and the corrosion resistance of the aluminum material and the cap, a phosphoric acid-chromate film is formed on the surface of the aluminum base material as a base film for resin coating. However, it is also known to apply resin coating through the film. However, in this case, if the aluminum material on which the phosphoric acid-chromate film has been formed is painted and baked on one side at a time, the phosphoric acid-chromate film on the surface to be painted later becomes dry-baked, and if this surface is painted, It has been recognized that cohesive failure can occur within the phosphoric acid-chromate coating during molding. Furthermore, since the phosphoric acid-chromate film is an inorganic film, it also has the disadvantage of poor surface slipperiness. Of course, DOS (day octyl sebacate) coating treatment is also used to improve sliding, but in this case, there is a problem that the adhesiveness of the resin is poor if the resin is applied directly to the treated surface. It was hot. Furthermore, the formation of the phosphoric acid-chromate film and the treatment of waste liquid are complicated, resulting in problems in terms of workability. This invention was made based on the above-mentioned technical background, and by forming a new base film for resin coating in place of the phosphoric acid-chromate film,
It has excellent adhesion with the resin to be painted, so the coating does not peel off during molding, and it also has excellent corrosion resistance against the contents of the container during long-term storage, and does not cause corrosion of the aluminum base material. The object of the present invention is to provide an aluminum material for caps that has excellent slip properties and improved workability during film forming. Means for Solving the Problems According to the present invention, on the surface of an aluminum base material,
A mixed film containing a chromium compound and a water-soluble resin as a base film for resin painting reduces the amount of chromium adhesion by 0.1.
The object of the present invention is to provide an aluminum material for caps having a coating base film, which is characterized in that the film is formed in a specified state of mg/m ² or more. The composition of the aluminum base material is not particularly limited as long as it has moldability and other properties required for cap use. The mixed film is formed using a treatment liquid in which a chromium compound and a water-soluble resin are mixed in an aqueous solution or emulsion state. Here, the chromium compound may include various salts and oxides (for example, Cr ₂ O ₃ ) containing trivalent or hexavalent chromium. On the other hand, the resin is a water-soluble polymer having a hydroxyl group or a carboxyl group, such as polyacrylic acid, polyvinyl alcohol, ethylene maleic anhydride, polyvinyl methyl ether, etc. Among them, polyacrylic acid is preferred.
The mixing ratio of such chromium compound and resin is preferably such that the content ratio of chromium and water-soluble resin in the mixed film is about 1:1 to 0.5 to 10: resin. It is preferable to set the value to about 1 to 5. Further, as a method for forming the mixed film on the surface of the aluminum base material, any method such as a spray method, a dipping method, a roll coating method, etc. can be adopted. Also, drying after coating is 15 to 250℃.
It is desirable to carry out the process at a temperature of about The drying time varies depending on the drying temperature; for example, at 150°C, it is recommended to dry for about 30 seconds. However, the present invention requires that the mixed film be formed with a chromium adhesion amount of 0.1 mg/m ² or more. Below 0.1mg/ ^m2 ,
It has poor adhesion with the resin coated in the subsequent process, and the coating film is likely to peel off when molded into a cap. Further, it is desirable that the amount of adhesion be 500 mg/m ² or less. Even if the amount exceeds 500 mg/m ² , it will not be possible to significantly increase the effects such as improving the adhesion of the coating film, and the material will be wasted. The preferred coverage range is 0.5-50 mg/ ^m2 . To set the amount of chromium deposited,
This may be done by adjusting the mixing ratio of the chromium compound and the water-soluble resin at the stage of producing the treatment liquid, or by adjusting the amount of the treatment liquid applied to the aluminum base material. In this case, it is desirable that the amount of coating, that is, the amount of mixed film, be about 0.5 to 3000 mg/ ^m2 from the viewpoint of film thickness, etc., and preferably 3000 mg/m2.
It is best to keep it at ^around 300mg/m2. Note that the cap is generally manufactured by applying resin coating, baking, etc. to an aluminum material as described above, and then molding it into a predetermined shape. Vinyl and epoxy resins are generally used as coating resins. When applying this resin coating, a size coat is no longer necessary. Effects of the Invention As explained above, the present invention provides a paint base film that is formed on the surface of an aluminum base material.
By replacing the phosphoric acid-chromate film with a mixed film containing a chromium compound and a water-soluble resin, the adhesion with the resin coated on it is improved, as will be clear from the examples below. The resin is excellent and stable against heat during baking, etc., and the coating film does not peel off when molded into a cap. Furthermore, the coating has excellent corrosion resistance, and can prevent the coating from being corroded by the contents of the container during long-term storage, and furthermore from corroding the aluminum base material, thereby improving the corrosion resistance of the cap. Furthermore, it has excellent slip properties, and also has the effect that film formation is easy because it is a non-rinsing operation, and waste treatment of processing liquid and washing water is not necessary. Examples Next, examples of the present invention will be shown in comparison with comparative examples. First, aluminum materials for caps shown in the following samples were prepared. JIS1200, 165 gravure mesh roll coating was applied to the surface of an aluminum base material with a thickness of 0.25 mm using a treatment solution having the composition shown in Table 1 at 10% (V/V) dilution, and then 150
C. for 30 seconds to form a mixed film as a base film for resin coating to obtain an aluminum material according to the present invention. The amount of chromium deposited at this time was approximately 2 mg/m ² .

[Table] Using the same aluminum base material as above, a phosphoric acid-chromate film was formed on the surface of the aluminum base material by a well-known method to obtain a conventional aluminum material. The amount of chromium deposited is approximately 13
mg/ ^m2 . An aluminum material (without film treatment) consisting of a rolled aluminum base material having the same composition and shape as above was obtained. The following tests were conducted on the above three types of aluminum materials for caps. [Adhesion test of coating film] A black acrylic resin was coated on the surface of each of the above aluminum materials to a thickness of about 10 μm, and dried at 200° C. for 10 minutes to form a coating film. When each sample material was directly stretched using an Erichsen tester based on JIS B7729 (primary adhesion)
After forming the coating film, it was immersed in hot water at 95℃ for 30 minutes.
Similarly, the state of peeling of the coating film after Erichsen overhang processing (secondary adhesion) was investigated. The results are shown in Table 2 as ○: No peeling was observed, Δ: Fine peeling was observed, and ×: Severe peeling. [Corrosion resistance test] For the above three types of aluminum materials,
The corrosion state of the surface was investigated after 150 hours of salt spray according to JIS Z2371. The results are shown in Table 2 as ○: No corrosion observed, Δ: Slight corrosion observed, ×: Severe corrosion. In addition, each aluminum material was examined for surface discoloration when immersed in hot water at 95°C for 30 minutes. The results are shown in Table 2 as ○: no discoloration observed, Δ: slight discoloration observed. [Slip Property Test] The three types of aluminum materials described above were subjected to molding under the same conditions, and their slip properties were evaluated. The results are shown in Table 2 as ○: Good slip property, ×: Poor slip property.

[Table] As is clear from the above results, the aluminum material according to the present invention has a phosphoric acid-based coating film.
It can be seen that the coating film has superior adhesion and slipperiness compared to a chromate film, and has the same corrosion resistance.

Claims (1)

[Claims] 1. A mixed film containing a chromium compound and a water-soluble resin as a base film for resin coating is formed on the surface of an aluminum base material with a chromium adhesion amount of 0.1 mg/m2 or ^more . Aluminum material for caps with a distinctive coating base film.