Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-05-31
2002-12-31
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C205S316000, C205S324000, C205S325000, C428S304400, C428S318400, C428S319100, C428S319300, C428S613000, C428S689000, C428S702000, C428S704000, C428S926000, C428S935000
Reexamination Certificate
active
06500558
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-treated aluminum material employed in various containers like beverage cans, caps and food containers, as well as deep-drawing containers and decorative boards. More specifically, the present invention improves the adhesive properties between an organic resin film and an aluminum material in the case where the organic resin film is laminated onto the surface of the aluminum material.
This application is based on a patent application filed in Japan (Japanese Patent Application No. 2000-163621), the contents of which are incorporated herein by reference.
2. Background Art
It has been the conventional practice to employ a surface-treated aluminum material in various types of containers, such as beverage cans, as well as in decorative boards used in furniture or interior building materials in which a chromate-phosphate or chromate conversion coating is formed to the surface of an aluminum material, and an organic resin film is laminated to the surface of this chromate-phosphate or chromate conversion coating.
A surface-treated aluminum material employed in a beverage can must have strong adhesive properties so that the laminated organic resin film does not peel away from the aluminum surface when the material is worked into a can. Moreover, the surface-treated aluminum material must be resistant to the corrosive effects of the material within the can. Furthermore, a surface-treated aluminum material employed in a decorative boards or the like must also have excellent resistance to corrosion over long periods of time, and strong adhesive properties so that the laminated organic resin film does not peel away from the aluminum surface during drawing.
The method for producing these surface-treated aluminum materials will first be explained using as an example the surface-treated aluminum material employed in a beverage can.
Prior to producing the surface-treated aluminum material, aluminum or an aluminum alloy starting material is first subjected to pre-treating. This pre-treatment is performed in order to remove oil or grease adhering to the surface of the starting material, as well as remove any heterogeneous oxide film on the surface. A step using alkali washing or the like is employed.
Next, the aluminum or aluminum alloy starting material is soaked in a solution comprising mainly phosphoric acid, chromic acid and a fluoride, or a solution comprising mainly chromic acid and a fluoride. An amorphous film of chromate-phosphate or chromate in the form of a thin gel is formed to the surface of the aluminum starting material, thereby obtaining a surface-treated aluminum material with chromate conversion coating.
An organic resin film is then laminated to the surface of the aluminum material that was surface-treated with chromate-phosphate or the like. Two-layer film or the like is frequently employed as the organic resin film, this two-layer film having polyester and an adhesive layer formed by adding a third component to polyester to lower its melting point. This organic resin film is laminated to the surface of a chromate-phosphate film by adhering the low melting temperature adhesive layer. The film is passed through a roller that has been heated to a temperature above the melting point of the adhesive layer, to laminate the organic resin film, thereby obtaining the surface-treated aluminum material. This chromate-phosphate or chromate conversion coating makes it possible to increase the adhesion of the organic resin film to the surface-treated aluminum material.
The thus-obtained aluminum material onto which the organic resin film was laminated does not require coating of a processing lubricant when working the aluminum material. Thus can production costs can be reduced. Moreover, since the material inside the can does not come into direct contact with the aluminum, it is possible to prevent an aluminum odor from tainting the beverage. In addition, management of the treatment bath is easily accomplished for the chromate-phosphate treatment. Thus, working efficiency is high and continuous processing is possible. Accordingly, this process is wildly used.
However, conventional surface-treated aluminum materials in which an organic resin film is laminated over a chromate-phosphate or chromate conversion coating have not sufficient adhesive strength between the aluminum material and the organic resin film. This is because in an extremely thin organic resin film, molecules around the size of moisture that are in the air permeate the organic resin film over a long period of time, and reach the chromate coating. When moisture is present in the coating, this leads to a decrease in the adhesion between the chromate conversion coating and the organic resin film. In addition, the conventional chromate-phosphate or chromate conversion coating is a deposit so that there is low compression. As a result, moisture or corrosive impurities can remain within.
When heat is applied to laminate the organic resin film onto these coatings, the moisture or corrosive impurities in the film, but particularly the moisture, erupts and damages the adhesion between the organic resin film and the film.
The harmful qualities of chrome with respect to environmental contamination have been pointed out, so that use of chromium phosphate and chromium chromate is limited.
A titanium phosphate or zirconium phosphate base layer has been proposed as a non-chrome base treatment. However, when carrying out these base treatments, the adhesive strength between the aluminum material and the organic resin film was less than in the conventional art, and therefore did not provide satisfactory adhesive strength.
A method has also been proposed employing a porous anodic oxide film such as sulfate anodic oxide coating or phosphate anodic oxide coating that takes advantage of the anchoring effect of this porous anodic oxide film to adhere the aluminum material and the organic resin film. However, the diameter of the pores in the anodic oxide film is extremely small, so that the organic resin film does not enter into the pores to any great extent. Thus, a sufficient anchoring effect could not be obtained.
On the contrary, since the aforementioned anodic oxide film is porous, the area of joining with the organic resin film is small so that sufficient adhesive strength is not obtained. Further, moisture remains in the pores even in the case where a pore sealing treatment is performed on the anodic oxide film. Thus, the moisture in the pores erupts when the aluminum material is heated in laminating the organic resin film as described above. As a result, the adhesion between the organic resin film and the aluminum material is inhibited.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the above-described circumstances and has as its objective the provision of a surface-treated aluminum material, and production method therefor, that is superior with respect to its adhesive properties with an organic resin film.
The present invention has as a further objective the provision of a surface-treated aluminum material and production method therefor in which the organic resin film is strongly laminated in place.
In order to resolve the above-described problems, a non-porous anodic oxide film is formed to the surface of the aluminum or aluminum alloy in the first surface-treated aluminum material according to the present invention. This non-porous anodic oxide film has a thickness in the range of 5~800 nm, a porosity of 20% or less, and contains in an amount of 50 ppm or more at least one of silicon, phosphorous, boron or carbon as a component.
It is possible to reduce the amount of moisture contained in the non-porous anodic oxide film by restricting the porosity thereof to be 20% or less. As a result, it is possible to control the amount of moisture erupted from these pores when heating in order to laminate the organic resin film to the surface. Thus, a fixed adhesion between the non-porous anodic oxide film and the organic resi
Koehler Robert R.
Mitsubishi Aluminum Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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