e contained in aluminum, since production of perfectly pure aluminum is difficult in view of refining technology. The composition of the aluminum plate to be used in the present invention is not particularly restricted, and aluminum plates of conventionally known and used material may be appropriately used. The aluminum plate to be sued in the present invention has a thickness of about 0.1 to 0.6 mm, preferably 0.15 to 0.4 mm, and a thickness of 0.2 to 0.3 mm is particularly preferable.
Prior to roughening the surface of the aluminum plate, a degreasing treatment with a surfactant, an organic solvent, or an alkaline water solution may be administered to the aluminum plate in order to eliminate rolling oil on the surface as needed.
The surface of the aluminum plate may be roughened in accordance with various methods. Examples thereof include a method in which the surface is mechanically roughened, a method in which the surface is electrochemically dissolved and roughened, and a method in which the surface is chemically roughened by selectively dissolving the surface. Methods such as ball polishing, brush polishing, blast polishing and buff polishing methods may be used for the mechanical roughening method. Examples of the electrochemical roughening method include a method in which an alternating current or a direct current is passed through an electrolytic solution of hydrochloric acid or nitric acid. A method in which both may be also used, as disclosed in Japanese Patent Application Laid-Open (JP-A) No. 54-63902.
Following alkaline etching and neutralization processing as needed, the aluminum plate thus roughened may be subjected to anodic oxidation as desired in order to raise the water retention and wear resistance of the surface. Various electrolytes that form a porous oxidation film can be used for the anodic oxidation of the aluminum plate, and sulfuric acid, phosphoric acid, citric acid, chromic acid or a mixed acid thereof may be used for that purpose. The concentration of the electrolyte is appropriately