PURPOSE: To improve the adhesivity of a copper plate in water, and to maintain the adhesivity for a long period, by applying a cuprous oxide film to one surface of a copper plate or copper alloy plate by the chemical conversion treatment, and coating the oxide film surface with a phenolic resin or an epoxy resin primer.

CONSTITUTION: A cuprous oxide film 3 is formed to one surface of a copper plate or a copper alloy plate 1 by the chemical conversion treatment, and the treated surface is coated with the primer 2 composed of phenolic resin or epoxy resin. The primer-coated part 2 of the above copper plate 1 is bonded with the adhesive layer 4 to the insulation layer 5 of the copper plate 6 to prevent the adhesion of aquatic life at the part of a ship contacting water.