| 摘要 |
PURPOSE:To improve resistance to wear and corrosion by providing a synthetic resin protective layer which consists essentially of polyvinyl butyral resin and a moisture-curable type polyurethane resin and of which the weight ratio of the resins is a specific ratio value on a thin magnetic metallic layer. CONSTITUTION:A protective layer 5 consists essentially of a polyvinyl butyral resin and a moisture-curable type polyurethane resin and the weight ratio of both resins is 2:1-1:2. If the moisture-curable type polyurethane resin decreases off said range, the wear resistance of the protective layer is not enough and if the polyvinyl butyral resin decreases off said range, the corrosion preventive effect of the resulting protective layer is not enough. Such protective layer is formed by mixing the two resins at the prescribed weight ratio and coating the mixture by a known method. Since the moisture-curable type polyurethane resin is used, the curing progresses by absorbing the moisture in air if the protective layer is allowed to stand in the air and therefore there is the advantage of not requiring any special curing stage. |
