PLATING UNDERCOAT LAYER

PROBLEM TO BE SOLVED: To solve the problem that a substrate made from a thermoplastic resin swells, shrinks, or dissolves because the substrate contacts with an organic solvent contained in a coating material for forming a plating undercoat layer, consequently forms irregularities on its surface, so that the wet film under drying formed on the substrate moves due to the irregularities and causes cracks due to lack of the following ability of the film itself, and when a metal plating film is formed by an electroless plating method in a state having cracks, electric disconnection occurs.SOLUTION: In the plating undercoat layer, synthetic resin having a solid matter ratio of synthetic resin and inorganic filler being 0.1-0.7 pts.mass with respect to 1 pts.mass of synthetic resin, and having a Tg (glass transition point) of 30°C or less is contained in the undercoat layer at an amount in a solid matter ratio of 15 mass% or more. The plating undercoat layer containing such synthetic resin can prevent the crack formation of the undercoat layer and can form a plated metal film excellent in deposition ability and adhesion on the undercoat layer by the electroless plating method.