Mixture of chromic acid and sulfuric acid has been widely applied for hydrophilization of ABS resin. However, it is difficult to make the hydrophilic surface of PP resin, because chromic acid has poor oxidizing power for PP resin. In addition, due to environmental concerns, alternative technologies that do not use hexavalent chromium are required. The authors have confirmed that PP resin and ABS resin can be hydrophilized with electrolyzed sulfuric acid solution and then be plated to obtain enough adhesion strength in practical use. In this report, focusing on its hydrophilization behavior, we investigated the reason why hydrophilization is created, and assumed that hydrophilization is due to oxygen entering between bonds of carbon and hydrogen to become hydroxyl groups.
