Methods such as dipping or immersion, brush coating, spray coating, roller coating, etc. may be used as the treating method.Examples of the resin plate to which the present invention is applicable include polyvinylalcohol resin plates, e.g. NAPP (phonetic) sold by Napp System Japan K.K., Rigiron (phonetic) and POP sold by Tokyo Oka Kogyo K.K.; polyester resin plates, e.g. APR sold by Asahi