Patent ID: 7364645
Filing Date: 2008-04-29
Classification: B05D,C09D

Abstract:
1. A process for forming a cured gradient coating film, comprising the steps of: applying an aqueous electrodeposition coating composition comprising at least two resins and a curing agent, on an electrically conductive substrate by electrodeposition coating to form an electrodeposition film, wherein an electrically conductive substrate to be coated is immersed in an electrodeposition coating composition and an electric voltage is applied, heating the electrodeposition coating film to form a layer separation, and then curing the heated electrodeposition coating film to form a cured gradient coating film; wherein the resins include one resin component constituting a resin layer (a) in direct contact with air before applying top coating and the other resin component constituting a resin layer (b) in direct contact with the electrically conductive substrate, and a solubility parameter (δa) of a resin component constituting the resin layer (a) in direct contact with air and a solubility parameter (δb) of a resin component constituting the resin layer (b) in direct contact with the electrically conductive substrate have a relationship represented by the following formula: the gradient coating film comprises the resin layer (a) in direct contact with air, the resin layer (b) in direct contact with the electrically conductive substrate, and a mixing resin layer (c) which is formed between the resin layer (a) and the resin layer (b) and is formed from the resin components each constituting resin layer (a) and (b), wherein the resin component constituting the resin layer (a) contains a cation-modified acrylic resin, the resin component constituting the resin layer (b) contains a cation-modified epoxy resin and the curing agent is a blocked polyisocyanate, and solubility parameter (δi) of the blocked polyisocyanate, the solubility parameter of the resin component constituting the resin layer (a) and the solubility parameter of the resin component constituting the resin layer (b) have a relationship of δa<δi<δb.