FORMING METHOD FOR ELECTRODEPOSITION COATING FILM, CATIONIC ELECTRODEPOSITION COATING COMPOSITION, AND ELECTRODEPOSITION COATED ARTICLE

摘要

PROBLEM TO BE SOLVED: To form a coating film which prevents the occurrence of gas pinholes on a steel sheet, especially on a zincified steel sheet or a galvanized steel sheet, and exhibits a high throwing power by specifying the lowest film-forming temperature and electrical conductivity during coating of a cationic electrodeposition coating material. SOLUTION: Electrodeposition coating is conducted at a set electrodeposition coating temperature and by using a cationic electrodeposition coating material of which the lowest film-forming temperature is adjusted to in the range of ±5 deg.C of the set electrodeposition coating temperature (preferably from -2 to 0 deg.C) and of which the electrical conductivity during coating is adjusted to 1,000-1,500 μS/cm. The lowest film-forming temperature is adjusted to in the range of ±5 deg.C of the set electrodeposition coating temperature e.g. by increasing the mol.wt. of a cationic substrate resin contained in the coating material, The electrical conductivity during coating is adjusted to 1,000-1,500 μS/cm e.g. by partially reacting epoxy terminals with an alkylphenol or a carboxylic acid and cationizing with an amine to decrease the amount of cationization of the cationic substrate resin. The cationic electrodeposition coating material contains the cationic substrate resin, a curing agent, and an organic solvent.