Shining coating film formation method and coated article
There are provided: a method for forming a shining coating film which can form a coating film extremely excellent in a leveling property and a brightness with good workability and can also realize the reduction of environmental burden; and a coated article excellent in a design property obtained by this method. In a method comprising the steps of sequentially coating a shining material-containing solvent type first base coat coating, a shining material-containing solvent type second base coat coating and a top clear coating onto a base material and baking a formed multilayered coating film at the same time, an improvement is made so that the resin composition and coating nonvolatile concentration of the first and second base coat coatings and the amount of nonvolatiles in the first and second base coating films will have specific conditions.
1. A method for forming a shining coating film, comprising the steps of: coating a shining material-containing solvent type first base coat coating onto a base material to form a first base coating film; coating a shining material-containing solvent type second base coat coating onto the first base coating film to form a second base coating film; coating a top clear coating onto the second base coating film to form a clear coating film; and then baking a formed multilayered coating film at the same time;
wherein:
the first base coat coating contains a polyester-polycarboxylic acid in a ratio of 50 to 95 mass % in terms of nonvolatile concentration based on a total resin nonvolatile concentration, wherein the total resin nonvolatile concentration relating to the first base coat coating is the total concentration of the nonvolatiles of the polyester-polycarboxylic acid and other resins in the first base coat coating, and wherein the first base coat coating has a nonvolatile concentration of 50 to 65 mass % when coated, and the first base coat coating is a coating such that the first base coating film will have a nonvolatile concentration of not less than 75 mass % when the second base coat coating is coated; and
the second base coat coating contains a non-aqueous dispersion resin in a ratio of 5 to 80 mass % in terms of nonvolatile concentration based on a total resin nonvolatile concentration, wherein the total resin nonvolatile concentration relating to the second base coat coating is the total concentration of the nonvolatiles of the non-aqueous dispersion resin and other resins in the second base coat coating, and wherein the second base coat coating has a nonvolatile concentration of 25 to 35 mass % when coated, and the second base coat coating is a coating such that the second base coating film will have a nonvolatile concentration of 50 to 60 mass% when the second base coating film is formed.
2. The method for forming a shining coating film according to claim 1 , wherein the ratio of the dry film thickness of the first base coating film to the dry film thickness of the second base coating film is in the range of 2.5 to 5.
3. The method for forming a shining coating film according to claim 1 , wherein the shining materials contained in the first and second base coat coatings are, independently of each other, at least one member selected from the group consisting of an aluminum flake pigment, an interference mica pigment, a colored mica pigment, and alumina flake pigment.
4. The method for forming a shining coating film according to claim 1 , wherein the first base coat coating has a shining material content of 5 to 25 mass % based on the nonvolatile concentration of the coating.
5. The method for forming a shining coating film according to claim 1 , wherein the second base coat coating has a shining material content of 6 to 35 mass % based on the nonvolatile concentration of the coating.
6. The method for forming a shining coating film according to claim 1 , wherein the first and second base coat coatings are compositionally designed so that the mass ratio P1/P2 between the shining material content P1 in the first base coating film and the shining material content P2 in the second base coating film will be in the range of 1/1 to 1/4, and further that when the top clear coating is coated, the total coating film nonvolatile concentration of two layers of the first and second base coating films will not be lower than 75 mass %.
7. The method for forming a shining coating film according to claim 1 , wherein the base material is a steel for automobiles or a plastic base material.
8. A coated article, having a coating film, wherein the coating film is formed by the method for forming a shining coating film as recited in claim 1 .
9. The method for forming a shining coating film according to claim 1 , wherein the polyester-polycarboxylic acid is obtained by modifying a terminal end hydroxyl group of a polyester-polyol with an acid anhydride wherein the polyester-polyol is obtained by ring-opening addition of a lactone compound to a polyfunctional polyol.