In recent years, much attention has been paid to problems of environmental destruction on global scale such as global warming, ozone depletion, acid rain, etc. and it is urged to internationally take countermeasures against global pollution. Along with this problem, various regulations have been set for environmental conservation. Under such circumstances, it is a serious problem to discharge organic solvents (VOC) into the atmosphere, and in each industrial field, along the trend for tightening regulations against VOC, it is promoted to seek alternatives to organic solvents (alternatives to VOC). In the paint industry, as an alternative to a conventional organic coating material, a powder coating material is expected to be promising as a coating material which contains no VOC and which is environmentally friendly such that it does not require exhaust treatment or waste water treatment, and it can be recovered for reuse.
As a powder coating material, an acrylic resin type, a polyester resin type and an epoxy resin type have been mainly used. However, there is a problem that such coating materials are poor in weather resistance.
On the other hand, as a coating material to solve such a problem, a fluorinated resin powder coating material comprising a fluorinated resin has been developed (for example, Patent Document 1).
Further, for reducing the cost, etc. a powder coating material in which a polyester resin and a fluorinated resin are blended has been proposed (for example, Patent Document 2).
As compared to the acrylic resin type, polyester resin type and epoxy resin type powder coating materials, the powder coating material in which a polyester resin and a fluorinated resin are blended is excellent in weather resistance, however, depending on a kind of a polyester to be used, it is difficult to obtain the effect to improve the weather resistance derived from a fluorinated resin layer in some cases.
Further, by coating a polyester resin with a fluorinated resin to form a double coating, a coating film which is excellent in weather resistance can be formed at a low cost. However, steps for forming the coating film are complicated since it is necessary to carry out double coating.