Method for forming electrodeposition coating film

#The present invention relates to a coating film forming method which is excellent in environmental protection, an energy-saving property, a finishing property and a coating film property and in which an article to be coated is heated/dried by an induction heating system before or after electrodeposition coating of the article to be coated.

#In Japan or Europe and the United States, a paint or a coating system produced in view of environmental problems has been heretofore described, and a cationic electrodeposition paint not containing a poisonous metal such as a heavy metal has been used as an electrodeposition paint in many cases.

#In the coating system, a coating film forming method of omitting a baking step is employed in a production line, and reduction in load on the environment, reduction in energy, economic aspect and performance of the coating system are regarded as important. In dry-hard of the coating film, a hot-air drying furnace by a hot-air heating system is mainly used and a method of simultaneously heating/drying the whole article to be coated is being performed.

#The present inventions will now be described by way of example with reference to the following FIGURE in which:

#FIG. 1 is a model figure of an electrodeposition facility for a vehicle body.

#An electrodeposition coating film forming method of selectively heating/drying an article to be coated by an induction heating system of the present invention is described in detail.

#For dry-hard of the electrodeposition coating film, a hot-air heating system is mainly used and has problems as follows: (a) it takes a long time to heat the coating film up to a necessary temperature; (b) since a hot-air temperature must be kept to a temperature higher than a baking temperature of the coating film, a part of the steric article to be coated is excessively heated to reduce a coating film property; (c) it is not easy to change a furnace temperature or a gas volume depending on a thickness or size of a steel plate; (d) it is not easy to intensively heat/dry a specific part only of a vehicle body; (e) it is difficult to heat/dry the vehicle body composed of integrated metal and plastic; and (f) in a wet on wet step of performing electrodeposition coating/preheating/water-base intermediate coating or water-base top coating, facilities cost and maintenance cost for the preheating are heavy.

#Consequently, the inventors have found that by using a plurality of induction heating devices, the coating film obtained in the electrodeposition coating can be selectively heated/dried, and therefore, an excellent finishing property or the coating film property can be obtained in addition to the following characteristics: (a) heat is generated on the metallic article to be coated and the heat is not generated on a part other than the metallic article to be coated (e.g., plastic) and therefore, heat efficiency is high, (b) rapid, high-temperature and partially selective heating can be performed; (c) the system is suitable for various heating conditions such as a heating order, a heating temperature or a heating time; (d) the facilities are relatively small; (e) the system is soft for the environment; (f) automation is easily attained. Of course, the coating film can also be simultaneously heat/dried at the different heating temperature every each part of the article to be coated. Alternatively, the coating film can also be simultaneously heat/dried at the same heating temperature while changing the heating time.