Pretreatment method for coating

#The present invention relates to a pretreatment method for coating.

#When a cationic electrocoating or a powder coating is applied to the surface of a metal material, a chemical conversion treatment is generally applied in order to improve the properties such as corrosion resistance and adhesion to a coating film. With respect to a chromate treatment used in the chemical conversion treatment, from the viewpoint of being able to further improve the adhesion to a coating film and the corrosion resistance, in recent years, a harmful effect of chromium has been pointed and the development of a chemical conversion coating agent containing no chromium is required. As such a chemical conversion treatment, a treatment using zinc phosphate is widely adopted (cf. Japanese Kokai Publication Hei-10-204649, for instance).

#However, since treating agents based on zinc phosphate have high concentrations of metal ions and acids and are very active, these are economically disadvantageous and low in workability in a wastewater treatment. Further, there is a problem of formation and precipitation of salts, being insoluble in water, associated with the metal surface treatment using treating agents based on zinc phosphate. Such a precipitated substance is generally referred to as sludge and increases in cost for removal and disposal of such sludge become problems. In addition, since phosphate ions have a possibility of placing a burden on the environment due to eutrophication, it takes efforts for treating wastewater; therefore, it is preferably not used. Further, there is also a problem that in a metal surface treatment using treating agents based on zinc phosphate, a surface conditioning is required; therefore, a treatment process become long.

#Hereinafter, the present invention will be described in detail.

#The present invention is directed to a pretreatment method for coating, which uses a chemical conversion coating agent containing at least one kind selected from the group consisting of zirconium, titanium and hafnium, and fluorine and substantially containing no phosphate ions and harmful heavy metal ions. When a substance is treated with conventional chemical conversion coating agents containing zirconium and the like in place of a zinc phosphate treatment which is generally used as a chemical conversion treatment method, a problem that sufficient adhesion to a coating film cannot be attained particularly in an iron material arises. Therefore, the present invention is directed to a pretreatment method for coating capable of resolving the above problem and forming a chemical conversion coat having sufficient adhesion to a coating film even for the iron material by using a chemical conversion coating agent comprising at least one kind selected from the group consisting of zirconium, titanium and hafnium, and fluorine.

#At least one kind selected from the group consisting of zirconium, titanium and hafnium contained in the chemical conversion coating agent used in the present invention is a component constituting a chemical conversion coat and, by forming a chemical conversion coat including at least one kind selected from the group consisting of zirconium, titanium and hafnium on a material, the corrosion resistance and the abrasion resistance of the material can be improved and further the adhesion to the coating film can be enhanced.