PURPOSE:To prevent the generation of blisters from the end parts of paint films by contg. chromate rust preventive pigments having low water solubility and chromate rust preventive pigments having high water solubility into undercoating paint for painting of Al-Zn alloy plated steel plates. CONSTITUTION:The undercoating paint obtd. by mixing resins for forming paint films such as epoxy resin varnish, body pigments such as titanium oxide, chromate rust preventive pigments having low water solubility such as strontium chromate and chromate rust preventive pigments having high water solubility such as calcium chromate is coated on Al-Zn alloy plated steel plates, and top coating paint of oil-free polyester or the like is coated thereon. The amt. of the rust preventive pigments to be used in said undercoating paint is about 5- 60pts. of 100pts.wt. the solids of the paint, and for example, the rust preventive pigments compounded with about 80/20-5/95 weight ratio strontium chromate/calcium chromate are preferable.
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