| 摘要 |
PROBLEM TO BE SOLVED: To exhibit the color brightness to be required and to reduce the production of white basic zinc carbonate by executing degreasing treatment with a degreasing soln. essentially consisting of metasilicate of a specified concn. as pretreatment and dipping it into a specified amt. of zinc phosphate treating soln. contg. nickel nitrate and zinc nitrate of specified concns. as posttreatment. SOLUTION: Preferably, hot dip galvanized steel is subjected to degreasing treatment with a degreasing soln. essentially consisting of 10.0 to 50.0 g/l metasilicate and is thereafter subjected to dipping treatment into a zinc phosphate treating soln. of 75.0 to 150.0 l contg. 5.0 to 10.0 g/l nickel nitrate and 1.0 to 5.0 g/l zinc nitrate. By this pretreatment, the corrosion reaction between zinc and an alkali soln. is suppressed, and it can be executed in a state in which the surface roughness of the hot dip galvanized steel is actually reduced. Moreover, the steel surface subjected to this pretreatment can be coated with a uniform and dense zinc phosphate film by zinc phosphate treatment as the posttreatment, and this film is remarkable in the irregular reflection and absorption of light, so that the color brightness of 4.0 can be exhibited even without executing dipping into nitric acid.
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