| 摘要 |
PROBLEM TO BE SOLVED: To provide a discoloration preventing agent to be added to a cleaning soln. for preventing the discoloration of a metallic surface after pickling and to provide a method for preventing the discoloration of the metallic surface after pickling. SOLUTION: This discoloration preventing agent is the one contg. organic phosphonic acid and the salt thereof. Moreover, the organic phosphonic acid and the salt thereof is formed into a more excellent discoloration preventing agent by being used jointly with 1 to 30C carboxylic acid, oxycarboxylic acid, aminocarboxylic acid and the salt thereof. The discoloration preventing agent is used by being brought into contact with a metallic surface after pickling as an aq. soln. dissolved by 1 to 100,000 mg, preferably 2 to 50,000 mg, further preferably 2 to 5,000 mg into 1 L of water.
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