Surface-treating aqueous solution and treatment methods for forming corrosion-resistant coating film over zinc or zinc alloy deposit

Abstract

A chromium-free treating liquid and treatment methods which are for imparting to a zinc or zinc alloy deposit a coating film which is highly corrosion-resistant, has a uniform appearance free from sag stains/puddle stains, has no failure concerning thickness unevenness, and has satisfactory adhesion. The surface-treating aqueous solution, which is for forming a corrosion-resistant coating film over a zinc or zinc alloy deposit, is characterized by comprising (a) an alkali metal silicate (M 2 O.nSiO 2 (wherein M represents an alkali metal and n indicates SiO 2 /M 2 O molar ratio)), (b) a water-soluble or water-dispersible silane coupling agent, and (c) a water-soluble or water-dispersible glycidyl ether compound. One of the surface treatment methods for forming a highly corrosion-resistant coating film over a zinc or zinc alloy deposit includes bringing the surface of the zinc or zinc alloy deposit into contact with the surface-treating aqueous solution. The surface-treating aqueous solution is applicable also to the surface of a chemical conversion coating film formed on a zinc or zinc alloy deposit and free from hexavalent chromium or from chromium in any form. Namely, another surface treatment method for forming a highly corrosion-resistant coating film over a zinc or zinc alloy deposit comprises bringing the surface of a chemical conversion coating film formed on a zinc or zinc alloy deposit into contact with the surface-treating aqueous solution. Furthermore provided is a highly corrosion-resistant coating film formed by bringing the solution into contact with the surface of a zinc or zinc alloy deposit or with the surface of a chemical conversion coating film formed on a zinc or zinc alloy deposit.

1 - 11 . (canceled) 
     
     
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         23 . A surface-treating aqueous solution for forming a corrosion resistant coating film on a zinc or zinc alloy plating, the surface-treating aqueous solution characterized by comprising:
 (a) 0.25 to 5% by weight of an alkali metal silicate M 2 O.nSiO 2  where M represents an alkali metal and n represents a SiO 2 /M 2 O molar ratio in a range from 2/1 to 4/1;   (b) 0.05 to 3% by weight of a water-soluble or water-dispersible silane coupling agent;   (c) 0.05 to 3% by weight of a water-soluble glycidyl ether compound(s) which is selected from the group consisting of glycidol, glycerol polyglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, diethylene glycol diglycidyl ether, and combinations thereof; and   (d) 0.25 to 5% by weight of a water-soluble or water-suspendable organic resin,   
       wherein the total solid content concentration of the surface-treating aqueous solution is 0.6 to 9%. 
     
     
         24 . The surface-treating aqueous solution according to  claim 23 , wherein the alkali metal in the alkali metal silicate is selected from the group consisting of Li, Na, and K. 
     
     
         25 . The surface-treating aqueous solution according to  claim 23 , wherein the water-soluble or water-dispersible silane coupling agent is a water-soluble or water-dispersible silane coupling agent having a group selected from the group consisting of an epoxy group, an amino group, a (meth)acrylic group, a vinyl group, and a mercapto group. 
     
     
         26 . The surface-treating aqueous solution according to  claim 23 , wherein the organic resin is selected from the group consisting of acrylic resins, urethane resins, and epoxy resins. 
     
     
         27 . A surface treatment method for forming a highly corrosion resistant coating film on a zinc or zinc alloy plating, the method comprising the step of bringing a surface of the zinc or zinc alloy plating into contact with the surface-treating aqueous solution according to  claim 23 . 
     
     
         28 . A surface treatment method for forming a highly corrosion resistant coating film on a zinc or zinc alloy plating, the method comprising the step of bringing a surface of a chemical conversion coating film into contact with the surface-treating aqueous solution according to  claim 23 , the chemical conversion coating film being formed on the zinc or zinc alloy plating. 
     
     
         29 . A highly corrosion resistant coating film formed by bringing the surface-treating aqueous solution according to  claim 23  into contact with a surface of the zinc or zinc alloy plating or with a surface of a chemical conversion coating film formed on the zinc or zinc alloy plating.