Agent for reducing conversion film overall friction coefficient for trivalent chromate treating solution, trivalent chromate treating solution and method for production thereof, and trivalent chromate conversion film reduced in overall friction coefficient and method for production thereof

Abstract

It is an object of the present invention to provide a conversion film obtained by contacting a treating solution based on trivalent chromium with zinc or zinc alloy plating layers, which film does not contain hexavalent chromium, which film has corrosion resistance identical to that of the conversion film obtained by the conventional chromate treatment based on hexavalent chromium, and furthermore which has an overall friction coefficient identical to or lower than that of the conventional hexavalent chromate conversion film. The present invention also provides an agent for reducing a conversion film overall friction coefficient for a trivalent chromate treating solution, which agent contains a quinoline based compound or its derivative.

1 . An agent for reducing a conversion film overall friction coefficient for a trivalent chromate treating solution, which agent contains a quinoline based compound or its derivative.  
     
     
         2 . Use of a quinoline based compound or its derivative for reducing an overall friction coefficient of a trivalent chromate conversion film.  
     
     
         3 . A method for producing a trivalent chromate treating solution for forming a conversion film reduced in an overall friction coefficient comprising the step of adding a quinoline based compound or its derivative to said trivalent chromate treating solution.  
     
     
         4 . A trivalent chromate treating solution, which contains from 0.1 to 25 g/L of a quinoline based compound or its derivative.  
     
     
         5 . The treating solution according to  claim 4 , which comprises: 
 a trivalent chromium ion and an oxalate ion in a molar ratio (a trivalent chromium ion/oxalate ion) ranging from 0.5/1 to 1.5/1, wherein the trivalent chromium is present in the form of a water-soluble complex with an oxalic acid; and    cobalt ions are stably present in the treating solution without causing any precipitation due to their forming a hardly soluble metal salt with an oxalic acid;    the treating solution reacting with zinc when it is brought into contact with the zinc or zinc alloy plating to form a trivalent chromate conversion film containing zinc, chromium, cobalt, oxalic acid and a quinoline based compound or its derivative on the plating.    
     
     
         6 . The treating solution according to  claim 4 , which comprises: 
 a trivalent chromium ion;    an ion selected from the group consisting of an Al ion, Si ion, Ti ion, Mn ion, Fe ion, Co ion, Ni ion, Zn ion and the combination thereof; and    an inorganic acid ion selected from the group consisting of a chlorine ion, nitrate ion, sulfate ion, phosphate ion and the combination thereof.    
     
     
         7 . The treating solution according to  claim 4 , which comprises: 
 a trivalent chromium ion;    an ion selected from the group consisting of an Al ion, Si ion, Ti ion, Mn ion, Fe ion, Co ion, Ni ion, Zn ion and the combination thereof;    an inorganic acid ion selected from the group consisting of a chlorine ion, nitrate ion, sulfate ion, phosphate ion and the combination thereof; and    an organic acid that forms a water-soluble complex with the trivalent chromium ion.    
     
     
         8 . A method for forming a trivalent chromate conversion film comprising: 
 a step of bringing zinc or zinc alloy plating layers into contact with the treating solution according to  claim 4 .    
     
     
         9 . The method according to  claim 8 , further comprising: 
 a step of preparing a trivalent chromate treating solution by taking a part of the treating solution, adding the reducing agent according to  claim 1  to the taken part of the treating solution and putting the taken part back into the treating solution.    
     
     
         10 . A trivalent chromate conversion film, which contains a quinoline based compound or its derivative.