Chromium plating method

Abstract

A chromium plating method wherein an article to be plated is immersed in an acidic chromium electroplating bath and electrolysis is carried out using a positive electrode that has an iridium oxide-containing film at least on the surface. The acidic chromium electroplating bath contains a trivalent chromium compound and a hexavalent chromium compound at a ratio such that the total chromium concentration of trivalent chromium and hexavalent chromium is 60-140 g/L, the hexavalent chromium concentration is 5-40 g/L, and the ratio of the hexavalent chromium concentration is 5-35% by mass of the total chromium concentration, while containing 50-400 g/L of organic carboxylate ions and having a lead ion concentration of not more than 2 mg/L. By the method, a chromium plating film that is good and stable over a long time period can be obtained. In addition, the plating bath can be controlled extremely easily in the chromium plating method.

1 . A chromium plating method comprising the steps of:
 immersing an object to be plated into an acidic chromium electroplating bath comprising:   a trivalent chromium compound and a hexavalent chromium compound such that the total amount of trivalent chromium ions and hexavalent chromium ions is 60 to 140 g/L, the amount of hexavalent chromium ions is 5 to 40 g/L, and the amount of hexavalent chromium ions accounts for 5 to 35 wt % of the total amount of chromium ions; and   organic carboxylate ions in an amount of 50 to 400 g/L; and   a concentration of lead ions in said acidic chromium electroplating bath being no greater than 2 mg/L,   performing electrolysis by using an anode having an iridium oxide-containing coating at least on the surface thereof.   
     
     
         2 . The chromium plating method of  claim 1 , wherein the trivalent chromium compound is chromium organic carboxylate complex or a mixture of chromium sulfate and chromium organic carboxylate complex, said mixture containing said chromium organic carboxylate complex in an amount that accounts for, in terms of trivalent chromium, 50 wt % or more of the total amount of trivalent chromium. 
     
     
         3 . The chromium plating method of  claim 1 , wherein the chromium plating bath further comprises sulfate ions in an amount of 20 to 200 g/L and has a pH of 1.8 to 2.6. 
     
     
         4 . The chromium plating method of  claim 1 , wherein the chromium plating bath is halogen free. 
     
     
         5 . The chromium plating method of  claim 1 , wherein plating is accomplished in such a way that the anode and the object to be plated are immersed in the same plating bath of a plating tank without being separated from each other by a diaphragm.