Sulfate based, ammonium free trivalent chromium decorative plating process

Abstract

The present invention refers to an electroplating bath for electroplating a chromium or chromium alloy layer, the bath comprising trivalent chromium ions, organic carboxylic acid, sulfate ions, sodium conductive ions, and additives in the form of inorganic sulfur compound and boric acid as well as a process using such an electroplating bath.

1 - 15 . (canceled) 
     
     
         16 . An electroplating bath for depositing a chromium or chromium alloy layer, the bath comprising:
 a) at least one source of trivalent chromium ions,   b) at least one source of sulfate ions,   c) at least one organic acid as a complexing agent,   d) sodium saccharin,   e) at least one polyalkylene glycol,   f) sodium vinyl sulfonate,   g) at least one inorganic sulfur compound,   h) at least one pH buffer, and, optionally,   i) at least one source of ferric or ferrous ions.   
     
     
         17 . The bath according to  claim 16 , wherein the concentration of the ferric or ferrous ions is preferably from 20 to 200 mg/L, more preferably from 30 to 150 mg/L, and even more preferably from 40 to 100 mg/L. 
     
     
         18 . The bath according to  claim 16 , wherein the at least one inorganic sulfur compound is selected from the group of oxyacid anions comprising sulfur having a valence lower than 6, preferably selected from the group consisting of:
 disulfite or metabisulfite,   dithionite or hydrosulfite,   thiosulfate,   tetrathionate,   sulphite and   mixtures thereof.   
     
     
         19 . The bath according to  claim 16 , wherein the concentration of the at least one inorganic sulfur compound is from 5 to 500 mg/L, preferably from 10 to 200 mg/L. 
     
     
         20 . The bath according to  claim 16 , wherein the at least one polyalkylene glycol has a molecular weight of lower than 2000 g/mol and is preferably selected from the group consisting of:
 polyethylene glycol monomethyl ether,   ethyleneoxide/propyleneoxyde copolymer,   polyethylene glycol and   mixtures thereof.   
     
     
         21 . The bath according to  claim 16 , wherein the concentration of the at least one polyalkylene glycols is from 1 to 15 g/L, preferably from 5 to 10 g/L. 
     
     
         22 . The bath according to  claim 16 , wherein the at least one organic acid is
 i) selected from the group consisting of dicarboxylic acids, preferably selected from the group consisting of malic acid, oxalic acid, succinic acid, glutaric acid, adipic acid, and mixtures thereof, preferably malic acid wherein the at least one organic acid is particularly preferred malic acid; and/or   ii) comprised in a concentration from 5 to 40 g/L, preferably from 10 to 30 g/L, more preferably from 15 to 25 g/L.   
     
     
         23 . The bath according to  claim 16 , wherein the at least one pH buffer is selected from the group consisting of boric acid, wherein the pH of the bath is preferably from 1 to 5, more preferably from 2 to 4, and even more preferably from 3.1 to 3.9. 
     
     
         24 . The bath according to  claim 16 , wherein the bath is substantially free of, preferably free of at least one ion selected from the group consisting of chloride ions, ammonium ions, amino carboxylic acid ions, hexavalent chromium ions and combinations thereof. 
     
     
         25 . A method for preparing an electroplated product by electroplating a substrate comprising the following steps:
 A) providing an electroplating bath comprising:
 a) at least one source of trivalent chromium ions, 
 b) at least one source of sulfate ions, 
 c) at least one organic acid as a complexing agent, 
 d) sodium saccharin, 
 e) at least one polyalkylene glycol, 
 f) sodium vinyl sulfonate, 
 g) at least one inorganic sulfur compound, 
 h) at least one pH buffer, and, optionally, 
 i) at least one source of ferric or ferrous ions; 
   B) immersing a substrate into the electroplating bath and   C) applying an electrical current between an anode and the substrate as a cathode for depositing the chromium or chromium alloy layer on the substrate.   
     
     
         26 . The method according to  claim 25 , wherein the cathode current density is in a range from 3 to 14 A/dm 2 , preferably from 5 to 10, and/or the anode current density is in a range from 4 to 12 A/dm 2 , preferably from 5 to 10 A/dm 2 . 
     
     
         27 . The method according to  claim 25 , wherein the at least one anode consists of a mixed metal oxide, preferably a mixed metal oxide selected from the group consisting of mixed metal oxides of at least two of platinum, ruthenium, iridium and tantalum, more preferably a mixed metal oxide of iridium and tantalum. 
     
     
         28 . The method according to  claim 25 , wherein the deposition rate during the step bis in the range from 0.01 to 0.5 μm/min, preferably from 0.02 to 0.3 μm/min, and more preferably from 0.03 to 0.2 μm/min. 
     
     
         29 . The method according to  claim 25 , wherein step C) is conducted at a temperature from 35 to 60° C., preferably from 40 to 58° C., more preferably from 45 to 55° C. 
     
     
         30 . An alloy obtainable by the method according to  claim 25 , wherein the alloy comprises from 1 to 5 at % of carbon, from 0.5 to 4 at % of sulfur, from 1 to 5 at % of oxygen, from 0 to 12 at % of iron and/or from 74 to 94.5 at % of chrome.