# US 7,745,008 B2 · Processing solution for forming hexavalent chromium free and corrosion resistant conversion film on zinc or zinc alloy plating layers, hexavalent chromium free and corrosion resistant conversion film, method for forming the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,745,008 B2 - Document ID: US7745008B2 - Status: Granted - Kind: B2 - Application number: 11/019,277 - Filed: 2004-12-23 - Published: 2005-05-19 - Granted: 2010-06-29 - Earliest claimed: 2001-11-30 - Assignees: Dipsol Chemicals Co., Ltd. - Inventors: Katsuhide Oshima; Shigemi Tanaka; Manabu Inoue; Tomitaka Yamamoto - Web page: https://patentgrep.com/patent/US7745008B2 ## CPC - C23C 22/46: containing oxalates - C23C 22/47: containing also phosphates - C23C 2222/10: Use of solutions containing trivalent chromium but free of hexavalent chromium - Y10T 428/12583: Component contains compound of adjacent metal - Y10T 428/12792: Zn-base component - Y10T 428/12799: Next to Fe-base component [e.g., galvanized] - C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04) - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract A processing solution for forming a hexavalent chromium free, corrosion resistant trivalent chromate conversion film on zinc or zinc alloy plating layers comprises: trivalent chromium and oxalic acid in a molar ratio ranging from 0.5/1 to 1.5/1, wherein the trivalent chromium is present in the form of a water-soluble complex with oxalic acid; and cobalt ions, which do not form a hardly soluble metal salt with oxalic acid and are stably present in the processing solution without causing any precipitation; wherein the solution reacts with zinc when bringing it into contact with the zinc or zinc alloy plating to form a hexavalent chromium free, corrosion resistant, trivalent chromate conversion film containing zinc, chromium, cobalt, oxalic acid and silicon on the plating. The film is quite thin, free of any hexavalent chromium, has corrosion resistance identical to or higher than that achieved by the conventional hexavalent chromium-containing film and can be formed using a processing solution having a quite low concentration. ## Claims ### Claim 1 A hexavalent chromium free, corrosion resistant, trivalent chromate conversion film containing zinc, trivalent chromium, cobalt and oxalic acid and formed on zinc or zinc alloy plating layers, wherein the thickness of the film is 0.02 to less than 0.1 μm, the mass ratio of trivalent chromium to (trivalent chromium+zinc) [Cr/(Cr+Zn)] is not less than 15/100, the mass ratio of cobalt to (trivalent chromium+cobalt) [Co/(Cr+Co)] ranges from 5/100 to 40/100 and the mass ratio of the oxalic acid to (trivalent chromium+oxalic acid) [oxalic acid/(Cr+oxalic acid)] ranges from 5/100 to 50/100, and which conversion film exhibits a corrosion resistance as measured by the salt spray test (JIS-Z-2371) of 240 hours or more. ### Claim 2 (depends on 1) The hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 1, wherein the thickness of the film is 0.02 to 0.09 μm. ### Claim 3 (depends on 2) The hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 2, wherein the thickness of the film is 0.02 to 0.08 μm. ### Claim 4 (depends on 1) The hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 1, wherein the mass ratio of trivalent chromium to (trivalent chromium+zinc) [Cr/(Cr+Zn)] is from 20/100 to 60/100, the mass ratio of cobalt to (trivalent chromium+cobalt) [Co/(Cr+Co)] ranges from 10/100 to 40/100 and the mass ratio of the oxalic acid to (trivalent chromium+oxalic acid) [oxalic acid/(Cr+oxalic acid)] ranges from 10/100 to 50/100. ### Claim 5 (depends on 4) The hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 4, wherein the thickness of the film is 0.02 to 0.09 μm. ### Claim 6 (depends on 5) The hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 5, wherein the thickness of the film is 0.02 to 0.08 μm. ### Claim 7 A hexavalent chromium free, corrosion resistant, trivalent chromate conversion film containing zinc, trivalent chromium, cobalt and oxalic acid and formed on zinc or zinc alloy plating layers, wherein the thickness of the film is 0.02 to 0.1 μm, the mass ratio of trivalent chromium to (trivalent chromium+zinc) [Cr/(Cr+Zn)] ranges from 21/100 to 25/100, the mass ratio of cobalt to (trivalent chromium+cobalt) [Co/(Cr+Co)] ranges from 5/100 to 40/100 and the mass ratio of the oxalic acid to (trivalent chromium+oxalic acid) [oxalic acid/(Cr+oxalic acid)] ranges from 5/100 to 50/100 and which conversion film exhibits a corrosion resistance as measured by the salt spray test (JIS-Z-2371) of 240 hours or more. ### Claim 8 (depends on 7) The hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 7, wherein the mass ratio of cobalt to (trivalent chromium+cobalt) [Co/(Cr+Co)] ranges from 5.7/100 to 36.5/100 and the mass ratio of the oxalic acid to (trivalent chromium+oxalic acid) [oxalic acid/(Cr+oxalic acid)] ranges from 9.1/100 to 46.7/100. ### Claim 9 (depends on 1) A product comprising a metal substrate comprising a zinc or zinc alloy plating layer formed thereon, and the hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 1 formed on said plating layer. ### Claim 10 (depends on 4) A product comprising a metal substrate comprising a zinc or zinc alloy plating layer formed thereon, and the hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 4 formed on said plating layer. ### Claim 11 (depends on 2) A product comprising a metal substrate comprising a zinc or zinc alloy plating layer formed thereon, and the hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 2 formed on said plating layer. ### Claim 12 (depends on 3) A product comprising a metal substrate comprising a zinc or zinc alloy plating layer formed thereon, and the hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 3 formed on said plating layer. ### Claim 13 (depends on 5) A product comprising a metal substrate comprising a zinc or zinc alloy plating layer formed thereon, and the hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 5 formed on said plating layer. ### Claim 14 (depends on 6) A product comprising a metal substrate comprising a zinc or zinc alloy plating layer formed thereon, and the hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 6 formed on said plating layer. ### Claim 15 (depends on 7) A product comprising a metal substrate comprising a zinc or zinc alloy plating layer formed thereon, and the hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 7 formed on said plating layer. ### Claim 16 (depends on 8) A product comprising a metal substrate comprising a zinc or zinc alloy plating layer formed thereon, and the hexavalent chromium free, corrosion resistant, trivalent chromate conversion film according to claim 8 formed on said plating layer.