Cathodic treatment of chromium-plated surfaces

• US 3,928,157 A
• Filed: 05/07/1973
• Issued: 12/23/1975
• Est. Priority Date: 05/15/1972
• Status: Expired due to Term

• Current Assignee: Hironori Uchida, Mitsuyasu Kubo, Ryuhei Miyazaki, Tsuyoshi Uotani, Yasuo Suematsu
• Original Assignee: Hironori Uchida, Mitsuyasu Kubo, Ryuhei Miyazaki, Tsuyoshi Uotani, Yasuo Suematsu
• Inventors: Uotani, Tsuyoshi, Suematsu, Yasuo, Miyazaki, Ryuhei, Kubo, Mitsuyasu, Uchida, Hironori
• Primary Examiner(s): Mack, John H.
• Assistant Examiner(s): Weisstuch, Aaron
• Application Number:
  US05/357,534
• Time in Patent Office: 960 Days
• Field of Search: 204/181
• US Class Current: 205/704
• CPC Class Codes: C09D 5/4488 Cathodic paints C09D5/4403 - C09D5/4476 take precedence
• CPC Class Codes: Y10S 205/917 Treatment of workpiece between coating steps

Abstract

A method for treating a chromium-plated surface is provided characterized by the fact that a chromium-plated article is dipped as the cathode in a water-soluble or water-dispersible resin solution or dispersion prepared by diluting with water a resin salt of at least one synthetic polyamino resin with a water-soluble organic acid and/or a water-soluble inorganic acid, and then passing a direct current in the range of 10 - 300 volts through the aqueous bath so that there is formed a resin film on the chromium plated surface the chromium-plated surface is pretreated prior to the resin coating step by anodization in aqueous chromate solution or by heat treatment so that the surface electrode potential is greater than -0.42 volts.

Claims

1. A METHOD FOR TREATING A CHROMIUM-PLATED SURFACE CHARACTERIZED BY THE FACT THAT A CHROMIUM-PLATED ARTICLE HAVING AN UPPERMOST CHROMIUM-PLATED LAYER OF A THICKNESS OF AT LEAST 0.2 MICRON AND ADJACENT THERETO, AN INTERMEDIATE NICKEL OR NICKELALLOY LAYER, IS DIPPED AS THE CATHODE IN A WATER-SOLUBLE OR WATER-DISPERSIBLE RESIN SOLUTION OR DISPERSION PREPARED BY DILUTING WITH WATER A RESIN SALT OF AT LEAST ONE SYNTHETIC POLY AMINO RESIN AND A WATER-SOLUBLE ORGANIC ACID, A WATER-SOLUBLE INORGANIC ACID OR A MIXTURE OF SAID ACIDS AND THEN PASSING A DIRECT CURRENT IN THE RANGE OF 10-300 VOLTS THROUGH THE AQUEOUS BATH SO THAT THERE IS FORMED A RESIN FILM ON THE CHROMIUM PLATED SURFACE.

2. A method as claimed in claim 1 wherein after the electrodeposition the resin-coated article is subjected to an after-treatment with an aqueous treating agent, said treating agent being selected from the group consisting of antioxidants, surface-active agents, organic solvents, acids and bases, and is thereafter baked or cured.

3. A method as claimed in claim 2 wherein the aqueous treating agent for the after-treatment contains an anti-oxidant selected from the group consisting of phenolic-type antioxidants and phosphite-type antioxidants at a concentration of 0.01 to 2.0% by weight.

4. A method as claimed in claim 2 wherein the aqueous treating agent for the after-treatment contains a surface-active agent selected from the group consisting of silicone oils and anionic, cationic, nonionic and amphoteric surface-active agents at a concentration of 0.001 to 2.0 percent by weight.

5. A method as claimed in claim 2 wherein the aqueous treating agent for the after-treatment contains an organic solvent selected from the group consisting of glycol ethers, glycol ether esters, alcohols, ketones and esters at a concentration of 1 to 90 % by weight, preferably 5 to 70 % by weight.

6. A method as claimed in claim 2 wherein the aqueous treating agent for the after-treatment contains an acid selected from the group consisting of phthalic anhydride, trimellitic anhydride, pyromellitic anhydride and oxalic acid at a concentration of 0.1 - 5.0 %, preferablY 0.3 - 4.0 % by weight.

7. A method as claimed in claim 2 wherein the aqueous treating agent for the after-treatment contains a base selected from the group consisting of dicyandiamide and dibutylamine at a concentration of 0.1 - 5.0 %, preferably 0.3 - 4.0 % by weight.

8. A METHOD AS CLAIMED IN CLAIM 1 WHEREIN THE CHROMIUM PLATED SURFACE IS PRETREATED BEFORE THE ELECTRODEPOSITION SO THAT THE SURFACE ELECTRODE POTENTIAL AS DEFINED HEREIN BEFORE HAS A VALUE HIGHER THAN 0.42 VOLT BY MEANS OF AN ELECTROCHEMICAL OR PHYSICAL TREATMENT.

9. A method as claimed in claim 8 wherein the electrochemical treatment is conducted by the anodic-electrolysis of the chromium-plated surface in an aqueous solution selected from the group consisting of chromic acid, chromate or dichromate.

10. A method as claimed in claim 8 wherein the physical treatment is conducted by heating the chromium-plated surface such that the product of the temperature and time of treatment is at least 3000*C-min. and the upper limit of temperature is 300*C.

11. A method as claimed in claim 8 wherein the physical treatment is conducted by exposing the chromium-plated surface to air at the normal temperature for at least 24 hours.

12. A method as claimed in cliam 1 wherein the synthetic polyamino resin is a resin containing primary, secondary, or tertiary amino groups or quaternary ammonium groups or mixtures of these groups in the molecule, and is selected from the group consisting of (A) a vinylic or acrylic copolymer containing amino groups as pendant groups, (B) a resinous polymer made by introducing amino groups by making a dialkylamine or dialkanolamine react on an epoxy resin containing two or more epoxy groups in the molecule, (C) a polyester resin obtained by using an alkanolamine as one component of a polyol and cocondensing a polybasic acid with the other polyol, (D) a polyurethane resin obtained by using an alkanolamine as one component and cocondensing a polyisocyanate with the other polyol and (E) a terminal amino group-containing polyamide resin obtained by condensing a stoichiometrically excess polyamine with a polybasic acid at a solid part concentration in the electrodepositing bath solution in a range of 1 to 20 percent by weight.

13. A method as claimed in claim 1 wherein said water-soluble organic acid and water-soluble inorganic acid are selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, malonic acid, citric acid, hydrochloric acid, phosphoric acid, and sulfuric acid and wherein said water-soluble organic acid, water-soluble inorganic acid or mixture thereof is employed in an amount of 0.3 to 1.0 equivalent for 1.0 equivalent of the amino groups in the synthetic polyamino resin.