Zinc and zinc alloy plating black passivation solution and preparation method thereof

Abstract

The invention discloses zinc and zinc alloy plating black passivation solution and preparation method thereof. The passivation solution consists of 5 to 50g / L of trivalent chromic salt, 1 to 10g / L of auxiliary film forming agent, 0.2 to 10g / L of reducing agent, 2 to 15g / L of pH buffer agent, 1 to 50g / L of chelating agent, 0.5 to 10g / L of blackening agent, 1 to 50g / L of oxidant and 0 to 50g / L of pH regulator. The passivation solution has stable working solution performance and low cost, and is simple and convenient to operate and easy to learn; zinc and zinc alloy plated parts passivated by the working solution are black and bright, uniform in color and good in corrosion resistance, reach level 8 in 72 hours, and have good bonding force; and the plating solution and coatings totally contain no Cr(VI), and the Cr(VI) cannot be detected from workpieces placed for a long term, so the passivation solution has high market competitiveness and development potential.

Description

technical field [0001] The invention relates to a post-plating treatment agent, in particular to a galvanized and zinc alloy black passivation solution and its preparation and use method. The passivation solution has good stability, low cost, jet-black passivation layer, color and luster Uniform, no Cr(VI) coating, good corrosion resistance. Background technique [0002] Black passivation of galvanized and zinc alloy is one of the methods to obtain black decorative layer. Compared with other methods to obtain black decorative layer such as black chrome plating, black nickel, blue steel, galvanized layer coloring, etc., it has simple processing technology , low cost and good corrosion resistance. Galvanized and zinc alloy black passivation has the advantages of coating and corrosion-resistant coating. The coating after black passivation has good corrosion resistance and bonding force, and is pure black and shiny, with uniform and beautiful color tone, which can reduce visual...

AI Technical Summary

Problems solved by technology

However, after the passivation parts treated with trivalent chromium passivation solution are placed for a period of time, hexavalent chromium will appear in the passivation film, and as the storage time prolongs, hexavalent chromium will gradually increase, far exceeding the EU regulations RoHS Directive and the requirements of the WEEE Directive

This problem has become a problem that plagues the further promotion and application of trivalent chromium passivation technology, and has caused many companies to return products. It has become the most difficult problem in trivalent chromium passivation that needs to be solved urgently.

[0004] The trivalent chromium black passivation solution based on organic precursors described in patent CN101831648C is characterized in that the acid mordant dye is one or both of acid mordant black PV and acid mordant black T, forming a dye-chromium-dye Complex black lake, attached to the gel-like Cr(OH) 3 During the precipitation, a black passivation film is obtained, but the passivation film obtained from this is not well bonded, the black film is uneven, and it is easy to fall off

Patent CN101668882A describes a method for preparing a substantially chromium-free (VI) black passivation layer on a zinc-containing alloy layer, and describes in detail the composition of carboxylic acid, other components and methods of use, but due to the presence of oxidants in the passivation solution Components, such as nitric acid, etc., may be in contact with air during storage and use, which will cause Cr(VI) in the plating solution, and there is no substance in the working solution that can reduce the generated Cr(VI). It will remain in the coating, and as the storage time prolongs, the price of six will gradually increase, and it cannot be detected by the passivation layer without Cr(VI)

[0005] The common problems of black passivation agents used in the market are high cost, poor stability of passivation solution, difficult adjustment of passivation solution, a certain level of technology is required, uneven passivation layer, unsatisfactory appearance effect, resistance of passivation layer Poor corrosion performance, the coating contains or produces Cr(VI), etc.

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