Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • 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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8

Definitions

• the invention relates to a process for producing black coatings on zinc or zinc alloys by treatment with alkaline solutions which contain nickel ions and a complexing agent and have a pH ⁇ 11.
• JP-A-61-253381 describes a solution for blackening treatment which contains an oxidizing agent, copper ions in a concentration of more than 1 g / l and nickel ions in an amount corresponding to 1 to 30% by weight of the copper content, and has a pH of 1.5 to 4. Such solutions are applied at a temperature of 20 to 70 ° C for a period of 1 to 5 s.
• the black coating obtained in this way contains copper oxide and nickel, which improves the weldability of the treated workpieces.
• the above-mentioned process is disadvantageous in that the layer-forming components copper oxide and nickel are more noble than zinc and deposit in a granular form.
• the layer-forming components copper oxide and nickel are more noble than zinc and deposit in a granular form.
• an accelerated corrosion attack on the zinc takes place, as a result of which not only the corrosion resistance but also the adhesion of the Coating is adversely affected.
• Further disadvantages of the known method also result from the fact that acid-resistant containers are required to hold the treatment solution.
• the object of the present invention is to provide a method which leads to coatings of good properties in a simple manner.
• the object is achieved by the method of the type mentioned according to the invention is designed such that the coatings are produced with a solution containing at least 1 g / l Ni2+ ions and at least 6 times the molar amount of NH3 per mole of nickel contains.
• the coatings produced by the process according to the invention consist essentially of nickel and nickel oxides and have excellent adhesion to the metallic base and excellent corrosion resistance.
• the excellent corrosion resistance is largely due to the fact that the proportion of nickel oxide in the generated Plating is high and this nickel oxide considerably reduces the corrosion attack on zinc.
• the concentration of Ni2 ⁇ ions is ⁇ 1.0 g / l, a sufficient layer weight of the coating is not achieved and the effect achieved is not obtained to the required extent. If the ammonia content is less than 6 times the molar amount, based on one mole of nickel, the complex formation for nickel is inadequate and there are similar adverse effects as when the nickel concentration is too low.
• the treatment solution is preferably applied by dipping or spraying.
• the coatings can also be produced electrolytically.
• the fine-grained nature of the coating-forming substances namely nickel or nickel oxide
• coatings of nickel and nickel oxides have a better adhesion than those of nickel, copper, antimony, molybdenum, as are obtained in plating processes using acid baths.
• An essential advantage of the method according to the invention is that it enables black coatings to be produced using a single-stage process, the coatings produced nevertheless being highly resistant to corrosion and having excellent adhesion.
• the method can be carried out without the use of electricity with a comparatively simple composition of the treatment solution.
• the simple bathroom composition in turn, enables easy control of the bathroom quality and a low level Chemical expenses.
• the fact that comparatively simple materials - due to the alkaline setting of the treatment solution - can be used to construct the treatment plants rounds off the number of advantages of the method according to the invention.
• Electrolytically galvanized sheets (substrate A) and sheets electrolytically provided with zinc / nickel coatings (substrate B) according to Examples 1 to 6 were treated with solutions, the composition of which is given in Table 1. All treatments were carried out at 40 ° C in diving. The pH of the solutions was 9.5 in all. The Ni2 Ni ions were added in the form of nickel sulfate if the pH was adjusted with sulfuric acid, or in the form of nickel chloride if the pH was adjusted with hydrochloric acid. The ammonia was added in the form of a 28% by weight aqueous solution. If necessary, ammonium sulfate or ammonium chloride was added.
• the pH of the solution was 11.5, the treatment temperature 40 ° C, the treatment time 20 seconds.
• Both in Comparative Example 1 and in Comparative example 2 served as the substrate electrolytically galvanized sheets (substrate A).
• Table 1 The nature of the treatment solution according to the method according to the invention is given in Table 1 below.
• Column 2 contains the type of substrate treated
• column 3 the essential components of the treatment solution
• column 4 the additives used to adjust the pH
• Table 1 example Substrate essential bathroom components pH adjustment with Duration of treatment 1
• NH3 60 g / l 2nd B Ni2+ 20 g / l H2SO4 20 sec.
• NH3 60 g / l 4th A Ni2+ 2.0 g / l H2SO4 20 sec.
• the blackening was assessed by specifying the L value determined using an SM Color Computer (SUGA Tester) in accordance with JIS Z 8729 - 1980.
• the adhesive strength of the coating produced was determined using the cellophane tape method after the sheets had previously been bent by a sample sheet.

Applications Claiming Priority (2)

Publications (2)

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• 1988
  • 1988-08-08 JP JP19758588A patent/JPH0730458B2/ja not_active Expired - Lifetime
• 1989
  • 1989-08-04 DE DE19893925839 patent/DE3925839A1/de not_active Withdrawn
  • 1989-08-04 DE DE8989114428T patent/DE58904782D1/de not_active Expired - Fee Related
  • 1989-08-04 EP EP19890114428 patent/EP0356756B1/de not_active Expired - Lifetime

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