Coating processes – Immersion or partial immersion – Metal base
Reexamination Certificate
1995-11-06
2001-07-17
Utech, Benjamin L. (Department: 1765)
Coating processes
Immersion or partial immersion
Metal base
C427S443100, C427S443200
Reexamination Certificate
active
06261644
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for the electroless deposition of copper coatings on iron and iron alloy surfaces by means of solutions containing copper and hydrogen ions, and to a solid concentrate for carrying out this process.
It is known to facilitate the cold forming of iron and iron alloys by applying a copper coating onto the workpiece to be formed. Such coatings can be generated in an electroless way in that the metal surface is brought in contact with an aqueous, acid solution containing copper ions. In order to achieve good and in particular adhesive coatings, numerous proposals have been made, which provide for the addition of a variety of modifiers.
In the process in accordance with the DE-C-714 437 copper plating solutions are being used, which in addition to copper, hydrogen, chloride, bromide and/or fluoride ions contain strong organic pickling inhibitors for delaying the dissolution of iron. Useful pickling inhibitors include for instance coal tar bases, the bases extracted from animal distillates, aldehyde amine reaction products, aldehyde ketone reaction products, numerous amino acids, alkaloids and the sulfonated derivatives thereof.
Furthermore, it is known to add polyhydroxy thiols (U.S. Pat. No. 2,410,844) and brightening agents or grain refining agents, such as condensation products of fatty alcohols, fatty acids, tall oil, alkyl phenols, fatty amines, substituted thioureas, each comprising ethylene oxide, as well as long-chain organic amines, reducing sugars, and decomposition products of sugar (FR-A-1,257,758) to electroless copper plating solutions.
It is also known to provide a treatment with an aqueous, acid solution containing copper ions, chloride ions and an organic modifier for the electroless production of copper coatings on iron and iron alloys, where acridine and/or acridine derivatives are used as an organic modifier (DE-B-16 21 291).
Finally, it is known to use solutions containing copper, hydrogen and fluoride ions for the electroless deposition of copper, for which solutions both the fluoride concentration and the hydrogen ion concentration are chosen within certain coordinates in dependence on the temperature (DE-B-16 21 293).
Despite the multitude of known processes for the electroless deposition of copper, problems repeatedly arise in practice, as one does not, or not with the required safety, succeed in producing copper coatings which are both bright and adhesive, cover uniformly, and have a good appearance. A further problem is that the solid concentrates normally used for making the copper plating solutions have a poor flowability and are thus difficult to handle.
It is the object of the invention to provide a process for the electroless deposition of copper coatings on iron and iron alloy surfaces, which does not have the known, in particular the aforementioned disadvantages, and is able to produce uniform and adhesive coatings.
THE INVENTION
The object is accomplished in that the process of the above-mentioned type is conducted in accordance with the invention such that the workpiece surface is brought in contact with a solution containing
5 to 30 g/1 Cu as well as 0.2 to 5 g/1 Mg.
In accordance with a preferred embodiment of the invention the surfaces are brought in contact with a solution wherein the weight ratio of Cu:Mg lies in the range of (35 to 5):1. A weight ratio in the aforementioned range leads to an optimum gloss of the produced coating.
In accordance with a further advantageous embodiment of the invention, the iron or iron alloy surface is brought in contact with a solution which additionally contains polyglycol and/or sodium chloride. The addition of polyglycol gives an improvement in the adherence of the coating, and the addition of sodium chloride provides a more uniform attack on the iron or iron alloy surface.
Furthermore, it is advantageous to contact the iron or iron alloy surface with the solution for a duration of 3 sec to 15 min. The solution should advantageously have a temperature of 20 to 65° C.
The invention also comprises a solid concentrate for preparing and replenishing the solution designed for carrying out the process, which consists of at least 85 wt-% CuSO4 ·5H
2
O and MgSO
4
(anhydrous) with a weight ratio of (35 to 5):1 (calculated as Cu:Mg).
In accordance with a further advantageous embodiment the solid concentrate contains in addition a maximum of 10 wt-% polyglycol, and in accordance with a further advantageous embodiment a maximum of 5 wt-% sodium chloride.
Before the application of the copper plating solution, impurities, such as in particular rust and scale, are removed from the iron and iron alloy surfaces. The surface conditioning is performed by pickling in mineral acid, preferably by pickling in hydrochloric acid or sulfuric acid, followed by rinsing with water.
If the iron and iron alloy surfaces have additional impurities, it is advantageous to include a cleaning step before the pickling process.
The copper coatings produced by means of the inventive process have a considerable adherence and a strong gloss. A further advantage of this process is that the increase of iron in the copper plating solution is significantly retarded, so that a greater throughput of iron or iron alloy surface is possible without influencing the iron concentration in the solution.
The solid concentrate, which is likewise a subject-matter of the invention, exhibits a good flowability and can thus easily be handled even after a long storage period.
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G. Barrow, Physical Chemistry, 1979 by McGrow-Hill, Inc, pp. D618-D627.*
CRC Handbook of Chemistry and Physics, 1982-1983 by CRC Press, pp. 162-167.
Nittel Klaus-Dieter
Nuss Karl-Heinz
Fulbright & Jaworski LLP
Metallgesellschaft Aktiengesellschaft
Utech Benjamin L.
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