Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal coating
Patent
1992-11-19
1993-11-23
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal coating
205275, 106 121, 106 127, C25D 312
Patent
active
052641120
DESCRIPTION:
BRIEF SUMMARY
The invention relates to acidic nickel baths containing 1-(2-sulfoethyl)-pyridiniumbetaine.
Acidic nickel baths are known, for example, from the publications U.S. Pat. No. 3,862,019, DE-PS 36 32 514, EP-A-0343 559, 5DD-PS 0266 814, and EP-A 0341 167.
It is also known that certain organic substances are added to acidic, and especially weakly acidic, nickel electrolytes in small quantities in order to achieve a bright nickel deposit instead of a dull deposit.
One group of additives, which are also called substratum brighteners, comprises unsaturated and usually aromatic sulfonic acids, sulfinic acids, sulfonamides and their salts as the case may be. The best-known compounds are, for example, m-benzenedisulfonic acid or benzoic sulfimide (saccharin).
Added to the electroplating bath alone, these additives (substratum brighteners) generate a bright but not leveled deposit over a certain range of current densities. Using them alone, therefore, has no practical meaning since the quality of the nickel coatings obtained with them does not meet current requirements.
Their obvious deficiency is the ability [sic] to level rough surfaces without making the deposit brittle.
Substances are also known here that are termed levelers.
They are practically always used with one or more substratum brighteners.
Known levelers are, for example, triply unsaturated alcohols or triply unsaturated amines. They show dark deposits in the low current density range, especially during continuous operation, even with a slightly excessive addition. It is even common for there to be no deposition in the low current density range and for the substrate material to remain visible.
Other known levelers are quaternary, aromatic, nitrogenous compounds such as pyridinium compounds or quinolinium compounds. The characteristic shared by all these levelers is that they make the nickel deposit brittle either at the very outset or, mostly, during continuous operation. In this way, subsequent shaping of the nickel-plated parts is no longer possible; cracks also emerge spontaneously which extend into the base material and thus cause corrosion (for example, rust).
The task of the present invention is to avoid the disadvantages which have been described and to provide a bath which--with adequate depth dispersion--prevents good leveling and the deposition of brittle deposits under long-term operation of the acidic nickel baths with minimal consumption of the bath ingredients.
This task is accomplished by the subject of the invention in accordance with the claims.
It was found that the addition of 1-(2-sulfoethyl)-pyridiniumbetaine ##STR1## is particularly well-suited as a nickel brightener. 1-(2-sulfoethyl)-pyridinirumbetaine is a known substance (U.S. Pat. Specification No. 3,131,189; J. Org. Chem. 29, 2489 (1964); J. Org. Chem. 26, 4520 (1961)); it differs from 1-(3-sulfopropyl)-pyridiniumbetaine (DE-PS 1004011) in terms of its better effectiveness in starting and in terms of consumption.
With this compound, it is outstandingly possible to achieve very good leveling in conjunction with outstanding brightness. There is no brittleness. By combining the levelers in Table 2 with a triply unsaturated group, a bright plating region can be achieved down to the lowest current density region.
The bath for depositing nickel deposits formed by adding the substance according to the invention generally consists of a nickel salt solution to which a weak acid is added for buffering.
In practice, the Watts solution is primarily used with the following approximate composition:
The pH value is between 3 and 5.5 and primarily between 4 and 5. The temperature can be as high as 75.degree. C. in order to increase current densities but, as a rule, it is between 50.degree. and 60.degree. C.
Heavy-duty electrolytes have a chloride content of 10-50 g/l and show the best results when using the compounds according to the invention. The nickel chloride can be replaced in part or in full by sodium chloride. With the designated heavy-duty electrolytes at 55.degree. C., the current dens
REFERENCES:
patent: 2876177 (1959-03-01), Gundel
patent: 4673472 (1987-06-01), Morrissey
patent: 5024736 (1991-06-01), Clauss et al.
patent: 5164069 (1992-11-01), Cerwonka
patent: 5169514 (1992-12-01), Hendriks et al.
Atotech Deutschland GmbH
Bolam Brian M.
Niebling John
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