Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly alloy coating
Patent
1993-11-09
1995-06-06
Niebling, John
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly alloy coating
205245, 205314, C25D 322, C25D 356
Patent
active
054219906
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an improved process for the production of shining shaped articles coated with zinc or a zinc alloy by electrodeposition of zinc or a zinc alloy from acidic aqueous electrolytic baths.
In the electrodeposition of zinc or zinc alloys on metal substrates from acidic aqueous solution it is frequently the aim to produce a shining coating in order to confer an advantageous decorative appearance on the zinc-coated item, ie. a decorative effect is often required in addition to the prevention of corrosion. In order to achieve the required effects it is indispensable for the electrolytic baths to contain certain auxiliaries because otherwise the zinc coatings produced from acidic solution are usually dull and often irregular. Examples of one group of auxiliaries for acidic electrolytic baths are conducting salts which are employed to improve the conductivity of the baths, and another group of auxiliaries comprises the brighteners.
U.S. Pat. No. 3,694,330 (1) (reissue 27 999) describes acidic electrolytic zinc baths which contain ammonium salts and, as brighteners, aromatic carbonyl compounds. Specified as the latter are aromatic carboxylic acids and aromatic aldehydes and ketones. Explicitly mentioned are, inter alia, cinnamic acid, cinnamaldehyde, benzoic acid, benzalacetone and ethyl benzoylacetate.
U.S. Pat. No. 4,422,908 (2) describes acidic electrolytic zinc baths which contain sulfamate ions and, as brighteners, aromatic carbonyl compounds. Aldehydes and ketones are mentioned, including benzalacetone as preferred substance.
The principal representative of the brighteners for acid zinc baths is benzylideneacetone (benzalacetone). A serious disadvantage of benzylideneacetone and its homologs is, however, the fact that these compounds cause allergic reactions, such as skin rashes and itching, in many of those using them.
It is an object of the present invention to replace brighteners based on benzylideneacetone in acidic aqueous electrolytic baths for the deposition of zinc or zinc alloys by other substances which are as effective as the known brighteners but do not have adverse effects on the health of those who use these substances.
We have found that this object is achieved by a process for the production of shining shaped articles coated with zinc or a zinc alloy by electrodeposition of zinc or a zinc alloy from acidic aqueous electrolytic baths which contain as essential components one or more zinc salts and, where appropriate, salts of the other alloy metals, one or more conducting salts, one or more surfactants and one or more brighteners, which comprises employing as brighteners compounds of the formula I ##STR2## where R.sup.1 is C.sub.1 -C.sub.8 -alkoxy, phenoxy, benzyloxy, amino, C.sub.1 -C.sub.6 -alkylamino or di(C.sub.1 -C.sub.6)alkylamino, R.sup.1, and three C.sub.1 -C.sub.4 -alkyl groups or C.sub.1 -C.sub.4 -alkoxy groups.
Preferred meanings of R.sup.1 are C.sub.1 -C.sub.8 -alkoxy such as n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, n-hexoxy, n-heptoxy, 2-ethyl-hexoxy, octyloxy and, in particular, methoxy and ethoxy.
Preferred meanings of R.sup.2 are C.sub.1 -C.sub.4 -alkyl such as ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl and, in particular, methyl, and C.sub.1 -C.sub.6 -alkoxy such as n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, n-hexoxy and, in particular, methoxy and ethoxy.
The preferred meaning of Ar is phenyl, which can additionally be substituted by one or two methyl, ethyl, methoxy or ethoxy groups, but especially unsubstituted phenyl.
Very particularly preferred compounds I are methyl and ethyl 2-benzylideneacetoacetate (R.sup.1 =OCH.sub.3 and OC.sub.2 H.sub.5 respectively, R.sup.2 =CH.sub.3, Ar=Ph) and dimethyl and diethyl 2-benzylidenemalonate (R.sup.1 =R.sup.2 =OCH.sub.3 and OC.sub.2 H.sub.5 respectively, Ar=Ph).
These substances can be obtained easily and at low cost by condensation of benzaldehyde with the appropriate acetoacetic or malonic ester. The prep
REFERENCES:
patent: Re27999 (1974-04-01), Korpiun et al.
patent: 4422908 (1983-12-01), Welch
patent: 4528075 (1985-07-01), Anchor
Burkhart Bernd
Dung Bernhard
Hahn Erwin
Tschang Chung-Ji
BASF - Aktiengesellschaft
Niebling John
Wong Edna
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