Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal coating
Patent
1998-07-02
2000-02-29
Mayekar, Kishor
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal coating
205254, 106 125, C25D 332
Patent
active
060305169
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electrolyte compositions suitable for electroplating surfaces with tin and to methods of electroplating surfaces with tin. The invention is particularly suitable for use in high speed strip or wire plating.
Ideally an electrolyte should posses the following properties:- produce a wide plating range, give a good quality deposit, have low corrosivity, have good conductivity, have good antioxidant properties, have low toxicity and have low environmental impact.
Many electrolyte compositions have been made known and are available in the art. Typical baths include aqueous acidic baths based upon fluoroborate and fluorosilicate electrolytes as described, for example, in U.S. Pat. No. 3,769,182 and U.S. Pat. No. 4,118,289. Aryl sulphonic acids have been used in electroplating baths as disclosed, for example, in U.S. Pat. No. 3,905,878 . Traditionally, the aryl sulphonic acid of choice is phenolsulphonic acid as used in the Ferrostan process. The use of toluenesulphonic acid in electroplating baths has also been specifically described, for example in U.S. Pat. No. 2,271,209.
Mineral acid (especially sulphuric acid) electroplating baths have also been described. For example, U.S. Pat. No. 2,156,427 describes a bath containing tar acids and sulphuric acid for producing tin coatings of a fine crystalline texture.
Alkane sulphonic acids containing 1 to 5 carbon atoms in the alkyl group have previously been used in certain electrolytic plating baths and were first disclosed for this use in U.S. Pat. No. 2,522,942. More recently, methane sulphonic acid has been claimed as a specific preferred example of an alkane sulphonic acid in combination with a number of brightening agents for use in the electroplating of tin, lead and tin-lead alloys for example as in U.S. Pat. No. 4,565,610 and U.S. Pat. No. 4,617,097. Systems based on methane sulphonic acid however suffer from high cost, toxicity, odour problems and have been known to introduce surface defects on flow brightened strip steel plate.
Various plating bath compositions comprising an alkane or alkanol sulphonic acid (normally methane sulphonic acid), a tin and/or a lead salt and various auxiliary additives are known. Known auxiliary additives range from smaller organic molecules to large polymeric surfactant molecules and are described in U.S. Pat. Nos. 4,555,314, 4,565,609, 4,582,576, 4,599,149, 4,617,097, 4,666,999, 4,673,470, 4,701,244, 4,828,657 and U.S. Pat. No. 4,849,059.
Plating bath compositions containing mixtures of aryl and alkyl sulphonic acids are also known in the art, for example, as described in EP 0 490 575.
Various addition agents have been proposed which enhance the quality of the tin plate. They can include condensates of hydrophobic organic compounds with alkylene oxides such as, for example, alpha naphthol 6 mol ethoxylate ("ENSA 6" as supplied by Emery-Trylon); alkylbenzene alkoxylates such as the `Tritons`; derivatives of N-heterocycles such as, for example, 2-alkylimidazolines; aromatic aldehydes such as naphthaldehyde; derivatives of 2,2-bis(4-hydroxyphenyl)propane, for example, as "Diphone V" (as supplied by Yorkshire Chemicals) formed by reacting 2,2-bis(4-hydroxyphenyl)propane with a sulphonating agent; and 2,4,6-substituted phenols in which at least one of the substituents includes a secondary, tertiary or quaternary nitrogen atom as described in U.S. Pat. No. 3,954,573. The latter addition agents have, however only been described for use in fluoroborate tin plating systems.
It is generally accepted that it is the addition agent which has the greatest effect on tin plate quality and little work has been done on how acids affect plate quality such as plating width and brightness.
In the case of strip tinplate manufacture it is desirable from a commercial point of view to have a system capable of giving satisfactory tin deposits over as wide as possible a range of current densities to accommodate all variations in speed of production and minimise the incidence of current density defects.
We have unexpectedly found
REFERENCES:
patent: 5258112 (1993-11-01), Wild et al.
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