TIN PLATING ELECTROLYTE COMPOSITIONS

Abstract: There is disclosed a composition suitable for use in a process for electroplating surfaces with tin, comprising: an unsubstituted or substituted para alkylbenzene sulphonic acid (component a), one or more acids capable of giving good plating at low current density (component b), one or more addition agents, a tin source, water. There are also described methods of tin plating by the compositions of the invention.

Description: DESCRIPTION TIN PLATING ELECTROLYTE COMPOSITIONS 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 ar . Typical baths include aqueous acidic baths based upon fluoroborate and fluorosilicate electrolytes as described, for example, in US-A-3 7 . 69 182 and US-A-4 118 289. Aryl suiphonic acids have been used in electroplating baths as disclosed, for example, in US-A-3 905 878 . Traditionally, the aryl suiphonic 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 US-A-2 271 209. Mineral acid {especially sulphuric acid) electroplating baths have also been described. For example, US-A-2 156 427 describes a bath containing tar acids and sulphuric acid for producing tin coatings of a fine crystalline texture. Alkane suiphonic 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 US-A-2 522 942. More recently, methane suiphonic acid has been claimed as a specific preferred example of an alkane suiphonic 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 US-A-4 565 610 and US-A-4 617 097. Systems based on methane suiphonic 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 suiphonic acid (normally methane suiphonic 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 US-A-4 555 314, US-A- 4 565 609, US-A-4 582 576, US-A-4 599 149, US-A-4 617 097, US-A-4 666 999, US-A- 4 673 470, US-A-4 701 244, US-A-4 828 657 and US-A-4 849 059. Plating bath compositions containing mixtures of aryl and alkyl suiphonic 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 'TritonsX- 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-hydroxypheny1)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 US-A-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 that certain acids have a beneficial effect on the efficiency of the addition agents. Certain acids are capable of improving the addition agents performance at high current density whilst other acids are able to improve performance at low current density. When combined, synergistic effects are produced which give even wider plating ranges and bright plates, this synergistic effect is further enhanced when the acid combination is used in conjunction with specific additives. The electrolyte compositions of the present invention also have the advantage that lead salts are much less soluble therein, than in prior art electrolytes. Accordingly this invention provides a composition suitable for use in a process for electroplating surfaces with tin, which exhibits all the aforementioned benefits in wide plating range, good quality deposits and enhanced environmental benefits. It comprises : - a) An unsubstituted or substituted para alkyl benzenesulphonic acid. (component a) b) One or more acids capable of giving good plating at low current density (component b) c) One or more addition agents d) A tin source e) An antioxidant (optional) f) Water. Preferably the tin source is a tin salt. Alternatively the tin source may be elemental tin. The para alkyl benzene suiphonic acid has the formula: - Wherein R is an alkyl group preferably containing 1 - 10 carbon atoms and more preferably containing 1-4 carbon atoms. R' is hydrogen or an alkyl group containing 1 to 10 carbon atoms which may be substituted, for example, by hydroxyethyl or hydroxypropyl groups . The preferred para alkyl benzenesulphonic acid is para toluene suiphonic acid. The acid capable of enhancing plating at low current density (component b) may be any known to those skilled in the art. Preferred examples include ortho substituted benzenesulphonic acids, sulphuric acid, sulphamic acid, phenolsulphonic acid and methanesulphonic acid. Component b may be a single acid or a mixture of such acids. The acids (i.e. component a plus component jb) are preferably present in a total concentration of 25 - 500 g/1 of the composition (with respect to the composition) , more preferably 30 - 250g/l, even more preferably 30-100g/l. The preferred weight / weight ratio of component a to component b is from 90 /10 to 10 / 90. The tin source is preferably present in the composition at a concentration of 5 - 100 g/1 (more preferably 15 to 60g/l) with respect to the composition. Where a tin salt is the tin source it does not have to be a salt of the mono-substituted benzene suiphonic acid or inorganic acid. Thus the composition may contain ions other than tin, sulphonate and those from the inorganic acid. Where the tin source is solid tin, it may be as a tin anode which gradually dissolves as electrolysis proceeds to maintain a substantially constant concentration of tin ions in an electroplating bath. Where the tin source is a tin salt it may be metered to the electroplating bath so that as tin is electro-deposited from the bath, tin salt is added to the bath to maintain the concentration of tin ions in the bath at a constant level. An antioxidant may optionally be added. These materials retard the oxidation of divalent tin to tetravalent tin which may lead to sludge formation and stannous tin loss. The preferred amount of antioxidant to be added is in the range 1 to 50g/l of the composition and most preferably from 2.5 to 20g/l of the composition. Typical antioxidants have been described for example in US-A- 3 749 649 and include 1, 2, 3-trihydroxybenzene, 1, 2-dihydroxybenzene, 1,2- dihydroxybenzene-4-suiphonic acid, 1,2- dihydroxybenzene-3, 5-disulphonic acid, 1,4- dihydroxybenzene, 1, 4-dihydroxybenzene-2-suiphonic acid, 1, 4-dihydroxybenzene-2, 5-disulphonic acid or vanadium pentoxide. The composition of the present invention also comprises one or more addition agents capable of enhancing the synergistic effects of mixtures of component a and component b . Although any additive known to those skilled in the art may be used, preferred additives are mono-, di- and tri-substituted phenols. (each optionally alkoxylated) having at least one substituent containing at least one secondary tertiary or quaternary nitrogen atoms; or mixtures of two or more such components. The preferred phenols are 2,4- or 2,6- disubstituted or 2 , 4 , 6 , -trisubstituted phenols . Addition agents have the general formula: In which: - Y = alkylene, CH 2 CH 2 0 0 r CH(CH 3 )CH 2 0 n > = 0 - 10 Γ. ' = 1 when Y = al yicne R. - a grcuc of fαπnula. ■ R* (CHR 3 )-: 2 - • H in which: - R 3 = H, alkyl, aryl, hydroxyl or CHO, with the proviso that when R 3 is hydroxyl or CHO, n 2 =l-3, and when R 3 is H, alkyl or aryl, n 2 is 1, R 4 = H, alkyl, cycloalkyl, hydroxyalkyl or alkoxyalkyl, R 5 = alkyl, optionally interrupted by O or N atoms, which may be further substituted, X = a phenol (optionally alkoxylated) radical, optionally further substituted, n = 0 or 1, n 1 = 1 to 7, when n = 0, n 1 = 1, when n = 1, n 1 = 1-7. R may optionally be the quaternary ammonium salt formed by reaction with acids such as, sulphuric acid, toluenesulphonic acid, sulphamic acid, phenolsulphonic acid and methanesulphonic acid. R x and R 2 = (same or different) R, H or optionally substituted alkyl. Especially preferable examples include :- R 1= CH3 , CH 2 CH 3 . CH( CH 3 ) 2 or C( CH 3 ) 3 ; n=l-7 R - - CH -NHCH-CH,NHCH H 2 OH «' = -CH 3 . -CH H 3 or - C (CH 3)3 R 3 = H or R As will be known to those skilled in the art such additives can conveniently be made by condensation of the phenol with an aldehyde and an amine under acidic or basic conditions. The molar proportions of phenol to amine to aldehyde may be varied over a wide range, typically the range will be from 1:1:1 to 1:2:2. As will be obvious to those skilled in the art such reaction will give rise to a mixture of monomeric and polymeric products. The reaction products may be alkoxylated with either ethylene or propylene oxide. Although any phenol, amine and aldehyde may be used preferred examples include : - Phenols:- ortho and/or para alkylphenols, where the alkyl group is methyl, ethyl, isopropyl, n- butyl, sec-butyl, tert-butyl, isoamyl, hexyl, and nonyl; Diphenols : - 2, 2-bis (4-hydroxyphenyl) propane or 4,4' -dihydroxydiphenylsulphone. Aldehydes:- formaldehyde, acetaldehyde, glyoxal . Amines:- methylamine, dimethylamine, ethylamine, diethylamine, n- or iso-propylamine, n- or sec-butylamine, n-hexylamine, ethanolamine, diethanolamine, n- or iso-propanolamine, 2-aminobutanol, 4-aminobutanol, 2-amino-5-diethylaminopentane, 2- (2-aminoethoxy) ethanol, 2- (2aminoethylamino) ethanol, 2-amino-2-ethyl-1, 3-propandiol . The composition of this aspect of the invention demonstrates the aforementioned synergistic effect with respect to compositions which contain only acids of component a or acids of component J alone. The compositions of the present invention when used for tin plating provides a wider plating range than can be obtained by using either acids of component a or acids of component b alone. The preferred acid of component a is para toluenesulphonic acid and preferred acids of component b are ortho toluenesulphonic acid and sulphuric acid. The surfaces which can be tin-plated using the compositions and methods of the invention are those surfaces which may normally be tin-plated e.g. steel or copper. Examples Example 1 This example illustrates how the preferred addition agents may be synthesised using base catalysis . Substituted phenol (1 mole) , water ( equ i valent weight based on phenol) and sodium hydroxide ( 0.2 mole ) were charged to the reactor. The mixture was heated at 60°C with agitation until a clear solution was obtained. Amine ( 2 moles ) was charged into a second reactor and formaldehyde (2 moles) slowly added with stirring whilst keeping the temperature below 60°C. This solution was added to the -alkylphenol solution in this first reactor and the mixture heated at 1 00°C for half an hour. The following examples shown in Table 1 are illustrative of this method of synthesis. TABLE l EXAMPLE NUMBER PHENOL AMINE -METHYL PHENOL ETHANOLA INE 4-TERT BUTYL PHENOL 2- ( 2-A INOETHYLA INO) ETHAWOL 4 , 4 ' -ISOPROPYLIDENPIPHENOL DIETHANOLAMINE The electroplating characteristics of various compositions were determined in a Hull Cell at 3 amps total current for 1 minute at 45°C. A 10 cm x 6 cm steel plate, pre-cleaned by immersion in sodium hydroxide followed by a water rinse and immersion in 18.5% hydrochloric acid, was used in all the following examples . The aqueous compositions used are set out in Table 2, Examples 6, 11, 14, 16, 20 and 24 are according to the invention, whilst Examples 7, 8, 10, 12, 17, 18, 21, 22 and 23 illustrate the synergistic effect with respect to the plating range. Examples 5, 9, 15, 19 and 23 also illustrate the performance of the additives in the known phenol-4-suiphonic acid electrolyte for comparative purposes. All compositions, except the phenolsulphonic acid electrolytes of Examples 5, 9, 15, 19 and 23, included lg/1 of antioxidant (1, 2-dihydroxybenzene-4-suiphonic acid) . The tin source in all cases was tin sulphate in an amount of 30g/l calculated as Sn ** TABLE 2 All concentrations are in grams/litre of the composition including water. PTSA is para toluenesulphonic acid. OTSA is ortho toluenesulphonic acid. PSA is phenol-4-sulphonιc acid.

Claims: CLAIMS 1. A composition suitable for use in a process for electroplating surfaces with tin, comprising: - a) An unsubstituted or substituted para alkyl benzene suiphonic acid (component a) , b) One or more acids capable of giving good plating at low current density (component b) , c) One or more addition agents, d) A tin source, e) Water. 2. A composition as claimed in claim 1, wherein the tin source is a tin salt. 3. A composition as claimed in claim 1 or 2 , wherein the para alkyl benzene suiphonic acid has the formula: - SO3K Wherein R is an alkyl group containing 1 - 10 carbon atoms, R' is hydrogen or an alkyl group containing 1 to 10 carbon atoms which may be substituted, for example, by hydroxyethyl or hydroxypropyl groups . 4. A composition as claimed in any one of the preceding claims, wherein the para alkyl benzene suiphonic acid is para toluenesulphonic acid. 5. A composition as claimed in any one of the preceding claims, wherein the component is selected from ortho substituted benzenesulphonic acids, sulphuric acid, sulphamic acid, phenolsulphonic acid and methanesulphonic acid. 6. A composition as claimed in any one of the preceding claims, wherein the acids (i.e. component a plus component J ) are present in a total concentration of 25 - 500 g/1 of the composition (with respect to the composition) . 7. A composition as claimed in claim 6, wherein the acids are present in a total concentration of 30 - 250g/l. 8. A composition as claimed in claim 7, wherein the acids are present in a total concentration of 30 - lOOg/l. 9. A composition as claimed in any one of the preceding claims, wherein the weigh /weight ratio of component a to component b is 90/10 to 10/90. 10. A composition as claimed in any one of the preceding claims, wherein the tin source is present in the composition at a concentration of 5 - 100 g/1 with respect to the composition. 11. A composition as claimed in claim 10, wherein the tin source is present at a concentration of 15 to 60 g/1. 12. A composition as claimed in any one of the preceding claims, which also contains an antioxidant. 13. A composition as claimed in claim 12, wherein the amount of antioxidant added is in the range 1 to 50g/l of the composition. 14. A composition as claimed in claim 13, wherein the amount of antioxidant added is from 2.5 to 20g/l of the composition. 15. A composition as claimed in any one of the preceding claims, wherein the addition agents have the general formula: In which: - Y = alkylene, CH 2 CH 2 0 or CH(CH 3 )CH 2 0 α '=o-ιo α »_. l when Y- -ϋ-yteπe R-i rou offαrn-uia. in which: - R 3 = H, alkyl, aryl, hydroxyl or CHO, with the proviso that when R 3 is hydroxyl or CHO, n 2 =l-3, and when R 3 is H, alkyl or aryl n 2 is 1, R" = H, alkyl, cycloalkyl, hydroxyalkyl or alkoxyalkyl, R 5 = alkyl, optionally interrupted by 0 or N atoms, which may be further substituted, X = a phenol (optionally alkoxylated) radical, optionally further substituted n = 0 or 1 n 1 = 1 to 7 when n = 0, n 1 = 1 when n = 1, n 1 = 1-7, or R is the quaternary ammonium salt formed by reaction with acids such as, sulphuric acid, toluenesulphonic acid, sulphamic acid, phenolsulphonic acid and me hanesulphonic acid, and R L and R 2 which may be the same or different, are R, H or optionally substituted alkyl. 16. A composition as claimed in claim 15, wherein the one or more addition agents is selected from R 1 =CH 3 , CH 2 CH 3 , CH(CH 3 ) 2 or 0(0*3)3; n=l-7 R' R = -CH,NHCH 2 CH,NHCH,CH 2 OH R ' = -CH-. -CH 2 CH. or -C(CH 3)3 R 2 = H or R 17. A method of tin plating a surface, which comprises using a composition as claimed in any one of the preceding claims. 18. A method as claimed in claim 18, wherein said process is a strip or wire plating process. 19. A surface whenever tin-plated using a composition as claimed in any one of claims 1 to 14 and/or a method as claimed in claim 15 or 16.

Inventors: O'DRISCOLL CAVAN HUGH, O'DRISCOLL, CAVAN, HUGH
Applicants: DRISCOLL CAVAN HUGH O, YORKSHIRE CHEMICALS PLC, O'DRISCOLL, CAVAN, HUGH
Application year: 1996
Main classification: C25D3
IPC codes: C25D3