EP1137825A2

EP1137825A2 - Aqueous solution for electrodepositing tin-zinc alloys

Info

Publication number: EP1137825A2
Application number: EP99960973A
Authority: EP
Inventors: Manfred Jordan; Gernot Strube
Original assignee: Dr Ing Max Schloetter GmbH and Co KG
Current assignee: Dr Ing Max Schloetter GmbH and Co KG
Priority date: 1998-11-12
Filing date: 1999-11-12
Publication date: 2001-10-04
Anticipated expiration: 2019-11-12
Also published as: CZ20011633A3; PL194304B1; CN1195904C; PL348755A1; WO2000029645A2; KR20010086017A; DE59902696D1; JP4355987B2; CN1321205A; EP1137825B1; ATE223979T1; US20020046954A1; CZ296310B6; DE19852219C1; JP2002530528A; US6770185B2; WO2000029645A3; AU1775200A

Abstract

The invention relates to an aqueous solution comprising the following components: Zn(II) ions, Sn(II) ions, aliphatic carboxylic acids and/or their alkaline salts, anionic surfactants, non-ionogenic surfactants and optionally aromatic aldehydes, aromatic ketones, aromatic carboxylic acids and heterocyclic carboxylic acids or their alkaline salts or conducting salts. The inventive solution provides a means for electrodepositing uniform light-colored tin-zinc alloys without having to use cyanide ions, allowing low energy consumption and few requirements in terms of the control of the bath.

Description

^W ä ^ß ri e ^g solution elektrolytisc _h s _Ab sc _h ei _d ung of tin-zinc alloys.

The present invention relates to an aqueous solution for the deposition of tin-zinc alloys and in particular to an electroplating bath which enables the deposition of tin-zinc alloys from a cyanide-free tin (II) -zinc (II) solution with a simple bath control.

Products that are electroplated with a tin-zinc alloy are characterized by excellent corrosion resistance. In particular, the resistance to hydraulic fluid and aqueous salt solutions make products coated in this way appear interesting for the automotive industry. Products coated with tin-zinc alloys are also used in the broadcasting, electrical and construction industries due to their corrosion resistance and excellent solderability.

The electroplating baths that were common until now contained tin in the + iv oxidation state and cyanide ions. However, such electroplating baths have the disadvantage that a higher energy expenditure is required for the deposition of tin (IV) ions than for the deposition of tin (II) ions. In addition, the bath management involves the difficulty that when the anode is dissolved, which advantageously also consists of a tin-zinc alloy, the formation of tin (IV) ions must be promoted by forming a film by means of polarization. Furthermore, the thickness and composition of the deposited tin-zinc alloy depend on the current density and thus dependent on the geometry of the substrate. The toxicity of the cyanide ions also complicates industrial use.

The latter problem was solved in US 5,378,346 by replacing the cyanide ions with alkali tartrates as complexing agents. However, the problems arising from the use of tin (IV) ions are not solved here.

According to EP 0 663 460, an electroplating bath is known which allows the deposition of tin from the stage of the divalent tin, so that the required energy expenditure is reduced. The dependence of the speed and composition of the tin-zinc deposition on the current density was also reduced. However, the amphoteric surface-active surfactants proposed in this publication mean that the bath guidance remains critical and must be set and monitored very precisely in order to prevent dark and disturbed deposits.

It is therefore an object of the present invention to provide an electroplating bath solution for the deposition of tin-zinc alloys which does not contain cyanide, which enables a low energy consumption in the deposition by deposition of tin from a tin (II) ion solution, and the bath management thereof is uncritical over wide ranges of the freely selectable parameters and enables flawless and discoloration-free depositions.

The above object is achieved with an aqueous solution which, in addition to tin (II) and zinc (II) ions, contains aliphatic carboxylic acids and / or their alkali metal salts as complexing agents, and also a mixture of anionic and nonionic surfactants as grain refiners. In an advantageous embodiment, the aqueous solution according to the invention further contains aromatic aldehydes and / or aromatic ketones as brighteners. Aldehydes or ketones of the following formulas (I) or (II) are preferably used:

AR-R-CO-R '(I)

with AR = phenyl, naphthyl; R _ CH ₂ , CH = CH and R '= H, Cτ__ ₃ - alkyl;

with X = H, CH ₃ , OCH ₃ , Cl, Br.

A special, advantageous compound of formula (II) is o-Cl-benzaldehyde.

The pH of the solution is preferably 2-8, particularly preferably 3-5.

The tin (II) and zinc (II) ions are preferably used in the form of chlorides, sulfates or alkyl sulfonates.

If necessary, one or more conductive salts of the corresponding anions are additionally used. NH ₄ C1 and / or NH (CH ₃ S0 ₃ ) are preferred.

Preferred aliphatic carboxylic acids in the aqueous solution according to the invention are hydrocarboxylic acids and aminocarboxylic acids and particularly preferred is citric acid or its alkali salts.

The nonionic surfactants of the present invention preferably have the formula (III):

R-0- (C ₂ H ₄ 0) _n H (III)

with R = alkyl, aryl, alkylaryl; and n = 1-100. Particularly preferred is n = 6-15 and a total of 8-20 carbon atoms in the aryl radical.

In addition to these nonionic surfactants, thioethers or amines with the formulas (IV) and (V)

R * -S- (C ₂ H ₄ 0) _n H (IV)

R "-N [(C ₂ H4θ) _n H] 2 ⁽ V ⁾

with R '= Cτ__ ₃ -alkyl or - (C ₂ H ₄ 0) _n H and R "= C ₅ _ ₂ o- ^Alk y ^{1 with} n = 1 - 100, particularly preferably n = 6 - 15, as nonionic surfactants H (C ₂ H 0) _n -S- (C ₂ H ₄ 0) _n H with n = 8-12 and C ₁₂ H ₂₅ -N [(C ₂ H ₄ 0) _n H] are particularly advantageous. ₂ with n = 15 - 25.

Aliphatic or aromatic sulfonates are preferably used as anionic surfactants. In a preferred embodiment, one or more compounds of the formulas (VI) to (IX) are selected:

with R = C ₃ _ ₁₂ alkyl; X = H, -S0 ₃ M; M = Na, K, NH ₄ b ') R'-O- (C ₂ H ₄ O) _ιr -R'iSO ₃ M (VII)

with R '= C ₃ _ ₁₂ alkyl; R ^» = C ₂ _ ₅ alkyl; M = Na, K, NH ₄

with R "'= H, C-L_5-alkyl. 0- (C ₂ H ₄ 0) _n -X;

or and X = S0 ₃ with M = Na, K, NH ₄

with R " ¹ = H, C ₁ _ ₅ alkyl, 0- (C ₂ H ₄ 0) _n -X;

or and X = S0 ₃ M with M = Na, K, NH ₄ with n = 8 - 14.

A particularly preferred selection from the series above is the anionic surfactants according to the following formulas (X) to (XIII)

(XI)

C ₁₂ H25-O- (C2H4θ) nC ₃ H ₆ SO ₃ K

and

with n = 8 - 14.

Optionally, the electroplating bath for the deposition of zinc-tin alloys can also contain aromatic and / or heterocyclic carboxylic acids or their alkali salts according to formula (XIV)

R-COOM, it R = 'and M = H, Na, K, Ntt, _(XIV)

contain. Preferred embodiments of these carboxylic acids are nicotinic acid and / or Na benzoate.

^V orteilhafterweise be selected, the concentrations of the individual components within the following _ranges:

Zinc (II) ions 5 g / i to 50 g / 1, particularly preferably 20 g / 1 to 25 g / 1 tin (II) ions 0.5 g / 1 to 5 g / 1, particularly preferably ig / i to 3 g / 1 aliphatic carboxylic acids 30 g / 1 to 200 g / 1 particularly preferably 60 g / 1 to 140 g / 1 non-ionic surfactants

- According to formula (III) 0 g / 1 to 10 g / 1, particularly preferably o g / i to 2 g / i

- According to formula (IV) or (V) og / i to 10 g / 1, particularly preferably og / l to 2 g / 1, anionic surfactants 5 g / l to 30 g / 1, particularly preferably 10 g / l to 15 g / 1 aromatic aldehydes and / or aromatic ketones og / l to 0.5 g / 1 particularly preferably og / l to 0.2 g / 1 aromatic and / or heterocyclic carboxylic acids or their alkali metal salts 0.5 g / 1 to 10 g / 1 in particular preferably ig / i to 3 g / 1 conductive salts 10 g / 1 to 150 g / 1, particularly preferably 30 g / 1 to 70 g / 1

The present invention also includes the use of the aqueous solution described above for the deposition of tin Zinc coatings, in particular tin-zinc coatings with a zinc content of 10 to 50% by weight.

The invention is explained in more detail using the following exemplary embodiment.

An aqueous solution was prepared from the following components:

Citric acid 100 g / 1

NH ₄ C1 50 g / 1

NH ₄ 0H, 25% 90 g / 1

H ₃ B0 ₃ 30 g / 1

Sn ² + as Sn (CH ₃ S0 ₃ ) ₂ ³ ST ¹

ZnCl ₂ 33 g / 1

C ₁₂ H ₂ 5 -0- (C ₂ H ₄ O) n C ₃ H ₆ SO ₃ K ^{5 g / 1}

Nonyl - QV- ₀ - (C ₂ H ₄ θ) ₁₄ H 2 g / 1 Na benzoate 2 g / 1

Nicotinic acid 0.1 g / 1 o-Cl-benzaldehyde 0.05 g / 1

This solution was used to make a tin-zinc alloy with 30% zinc on one under the following conditions

Substrate surface with a thickness of 10 microns and deposited with a light gray color.

1 = 1 A / dm ² t = 20 min T = 40 ° C

The above result shows that the aqueous solution according to the invention can be used to deposit tin-zinc alloys of uniform thickness and composition with a uniform light color without the use of cyanide ions with low energy consumption.

Claims

claims

1. Aqueous solution for the electrolytic deposition of tin-zinc alloys, which comprises the following components ¹ :

a) Zn (II) ions; b) Sn (II) ions; c) aliphatic carboxylic acids and / or their alkali salts; d) anionic surfactants; e) nonionic surfactants.

2. Solution according to claim 1, wherein aromatic aldehydes and / or aromatic ketones are additionally included.

3. Solution according to claim 2, wherein the aromatic aldehydes and / or aromatic ketones have the formula (I)

AR-R-CO-R '(I)

have, where AR = phenyl, naphthyl; R = CH ₂ , CH = CH and R '= H, Cτ__ ₃ alkyl.

4. Solution according to claim 2, characterized in that the aromatic aldehydes have the formula (II)

with X = H, CH ₃ , OCH, Cl, Br.

5. Solution according to one of claims 1 to 4, wherein the solution has a pH of 2-8, in particular 3-5.

6. Solution according to one of claims 1 to 5, wherein the Sn (II) - and Zn (II) ions are present as chlorides, sulfates or alkyl sulfonates and optionally additional conductive salts of corresponding anions.

7. Solution according to one of claims 1 to 6, wherein the aliphatic carboxylic acids are hydroxycarboxylic acids and / or A inocarboxylic acids or their alkali metal salts.

8. Solution according to claim 7, wherein the carboxylic acids are citric acid or its alkali salts.

9. Solution according to one of claims 1 to 8, wherein the nonionic surfactants have the formula (III)

RO- (C ₂ H ₄ 0) _n H (III)

have, wherein R represents an alkyl, aryl, alkyl-aryl radical and n = 1 - 100.

10. Solution according to claim 9, wherein additionally nonionic surfactants of the formula (IV)

R'-S- (C ₂ H ₄ 0) _n H (IV)

and / or the formula (V)

R "N [(C ₂ H ₄ 0) _n H] ₂ (V)

are contained, wherein R '= C ₁ _ ₃ alkyl or - (C ₂ H ₄ 0) _n H;

^R "= ^c 5-20 ^_Alk y ^{1 and n} = 1-100. Solution according to one of claims 1 to 10, wherein the anionic surfactants contain one or more of the compounds of the formulas (VI) to (IX):

^a ' ^{) R- <} ö> - 0- (C ₂ H4θ) _n -SO ₃ M ^(VI >

with R = C ₃ _ ₁₂ alkyl; X = H, -S0 ₃ M; M = Na, K, NH ₄

b ¹ ) R'-O- (C2H4θ) n-R'iSθ ₃ M ⁽ VII ⁾

with R ^"= C ₃ _ ₁₂ alkyl; R "= C ₂ _ ₅ alkyl; M = Na, K, NH ₄

with R "'= H, Ci - ^ - alkyl, 0- (C ₂ H ₄ 0) _n -X; or

and X = S0 ₃ M with M = Na, K, NH

with R '" 0- (C ₂ H ₄ 0) _n -X; or and X = S0 ₃ M with M = Na, K, NH ₄ with n = 0-100, preferably 6-15.

12. Solution according to one of claims 1 to 11, wherein aromatic and / or heterocyclic carboxylic acids or their alkali metal salts are additionally contained.

13. Solution according to claim 12, wherein the carboxylic acids have the formula (XIV)

R-COOM, ^(χιv)

ώR = O'IQJ _' 0> JUJ and M = H, Na, K, NH4

exhibit.

14. Use of an aqueous solution according to one of claims 1 to 13 for the deposition of tin-zinc coatings.

15. Use of an aqueous solution according to claim 14 for the deposition of tin-zinc coatings with a zinc content of 10 to 50 wt .-%.