U.S. patent application number 13/003209 was filed with the patent office on 2011-07-21 for copper-tin electrolyte and process for the deposition of bronze layers.
This patent application is currently assigned to UMICORE GALVANOTECHNIK GMBH. Invention is credited to Sascha Berger, Klaus Bronder, Uwe Manz, Frank Oberst, Bernd Weyhmueller.
Application Number | 20110174631 13/003209 |
Document ID | / |
Family ID | 41258161 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110174631 |
Kind Code |
A1 |
Bronder; Klaus ; et
al. |
July 21, 2011 |
COPPER-TIN ELECTROLYTE AND PROCESS FOR THE DEPOSITION OF BRONZE
LAYERS
Abstract
Consumer goods and industrial articles are electroplated with
bronze layers for decorative purposes and for protection against
corrosion. The electrolytes used hitherto for producing decorative
bronze layers are cyanide-containing or, as in the case of baths
based on organosulfonic acids, highly corrosive, or, as in the case
of cyanide-free baths based on diphosphoric acid, give
unsatisfactory brightness and shine. The present invention provides
a nontoxic electrolyte for the electrochemical deposition of
uniformly bright and shiny bronze layers and a corresponding
process for the application of such decorative bronze layers to
consumer goods and industrial articles, by means of which
relatively thick bronze layers can also be deposited
electrochemically in a satisfactory way.
Inventors: |
Bronder; Klaus; (Schwaebisch
Gmuend, DE) ; Weyhmueller; Bernd; (Alfdorf
Hintersteinenberg, DE) ; Oberst; Frank; (Schwaebisch
Gmuend, DE) ; Berger; Sascha; (Schwaebisch Gmuend,
DE) ; Manz; Uwe; (Aalen, DE) |
Assignee: |
UMICORE GALVANOTECHNIK GMBH
Schwaebisch Gmuend
DE
|
Family ID: |
41258161 |
Appl. No.: |
13/003209 |
Filed: |
July 6, 2009 |
PCT Filed: |
July 6, 2009 |
PCT NO: |
PCT/EP2009/004879 |
371 Date: |
March 30, 2011 |
Current U.S.
Class: |
205/236 |
Current CPC
Class: |
C25D 3/58 20130101 |
Class at
Publication: |
205/236 |
International
Class: |
C25D 3/56 20060101
C25D003/56 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2008 |
DE |
10 2008 032 398.5 |
Claims
1. A nontoxic electrolyte for the deposition of decorative bronze
alloy layers on consumer goods and industrial articles, which
contains the metals to be deposited in the form of water-soluble
salts, wherein the electrolyte comprises one or more phosphonic
acid derivatives as complexing agents and a brightener system
composed of a disulfide compound and a carbonate or
hydrogencarbonate salt.
2. The electrolyte as claimed in claim 1, wherein, it contains the
metal ions of copper and tin or copper, tin and zinc to be
deposited.
3. The electrolyte as claimed in claim 2, wherein the water-soluble
salts of the metals to be deposited are selected from the group
consisting of pyrophosphates, carbonates, hydroxide-carbonates,
hydrogencarbonates, sulfites, sulfates, phosphates, nitrites,
nitrates, halides, hydroxides, oxide-hydroxides, oxides and
combinations thereof.
4. The electrolyte as claimed in claim 1, wherein the metals to be
deposited are present in dissolved form, with the ion concentration
of copper being in the range from 0.2 to 10 gram per liter of
electrolyte, the ion concentration of tin being in the range from
1.0 to 30 gram per liter of electrolyte and the ion concentration
of zinc, if present, being in the range from 1.0 to 20 gram per
liter of electrolyte.
5. The electrolyte as claimed in claim 1, wherein it comprises, as
carbonate or hydrogencarbonate salt, a salt of this type selected
from the group consisting of alkali metal and alkaline earth metal
salts.
6. The electrolyte as claimed in claim 5, wherein the carbonate or
hydrogencarbonate ions are present in an amount of 0.5-100 g/l of
electrolyte.
7. The electrolyte as claimed in claim 1, wherein it comprises, as
disulfide compound, a compound of this type selected from the group
consisting of substituted and unsubstituted bisalkyl or
bis(hetero)aryl or alkyl (hetero)aryl disulfides.
8. The electrolyte as claimed in claim 7, wherein the disulfide
compound is present in the electrolyte in an amount of 0.01
mg/l-10.0 g/l.
9. The electrolyte as claimed in claim 1, wherein it contains, as
phosphonic acid derivatives, one or more compounds selected from
the group consisting of 1-aminomethylphosphonic acid AMP,
aminotris(methylenephosphonic acid) ATMP, 1-aminoethylphosphonic
acid AEP, 1-aminopropylphosphonic acid APP,
(1-acetylamino-2,2,2-trichloroethyl)phosphonic acid,
(1-amino-1-phosphonooctyl)phosphonic acid,
(1-benzoylamino-2,2,2-trichloroethyl)phosphonic acid,
(1-benzoylamino-2,2-dichlorovinyl)phosphonic acid,
(4-chlorophenylhydroxymethyl)phosphonic acid,
diethylenetriamine-penta(methylenephosphonic acid) DTPMP,
ethylenediaminetetra(methylenephosphonic acid) EDTMP,
1-hydroxyethane(1,1-di-phosphonic acid) HEDP,
hydroxyethylaminodi(methylenephosphonic acid) HEMPA,
hexamethylenediaminetetra(methylphosphonic acid) HDTMP,
((hydroxymethylphosphonomethylamino)methyl)phosphonic acid,
nitrilotris(methylenephosphonic acid) NTMP,
2,2,2-trichloro-1-(furan-2-carbonyl)amino-ethylphosphonic acid,
salts derived therefrom and condensates derived therefrom, or
combinations thereof.
10. The electrolyte as claimed in claim 1, wherein the pH of the
electrolyte is in the range from 6 to 14.
11. The electrolyte as claimed in claim 1, wherein pyrophosphate
ions are present in the electrolyte.
12. The electrolyte as claimed in claim 1, wherein one or more
stabilizing compounds selected from the group consisting of
monocarboxylic and dicarboxylic acids, alkanesulfonic acids,
betaines and aromatic nitro compounds are present.
13. A process for the electrochemical application of decorative
bronze alloy layers to consumer goods and industrial articles, in
which the substrates to be coated are dipped into an electrolyte
containing the metals to be deposited in the form of water-soluble
salts, wherein a nontoxic electrolyte as claimed in claim 1 is
used.
14. The process as claimed in claim 13, wherein the electrolyte is
maintained in the range from 20 to 70.degree. C. during deposition
of the metals.
15. The process as claimed in claim 13, wherein a current density
in the range from 0.01 to 100 ampere per square decimeter is set.
Description
[0001] The invention relates to a copper-tin electrolyte which is
free of toxic constituents such as cyanides. In particular, the
invention relates to a corresponding electrolyte having a novel
brightener system. It likewise encompasses a process for the
deposition of decorative, white and yellow bronze layers on
consumer goods and industrial articles using the electrolyte of the
invention.
[0002] Consumer goods or consumer articles as defined in the
consumer articles regulations are finished with thin,
oxidation-stable metal layers for decorative reasons and in order
to prevent corrosion. These layers have to be mechanically stable
and should not display any tarnishing or signs of wear even after
prolonged use. Since 2001, the sale of consumer goods coated with
nickel-containing finishing alloys has no longer been permitted, or
is possible only with observance of strict conditions, in Europe
pursuant to EU directive 94/27/EC since nickel and
nickel-containing metal layers are contact allergens. Bronze alloys
in particular have become established as a replacement for
nickel-containing finishing layers and these enable such
mass-produced consumer goods to be finished inexpensively in barrel
or rack electroplating processes to give allergen-free, attractive
products.
[0003] In the production of bronze layers for the electronics
industry, the solderability of the resulting layer and, if
appropriate, its mechanical adhesive strength are the critical
properties of the layer to be produced. For use in this field, the
appearance of the layers is generally less important than their
functionality. On the other hand, for production of bronze layers
on consumer goods, the decorative effect (shine and brightness) and
also a long service life of the resulting layer with an essentially
unchanged appearance are the important target parameters.
[0004] Apart from the conventional processes for producing bronze
layers, which use cyanide-containing and thus highly toxic,
alkaline baths, various electroplating processes which can,
according to the composition of their electrolytes, usually be
assigned to one of two main groups found in the prior art are also
known: processes using electrolytes based on organosulfonic acids
or processes using baths based on diphosphoric acid (pyrophosphoric
acid). For the purposes of the present text, "nontoxic" means that
the electrolytes according to the invention described in this way
do not contain any materials which are classified as "toxic" (T) or
"very toxic" (T.sup.+) according to the regulations applicable in
Europe for handling dangerous goods and hazardous materials.
[0005] For example, EP 1 111 097 A2 describes an electrolyte
comprising an organosulfonic acid and ions of tin and copper
together with dispersants and brightening additives and also, if
appropriate, antioxidants. EP 1 408 141 A1 describes a process for
the electrochemical deposition of bronzes, in which an acidic
electrolyte comprising tin and copper ions together with an
alkylsulfonic acid and an aromatic, nonionic wetting agent. DE 100
46 600 A1 describes an alkylsulfonic or alkanolsulfonic
acid-containing bath which comprises soluble tin and copper salts
together with organic sulfur compounds, and a process using this
bath.
[0006] A significant disadvantage of such electrolytes produced on
the basis of organosulfonic acids is their high corrosivity. For
example, baths based on methanesulfonic acids frequently have pH
values below one. The high corrosivity of these baths limits their
use range in respect of the substrate materials to be finished and
requires the use of particularly corrosion-resistant working
materials for carrying out the process.
[0007] EP 1 146 148 A2 describes a cyanide-free copper-tin
electrolyte based on diphosphoric acid, which in addition to the
reaction product of an amine and an epihalohydrin in a molar ratio
of 1:1 contains a cationic surfactant. WO 2004/005528 describes a
cyanide-free diphosphoric acid-copper-tin electrolyte which
contains an additive composed of amine derivative, an epihalohydrin
and a glicidyl ether compound. Electrolytes based on diphosphoric
acid generally have very limited long-term stabilities and have to
be renewed frequently.
[0008] In addition, processes for producing solderable copper-tin
layers which can be used as replacement for tin-lead solders and in
which a wide selection of acidic base electrolytes can be used are
known from the electronics industry. Thus, EP 1 001 054 A2
describes a tin-copper electrolyte which comprises a water-soluble
tin salt, a water-soluble copper salt, an inorganic or organic acid
or a water-soluble salt thereof and also one or more compounds from
the group consisting of generally toxic thiourea or thiol
derivatives. The inventive bath described there can additionally
contain one or more compounds selected from the group consisting of
carboxylic acids, lactones, phosphoric acid condensates, phosphonic
acid derivatives or water-soluble salts of these or combinations
thereof.
[0009] WO2004/005528 describes a cyanide-free diphosphoric
acid-copper-tin electrolyte which contains an additive composed of
an amine derivative, an epichlorohydrin and a glycidyl ether
compound in a molar ratio of 1:0.5-2:0.1-5. It was an object of
this document to further widen the current density range in which
uniform deposition of the metals in a shiny layer can be achieved.
It is explicitly mentioned that such deposition can only be
attained when the additive added is made up of all three of the
abovementioned components.
[0010] In view of the prior art just cited, it can be noted that
those deposition processes which ensure uniform deposition on
metals over a wide current density range and also use electrolytes
which appear economically and ecologically advantageous in terms of
their composition are particularly advantageous. Furthermore, a
successful electrolyte should allow uniformly bright and shiny
layers to be obtained, regardless of the thickness of the bronze
layer deposited.
[0011] It is therefore an object of the present invention to
provide an electrolyte which has long-term stability, is suitable
for appropriately advantageous deposition of mechanically stable
and decoratively advantageous bronze layers on consumer goods and
industrial articles and is free of toxic constituents. It is a
further object of the present invention to provide a process for
the application of decorative bronze layers to consumer goods and
industrial articles using such an electrolyte.
[0012] These objects and further objects which are not mentioned at
the present juncture but can be derived in an obvious way from the
prior art are achieved by specification of an electrolyte having
the features of the present claim 1 and its use in a deposition
process according to the invention as set forth in claim 13.
Preferred embodiments referring back to these claims are defined in
claims 2 to 12 and 14-15.
[0013] The provision of a nontoxic electrolyte for the deposition
of decorative bronze alloy layers on consumer goods and industrial
articles, which electrolyte contains the metals to be deposited in
the form of water-soluble salts and further comprises one or more
phosphonic acid derivatives as complexing agents and also a
brighter system composed of a disulfide compound and a carbonate or
hydrogencarbonate salt, completely surprisingly but nonetheless
advantageously achieves the stated objects. The inventive
electrolyte having a different composition than in the prior art
makes it possible to obtain excellent electrolytic deposits of
bronze layers. In particular, the good brightness and shine of the
bronze layers can be obtained independently of their thickness. The
alloy composition remains approximately constant over a wide
current density range, which is in no way suggested by the prior
art.
[0014] In the electrolyte of the invention, the metals copper and
tin or copper, tin and zinc to be deposited are present in
dissolved form as their ions. They are preferably introduced in the
form of water-soluble salts which are preferably selected from the
group consisting of pyrophosphates, carbonates,
hydroxide-carbonates, hydrogencarbonates, sulfites, sulfates,
phosphates, nitrites, nitrates, halides, hydroxides,
oxide-hydroxides, oxides or combinations thereof. Very particular
preference is given to the embodiment in which the metals are used
in the form of salts with ions selected from the group consisting
of pyrophosphate, carbonate, hydroxide-carbonate, oxide-hydroxide,
hydroxide and hydrogencarbonate. Which salts are introduced in
which amount into the electrolyte can determine the color of the
resulting decorative bronze layers and can be adjusted according to
customer requirements. The metals to be deposited are, as
indicated, present in ionically dissolved form in the electrolyte
for application of decorative bronze layers to consumer goods and
industrial articles. The ion concentration of copper can be set in
the range from 0.2 to 10 g/l, preferably from 0.3 to 4 g/l, of
electrolyte, the ion concentration of tin can be set in the range
from 1.0 to 30 g/l, preferably 2-20 g/l, of electrolyte and, if
present, the ion concentration of zinc can be set in the range from
1.0 to 20 g/l, preferably 0-3 g/l, of electrolyte. For the
finishing of consumer goods, the metals to be deposited are
particularly preferably introduced as salt of a pyrophosphate,
carbonate, hydrogencarbonate or hydroxide-carbonate in such a way
that the resulting ion concentration is in the range from 0.3 to 4
gram of copper, from 2 to 20 gram of tin and from 0 to 3 gram of
zinc, in case per liter of electrolyte.
[0015] The electrolyte of the invention has some concentration of
carbonate or hydrogencarbonate ions. These can be present in the
electrolyte in the form of preferably soluble salts selected from
the group consisting of alkali metal and alkaline earth metal
salts, in particular sodium or potassium carbonate or sodium or
potassium hydrogencarbonate. However, the embodiment in which the
metals which are used and are to be deposited are also added either
completely or partly in the form of carbonates or
hydrogencarbonates to the electrolyte is preferred. The embodiment
in which only copper is present as carbonate in the bath
formulation is advantageous. Tin and zinc and also, during
operation of the bath, copper are then advantageously added as
pyrophosphate. Addition of the abovementioned salts enables a
concentration of carbonate or hydrogencarbonate ions in the
electrolyte of from 0.5 to 100 g/l of electrolyte to be set. The
concentration is particularly preferably in the range from 5 to 40
g/l and very particularly preferably from 15 to 30 g/l.
[0016] As further components of the electrolyte, mention may be
made of disulfide compounds. These can advantageously be selected
from the group consisting of substituted and unsubstituted bisalkyl
or bis(hetero)aryl or alkyl (hetero)aryl disulfides, in particular
those of the general formula (I),
R--S--S--R' (I)
wherein
[0017] R and R' can each be, independently of one another,
substituted or unsubstituted (C.sub.1-C.sub.8)-alkyl,
(C.sub.3-C.sub.6)-cycloalkyl, (C.sub.7-C.sub.19)-alkylaryl,
(C.sub.6-C.sub.18)-aryl, (C.sub.7-C.sub.19)-aralkyl,
(C.sub.3-C.sub.18)-heteroaryl, (C.sub.4-C.sub.19)-alkylheteroaryl,
(C.sub.4-C.sub.19)-heteroaralkyl. R and R' can also be joined to
form a ring. Possible substitutents for R and R' are in principle
all groups of substituents which a person skilled in the art would
consider for this purpose. These are, in particular, substituents
selected from the group consisting of amine radicals, nitro groups,
hydroxyl radicals, halide radicals, acid radicals such as
carboxylic acids, sulfonic acids and phosphonic acids.
[0018] Particularly advantageous disulfide compounds are compounds
selected from the group consisting of 2,2'-dithiodipyridine,
4,4'-dithiodipyridine, 6,6'-dithiodinicotinic acid,
bis(4-aminophenyl) disulfide, 2,2'-dithiosalicylic acid, D-cystine,
L-cystine, DL-cystine, 2,2'-dithio(bis)benzothiazole,
2,2'-dithiobis(5-nitropyridine). Very particular preference is
given in this context to the compound bis-(3-sodium sulfopropyl)
disulfide, referred to as SPS for short. The disulfide compounds
are preferably used in an amount of from 0.01 mg per liter to 10.0
g per liter of electrolyte. Particular preference is given to use
in a concentration range from 0.5 mg per liter to 7.5 g per liter
of electrolyte. The disulfide compound, in particular the
abovementioned SPS, is very particularly preferably used in a
concentration range from 0.1 mg per liter to 5 g per liter in the
electrolyte.
[0019] The application of the decorative bronze layers to consumer
goods and industrial articles using the electrolyte of the
invention is effected, as indicated, in an electroplating process.
It is important here that the metals to be deposited are kept
permanently in solution during the process, regardless of whether
electroplating is carried out in a continuous process or in a batch
process. To ensure this, the electrolyte of the invention contains
phosphonic acids as complexing agents.
[0020] Preference is given to using compounds selected from the
group consisting of hydroxyphosphonic, nitrilophosphonic or
aminophosphonic acid, e.g. 1-aminomethylphosphonic acid AMP,
aminotris(methylenephosphonic acid) ATMP, 1-aminoethylphosphonic
acid AEP, 1-aminopropylphosphonic acid APP,
(1-acetylamino-2,2,2-trichloroethyl)phosphonic acid,
(1-amino-1-phosphonooctyl) phosphonic acid,
(1-benzoylamino-2,2,2-trichloroethyl)phosphonic acid,
(1-benzoylamino-2,2-dichlorovinyl)phosphonic acid,
(4-chlorophenylhydroxymethyl)phosphonic acid,
diethylenetriaminepenta(methylenephosphonic acid) DTPMP,
ethylenediaminetetra(methylenephosphonic acid) EDTMP,
1-hydroxyethane(1,1-diphosphonic acid) HEDP,
hydroxyethylamino-di(methylenephosphonic acid) HEMPA,
hexamethylenediaminetetra(methylphosphonic acid) HDTMP,
((hydroxymethylphosphonomethylamino)methyl)phosphonic acid,
nitrilotris(methylenephosphonic acid) NTMP,
2,2,2-trichloro-1-(furan-2-carbonyl)amino ethylphosphonic acid,
salts derived therefrom and condensates derived therefrom, or
combinations thereof.
[0021] Particular preference is given to using one or more
compounds selected from the group consisting of
aminotris(methylenephosphonic acid) ATMP,
diethylenetriamine-penta(methylenphosphonic acid) DTPMP,
ethylenediaminetetra(methylenephosphonic acid) EDTMP,
1-hydroxyethane(1,1-diphosphonic acid) HEDP,
hydroxyethylamino-di(methylenephosphonic acid) HEMPA,
hexamethylenediaminetetra(methylphosphonic acid) HDTMP, salts
derived therefrom and condensates derived therefrom, or
combinations thereof. Preference is given to using from 10 to 400
gram of phosphonic acid derivatives per liter of electrolyte,
particularly preferably from 20 to 200 gram per liter of
electrolyte and very particularly preferably from 50 to 150 gram
per liter of electrolyte.
[0022] The pH of the electrolyte is in the range from 6 to 14
required for the electroplating application. Preference is given to
a range of 8-12 and very particular preference to about 10.
[0023] Apart from the metals to be deposited, the phosphonic acid
derivatives used as complexing agent and the brightener system
composed of hydrogencarbonate salt and disulfide compound which is
used, the electrolyte can contain further organic additives which
assume functions as complexing ligands, brighteners, wetting agents
or stabilizers. The electrolyte of the invention can also dispense
with the use of cationic surfactants. The addition of further
brighteners and wetting agents is only preferred in the case of the
appearance of the decorative bronze layers to be deposited having
to meet special requirements. They make it possible to adjust not
only the color of the bronze layers, which depends critically on
the ratio of the metals to be deposited, but also the shine of the
layers in all gradations from matt silk to high gloss.
[0024] Preference is given to adding one or more compounds selected
from the group consisting of monocarboxylic and dicarboxylic acids
and their salts, sulfonic acids and their salts, betaines and
aromatic nitro compounds. These compounds act as electrolyte bath
stabilizers. Particular preference is given to using oxalic acid,
alkanesulfonic acids, in particular methanesulfonic acid, or
nitrobenzotriazoles or mixtures thereof. Suitable alkanesulfonic
acids are disclosed, for example, in EP1001054.
[0025] As sulfonic acids, it can also be advantageous to use those
of the general formula (II) or salts thereof.
R--SO.sub.3H (II)
where
[0026] R is substituted or unsubstituted (C.sub.1-C.sub.8)-alkyl,
(C.sub.3-C.sub.6)-cycloalkyl, (C.sub.7-C.sub.19)-alkylaryl,
(C.sub.6-C.sub.18)-aryl, (C.sub.7-C.sub.19)-aralkyl,
(C.sub.3-C.sub.18)-heteroaryl, (C.sub.4-C.sub.19)-alkylheteroaryl,
(C.sub.4-C.sub.19)-heteroaralkyl. Possible substituents for R and
R' are in principle all groups of substituents which a person
skilled in the art would consider for this purpose. These are, in
particular, substituents selected from the group consisting of
amine radicals, nitro groups, hydroxyl radicals, halide radicals,
acid radicals such as carboxylic acids, sulfonic acids and
phosphonic acids. This applies analogously to the corresponding
salts, in particular salts with cations of the alkali metals or
alkaline earth metals.
[0027] Preferred compounds are those selected from the group
consisting of 3-mercapto-1-propanesulfonic acid Na salt,
3-(2-benzothiazolyl-2-mercapto)propanesulfonic acid Na salt,
saccharin-N-propylsulfonate Na salt, 3-sulfopropyl N,N-dimethyl
dithiocarbamate Na salt, 1-propanesulfonic acid and
3[(ethoxythioxomethyl)thio] K salt.
[0028] In this context, very particular preference is given to the
disulfide required for the brightener system and the sulfonic acid
being present in one compound, as is the case, for example, for
bis-(3-sodium sulfopropyl) disulfide.
[0029] It is also possible to use, for example, citric acid as
carboxylic acid (Jordan, Manfred, Die galvanische Abscheidung von
Zinn und Zinnlegierungen, Saulgau 1993, page 156). Betaines to be
used can preferably be found in WO2004/005528 or in Jordan, Manfred
(Die galvanische Abscheidung von Zinn und Zinnlegierungen, Saulgau
1993, page 156). Particular preference is given to those presented
in EP636713. Further additives may be found in the literature
(Jordan, Manfred, Die galvanische Abscheidung von Zinn und
Zinnlegierungen, Saulgau 1993).
[0030] Further complexing ligands which can advantageously be used
are pyrophosphate ions. These can be present in the electrolyte and
can advantageously be introduced into the electrolyte as anions of
the metal salts to be deposited. However, the embodiment in which
the pyrophosphate ions are added in the form of salts of other
metals, in particular of alkali and alkaline earth metals in the
electrolyte, is likewise possible. The amount of pyrophosphate ions
can be set in a precise manner by a person skilled in the art. It
is limited by the fact that the concentration in the electrolyte
should be above a minimum amount in order to be able still to bring
about the effect discussed to a sufficient extent. On the other
hand, the amount of pyrophosphate to be used is guided by economic
aspects. In this context, reference may be made to EP1146148 and
the relevant information presented there. The amount of
pyrophosphate to be used in the electrolyte is preferably 1-400
g/l. Particular preference is given to using an amount of 2-200 g/l
of electrolyte. The pyrophosphate can, if it is, as indicated, not
introduced as salt constituent of the metals to be deposited, be
used as sodium or potassium diphosphate or as H.sub.2P.sub.2O.sub.7
in combination with a base of the alkali or alkaline earth metals.
Preference is given to using K.sub.2P.sub.2O.sub.7 for this
purpose.
[0031] The electrolyte of the invention is free of hazardous
materials classified as toxic (T) or very toxic (T.sup.+). No
cyanides, no thiourea derivatives or similarly toxic materials are
present. The nontoxic electrolyte of the invention is particularly
suitable for the electrochemical application of decorative bronze
layers to consumer goods and industrial articles. It can be used in
barrel, rack, belt or reel to reel electroplating plants.
[0032] In a corresponding process for the electrochemical
application of decorative bronze alloy layers, the consumer goods
and industrial articles to be coated (hereinafter referred to
collectively as substrates) dip into the nontoxic electrolyte of
the invention and form the cathode. The electrolyte is preferably
maintained in the range from 20 to 70.degree. C. It is possible to
set a current density which is in the range from 0.01 to 100 ampere
per square decimeter [A/dm.sup.2] and depends on the type of
plating plant. In barrel plating plants, current densities in the
range from 0.05 to 0.75 A/dm.sup.2 are preferred, more preferably
from 0.1 to 0.5 A/dm.sup.2 and very particularly preferably about
0.3 A/dm.sup.2. In rack plating processes, current densities in the
range from 0.2 to 10.0 A/dm.sup.2 are preferably chosen,
particularly preferably from 0.2 to 5.0 A/dm.sup.2 and very
particularly preferably from 0.25 to 1.0 A/dm.sup.2.
[0033] Various anodes can be employed when using the nontoxic
electrolyte of the invention. Soluble or insoluble anodes are
suitable, as is the combination of soluble and insoluble
anodes.
[0034] As soluble anodes, preference is given to using anodes made
of a material selected from the group consisting of electrolytic
copper, phosphorus-containing copper, tin, tin-copper alloy,
zinc-copper alloy and zinc-tin-copper alloy. Particular preference
is given to combinations of different soluble anodes made of these
materials, and also combinations of soluble tin anodes with
insoluble anodes.
[0035] As insoluble anodes, preference is given to using anodes
made of a material selected from the group consisting of platinized
titanium, graphite, iridium-transition metal mixed oxide and
special carbon material ("Diamond Like Carbon", DLC) or
combinations of these anodes. Particular preference is given to
mixed oxide anodes composed of iridium-ruthenium mixed oxide,
iridium-ruthenium-titanium mixed oxide or iridum-tantalum mixed
oxide.
[0036] If insoluble anodes are used, this is a particularly
preferred embodiment of the process when the substrates to be
provided with decorative bronze layers, which represent the
cathode, are separated from the insoluble anode by an ion-exchange
membrane so as to form a cathode space and an anode space. In such
a case, only the cathode space is filled with the nontoxic
electrolyte of the invention. An aqueous solution containing only a
conductive salt is preferably present in the anode space. Such an
arrangement prevents the anodic oxidation of tin(II) ions Sn.sup.2+
to tin(IV) ions Sn.sup.4+, which would have an adverse effect on
the plating process.
[0037] In membrane processes which are operated using insoluble
anodes and the nontoxic electrolyte of the invention, current
densities in the range from 0.05 to 2 A/dm.sup.2 are preferably
set. The electrolyte is preferably maintained in the range from 20
to 70.degree. C. As ion-exchange membranes, it is possible to use
cationic or anionic exchange membranes. Preference is given to
using membranes composed of Nafion which have a thickness of from
50 to 200 .mu.m.
[0038] The disadvantage of additive-free phosphonate-based
copper-tin electrolytes is the restriction to a narrow current
density range and the lack of shine and the lower brightness of the
layers deposited. The novel brightener system avoids these
disadvantages in the phosphonate-based electrolyte system. Only
when the electrolyte of the invention is used is the deposition of
bright and shiny layers made possible over a wide current density
range. None of the known cyanide-free substitute processes
(pyrophosphate, phosphonate, alkylsulfonate) achieves the
properties of cyanide-containing baths (particularly in the case of
shine and brightness, also only to an extent). The use of the
brightener combination according to the invention for the first
time makes it possible to achieve the shine and brightness which is
comparable to the cyanide-containing electrolytes of the prior art
and is thus significantly better than in all known cyanide-free
substitute processes.
[0039] In addition, management of the bath is simpler in the case
of the electrolyte of the invention. The novel brightener system
enables the electrolyte to be operated at higher copper contents.
The combination of the compounds used, in particular those of the
brightener system comprising carbonate ions and disulfide
compounds, is critical here. In the presence of carbonate ions,
even very small amounts of organic disulfidates influence
copper-tin alloy formation. In contrast to additive-free baths, a
largely constant alloy composition is obtained over a wider current
density range as a result of the addition of the brightener system
(FIG. 1--comparison of copper-tin electrolyte based on phosphonic
acid with and without brightener system). In the case of
additive-free baths, tin is deposited preferentially at higher
current densities, which leads to a loss of shine of the
layers.
[0040] For the purposes of the invention, (C.sub.1-C.sub.8)-alkyl
is an alkyl radical having from 1 to 8 carbon atoms. This can be
branched as desired or in the case of (C.sub.3-C.sub.6)-cycloalkyl
be cyclic. This is, in particular, radicals such as methyl, ethyl,
propyl, isopropyl, butyl, sec-butyl, isobutyl, pentyl, hexyl,
cyclopropyl, cyclopentyl, cyclohexyl etc.
[0041] (C.sub.8-C.sub.18)-Arryl is an aromatic system which is made
up entirely of from 6 to 18 carbon atoms. This is, in particular,
selected from the group consisting of phenyl, naphthyl, anthracenyl
etc.
[0042] (C.sub.7-C.sub.19)-Alkylaryl radicals are radicals which
have a (C.sub.1-C.sub.8)-alkyl radical on the
(C.sub.6-C.sub.18)-aryl radical.
[0043] (C.sub.7-C.sub.19)-Aralkyl radicals are radicals which have
a (C.sub.6-C.sub.18)-aryl radical on a (C.sub.1-C.sub.8)-alkyl
radical, via which the radical is bound to the molecule
concerned.
[0044] According to the invention, a (C.sub.3-C.sub.18)-heteroaryl
radical is an aromatic system which has at least three carbon
atoms. In addition, further heteroatoms are present in the aromatic
system. These are preferably nitrogen and/or sulfur. Such
heteroaromatics are described, for example, in the book
Bayer-Walter, Lehrbuch der Organischen Chemie, S. Hirzel Verlag,
22nd edition, p. 703 ff.
[0045] For the purposes of the invention,
(C.sub.4-C.sub.19)-alkylheteroaryl is a
(C.sub.3-C.sub.18)-heteroaryl radical which is supplemented by a
(C.sub.1-C.sub.8)-alkyl substituent. The bonding to the molecule
under consideration is via the heteroaromatic here.
[0046] Conversely, (C.sub.4-C.sub.19)-heteroaralkyl is a
(C.sub.3-C.sub.18)-heteroaryl which is bound to the molecule
concerned via a (C.sub.1-C.sub.8)-alkyl substituent.
[0047] For the purposes of the invention, halide encompasses
chloride, bromide and fluoride.
[0048] The examples described below and the comparative example
illustrate the invention.
[0049] Alkyl(hetero)aryl is alkylaryl and alkylheteroaryl.
EXAMPLES
[0050] Comparison of brightness values for phosphonate electrolyte
with and without brightener system (in L units according to the
Cie-Lab method [http://www.cielab.de])
TABLE-US-00001 L*-values Current Current density density Current
density 0.05 A/dm.sup.2 0.1 A/dm.sup.2 0.2 A/dm.sup.2 Phosphonate
electrolyte 79.5 81.5 81.9 "without brightener system" Phosphonate
electrolyte 83.5 83.5 83.8 "with brightener system"
[0051] The formation of dark streaks is significantly suppressed.
Furthermore, the quality of the layer is maintained even in the
case of thick deposits.
[0052] An insoluble platinum-titanium anode was used in all
experiments described.
Example 1
General Procedure
[0053] Barrel deposition of white bronze layers was carried out
using a nontoxic electrolyte according to the invention containing
100 g/l of ethylenediaminetetra(methylenephosphonic acid) EDTMP,
1.5 g/l of copper as copper hydroxide carbonate, 5 g/l of tin as
tin pyrophosphate, 2 g/l of zinc as zinc pyrophosphate, 10 ml/l of
methanesulfonic acid (70%), 20 g/l of potassium hydrogencarbonate
and 10 mg/l of bis(3-sodium sulfopropyl) disulfide.
[0054] During the entire deposition procedure, the electrolyte was
maintained at 50.degree. C. At a set current density of from 0.05
to 0.5 A/dm.sup.2, optically uniform, high-shine bronze layers
having the color typical of white bronze were obtained in a drum
plating apparatus.
Example 2
80 g/l of HEDP
[0055] 50 ml/l of methanesulfonic acid (70%) 10 g/l of potassium
carbonate 30 mg/l of 2,2'-dithiodipyridine 1.47 g/l of copper
pyrophosphate 10.2 g/l of tin pyrophosphate 2.5 g/l of zinc
pyrophosphate Parameters: pH 8.0/40.degree. C./current densities:
0.05-0.5 A/dm.sup.2
Example 3
200 g/l of HEMPA
[0056] 5 ml/l of propanesulfonic acid 2 g/l of potassium
hydrogencarboonate 25 mg/l 2,2'-dithiodipyridine 1.47 g/l of copper
pyrophosphate 10.2 g/l of tin pyrophosphate 1.5 g/l of zinc
pyrophosphate 10 g/l citric acid Parameters: pH 11.0/25.degree.
C./current densities: 0.05-0.5 A/dm.sup.2
Example 4
50 g/l of ATMP
[0057] 100 g/l of potassium pyrophosphate 20 g/l of citric acid 4.2
g/l of copper hydroxide carbonate 8.66 g/l of tin pyrophosphate 4.5
g/l of zinc pyrophosphate 10 g/l of potassium hydrogencarbonate 0.5
g/l of 6,6'-dithiodinicotinic acid Parameters: pH 9.0/60.degree.
C./current densities: 0.05-0.5 A/dm.sup.2
Example 5
Yellow Bronze
150 g/l of EDTMP
[0058] 10 ml/l of methanesulfonic acid (70%) 20 g/l of potassium
carbonate 9 g/l of copper hydroxide carbonate 8.66 g/l of tin
pyrophosphate 5.5 g/l of zinc pyrophosphate 15 mg/l of bis(3-sodium
sulfopropyl) disulfide Parameters: pH 10/60.degree. C./current
densities 0.05-0.5 A/dm.sup.2
* * * * *
References