U.S. patent application number 12/308615 was filed with the patent office on 2010-09-23 for aqueous,alkaline,cyanide-free bath for the galvanic deposition of zinc and zinc alloy coatings.
This patent application is currently assigned to Atotech Deutschland GmbH. Invention is credited to Heiko Brunner, Ellen Habig, Lars Kohlmann, Konstantin Thom, Roland Vogel.
Application Number | 20100236936 12/308615 |
Document ID | / |
Family ID | 37395875 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100236936 |
Kind Code |
A1 |
Brunner; Heiko ; et
al. |
September 23, 2010 |
Aqueous,alkaline,cyanide-free bath for the galvanic deposition of
zinc and zinc alloy coatings
Abstract
The invention relates to an aqueous, alkaline cyanide-free
electrolyte bath for de-positing zinc and zinc alloy coatings on
substrate surfaces comprising (a) a source for zinc ions and
optionally a source for further metal ions, (b) hydroxide ions, (c)
a polymer of general formula I which is soluble in the bath and (d)
at least one pyridinium compound of general formula II or III. The
electrolyte bath is suitable for the galvanic deposition of bright
and even zinc and zinc alloy coatings. ##STR00001##
Inventors: |
Brunner; Heiko; (Berlin,
DE) ; Kohlmann; Lars; (Berlin, DE) ; Habig;
Ellen; (Berlin, DE) ; Thom; Konstantin;
(Berlin, DE) ; Vogel; Roland; (Berlin,
DE) |
Correspondence
Address: |
EDWARDS ANGELL PALMER & DODGE LLP
P.O. BOX 55874
BOSTON
MA
02205
US
|
Assignee: |
Atotech Deutschland GmbH
Berlin
DE
|
Family ID: |
37395875 |
Appl. No.: |
12/308615 |
Filed: |
June 21, 2007 |
PCT Filed: |
June 21, 2007 |
PCT NO: |
PCT/EP2007/005490 |
371 Date: |
February 9, 2009 |
Current U.S.
Class: |
205/244 ;
205/312 |
Current CPC
Class: |
C25D 3/22 20130101; C25D
3/565 20130101; C07D 213/82 20130101 |
Class at
Publication: |
205/244 ;
205/312 |
International
Class: |
C25D 3/56 20060101
C25D003/56; C25D 3/22 20060101 C25D003/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2006 |
EP |
06012766.9 |
Claims
1. Aqueous, alkaline, cyanide-free electrolyte bath for the
deposition of zinc and zinc alloy coatings on substrate surfaces,
which bath comprises the following components: a) a source of zinc
ions and, optionally, a source of further metal ions, b) hydroxide
ions, c) a polymer which is soluble in the bath of the general
formula I ##STR00009## wherein m represents an integer of 1 to 5, n
represents an integer greater than 1, R1, R2, R3, R4 may be the
same or different and each represents a substituted or
unsubstituted hydrocarbon residue having 1 to 6 carbon atoms or
--CH.sub.2CH.sub.2(OCH.sub.2CH.sub.2).sub.y--OH, wherein y lies
between 0 and 6, R5 represents (CH.sub.2).sub.p, wherein p
represents an integer of 2 to 12 or a
--(CH.sub.2).sub.2--O--(CH.sub.2).sub.2-- or
--(CH.sub.2).sub.2--O--(CH.sub.2).sub.2--O--(CH.sub.2).sub.2--
group and X.sup.- represents a counter ion, and d) at least one
pyridinium compound of general formula II or III ##STR00010##
wherein R.sub.1 represents a substituted or unsubstituted,
saturated or unsaturated, aliphatic or araliphatic hydrocarbon
residue having 1 to 12 carbon atoms, R.sub.1' represents a
divalent, substituted or unsubstituted, saturated or unsaturated,
aliphatic or araliphatic hydrocarbon residue having 1 to 12 carbon
atoms, X.sub.1 and X.sub.2 represent NR.sub.xR.sub.y, wherein
R.sub.x and R.sub.y may be the same or different and represent
hydrogen or linear or branched alkyl groups having 1 to 12 carbon
atoms, and Y.sup.- is a counter ion.
2. Electrolyte bath according to claim 1, wherein R.sub.1 in
formula II represents a substituted aryl residue of the following
formulae R1a to R1I: ##STR00011## ##STR00012## wherein FG
represents a residue selected from the group consisting of carboxy,
ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy,
hydroxy, trifluoromethyl, allyl, propargyl-, 4-sulfobutyl,
3-sulfopropyl, 4-carboxybutyl, 3-carboxypropyl residues, hydrogen
and halogens, selected from fluorine, chlorine and bromine wherein
all rings or individual fused rings may be substituted.
3. Electrolyte bath according to claim 1, wherein R.sub.1' in
formula III represents but-2-enyl, but-2-ynyl or an aryl residue of
the following formulae R.sub.1' a to R.sub.1'r: ##STR00013##
##STR00014## ##STR00015## wherein FG represents a residue selected
from the group consisting of carboxy, ester, sulfonic acid,
carbamoyl, amino, cyano, alkyl, alkoxy, trifluoromethyl residues,
hydrogen and halogens, selected from fluorine, chlorine and
bromine, wherein all rings or individual fused rings may be
substituted.
4. Electrolyte bath according to claim 1, wherein R.sub.1 in
Formula II and/or R.sub.1' in Formula III is/are bound to the
pyridinium residue via a methylene group.
5. Electrolyte bath according to claim 1, wherein Y.sup.- in
Formula II or III is a halide or pseudo-halide.
6. Electrolyte bath according to claim 1, wherein the polymer of
general formula I which is soluble in the bath is present in an
amount of 0.1 to 50 g/l.
7. Electrolyte bath according to claim 6, wherein the polymer of
general formula I which is soluble in the bath is present in an
amount of 0.25 to 10 g/l.
8. Electrolyte bath according to claim 1, wherein the at least one
pyridinium compound of formula II or III is present in an amount of
0.001 to 20 g/l.
9. Electrolyte bath according to claim 8, wherein the at least one
pyridinium compound of formula II or III is present in an amount of
0.001 to 10 g/l.
10. Electrolyte bath according to claim 1, containing a combination
of pyridinium compounds of formulae II and III.
11. Electrolyte bath according to claim 1, containing a combination
of different soluble polymers of general formula I.
12. Electrolyte bath according to claim 1, wherein the source of
zinc ions is zinc oxide or zinc hydroxide.
13. Electrolyte bath according to claim 1, wherein the
concentration of zinc ions is from 0.1 to 100 g/l.
14. Electrolyte bath according to claim 13, wherein the
concentration of zinc ions is from 0.1 to 30 g/l.
15. Electrolyte bath according to claim 1, wherein the further
metal ions are cobalt, nickel, manganese and/or iron ions.
16. Electrolyte bath according to claim 15, wherein the zinc is
present in an amount of 0.1 to 30 g/l and the cobalt is present in
an amount of 10 to 120 mg/l, the nickel is present in an amount of
0.3 to 3 g/l, the manganese is present in an amount of 10 to 100
g/l and/or the iron is present in an amount of 10 to 120 mg/l.
17. Electrolyte bath according to claim 1, containing alkali metal
hydroxide as base.
18. Electrolyte bath according to claim 17, wherein the alkali
metal hydroxide is lithium hydroxide, sodium hydroxide and/or
potassium hydroxide and is present in an amount of 50 to 250
g/l.
19. Electrolyte bath according to claim 1, wherein the pH of the
bath is at least 10.
20. Electrolyte bath according to claim 1, wherein the bath does
not contain additional brightening agents.
21. Electrolyte bath according to claim 1, containing a complexing
agent or a water-softening agent.
22. Electrolyte bath according to claim 21, wherein the complexing
agent is a chelate-forming agent.
23. Electrolyte bath according to claim 21, wherein the complexing
agent is present in an amount of 2 to 200 g/l.
24. Electrolyte bath according to claim 1, wherein the bath
contains a sulfur compound as leveling agent.
25. Electrolyte bath according to claim 24, wherein the leveling
agent contains 3-mercapto-1,2,4-triazole and/or thiourea.
26. Electrolyte bath according to claim 24, wherein the sulfur
compound is present in an amount of 0.01 to 0.50 g/l.
27. Process for the galvanic deposition of bright and even zinc and
zinc alloy coatings, comprising the step of immersing the substrate
to be coated into a bath according to claim 1.
28. Process according to claim 27, wherein the bath is operated at
a current density of 0.01 to 10 A/dm.sup.2.
29. Process according to claim 27, wherein the bath is operated at
a temperature of 15 to 50.degree. C.
30. Process according to claim 29, wherein the bath is operated at
a temperature of 25 to 35.degree. C.
31. Process according to claim 27, wherein the coatings are
deposited on a conductive substrate by using a drum electroplating
process.
32. Process according to claim 27, wherein the coatings are
deposited on a conductive substrate by using a rack electroplating
process.
33. Process according to claim 27, wherein a zinc coating is
deposited on the substrate.
34. Process according to claim 27, wherein a zinc alloy coating is
deposited on the substrate.
35. Process according to claim 34, wherein a coating of a zinc
alloy with one or more metals from the group consisting of cobalt,
nickel, manganese and/or iron is deposited on the substrate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an aqueous, alkaline
galvanic bath without addition of cyanide ions as complexing agents
for the deposition of zinc and zinc alloy coatings, which bath
contains as additives
bis-(N,N-diaminoalkyl)urea-.alpha.,.omega.-dihaloalkyl copolymers
or oligomers and 3-carbamoyl pyridinium compounds quaternized in
the 1-position. Furthermore, the invention relates to a process for
the deposition of bright and even zinc and zinc alloy coatings in
which the bath is used.
BACKGROUND OF THE INVENTION
[0002] The zinc deposition from cyanide-containing alkaline
solution has had a significant market share for many years.
However, increasingly stringent statutory requirements regarding
the disposal of used zinc and zinc alloy electrolyte baths and the
consequent strict control regarding waste water have resulted in
increased interest in cyanide-free zinc and zinc alloy
electrolytes.
[0003] Such metal coatings are used for improving corrosion
properties and for achieving certain optical properties. Thus, the
automotive industry has used electroplated zinc for decades in
order to provide highly corrosion-resistant coatings at reasonable
cost.
[0004] Cyanide-free zinc electrolytes and corresponding alloy baths
can be classified into two types of baths, namely weakly acidic
zinc electrolytes (containing zinc chloride or zinc sulfate) and
alkaline zinc electrolytes. Weakly acidic zinc baths result in the
deposition of a uniformly bright zinc layer. However, they have the
disadvantage that their current efficiency is always 100% across a
wide range of current densities. In the case of substrates having a
simple shape, this may be advantageous since the electric current
is used only for the deposition of zinc. However, in the case of
substrates having a complex geometry, this results in excessively
thick zinc layers in areas of high current density and to thin zinc
layers in areas of low current density.
[0005] The ratio of the zinc layer thickness in the area of high
current density to the zinc layer thickness in the area of low
current density is referred to as layer thickness distribution and
should ideally be 1 (scattering coefficient). From a technical and
functional point of view, the zinc layer on the substrate should
have the same or approximately the same layer thickness across the
entire substrate and should have high brightness.
[0006] A good layer thickness distribution may be achieved by
lowering the current efficiency in the area of high current density
while the current efficiency is maintained in the area of low
current density. So far, this kind of equalizing the zinc layer
thickness across a wide range of current densities has been
achieved in the deposition of zinc from alkaline, cyanide-free
electrolytes.
[0007] Alkaline zinc electroplating baths are generally constituted
on the basis of an aqueous solution of zincate ions in the presence
of alkali metal hydroxides. DE 25 25 264 and U.S. Pat. No.
3,884,774 describe such electrolytes; however, the zinc layers
obtained according to these documents do not show a uniform layer
thickness distribution.
[0008] The state of the art contains numerous suggestions for
improving the layer thickness distribution by addition of suitable
additives.
[0009] Such additive systems are described in U.S. Pat. No.
5,405,523, U.S. Pat. No. 5,435,989, DE 19 50 9713 and U.S. Pat. No.
4,030,987.
[0010] EP 1 114 206 B1 describes a formulation consisting of
quaternary derivatives of pyridinium-3-carboxylic acid, copolymers
consisting of N,N-bis-[3-(dialkylamino)-alkyl]ureas with
.alpha.,.omega.-dihaloalkanes and an aromatic aldehyde, which are
characterized in that the formation of bubbles frequently described
in connection of the deposition of zinc can be avoided. Further
copolymers of the aforementioned type are described in U.S. Pat.
No. 5,405,523, U.S. Pat. No. 5,435,898 and WO 2004/044269 A2. Apart
from the aforementioned ingredients, WO 2004/044269 A2 uses
reducing sugars in order to obtain bright depositions. A
disadvantage of this method is the high concentration of reducing
sugars which results in increased COD and TOC contents in the
effluent water.
[0011] The copolymers described in EP 1 114 206 B1, U.S. Pat. No.
5,405,523 and U.S. Pat. No. 5,435,898 are used as brightening
agents together with the commercially readily available quaternized
derivatives of nicotinic acid, in particular,
N-benzyl-nicotinate.
[0012] The use of 1-benzyl-3-carbamoyl-pyridinium-chloride for
cyanide-containing alkaline zinc electrolytes is described in
"Kinzoku Hyomen Gijutsu" (1980), 31, p. 244-248.
[0013] U.S. Pat. No. 4,071,418 describes a bath formulation
consisting of a quaternary pyridinium derivative and a cationic
copolymer of a diamine with 1,3-dihalopropane-2-ol.
[0014] Despite the aforementioned suggestions, the electroplating
industry still has, in view of increasingly stringent economic and
ecological requirements, a constant need for improved alkaline,
cyanide-free zinc and zinc alloy electrolytes which are
characterized, on one hand, by reduced amounts of additives and
improved layer thickness distribution as well as, on the other
hand, increased current efficiency and good brightness. Apart from
the aforementioned aspect of layer thickness distribution, in times
of steadily increasing energy costs, current efficiency plays an
important role since it is inversely proportional to investment and
operational costs.
DESCRIPTION OF THE INVENTION
[0015] It is the object of the invention to provide zinc and zinc
alloy electrolytes which result in zinc and zinc alloy layers
having high brightness and good or improved layer thickness
distribution at high current efficiency.
[0016] It has now been found that, by combination of the copolymers
known from EP 1 114 206 B1, U.S. Pat. No. 5,405,523 and U.S. Pat.
No. 5,435,898 with suitable brightening agents, it is possible to
obtain electrolytes resulting in the deposition of zinc and zinc
alloy layers with surprisingly improved layer thickness
distribution, improved brightness and increased current efficiency.
In particular, it has been found that the use of
pyridine-3-carboxylic acid amides as brightening agents results in
electrolyte compositions which are characterized by high
brightness, improved layer thickness distribution and increased
current efficiency.
[0017] Thus, the invention provides an aqueous, alkaline,
cyanide-free electrolyte bath for the deposition of zinc and zinc
alloy coatings on substrate surfaces, which bath comprises the
following components:
a) a source of zinc ions and, optionally, a source of further metal
ions, b) hydroxide ions, c) a polymer which is soluble in the bath
of the general formula I
##STR00002##
[0018] wherein [0019] m represents an integer of 1 to 5, preferably
2 to 5, or 1 to 4, more preferably 2 to 3, [0020] n represents an
integer greater than 1, preferably greater than 2, [0021] R1, R2,
R3, R4 may be the same or different and each represents a
substituted or unsubstituted hydrocarbon residue having 1 to 6
carbon atoms, preferably methyl, ethyl, hydroxyethyl or
--CH.sub.2CH.sub.2(OCH.sub.2CH.sub.2).sub.y--OH, wherein y lies
between 0 and 6, [0022] R5 represents (CH.sub.2).sub.p, wherein p
represents an integer of 2 to 12, preferably a methylene or
propylene group or a --(CH.sub.2).sub.2--O--(CH.sub.2).sub.2-- or
--(CH.sub.2).sub.2--O--(CH.sub.2).sub.2--O--(CH.sub.2).sub.2--
group and [0023] X.sup.- represents a counter ion, preferably
halide or pseudo-halide; and d) at least one pyridinium compound of
general formula II or Ill
##STR00003##
[0024] wherein [0025] R.sub.1 represents a substituted or
unsubstituted, saturated or unsaturated, aliphatic or araliphatic
hydrocarbon residue having 1 to 12 carbon atoms, [0026] R.sub.1'
represents a divalent, substituted or unsubstituted, saturated or
unsaturated, aliphatic or araliphatic hydrocarbon residue having 1
to 12 carbon atoms, [0027] X.sub.1 and X.sub.2 represent
NR.sub.xR.sub.y, wherein R.sub.x and R.sub.y may be the same or
different and represent hydrogen or linear or branched alkyl groups
having 1 to 12 carbon atoms, and [0028] Y.sup.- is a counter
ion.
[0029] In a preferred embodiment, R.sub.1 in formula II represents
substituted aryl of the following formulae R1a to R1I:
##STR00004## ##STR00005##
wherein FG represents a residue selected from the group consisting
of carboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl,
alkoxy, hydroxy, trifluoromethyl, allyl, propargyl-, 4-sulfobutyl,
3-sulfopropyl, 4-carboxybutyl, 3-carboxypropyl residues, hydrogen
and halogens, selected from fluorine, chlorine and bromine, and
R.sub.1' in formula III represents but-2-enyl, but-2-ynyl or aryl
of the following formulae R1'a to R1' r:
##STR00006## ##STR00007## ##STR00008##
wherein FG represents a residue selected from the group consisting
of carboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl,
alkoxy, trifluoromethyl residues, hydrogen and halogens, selected
from fluorine, chlorine and bromine, wherein all rings or
individual fused rings may be substituted.
[0030] Preferably, residues R.sub.1 and R.sub.1' in formulae II and
III are bonded to the pyridinium residue via a methylene group.
[0031] Preferred araliphatic hydrocarbon residues are, for example,
benzyl (R1a) and naphthyl methyl (R1b).
[0032] In the context of the present invention, fluorides,
chlorides and bromides may be used as halides. Furthermore, the
bath according to the invention may contain compounds, which are
similar, with respect to their physical and chemical properties, to
the halides, i.e., so-called pseudo-halides. Such pseudo-halides
are known to the skilled person as such and are described, for
example, in Rompp-Lexikon, Chemie, 10.sup.th edition, page 3609. In
the context of the present invention, pseudohalides also comprise
residues such as mesitylate and triflate.
[0033] The soluble polymers of general formula I contained in the
bath may be obtained according to EP 1 114 206 B1 by reaction of
N,N-bis-[(dialkylamino)-alkyl]-ureas with
.alpha.,.omega.-dihaloalkanes. A particularly preferred copolymer
of this class is, apart from the compounds described in EP 1 114
206 B1, Mirapol.TM. WT available from Rhodia or Lugalvan.TM. P
available from BASF.
[0034] The polymer of formula I is contained in the bath according
to the invention preferably in an amount of 0.1 to 50 g/l, more
preferably 0.25 to 10 g/l. The bath may contain a combination of
different soluble polymers of general formula I.
[0035] The electroplating baths according to the invention contain
an inorganic alkaline component, preferably a hydroxide of an
alkali metal and, particularly preferably, sodium hydroxide,
potassium hydroxide and/or lithium hydroxide, in order to adjust
the pH of the bath to at least 10 and preferably to at least 11. To
this end, amounts of 50 to about 250 g/l, preferably 90 to 130 g/l
of the alkaline component may be used.
[0036] The electroplating baths according to the invention
generally contain zinc ions at concentrations ranging from about
0.1 to about 100 g/l, concentrations of 4 to 30 g/l being
preferred. The zinc ion may be present in the bath according to the
invention in the form of a soluble salt, for example zinc oxide,
zinc sulfate, zinc carbonate, zinc acetate, zinc sulfamate, zinc
hydroxide, zinc tartrate.
[0037] As alloying metal, the baths according to the invention
contain about 0.1 to 50 g/l of metal ions, suitable metal salts are
hydroxides, sulfates, carbonates, ammonium sulfates, sulfamates,
acetates, formates and halides, preferably chloride and bromide.
Suitable alloying metals are preferably cobalt, nickel, manganese
and/or iron. The concentration of the alloying metal ions in the
baths according to the invention may be varied across a wide range
and preferably is 0.01 to 100 g/l. Since different types of alloys
require different contents of alloying metals, for example in order
to improve protection against corrosion, this concentration varies
from metal ion to metal ion.
[0038] Preferably, the baths according to the invention contain
about 0.1 to 50 g/l of nickel ions as alloying metal. Suitable
nickel salts are nickel hydroxide, nickel sulfate, nickel
carbonate, ammonium nickel sulfate, nickel sulfamate, nickel
acetate, nickel formate and nickel halides.
[0039] In a preferred embodiment, the electrolyte bath contains
zinc in an amount of 0.1 to 30 g/l and cobalt in an amount of 10 to
120 mg/l, nickel in an amount of 0.3 to 3 g/l, manganese in an
amount of 10 to 100 g/l and/or iron in an amount of 10 to 120
mg/l.
[0040] The electrolyte baths according to the invention contain the
aforementioned aromatic heterocyclic nitrogen-containing compounds
of general formulae II and III for substantial improvement of
leveling and brightness properties of the deposited layers across a
wide range of current densities. Therefore, the compounds of
formulae II and III are hereinafter referred to as brightening
agent according to the invention.
[0041] Preferred compounds of formulae II and III are
1-benzyl-3-carbamoyl-pyridinium-chloride,
1-(2'-chloro-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(2'-fluoro-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(2'-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(2'-carboxy-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(2'-carbamoylbenzyl)-3-carbamoyl-pyridinium-chloride,
1-(3'-chloro-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(3'-fluoro-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(3'-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(3'-carboxy-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(3'-carbamoyl-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(4'-chloro-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(4'-fluoro-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(4'-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(4'-carboxy-benzyl)-3-carbamoyl-pyridinium-chloride,
1-(4'-carbamoylbenzyl)-3-carbamoyl-pyridinium-chloride, (1
`-methyl-naphthyl)-3-carbamoyl-pyridinium-chloride,
1-(1'methyl-naphthyl)-3-carbamoyl-pyridinium-bromide,
1-(1`-methyl-naphthyl)-3-carbamoyl-pyridinium-fluoride,
1,1'-(but-2-enyl)-3,3'-biscarbamoyl-bispyridinium-dichloride,
1,1'-(but-2-enyl)-3,3'-bis-carboxy-bispyridinium-dichloride,
1-allyl-3-carbamoyl-pyridinium-chloride,
1-allyl-3-carboxypyridinium-chloride,
1-propargyl-3-carbamoyl-pyridinium-chloride,
1,1'-(but-2-ynyl)-3,3'-bis-carbamoyl-bispyridinium-dichloride,
1,1'-(but-2-ynyl)-3,3'-bis-carboxy-bis-pyridinium-dichloride,
1,1'-(xylenyl)-3,3'-bis-carbamoyl-bis-pyridinium-dibromide,
1-(3'-sulfopropyl)-3-carbamoyl-pyridinium-betaine as well as the
corresponding bromides, fluorides, iodides and pseudo-halides (for
example, triflates, tosylates) of the aforementioned compounds.
[0042] The brightening agents can be readily prepared by reacting
the corresponding nicotinic acid amide derivatives with the
corresponding benzyl halides in a suitable solvent, such as
ethanol, propanol, iso-propanol, butanol, iso-butanol, methanol or
their mixtures, DMF, DMAc; NMP, NEP, in substance or in an aqueous
medium, while heating under normal or increased pressure. The
reaction times required range from 1 to 48 hours, depending on the
starting material used. In this connection, apart from conventional
sources of heat, a microwave oven may be used. The pyridinium
compounds obtained can either be used directly as the aqueous or
alcoholic reaction solution or they can be isolated after cooling
by filtration or by removal of the corresponding solvent. The
compounds can be purified by recrystallization from a suitable
solvent such as ethanol, precipitation or column
chromatography.
[0043] The bis-pyridinium compounds of general formula II can be
prepared according to U.S. Pat. No. 6,652,728.
[0044] The compounds of formula II or Ill can be used alone or as a
mixture at a concentration of 0.001 to 20 WI, preferably of 0.001
to 10 g/l. The bath may contain a combination of pyridinium
compounds of formulae II and III.
[0045] The baths according to the invention may be prepared
according to conventional methods, for example by adding the
specific amounts of the aforementioned components to water. The
amount of the basic component, such as sodium hydroxide, should be
sufficient to achieve the desired pH of the bath of at least 10 and
preferably above 11.
[0046] The baths according to the invention deposit a bright, even
and ductile zinc or zinc alloy layer at any conventional
temperature of about 15.degree. C. to 50.degree. C., preferably
20.degree. C. to 30.degree. C., more preferably about 25.degree. C.
At these temperatures, the baths according to the invention are
stable and effective over a wide range of current densities of 0.01
to 10 A/dm.sup.2, preferably 0.5 to 4 A/dm.sup.2.
[0047] The baths according to the invention can be used in
continuous or batch-wise mode and the components will have to be
replaced from time to time. The components of the bath can be added
alone or in combination. Moreover, depending on the type and the
properties of the zinc and the zinc alloy baths to which the
substances are added, they may be varied across a wide range.
[0048] Table 1 shows, according to a particularly preferred
embodiment, the influence with respect to the layer thickness (and
thus current efficiency), brightness and layer thickness
distribution in the electrolytes according to the invention for
deposition of a zinc layer (using 10.sup.4 mmol/l of pyridinium
compound and a polymeric additive according to Preparation Example
2.2 of EP 1 114 206 B1):
TABLE-US-00001 TABLE 1 Layer Layer thickness thickness Layer
[.mu.m] [.mu.m] thickness Ex. Pyridinium compound Brightness j =
3.0 A/dm.sup.2 j = 0.5 A/dm.sup.2 coefficient 1 1-benzyl-3-carboxy-
+++ 3.84 2.41 1.59 pyridinium-chloride* 2 1-benzyl-3-carbamoyl- +++
4.74 3.76 1.26 pyridinium-chloride 3 1-(4'-methoxy-benzyl)-3- +++
4.20 3.18 1.32 carbamoyl-pyridinium- chloride 4
1-(4'-trifluoromethyl-benzyl)- +++ 4.98 3.71 1.34
3-carbamoyl-pyridinium- chloride 5 1,1'-(xylenyl)-3,3'- ++ 4.80
3.18 1.51 biscarbamoyl-bispyridinium- chloride 6
1-(4'-chloro-benzyl)-3- +++ 4.20 3.15 1.33 carbamoyl-pyridinium-
chloride 7 1-benzyl-3-N,N- +++ 4.15 2.99 1.39 dimethylcarbamoyl-
pyridinium-chloride *Comparative Example according to Example 13 of
EP 1 114 206 B1
[0049] As Table 1 clearly shows, the novel electrolytes according
to the invention show markedly better layer thickness distributions
while the current efficiency is increased at the same time. In the
areas of both high and low current density, there are achieved
current efficiencies which are 10 to 30% (in the area of high
current density) or 30 to 50% (in the area of low current density)
higher compared to the classic pyridinium compound. Especially the
much higher current efficiencies in the area of low current density
are very interesting in connection with applications using drum
electroplating methods.
[0050] The formulation according to the invention of the
aforementioned pyridinium compounds (which are known from U.S. Pat.
No. 4,071,418) with the aforementioned copolymers of general
formula I results in unexpected advantageous properties of the
deposited layers. Table 2 shows these synergistic effects of the
electrolyte compositions according to the invention:
TABLE-US-00002 TABELLE 2 Layer Layer thickness thickness Layer
[.mu.m] [.mu.m] thickness Ex. Formulation Brightness j = 3.0
A/dm.sup.2 j = 0.5 A/dm.sup.2 coefficient 8 Formulation according
to +++ 4.9 3.7 1.32 the invention with 100 mg/l of
1-benzyl-3-carbamoyl- pyridinium-chloride 9 Formulation according
to + 5.4 2.3 2.35 Example 6 of U.S. Pat. No. 4,071,418 with 100
mg/l 1-benzyl-3- carbamoyl-pyridinium- chloride instead of sodium
nicotinate 10 Formulation according to + 6.1 3.3 1.85 Example 6 of
U.S. Pat. No. 4,071,418
[0051] As Table 2 shows, the formulations according to U.S. Pat.
No. 4,071,418 do achieve high current efficiencies at high current
density; however, both the brightness and the layer thickness
distribution coefficient obtained with these electrolytes are
significantly worse than with the formulations according to the
invention. Actually, the pyridinium compounds of general formula II
and III give worse results in combination with the cationic
polymers described in U.S. Pat. No. 4,071,418 than the classic,
widely used benzyl nicotinate.
[0052] A further advantage of the electrolytes according to the
invention, compared to the electrolyte of EP 1 114 206 B1 is the
surprisingly lower consumption of the quaternized nicotinamide
derivatives according to the invention, compared to the
N-benzyl-nicotinate. As Application Example 12 shows, the
consumption of pyridinium compounds acting as brightening agent in
the electrolytes according to the invention is significantly lower
and thus more economical than the conventionally used pyridinium
derivatives based on nicotinic acid.
[0053] Apart from the additives mentioned above, the baths
according to the invention may contain known levelling agents such
as 3-mercapto-1,2,4-triazole and/or thiourea, thiourea frequently
being preferred.
[0054] In principle, the electrolyte bath according to the
invention may contain additional brightening agents from the group
of sulphur compounds, aldehydes or bisulfite adducts thereof,
ketons, amines, polyvinyl alcohol, polyvinyl pyrrolidone, proteins
or reactions products of halohydrines with aliphatic or aromatic
amines, polyamines or heterocyclic nitrogen compounds and mixtures
thereof. As additional brightening agents, there may be used, in
particular, aromatic aldehydes from the group of
4-hydroxybenzaldehyde, 4-hydroxy-3-methoxy-benzaldehyde,
3,4-dimethoxy-benzaldehyde, 3,4-methylenedioxy-benzaldehyde,
2-hydroxy-benzaldehyde and mixtures as well as bisulfite adducts
thereof, in an amount of 0.001 to 1.0 g/l.
[0055] Surprisingly, it was found that, with the electrolytes
according to the invention, the conventional use of aromatic
aldehydes or their bisulfite adducts as additional brighteners, for
example 4-hydroxybenzylaldehyde, 4-hydroxy-3-methoxybenzaldehyde,
3,4-dimethoxybenzaldehyde, 3,4-methylenedioxybenzaldehyde,
2-hydroxybenzaldehyde or mixtures thereof as well as bisulfite
adducts thereof, is unnecessary.
[0056] In a preferred embodiment, the electrolyte bath according to
the invention thus contains no aromatic aldehydes or their
bisulfite adducts as additional brighteners, in particular, it
contains no 4-hydroxybenzylaldehyde,
4-hydroxy-3-methoxybenzaldehyde, 3,4-dimethoxybenzaldehyde,
3,4-methylenedioxybenzaldehyde or 2-hydroxybenzaldehyde or
bisulfite adduct thereof.
[0057] The electrolyte bath according to the invention may contain
a complexing agent or a water softening agent. The complexing agent
is preferably a chelate forming agent, which is preferably present
in an amount of 2 to 200 g/l.
[0058] The electrolyte bath according to the invention can also
contain, as leveling agent, a sulfur compound, for example,
3-mercapto-1,2,4-triazole and/or thiourea, preferably in an amount
of 0.01 to 0.50 g/l.
[0059] The aqueous, alkaline baths according to the invention can
generally be used for all types of substrates on which zinc and
zinc alloys can be deposited. Examples of suitable substrates are
soft steel, spring steel, chromium steel, chromiummolybdenum steel,
copper, copper/zinc alloys.
[0060] Therefore, the invention also provides a process for the
galvanic deposition of zinc and zinc alloy coatings on conventional
substrates, wherein the electrolyte bath according to the invention
is used. In the process according to the invention, the deposition
of coatings is preferably carried out at a current density of 0.01
A/dm.sup.2 to 10 A/dm.sup.2 and at a temperature in the range of 15
to 50.degree. C., preferably 20 to 30.degree. C., more preferably
about 25.degree. C.
[0061] The process according to the invention may be carried out,
for example, as barrel electroplating process when applied to small
pieces and as a rack electroplating process when applied to larger
pieces. The process involves the use of anodes, which may be
soluble, for example, zinc anodes, which may serve as zinc ion
source at the same time so that the zinc deposited on the cathode
is replaced by dissolution of zinc from the anode.
[0062] However, insoluble anodes (for example, platinized titanium
mixed oxide anodes) may also be used, in which case the zinc ions
and/or further metal ions removed from the electrolyte by
deposition of the alloy have to be added to the electrolyte in
other ways, for example by using a zinc dissolution container.
[0063] As generally possible in electroplating, the process
according to the invention, too, can be carried out with injection
of air, with or without agitation of the substrate, which has no
negative effects on the coatings obtained. In order to avoid or
reduce the oxidation of additives, the electrode regions may be
separated or membrane anodes may be used.
[0064] The current source may be a conventional rectifier or pulse
rectifier.
EXAMPLES
[0065] The following examples illustrate the invention, but the
invention is not limited thereto.
Preparation Example 1
Synthesis of
1-(4'-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride
[0066] In a 100 ml round-bottom flask with reflux condenser, 60 ml
of water, 9.2 g of nicotinic acid amide (98%) (0.0738 mol), 11.68 g
of 4-methoxybenzylchloride (99%) (0.07378 mol) are heated under
reflux for 24 hours. After completion of the reaction, the water is
removed in vacuo and the residue is taken up in 200 ml of ethanol
and heated under reflux for another hour. The reaction mixture is
then cooled to 4.degree. C. and the white solid obtained is removed
by filtration and dried in vacuo. This yielded 16.92 g of a white
solid (82.26% of the theoretical yield).
Preparation Example 2
Synthesis of
1-(4'-chloro-benzyl)-3-carbamoyl-pyridinium-chloride
[0067] In a 100 ml round-bottom flask with reflux condenser, 60 ml
of ethanol, 10 g of nicotinic acid amide (98%) (0.0802 mol), 13.05
g of 4-chloro-benzylchloride (99%) (0.0802 mol) are heated under
reflux for 24 hours. After completion of the reaction, the solid
residue is heated in an ethanol/methanol mixture for another 15
minutes and then cooled to 4.degree. C. The solid obtained is
removed by filtration and dried in vacuo. This yielded 18.82 g of a
white solid (82.87% of the theoretical yield).
Preparation Example 3
Synthesis of
1,1'-(xylenyl)-3,3'-bis-carbamoyl-bis-pyridinium-dichloride
[0068] In a 100 ml round-bottom flask with reflux condenser, 60 ml
of ethanol, 10 g of nicotinic acid amide (98%) (0.0802 mol), 7.16 g
of .alpha.,.alpha.'-dichloro-p-xylene (98%) (0.0401 mol) are heated
under reflux for 24 hours. After completion of the reaction, the
solid residue is heated in 200 ml of an ethanol/methanol mixture
for another 15 minutes and then cooled to 4.degree. C. The
resulting solid is removed by filtration and dried in vacuo. This
yielded 12.29 g of a white solid (73.13% of the theoretical
yield).
Preparation Example 4
Synthesis of
1-(4'-trifluoromethyl-benzyl)-3-carbamoyl-pyridinium-chloride
[0069] In a 100 ml round-bottom flask with reflux condenser, 80 ml
of water, 3.11 g of nicotinic acid amide (98%) (24.93 mmol), 4.95 g
of .alpha.-chloro-.alpha.,.alpha.,.alpha.-trifluoro-paraxylene
(98%) (24.93 mmol) are heated under reflux for 24 hours. After
completion of the reaction, the reaction mixture is concentrated in
vacuo and the resulting solid is dried in vacuo. This yielded 5.99
g of a white solid (75.82% of the theoretical yield).
Preparation Example 5
Synthesis of benzyl-3-carbamoyl-pyridinium-chloride
[0070] In a 100 ml round-bottom flask with reflux condenser, 60 ml
of ethanol, 10 g of nicotinic acid amide (98%) (0.0802 mol), 10.252
g of benzyl chloride (99%) (0.0802 mol) are heated under reflux for
24 hours. After completion of the reaction, the reaction mixture is
cooled to 4.degree. C. and the resulting solid is removed by
filtration and re-crystallized from 1 liter of ethanol. This
yielded 19.00 g of a white solid (95.33% of the theoretical
yield).
Preparation Example 6
Synthesis of
1-benzyl-3-N,N-dimethylcarbamoyl-pyridinium-chloride
[0071] Into a 50 ml round bottom flask with reflux condenser are
charged 1 g of pyridine-3-N,N-dimethyl-carboxylic acid amide (6.658
mmol), 0.841 g of benzylchloride (99%) (6.658 mmol) in 10 ml of DMF
and heated for 12 hours at 120.degree. C. After completion of the
reaction, the excess solvent is removed in vacuo and the crude
product is extracted for a prolonged time with water/ethyl acetate.
The resulting ethyl acetate phase is discarded and the aqueous
phase is concentrated in vacuo. The resulting solid is dried in oil
pump vacuum. This yielded 1.8 g of a caramel color product (97.7%
of the theoretical yield).
Application Example 1
Comparative Example according to EP 1 114 206 B1
[0072] An electrolyte having the following composition is used:
TABLE-US-00003 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 25 mg/l
1-benzyl-3-carboxy-pyridinium-chloride 1 g/l a polymeric additive
according to Preparation Example 2.2 of EP 1 114 206 B1 (amount
stated is relative to solid content)
[0073] 250 ml of the electrolyte are filled into a Hull cell. A
steel anode is used. The cathode sheet is coated for 15 minutes at
1 A. After completion of the reaction, the sheet is rinsed and
dried with compressed air. The measurement of layer thickness is
carried out at two points (3 cm from the bottom edge and 2.5 cm
from the right- and left-hand edge) at high (3 A/dm.sup.2) and low
current density (0.5 A/dm.sup.2).
[0074] The thickness layer coefficient is the ratio of the layer
thickness at high current density and the layer thickness at low
current density.
[0075] A very bright deposition with the following layer
thicknesses was obtained:
TABLE-US-00004 Layer Layer thickness [.mu.m] Layer thickness
[.mu.m] thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient +++ 3.84 2.41 1.59
Application Example 2
[0076] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00005 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 25 mg/l
1-benzyl-3-carbamoyl-pyridinium-chloride 1 g/l a polymeric additive
according to Preparation Example 2.2 of EP 1 114 206 B1 (amount
stated is relative to solid content)
A very bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00006 Layer Layer thickness [.mu.m] Layer thickness
[.mu.m] thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient +++ 4.74 3.76 1.26
Application Example 3
[0077] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00007 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 27.8 mg/l
1-(4'-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride 1 g/l a
polymeric additive according to Preparation Example 2.2 of EP 1 114
206 B1 (amount stated is relative to solid content)
A very bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00008 Layer Layer thickness [.mu.m] Layer thickness
[.mu.m] thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient +++ 4.20 3.18 1.32
Application Example 4
[0078] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00009 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 31.7 mg/l
1-(4'-trifluoromethyl-benzyl)-3-carbamoyl-pyridinium-chloride 1 g/l
a polymeric additive according to Preparation Example 2.2 of EP 1
114 206 B1 (amount stated is relative to solid content)
A very bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00010 Layer Layer thickness [.mu.m] Layer thickness
[.mu.m] thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient +++ 4.98 3.71 1.34
Application Example 5
[0079] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00011 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 41.9 mg/l
1,1'-(xylenyl)-3,3'-biscarbamoyl-bispyridinium-dichloride 1 g/l a
polymeric additive according to Preparation Example 2.2 of EP 1 114
206 B1 (amount stated is relative to solid content)
A very bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00012 Layer Layer thickness [.mu.m] Layer thickness
[.mu.m] thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient ++ 4.80 3.18 1.51
Application Example 6
[0080] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00013 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 28.3 mg/l
1-(4'-chloro-benzyl)-3-carbamoyl-pyridinium-chloride 1 g/l a
polymeric additive according to Preparation Example 2.2 of EP 1 114
206 B1 (amount stated is relative to solid content)
A very bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00014 Layer Layer thickness [.mu.m] Layer thickness
[.mu.m] thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient +++ 4.20 3.15 1.33
Application Example 7
[0081] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00015 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 27. mg/l
1-benzyl-3-N,N-dimethylcarbamoyl-pyridinium-chloride 1 g/l a
polymeric additive according to Preparation Example 2.2 of EP 1 114
206 B1 (amount stated is relative to solid content)
A very bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00016 Layer Layer thickness [.mu.m] thickness [.mu.m]
Layer thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient +++ 4.15 2.99 1.39
Application Example 8
[0082] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00017 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 100 mg/l
1-benzyl-3-carbamoyl-pyridinium-chloride 1 g/l a polymeric additive
according to Preparation Example 2.2 of EP 1 114 206 B1 (amount
stated is relative to solid content)
A very bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00018 Layer Layer thickness [.mu.m] thickness [.mu.m]
Layer thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient +++ 4.90 3.70 1.32
Application Example 9
Comparative Example according to U.S. Pat. No. 4,071,418 with
1-benzyl-3-carbamoyl-pyridinium-chloride
[0083] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00019 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 100 mg/l
1-benzyl-3-carbamoyl-pyridinium-chloride 1 g/l a polymeric additive
according to Preparation Example 1 of U.S. Pat. No. 4,071,418
(amount stated is relative to solid content)
A bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00020 Layer Layer thickness [.mu.m] thickness [.mu.m]
Layer thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient + 5.40 2.30 2.35
Application Example 10
Comparative Example according to U.S. Pat. No. 4,071,418
[0084] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00021 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 200 mg/l
1-benzyl-3-carboxy-pyridinium-chloride (N-benzyl nicotinate) 1 g/l
a polymeric additive according to Preparation Example 1 of U.S.
Pat. No. 4,071,418 (amount stated is relative to solid content)
A bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00022 Layer Layer thickness [.mu.m] thickness [.mu.m]
Layer thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient + 6.10 3.30 1.85
Application Example 11
[0085] Application Example 1 is repeated with the exception that an
electrolyte having the following composition is used:
TABLE-US-00023 12.5 g/l Zn(OH).sub.2 120 g/l NaOH 25 mg/l
1-benzyl-3-carbamoyl-pyridinium-chloride 1 g/l Mirapol .TM. WT
(rel. 100%)
A very bright deposition with the following layer thicknesses was
obtained:
TABLE-US-00024 Layer Layer thickness [.mu.m] thickness [.mu.m]
Layer thickness Brightness j = 3 A/dm.sup.2 j = 0.5 A/dm.sup.2
coefficient +++ 4.70 3.60 1.305
Application Example 12
Long-Term Experiment with a 5 Liter Bath for Determining the
Additive Consumption
[0086] In a comparative experiment, electrolytes having the
following composition are used:
TABLE-US-00025 12.5 g/l zinc oxide 130 g/l NaOH 20 g/l sodium
carbonate 1 g/l 1 g/l of a polymeric additive according to
Preparation Example 2.2 of EP 1 114 206 B1 (amount stated is
relative to solid content) 25 mg/l a pyridinium compound (N-benzyl
nicotinate or 1-benzyl-3- carbamoyl-pyridinium-chloride) 100 mg/l
3-mercaptotriazol 50 mg/l p-hydroxybenzaldehyde (active substance
as bisulfite adduct)
[0087] The use of N-benzylnicotinate corresponds to the teaching of
the prior art (Example 14 of EP 1 114 206 B1).
[0088] In order to compare the consumption of additives of the
electrolyte according to the invention and the electrolyte
according to the prior art, both electrolytes are used in a 5 liter
bath as in the Application Examples described above in order to
electroplate Norton sheets. In this experiment, a Norton sheet is
electroplated at 6 A for 30 minutes, whereafter the layer thickness
and the visual appearance are evaluated. When the zinc and nickel
contents which could be determined by titration with EDTA solution,
were sufficient and the visual appearance of the Norton sheets was
good and bright, the electroplating is continued. At intervals of
50 Ah (10 Ah/l), a complete bath test is carried out, consisting of
the Hull cell test (as described above) and the determination of
the zinc and NaOH concentration. If too little zinc (target value:
10 g/l zinc oxide) or NaOH is present, the missing amount is added.
After the brightness has decreased, the corresponding pyridinium
compound is replenished.
[0089] Relative to 10,000 Ah, the following additive consumption of
pyridinium compounds used as brightening agents was determined:
TABLE-US-00026 Consumption/ Entry Pyridinium compound 10 kAh
Percent consumption 1 N-benzyl nicotinate 20 g 100% (reference)
(comparison) 2 1-benzyl-3-carbamoyl- 3.5 g 17.5%
pyridinium-chloride
Application Example 13
[0090] An electrolyte having the following composition is used:
TABLE-US-00027 12 g/l ZnO 9.5 g/l nickel sulphate hexahydrate 120
g/l NaOH 30 g/l tetraethylenepentamine 0.1 g/l a polymeric additive
according to Preparation Example 2.2 of EP 1 114 206 B1 (amount
stated is relative to solid content) 50 mg/l
1-benzyl-3-carbamoyl-pyridinium-chloride
[0091] 250 ml of the electrolyte are filled into a Hull cell. A
nickel anode is used. The cathode is electroplated at 1A for 15
minutes. After completion of the electroplating, the metal sheet is
rinsed and dried with compressed air. The layer thickness is
measured at two points (3 cm from the bottom edge and 2.5 cm from
the right- and left-hand edge) at high (3 A/dm.sup.2) and low
current density (0.5 A/dm.sup.2). The measurement of the nickel
content is carried out at the same places. The measurement is done
by XRF and four points in each position so as to minimize
measurement errors. The coating obtained was highly bright.
[0092] The following layer thicknesses and nickel contents were
obtained:
TABLE-US-00028 Current density [A/dm.sup.2] Layer thickness [.mu.m]
Ni conc. [%] 3.0 6.7 15.1 0.5 2.6 13.1
Application Example 14
[0093] An electrolyte suitable for deposition of a zinc iron layer
was prepared. The electrolyte had the following composition:
TABLE-US-00029 12.5 g/l ZnO 120 g/l NaOH 50 mg/l iron (in the form
of FeSO.sub.4.cndot.7 H.sub.2O) 25 g/l sodium gluconate 1 g/l a
polymeric additive according to Preparation Example 2.2 of U.S.
Pat. No. 6,652,728 (rel. 100%) 100 mg/l
1-benzyl-3-carbamoyl-pyridinium-chloride
[0094] A Hull cell sheet was coated for 10 minutes at 1 ampere. A
very bright deposition is obtained. The Hull cell sheet was rinsed
and chromated in a commercially available black chromation for zinc
iron layers (Tridur.TM. black liquid ZnFe, Atotech). The chromated
sheet showed good black coloration.
* * * * *