Note: Descriptions are shown in the official language in which they were submitted.
Bac~kground of the Invention
The present invention relates to an improved
process for electrodepositing a composite nickel containing
electroplate on a corrosion susceptible base metal to achieve
corrosion protection thereof. The composi-te electroplate com-
prises three adjacent, bonded nickel~containing layers each of
a controlled thickness and controlled sulfur content which
normally are provided with a conventional chrome plate over the
surface of the outer nickel layer achieving exceptional outdoor
corrosion protection of the basis metal in comparison to a
single or even a duplex nickel-containing electroplate of the
same thickness.
Composite nickel-containing electroplates are in
widespread commercial use for protecting basis metals such as
steel, copper,.brass, aluminum or zinc die castings which are
subject to outdoor exposure during service, particularly, to
marine and automotive service conditions. Beneficial results in
corrosion protection are also achieved in the use of such
composite nickel-containing layers on plastic substrates which
have been subjected to a suitable pretreatment in accordance
with well-known techniques to provide an electrically conductive
coating thereof such as a copper layer rendering the plastic
substrate receptive to nickel electropla-ting. Typical of such
plastic materials which can be electroplated are A~S, polyolefin,
polyvinyl chloride, and phenol formaldehyde polymers. Such
composite nickel-containing electroplates when used in connection
with plastic substrates substantially reduce or eliminate so-
called "green" corrosion stains produced by a corrosive attack
on a copper basis layer or flash.
Typical of such prior art ccmposite nickel-containing
....
electroplating processes and compositions are those disclosed
in United States Patent Nos. 3,090,733 and 3,703,448. In
accordance with U.S. Patent No. 3,090,733 issued May 21, 1963
a process is disclosed for electrodeposlting a three-layered
nickel~containing deposit on a substrate in which at least
the operating bath for applying the intermediate nickel layer
contains selected sulfur compounds to effect a controlled sul-
fur content in the intermediate nickel~containing layer to
achieve the requisite adherence between the composite layers
and corrosion protection of the underlying substrate. A
further improvemen-t in the foregoing process is disclosed in
United States Patent No. 3,703,448 issued November 21, 1972
in which alternative sulfur compounds comprising thiosulfo-
nates of nitriles or amides are employed at least in the ope-
rating bath for electrodepositing the intermediate layer.
The process of the present invention provides for still
further improvements over the compositions and processes
disclosed in the aforementioned two patents employing novel
sulfur compounds at least in the operating bath for electrode-
positing the intermRdiate layer which provides for impro~.~ed
bath stability in the presence of air agitation, high tempera-
ture and low pH providing for increased plating speeds and
reduced consumption of the additive compound. The sulfur ad-
ditive compound of this invention provides the further advan-
tage in that it can readily be analyzed in the operating bath
to maintain its concentration within the opt.imum operating
range and in that contamination of the operating bath for
applying the outer nickel-containing layer with the sulfur
additive co~pound by drag-in frcm the intermediate layer ope-
rating bath does not appreciably affect the sulfur concentra-
tion of the outer nickel-containing layer. This latter advan-
tage is important because normally a water rinse step is not
employed between the intermediate and outer nickel plating
steps and an undesirable increase in sulfur content of the
outer nickel layer can in some instances interfere with cove-
rage of the final chromium electrodeposit.
Summary of the Invention
The benefits and advantages of the present invention
are achieved in accordance with the composition aspects thereof
by providing an electrolyte comprising an aqueous acidic
solution containing nickel ions present in an amount sufficient
to deposit an intermediate nickel-containing layer and a thia-
zole compound and/or a tAiazoline compound present in an
-- 3 --
f
V
a~o~nt to prcvide a sulfur content in t~e deposit~d inte~ediate
nic~el-containing layer of a~out 0.05 to a~out 0.5 percent æ.
of t~e s~-uc~ural for~Nlae:
X-R ~D < ~ X-R
~' N
Wherein:
X is S, NH;
R is H, R';
R' is -(CH2)n,-503~1, ~(CH2)n C2
n is an integer from 1 to 4;
Y is -503~i
~1 is Na, K, NH4, H
as well as nNL~tures there~f.
In order to attain a sulfur concentration in the
lnter~ediate layer within the range hereina~ove s~ecified, the
thiazole ccmpound and/or thiazoline c~mpound are typically
present in an amount of a~out 0.01 to about 0.4 gr~ms per liter
(g/l) with amounts of a~out 0.03 to akout 0.1 g/l ~eing
preferred. Ihe inter.~ediate operating bath ~ay also optionally
and preferably contain wetting agents and buffering agents such
as koric acid, for e~2mple.
,, j, .
:~5~
In accordance with the process aspects of the present
invention, a metal substrate, or a plastic substrate the sur-
face of which has been rendered electrically conductive, is
electroplated to form an inner nickel-containing layer gene-
rally of a thickness of about 0.15 to about 1.5 mils (3.8 -38 ~)
containing an average sulfur concen-tration of less than about
0.03 percent followed by the electrodeposition of an interme-
diate nickel-containing layer at a thickness of about 0.005
to about 0.2 mils (0.1 - 5 ,u) and a sulfur content of about
0.05 to about 0.5 percent followed by an outer nickel~containing
layer of a thickness genererally about 0.2 to about 1.5 mils
(5 - 38 ,u) and a sulfur content of about 0.02 to about 0.15
percent The sulfur concentration of the outer nickel layer
is less than that of the intermediate layer but is greater
than that of the inner layer which may be substantially sulfur
free. Typically, each of the three nickel-containing layers
can be ele~trodeposited from a Watts-type nickel plating bath
with the intermediate and outer operating baths containing
the thiazole and/or thiazoline additive ccmpound in concentra-
tions sufficient to deposit the requisite sulfur content in
the respective layers. The individual operating baths general-
ly are operated within a temperature of about room temperature
(20C)up to about 85C and in the case of acidic operating
baths, within a p~ range of about 1 to 6.
Additional benefits and advantages of the present in-
vention will become apparent upon a reading of the Description
of the Preferred Embodiments taken in conjunction with the
specific examples provided.
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~escription of the Preferred Embodirnents
The cornposite nickel-containlng electroplate can
be produced ernploying electrolytes of the types disclosed
in United States Paten~ 3,090,733 and 3,703,448, ~Jith
the exception that in at least the intermediate operating
bath, the sulfur cornpound comprises the thiazole and/or
thia~oline ccmpound or derivatives thereof of the specific
types hereinafter to be described. Accordingly, the elec-
trolyte for depositing the inner nickel layer may comprise
a Watts-type nickel plating bath, a fluoroborate, a high
chloride, a sulfamate nickel plating bath or a substan-
tially sulfur-free semi-bright nickel plating baLh of the
types heretofore known. The electrolyte for depositing
the intermediate nickel-containing layer may be of the
same type ernployed for depositing the inner nickel-contain-
ing layer but further containing the thiazole and/or thia-
zoline additive compound in approprlate amounts to achieve
the re~uisite sulfur content in the intermediate layer.
Similarly, the electrolyte for depositing the outer nickel-
containing layer may be similar to that employed for the
intermediate layer with -the exception that the concentra-
tion of the thiazole and/or thiazoline compound or alter-
native sulfur-containing cornpounds will be controlled to
provide a net sulfur content in the outer layer in an
amount less than that of the intermediate layer. When
a decorative plating finish is desired, the outer nickel-
containing layer is preferably produced from a bright nickel
:.~
plating bath employing one or more of the organic
sulfo-oxygen compounds such as set forth in Table II of
United States Patent No. 2,512,280 and Table II of
United States Patent No. 2,800,440 which compo~nds are
also preferably used with unsaturated compounds or
amines to give both leveling and brilliance. The three
nickel-containing electrolytes may also contain
optional components of the types conventionally
employed including bath soluble and compatible wetting
agents to prevent pitting, buffering agents such as
boric acid, formic acid, citric acid, acetic acid,
fluoboric acid, or the like.
An electrolyte suitable for depositing the
inner nickel containing layer comprises a Watts-type -
bath containing about 200 to about 400 g/l nickel
sulfate hexahydrate, about 30 to about 100 g/l nickel
chloride hexahydrate, and about 30 to about 60 g/l
boric acid as a buffering agent. The bath can be
operated at a temperature of about room temperature
t20C) up to about 85C at a pH of about 1 to about 6.
The intermediate high sulfur
nickel-containing layer can be deposited from an
electrolyte as employed for the inner nickel-containing
layer but further containing from about 0.01 to about
0.4 g/l and preferably from about 0.03 to about 0.1 g/l
of the thizole and/or thiazoline additive compound of
the structural formulae:
3 ~S~
,~X~ X-II
Y N
Wherein:
X is S, NH;
R is H, R';
Rl is -(CH2)nH~ S03M, (CH2)nC02M;
n is an integer from 1 to 4;
Y is -S03M7
M is Na, K, ~14, H;
as well as mixtures thereof.
Particularly suitable thiazole compounds corresponding
to the first structural formula are 2-mercapto thiazole pro-
pane sulfonic acid, sodium salt, and 2-amino thiazole propane
sulfonic acid, sodium salt. Particularly suitable thiazoline
compounds corresponding to the second structural formula
hereinbefore set forth are l-amino-5-sulfo thiazoline, sodi~m
salt, and 2-mercapto thiazoline.
The specific quantity of the thiazole and~or thiazoline
additive compound added to the electrolyte for the interme-
diate nickel-containing layer will vary depending upon
the specific molecular weight of the compound or mixture of
tv
compounds employed, the concentration of other constituents
present in the electrolyte, the operating parameters under ~hich
the bath is operated and the relative concentration of sul~ur in
the outer nickel layer to be deposited. Conventionally, the
thiazole and/or thiazoline additive compound is controlled so as
to provide a sulfur content in the intermediate layer fr~m about
0.05 up to about 0.5 percent by weight, and preferably, about
0.1 to about 0.2%. This sulfur content can usually be attained
by employing the thiazole and/or thiazoline additive with
amounts of either ccmpound or mLxtures thereof of about 0.03 to
about 0.1 g/l usually being preferred.
The outer nickel-containing layer is electrodeposited
from an ele~ctrolyte similar to that employed for depositing the
inner layer with the exception that the outer layer electrolyte
contains appropriate sulfur campounds so as to deposit sulfur in
the outer nickel-containing layer within a ranse of about 0.02
to about 0.15 percent by weight. Appropriate sulfur c~mpounds
which are preferred are those conventionally ~.,~loyed in bright
and satin nicXel baths such as, for example, sodium allyl
sulfonate, sodium styrene sulfonate, saccharin, benzene
sulfonamide, naphthalene trisulfonic acid, benzene sulfonic acid
and the liXe. The thiazole and/or thiazoline additive, benzene
sulfinate and thiosulfonates of ni riles or amides are generally
not preferred. In any event, the sulfur contPnt in the outer
nickel-containing layer is less than that of the intenmediate
layer but greater than that of the inner layer. The inner layer
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should have a sulfur content no more than about 0.03
percent by weight, and preferably less than about 0.01
percent by weight.
In accordance with the process aspects of
the present invention, the tri-layered composite
nickel-containing electrodeposit is sequentially
applied usually without an intervening water rinse
between successive electrolytes. The composite
nickel-containing layer is usually applied to a
substrate having a strike of copper, brass, nickel,
cobalt or nickel-iron alloy. The inner
nickel-containing layer is usually applied in a
thickness greater than the outer nickel-containing
layer. In order to achieve optimum corrosion
protection from the composite electroplate, the ratio
of thickness of the inner to the outer
nickel-containing layers may range from about 50:S0 up
to about 80:20~ The intermediate layer is
conventionally applied at a thickness of about 0.005 to
about 0.2 mils followed by an outer layer of a
thickness of about 0.2 to about 1.5 mils.
In order to achieve optimum atmospheric
corrosion protection and decorative appearance, it is
usually preferred to apply a final bright conventional
chromium plate or a micro-cracked chromium plate or a
micro-porous chromium plate of a thickness of about
0.005 to about 0.2 miles over the outer
v
n~ckel-containing layer. For substrates that are to be ~posed
to less severe corrosive conditions during service, the inner
and outer nic~el-containing layers may be only about 0.15 mils
thick to provide for improved corrosion protection.
It will be appreciated that the nickel-containing
layers ccmprising the cGmposite plate may contain other
conventional contaminants present in conventional amounts which
are introduced into the electrolyte and incorporated in the
electrodeposit by way of drag-in or the like. Additionally,
cobalt may also be present in the nickel-containing layers in
appreciable quantities, such as amounts up to about 50 percent
cobalt. For general purposes, however, it has been found
preferable that the inner nickel-containing layer be as pure a
nickel as possible.
In order to further illustrate the improved
composition and process of the present invention, the following
examples are provided. It will be understood that the examples
are provided by way of illustration and are not intended to be
limiting of the scope of the invention as herein described and
as set forth in the subjoined claims.
A test solution A comprising a Watts-type nickel
plat mg solution is prepared containing about 40 ounces per
gallon nickel sulfate hexahydrate, 8 ounces per gallon nickel
chloride hexahydrate and 6 ounces per gallon of boric acid.
800 milliliters of test Solution A is added to a 1 liter
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container equipped with nickel anodes and air
agitation. The pH of the test solution A is adjusted
to 2.5 and the temperature raised to 140F (60C). 75
mg/l of a wetting agent comprising dihe~yl
sulfosuccinate is added to the test solution A.
A test solution B is prepared by adding 35
mg/l of 2-mercapto thiazole propane sulfonic acid,
sodium salt, to test solution A~ A nickel foil is
plated from test solution B and upon chemical analysis
is found to contain 0.127 percent sulfur.
The nickel foil is prepared by
electrolytically cleaning a two inch by 4 inch steel
panel in an alkaline cleaner followed by water rinsing
and an acid dip in a 20 percent solution of sulfuric
acid. The acid dipped panel is thereafter water rinsed
and plated in a Woods nickel strike to provide a nickel
strike layer. The resultant panel is passivated by
anodically electrolyzing the panel for a period of from
one to two seconds in an alXaline cleaner. Thereafter
the panel is plated in a test solution B at a current
density of 45 ASF for a period of 35 minutes. The
panel thereafter is water rinsed, dried and the edges
are cut and the resultant nickel foil is removed.
EXAMPLE 2
A test solution C is prepared in accordance
with the procedure described in Example 1 by adding 50
ms/l of 2-mercapto thiazole propane sulfonic acid,
sodium salt, to test solution A. A nickel foil is
prepared employing the procedure of Example 1 and upon
analysis is found to contain 0.175 percent sulfur.
, . . .
~5~i~V
E~LE 3
A test solution D is prepared by adding 35 mg/1 of
2-~no-5-sulfo thiazoline, sodium salt, to test solution A and
a nickel foil is prepared employing the procedure as described
in E~ample 1. A chemical analysis of the sul~r content of the
foil reveals a concentration of 0.150 percent.
E~LE 4
A test solution E is prepare~ by adding 50 mg/l of
2-amino-5-sulfo thiazoline, sodium salt, to test solution A and
a nickel foil is prepared employing the procedure as described
in E~le l. A chemical analysis of the sulfur content of the
foil reveals a concer.tration of 0.201 percent sul,'ur.
EX~IPT.F~ 5
A test solution F is prepared by adding 35 mg/1 of
2 amino thiazole propane sulfonic acid, sodium salt, to test
solution A and a niekel foil is prepared employing the
procedure as deseribed in Example 1. A ehemieal analysis of
the sulfur eontent of the foil reveals a concentration of
0.l32 percent sulfur.
~ ~PLE 6
A test solution G is prepared by adding 50 mg/l of
2-amino thiazole propane sulfonic acid, sodium salt, to test
solution A and a nickel foil is prepared employing the
procedure as described in Example 1. A chemical analysis of
the sulfur content of the foil reveals a concentration of
0.178 percent sulfur.
EXAMær~ 7
A test solution H is prepared by adding lr) mg/l of
2-mercapto thiazoline to test solution A and a nickel foil is
prepared employing the procedure as descri~ed in EXample 1. A
chemical analysis of the sulfur content of the foil reveals a
concentration of 0.139 percent sulfur.
EY~LE 8
A test solution I is prepared by adding 20 mg/l of
2-mercapto thiazoline to test solution A and a nickel foil is
prepared employing the procedure as described ln Example 1. A
chemical analysis of the sulflr content of the foil reveals a
concentration of 0.305 percent sulfur.
E~IPT,F~ 9
A test -solution C as descri~ed in EXample 2 is
prepared and used under the conditions described in Example 1
for plating a 1.25 by 6 mch steel panel rolled at one end to
prcduce an extremely low ~urrent density area. me plating of
the panel is conducted at 30 amperes per square foot IASF) for a
period of 7 minutes. The resulting nickel deposit is of a
sei~i-bright lustre with good coverage over the low to high
current denslty areas.
The test solutions B through I as described in the
foregoing examples are eminently satisfactory for use as ar.
electrolyte for depositing the nickel-containing intermediate
layer to provide a sulfur concentration within the desired range
14
.
,, _ _ . _ , , , _ ,
5~
of about 0.05 to about 0.3 percent by weight. The thiazole
and/or thiazoline additive ccmpound provides not only the
advantage of improved stability of the electrolyte and high
speed plating rates but additionally does not appreciably affect
the performance and sulfur content of the outer nickel-
containing layer as a result o~ drag-in of the intermediate
layer electrolyte into the outer layer electrol~te. It has ~een
discovered that when using such thiazole and/or thiazoline
additive ccmpounds, less sulfur is deposited with an increase in
pH~ Accordingly, the operation of the intermediate layer
electrolyte at a pH of about 2.5 provides satisfactory sulfur
content in the intermediate layer. However, drag-in of t~e
additive into the bright nickel electrolyte for depositing the
outer nickel-containing layer which typically is at a pH of
about 3.5 to about 4.5 does not appreciably raise the sulfur
content of the bright nickel outer deposit.
EXAMPLE 10
A series of test solutions designated as J, K and L is
prepared by the addition to test solution A of Example 1, 25
~g/l, 50 mg/l and 100 mg/l, respectively, of 2-~ercapto
thiazoline of a molecular weight of 119.2.
A brass appearance panel and a nickel foil are plated
from each of test solutions J, K and L at a temperature of about
135 to about 145F at a pH of 2.5 in the presence of air
agitation with each solution containing 75 mg/l of the wetting
agent dihexyl sulfosuccinate. The 1 by 6 inch brass appearance
p2nel is first electrolytically cleaned in an aIkaline cleaner,
rolled at one end to create a lcw current density area, ~7ater
rinsed, acid dipped in a 20 percent sulfuric acid solution,
water rinsed and thereafter plated in the test solution at about
40 ASF for a period of 5 minutes. The appearance panel is
thereafter unrolled and the overall deposit evaluated for
appearance in khe high and 1c~7 current density areas as ~7ell as
for adhesion of ~he deposit. me nickel foils prepared as
described in Example 1 are also analyzed for percent sulfur
content.
Subsequent analysis and observation revealed a nickel
foil containir.g 0.348 percent sulfur produced by test solution
J, a sulfur content of 0.396 in the nicXel foil produced by test
solution K and a sulfur content of 0.848 percent in the foil
prc~uced e~ploying test solution L. It is apparent that the use
of this additive ccmpound at the sa~e general molecular
concentrations as the ccmpounds previously described in the
foregoing ex2mples results in an appreciable increase in the
sulfur content of the nicXel layer above that normally desired
to achieve satisfactory adherence of the overlying outer nicXel
layer of the ccmposite plate. Nevertheless, the general
appearance of the panel was satisfactory and adhesion ~as
acceptable. Accordingly, the concentration of 2-mercapto
thiazoline is preferably contr~lled at concentrations less than
about 60 ng/l in accordance with the compositions of test
solukions H and I of Examples 7 and 8 to provide an intermediate
16
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nickel layer containing the desired amount of sulfur.
While it will be apparent that the preferr~d
embodi~ents of the invention disclosed are well calculated to
fulfill the objects above stated, it will be appreciated that
the invention is susceptible to modification, variation and
change without departing from the proper scope or fair meaning
of the subjomed claims.
