Note: Descriptions are shown in the official language in which they were submitted.
1070637
IMPROVED ELECTROPLATING PROCESS
- Background of the Invention
An important consideration in the commercial electro-
plating of bright nickel at the present time and for the
forseeable future is minimizing the cost of depositing nickel
and conserving the nickel metal itself, which is not an
unlimited resource, and often in short supply or available
only at high cost. To conserve nickel and reduce costs a
number of procedures have been tried by the nickel plating
industry. One of the earliest approaches to the problem was
to reduce the thickness of nickel deposited. However, in order
to retain the degree of brightening and leveling to which the
I nickel plating industry has grown accustomed, it is necessary
to use more effective or "powerful" nickel brighteners or
higher concentrations of nickel brighteners, so that a bright
~and well-leveled nickel deposit might be obtained with the
thinner deposits. The more "powerful" nickel brighteners or
; high concentrations of brighteners, while capable of producing
the desired brightening and leveling, may nevertheless cause
I unacceptable side effects. The nickel deposits may be highly
~¦ ~ stressed, severely embrittled, less receptive to subsequent
chromium deposits or exhibit hazes, reduced low current
density covering power or "throw~ or striations and skip
¦ plate, i. areas ln which a deposit is not obtained.
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Another method of saving nickel has been to substitute
cobalt for some portion of the nickel, and thereby deposit
nickel-cobalt alloys. Generally, cobalt is more expensive
than nickel, but at times cobalt may be more readily available
than nickel. If thinner deposits of nickel-cobalt alloys are
then deposited in order to reduce costs, but higher concentra-
tions of brighteners, or more "powerful" brighteners.are
employed in the plating bath to retain the desired degree of
. brightening and leveling, the same problems mentioned.previously
with respect to nickel.plating may become manifest; that is,
the deposits may be highly stressed, severely embrittled,
. hazy, striated, etc.
More recently, electrodeposited alloys of nickel-
iron, nickel-cobalt-iron or.cobalt-iron have begun to be used
commercially as substitutes for.decorative nickel electro-
. deposits in periods when nickel has been in short supply or
: to reduce the cost of nickel electrodeposits by substituting
relatively inexpensive iron for a portion of the more expensive
nickel and/or cobalt. Electrodeposited alloys containing
as much as 60% by weight iron (with.the remainder predomin-
antly nickel and/or cobalt):are thus being used commercially
: . in applications where formerly all nickel.electrodeposits were - .
considered necessary.
. Although in many respects, the electrodeposition
of nickel-iron, cobalt-iron or nickel-cobalt-iron aIloys is
very similar to the electrodeposition of nickel in that
similar equipment, operating conditions and organic additives
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1070637
are employed; nevertheless, electroplating with iron containing
alloys of nickel and/or cobalt presents some special problems.
For example, in order to maintain the desired ratio of nickel
. or cobalt ions to iron.ions.in the electroplating solution,
a portion.of the nickel or cobalt anodes are desirably replaced
with iron anodes to provide ferrous ions to the plating solution
as a replenishment for the iron plated out of the bath.
. These iron anodes should corrode evenly, smoothly and efficiently
. to avoid anode polarization, as well as to preclude the
sloughing off of particles of the iron anodes thereby clogging
anode bags and filters or causing rough deposits. 5ince the
introduction of undesirable foreign materials to a plating
bath must always be guarded against, the iron anodes should
be of high purity. Unfortunately, iron of suitable purity
for use as anodes in an iron alloy bath may not corrode evenly
.in the bath and can result in the aforementioned problems.
Another requirement in the electrodeposition of
iron alloys of-nickel and/or cobalt is that the iron in the ~
electroplating solution should be predominantly in the ferrous
state rather than the ferric.. At a pH of about 3.5, basic
ferric salts precipitate and can clog the anode bags and
filters and may produce rough electrodeposits.. It is, therefore,
advantageous to prevent any ferric basic salts from precipitating.
. This ¢an be accomplished by the addition of suitable complexing,
chelating, anti-oxidant or reducing agents to the iron containing
¦ electropla ng alloy bath ac taught by Koret~ky in U. S.
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1C~70637
Patent 3,354,059; Passal in U. S. Patent 3,804,726; or
Clauss et al in U. S. Patent 3,806,429. While these complexing
or chelating agents are necessary in order to provide a solution
to the ferric iron problem, their use may result in several
5 undesirable side effects. They can cause a reduction in
deposit leveling and can also produce striated, hazy or dull
deposits which may further exhibit step plate or even skip plate,
i.e., areas which are not plated, or else plated only very
, thinly compared to other sections of the deposits.
Object fff the I-nvention
It is an object of this invention to provide processes
and compositions for depositing electrodeposits of nickel,
cobalt, or binary or ternary alloys of the metals selected
from nickel, cobalt and iron which possess a greater tolerance
for high concentrations of brighteners. It is a further object
of this invention to provide deposits of nickel, cobalt or
binary or ternary alloys of the metals selected from nickel,
cobalt and iron characterized by increased ductility, brightness,
covering power, and leveling or scratch hiding ability. It is
a further object of this invention to provide for more uniform
corrosion or dissolution of iron anodes in iron containing
alloy electroplating baths of nickel, cobalt or nickel and
cobalt. Other objects of this invention will be apparent from
the following detailed description of this invention.
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. Description of the Invention
.
In accordance with certain of its aspects, this
invention relates to.a process for the preparatian of an
electrodeposit which contains at least one metal..selected from
the group consisting of.nickel and cobalt and which may also
contain iron, which comprises.passing current through an
.. . aqueous, acidic plating solution containing at least one member
.. selected from the group consisting of nickel compounds and
. cobalt compounds, and.which may also contain iron compounds
to provide nickel, cobalt and iron ions for electrodepositing
nickel, cobalt, or binary or ternary alloys of nickel, cobalt
and iron; the improvement.comprising the presence of.10 micro-
moles per liter to 2000 micromoles per liter of an organic
disulfide compound or salt thereof having the formula:
Rl-S-S-R2 .
wherein Rl and R2 are independently selected from
~:~ ~ Xl ~ X2, and -(CH2)n-CH 3
: where n is an integer from 0 to 5, Xl is selected from -OH,
-NH2, -C~OH , and -C~'~NH or salts thereof and X2, X3 and X4
~: are independently selected from -H, -OH, -NH2, -C$oH, and
-C~NH or salts thereof, provided that X3 and X4 are not
¦ simultaneously hydrogen; for a time period sufficient to form
a tal ele troplate upon sdid cathode.
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; 107~637
The baths of this invention may also contain an
effective amount of at least one member selected fro~ the
group consisting of:
(a). Class I brighteners
~ b) Class II brighteners
(c) Anti-pitting or wetting agents
~ he term "Class I brighteners" as used herein, and
as described in Modern Electroplatin~, Third Edition,
F. Lowenheim, Editor, is meant to include aromatic sulfonates,
sulfonamides, sulfonimides, sulfinates, etc., as well as
aliphatic or aromatic-aliphatic olefinically or acetylenically
unsal-urated sulfonates, sulfonamides, sulfonimides, etc.
. Specific examples of such plating additives are:
: (1) sodium o-sulfobenzimide . .
(2) disodium 1,5-naphthalene disulfonate
(3) trisodium 1,3,6-naphthalene trisulfonate
(4) sodium benzene monosulfonate
. (5) dibenzene sulfonimide
(6) sodium benzene monosulfinate
(7) sodium allyl sulfonate
(8) sodium 3-chloro-2-butene-1-sulfonate
(9) sodium ~-styrene sulfonate
(10) sodium propargyl sulfonate
(11) monoallyl sulfamide
(12) diallyl sulfamide
~13) allyl sulfonamide
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637
Such plating additive compounds, which may be used
I singly or in suitable combinations, are desirably employed
¦ in amounts ranging from about 0.5 to 10 grams per liter and
l have one or more of the following functions:
5 ¦ (1) To obtain semi-lustrous deposits or to
¦ produce substantial gr~in-refinement over
the usual dull, matte, grainy, non-relective
deposits from additive free baths.
¦ (2) To act as ductilizing agents when used
10 ¦ in combination with other additives such as
¦ Class II brighteners.
¦ (3) To control internal stress of deposits,
¦ generally by making the stress desirably
¦ compressive.
15 ¦ t4) To introduce controlled sulfur contents
¦ into the electrodeposits to desirably affect
¦ chemical reactivity, potential differences
¦ in composite coating systems, etc. thereby
¦ decreasing corrosion, better protecting the
20 ¦ basis metal from corrosion, etc.
¦ t5) They may act to prevent or minimize pitting.
¦ t6) They may condition the cathode surface by
¦ catalytic poisoning, etc. so that the rates of
¦ consumption of cooperating additives (usually
of the Class II brightener type) may be
substantially reduced, making for better economy
o peration and control.
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1070637
The term "Class II brighteners~ as used herein,
and as described in Modern Electroplating, Third Edition,
F. Lowenheim, Editor, is meant to.include plating additive
compounds such as reaction products of epoxides with alpha-
hydroxy acetylenic alcohols such as diethoxylated.2-butyne-1,
4-diol.or dipropoxylated.2-butyne-1,4-diol, other a~etylenics,
N-heterocyclics, active sulfur compounds, dye-stuffs, etc.
Specific examples of such plating additives are:
(1) 1,4-di-(~-hydroxyethoxy)-2-butyne
(2) 1,4-d~ -hydroxy-y-chloropropoxy)-2-butyne ..
(3~ 1,4-di-(~ -epoxypropoxy)-2-butyne
(4) 1,.4-di-(~-hydroxy-y-butenoxy)-2-butyne
(5) 1,4-di-(2'-hydroxy-4'-oxa-6'-heptenoxy)-2-butyne
(6) N-(2,3-dichloro-2-propenyi)-pyridinium chloride
. (7~ 2,4,6-trimethyl N-propargyl pyridinium bromide
. . . (8) N-allylquinaldinium bromide
(9) 2-butyne-1,4-diol
(10) propargyl alcohol
. (11) 2-methyl-3-butyn-2-ol
(12) quinaldyl-N-propanesulfonic acid betaine
. . ~13) quinaldine dimethyl sulfate
(14) N-allylpyridinium bromide
(15) isoquinaldyl-N-propanesulfonic acid betaine
(16) isoquinaldine dimethyl sulfate
(17) N-allylisoquinaldine bromide
( disullonated 1,4-di-(~-hydroxyethoxy)-2-butyne
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1(~70637
~19) 1~ hydroxyethoxy)-2-propyne
(20) 1-(~-hydroxypropoxy)-2-propyne
(21) sulfonated 1-(~-hydroxyethoxy)-2-propyne
(22) phenosafranin
(23) fuchsin .
When used alone or in combination, desirably in
amounts ranging from about 5 to 1000 milligrams per liter,
a Class II brightener may produce no.visual ef-fect on the
. electrodeposit, or may produce semi-lustrous, fine-grained
:10 deposits. However, best results are obtained when Class II
brighteners are used with one or more Class I brighteners
in order to provide optimum deposit luster, rate of brightening,
leveling, bright plate current density range,. low current
density coverage, etc.
~: I Ihe term "anti-pitting.or wetting agents" as used
herein is meant to include a material which functions to
. prevent or minimize gas pitting. An anti-pitting agent, when
::~ used alone or.in combination,.desirably in amounts ranging
from about 0.05 to l gram.per liter, may also function to
9 : 20 .make.the baths more compatible with contaminants such.as oil,
~ qrease, etc. by their emulsifying, dispersing, solubilizing,
:~: etc. action on such contaminants and thereby promote attaining
of sounder deposits. Preferred anti-pitting agents may
include sodium lauryl sulfate, sodium lauryl ether-sulfate
1~ and sodi -alky1~u1fosuccinates.
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1~706:~7
The nickel compounds, cobalt compounds and iron
compounds employed to provide nickel, cobalt and iron ions
for electrodepositing nickel, cobalt, or binary or ternary
alloys of nickel, cobalt and iron, (such as nickel-cobalt,
nickel-iron, cobalt-iron and nickel-cobalt-iron alloys) are
typically added as the sulfate, chloride, sulfamate or
fluoborate salts. The sulfate, chloride, sulfamate or
fLuoborate salts of nickel or cobalt are employed in concer.-
trations sufficient to provide nickel and/or cobalt ions in
the electroplating solutions of this invention in concentrations
ranging from about 10 to 150 grams per liter. The iron
compounds, such as the sulfate, chloride, etc. when added
to the nickel, cobalt, or nickel and cobalt containing electro-
plating solutions of this invention, are employed in concen-
trations sufficient to provide iron ions ranging in concen-
tration from about 0.25 to 25 grams per liter. The ratio of
nickel ions or cobalt ions or nickel and cobalt ions to iron
ions may range from about 50 to 1 to about 5 to 1.
The iron ions in the electroplating solutions of
this invention may also be introduced through the use of iron
anodes, rather than through the addition of iron compounds.
Thus, for example, if some percentage of the total anode area
-in a nickel electroplating bath is composed of ixon anodes,
after some period of electrolysis enough iron will have been
introduced into the bath by chemical or electrochemical
dissolution of the iron anodes to provide the desired concen-
tration of iron ions.
637
The nickel, cobalt, nickel-cobalt, nickel-iron,
cobalt-iron and nickel-cobalt-iron electroplating baths of
this invention additionally may contain from about 30 to 60
grams per liter, preferably about 45 grams per liter of boric
S acid or other buffering agents to control the p~ (e.g. from
about 2.5 to 5, preferably about 3 to 4) and to prevent high
current density burning.
-When iron ions are present in the plating baths of
-this invention, the inclusion of one or more iron complexing,
chelating, anti-oxidizing, reducing, or other iron solubilizing
agents such as citric, malic, glutaric, gluconic, ascorbic,
isoascorbic, muconic, glutamic, glycollic, and aspartic acids
or similar acids or their salts are desirable in the iron
containing baths to solubilize iron ions. These iron complexing
or solubilizing agents may range in concentration in the
plating solution from about one gram per liter to about 100
grams per liter, depending, of course, on how much iron is
present in the plating bath.
In order to prevent nburning" of high current density
areas, provide for more even temperature control of the solution,
and control the amount of iron in the iron containing alloy
deposits, solution agitation may be employed. Air agitation.
mechanical stirring, pumping, cathode rod and other means of
solution agitation are all satisfactory. Additionally, the
bath may be operated without agitation.
,
1070637
The operating temperature of the electroplating
baths of this invention may range from about 45C to about
85C, preferably from about 50C to 70.
The average cathode current density may range from
about 0.5 to 12 amperes per square decimeter, with 3 to 6
amperes per square decimeter.providing an.optimum range.
Typical aqueous nickel-containing electroplating
baths (which may be used in combination with effective amounts
of cooperating additives) include the following wherein all
concentrations are in grams per liter (g/l) unless otherwise
indicated:
TABLE I .
AQUEOUS NICKEL-CONTAINING ELECTROPLATING BATHS .
Minimum. Maximum Preferred
Component:
NiS04.6H20 75 500 300
NiC12-6H2 20 100 60
H3B03 30 60 45
pH (electrometric)3 . 5 4
When.ferrous sulfate (FeS04~7H20) is included in
the foregoing bath the concentration is about 2.5 grams per
liter to about 125 grams per liter. .
Typical sulfamate-type nickel plating baths which
may be used in the practice.of this invention may include
¦ the follo~ ng components:
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1070637
'~ABLE'II
Minimum Maximum' Preferred
Component:
Nickel Sulfamate 100 500 375
2 2 10 ~oo 60
H3B03 , 60 45
pH (Electrometric) 3 5 4
When ferrous sulate (FeS04-7H20) is included in
. the foregoing bath the concentrati.on is about 2.5 grams per
liter to about I25 grams per liter.
Typical chloride-free sulfate-type nickel plating
. baths which may be used in the practice of this invention may
include the following components:
~ABLE III
Minimum Maximum Preferred
Component:
NiS04 6 2100 500 300
H3B03 30 ' 6Q 45
pH (Electrometric) 2.5 4 3-3.5
When ferrous sulfate (FeS04-7H20) is included in
the foregoing baths the concentration is about 2.5 grams per
liter to about 125 grams per liter.
Typical chloride-free sulfamate-type nickel plating
baths which may be used in the practice of this invention may '.
include th following components:
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~070637 ~
TABLE IV
Minimum Maximum ~referred
Component:
Nickel sulfamate 200 500 350
H3BO3 30 . 60 45
pH (Electrometric) 2.5 4 3-3.5
When.ferrous sulfate (FeSO4-7H2O) is included in the
foregoing baths the concentration.is about 2.5 grams per liter
to about 125 grams per liter.
10 The following are aqueous cobalt-containing and
cobalt-nickel-containing electroplating baths which may be used
in the practice of this invention:
. ~A~LE V
-AQUEOUS COBALT-CONTAINING AND COBALT-NICKEL-
15 ~ONTAINING ELECTROPLATIN~ BATHS
.(All concentrations in g/l unless otherwise noted)
Minimum Maximum -Preferred
: Cobalt bath
:~ . CoSO4-?H2O 50 500 300
.Ccl2~6H2o 15 125 60
H3BO3 60 45
: Cobalt bath
CoSO4 7H2O 100 .500 400
NaCl 15 60 30
H3BO3 30 60 45
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1~70637
. TAB:LE V (cont.)
Minimum ~Maximum Prefer~ed
High chloride cobalt bath
. CoSO4-7H2O 75 350 225
CoC12-6H2O 50 350 225
H3BO3 30 60 45
Cobalt-nickel alioy bath
4 2
C 4 2 15 300 80
NiC12 6H2 15 75 60
H3BO3 30 60 45
All-chloride cobalt bath
CoCl 6H O 100 500 300
H3BO3 30 60 45
Sulfamate cobalt bath
. Cobalt sulfamate 100 400 290
CoC12-6H2O 15 75 60
H3BO3 60 45
The pH in the typical formulations of Table V
may range from about 3 to 5 with 4 preferred.
When ferrous sulfate (FeSO4-7H2O) is included in
the foregoing baths.the concentration is about 2.5 grams per
liter to 125 grams per liter.
Typical nickel-iron containing electroplating baths
which may be used in the practice of this invention may include
; the follow component~:
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~A~LE VI
M~nimum Maximum Preferred
Component:
NiSO4-6H2o 20 500 200
2 2 15 300 60
FeSO4-7H2O 1 125 40
; H3BO3 30 60 45
pH (Electrometric) 2.5 5 3.5-4
With the inclusion of ferrous sulfate (FeSO4-7H2O)
in the foregoing bath formulations it is desirable to additionally
include one or more iron complexing, chelating or solubilizing
agents ranging in concentration from about 1 gram per liter
to about 100 grams per liter, depending, of course, on the
actual iron concentration.
It will be apparent that the above baths may contain
compounds in amounts falling outside the preferred minimum
and maximum set forth, but.most satisfactory and economical
. operation may normally be effected when the compounds are present
: in the baths in the amounts indicated. A particular advantage
of.the chlori.de-free baths of Tables III and.IV,-supra, is that
. the deposits obtained may be substantially free of tensile
:: stress and may permit high speed plating involving the use of
"high speed" anodes. .
The pH of all of the foregoing illustrative aqueous
nickel-containing, cobalt-containing, nickel-cobalt-containing,
nickel-iron, cobalt-iron and nickel-cobalt-iron-containing
compositions.may be maintained during plating at pH values of
2..5.to 5.0, and preferably from about 3.0 to 4Ø During bath
operation, the pH may normally tend to rise and m~y be adjusted
~0 with acids such as hydrochloric acid, sulfuric acid, etc.
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~o70637
Anodes used in the above baths may consist of the
particular single metal being plated at the cathode such as
nickel or cobalt for plating nickel or cobalt respectively. For
plating binary or ternary alloys such as nickel-cobalt, cobalt-
S iron, nickel-iron or nickel-cobalt-iron, the anodes may consist
of the separate metals involved suitable suspended in the bath
as bars, strips or small chunks in titanium baskets. In such
cases the ratio of the separate metal anode areas is adjusted
to correspond to the particular cathode alloy composition
~esired. For plating binary or ternary alloys one may also
use as anodes alloys of the metals involved in such a percent
weight ratio of the separate metals as to correspond to the
percent weight ratio of the same metals in the cathode alloy
deposits desired. These two types of anode systems will
generally result in a fairly constant bath metal ion concentra-
tion for the respective metals. If with fixed metal ratio
alloy anodes there does occur some bath ion imbalance, occasional
adjustments may be made by adding the appropriate corrective
concentration of the individual metal salts. All anodes are
usually suitably covered with cloth or plastic bags o~ desired
porosity to minimize introduction into the bath of metal
particles, anode slime, etc. which may migrate to the cathode
; either mechanically or electrophoretically to give roughness
in cathode deposits.
~he substrates on which the nickel-containing,
cobalt-containing, nickel-cobalt-containing, nickel-iron-
containing, cobalt-iron-containing or nicke]-cobalt-iron_
containing electrodeposits of this invention may be applied
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10 70C37
may be metal or metal alloys such as are commonly electro-
deposited and used in the art of electroplating such as nickel,
cobalt, nickel-cobalt, copper, tin, brass, etc. Other typical
substrate basis metals from which articles to be plated are
manufactured may include ferrous metals such as steel, copper,
tin and alloys thereof such as with lead, alloys of copper
such as brass, bronze, etc., zinc, particularly in the form of
zinc-base die castings; all of which may bear plates of other
metals, such as copper, etc. Basis metal substrates may have
a variety of surface finishes depending on the final appearance
desired, which in turn depends on such factors as luster,
brilliance, leveling, thickness, etc. of the cobalt, nickel,
or iron containing electroplate applied on such substrates.
While nickel, cobalt, nickel-cobalt, nickel-iron,
cobalt-iron or nickel-iron-cobalt electrodeposits can be
obtained employing the various parameters described above, the
brightness, leveling, ductility and covering power may not
be sufficient or satisfactory for a particular application.
In addition, the deposit may be hazy or dull, and also exhibit
striations ard step plate. These conditions may especially
result after the addition of excessive replenishment amounts
of Class II brighteners, or from the use of especially "powerful"
Class II brighteners. In the case of the iron-containing
~ plating baths which additionally contain iron solubilizing
; 25 agents, the solubilizing agents may also cause a loss of
leveling and brightness, or may result in hazy, dull or striated
deposits. I have discovered that the addition or inclusion
of certain bath compatible disulfide compounds to an aqueous '
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acidic nickel, cobalt, nickel-cobalt, nickel-iron, cobalt-
iron or nickel-iron-cobalt electroplating bath will correct
the aforementioned deficiencies. Additionally, the disulfide
compounds of this invention permit the use of higher than
normal concentrations of Class II brighteners, thus permitting
higher rates of brightening and leveling without the undesirable
striations, skip plate, brittleness, etc. normally expected
under these conditions. In addition, in those electroplating
baths employing iron anodes, the disulfide compounds of this
invention also provide for improved iron anode corrosion or
dissolution. These bath soluble disulfide compounds are
exemplified by the following ~eneralized formula:
. Rl-S-S-R2
where Rl and R2 are independently selected from
~ Xl ~ X2 and ~(CH2)n~CH~
where n is an integer from 0 to 5, Xl is selected from -OH,
2' ~OH nd C-NH2 and X2~ X3 and X4 are independently
1 ted from -H, -OH, -NH2, -C~OH and C~NH2
that X3 and X4 are not simultaneously hydrogen. It will
; 20 be appreciated that quaternary salts of the amine groups or
salts or esters of the carboxyli.c acid groups may also be
; successfully employed. ~'or example, the hydrochloride or
hydrosulfate salts of the amine functions can improve the
solubility of the parent compound, while the ammonium, lithium,
potassium, sodium and similar salts of the carboxy acids with
¦ bath compatible cations may also be advantageously employed
while the simple esters (e.g., methyl, ethyl, etc.) of the acids
¦ hydrolyze the plating bath to give the parent acid.
Il 19
~070637
Typical or representative compounds which are
characterized by the above generalized formula are listed
but not limited to the following:
(CH2)2 S S (CH2)2-OH HCo~,C~CH2~S~S~CH2~C'~O
2,2'-dithiodiethanol 2,2'-dithiodiacetic acid
~C-(CH2)2-S-S-(CH2)2-C~oH HO,C (CH2)3 2 3 `OH
3,3'-dithiodiproprionic acid 4,4'-dithiodibutyric acid
H2N- (CH2) 2-S-S- (CH2) 2-NH2 HoQ~c-cH-cH2-s-s-cH2-cH-c~o
cystamine cystine
ÇOOH ÇOOH
~ ~ --5-5-(~ 112N-~-5-5-~3_N~12
2,2'-dithiodibenzoic acid 4,4'-dithiodianiline
¦ ~ N ~ -S-S- ~ N ~ S s_
HOOC COOH
4,4'-dithiodipyridine 6,6'-dithiodinicotinic acid
The above compounds or salts or esters thereof are additionally
advantageous in that they are commercially available; and thus,
: . complex, difficult or dangerous syntheses need not be carried
out in ord to obtain these materi~1s.
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1070637
The use of sulfide compounds of the type
NC-(CH2)n-S-(CH2)n-CN
where n is an integer from 1 to 4
have been shown by DuRose in U. S. Patent No. 2,978,391 to be
useful brighteners in nickel electroplating baths. However,
it has been found that monosulfide compounds of this type are
undesirable in a nickel-iron, cobalt-iron or nickel-iron-cobalt
electroplating bath because even at concentrations as low as
0.005 g/l :hey severely embrittle the deposit, produce
iridescent medium and low current density hazes, cause the
deposit to be dark in color and also cause the plating solution
to be extremely sensitive to agitation. The monosulfides as
well as similar compounds containing the mercapto (-SH) group
have also been found to cause exfoliation of nickel-iron,
cobalt-iron and nickel-iron-cobalt deposits from the basis
metal. The disulfide compounds of this invention, quite
unexpectedly, produce just the opposite effects when added
to nickel, cobalt, nickel-iron, cobalt-iron or nickel-iron-
cobalt electroplating baths, i.e., they eliminate medium and
low current density hazes, improve the deposit coverage or
throwing power (that is, extend the low current density
plating range), and increase the deposit ductility.
Clauss et al in U. S. Patent No. 3,795,591 claim
the use of compounds containing d sulfide and a sulfonate
group in the same molecule to extend the current density
range of a nickel-iron electroplating bath. The sulfonate
group is thought to play an essential role in making these
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1~70637
sulfide compounds useful additives, as indeed sulfonate groups
have been found to be essential to bright nickel plating in
general, (see Modern Electroplating, Third Edition, pp.297-306).
It was, therefore, most unexpected and surprising to find that .
the disulfide compounds of this invention, which additionally
contain carboxylic acid, hydroxy, amine and amide groups
function in such a superior dnd beneficial manner to the
sulfides of the prior art and yet do not contain the sulfonic
acid moiety which heretofore appears to have been an essential
component of nickel, cobalt and nickel-iron alloy electroplating
additives.
The disulfide compounds of this invention are unusual
in that they do not act as brighteners per se in the same way
as brighteners of the. first or second class and therefore
should not be thought of as brighteners, but rather as addition
; agents whose function in the bath is to overcome haze, striation
and skip plate. Finally, these materials promote improved
corrosion of iron anodes and thereby reduce the propensity
for clogged anode bags and filters and rough deposits.
~ 20 The disulfide compounds of this invention are
:: employed in the electroplating baths of this invention at
concentrations of from about 10 micromoles per liter to
2000 micromoles per liter and preferably from about 20 micromoles
per liter to 1000 micromoles per liter. .
.
Il 1070637
The following examples are presented as an illustration
to provide those skilled in the art of eleatroplating a better
understanding of the various embodiments and aspects of this
invention. These examples should not be construed as limiting
the scope of the invention in any way.
EXAMPLE 1
An aqueous nickel electroplating bath was prepared
having the ~ollowing composition:
Composition in g/l
NiS4-6H2 300
NiC12 6 2 60
H3B03 45
Sodium 1,5-naphthalene 4
disulfonate
l-~-hydroxyethoxy)-~-propyne 0.3
pH 3.7
Temperature 55C.
A polished brass panel was scribed with a horizontal
single pass of 4/0 grit emery polishing paper to give a band
about 1 cm wide at a distance of about 2.5 cm from and parallel
to the bottom edge of the panel. The cleaned panel was then
plated in a 267 ml Hull Cell, using the above solution, for
10 minutes at 2 amperes cell current, using magnetic stirring.
The resulting test panel was essentially devoid of deposit
~i.e., skip plate) in the current density range from zero to
about 8.0 amperes per square decimeter (asd) except for a
number of scattered "islands" of nickel averaging about 0.5 mm
Il . . . I
.
. .
1070637
in diameter. From about 8.0 asd to the high current density
edge of the panel, the deposit was bright but severely s~riated.
On adding 415 micromoles per liter (0.1 g/l) of
cystine to the plating solution (added as a 25 g~l aqueous
solution, prepared by dissolving L(-) Cystine in water with
enough dilute sulfuric acid to give the quaternary sulfate
salt, thereby incr~asing the solubility) and r~peating the
plating test, the resulting nickel deposit was bright and
covered the entire test panel. There were no areas of skip
plate.
EXAMPLE 2
An aqueous cobalt electroplating bath was prepared
havîng the following composition:
Composition in g/l
CoSO4-7H2O 300
CoC12-6H2O 60
BO3 45
Sodium o-sulfobenzimide 3.6
1,4-di~-hydroxyethoxy~-2-butyne 0.1
pH 3.6
Temperature 55& .
A polished brass panel was scribed with a horizontal
single pass of 4/0 grit emery polishing paper to give a band
about 1 cm wide at a distance of about 2.5 cm from and
parallel to the bottom edge of the panel. The cleaned panel
was then plated in a 267 ml Hull Cell, using the above solution,
- 24 -
11
1~70637
for 10 minutes at 2 amperes cell current, using magnetic stirring.
The resulting cobalt deposit was bright to brilliant across the
entire current density range of the test panel except that there
was a dense irregular haze extending from the low current density
edge of the panel up to about i.2 asd. In addition, the low
current density coverage on the back of the test panel was quite
limited and exhibited a sharp line of demarkation between plated
and unplated areas.
~n adding 79 micromoles per liter (0.02 g/11 Of
sodium 3,3'-dithiodiproprionate to the plating solution and
repeating the plating test, a bright to brilliant deposit was
again obtained, except that the dense haze noted above had been
completely eliminated. The low current density coverage on the
back of the test panel had been greatly extended and covered
the entire rear of the test panel and the deposit shaded off
gradually without a sharp cut-off.
EXAMPLE 3
An aqueous nickel electroplating bath was prepared
having the following composition:
Composition in g/l
NiS4-6H2 300
NiC12 6 2 60
H3B 3
Sodium benzenesulfonate - 8
Sodium allyl sulfonate 3.7
; 1~ hydroxyethoxy)-2-propyne 0.1
Temperature 55C.
.
ll -25- l ll
I , . . I
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10706-~
A polished brass panel was scribed with a horizontal
single pass of 4/0 grit emery polishing paper to give a band
about 1 cm wide at a distance of about 2.5 cm from and parallel
to the bottom edge of the panel. The cleaned panel was then
plated in a 267 ml Hull Cell, using the above solution, for
10 minutes at 2 amperes cell current, using magnetic stirring.
~he resulting nicke] deposit was briliant and lustrous, but
exhibited severe striations and step plate across the entire
current density range of the test panel. In addition, the low -¦
current density areas, from 0.05 to about 0.6 asd had areas of
skip plate (i.e., no deposit), while the rear of the panel
(away from the anode) was completely devoid of deposit.
On adding 137 micromoles per liter ~0.025 g/l) f
2,2'-dithiodiacetic acid to the plating solution and repeating
the plating test, the resulting nickel deposit was brilliant,
lustrous, well leveled and completely free of striations,
step plate or skip plate. In addition, the rear of the test
panel, representing an extremely low current density region,
was completely covered with a sound nickel deposit.
EXAMPLE 4
¦ An aqueous nickel-cobalt electroplating bath was
prepared having the following composition:
Composition in g/l
NiS4-6H2 - 240
~iCl2-6~l2 48
CoSO4 7H2O 60
CoC12-6H2O 12
- 26
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Il l
1070637
H3BO3 45
Sodium benzenesulfonate 12.5
Sodium allyl sulfonate 4.6
~1-(2,3-dichloro-2-propenyl)-
pyridinium chloride 0.096
2-Methyl-3-butyn-2-ol 0.083
pH 2.5
Temperature 55 C.
~ he Hull Cell test procedure and conditions described
in Example l were employed to obtain a nickel-cobalt alloy
deposit from the above solution. The resulting deposit was
dark, hazy and thin in the region from about 0.05 asd to about
0.6 asd. From 0.6 asd to the high current density edge of the
test panel, the deposi~ was so severely stressed that the entire
deposit was exfoliating from the basis metal. In addition,
the back of the test panel, an area of extremely low current
density, was practicaily devoid of a deposit.
On adding 1224 micromoles per liter (0,375 g/l) of
2,2'-dithiodibenzoic acid to the plating solution and repeating
the plating test, the resulting nickel-cobalt alloy deposit was
sound across the entire current density range of the test panel
with no evidence of the stress and deposit exfoliation noted
earlier. The back of the test panel was also covered with a
deposit of ckel-cobalt.
- 27
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10 70637
EXAMPLE 5
An aqueous nickel-cobalt electroplating bath was
prepared having the following composition:
Composition in-g/l
NiS4-6H2 240
S NiC12-6H2 48
CoS4-7H2 60
CoC12.6H20 12
H3B03 45
Sodium o-sulfobenzimide 1.8
Sodium allyl sulfonate 4.6
N-(2,3-dichloro-2-propenyl)-
pyridinium chloride 0.048
2-Methyl-3-butyn-2-ol 0.042
pH 3.6
Temperature 55C.
Using the Hull Cell test procedure and conditions
described in Example 1, a nickel-cobalt alloy deposit was
obtained from the above solution. The deposit was brilliant
across the entire current density range of the test panel.
However, the deposit in the very low current density areas was
rather thin and coverage on the back of the test panel was
very poor, while the medium to high current density areas
(i.e., about 2 asd and higher) were so highly tensile stressed
that the de sit had a network of seress ~raokc.
- 28
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Il
1070637
On adding 125 micromoles per liter (0.03 g/l) of
Cystine to the above solution and repeating the plating test,
a brilliant deposit was again obtained, except that the deposit
was completely free of stress cracks and the low current density
areas, such as the rear of the test panel, were well covered
with a sound deposit of nickel-cobalt.
~XAMPLE 6
An aqueous nickel-iron ele-troplating bath was
I prepared having the following composition:
Composition in g/1
NiS4-6H2 300
NiC12 6 2 60
FeSO4-7H2O 40
H3BO3 45
Sodium iso-ascorbate 8
Sodium o-sulfobenzimide 2
Sodium allyl sulfonate 3.7
1,4-di(~-hydroxyethoxy)-2-butyne0.2
pH 3.6
Temperature 55C.
A polished brass panel was scribed with a horizontal
single pass of 4/0 grit emery polishing paper to give a band
about 1 cm wide at a distance of about 2.5 cm from and parallel
to the bottom edge of the panel. The cleaned panel was then
plated in a 267 ml Hull Cell, using the above solution, for
10 minutes at 2 amperes cell current, using magnetic stirring.
29
107063q
The resulting nickel-iron alloy electrodeposit was bright but
rather thin and without leveling in the current density range
below about 1.2 amperes per square decimeter (asd). The deposit
in the region from about 1.2 to 5 asd was badly striated,
exhibited step plate, poor leveling, and an iridescent haze,
while from about 5 asd to the high current density edge of the
; test panel, the deposit was brilliant and lustrous with
I excellent leveling.
On adding 83 micromoles per liter (0.02 g/l) of
~ystine to the plating solution (added as a 25 g/l aqueous
solution, prepared by dissolving L(-) Cystine in water with
enough dilute sulfuric acid to give the quaternary sulfate
salt, thereby increasing the solubility) and repeating the
plating test, the resulting nickel-iron alloy deposit was
brilliant, lustrous and completely free of haze, s riations
or step plate across the entire current density range of the
test panel. In addition, the deposit exhibited good ductility
and leveling as evidenced by the degree of obliteration or
filling in of the emery scratches.
EXAMPLE 7
~ he test conditions and procedure described in
Example 6 were repeated except that 89 micromoles per liter
~0.02 g/1) of cys,amine dihydxochloride were substituted for
the cystine. The resulting nickel-iron alloy electrodeposit
was essentially the same as obtained in Example 6 when using
cystine, except that a sli~ht haze was present at the low
current density edge of the test panel.
. .. ~,
. .
_ 30 ~ I I
!
~i I
` ~070~37
¦EXAMPLE 8
The test conditions and procedure described in
Example 6 were repeated except that 137 micromoles per liter
(0.025 g/l) of 2,2'-dithiodiacetic acid were substituted for
the cystine and only 0.1 g/l rather than 0.2 g/l of 1,4-di-
(~-hydroxyethoxy)-2-butyne were employed. The resulting nickel-
iron alloy deposit was uniformly brilliant, lustrous and free
of any haze, striations, step plate, skip plate or thin areas
across the entire current density range of the test panel.
In addition, the deposit was very ductile and exhibited good
leveling.
¦EXAMPLE 9
An aqueous nickel-iron electroplating bath was
prepared ha~ing the following composition:
Compositi-on in g/l
NiS4-6H2 300
NiC12 6 2 60
; Fe804-7H20 40
H3B03
Sodium iso-ascorbate 8
Sodium o-sulfobenzimide 3.6
Sodium allyl sulfonate 3.7
1,4-di-(~-hydroxyethoxy)-2-butyne 0.1
- pH 3.8
¦1 ~erpera re 55C.
_ 31 ~
11 1
10706W
Using the Hull Cell test conditions and procedure
described in Example 6, a deposit was obtained from the above
solution which was bright but hazy, thin and without leveling
in the current density range below about 1.2 asd. The deposit
in the region from about 1.2 to 5 asd was badly striated,
exhibited step plate, poor leveling, and an iridescent haze,
while from about 5 asd to the high current density edge of the
test panel the deposit was brilliant and lustrous with excellent
leveling.
10 On adding 81 micromoles per liter (0.0125 g/l) of
2,2'-dithiodiethanol to the plating solution and repeating the
plating test, the resulting nickel-iron alloy deposit was
brilliant and lustrous, free of any striations, step plate,
skip plate, or thin areas across the entire current density
range of the test panel. ~dditionally, the deposit possessed
excellent ductility, fair leveling and exhibited a faint low
current density haze.
The concentration of 1,4-di-~-hydroxyethoxy)-2-butyne
was increased to 0.2 g/l and the above plating test repeated.
The resultin~; nickel-iron alloy electrodeposi~ was completely
brilliant, lustrous and free of haze, striations, step plate,
skip plate or thin areas across the entire current density
range of the test panel. In addition,-the deposit exhibited
good leveling, very good ductility and outstanding low current
density coverage.
.
_ 32 ~
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. 1'
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1070637
The concentration of tha 1,4-di-(~-hydroxyethoxy)-2-
butyne was then increased to 0.4 g/l and the plating test again
repeated. The results were essentially identical to the results
using 0.2 g/l of 1,4-di-(~-hydroxyethoxy)-2-butyne except that
the deposit was less ductile. These outstanding results were
obtained in spite of the fact that an exceptionally high
concentration of Class II brightener (namely 0.4 g/l of
1,4-di-(~-hydroxyethoxy)-2-butynP) was employed in the plating
test, which normally would result in a completely unacceptable
deposit.
EXAMPLE 10
The test conditions and procedure described in
Example 6 were repeated using the bath composition of Example 9
except that 82 micromoles per liter (0.025 g/l) of 2,2'- ..
dithiodibenzoic acid (added as an aqueous solution of the
sodium salt) were substituted for the 2,2'-dithiodiethanol.
The resulting nickel-iron alloy electrodeposit.was uniformly
brilliant.and lustrous, completely free of any.haze, striation,
. step plate or low current.density thinness or-skip plate, and .
exhibited good leveling and excellent duct.lity across the
entire current density range of.the test panel.
The concentration of 1,4-di-(~-hydroxyethoxy)-2-
butyne was increased to 0.2 g/l and the above plating test
repeated. The resulting deposit was essentially identical
to the one described above, except that the leveling was better
while the ctility remained excellent.
_ 33
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1070637 .
EXAMPLE ll
An aqueous nickel-iron electroplating bath was
prepared having the following composition:
Co~position in g/l
NiS4-6H2 300
NiC12-6H2 60
FeSO4.7H2O 40
H3BO3 45
Sodiu;,l citrate dihydrate 49
Sodium o-sulfobenzimide 3.6
Sodium allyl sulfonate 3.7
1,4-di-(~-hydroxyethoxy)-2-butyne 0.2
pH 3.0
Temperature 55C.
Using the Hull Cell test conditions and procedure
described in Example 6, a deposit was obtained from the above
solution which was bright to brilliant from about 2 asd to
the high current density edge of the panel. At a current density
of less than about 2 asd there was an iridescent haze.
On adding 95 micromoles per liter (0.024 g/l) of
sodium 3,3'-dithiodiproprionate to the plating solution and
repeating the plating test, the resulting deposit was essentially ;
identical to the previous deposit except that the iridescent
haze was no longer present. The over~ll deposit brightness,
however, s diminished somewhat.
_ 34 _
1070637
The concentration of 1,4-di-(~-hydroxyethoxy)-2-butyne
was increased to 0.6 g/l and the above plating test repeated.
The resulting deposit was bright to brilliant and completely
haze-free across the entire current density range of the panel.
In spite of the extremely high concentration (i.e., 0.6 g/l) of
Class II brightener (i.e., 1,4-di-(~-hydroxyethoxy)-2-butyne),
the deposit was completely ductile and the low current density
coverage was exceller,t; without any avidence OL thim~ess or
skip plate.
EXAMPLE 12
An aqueous nickel-iron electroplating bath was
prepared having the following composition:
Composition in g/l
NiS4-6~2 300
lS NiC12 6H2 60
FeSO4.7H2O 40
H3BO3 45
Sodium citrate dihyrate 32
Sodium p-toluenesulfonate 4 -
Sodium o-sulfobenzimide 0.4
Sodium allyl sulfonate 3.7
Sodium lauryl sulfate 0.125
l-(~-hydroxyethoxy)-2-propyne 0.05
25 ~¦ ~emperature 55C. I
~,
- 35 -
~\
:
A polished brass panel was scribed with a horizontal
single pass of 4/0 grit emery polishing paper to give a band
about 1 cm wide at a distance of about 2.5 cm from.and parallel
to the bottom edge of the panel. The cleaned panel was then
plated in a 267 ml Hull Cell, using the above solution, for
10.minutes at 2 amperes cell current, using.magnetic stirring.
The resulting nickel-iron alloy electrodeposit had poor leveling,
: was dull, hazy, severely striated and brittle across the entire
. current density range of the test panel. In.addition the low
current density range below about 0.6 asd was thin.
On adding 110 micromoles per liter .(0.02 g/l) of
. 2,2'-dithiodiacetic acid to the plating solution and repeating
the plating test, the resulting nickel-iron alloy deposit was
bright to brilliant across.the entire current density range of
the test panel. In addition,.the deposit was very ductile
and free of the striations and dull haz~ observed before
adding the 2,2'-dithiodiacetic acid.. The low current density
. coverage was excellent and.the deposit was not thin.
1~ .EX~MPLE 13
An aqueous nickel-iron electr~plating bath was
prepared having the composition listed in.Example 11.
Using the Hull Cell test conditions and procedure
described in Example 6, a deposit.was ob~ained from the above
solution.which was bright to brilliant from about 2 asd to
the high current density edge of the panel. At a current
density of less than about 2 asd there was an.iridescent haze.
: _ 36 ~
Il . ' I
1070637
On adding.408 micromoles per liter (0.125 g/l) of
2,2'-dithiodibenæoic acid (added as an alcoholic solution) to
the plating solution and repeating the plating test, the
resulting deposit was again bright, but no longer had the
irideiscent haze noted above.
EXAMPLE 14 . ...
An aqueous nickel-cobalt-iron electroplating bath
was prepared having.the following composition:
. Composi~ion in g~l
NiS04 6H2 255
NiC12 6H20 .. 51
CoSO4-7H2O 45
CoC12-6H20 9
FeSO4-7~2O 40
H3BO3 45
Sodium citrate dihydrate 20
. Sodium iso-ascorbate. 2
Sodium o-sulfobenzimide 3.6
Sodium allyl sulfonate .. 3.7
1,4-di~ hydroxyethoxy)-2-butyne 0.2
: pH . 3.. 7
Temperature 50C. ,;
The Hull Cell test procedure and conditions described
in Example 1 were employed.to obtain a.nickel-cobalt-iron
alloy deposit from.the.above solution..: .The resulting.deposit
was bright across the entire current density range.of the test
. panel. However, the deposit exhibited a dense blue-grey haze
1,
-37_ 11
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Il
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~070637
in the region from aboutØ8 asd to about 4 asd and a stirring
pattern haze was evident in the region from about 4 asd to
10 asd. The deposit was also very brittle.
On adding 330 micromoles.per liter (0.06 g/l) of
2,2'-dithiodiacetic acid to the plating solution and repeating
the plating test, the resulting nickel-cobalt-iron alloy
deposit was bright as before,.except that the blue-grey haze
and stirrina pattern noted above were no longer present. The
deposit was.also significantly more ductile.
Although th.is invention has been.. i.llustrated by
reference to specific embodiments, modifications thereof
which are clearly within the scope of the invention will be
apparent to those skilled in the art.
