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BACKGROUND OF THE INVENTION
This invention relates to acidic electroplating baths and, more
particularly, relates to the electrodeposition or electroplating of
metals.
The electrodeposition of metals from aqueous solutions of the metal ions is
well known. The present invention is concerned particularly with aqueous
acid electroplating baths for depositing metals such as tin, lead, copper,
zinc, cadmium or tin-lead mixtures. The composition of the metal
electroplating bath will be determined at least in part by the particular
metal to be electrodeposited. Various additives have been proposed in the
art for improving the effectiveness of electroplating baths containing
various metals.
In acidic electroplating baths, it is conventional to utilize a surfactant
therein to control properties of the metal deposit and to assist in
solubilizing other organic components. A wide variety of compositions have
been suggested as surfactants in acid electroplating baths, and many of
these are commercially available polyethylene oxide-based materials, and,
therefore, typically contain a hydrophilic and hydrophobic portion within
their chemical structure.
The present invention is directed particularly to improved aqueous acidic
plating baths for depositing tin and/or lead coatings. Generally, these
plating baths contain, in addition to the water-soluble tin and/or lead
salts, at least one group selected from the group consisting of
fluoborates, fluosilicates, sulfates, sulfamates, etc. In addition to
these basic ingredients, the prior art has suggested improvements in such
baths by including additives which will improve the brightness of the
deposit obtained from such baths. In U.S. Pat. No. 3,875,029, the use of a
naphthalene monocarboxyaldehyde either alone or in combination with
certain substituted olefins described in the patent results in an
improvement in the brightness of the deposit. Other ingredients which have
been suggested as being useful additives in tin and/or lead plating baths
include various combinations of carbonyl-containing compounds such as
aldehydes, ketones and carboxylic acids, etc. For example, U.S. Pat. No.
3,749,649 describes the advantages of utilizing tin-lead plating baths
containing at least one polyether surfactant and at least one aromatic
aldehyde containing a chloro substituent. Another bath for producing
bright deposits of tin-lead alloys is described in U.S. Pat. No.
3,785,939.
Typically, acid zinc plating baths have been based on a suitable inorganic
zinc salt such as zinc sulfate or zinc chloride, and other additives to
promote and improve ductility, brightness, throwing power and covering
power. Surface active agents may be included to improve crystal structure,
reduce pitting and increase the solubility of other additives.
Aromatic carbonyl-containing compounds generally are incorporated into acid
zinc baths as a supplemental brightener additive and for improving
fineness of the grain of the zinc deposit. Wetting agents or surfactants
have been added to these baths to solubilize or improve the solubility of
the carbonyl-containing compounds in the baths, but such wetting agents
and surfactants generally result in a bath exhibiting a tendency to foam
excessively, particularly on agitation with air.
A variety of plating baths have been developed and employed for
electroplating cadmium onto metallic substrates. These baths typically
utilize sulfates and cyanides as the primary electrolytes. The cyanide
baths have proven effective and generally satisfactory despite certain
objectionable features such as high toxicity, low current efficiency and
hydrogen embrittlement of certain steels. The sulfate baths which have
been suggested overcome many of the objectionable features of the cyanide
baths. However, some of the sulfate-based baths contain such components as
ammonium ions and chelating agents. Because of the ability of these agents
to complex with heavy metal ions, there is a significant increase in the
difficulty of eliminating heavy metals from spent baths. Sulfate-based
baths which do not utilize ammonium ions or chelating agents have more
recently been suggested in the prior art. For example, in U.S. Pat. No.
3,998,707, an aqueous acidic cadmium electrolytic bath composition is
described which comprises cadmium ions, free acid, and a particular
surfactant combination which comprises a cationic polyoxyalkylated amine
and an anionic surfactant. Preferably the cadmium plating bath also
contains at least one brightener. Examples of brighteners include aryl
aldehydes such as anisic aldehyde, ring halogenated aryl aldehydes such as
ortho-chlorobenzaldehyde, heterocyclic aldehydes such as thiophenaldehyde,
aryl olefinic conjugated ketones such as benzylidine acetone, and
heterocyclic carboxylic acids such as nicotinic acid. U.S. Pat. No.
4,045,305 describes cadmium plating baths which contain cadmium ions, free
acid, a surfactant combination comprising a condensed naphthalene
sulfonate compound and a non-ionic polyoxyalkylated surfactant. Preferably
this bath also contains a brightener of the type described in U.S. Pat.
No. 3,998,707.
Acid copper plating baths for producing a brilliant copper finish on
articles have been known in the art, and a number of patents have
described various brightening agents which can be added to acidic copper
baths. Examples of such patents include U.S. Pat. Nos. 2,707,166;
2,707,167; 2,830,014; 3,276,979 and 3,288,690. In U.S. Pat. No. 3,725,220
it has been suggested that the utilization of organic sulfonates or
carboxylates as brightening additives in acid aqueous copper plating baths
results in improved stability of the bath and effective deposition of
copper over a satisfactory current density range.
In a number of instances in the prior art acid copper plating baths, a
sufficiently brilliant finish is obtained but little or no smoothing
effect on the surface is obtained. The ability of a plating bath to
produce deposits relatively thicker in small recesses and relatively
thinner on small protrusions thereby decreasing the depth of surface
irregularities is known as "leveling". For example, a copper plating bath
with satisfactory leveling ability can be utilized to reduce or eliminate
the effect of microscopic cracks or scratches on the surfaces of the
articles being plated. Accordingly, a number of additives have been
described in the prior art for increasing the leveling effect of acid
copper plating baths. For example, U.S. Pat. No. 3,101,305 describes a
leveling additive obtained from the condensation of thiourea with
aliphatic aldehyde such as formaldehyde. Since the additives which have
been described in the prior art are useful either as brightening agents or
leveling agents, it generally has been necessary to utilize two additives
in acid copper plating baths, one for brightness and another for leveling.
SUMMARY OF THE INVENTION
The present invention relates to the discovery that bright level metal
deposits can be obtained on substrates from aqueous acid plating baths
containing water soluble salts of the metal to be deposited and at least
one surfactant of the formula
ROCH.sub.2 CH(CH.sub.3)OCH.sub.2 CH(CH.sub.3)N(H)CH.sub.2 CH.sub.2 COOH (I)
or
##STR2##
wherein R is an alkyl group containing 10 to 12 carbon atoms; x and y are
integers, the sum of which is from 2 to about 20. The aqueous acid plating
baths of the invention which each preferably contain as a brightening
agent, at least one carbonyl-containing compound, exhibit low foaming
characteristics.
Generally, the acid plating baths of the invention will contain as the
metal ions to be plated, zinc, cadmium, tin, lead, copper, and tin-lead
mixtures. Other additives normally included in aqueous acid plating baths
such as wetting agents, etc., can be included in the plating baths of the
invention. The invention also relates to a method of electrodepositing the
above metals on substrates and to additive compositions useful in the
preparation of aqueous acid plating baths.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the practice of the present invention, the metal ions contained in the
aqueous acid plating baths are preferably divalent or polyvalent metal
ions. The divalent metal ions such as copper, zinc, cadmium, tin, lead or
tin-lead mixtures are preferred. Mono and trivalent metals such as silver,
chromium and gold also may be included in the plating baths of the
invention.
The electroplating bath compositions of the present invention comprise an
aqueous solution of the metal to be plated, and as a surfactant, at least
one compound of the formula
ROCH.sub.2 CH(CH.sub.3)OCH.sub.2 CH(CH.sub.3)N(H)CH.sub.2 CH.sub.2 COOH (I)
or
##STR3##
wherein R is an alkyl group containing 10 to 12 carbon atoms; x and y are
integers, the sum of which is from 2 to about 20. The plating baths also
will contain pH adjusters and one or more additives including brighteners,
buffering agents, levelers, wetting agents, etc., which are intended to
improve the performance or life of the bath, the quality of the metal
deposit and/or to impart other beneficial effects. It is common in
electroplating art to utilize many and varied additives which are selected
according to the particular system being used, including the type of metal
to be deposited. The use of such supplementary additives in the
electroplating bath compositions of the present invention in order to
adapt the compositions to particular circumstances are included within the
scope of the present invention.
The metal ions to be deposited are incorporated into the aqueous acidic
plating baths in the form of their bath-soluble salts such as the salts of
hydrochloric acid, sulfuric acid, fluoboric acid, boric acid, etc.
The surfactant utilized in the plating baths of the invention can be
characterized by one of the following formulas
ROCH.sub.2 CH(CH.sub.3)OCH.sub.2 CH(CH.sub.3)N(H)CH.sub.2 CH.sub.2 COOH (I)
or
##STR4##
wherein R is an alkyl group containing 10 to 12 carbon atoms, x and y are
integers, the sum of which is from 2 to about 20.
The surfactant represented by formula I is amphoteric, and depending upon
the pH of the plating bath, it will show either cationic or anionic
properties.
The amine ethoxylate surfactants of the type represented by formula II
exhibit the characteristics of both cationic and nonionic surfactants with
the nonionic properties increasing at the higher levels of ethoxylation.
That is, as the sum of x and y increases, the ethoxylated amine behaves
more like a nonionic surfactant.
The surfactants represented by formulas I and II are available commercially
from Texaco Chemical Company under the trade designation "MA300" and
"M-300 Series" respectively. The M-300 Series compounds currently
available from Texaco and which have been found to be useful in the
aqueous acid plating baths of the invention include those designated as
M-302, M-305, M-310, M-315 and M-320 which contain a total of two, five,
ten, fifteen and twenty moles of ethylene oxide respectively. In all of
these compounds, R is a mixture of 10 and 12 carbon alkyl groups.
The amount of the amine derivative surfactant represented by formula I and
II incorporated in the aqueous acidic plating baths of the invention can
vary over a wide range depending upon the nature and composition of the
plating bath. Generally, however, the plating bath will contain from about
0.5 to about 15 grams or more of the surfactants I and II per liter of
plating bath.
The aqueous acidic plating baths of the invention can be prepared according
to conventional techniques by simply dissolving the desired ingredients
into a given quantity of water. The metal to be plated is added to the
water in the form of a water soluble salt such as a metal sulfate,
chloride, phosphate, citrate, carbonate or acetate. The amine surfactants
represented by formulas I and II may be added directly to the plating
baths as such or they may be prereacted through either the hydroxyl
functions or the amine group to form bath soluble esters, salts,
quaternary ammonium compounds, etc., which then may be added to the
plating baths.
In one preferred embodiment, the plating baths also contain at least one
compound which will enhance the brightness of the deposit. A variety of
compositions have been suggested as being useful as brightener
compositions in the electroplating art, and any of these may be included
in the plating baths of the invention. The particular choice of brightener
composition will be made in accordance with the particular electroplating
system being utilized.
The most widely used brightening compounds in aqueous acid plating baths
are carbonyl-containing compounds which may be either aromatic
carbonyl-containing compounds or aliphatic carbonyl-containing compounds.
Among the useful carbonyl-containing compounds are the aldehydes, ketones,
carboxylic acids and bath soluble salts of carboxylic acids. Mixtures of
more than one type of carbonyl group often is advantageous, and such a
mixture would include the mixture of a bath-soluble salt of benzoic acid
and an aromatic ketone.
The plating baths of the invention may contain at least one aldehyde which
may be an aliphatic aldehyde, an aromatic aldehyde, or mixtures of such
aldehydes. The aliphatic aldehydes which are particularly useful in the
plating baths of the invention are those containing up to about four
carbon atoms and these include, for example, formaldehyde, acetaldehyde,
propionaldehyde, butyraldehyde, crotonaldehyde, and 3-hydroxy-butanal. Up
to about 25 grams per liter of the aliphatic aldehyde may be included in
the baths and preferably, from about one to about 25 grams per liter of
the aliphatic aldehyde is utilized.
Preferred examples of the aromatic aldehydes which have been found useful
are the naphthaldehydes and benzaldehydes. It is preferred that the
benzaldehydes contain at least one chloro substituent. Examples of
aromatic aldehydes which may be utilized in the plating baths of the
invention include o-chlorobenzaldehyde; 2,4-dichlorobenzaldehyde;
3,4-dichlorobenzaldehyde; 3,5-dichlorobenzaldehyde;
2,6-dichlorobenzaldehyde; tolualdehyde; 3,4-dimethoxybenzaldehyde;
cinnamaldehyde; and anisaldehyde. Examples of the naphthaldehydes include
1-naphthaldehyde; 2-naphthaldehyde; 2-methoxy-1-naphthaldehyde;
2-hydroxy-1-naphthaldehyde; 2-ethoxy-1-naphthaldehyde;
4-methoxy-1-naphthaldehyde; 4-ethoxy-1-naphthaldehyde; and
4-hydroxy-1-naphthaldehyde. In some applications, a combination of the
naphthaldehyde with a benzaldehyde such as 1-naphthaldehyde with
2,6-dichlorobenzaldehyde provides a superior deposit on the substrates.
Examples of other carbonyl compounds includes ketones which may include
aliphatic ketones such as acetone and methyl ethyl ketone, and aromatic
ketones such as benzylidene acetone, coumarin, acetophenone,
propiophenone, 3-methoxybenzol acetone. Other carbonyl compounds include
furfurylidine acetone, 3-indole carboxyaldehyde and thiophene
carboxyaldehyde.
Mixtures of aliphatic aldehydes and the above-described aromatic aldehydes
and mixtures of naphthaldehydes and benzaldehydes have been found to be
particularly useful. Examples of suitable combinations include: the
mixture of acetaldehyde and 4-methoxy-1-naphthaldehyde; the mixture of
formaldehyde, 1-naphthaldehyde, and 2,6-dichlorobenzaldehyde; etc.
Examples of useful carboxylic acids and salts, ester, amides, include
benzoic acid, sodium salicylate, 3-pyridine carboxylic acid, benzamide,
ethyl benzoate, propyl benzoate. The benzoic and salicylic acids and salts
are preferred.
Mixtures of one or more of the aldehydes with one or more ketones also are
useful. When employed in the baths of the invention, the
carbonyl-containing brighteners will be included within the range of from
about 0.02 to about 10 grams per liter and preferably from about 0.03 to
about 1 gram per liter of bath.
Pyridine compounds also are useful as brighteners, particularly in acid
cadmium plating baths.
The pyridine compounds which are the preferred brighteners in the plating
baths of the invention have the formula
##STR5##
wherein R.sub.1, R.sub.2 and R.sub.3 are each independently hydrogen,
alkyl, alkoxy, alkene, mercapto, amino, halogen, aryl, arylalkyl,
aminoalkyl, hydroxy, hydroxyalkyl, cyano, dialkylamide, aldoxime, benzo
(b), pyrrolidinyl groups and the corresponding N-oxide compounds. The
alkyl, alkoxy and alkene groups will generally be lower alkyl, alkoxy or
alkene groups containing up to six carbon atoms. The aryl groups may
contain one or more groups attached to the aromatic moiety including lower
alkyl, hydroxy, amino and halogen groups.
The pyridine compounds of the type represented by formula III are available
and well known compounds. For example, most of the compounds listed in
Table I below are available from the Aldrich Chemical Company, Milwaukee,
Wis. Mixtures of the pyridine compositions may be included in the plating
baths. The amount of pyridine composition included in the cadmium baths of
the invention is an amount which is effective to provide a bright or
semi-bright and level cadmium deposit as desired. Generally amounts of
from about 0.05 to 10 grams per liter of bath will provide satisfactory
semi-bright to bright deposits over a wide current density.
TABLE I
Pyridine Brightener Compounds
4-pyridine aldoxime
3,4-dimethylpyridine
4-benzylpyridine
3-bromopyridine 7.85
Quinoline (Benzo (b) pyridine)
Quinaldine
3-picoline-N-oxide
2-aminopyridine
3-aminopyridine
2,6-diaminopyridine
3-picoline
4-picoline
3-aminomethylpyridine
2-amino-4-picoline
2-amino-3-hydroxy-pyridine
3-chloropyridine
3,5-dichloropyridine
4-tert-butylpyridine
4-bromopyridine
3-cyanopyridine
N,N-diethylnicotinamide pyridine
2,6-dimethoxypyridine
3-hydroxypyridine
4-vinylpyridine
4-methoxypyridine
3-pyridylcarbinol-N-oxide
3,5-lutidine
4-mercaptopyridine
2-methoxypyridine
2,4-lutidine
2,4,6-collidine
benzoyl pyridine
Other materials which have been suggested in the art as brighteners for
acid plating baths also can be used in the plating baths of the present
invention. For example, U.S. Pat. No. 4,139,425 described brightener
additive compositions for aqueous acidic tin, lead or tin-lead plating
baths which are the reaction products of an unsaturated
nitrogen-containing heterocyclic compound with a mixture of formaldehyde,
an unsaturated aliphatic aldehyde, and, optionally, an aliphatic
carboxylic acid. The unsaturated nitrogen-containing heterocyclic
compounds preferably are imidazoles, pyrazoles, pyrazines or pyridines
which may be substituted or unsubstituted. The disclosure of U.S. Pat. No.
4,139,425 is incorporated by reference.
Nitrogen and sulfur compositions are described as being useful as
brightening and leveling additives for acid copper plating baths in U.S.
Pat. No. 4,134,803. The nitrogen and sulfur compositions are prepared by
reacting a mixture of a disulfide and a halo hydroxy sulfonic acid in an
aqueous alkaline medium. These compositions are useful as brighteners and
leveling agents in the plating baths of the present invention and
particularly in the copper plating baths of the invention. Accordingly,
the disclosure of U.S. Pat. No. 4,134,803 hereby is incorporated by
reference.
Polymeric sulfur-containing compounds are described in U.S. Pat. No.
4,229,268 as being useful leveling and brightening additives for aqueous
acidic zinc plating baths. The description of the polymeric
sulfur-containing compositions in U.S. Pat. No. 4,229,268 hereby is
incorporated by reference. As noted therein, the polymeric
sulfur-containing compositions useful as brighteners are available
commercially such as, for example, from Crucible Chemical Company,
Greenville, S. Carolina. These compounds are available containing various
ratios of ethylene and/or propylene oxide to hydrogen sulfide,
2-hydroxymethyl sulfide or mercaptan. One example of such a compound is
Cru Peg HS-2000 which is believed to be the reaction product of one mole
of hydrogen sulfide or 2-hydroxyethyl sulfide with 46 or 44 moles of
ethylene oxide.
The properties of the metal deposits obtained from the bath of the
invention, particularly the tin and/or lead deposits, may be improved in
some instances by the inclusion of an aromatic amine in the bath.
Generally, the bath may contain up to about 15 grams of aromatic amine per
liter of bath. Examples of aromatic amines which are useful include
aniline; o-toluidine; p-toluidine; m-toluidine; and o-chloroaniline.
The baths of the invention, particularly the tin and/or lead plating baths,
also may contain small amounts of one or more chlorinated benzenes such as
1,2-dichlorobenzene; 1,2,4-trichlorobenzene; 1,2,3-trichlorobenzene and
1,3,5-trichlorobenzene. Amounts up to about 5 grams of the chlorinated
benzene per liter of bath, and preferably from about 0.5 to about 3 grams
per liter may be utilized.
The incorporation of one or more wetting or surface active agents into the
additive compositions and acid plating baths of the invention also results
in a plating with improved leveling and brightness, and the additive
compositions and plating baths exhibit improved stability. Copper, tin,
lead and tin-lead plating baths particularly are improved in the presence
of a wetting agent.
Polyoxyalkylated naphthols are one type of wetting agent found to be useful
in improving the quality of the metal deposits. Amounts of the substituted
naphthol of up to about 1 gm. per liter and preferably from about 0.2 to
about 0.8 gm. per liter provide improved metal deposits.
The polyoxyalkylated naphthols useful in the baths of this invention are
obtained by reacting a naphthol with an alkylene oxide such as ethylene
oxide and propylene oxide and more particularly, with from about 6 to
about 40 moles of ethylene oxide per mole of naphthol. The naphthol
reactant may be either alpha- or beta-naphthol and the naphthalene ring
may contain various substituents such as the alkyl groups or alkoxy
groups, especially lower alkyl and lower alkoxy groups of up to seven
carbon atoms each, so long as the polyoxyalkylated naphthol remains
bath-soluble. When present, there usually will not be more than two such
substituents per polyoxyalkylated naphthol; that is, two lower alkoxy
groups, two lower alkyl groups, or a lower alkyl or a lower alkoxy group.
The preferred polyoxyalkylated naphthols are ethoxylated naphthols having
the formula
##STR6##
wherein y is from about the 6 to about 40 and preferably from about 8 to
about 20.
Wetting agents based on ethylene oxide, for example, polyglycol compounds
and the like, and sulfonated wetting agents also are useful. In general,
the nonionic wettng agents such as those containing ether linkages are
particularly useful additives. Examples of such ether-containing wetting
agents are those having the general formula
R--O--(CH.sub.2 CH.sub.2 O).sub.n H
wherein R is an aryl or alkyl group containing from about six to 20 carbon
atoms and n is an integer between 2 and 100. Such wetting agents are
produced generally by treating fatty alcohols or alkyl-substituted phenols
with excess ethylene oxide. The alkyl carbon chain may contain from about
14 to 24 carbon atoms and may be derived from alcohol such as oleyl
alcohol or stearyl alcohol. Nonionic polyethylene compounds of this type
are described more completely in U.S. Pat. No. 3,855,085. Such compounds
are available commercially under general trade designations such as
"Surfynol" (Air Products and Chemicals, Inc.) and "Pluronic" or "Tetronic"
(BASF Wyandotte).
Amine, alkanol amines, amides and polyglycol-type wetting agents known in
the art are also useful. One type of amine wetting agent found
particularly useful when combined with the nitrogen and sulfur composition
of the invention in a copper plating bath is the group obtained by the
addition of a mixture of propylene oxide and ethylene oxide to diamines.
More specifically, compounds formed by the addition of propylene oxide to
ethylene diamine followed by the addition of ethylene oxide are useful and
are available commercially from BASF Wyandotte Ind. Chemical Group under
the general trade designation "Tetronic".
Carbowax-type wetting agents which are polyethylene glycols having
different molecular weights have been found to give good results. For
example Carbowax No. 1000 has a molecular weight range of from about 950
to 1,050 and contains from 20 to 24 ethoxy units per molecule. Carbowax
No. 4000 has a molecular weight range of from about 3000 to 3700 and
contains from 68 to 85 ethoxy units per molecule. Other known nonionic
glycol derivatives such as polyalkylene glycol ethers and methoxy
polyethylene glycols which are available commercially can be utilized as
wetting agents in the compositions of the invention. The amount of wetting
agents incorporated into the compositions will depend upon types and
amounts of other ingredients in the compositions, but generally from 0 to
about 5 grams and preferably from 0. 4 to about 1.5 grams per liter of the
wetting agent may be incorporated into the compositions.
Other supplementary additives generally utilized in aqueous acidic metal
electroplating baths can be utilized in the plating baths of the
invention. Thus, supplementary additives which have been suggested in the
art as being useful in, for example, zinc plating baths, can be utilized
in combination with the amine surfactants of the present invention
represented by formulas I and II described above, and, similarly,
supplementary additives normally used in tin and/or lead electroplating
baths can be utilized in combination with the amine surfactants of the
invention in tin and/or lead plating baths.
Aromatic sulfonic acids or salts also are useful additives to the plating
baths and these include the acids and salts having the general formula
##STR7##
wherein R.sub.1, R.sub.2 and R.sub.3 are each independently hydrogen or
lower alkyl groups,
X is hydrogen, ammonia or any metal with the proviso that the metal
sulfonate is soluble in the bath, and
A is a saturated unsaturated or aromatic ring.
As can be seen from the formulas, the sulfonic acids may be derived from
benzene sulfonic acids, naphthalene sulfonic acids and di- or
tetrahydronaphthalene sulfonic acids. The lower alkyl groups can be
straight or branched chain and may contain up to about 6 carbon atoms. The
aromatic sulfonic acids and salts of formulas V and VI containing two
alkyl groups have been found to be particularly effective in the acid zinc
plating baths of the invention. Of the metals included in the salts of the
sulfonic acids, the alkali metals, particularly sodium, are preferred.
Examples of aromatic sulfonic acids which are useful particularly in the
acid zinc plating baths of the invention include benzene sulfonic acid,
toluene sulfonic acid, isopropylbenzene sulfonic acid, xylene sulfonic
acid, diethylbenzene sulfonic acid, naphthalene sulfonic acid,
methylnaphthalene sulfonic acid, dimethylnaphthalene sulfonic acid,
tetrahydronaphthalene sulfonic acid, etc. The aromatic sulfonic acids
preferably are added to the acid zinc plating baths in the form of their
salts which may be metal salts or an ammonium salt. Any metal can be used
to form the metal salts of the aromatic sulfonic acids so long as the
metal does not cause any detrimental effects in the plating bath or render
the sulfonates insoluble in the plating bath.
The aromatic sulfonic acids and salts which are utilized in the plating
baths of the invention generally are referred to in the art as
hydrotropes. Hydrotropes have been defined as compounds which solubilize
sparingly water-soluble compounds. The aromatic sulfonic acids and salts
used in the present invention are effective in solubilizing sparingly
water soluble materials such as aromatic carbonyl-containing compounds,
and it has been found that the acid zinc plating baths containing the
above described aromatic sulfonic acids and salts are not subject to
excessive foaming during plating operations. This is in contrast to
plating baths wherein wetting agents and surfactants are used to stabilize
the baths since such plating baths generally are characterized by excess
foaming on use which requires careful control of plating methods. The
plating baths of the invention, however, can be vigorously air agitated
even at high current densities without excessive foaming.
The amount of aromatic sulfonic acid or salt incorporated into the plating
baths of the invention may vary over a wide range, and the optimum amount
for any particular plating bath combination can be determined readily by
one skilled in the art. Generaly, the amount of sulfonic acid or salt
included in the plating baths of the invention will vary from about one to
about 20 or more grams per liter of bath. Greater or lesser amounts of the
sulfonic acid or salts can be included in the plating baths depending
particularly on the water solubility characteristics of the additive
desired to be included in the bath.
Mixtures of the aromatic sulfonic acids or salts appear to be particularly
effective in the acid zinc plating baths of the invention. More
particularly, mixtures comprising at least one sulfonic acid or salt
represented by formula V and at least one sulfonic acid or salt
represented by formula VI are useful. An example of such a mixture is a
mixture of sodium dimethylnaphthalene monosulfonate and sodium xylene
monosulfonate.
Some examples of aromatic sulfonic acids which may be used include: a
bath-soluble salt of tetrahydronaphthalene sulfonic acid such as those
available commercially from DuPont; a bath-soluble salt of a xylene
sulfonic acid such as those available from Arco Chemical Company under the
general trade designation "Ultrawet"; and a bath-soluble salt of cumyl
sulfonic acid.
The inclusion of the aromatic sulfonic acids and salts described above in
plating baths generally improves the performance of most plating baths at
a high current density range. Accordingly, the plating baths containing
the sulfonic acids and salts are found to produce bright level metal
plating over a current density range of from below 0.3 amps/dm.sup.2 to
above 12 amps/dm.sup.2.
The following examples illustrate the plating baths of the invention.
Unless otherwise indicated, all parts and percentages are by weight. In
all of the following examples, the components identified are mixed with
sufficient water to make one liter.
EXAMPLE 1
______________________________________
Components Concentration g/l
______________________________________
Stannous Sulfate 45
Sulfuric Acid 200
1-naphthalene carboxaldehyde
0.2
Methacrylic Acid 0.5
Texaco M-302 (Formula II wherein
x and y are each 1) 4.0
______________________________________
EXAMPLE 2
______________________________________
Components Concentration g/l
______________________________________
Stannous Sulfate 45
Sulfuric Acid 200
1-naphthalene carboxaldehyde
0.2
Methacrylic Acid 0.5
Texaco M-305 (Formula II wherein sum of
x + y = 5) 2.0
______________________________________
EXAMPLE 3
______________________________________
Components Concentration g/l
______________________________________
Stannous Sulfate 45
Sulfuric Acid 200
1-naphthalene carboxaldehyde
0.2
Methacrylic Acid 0.5
Texaco M-310 (Formula II wherein sum of
x + y = 10) 2.0
______________________________________
EXAMPLE 4
______________________________________
Components Concentration g/l
______________________________________
Stannous Sulfate 45
Sulfuric Acid 200
1-naphthalene carboxaldehyde
0.2
Methacrylic Acid 0.5
Texaco M-315 (Formula II wherein sum of
x + y = 15) 2.0
______________________________________
EXAMPLE 5
______________________________________
Components Concentration g/l
______________________________________
Stannous sulfate 45
Sulfuric Acid 200
1-naphthalene carboxaldehyde
0.2
Methacrylic Acid 0.5
Texaco M-320 (Formula II wherein sum of
x + y = 20) 2.0
______________________________________
EXAMPLE 6
______________________________________
Components Concentration g/l
______________________________________
Stannous Sulfate 45
Sulfuric Acid 200
1-naphthalene carboxaldehyde
0.2
Methacrylic Acid 0.5
Texaco MA-300 (Formula I)
2.0
______________________________________
EXAMPLE 7
______________________________________
Components Concentration g/l
______________________________________
Stannous ion 50
Lead ion 25
Fluoboric Acid 140
Methoxynaphthaldehyde
0.2
Aniline 1.5 ml
1,2,4-trichlorobenzene
1.0
2,6-dichlorobenzaldehyde
0.05
Texaco M-302 4.0
______________________________________
EXAMPLE 8
______________________________________
Components Concentration g/l
______________________________________
Stannous ion 50
Lead ion 25
Fluoboric Acid 140
Methoxynaphthaldehyde
0.2
Aniline 1.5 ml
1,2,4-trichlorobenzene
1.0
2,6-dichlorobenzaldehyde
0.05
Texaco M-305 4.0
______________________________________
EXAMPLE 9
______________________________________
Components Concentration g/l
______________________________________
Stannous ion 50
Lead ion 25
Fluoboric Acid 140
Methoxynaphthaldehyde
0.2
Aniline 1.5 ml
1,2,4-trichlorobenzene
1.0
2,6-dichlorobenzaldehyde
0.05
Texaco M-310 4.0
______________________________________
EXAMPLE 10
______________________________________
Components Concentration g/l
______________________________________
Stannous ion 50
Lead ion 25
Fluoboric Acid 140
Methoxynaphthaldehyde
0.2
Aniline 1.5 ml
1,2,4-trichlorobenzene
1.0
2,6-dichlorobenzaldehyde
0.05
Texaco M-315 4.0
______________________________________
EXAMPLE 11
______________________________________
Components Concentration g/l
______________________________________
Stannous ion 50
Lead ion 25
Fluoboric Acid 140
Methoxynaphthaldehyde
0.2
Aniline 1.5 ml
1,2,4-trichlorobenzene
1.0
2,6-dichlorobenzaldehyde
0.05
Texaco M-320 4.0
______________________________________
EXAMPLE 12
______________________________________
Components Concentration g/l
______________________________________
Stannous ion 50
Lead ion 25
Fluoboric Acid 140
Methoxynaphthaldehyde
0.2
Aniline 1.5 ml
1,2,4-trichlorobenzene
1.0
2,6-dichlorobenzaldehyde
0.05
Texaco MA-300 4.0
______________________________________
EXAMPLE 13
______________________________________
Concentration
Components g/l
______________________________________
ZnCl.sub.2 50
KCl 200
Boric Acid 30
Benzylidene Acetone 0.1
Sodium xylene monosulfonate (Ultrawet 40SX)
12
Cru Peg HS-2000 5
Benzoic Acid NaSalt 2.5
Texaco M-320 5
______________________________________
EXAMPLE 14
______________________________________
Components Concentration g/l
_____________ | | |
