Note: Descriptions are shown in the official language in which they were submitted.
103789~
The present invention is concerned with electro-
deposition and more particularly with electroplating of a
non-electrically conductive substrate.
- Background of the Invention
Since the start of electroplating, a large number of
proposals have been made with respect to electroplating on
non-electrically-conductive substrates ranging in size and
shape across the gamut of leaves, flow~ers, baby shoes, plastic
knobs, bottle tops, molded plastic parts for automotive usage
and uncounted other practical and decorative structures.
Basically, two processes have been used. The first process
involves the coating of the non-conductive object with an
electrically conductive lacquer followed by electroplating.
: The second process involves sensitizing the non-conductive
object, chemically depositing a metal on the sensitized surface
and thereafter electroplating the thus metallized surface.
The two generally available processes as practiced
in the prior art have certain disadvantages. Because of high
loadings of conductive pigments such as graphite or metal,
prior art conductive lacquers are generally very weak and thus
constitute a weak link in the ultimate electroplated structure.
A variation of the lacquer process which involves coating the *
tacky lacquer surface with graphite again produces very weak
' bonds between electrodeposited metal and the lacquer much like
the ephemeral bond produced between graphitized wax and electro-
deposited metal in the electrotyping process. If lower pigment
loadings are used in a conductive lacquer to give greater
strength in the lacquer, the rate of initial metal coverage of
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- 1037896
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the article during electroplating is radically decreased
necessitating the use of multiple electrical contact points on
the object to be plated or allowance of a long time for metal
coverage and consequent uneven plating thicknesses.
The second process as generally practiced by the prior
art, can achieve good results but only at a cost of employing
a large number of individual processing operations carried
out with very great care by skilled personnel. Furthermore, -~
because the underlying chemically deposited metal can be
different from metal subsequently electrochemically deposited,
there is a good chance of forming an electrochemical couple
between the two even when, nominally the metals are the same.
-- Thus the possibility of accelerated, localized corrosion
exists wherever and whenever the outer electrodeposited layer
is not continuous. '
Recently, U.S. Patents No. 3,523,875 to Minklei and
No, 3,682,786 to Brown et al have issued. These recently -
issued patents are worthy of discussion because, superficially
they might appear to resemble the process of the present
-~ 20 invention. Minklei proposed to treat a plastic surface with
- an aqueous solution of alkali metal sulfide followed by contact-
ing the treated surface with a metal salt prior to electro- ~-
plating. Brown et al proposed contacting a plastic surface
with a solution or dispersion of sulfur in an organic medium
and contacting the treated surface with an aqueous solution
; of cuprous salt priorlto plating. In both instances, the
proposals involve the formation of a metal sulfide on the ;
plautic uurface and not the type of metal-polymer bond, whloh,
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~037896
as will become apparent from the subsequent description, is formed by
virtue of the process of the present invention.
Objects
It is an object of the present invention to provide a process for
electrodepositing metal on non-electrically-conductive substrates.
It is another object of the present invention to provide a process
for electrodeposition on substrates which are not amenable to ordinary
electrodeposition techniques.
Other objects and advantages will become apparent in light of the
following description taken in conjunction with the drawing in which Figure 1
depicts electrodeposit growth obtained in accordance with the present
invention and; Figure 2 depicts undesirable electrodeposit growth obtained
when an essential requirement of the process of the present invention is
omitted.
Description of the Invention
Generally speaking, the present invention may be generally defined
as a process for metallizing comprising (1) introducing an essentially solid
surface in contact with a metallic conductor into an electroplating bath
from which a metal from the Group VIII of the periodic table and alloys
thereof can be plated; (2) said essentially solid surface comprising an
intimate mixture of an organic polymer reactive with sulfur, a carbon black ,
and a substance from the group of sulfur and sulfur donors and having a
volume resistivity of less than about 1000 ohm-centimeters; and (3) applying
a potential to said surface through said metallic conductor to cause metal
from said group to deposit upon said surface in an essentially uniform manner
from the locus of said metaliic conductor. Thereafter the metal coated
object can be subjected
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103789~;
to further electrodeposition in ways well known to those
skilled in the art.
The polymer used along with conductive carbon
black in the coating layer (and which may also constitute
the substrate) is, advantageously a member of the group of
organic polymers which readily react with molecular sulfur
or a sulfur donor of the type described herein. Advanta- --
geous polymers for use in the process of the present inven-
tion include hydrocarbonaceous and substituted hydrocarbon-
aceous elastomers such as natural rubber, polychloroprene,
butyl rubber, chlorinated butyl rubber, polybutadiene rubber,
- acrylonitrile-butadiene rubber,styrene-butadiene rubber, etc. -
These elastomers are unsaturated and readily combine with
molecular sulfur through either unsaturated linkages in the
carbon skeletal structure of the polymer or through activated - -
sites on the polymer structure associated with unsaturated
linkages or pendant substituent atoms. Another advantageous
type of polymer for use in the process of the present inven- -
tion is an ethylene-propylene terpolymer comprising a sa~ura-
ted poly-ethylene-propylene main chain having unsaturated ,groups derived from non-conjugated dienes, e.g., hexadiene, ;
dicyclopentadiene etc., pendant fro~ the main chain. Such a -
terpolymer is readily vulcanized with sulfur. Other polymers
useful in the process of the present invention include essen-
tially saturated polymers such as polystyrene, polyvinyl
chloride, polyurethlne etc., which apparently possess active
sites for reaction with sulfur. While polyethylene (and
similar polymers of limited solubility) are not readily
suited for use in c~a~i-ng formulations, it has been found
- ~ ^ , ' ' .
103789fi
that milled and molded polyethylene compositions containing
carbon black and a sulfur donor can advantageously be em-
ployed in the process of the present invention. Undoubtedly
some organic polymers, for example, perhaps, polytetrafluoro-
ethylene are too inert to react with sulfur and these polymers
are excluded from the ambit of the present invention.
However, the great bulk of normally used organic polymeric
materials appears to be useable in the process of the present
invention.
Of those polymers which react with sulfur, those
having elastomeric characteristics e.g., rubbers, elastomeric
polyurethane etc., are considered to be advantageous when
used as a coating covering a rigid base and overlied by the
deposited metal because an elastomer has the ability
to dampen stress concentrations which can result in failure
of the deposited coating upon exposure to applied stress
or thermal cycling. In addition, with most elasto~ers, the
carbon black included for the purpose of providing a proper
degree of electrical conductivity acts as a reinforcement
agent to improve the physical characteristics of the
elastomer. Further factors which make elastomers most advan- ;
: tageous include rapidity of metal coverage and relatively
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~037896
low cost of materials. Among the elastomers, the unsaturated
elastomers are deemed to be the most advantageous.
Those skilled in the art will appreciate that in
the foregoing description of polymers operable in the process
of the present invention the examples given are merely
illustrative and that many other polymeric and copolymeric
materials and mixtures can be used in place of the specifically ; ~ -
mentioned substances. For example, very often in rubber
formulations amounts of compatible non-elastomeric resinS ~-
are included for various purposes. Polymers other than --
rubber can, and often are compounded with plasticizers in
order to obtain a product having flexibility. Such compounded
materials as well as copolymers and mixed polymers are operable
for purposes of the present invention. ~-
When as is always advantageous the exposed surface -~
of the polymer-conductive carbon black composition is caused '
to contain sulfur it is possible that the sulfur initially
attacks the polymer chain at activated positions, to provide -
activated sites for bonding of nickel to the polymer. Re-
gardless of the theoretical explanation however, applicant's
experiments have shown that when nickel deposits are made in
accordance with the teachings of the present invention very
strong, highly useful metal to organic bonds are formed very ~,
rapidly on polymer-carbon black surfaces. It is important to
avoid overcuring of a polymer with sulfur (or other curative)
prior to plating. Itl appears that a polymer-sulfur-metal
bond can occur with most polymers as long as activated sites `
on the polymer chain ex~st. ~eavy curing, especially in
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~037896
sulfur monochloride will remove these sites from an unsatu-
rated elastomer causing poor plating both as to speed of
coverage and as to adherence of the metal.
The exposed surface of the polymer-carbon black -
plating substrate can contain sulfur by inclusion of sulfur
in the whole mass of the plating substrate or by enriching
the exposed surface with sulfur. -
Normally, a plating substrate containing an unsatu-
rated polymeric elastomer will contain about 0.5% to about 5
of sulfur based upon weight of elastomer in order to permit
curing of the elastomer. When agents other than sulfur or
sulfur compounds are used for curing the exposed surface of
the elastomer can be enriched in sulfur by contacting the
Il .- . . . .
surface with a solution containing elemental sulfur or by
exposing the surfaces to a sulfur-containing vapor e.g.,
the vapor of sulfur monochloride (S2C12). The plating sub-
strate will normally contain ingredients other than sulfur,
elastomer and conductive carbon black such are normally ,
included in rubber compositions. Such other ingredients
include vulcanization accelerators and modifiers, anti-
oxidants and similar types of materials which have been
found to be useful in rubber technology. For best results,
particularly with respect to adhesion of electrodeposited
, metal all ingredients should be limited in amount to amounts
which will be permanently soluble in the cured elastomer
at normal temperatures i.e., about 25C. ,
Plating substrates used in the present invention
usually contain carbon black and polymer in weight ratios ,`
of about 0.2 to about 1 S (conductive carbon black to polymer)
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1037896
although somewhat higher or lower weight ratios ean be used.
It is usually more advantageous to employ weight ratios of
conductive carbon black to polymer in the range of about
0.5 to 1Ø It has been noted with coatings on non-
electrically conductive substrates that speed of coverage
of polymer-carbon black surfaces beeomes very low at very
high loadings of earbon black indicating that a minimum
surface concentration of polymer is necessary not only for
attaining mechanical strength but also for purposes of faeili-
tating the metal spreading meehanism of the invention.Beeause earbon blaeks vary greatly depending upon sourees and
methods of manufaeture, it is not practical to specify with
more precision the relative amounts of polymer and carbon
black required in aceordance with the present invention. In
addition to variations involved in different types of carbon
blaek, differenee in dispersion eonditions when eompounding -~
with polymer can also introduce variations in the polymer-
carbon black mixtures. For example, if an acetylene blaek
sold by Shawinigan Produets Corp. of Englewood Cliffs, New
Jersey, is milled with an elastomer in a Banbury-type mill,
it is likely that at least part of the chain-like structures
of the acetylene blaek will be broken. On the other hand
using less agressive mixing techniques, the chain structure
will be retained. Consequently, the composition milled in
the Banbury mixer will exhibit a higher volume resistivity
than will a com~osition milled in solution form in a blender
even though the loading of the carbon blaek is the same.
Thus for purposes of the invention, the eriterion of opera-
bility of a particular polymer-carbon blaek mixture is the
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1037896
electrical volume resistivity. As stated hereinbefore,
the volume resistivity must be less than about 1000 ohm-
centimeters and more advantageously is less than about
10 ohm-centimeters. Ordinarily it is neither possible nor
desirable to obtain polymer-carbon black mixtures having
volume resistivities less than about 1 ohm-centimeter. At
such low resistivities, the strength of the polymer-carbon
black mixture is low. Optimum results have been obtained
using conductive carbon blacks made from acetylene such as
sold by Shawinigan Products Corporation under the trade de~
signation Acetylene Carbon Black. Another commercially
available conductive carbon black which possesses relatively
high resistance to mechanical breakdown during milling with
a polymer is sold by Cabot Corporation under the trade mark
of Vulcan XC72. If desired, mixtures of conductive and non-
conductive carbon blacks can be used provided that the final
polymer-carbon black product has a volume resistivity in the
range set forth hereinbefore. In some instances the proper
volume resistivity can be achieved in polymer-carbon black
compositions which are made entirely with non-conductive
carbon blacks for example, furnace blacks. Such compositions
ordinarily do not have adequate electrical characteristics
when used as coatings and dried on a substrate. However,
these compositions may have adequate characteristics for use
as molded, extruded or like-formed shapes which can be treated
electrochemically i~ accordance with the present invention
without a separate preliminary coating step.
The rate of coverage of nickel cobalt or iron on a
cathode having a surface of polymer-carbon black mixture ~`
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103789~;
in accordance with the presen~ invention extending from
a point of contact with an electronic conductor (e.g., a metal)
is dependent at least upon the resistivity of the mixture,
the sulfur content at the mixture surface, the applied voltage
across the anode-electrolyte-cathode circuit; and the nature
of the polymer. Generally speaking in accordance with the
present invention the minimum rate at which nickel spreads
across the cathode surface at a voltage of 3.0 volts is
about 0.5 centimeter per minute (cm/min.). A series of
polymer-acetylene black compositions were made containing
100 parts by weight of polymer and 50 parts by weight of the
carbon black. The compositions devoid of sulfur were coated
on an ABS panel having a metal contact point at one end. In
a first series of tests the panels were immersed in a Watts-
type nickel plating bath as cathodes at a voltage of 3Ø
The rate of nickel coverage was measured. In a second series
of tests, the panels were dipped in a solution of 1~ (by weight)
; of sulfur in cyclohexane, removed and the cyclohexane allowed
to evaporate prior to electrolytic treatment in exactly the
same manner as was the first series. The results of these
tests are set forth in Table I.
TABLE I
Polymer Ni coverage rate (cm/min)
Series I Series II
Polystyrene 0.25 1.19
Polyvinyl chloride 0.15 0.99
Chlorinated Rubber (Parlon*) 0.31 0.89
Nitrile Rubber (Paracril* BJLT) 0.31 2.24
Natural Rubber (Smoked Sheet) 0.31 0.89
Neoprene Rubber (Neoprene* AD) 0.58 1.78
" - 1 0 .,
* Trademark
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~037896
Table I shows that a very small amount of sulfur
incorporated in the exposed surface of the polymer increases
nickel coverage rates by a factor of at least about 2.5.
When sulfur is included in the polymer-carbon black composi-
tions and not merely in the very surface layer as in the
materials of Series II Table I, rates of nickel coverage can
be much higher. For example, with a composition containing
100 parts by weight nitrile rubber, 50 parts by weight acety-
lene black and 4 parts by weight sulfur, nickel coverage
rates at 3.0 volts of over 6 cm/min. can be obtained. The
rate of nickel coverage increases linearly with increases
in voltage. Using a composition containing a weight ratio
of 2 to 1 of nitrile rubber to acetylene black and 2.5~ by
weight of sulfur based upon the weight of rubber, a nickel
coverage rate of about 9.5 cm/min. was obtained at a voltage
of 3.0 and a rate of about 14.7 cm/min. at a voltage of 4.5.
It is important that the sulfur present in the polymer-carbon
black compositions be in the form of non-ionic sulfur, i.e., -
that it not be tied up as a metal sulfide or in a stable
ion such as the sulfate ion. Ordinarily, elemental sulfur is
used but, if desired, sulfur in the form of a sulfur donor
such as sulfur chloride, 2-mercapto-benzothiazole, N-cyclo-
hexyl-2-benzothiozole sulfonomide, dibutyl xanthogen disulfide
and tetramethyl thiuram disulfide or combinations of these
and sulfur can also be employed. Those skilled in the art
will recognize that these sulfur donors are the materials ~ -
which have been used or have been proposed for use as
vulcanizing agents or accelerators.
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1037896
The advantage obtained when sulfur is included in
the polymer-carbon black surface is dramatically depicted
in the drawing. Referring now thereto both Figures 1 and 2
depict indentical acrylonitrile-butadiene-styrene plaques 11
coated with polymer-carbon black coating 12 containing 20
parts by weight of neoprene and 10 parts by weight of acetylene
black and having a wire contact 13.
The coating 12 of Figure 1 initially contained a
small amount of thiuram and was treated with a 1~ by weight
solution of sulfur in cyclohexane prior to plating so as to
incorporate a small effective amount of sulfur in the coating.
Coating 12 of Figure 2 was made with a neoprene free of
thiuram, was not exposed to a sulfur solution and therefore
contained no sulfur. Both plaques were made cathodic under
identical voltage conditions (3 volts closed circuit cell
potential) in the same nickel plating bath. After 1 1/2
minutes the area 15 above l~ne 14 in Figure 1 was uniformly ~;
coated with a highly adherent nickel deposit. At this time
the plaque was removed from the plating bath. If it were ;
not removed from the bath, the plating front, as depicted
by line 14, would continue downwardly across plague 11 of
Figure 1 until, at the end of about 5 minutes the whole 'plaque would be coated with a firm, adherent, even deposit
of nickel. In contrast, the plaque of Figure 2, after 20
minutes in the plating bath, had a loosely adherent fern~
like deposit on the area external of closed, irregular
curves 16 and 17 leaving sulfur-free coating 12 exposed
internally of closed irregular curves 16 and 17. A compari-
12 `
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1037895
son of Figures 1 and 2 of the drawing clearly shows that
plating practice in accordance with the present invention
is highly advantageous.
The cathodic electrolytic treatment used according
to the present invention to induce nickel coverage across --
the expanse of polymer-carbon black mixture surface is carried
out in an electrolytic bath from which nickel can be deposited
and which, ordinarily is aqueous and contains about 70 to
about 120 grams per liter (gpl) of nickel ion, complementing
anion from the group of sulfate, chloride, sulfamate, fluo- -
borate and mixtures thereof and exhibits a pH of about 2.8
to about 4.5 stabilized by inclusion of a buffer such as
boric acid in the bath. An ordinary Watts bath is quite
- satisfactory for use both as the initial bath for nickel
coverage and for subsequent plating. If desired, after nickel
coverage has been established, one can plate in a nickel bath
. containing any kind of additive, e.g., levelling agents or
brightening agents, etc., known to the art. Further, after
nickel coverage is established one can plate not only with
~i 20 nickel but also with any other electrodepositable metal
compatible with nickel, e.g., chromium, copper. zinc, tin,
silver, gold, platinum, palladium, cadmium etc.
The cathodic treatments in accordance with the
invention to induce the growth of iron or cobalt across the
polymer carbon-black surface can be carried out in any electro-
plating bath from which these metals can be deposited. For
example, the process of the invention has been carried out
, using an aqueous ferrous chloride bath to deposit iron and an
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1037~
aqueous cobalt chloride-cobalt sulfate bath to deposit cobalt.
Details of operation for these and other iron, cobalt and
nickel baths can be obtained from any text on electroplating,
for example, Electoplating Engineering Handbook, Edited by
A. Kenneth Graham, Reinhold Publishing Corporation,Copyright
1955. Those skilled in the art will appreciate that for parti- -
cular purposes it may be advantageous to deposit alloys of
nickel, cobalt and iron such as iron-nickel alloys, nickel- ~ -
cobalt alloys etc.
In addition to iron, nickel and cobalt, other metals -
of Group VIII of the Periodic Table of Elements can be deposited
in the manner as depicted in Figure 1 of the drawing, that is
initially behind a deposition front moving across the polymer-
carbon black surface. In particular palladium has been found ; -
to spread across a polymer-carbon black surface at a rate roughly ;
equivalent to the rate at which iron spreads,which rate is
somewhat slower than the spreading rate of nickel and cobalt
all other conditions being equal.
While the present invention is especially concerned
.. .. .
with electrodeposition of metal on a wide variety of plastic
- and other non-conductors (and on other materials which are
not generally amenable to ordinary electroplating techniques)
using a coating technique involving an essentially solid
polymer carbon-black-sulfur-containing coating adhered
directly or through an intermediate layer onto a base, the
invention is also applicable to bases having the requisite ;
carbon black-polymer-sulfur composition. As an example, a -~
saaple of EPDM synthetic rubber having a volume resistivity
of about 235 ohm-centimeters and containing reinforcing type,
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1037896
furnace carbon black and sulfur is directly plateable in a
Watts-type nickel bath to provide a highly adherent, rapidly
formed overall deposit of nickel. The spreading of the deposit
from a point of metallic conduction differs somewhat in the
case of a solid base of polymer-carbon black-sulfur from the
spreading depicted in Figure 1 of the drawing which is typical
of metal spreading using coatings. With a solid polymer-
carbon black-sulfur base the electrodeposited metals tends to
rapidly film over the entire surface of the object blurring ~-
to a certain extent the metal deposition front depicted in
Figure 1 of the drawing.
In order to give those skilled in the art a better
understanding and appreciation of the invention the following
examples are given:
EXAMPLE I
' A coating formulation was made up as follows: -
MaterialParts-by-weight
Natural Rubber (Smoked Sheet) 100
Nitrile Rubber (Paracril* BJLT)l 100
Acetylene Carbon Black2100
Sulfur 4
Trichloroethylene 10,000
* ~rademark
(1) Product of Uniroyal Chemical, Naugatuck, Conn.
(2) Product of Shawinigan Products Corp., Englewood Cliffs, N.J.
The aforedescribed Coating formulation was sprayed on an
. acrylonitrile-butadiene-styrene (ABS) surface to provide a
dried coating about 0.0025cm. thick. The coated and dried
ABS surface was then exposed for 40 seconds to the vapor above ~
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- 103789~i
- sulfur monochloride held at room temperature ~about 25C).
The surface having a single metal contact was then placed in
- a Watts-type nickel plating bath as a cathode with a driving
voltage of about 3 volts in opposition to a nickel anode.
The nickel deposit grew rapidly across the coated ABS surface
and deposition was continued until the deposited nickel had
a substantially uniform thickness of about 0.0025 cm. The
electrodeposit showed a 90 peel strength of about 1.88 kilo-
gram per centimeter (kg/cm) width tlO.5 lb/in width) when
pulled at 2.54 cm/minute.
EXAMPLE II
~ The following coating formulations were prepared:
- Coating A
Material Parts-by-Weight
Nitrile Rubber (Paracril* BJLT)9.87
: Stearic Acid 0.099
Zinc Oxide 0.493
Dibutyl Xanthogen Disulfide (C-P-B)l 0.394
Zinc diethyl dithiocarbamate (Ethazate*)l 0.025
Dibenzylamine (D-B-A)l 0.394
Sulfur 0.394
Methyl Ethyl Ketone (MEK) 11.3
,, Xylene 77 5
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* Trademark
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~037~96
Coating B
Material Parts-by-Weight
Acetylene Carbon Black 4.39
Nitrile Rubber (Paracril* BJLT) 8.78
Stearic Acid 0.088
Zinc Oxide 0.044
Butyl Rubber 0-044
Dibutyl Xanthogen Disulfide ~C-P-B)l 0.351
Zinc diethyl dithiocarbamate (Ethazate*)l 0.022
Dibenzylamine (D-B-A)l 0.351
Sulfur 0.351
Trichloroethylene 32.9
Xylene 52.6
Products of Uniroyal Chemical, Naugatuck, Conn.
* Trademark
., ,
Coating A was applied by brushing onto a poly-vinyl chloride
(PVC) plaque, and then coating B was applied in similar fashion `
over the dried coating A. After curing in an air oven for
3 hours at 90C. the plaque was dipped into a 1 w/o solution
of sulfur in cyclo-hexane, then plated to a thickness of about
.001 inch with Watts nickel. Initially the nickel deposit
grew rapidly across the surface of the plaque from a single
metal contact. A 90 degree peel strength of 2.5 kg/cm (12 lb/in)
- was achieved for the electrodeposit.
- 17
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1037896
EXAMPLE III
The following coating formulations were prepared: :
Coating C --
~ Material Parts-by-Weight
; Neoprene* AFl 50
- Neozone* Dl 1
: Magnesia 2
Zinc Oxide 2.5
Alkyl Phenolic Resin (SP-136)220
Ethyl Acetate 80
Hexane 82
Toluene 81
Water 0.5
Coating D
Material Parts-by-Weight
Acetylene Carbon Black 15
Natural Rubber (Smoked Sheet)7.5
- Styrene Butadiene Rubber (Naugapel* 1503)3 7.5 :
Sulfur 0.9
Heptane 240
Turpentine 70
.: Trichloroethylene 75
Products of E.I. Dupont de Nemours and Co.
2Product of Schenectady Chemical Inc., Schenectady, N.Y.
3Product of Uniroyal Chemical, Naugatuck, Conn.
* Trademar~
I
An ABS panel was dipped in coating C, air dried, then dipped
into coating D, and again air dried. It was then directly
electroplated in a Watts bath and the resulting nickel electro-
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deposit had a 90 degree peel strength of 1.79 kg/cm of width
(10 lb/in.).
EXAMPLE IV
Coatings A and B from Example II were modified so
that the concentration of curatives (C-P-B, Ethazate*, D-B-A
and sulfur) was doubled. In addition, MEK was added to coating
A such that its final weight equaled that of the xylene ti.e.,
from 11.3 to 77.5). An ABS panel was successively dipped in
modified coating A, then into modified coating B. The panel
was cured at 85C for 1-1/2 hours, during which time a notice-
able sulfur bloom appeared on the surface. The panel was then
- directly electroplated with Watts nickel with a rapid initial
rate of coverage. The resulting metal deposit exhibited a 90
degree peel adhesion of about 3.58 kg/cm of width (20 lb/in).
EXAMPLE V
,':`
`- An ABS panel (Cycolac* standard test plaque) was
coated by successively dipping in first coating A, then coating -
~-~ B of Example II. After curing 15 hours in air at 85C, the
panel was dipped into a 1 w/o solution of sulfur in cyclohexane.
; 20 It was then plated with a Watts FLASH, 0.0009 inch of semibright
(Perflow*) nickel, 0.0003 inch of bright (Udylite*) nickel and
15~ in conventional chromium. The plated panel was given a
thermal cycle of 90C for 2 hours, room temperature for 1 hour,
~ -40C for 2 hours, and then given a 16-hour exposure to CASS
- testing. ~o detectable failure resulted on the panel from
this treatment.
Those s~illed in the art will appreciate that although
` in most of the foregoing examples ABS plastic pla~ues were
.
; *Trademark
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~037896
used, the process of the present invention iq equally as well
adapted to the electroplating of utilitarian and decorative
objects made of other plastics such as polystyrene, phenol
formaldehyde resins, urea-formaldehyde resins, polyacrylates ~-~
and methacrytates, polyurethane, silicones, vinyls, vinyl-
idenes, epoxys, polyolefins and similar thermoplastic and
thermosetting resinous materials. In addition, the process
of the present invention can also be used to plate metals
which are coated with non-metallic, non-electrically conduc-
tive coatings, e.g., varnished aluminum and the like. ~hose
skilled in the art, in considering the scope of utility of the
process of the present invention, will recognize that with
some base materials it will be necessary to include an adhesive
layer between the polymer carbon black plating substrate and
the particular base material. While the form and character
of the base material is not of significance to the operability
of the process of the present invention, particular base
materials can provide qualities of utility not ordinarily con-
- templated. For example, a loosely matted paper was coated with -
a polymer-carbon black-sulfur mixture to provide after metal
deposition a novel useful electrode skeleton for a battery
plaque, fuel cell electrode or the like. In this regard
special attention is directed to the desposition of precious
metals from Group VIII. While economic factors make it un-
likely that platinum, palladium, rhodium, iridium, ruthenium
and osmium would find much use in the decorative plating of
plastics, these metals can be usefully deposited in the form
. ~ .
~; of electrodes, catalysts, etc., where their particular
chemical and electrochemical characteristics can be utilized.
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103789~
EXAMPLE VI
A sample plastic treated and coated as in Example III
was immersed as a cathode in an aqueous plating bath contain-
ing 300 gpl of ferrous chloride, 150 gpl of calcium chloride
adjusted to a pH of 1.2 to 1.8 and held at a temperature of
about 87C. Upon passage of current through the bath at a
voltage of 6 volts, the surface of the sample became covered - -
with a smooth adherent coating of iron.
EXAMPLE VII
The sample of Example VI was immersed as a cathode in
an aqueous cobalt plating bath containing about 335 gpl of
cobalt sulfate, about 74 gpl of cobalt chloride, about 46.5
gpl of boric acid and about 1.2 gpl of sodium fluoborate.
Upon passage of current through the bath, the sample rapidly -
filmed over with cobalt. ~ -
EXAMPLE VIII
One hundred parts by weight of a low-density, general
purpose polyethylene were milled in a Banbury type mixer at a
temperature of about 178C. along with 50 parts by weight of
Vulcan* XC72 carbon black (supplied by Cabot Corporation) and ~;
Tetrone* A brand dipentamethylenethiuram hexasulfide. The
milled composition was then molded and the molding thus pro-
duced was inserted as a cathode in a nickel plating bath.
Nickel rapidly spread over the surface from a metallic point
of contact and plating was continued to provide a firm, adherent
nickel electrodeposit having a 90 peel strength of about 1.8
kg/cm of width.
Although the present invention has been described
and illustrated in conjunction with preferred embodiments, it
is to be understood that modifications and variations may be
* Trademark
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103789~
resorted to without departing from the spirit and scope
of the invention. For example, those skilled in the art will
appreciate that the molding composition upon which nickel was
deposited in Example VIII is illustrative of a broader range
of polyethylene, polypropylene and mixtures and copolymers
thereof having blended therein about 15% to about 60% by
weight (of the total composition) of carbon black, to give a
volume resistivity of less than about 1000 ohm-centimeters,
along with sulfur or a sulfur donor for example of the
dipentamethylenethiuram hexasulfide type in an amount equivalent
in sulfur content to about l~ to about 10% by weight (of the
total composition) of dipentamethylenethiuram hexasulfide. In
plating massive polymer bodies as in Example VIII an inter-
esting phenomenon has been noted, that is, the bond strength
of nickel electrodeposited on the polymer surface improves
with aging at room temperature. Thus the 90~ peel strength
set forth in Example VIII is the peel strength observed
immediately after plating. After a few days aging the
observed bond strength is often double (or more) of that ~ ~:
strength as set forth in Example VIII. Such compositional
and processing modifications and variations are considered ~ ~ ,
to be within the purview and scope of the invention and
appended claims. ;
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