U.S. patent number 3,877,965 [Application Number 05/264,097] was granted by the patent office on 1975-04-15 for conductive nylon substrates and method of producing them.
This patent grant is currently assigned to Rohm and Haas Company. Invention is credited to Robert Broadbent, Sidney Melamed, Robert G. Minton.
United States Patent |
3,877,965 |
Broadbent , et al. |
April 15, 1975 |
CONDUCTIVE NYLON SUBSTRATES AND METHOD OF PRODUCING THEM
Abstract
A method for providing nylon substrates with a durable, adherent
silver coating and product by electroless deposition from a plating
bath comprising silver salt, ammonia, anionic surfactant,
formaldehyde, and sufficient acid to bring the pH to about 8.4-9.4.
The substrates are sensitized with stannic chloride solution.
Inventors: |
Broadbent; Robert
(Philadelphia, PA), Melamed; Sidney (Elkins Park, PA),
Minton; Robert G. (Cornwells Heights, PA) |
Assignee: |
Rohm and Haas Company
(Philadelphia, PA)
|
Family
ID: |
26757851 |
Appl.
No.: |
05/264,097 |
Filed: |
June 19, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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76245 |
Sep 28, 1970 |
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Current U.S.
Class: |
427/304; 2/243.1;
106/1.05; 106/1.11 |
Current CPC
Class: |
C23C
18/44 (20130101); D06Q 1/04 (20130101); C23C
18/285 (20130101) |
Current International
Class: |
C23C
18/20 (20060101); C23C 18/31 (20060101); C23C
18/28 (20060101); D06Q 1/04 (20060101); D06Q
1/00 (20060101); C23C 18/44 (20060101); C23c
003/02 () |
Field of
Search: |
;117/138.8N,47A,16R,212,213,35S,13E ;106/1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Van Horn; Charles E.
Assistant Examiner: Ball; Michael W.
Parent Case Text
This application is a division of our copending U.S. application
Ser. No. 76,245, filed Sept. 28, 1970 now abandoned.
Claims
1. A process for producing a silver-coated fibrous nylon substrate
which comprises subjecting a fibrous nylon substrate to a
sensitizing polyvalent metal salt bath, then washing the substrate
with water, subjecting it to a bath of deionized water, removing it
from the deionized water and squeezing excess water out of it, then
allowing the resulting wet fibrous substrate to stand, with
periodic agitation, within an aqueous solution consisting
essentially of water, a silver salt dissolved therein, 3 to 3.5
mols of ammonia per mol of silver salt, 0.025 to 0.1 percent, based
on the solution, of an anionic surfactant, formaldehyde, and
sufficient acid to bring the solution to a pH of about 8.4 to about
9.4 prior to introduction of the substrate, rinsing the
silver-coated fibrous substrate, and drying it, the time of the
silvering step being sufficient to deposit a substantially
continuous coating of silver on the substrate fiber without
2. A method in accordance with claim 1 wherein said anionic
surfactant is
3. A method in accordance with claim 1 wherein said nylon substrate
is
4. A process for producing a silver-coated fibrous nylon substrate
which comprises subjecting a fibrous nylon substrate to a
sensitizing ethanol solution of a stannic salt, then washing the
substrate with water, subjecting it to a bath of deionized water,
removing it from the deionized water and squeezing excess water out
of it, then allowing the resulting wet fibrous substrate to stand,
with occasionally stirring within an aqueous solution consisting
essentially of water, silver nitrate, 3 to 3.5 mols of ammonia per
mol of silver nitrate, 0.025 to 0.1 percent, based on the solution
of sodium lauryl sulfate, formaldehyde in an amount sufficient to
reduce the silver nitrate to metallic silver, and sufficient acid
to bring the solution to a pH of about 8.4 to about 9.4 prior to
introduction of the substrate, rinsing the silver-coated fibrous
substrate, and drying it, the time of the silvering step being
sufficient to deposit a substantially continuous coating of silver
on the substrate fiber without changing the modulus characteristics
of the fiber.
Description
DESCRIPTION OF THE INVENTION
This invention relates to a method for plating nylon with silver.
The plating of metals such as silver onto a nylon substrate has
been known for some time and can be effected with relative ease.
For many purposes a minimum of adherence of the silver to the
substrate is sufficient for the intended use of the plated
substrate. In some instances, however, it is critical that the
silver plating be extremely durable and adherent. It is extremely
difficult to obtain such a durable and adherent coating on a
consistent and readily reproducible basis by the techniques of the
prior art.
It has now been found that a process involving a series of
carefully controlled process steps can provide nylon substrates
with a durable and adherent coating without significantly altering
the basic mechanical characteristics of the product.
The process of the present invention is applicable to nylon
substrates irrespective of the substrate form. Thus, it is
effective in the silver plating of monofilaments, nylon fabrics,
including both knit and woven fabrics, bundles of filaments in yarn
form, nylon staple and nylon films. Somewhat more massive nylon
forms may also be treated by the process of the present invention,
but the need for the exceptional characteristics provided by the
present invention are less commonly required for such articles. The
term "nylon" is used in its broadest sense to cover fiber-and/or
filmforming polyamides; the invention is of particular use,
however, in the silver plating of polycaprolactam and
polyhexamethylene adipamide.
As is customary in the art, any finishes on the substrate which
tend to interfere with the plating process should be cleansed from
the substrate prior to the process. Typically, fabrics and fibers
may have some sort of finish or lubricant which might interfere
with the process; generally, these can be removed by treatment of
the material with suitable surface active agents and/or
solvents.
The substrate is customarily "sensitized" by treatment with a water
soluble salt having a polyvalent metal cation. For example, an
aqueous solution of stannous chloride is commonly used for this
purpose. Such solutions can also be used for the purposes of the
present invention to the extent that suitable penetration of the
sensitizer into the substrate surface can be effected and to the
extent that interfering ions and/or precipitates can be removed by
simple washing procedures prior to the silver deposition. In the
preferred and quite superior practice of the present invention, a
stannic salt such as stannic chloride is utilized instead of the
stannous salt, and a water-soluble organic solvent for the stannic
salt is used instead of water to form a solution of the sensitizing
agent. For example, lower molecular weight alcohols such as ethanol
and isopropanol are quite effective. Methanol offers no real
advantage over water insofar as improving the activity of the
sensitizing agent, although the use of methanol alone or in
combination with the other sensitizer solvents can be employed as
necessary to the particular practice contemplated.
In order to obtain a product having the desired characteristics for
the purposes of the present invention, careful control of the
silvering solution is essential. In the normal practices of the
prior art, silvering solutions prepared with a slight deficiency of
ammonia, i.e., less than the two equivalents of ammonia required to
form the silver-ammonia complex, is utilized. In accordance with
the practice of the present invention at least three mols of
ammonia up to 4 mols of ammonia per mol of silver nitrate or its
equivalent are incorporated in the silver plating bath. If less
than this amount is included in the bath, the silver plating
solution is insufficiently stable for effective deposition without
bath decomposition. If greater than this amount is used, the
process proceeds too slowly, if at all, and it is difficult to
obtain a good silver coating in a reasonable time. Preferably, the
bath incorporates less than about 3.5 mols of ammonia per mol of
silver nitrate.
The silvering bath should contain a small amount of anionic
surfactant to stabilize the system and thereby to insure that the
plating occurs essentially only on the sensitized surface without
seriously affecting the metal of the silver coating applied to the
substrate. Typically, 0.0l% up to about 0.1% defines the operable
concentration of sodium lauryl sulfate. At the higher end of the
range, this surfactant tends to destroy the boiling water
resistance of the coating, while at the lower end of the range, the
amount of surfactant present is not sufficient to give the
necessary bath stabilization. In general, optimum results are
obtained if the bath contains the equivalent of 0.025% of sodium
lauryl sulfate.
With the large quantities of ammonia recommended for the practice
of the present invention, the pH of the bath is in excess of 10,
e.g., about 10.4. It has been found that if the pH is not reduced,
the bath tends to decompose before the nylon substrate is silvered.
More importantly, if the bath is not adjusted to a pH of about 9.4
or lower, the silver coating that does result is not particularly
resistant to boiling water. However, if the pH is lowered to about
8.0, a good coating is not obtained. Accordingly, it has been found
necessary to maintain the pH of the silvering bath at a value from
about 8.4 up to about 9.4 to obtain results necessary for many
substrate uses.
The ammonia can be introduced into the solution, e.g., as ammonium
hydroxide, in which case it is necessary to add an acid to reduce
the pH to the desired level. Acetic acid is a typical acid useful
for this purpose. It should be understood, however, that the
ammonia stabilization and pH maintenance of the bath can be
accomplished by other essentially equivalent means. Thus, e.g.,
amines and/or certain ammonium salts may be used in place of
ammonium hydroxide in which case the need for acid adjustment to
obtain the desired pH may be minimized and/or eliminated. It is to
be understood that such methods are contemplated as included within
the scope of introducing ammonia and acid into the silvering
solution to provide an amount of ammonia and acid in the silvering
bath corresponding to the values previously described.
In accordance with the practices of the present invention, the
sensitized nylon substrate is introduced into the silvering bath
together with the customary reducing agents such as formaldehyde.
The reaction is standard and well known in the art and leads to the
deposition of silver on the nylon substrate. The resulting product
is a silvered nylon in which the silver coating is extremely
durable and adherent as well as electrically conductive. The
resulting product further possesses essentially all of the
mechanical characteristics of the substrate despite the
penetration, as shown by photomicrographs, of the silver into the
surface of the substrate.
In the examples which follow, the durability and adherence of the
silver plating on nylon is tested, inter alia, by a boiling water
test. In that test, a portion of the silvered nylon article is
placed in a beaker of boiling deionized water for 30 minutes and
dried by patting the excess water from the specimen with a paper
towel. Silvered portions of the specimen are placed across
electrodes spaced 1.5 inches apart and the electrical resistance
measured (e.g., using a Kiethley Electrometer Model 610C, or a Mura
Corporation Model 80M Multimeter). Samples are considered
non-conductive if their resistances is greater than a million ohms.
In the examples which follow, the substrate which was silvered was
a knit nylon sleeve. For these articles, a section at least two
inches long was cut from the sleeve and several cut filaments were
unravelled from different parts of the section (generally about
ten) and tested in the manner just described. Other tests are
described in the examples.
The invention is described with regard to the preferred practices
of the invention which include use of the stannic salt-ethanol
sensitizer and the treatment of knit fabrics. In its broadest
scope, however, the invention is not limited thereto and is broadly
useful in the manner described earlier herein. An interesting facet
of the invention is that the silvering of fabrics such as knitted
and woven fabrics can be effected in a manner such that the silver
coating on fibers removed from the fabric is continuous and does
not apparently change at the fiber crossover points which were
present in the fabric during the plating thereof. The individual
conductive filaments are basically nylon having the same modulus
characteristics as the uncoated filaments. Filamentary materials
can be uniformly silvered irrespective of the physical form of the
filament, i.e., irrespective of whether the filament has been
crimped, false twisted, or otherwise textured.
EXAMPLE I
A silvering bath was prepared, by dissolving in 14,200 ml. of
deionized water, 362 ml. of 1% aqueous sodium lauryl sulfate
solution, 700 ml. of a solution of 37.0 grams of silver nitrate in
deionized water, 325 ml. of 2.17N ammonium hydroxide and sufficient
1N acetic acid to reduce the pH to 9.0.
A sensitizing solution was prepared by dissolving 15 grams of
stannic chloride in 1500 ml. of denatured (one-half gallon of
benzene per 100 gallons of 95% ethanol) alcohol. A three-inch
diameter sleeve was knit from a 15-denier nylon monofilament. A 94
gram sample of the nylon sleeve was placed in the sensitizing
solution for five minutes, then drained and washed with running
water and placed in a bath of deionized water. To the silvering
solution were then added 725 ml. of 2.4% formaldehyde solution. The
nylon sleeve, after squeezing to remove water, was then fed into
the silvering solution and allowed to stand therein for 90 minutes
with periodic agitation. The sleeve was then removed from the
silvering bath, rinsed with water, and dried for 2 hours at
65.degree.C. in a circulating air oven. The dried sleeve weighed
105.7 grams and 10 filaments removed thereof had an average
resistance of 490 ohms per 1.5 inch length. After being subjected
to the boiling water treatment described previously herein, the ten
filaments had an average resistance of 600 ohms per 1.5 inch
length. The average resistance of 15 denier nylon filament which
has not been silvered is greater than the upper limit of the test
machine employed which is 10.sup.14 ohms.
EXAMPLE II
A 100-gram sample of nylon sleeve of the type described in Example
I was scoured with t-octylphenoxypoly(9) ethoxyethanol and sodium
tripolyphosphate to remove the finish therefrom. The scoured sample
was then placed in 2000 ml. of a sensitizing solution comprising
20.0 grams of anhydrous stannic chloride in denatured alcohol (as
described in Example I). The sleeve was soaked for five minutes,
withdrawn from the sensitizing solution and passed under two water
spray heads, passed through a aqueeze roll and then stored in 2,000
ml. of deionized water. A silvering bath was prepared by adding in
sequence, to 6,300 ml. of water, 1.58 grams of sodium lauryl
sulfate, 625 ml. of 0.30N silver nitrate solution, 612 ml. of 1N
ammonium hydroxide, 160 ml. of 1N acetic acid (to bring the
silvering bath pH to 9.0) and 371 ml. of 2.4% formaldehyde
solution. The nylon sleeve was removed from the deionized water,
squeezed to remove excess water, and placed in the silvering bath.
The sleeve was retained in the bath for 165 minutes with occasional
stirring and then removed from the bath, rinsed with water to
remove the silvering solution, and dried. Fibers (about 10) removed
from the sample had an average resistance of 860 ohms per 1.5 inch
length. After being subjected to the boiling water test described
previously, the sample had an average resistance of 570 ohms per
1.5 inch length. No non-conductive filaments were found in any of
the samples.
The products obtained by the present invention can be used for any
of the purposes for which silvered nylon has been employed in the
past. In particular, however, the process provides an excellent
method for the production of silvered fabrics, including films, for
use as electrical components of various electronic devices. The
individual fibers can be used in such various items as women's
apparel, including stockings and panty hose, and in carpeting and
other like uses wherein it is desired to reduce the static charge
accumulated on the article of which the silvered filament is a
part. In view of the extreme resistance of the silvered fiber to
boiling water, it is particularly useful for incorporation in
carpets in place of metal fibers employed in the past. Yarns
prepared containing the silvered nylon may be subjected to the
usual dyeing operations and scouring operations characteristic of
carpet industry practice without substantial loss of the
static-reducing conductivity. The fact that the fiber is basically
nylon and has the same modulus characteristics as the rest of the
filaments in the yarn bundle permits use of the silvered filament
in this manner without significantly changing the physical
characteristics of the yarn bundle other than the tendency to build
up a static charge. Metal fibers used in this manner tend to be
less durable in service due to the tendency of the metal filaments
to break. Previously silvered nylon filaments lacked the durability
and silver adhesion to permit treatment of the filament in dyeing,
scouring, and like operations.
Accordingly, the preferred products obtained by the practice of the
present invention can be subjected to 30 minutes treatment at
180.degree.F, in an aqueous bath containing 0.5 weight percent of
sodium lauryl sulfate and sufficient sodium tripolyphosphate,
trisodium phosphate or tetrasodium pyrophosphate to provide a pH of
9, followed by two hours in a boiling acetic acid solution at a pH
of 5 without the electrical resistance increasing beyond 10,000
ohms/inch. In general, the resistance will be less than about 1,000
ohms/inch.
A significant feature of the process defined herein is that both a
nylon monofilament and a nylon multiflament yarn, whether crimped
or uncrimped, can be processed to provide a silver-coated nylon
monofilament or yarn having the desired electrical conductivity and
resistance. The yarn can be silvered as a warp proceeding from a
beam in a manner similar to that used in slashing. The monofilament
or yarn can suitably be pre-textured or not, as desired, to provide
a package, i.e., a bobbin, spool, cone, pirn, tube, etc., of
silvered monofilament or yarn in continuous form, i.e., in
continuous lengths greater than 100 yards long.
The process can also be utilized with nylon staple fiber to provide
a silvered staple fiber having the previously described
characteristics. A staple fiber yarn can be produced from the
silvered staple fiber to provide a staple fiber yarn having
conductivity characteristics consistent with those earlier
defined.
* * * * *