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Nov. 19, 1946,
Filed June 29, 1943
` Halogepafëd âurface
Dire-¿cmi or) iba cool'ed Copper Wire.
Patented Nov. 1,9, 1946
Donald J. Miller, Akron, Ohio, assigner to Ameri
can Anode, lne., Akron, Ohio, a corporation oi’
Application June 29, 1943, Serial No. 402,689
2 Claims.
(C1. 117-79)
rl‘his invention relates t0 insulated electrical
conductors and to methods of making the same
and is particularly concerned with the application
of insulating coatings of latex rubber to copper
ency toward accelerated deterioration. Maximum
ilexibility of the copper wire is retained sub
stantially unimpaired. Although the reasons for
this surprising result are not fully understood,
it is believed that the greatly accelerated de
terioration encountered by prior workers has been
due to the fact that ammonia in the latex tends
It has been common practice to apply insulat
ing coatings to copper wires by passing a wire
through a bath of liquid rubber latex and dem
to dissolve small quantities o-f the copper and
that this soluble copper in the rubber has been
it has been considered necessary, however, rirst l0 responsible for its rapid deterioration. In the
to tin the wire or to Wrap it with cotton or paper
present invention, the latex is coagulated imme
or to apply a coating of lacquer to prevent direct
diately upon contact with the wire so that a skin
contact between the copper and the rubber coatn
of coagulated rubber is formed immediately ad
ing. Since it Was known that minute quantities
jacent to the wire and before there is opportunity
of'copper salts would cause very rapid deteriora
`for the ammonia to dissolve any substantial
tion of rubber and that copper would be attacked
amount of the copper. ri‘he powdery material
by sulfur in the rubber, it was considered abso
assists in obtaining a uniform coating of the
lutely necessary to provide a separating barrier
metal salt over the surface of the wire, prevents
between the two. In actual practice, pre-tinning
adhesion of the coating to the wire so that the
of the copper wire has been the most favored 20 insulation may be readily stripped when desired
method and has been used almost universally in
and also assists in guarding the copper against
positing a coating of latex rubber on the wire.
making latex coated wire.
Although not undesirable for many ordinary
Contact with the liquid latex.
If desired, the
benefits derived from the metal salts and the pow
uses, such prior products are not satisfactory in
dery material, respectively, may be enjoyed in
many special cases, as where great flexibility is of 25 dependently by using either without the other.
Vital importance, since the coating of tin or wraps
In order that the metal salt and powdery ma
of paper and the like greatly stiften the copper
terial may be applied in a uniformly thin coating .
over all the exposed copper surface, these ma
terials preferably should be suspended in a readily evapora-table liquid vehicle. The wire may be
immersed in the resulting composition to receive
an overall liquid ñlm coating which then may be
This problem recently has assumed major im
portance bacause of our Government’s need for
a highly ñexible and dependably insulated copper
wire for use in certain secret detection devices,
the nature of which was not disclosed to appli
cant. For some reason, also not disclosed to ap
plicant, the armed services insisted upon natural
rubber insulation so that it was not possible to
resort to synthetic insulations which might be
less susceptible to copper deterioration.
After considerable experimentation, applicant
dried to deposit the salt and powdery material
on the wire in uniformly distributed finely
divided condition.
In an illustrative example of the invention, a
flexible stranded copper wire made up of 40
strands of 2 mil. wire was utilized without pre
treatment of any kind. The stranded copper wire
has discovered a method which makes possible 40 was dipped in a suspension containing 11/2 lbs.
the application of latex rubber insulation directly
of soapstone in a gallon of alcohol. The Wire was
to copper wire without the interpo-sition of tin,
then withdrawn and dried until substantially all
paper, cotton, or like protective layers and with
the alcohol had evaporated from the coating,
out subjecting the rubber insulation to the danger
The thus treated wire was then dipped in a sec
of copper-accelerated deterioration.
45 ond liquid composition containing 50 g. of zinc
According to the invention, the copper wire to
nitrate, 50 g. of calcium nitrate, and 11/2 g. of a
be coated is pre-treated with a composition pref
wetting agent dissolved in 1000 cc. of water.
Again, the Wire was removed from the liquid com
valent metal salt and a lwater-insoluble powdery
position and dried until substantially all the
material. The pre-treated Wire then is passed 50 water had evaporated, a drying period of from
through liquid rubber latex and a coating of latex
10 to l5 minutes in hot air at 150° F. usually be
rubber is deposited on the Wire. An insulating
ing adequate. The so prepared wire was then
coating so deposited has been found to provide
dipped in an unvulcanized but vulcanizable latex
dependable insulation over a long period of time
composition and left therein for from 5 to 10
and to be apparently free of the expected tend
' seconds to coagulate on the Wire a coating of
erably comprising both a water-soluble poly~
latex rubber which, when dry, was about .0077
thick. The wire together with its freshly coagu
lated latex coating then was Washed thoroughly
for several hours in warm water, dried for several
hours in hot air, and ñnally vulcanized at a tem
perature appropriate to the particular vulcaniz
able composition utilized. To provide a smooth
non-tacky surface iinish, the rubbercoated wire
then was passed through a saturated water solu
tion of chlorine gas, or other halogen solution
to halogenate the surface.
The resulting product retained substantially
unimpaired the inherent flexibility of the strand
ed copper wire and proved to be entirely satis
factory to our governmental agencies from this
tity of a single salt or by other substantially neu
tral coagulants for aqueous dispersions of rub
ber as distinguished from the strongly corrosive
acid coagulants which should not be used. For
example, zinc chloride, calcium chloride, alumi
num nitrate, and the like are quite satisfactory
either singly or in mixtures. The quantity of
salt utilized and/or the time of immersion in the
latex may be varied to produce different thick
nesses of rubber in accordance with principles
well established in the art. Likewise, the soap
stone (talc) may be replaced by other finely-di
vided water-insoluble material such as finely-di
vided mica, magnesium carbonate, diatomaceous
earths such as fossil flour, and the like.
ln manufacturing short lengths of insulated
wire for use in special instruments, the process
rubber Was not subject to rapid deterioration.
may be carried out simply and conveniently by
«After 28 days in a Geer oven test the insulation
stretching the copper wire in a frame and dip
retained its original flexible rubbery character
substantially unimpaired. The Geer oven test 20 ping by hand in the successive liquid materials.
It is also possible, however, to perform the process
referred to is an accelerated aging test regularly
continuously in the manner, for example, shown
used in the rubber industry. Although norrpre
in the Strube Patent 2,179,965.
cise correlation with actual aging conditions is
Although developed particularly for the manu
possible, the 28 day period in the Geer oven may
of small gauge, ñexible stranded wire for
conservatively be said to equal from 5 to l0 years’ 25
the purpose indicated, the invention obviously
aging under ordinary conditions. Similar rub
may be used in applying insulating coatings to
ber compositions containing extremely minute
other types of Wire and it will also be appreciated
amounts of copper salts have been known to
that the principles herein set out are useful in
deteriorate to a semi-liquid mass when placed
applying latex rubber coatings to copper bases
in the Geer oven for less than a Week,
in general. Further, numerous modifications and
The single figure of the accompanying drawing
variations in details of the procedure and mate
is a more or less diagrammatic perspective view
rials herein described may be eiîected by the
showing an insulated conductor made in accord
skilled artisan without departing from the spirit
ance with the invention, portions of the struc
ture being shown bro-ken away and sectioned, and 35 and scope of the invention as deíined by the ap
point of view. Contrary to all expectations, the
significant features being designated by appro
priate legends. The figure has been drawn on a
pended claims.
I claim: '
l. A freely-flexible insulated wire comprising
a stranded copper wire, a coating consisting of
have been exaggerated in the interest of clear il
lustration. Thus, the coating of metal salt and 40 a substantially neutral water-soluble polyvalent
metal salt and a water-insoluble inert powdery
Y powdery material has been shown as having con
material directly on the wire,- and an insulating
siderable thickness while, as a matter of fact, it
permanent coating of vulcanized rubber mate
is barely though definitely perceptible in the
rial directly overlying the so-coated wire, the
coated wire itself. Similarly, the halogenated
rubber material being one normally subject to
surface shown as a distinct outer layer is in fact
deterioration whenin contact with copper, the
merely a hardened skin surface penetrating only
insulated Wire having the property of retaining
slightly into the body of the rubber.
its flexibility and insulating properties substan
The latex utilized in the invention ordinarily
tially unimpaired after 28 days in a Geer oven`
Will be a natural rubber latex in an unvulcanized
condition and containing vulcanizing agents for
2. An insulated wire comprising a copper wire,
the rubber such as dispersed sulfur and acceler
a coating consisting of a 'substantially neutral
ators as Well as antioxidants and other custo
salt coagulant for aqueous dispersions of rub
mary conditioning agents. It is also possible to
ber and a water-insoluble inert powdery mate
utilize artificial dispersions of natural rubber or
analogous rubber materials normally subject to .f rial directly on the wire, and an insulating per
manent coating of vulcanized rubber materiall di
deterioration in the presence of copper.
rectly overlying the so-coated wire, the rubber
The powdery material and the metal salt may
material having the characteristics of rubber de
be suspended in water, alcohol, acetone, or other
posited directly from an aqueous dispersion of
similar readily evaporatable volatile liquid for
rubber material and comprising rubber normal
application to the wire. The materials may be
ly subject to deterioration when in contact with
suspended in different liquids and applied sepa
copper, the insulated wire having the property
rately as in the preceding speciiic example or, if
of retaining its flexibility and insulating proper
desired, they may be suspended in a single liquid
ties substantially unirnpaired after 28 days in a
or mixture of liquids, The mixture of zinc ni
trate and calcium nitrate set out in the speciñc 65 Geer oven test.
example may be replaced by an equivalent quan
considerably enlarged scale and certain'features
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