Note: Descriptions are shown in the official language in which they were submitted.
1049769
Background of the Invention
1. Field of the Invention
This invention relates to an electrical insulation
composition and methods of covering a conductor therewith and,
more specifically, to an abrasion-resistan-t, insulating
coating for electrical conductors and methods of producing
electrical insulated conductors having a reproduceable
adhesion of the insulation to the conductor.
2. Technical Considerations and Description of Prior Art
Insulated electrical conductors, such as those
employed in telephony applications, are often subjected to
outdoor use or conditions under which the insulator is
exposed to the deteriorating influences of sunlight, weather
and abrasion. In the case of telephone drop wire, the
familiar black overhead wire which brings telephone service
to the home, it has been customary to employ extruded rubber
insulation covered by a cotton serving jacketed with a
neoprene compound of tire tread-like quality for protective
purposes. Although such protective coatings have been in
widespread use for many years and have proven satisfactory
from most standpoints, there has long been a desire to
develop an alternative, less expensive insulation.
Of course, any alternative covering must have
specific properties to satisfy the requirements of this type
of wire. For example, it is important that the plastic
covered drop wire be covered with an insulation material
which has adequate properties to withstand exposure to the
elements, as well as adequate low temperature flexibility,
impact resistance, and abrasion resistance.
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In the environment in which it is used, each end
portion of the wire is inserted into a metallic clamp. One
of the clamps is attached to a subscriber~s premises and the
other one to a telephone pole prior to the electrical
connection of the drop wire to wiring run inside the
subscriber's premises and aerial distribution cables,
respectively. At both the subscriber and the pole end of the
drop wire, the retention of the wire in engagement with the
clamp is effected by forces exerted by the clamp on the
la insulation. If this is not transferred from the insulation
to the conductors by the adhesion therebetween, the
insulation may pull from the conductors and the entire
weight of the drop wire would be held by -the terminal
connection. This may very well lead to a disconnection of
the circuit.
On the other hand, if the adhesion between the
composition and the conductors is too great, there may be
problems in attempting to strip the covering from the
conductors. Too great an adhesion could require an
excessive scraping activity tha-t would remove some of the
metallic conduc-tive material from the surface portion of the
conductors thereby increasing the electrical resistance and
changing the conductivity thereof. Excessive scraping also
unduly reduces the cross-sectional area of the wire or knicks
it thereby reducing the strength properties of the wire to
the detriment of its weight-supporting capability.
Drop wires have been manufactured in which
coverings other than the three layer covering hereinbefore
described have been used and which posses the requisite
properties which includes optimum adhesion. These have
generally involved the precoating of conductors with an
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~049769
adhesive followed by the extrusion of the final plastic
insulation. This disadvantageously involves an extra
manufacturing step and limits the line speed over that which
can be obtained by applying a one layer covering over the
conductors.
A composition of matter for producing a plastic
covered drop wire without the necessity of precoating the
conductors was disclosed and claimed in U. S. patent
3,579,608 issued on May 18, 1971 to John Be. DeCoste. In
that application, there was shown an abrasion-resistant
insulating coating which included a plasticized polyvinyl
chloride in combination with a brominated epoxy resin that
adhered directly to the surface of a heated conductor.
The conductors over which the plastic material is deposited
are preheated within the range of 200 to 250C (392F to
482F) prior to entering the cross head die of an extruder.
In the aforementioned DeCoste patent, a PVC ~ ;
composition incorporating a brominated epoxy resin, a
relatively expensive constituent, containing 18-48 percent
bromine was used as the adhesive promoter. It was believed
that the bromine was the functional portion of the epoxy
resin that was essential to the attainment of the required
adhesion. During the extrusion of the composition onto the
preheated conductor, it was believed that hydrogen bromide
was liberated which etched the conductor to facilitate
adhesion between the conductor and the plastic composition.
Although the DeCoste teachings have produced
samples of drop wire having adequate conductor-to-insulation
adhesion values, it has been found that a conductor preheat
range substantially above that disclosed in the above-mentioned
~04~
patent yields stil.l higllerl more conslstently obtalnable
adhcsion valucs~ See commonly assigned copending Canadian
Application Serial ~o, 207~153 filed on August 16, 1974 in
tlle names ~' E. J~ George, J. L Salter, E~ S. Sauer and
C. E Tidd, Jr.
Summary of thë Invention
According to one aspect of the invention there is
proYided a col~position of matter capable of being extruded
and which includes a mixture comprising 100 parts by weight
of a polyvinyl chloride homopolymer; 3 to 10 parts by weight
per 100 parts by weight of the polyvinyl chloride of a non-
brominated epoxy resin based on the condensation of epichloro-
hydrin and Bisphenol A, having a weight per epoxy equivalent
approximately in the range of 170 to 800; 55 to 66 parts by
weight per 100 parts by weight of oolyvinyl chloride of a
-. .. : -
' phthalate plasticizer; 3 to 7 parts by weight per 100 parts
by weight of polyvinyl chloride of a metallic stabilizer; 3
to 5 parts by weight per 100 parts by weight of the polyvinyl
chloride of antimony trioxide; 1 to 3 parts by weight per 100
parts by weight of the polyvinyl chloride of a carbon black
constituent, and 5 to 35 parts by weight per 100 parts of the
polyvinyl chloride of a filler constituent.
According to another aspect of the invention there
is provided an elongated member having at least one conductor
i covered with an extruded insulative composition of matter '
. which includes a reacted mixture comprising 100 parts by weight
of polyvinyl chloride homopolymer; 3 to 10 parts by weight per
100 parts by weight of the polyvinyl chloride of a non-
brominated epoxy resin based on the condensation of epichloro- : -
hydrin and Bisphenol A, having a weight per epoxy equivalent
approximately in the range of 170 to 800; 55 to 66 parts by
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~,' '. .'' ' ' . ,: "
~0'~ 7~;9
weight per .lOO parts hy weight of po].yvinyl chloride of a
phthalate plasticizer; 3 to 7 parts by weight per 100 parts
by weight of polyvinyl chloride of a metallic stabilizer; 3
to 5 parts by weight per 100 parts by weight of the polyvinyl
chloride of antimony trioxi.de; 1 to 3 parts by weight per 100
parts by weight of the polyv;nyl chloride of a carbon black
constituent; and 5 to 35 parts by weight per 100 parts of the
polyvinyl chloride of a filler constituent.
According to yet another aspect of the invention
10 there is provided a method of covering a conductive member
which includes the steps of advancing the conductive member
v along a path and contacting the member while the member is
maintained at a suitable temperature with a reaction mixture
'. comprising 100 parts by we;.ght of a polyvinyl chloride homo-
polymer; 3 to 10 parts by weight per 100 parts by ~eight of
.I the polyvinyl chloride of a non-brominated epoxy resin based
on the condensation of epichlorohydrin and Bisphenol A, having
a weight per epoxy equivalent approximately in the range of
~ 170 to 800; 55 to 66 parts by weight per 100 parts by weight
¦ 20 of polyvinyl chloride of a phth~late plasticizer; 3 to 7 parts
by weight per lOO parts by weight of polyvinyl chloride of a
metallic stabilizer; 3 to 5 parts by weight per 100 parts by
weight of the polyvinyl chloride of antimony trioxide; 1 to
3 parts by weight per 100 parts by weight of the polyvinyl
chloride of a carbon black constituent; and 5 to 35 parts by
, weight per 100 parts of the polyvinyl chloride of a filler
constituent, to form an adherent coating on the conductive
.' member comprising a reaction product of the reaction mixture.
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1 ~rief Desc-i~tio~ o, .he Dr~ ings
- 2 Other fe~tur_s of the present inven ion ~iill be
3 more readily understood from the follov~ing detailed
4 descrip.ion Oc specified em~odi~en.s thereof t-:hen read in
S conjunction with the acco~panying drawings, in ~hich:
6 FIG. 1 is a cross-sectional view of a drop wire
7 l, covered with an ins~la.ing co~position in accordance with
81' the pr-nciples o~ this inven-tion;
9¦ FIG. 2 is a cross-section view of conductors
101¦ having a three layer coverir.g and representing a prior art
drop wire;
12l FIG. 3 is a persepctive view sho-h~ing a typical
13! installation of the drop ~7ire from a support pole to a
1411 subscriber's premises;
lSI FIG. 4 is an enlarged view of the circled portio~
16,j of the subscri~er's premises shown in FIG. 3 and for
171i purposes of clarity illustrating the details of the
provisions for supporting one e~d of the drop ~ire adjacent
1911 the subscriber's premises; and
20j~ FIG. S is a vie~ of an apparatus for applying the
21¦1 composition to the wire in accordance ~7ith the principles
221~ of this invention.
23, Detailed Description
24l A strand material in the form of a conductor 10
251 to be insulated with a composition disclosed and claimed in
2~¦ this application is an electroror~Qd copper-clad steel
271! conductive ele~ent, e.g., typically having a diameter of
2~ ! apprcximately 0.038 inch.
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Two of the conductors 10-10 having the hereinbefore
described cons-truction are covered with a composition of
matter which forms an insulative covering 11. (see FIG. 1).
The insulation covering 11 is extruded simultaneously over a
spaced pair of spaced conductors 10-10 to form the configu-
ration shown in FIG. 1 which is commonly referred to as a
drop wire, designated generally by the numeral 12.
The drop wire 12 which includes electroformed
conductors 10-10 covered with the insulation 11 replaces the
priorly used three layer drop wire, designated generally by
the numeral 16 (see FIG. 2). As shown in FIG. 2, the conductors 10-10
were enclosed first with a rubber covering 17 followed by a
textile serving layer 18 and an outer covering 19 made of
neoprene.
As disclosed in the hereinbefore identified :~
Canadian application Serial No. 207,153,the plastic covered drop wire
12 may be manufactured advantageously in a single extrusion
operation as compared with the prior art drop wire 16 shown
in FIG. 2 manufactured in multiple steps.' Moreover, line
: 20 speeds may be increased since the slower process involving
the vulcanization of the neoprene and -the serving of textiles
has been eliminated.
The drop wire 12 is used to bring telephone
service from overhead aerial distribution cables 21-21
strung in a catenary between telephone poles 22-22 to
subscriber's premises. (see FIG. 3). One end of the drop
wire 12 is supported from a wedge-shaped clamp 23 attached
to a pole 22 while the o-ther end is supported from a similar
clamp attached to the subscriber's homes (see FIG. 4).
If there is insufficient adhesion between the
inwardly facing surface of the insulation 11 and the
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conductors 10-10 to transfer the weight of the drop wire 12
to the clamps 23-23, the integrity of the insulation layer
may be destroyed which may result undesirably in the drop
wire being supported solely by the terminal connections. It
follows that the composition as applied to the conductors
10-10 must form a drop wire 12 having at least a sufficien-t
minimum average adhesion of the conductors to the insulation.
There is a practical upper limit of adhesion values
as well as a critical lower limit thereof because of the use
to which the drop wire 12 is subjected. For example,
excessive adhesion would render the drop wire extremely
difficult to strip during an interconnection opera-tion. In
overcoming the adhesion to remove the insulation, an installer
could knick the conductors 10-10. This may affect adversely
the electrical properties of -the conductors 10-10 as well
as penetrate the copper cladding thereby exposing the steel
core to possible corrosion.
Lastly, the composition as applied to the
conductors 10-10 must have requisite physical, electrical and
service life properties and must not degrade during the
processing thereof,
The basic polymer which is utili~ed in the inven-
tive composition is a polyvinyl chloride (PVC) resin, a
homopolymer. The PVC resin has all of the characteris-tics
associated with a homopolymer including abrasion resistance,
but which, however, includes thermal instability which
creates processing problems. However, when the PVC resin is
caused to soften during process;ng made possible by the
; addition of additives to the compound, the
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1049769
resistance to abrasion is reduced. Fur-ther, the PVC must
be a suitable electrical grade PVC homopolymer.
The PVC resin may be any of a number of PVC resins
well known in the art for use as electrical insulation. In
accordance with the A.S.T.M. standard for 1966, suitable
homopolymers may be classified as within the range of from
GP5~0003 to GP6~0003, inclusive. Definition of these
characteristics are set forth in the A.S.T.M. standard under
designation D1755-66.
Briefly, the designation, GP, designates a general
purpose resin primarily intended for calendaring, extrusion
or molding processes. The first numerals (entries 5 through
6) represent a polymer molecular weight in terms of dilute
soluton viscosity and the last digit, 3, indicates the usual
preference for an electrical conductivity less than 6 micro-
mhos per centimeter per gram. This electrical characteristic
is, of course, not a basic requirement form the standpoint
of the inventive teaching. The bar under or the bar over a
numeral indicates a value less than or more than, respectively,
the cell classification for that numeral. The four ciphers
in the designations indicate that the properties of particle
size, apparent bulk density, plasticizer absorption and dry
flow are at the descretion of the customer in that any
A.S.T.M. cell classification may be used.
It is convenient to discuss concentrations in terms
of parts by weight based on 100 parts of the polymeric
material. The term polymeric material is defind as consist-
ing essentially of the PVC homopolymer. Concentrations so
designated, therefore, result in compositions having greater -
than 100 parts.
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Combined with the PVC to facilitate processing,
including the extrusion, of the composition is a monomeric
plasticizer. The selected monomeric plasticizer must be an
acceptable low temperature plasticizer. An acceptable low
temperature plasticizer is one which combines with the PVC
resin during compounding to become inserted between the
molecules of the resin. In this way, at low temperatures of
say 0F and below, the low temperature plasticizer acts as
bearings or rollers between the PVC resin molecules to
maintain the material in a flexible condition.
Ano-ther problem arises in attempting to optimize
the range of the monomeric plasticizer which is used. The
plasticizers employed typically are members of the ester
family which includes esters having a straight chain or a
branch chain. The straight chain ester materials are
generally more effective in maintaining flexibility at low
temperatures than branch chain materials, i.e~, esters
having at least 35 percent branch chains.
There are many commercially available monomeric
plasticizers, but the low temperature flexibility, electri-
cal properties and volatility of the plasticizers vary.
The monomeric plas-ticizer must cooperate with the other
constituents of the composition to provide the overall
requirements and service life of the drop wire. A suitable
plasticizer is one having suitable low temperature flexi-
bility and electrical properties. A preferred plasticizer
includes a phthalate plasticizer.
; A preferred concentration of the monomeric plasti-
cizer added to the PVC is 55-66 parts by weight of the phtha-
late plasticizer to 100 parts by weight of the PVC. Less
than 55 parts compromises low temperature flexing properties;
more than 66 parts reduces the flame retardancy and
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~049769
also results in a composition having poor elec-trical
properties and less than desireable compression resistance.
This could cause a possible movement of the end of the drop
wire 12 wi-thin the clamp 23.
Typical suitable phthalate plasticizers employed
in the inventive composition include, for example,
mixed normal alkyl phthalate such as N-octyl-n-decyl
phthalate (designated 810P), N-hexyl-n-octyl-n-decyl
phthalate (designated 610P), or a branch chain phthalate
trademark product of the Monsanto Company designated "Santi-
cizer" 711 or a blend of these monomeric plasticizers.
It has been found that NODP, as marketed by the
U. S. Steel Chemical Company under the designation PX-318 LTrade Mark~
is a suitable phthalate plasticizer.
Added to the polyvinyl chloride base and -the
phthalate plasticizer is a non-brominated unmodified liquid
epoxy resin based on the condensation of epichlorohydrin and
Bisphenol A. The epoxy resin is an important constituent
in the composition in that it is the primary vehicle for
ob-taining the adhesion of the insula-tion to the conductors
10-10. The epoxy resins are of the type as prepared and
characterized in accordance with ASTM D-1763, Type I, Grade
I regarding pure unmodified epoxies formulated from
epichlorohydrin and Bisphenol.
One of the characteristics of epoxy resin which
may be used as an indication of structure and usefulness is
; that of weight per epoxy equivalen-t (commonly referred to as
WPE) or weight per epoxide. The weight per epoxy equivalent
is the total molecular weight divided by the total number
of epoxide groups. ASTM D1652 describes methods of
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1049769
measuring the weight per epoxy equivalent. The higher the
weight per epoxy equivalent, the larger the epoxy resin
molecules. Also, as the weight per epoxy equivalent in-
creases, the softening point increases. Of course, as the
softening point increases, the more difficult is the process
of incorporating the epoxy resin into the composition and -
after approximately 90C becomes undesirable.
The above-mentioned ASTM, Type I, Grade I epoxy
resin is further broken down into four classes. Class I
includes liquid epoxy resins having a weight per epoxy equiva-
lent of 170-200. Class II is a more viscous liquid while
Class III includes semi-solids. Class IV include solids
having a weight per epoxy equivalent of 280-800 with a
Durrans' Softening Point of 40 to 90C.
It has been found that non-brominated epoxy resin
desirably is present in an amount of 3 to 10 parts by weight
per 100 parts by weight of the PVC. If less than three parts
~ of the epoxy resin is used, the adhesion between the plastic
; composition and the conductors is reduced. On the other hand,
no improvement in adhesion is achieved if more han ten parts
by weight of the epoxy resin would be used.
A suitable non-brominated unmodified epoxy resin is ~ -
a trademark product marketed by the Shell Chemical Company
under the designation "EPON" 828*. This constituent is an
uncured epoxy (liquid) having an epoxide equivalent of 175-
; 210 and an average molecular weight of 350-400.
It will be recalled that the drop wire insulated
with this composition is strung up to the subscriber's
premises. An antimony trioxide constituent must be used in
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~049769
order to render the inventive composition flame retardant.
It is desirable for drop wire manufactured in accordance
with certain requirements deemed necessary for subscriber
installation that a minimum limiting oxygen index of
twenty-six percent, as determined in accordance with
A.S.T.M. D-2863, be achieved. The antimony trioxide is
an essential part of the inventive composition in
achieving the minimum limiting oxygen index of twenty-six
percent.
A preferred concentration of the antimony trioxide
added to the PVC is 3 to 5 parts by weight of the antimony
trioxide to 100 parts by weight of the PVC.
A delicate balancing of the number of parts by
weight of the antimony trioxide in relation to the other
; constituents of the composition ;s necessary. If less than
three parts are employed, the limiting oxygen index require- -
ment is not met. On the other hand, the greater the number
of parts by weight of the antimony trioxide, the higher the
limiting oxygen index. However, the use of more than five
parts of antimony trioxide does not provide any subs-tantial
improvement in achieving additional flame retardancy. This
material also acts as a filler.
The antimony trioxide may be of several marketed
commercially. One antimony trioxide suitable for purposes
of this composition is marketed by N.L Industries under the
designation Regular Grade antimony trioxide.
Added to the PVC, the phthalate plasticizer, the
epoxy resin and the antimony trioxide is metallic stabilizer.
The metallic stabilizer is added to the PVC to protect the
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1049769
resultant composition against thermal degrada-tion during
the extrusion process and to improve the electrical
resistivity of the composition.
A preferred concentration of the metallic
stabilizer is three to seven parts by weight per 100 parts
by weight of the PVC. If less than three parts are used,
thermal heat stability is sacrificed which could result in
processing difficulties. Moreover, the electrical properties
of the insulation would be poor. While more than seven parts
could be used, no improvement in electrical properties nor
heat stability is realized.
The metallic stabilizer may be present in solid
form or dispersed in a carrier such as the phthalate
plasticizer. It has been found that a liquid metallic
stabilizer may be added to the compounding mixture together
with the other liquid constituents to benefit the composition -
at an early stage of preparation.
A suitable me-tallic stabilizer marketed by N L
Industries, Inc. as "Tribase" E-XL has been found satisfac-
tory for purposes of the composition. Tribase E-XL is a
trademark product including a ~asic lead silicate sulfate
and having a specific gravity of 4.0 and a lead oxide
content of 64.3%.
~ Added to the PVC, the phthalate plasticizer, the
; metallic stabilizer, the epoxy resin and the antimony
trioxide is a filler material. This material is generally
in powder form and is of assistance in promoting the adhesion
of the composition to the conductors 10-10.
A preferred concentration of the filler material
is 5 to 35 parts by weight per 100 parts by weight of the
~ ~49~69
PVC. If less than five parts are used, the electrical
properties are compromised since the composition would result
in a higher percent of plasticizers. If more than thirty-
five parts are used, impact resistance and low temperature
flexibility are sacrificed.
A trademark product, "Cab-O-Sil", is marketed by
the Cabot Corporation has been found to be acceptable for
purposes of the composition. Calcined clay and calcium
carbonate are also suitable filler constituents and several
combinations and/or subcombinations of these constituents
; suffice as a filler subsystem to the claimed composition.
In order to provide adequate light stability for
the inventive composition, ~n ultraviolet absorber is
combined with the PVC, the plasticizers and the metallic
stabilizer. The addition of the ultraviolet absorber is of
assistance in avoïding ultraviolet degradation of the drop
wire having the inventive composition covering the
conductors. This may occur, for example, when an unprote~ted
PVC is exposed to sunlight.
A preferred concentration added to the PVC is 1.0
to 3.0 parts by weight of the ultraviolet absorber per 100
parts by weight of the PVC homopolymer. If less than 1.0
part is used, the protection against ultraviolet exposure
and the environment is reduced thereby shortening the service
life of the wire. However, more than 3.0 parts are un- `
neoessary since adequate protection is achieved by an amount
falling within the stated range. The ultraviolet absorber
must be uniformly dispersed throughout the composition to
provide the desired weather resistance.
One family of ultraviolet absorbers which is
a~ailable and has been found to be acceptable are the
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1049769
carbon black family as marke-ted as a trademark product by the
Cities Service Company and designa-ted "Superba" 999. The
"Superba" 999 is a medium color channel type black with an
ash content of 0.05% by weight with a volatile matter maximum
content of 10% ~d a primary particle size of 20 millimicrons.
This material also acts as a filler and functions to promote
the adhesion of the insulation to the conductors lO-lO.
The hereinbefore described composition has been -
found to satisfy the requirements of a drop wire insulation.
Heat stability studies supported by actual extrusion trials
demonstrate that the inventive composition provides
excellent adhesion to the conductors as well as long term
heat stability. Specifically, the composition (1) is flame
retardant (2) is weather resistant (3) is extrudable and (4)
has excellent low temperature impact resistance properties.
Although the covering of conductors lO-lO with the
composition disclosed in the J. B. DeCoste patent 3,579,608
by using the process disclosed in the above identified E.J.Georgeet~l.
Application Serial No. 207,153 produces acceptable product,
the use of the reaction mixture herein disclosed including
a non-brominated epoxy resin results in substantial cost
savings as well as yielding reproducible average conductor-
to-insulation adhesion values in the desired range.
It is to be noted that a preferred composition
which gives optimum adhesion values comprises lO0 parts by
weight oE a polyvinyl chloride (PVC), 7 parts by weight per
100 parts by weight of the PVC of a non-brominated epoxy
resin having a weight per ap~,xy equivalen-t of approximately
l90, 66 parts by weight per lO0 parts by weight of the PVC of
a phthalate plasticizer, 5 parts by weight over 100 parts by
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10'~9'7~g
weight of the PVC of a metallic stabilizer, 3 parts by
weight per 100 parts by weight of the PVC of antimony
trioxide, 2.5 parts by weight per 100 parts by weight of the
PVC of a carbon black constituent, 5 parts by weight per
100 parts by weight of the PVC o~ fumed silica and 5 parts
by weight per 100 parts by weight of the PVC of calcined
elay.
Methods of Preparing and Applying the Composition
.
The principles of the methods of this invention
are used to apply an insulation to strand material such
as the copper-steel conductors 10-10 such that there is an
optimum adhesion between the conductors and the composition.
It has been found that an adhesion of the composition to
eaeh conductor in the neighborhood of approximately 15-25
pounds is preferred with limits of 8-32 pounds being
permitted providing the average adhesion of the two
conductors is a minimum of 12 pounds.
The use of eonduetor preheat temperatures as
taught in the above-identified George et al. Application
Serial No. 207,153 results in an insulated conductor
having the desired permanent adhesion characteristics of
insulation to metal. This oeeurred as a result of preheat-
; ing the conductor in the range of 525 to 675F and then
extruding thereover a eomposition such as that diselosed
and elaimed in DeCoste patent 3,579,603. It has also been
; found that the composition of this invention may also be
extruded thereover to provide a drop wire 12 having equally
exeellent properties including adhesion.
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In practicing -the method embodying the principles
of this invention, a pair of copper covered steel conductors
10-10 destined to be enclosed with the reactive mixture are
advanced along a manufacturing line, designated generally
by the number 31 (see FIG. 5) in spaced generally parallel
relationship. The composition is applied to the conductors
10-10 as they are advanced through a dual channel core tube
(not shown) of an extruder 32.
Prior to the entry of the wires 10-10 into the
lQ extruder 32, the wires are preheated to a temperature in the
range of 450F to 650F and preferably in a range of 575F
to 625F. The preheating of the wires 10-10 may be
accomplished by any number of conventional preheating
facilities, des;gnated generally by the numeral 33, includ-
ing inductive-resistance heating. In order to prevent
excessive heating of the conductors 10-10 and to minimize
convective and radiation heat losses, the conductors are
advanced through an insulated chamber 34 interposed between
the preheating facilities 33 and the extruder 32.
In the process of preparing -the composition for
application to the wires 10-10 in accordance with the
principles of this invention, the PVC admixed with a non-
brominated unmodified epoxy resin and other compounding
ingredients heretofore disclosed are fed into and through
the extruder 32. The details of the extruder 32 are well
known in the ar-t and are described in the aforementioned
; George et al. Application Serial No. 207,153.
The material flows toward a die 36 and ultimately
toward engagement with the conductors 10-10 pàssing through
the die. It will be recalled that a definite preheat has
been imparted to the conductors 10-10 which are moved
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continuously through the crosshead die 36. In this way, the
composition is extruded over the preheated conductors which
are moved continuously through the die 36 and which act as
internal forming mandrels.
Previously, the epoxy resin was identified as the
constituent primarily relied on to ob-tain the requisite
average adhesion of the insulation to the conductors 10-10.
However, when using epoxies, it is customary to use a two
part system, a resin and a hardener, which are mixed together
at the point of use, with the hardener curing the resin.
Reproducible acceptable average adhesion values are obtained
by practicing the principles of this inven-tion suprisingly
without the use of a hardener.
The engagement of the composition with conductors
10-10 preheated to within the specified range causes a
reaction to occur within the mixture which unexpectedly cures
the epoxy resin and promotes adhesion between the reaction product ;
and the wire. The preheated conductors 10-10 cause the poly-
vinyl chloride to degrade at the interface of the copper-clad
steel conductors and the covering composi-tion. Hydrochloric
acid is liberated as one of the byproducts of the degradation
of the PVC. The hydrochloric acid is believed to etch the
surfaces of the conductor 10-10 and acts as a catalytic
curing agent for the epoxy resin giving an instantbond at
the interface of the conductors and the composition to yield
consistently acceptable adhesion values.
The presence of a lubricant may interfere with the
adhesion of the composition to the conductors 10-10.
Although a lubricant constituent in and of itself is not an
element of the composition, the metallic stabilizer which is
used may be surface coated wi-th a lubricant.
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However, at the temperatures specified in
practicing this invention 9 the degradation of the PVC is
such that sufficient hydrochloric acid is produced to react
and cure the epoxy resin thereby minimizing the effect of
any lubricant which may be present.
It has been found that notwithstanding the use of
a stabilizer which does not include a lubricant that
temperature ranges below those specified will not result in
consistently reproducible adhesion values of the composition
to the conductors 10-10. While the use of the upper limit
of the temperature range ~392 to 482F) stated in the above-
identified DeCoste patent has resulted in adhesion values
of the composition which border in the range of 8-12 pounds,
the results may be improved and rendered reproducible
for in-line production control.
In order to achieve a reproducible average conductor-
to-composition-adhesion of at least 12 pounds, temperatures
in the preferred range of 575 to 625F are used.
It has been found that generally acceptable
20 average composition to conductor adhesion values have been
obtained when using conduc-tor preheat temperatures in the
range of 450 to 650F. The lower end of this range is
somewhat less than that disclosed in the hereinbefore
identified Application Serial No. 207,153 in which the
composition included 3 to 10 and preferably 7 parts by weight,
per 100 parts by weight of PVC, of a brominated epoxy resin.
Since that constituent included 48% bromine, less epoxide
radials were present. With the non-brominated epoxy resin
more epoxy groups are present for the same number of parts.
Hence, lower preheat temperatures could be used when
compounding the same number of parts of the epoxy resin or
less parts could be used with a higher preheat range.
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Tests have shown that the adhesion varies with
respect to the conductor preheat temperature. There is a
critical lower limit below which the adhesion begins a
generally rapid decline with non-reproducible results. As
an example, insulation extruded over conductors 10-10
preheated to generally below 450F was found to be capable
of being pulled manually from the conductors.
There is also an upper limit~of temperature beyond
which` the adhesion values are affected adversely by the
thermal degradation of the insulation. It has also been
found that after a conductor preheat temperature of
approximately 650 F, the adhesion of the insulation to the
conductor decreases. Apparently, conductor preheat tempera-
tures in excess of 650F causes the bonding process herein-
before described to become less effective. If the epoxy
resin constituent is subjected to this excessive heat upon
engaging the conductor 10, the bond between the conductor
and the insulation can become~degraded.
In order to test the adhesion of the composition
to the conductors 10-10, the plastic covered drop wire 12
is subjected to what is referred to as a slip-bff test.
This test is described in detail in the hereinbefore-referred-
to Application Serial No. 207,153. This test measures
in pounds the force applied parallel to the axis of the
conductors 10-10 and which is required to pull a 3/8 inch
length of insulation from one end of the conductor. The
applied force at which the insulation is pulled off the ~ -
conductor is recorded and is determined to be the magnitude
of adhesion of the composition to the conductor.
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1049'769
The drop wire 12 is also subjected to a compression
test, an elongation test, low temperature flexibility, clamp
holding and impact tests, all of which are described in the
aforementioned Application Serial No. 207,153.
The following examples illustrate various flexible
PVC insulation compositions prepared in accordance with the
invention. The examples are summarized in Table I and are
set forth in tabular form. For comparison purposes, all
examples set forth were carried out using the homopolymer
described hereinbefore. ~oreover, all amounts are in parts
by weight.
TABLE I
Exam~les
Ranges Constituent A B C D
100 PVC Resin 100 100 100 100
3-10 Epoxy Resin 7 7 10 4
55-66 Phthalate Plasticizers66 60 55 66
3-7 Metallic Stabilizer 5 3 7 5
3-5 Antimony Trioxide 3 5 4 3
1-3 Carbon Elack 2.5 3 1 2.5
5-35 Fillers
CaCO3 15 10
Fumed Silica 5 5 0 5
Calcined Clay 5 10 10 5
It has been found that the composition set forth
in Example A provides a drop wire 12 having the most
preferred characteristics.
E~ample A
In the preferred composition, 7.0 parts of a
non-bromin~ted unmodified epoxy resin ~epoxide equivalent
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typically 190), obtained from commercial sources, and
produced as the condensation product of epichlorohydrin
and Bisphenol, 100 parts, by weight, of a polyvinyl chloride
resin, GP5-00003-ASTM-D1755, 66.0 parts, by weight, of
mixed N-octyl, n-decyl phthalate, 5.0 parts by weight, of
lead silicate sulfate stabilizer, 5 parts, by weight, of
fumed silica and 5 parts by weight of calcined clay, 3.0
parts, by weight, of antimony trioxide and 2.5 parts, by
weight, of carbon black, were mixed together and extruded
over conductors preheated to a temperature of 600F.
Example B
The procedure of Example A was repeated with the
exception that 7 parts by weight of the non-brominated
unmodified epoxy resin, 60 parts bf the plasticizers, 3
parts of the metallic stabilizer, 5 parts of the antimony
trioxide, 3 parts of carbon black, 15 parts of calcium
carbonate, 5 parts of fumed silica and ten parts of calcined
clay were employed. The reaction mixture was extruded
; about conductors 10-10 preheated to a temperature of
approximately 600 F. The adhesion values of the reaction
product to the conductors were similar to those obtained
for Example A.
Example C
The procedure o~ Example A was repeated but with
the use of 10 parts of epoxy resin, 55 parts of a phthalate
plasticizer, 7 parts of a metallic stabilizer, ~ parts of an
antimony trioxide, 1 part of carbon black, 10 parts each of
calcium carbonate and calcined clay as fillers.
Example D
The procedure of Example A was repeated but
instead using ~ parts by weight per 100 parts by weight of
the PVC of the epoxy resin. While the preferred example
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~0497S9
employs an epoxy resin having an epoxide equivalent typical-
ly of l90, it has been found -that epoxy resins in the solid
class IV produce acceptable results. For example, an epoxy
resin which is the trademark product of Celanese Company and
designated "Epi-Rez" 522C has been used in the reaction
mixture.
Testing
The plastic drop wire insulation composition must
possess specified properties, some of which have been
described hereinbefore. The following tables indicate the
properties of a composition having the composi-tion designated
Example A in Table I:
TABLE II - Example A Tests
Property Results Method of Test
. .
Adhesion in lbs. > 12 Strip 3/8" length of
insula-tion from a
single conductor
Compression in lbs. > 850 Load required to
cursh insulation
Elongation
New % ~ 250 ASTM D470
Aged % ~ 200 ASTM D470 - 48 hrs.
at 212 t 2F
Clamp Holding Pass 290 lbs. static load
for 24 hrs. without
rupture
Low Temp. Impact Pass 40 inchOpounds and
-20 + 2 F
Wrap Test Pass 3/8" Mandrel and -30
+ 2F
Water Immersion Tests
Insulation Resistance
(Megohms-lO00 fO.)~ 200 Megohm Bridge
Corrected to 60 F
- Mutual Capacitance
(Micro-Farads/1000 ft.) ~ 0.040 Measured at l.0 KHz
frequency using auto-
matic bridge unit and
associated components
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TABLE III
Test Results for Example A
Preheat Temp. of 400450 500575 600625 650::
Wire (F)
Average Adhesion of
Reaction Product 8.5 1616.5 2122.5 21 23
to Conductors (Lbs.)
:: Wire preheat temperatures in excess of 650F tend to have
a degarding effect on the insulation composition. Moreover,
wire preheat temperatures beyond 650F undesirably require
extended cooling before being advanced in engagement with
sheaves.
It is to be understood that the above described ;~
arrangements are simply illustrative of the invention.
Other arrangemen-ts may be devised by those skilled in the
ar-t which will embody the principles of the invention to
fall within the spirit and scope thereof.
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