Note: Descriptions are shown in the official language in which they were submitted.
~ 755~8 3298
1 FLAME RETARDANT POLYMERIC COMPOSITIONS CAPABLE OF
PASSING THE CSA VARNISH TEST
This invention relates to crosslinkable polymeric
compositions which exhibit moisture and heat resistance and
flame resistance and which are useful in producing insulated
wire and cable as well as molded products. More particularly,
it relates to a crosslinkable ethylene-vinyl acetate copolymer
10 composition capable of passing a test procedure known as the
CSA Varnish Test.
one of the most important areas where fire resistant
polymer compositions find use is in the electrical environment,
15 i.e., where both insulating and fire resistant properties are
sought, most especially in the area of conductor insulation.
At one time, extrudable compositions available to the wire
and cable art were required, for flame resistance, to contain
halogenated polymers such as chlorinated polyethylene,
20 polyvinyl chloride, chlorobutadiene, chlorinated paraffin,
etc., together with antimony trioxide, both components being
present in sizable quantities. Alternatively, a coating of
chlorosulfonated polyethylene paint was applied to a non-
flame retardant insulating compound which constituted an
25 additional manufacturing operation.
For certain types of dry transformers, particularly
high voltage transformers, a problem existed in that
electrical failures occurred due to surface creepage of the
organic insulating component used. The problem was solved
3 through the addition of hydrated alumina to compositions
whose organic binder consisted of butyl rubber, epoxy resins
or polyester resins. However, these compositions do not
possess a balance of excellent extrudability characteristics,
physical and electrical properties, heat resistance and
35 flame retardance. Such compositions are disclosed in U.S.
1 17 S 5~ 8 3298
l Patent Nos. 2,997,526-7 and 8 of Kessel et al. The described
compositionS for such usage have poor tensile strength,
elongation and percent elongation retained after aging.
Fire retarding polymeric compositions exhibiting,
5 inter alia, improved moisture and heat resistance consist
essentially of an intimate mixture of at least one cross-
linkable polymer containing as a major component an ethylene-
vinyl acetate copolymer, one or more silanes and one or more
hydrated inorganic fillers have found wide acceptance in the
lO wire and cable art. Such compositions are disclosed in U.S.
Patent Nos. 3,832,326 and 3,922,442 of North et al. These
polymeric compositions exhibit a unique combination, or
balance, of improved physical and electrical properties
together with a high degree of flame and fire retardance.
15 These highly desirable results are achieved without the use
of halogenated polymers such as polyvinyl chloride and
chlorosulfonated polyethylene, thereby eliminating hydrogen
chloride fumes; without carbon black, thereby permitting its
use as colored insulations; without any flame retardant
20 coatings such as are currently required, thereby eliminating
an additional step in manufacturing operations when the
compositions are used as, e.g., insulating compounds extruded
onto a conductor; and without antimony trioxide, thereby
eliminating a very expensive compound.
Such compositions find particular use as white (an
inherent property) and colored uniinsulation compositions,
which can be sxtruded over metal, e.g., copper or aluminum,
conductors, to provide a single layer insulating and
jacketing composition which is rated according to U.S.
30 standards for 90C. operation, and in some cases operation
at temperatures as high as 125, at up to 600 volts.
These insulating compositions of North et al. have
found particular utility in the insulation of switchboard wire,
appliance wire, and automotive wire where a unique combina-
35 tion of superior electrical properties combined with
~3~ 1175S~ 3298
1 resistance to the degradative effects of heat and flame areeSsential~ and where low smoke density and non-corrosive
fumes are desirable.
Besides the three essential components, other
5 additives~ such as pigments, stabilizers, lubricants, and
~ntioxidants can be incorporated into th~ compositions of
North et al. Among the antioxidants, polymerized trimethyl
dihydro quinoline was found by North et al. to provide
effective oxidation inhibition.
In the CSA varnish test, three samples of polymeric
insulated wire are (1) heated in an oven, ~2) immersed in
insulating varnish, (3) reheated in an oven for an extended
period, (4) cooled, and (5) bent over a small diameter
mandrel. The polymeric composition under test fails if a
15 crack down to the conductor appears in the insulation of any
of the three samples when it is bent over the mandrel.
Compositions exemplifying the invention of North et al. which
employ polymerized trimethyl dihydro quinoline as an anti-
oxidant do not pass the CSA varnish test.
Many polymers are susceptible to oxidation which
causes impairment of their physical properties. This
degradation may be initiated by heat, light or other energy
forms. In most polymers, oxidation proceeds by a free radical
chain mechanism. The free radicals form in the polymer under
25 the influence of an internal energy source. These radicals
then react with oxygen to form peroxy radical which in turn
reacts with the polymer to form a hydroperoxide and an~ther
radical which then continues the chain reaction.
Antioxidants have been developed to inhibit
30 polymer degradation. They act either to tie up the peroxy
radicals so that these radicals are incapable of propagating
the reaction chain, or to decompose the hydroperoxides in such
a manner that carbonyl groups and additional free radicals
are not formed. The former, called chainbreaking anti-
35 oxidants, free radical scavengers, or inhibitors, usually are
4 3298
1175S~
1 hindered phenols, amines, and the like. The latter, calledperoxide decomposers, generally are sulfur compounds ~i.e.,
mercaptans, sulfides, disulfides, sulfoxides, sulfones,
thiodipropionic acid esters and the like~, or metal complexes
5 of dithiocarbamates and dithiophosphates.
The patent art discloses a number of antioxidants
used heretofore with olefinic resins.
U.S. Patent Nos. 3,160,680 of Tholstrup et al. and
3,282,890 of Hagemeyer et al. disclose an antioxidant combin-
10 ation of a sterically hindered phenol and a diester ofthiodipropionic acid for use in or-olefin hydrocarbon
polymers. U.S. Patent No. 3,033,814 of Tholstrup teaches the
use of a three component antioxidant consisting of a hindered
phenol, a diester of thiopropionic acid and phenyl salicylate
15 in a polymer of a C2-C10 alpha olefin hydrocarbon. U.S.
Patent No. 3,181,971 of Rayner employs the combination of a
phenolic antioxidant and a primary or secondary aromatic~or
aliphatic amino compound with propylene homopolymers or
copolymers of propylene with other hydrocarbons. U.S. Patent
20 No. 3,242,135 of Bown et al. combines an ester of boric acid
with a hindered phenol and a diester of thiodipropionic acid
to provide oxidation inhibition for homopolymers and copolymers
of C2-C8 alpha olefin hydrocarbons. U.S. 3,245,949 of Murdock
is directed to homo and copolymers of C2-C8 aliphatic olefin
25 hydrocarbons and mixtures thereof employing as an antioxidant
the combination of a phosphorous-containing polyphenolic
compound and the dilauryl or distearyl ester of dithiopropionic
acid. None of these patents discloses or suggests that the
antioxidant combinations can be usefully incorporated in other
30 than hydrocarbon polymers, i.e., no use is suggested with a
polymer containing a major amount of an ethylene-vinyl acetate
copolymer.
It is an object of this invention to provide a
crosslinkable ethylene-vinyl acetate copolymer composition
35 capable of passing the CSA varnish test.
~5~ 1 17S S~ ~ 3298
1 It is another object of this invention to provide an
ethylene-vinyl acetate copolymer composition containing silane-
treated hydrated inorganic filler which not only exhibits
superior moisture and heat resistance and flame retardance but also successfully passes the CSA varnish test.
All percentages and parts expressed in the specifi-
cation and claims are by weight, unless specifically indicated
otherwise.
In accordance with the present invention, it has
been found that if an antioxidant comprising a diester of
thiodipropionic acid is substituted for the polymerized
trimethyl dihydro quinoline antioxidant in the ethylene-vinyl
acetate (EVA) compositions of North et al., the resulting
15 compositions not only exhibit substantially the same moisture
and heat resistance, flame retardance and oxidation inhibition
as they formerly did but they unexpectedly pass the CSA
varnish test. More particularly, this invention is directed
to a crosslinkable polymeric composition capable of passing0 the CSA varnish test which comprises:
(a) a polymeric component containing at least 66
by weight of a copolymer of ethylene and a vinyl
ester of a C2-C6 aliphatic carboxylic acid, a Cl-C6
all-yl acryla~e or a C~-C6 alkyl methacrylate
(b~ from ~C tc ~0 parts of hydrated inorganic
filler per 100 parts of the polymer component,
(c) 0.5 to 5 parts of an alkoxy silane per 100
parts of hydrated inorganic fille., and
(d) an amount effective to enable said polymeric
composition to pass the CSA varnish test of an
antioxidant composition comprising at least 25%
distearyl-3, 3'-thiodipropionate.
This invention is also described as directed to a
crosslinkable polymeric composition capable of passing the CSA
35 varnish test which comprises:
. -6- 117S588 3298
1 (a) a polymeric component containing at least 66%
by weight of a copolymer of ethylene and a vinyl
ester of a C2-C6 aliphatic carboxylic acid, a Cl-C6
alkyl acrylate or a Cl-C6 alkyl methacrylate,
(b) from 80 to 400 parts of hydrated inorganic
filler per 100 parts of the polymer component,
(c) 0.5 to 5 parts of an alkoxy silane per 100
parts of hydrated inorganic filler, and
td) 0.1 to 5 parts of distearyl - 3, 3'-thiodi-
propionate per 100 parts of the polymeric component.
The present invention is also concerned with the
improvement in a crosslinkable polymeric composition of the
type comprising:
(a) a polymeric component containing at least 66%
by weight of a copolymer of ethylene and a vinyi
ester of a C2-C6 aliphatic carboxylic acid, a Cl-C6
alkyl acrylate or a Cl-C6 alkyl methacrylate,
(b) from 80 to 400 parts of hydrated inorganic
filler per 100 parts of the polymer component, and
(c) 0.5 to 5 parts of an alkoxy silane per 100
parts of hydrated inorganic filler, which comprises
admixing with said polymeric composition an amount
effective to enable said polymeric composition to
pass the CSA varnish test of an antioxidant compo-
sition comprising at least 25% distearyl - 3l 3'~
thiodipropionate.
Again this invention relates to an electrical
conductor coated with a uniinsulating layer comprising any of
the crosslinkable polymeric compositions described hereinabove
30 which are capable of passing the CSA varnish test.
The present invention relates to crosslinkable
polymeric compositions comprising copolymers of ethylene and
a vinyl ester of an aliphatic carboxylic acid, an alkyl
35 acrylate or an alkyl methacrylate and a silane-treated
~7~ 1175588 3298
1 hydrated inorganic filler which will pass the CSA varnish test.
These compositionS find particular utility as wire and cable
insulation.
The compositions of this invention contain, in
5 addition to a particular antioxidant composition, one or more
crosslinkable or curable ethylene copolymers, one or more
silanes and one or more hydrated inorganic fillers. The
copolymers, silanes and inorganic fillers include those
disclosed in U.S. Patent Nos. 3,832,326 and 3,922,442 of
10 North et al.
The Crosslinkable Copolymer Components
The terms crosslinkable or crosslinking are ascribed
their normal art recognized meaning in the present specifica-
15 tion, i.e., they denote the formation of primary valence bondsbetween polymer molecules.
Crosslinking can be accomplished by any of the known
procedures such as chemical means including peroxide crosslink-
ing; by radiation using cobalt - 60, accelerators, ~ -rays,
~ -rays, electrons, X-rays, etc.; or by thermal crosslinking.
The basic procedures for crosslinking polymers are extremely
well known to the art and need not be described here in detail.
The polymeric component of the present composition
is a copolymer of ethylene an~ a comonomer which may be a
25 vinyl ester, an acrylate or a methacrylate. The vinyl ester
may be a vinyl ester of a C2-C6 aliphatic carboxylic acid,
such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl
~entanoate or vinyl hexanoate. The acrylates and-methacryla~es
may be any of the Cl-C6 alkyl esters including, for example,
30 methyl, ethyl, propyl, butyl, pentyl or hexyl acrylate or
methacrylate, The preferred copolymer comprising the poly-
meric component of this invention is an ethylene-vinyl acetate
copolymer containing about 9 to about 90%, preferably about 9
to about 40~, most preferably about 9 to about 28%, vinyl
35 acetate, balance ethylene~
Although little is gained, and some properties are
even harmed, it is possible to include minor proportions of
other crosslinkable polymers or copolymers in the composition
-8- 1175588 3298
1 of this invention. However, ethylene copolymers, preferably,
ethylene-vinyl acetate copolymers, as described above, should
comprise at least about 66~ of the total polymers present.
Representative of such minor polymeric components which can be
5 used in such non-preferred embodiments include polyethylene,
copolymers of ethylene with propylene, butene ! the acrylates
and maleates, polydimethyl siloxane and polymethylphenylsiloxane,
copolymers of vinyl acetate with the acrylates, etc. Obviously,
mixtures of these minor polymeric components can be used.
Terpolymers of ethylene and vinyl acetate derived
from, e.g., any of the corresponding monomeric materials
listed above (other than ethylene or vinyl acetate) can be
used. A representative terpolymer would be an ethylene-vinyl
acetate-vinyl maleate terpolymer.
The ethylene-vinyl aceta~e copolymers used in our
invention preferably have a melt index of from about 1.0 to
about 20Ø
The polyethylenes useful in the present invention
include essentially all high, medium and low density poly-
20 ethylenes as well as mixtures thereof. The most preferred
polyethylenes for blending for use as uniinsulation for
electrical wires and cables generally have a density of from
about 0.900 to about 0.950 gm./cc. and a melt index of from
about 1.0 to about 10Ø
More specifically, the compositions of the present
invention provide a superior and unexpected balance of:
1. low temperature brittleness, i.e,, the
composition will not readily crack during low
temperature movement (ASTM D 746).
2. heat resistance after aging, i~e., excellent
elongation after extended service at 90~C. and
even 125C.
3. arcing and tracking resistance, as high as 5 KV,
whereas even porcelain shows surface breakdown at
4 KV. This property is not often required, however,
~75S8~ 3298
1 in the preferred environment of under 600 volt
service.
4. flame resistant and flame retardance.
5. moisture resistance, i.e., low mechanical
absorption of water which yields a superior di-
electric constant,
6. resistance to industrial chemicals.
It is not known why the compositions of this inven-
tion provide such a superior balance of properties. It is
lO possible that there is some synergistic relationship betweer. the
ethylene-vinyl acetate copolymer, silane and hydrated inorganic
filler, but there is no intention to be bound by such a theory.
However, it has been established that for low voltage environ-
ments, less than 5000 volts, even more particularly for less
15 than 600 volt environments, the compositions of this invention
are particularly useful for service as uniinsulation. Uni-
insulation is an art accepted term denoting insulation where
one layer is extruded around the conductor, and this one layer
serves as the electrical insulation and the jacketing to
20 provide physical and flame protection. The present compositions
are especially adapted for service as uni nsulation in the
under S000 volt, most especially in the under 600 volt range,
where only a single extruded coating is used, and it is in
the environment that a superior balance of proporties is
25 required. It has been further found that ethylene-vinyl
acetate copolymers will hold very large amounts of filler and
still provide high flexibility and a high degree of crosslinking.
The simultaneous achievement of high filler loading, flexibility
and crosslinking is quite surprising as high flexibility and
30 high crosslinking were generally believed incompatible, as are
high crosslinking and high filler loading (which implies low
crosslinkable polymer content). Ethylene-vinyl acetate co-
polymers further provide superior fire retardance to the
; ` polymeric compositions of the present invention.
-lo- 1175588 3298
1 The above described ethylene-vinyl acetate copolymers
may be crosslinked by irradiation with high-energy electron
beams or through the use of chemical crosslinking additives.
Fully crosslinked, these polymers become thermoset in behavior.
In the preferred compositions of this invention, chemical cross-
linking is preferred, particularly where superior physical
strength is required.
Chemical crosslinking is accomplished by incorporating
a crosslinking agent, e.g., dicumyl peroxide or alpha, alpha'
bis~t-butylperoxy) diisopropylbenzene, into the ethylene-vinyl
acetate copolymer. The peroxide is later activated during
processing to link the ethylene-vinyl acetate polymer chains
into a three-dimensional network (and other minor amounts of
crosslinkable polymer, if present).
The chemical crosslinking is carried out in accor-
dance with procedures well known to the art, and variations
in the general cross-linking conditions set out below will be
apparent to one skilled in the art. The present invention
is moreover, not limited to the use of tertiary organic
20 peroxides for chemical crosslinking, and other art recognized
materials which decompose to provide free radicals can be
used. Obviously such crosslinking agents should not decompose
during compounding of the composition, but the selection of
acceptable cross-linking agents will be apparent to those
skilled in the art.
Generally speaking, as the amount of crosslinking
agent used increases, the degree of polymer crosslinking
increases. Usually no more than 10~ (based on polymer) of
the organic tertiary peroxides need be used, with 3 to 6%
30 being more typical values. Other crosslinking agents may
require different amounts, but these can be readily determined.
It is often advisable to avoid very low amounts of crosslinking
agents, since some loss of resistance to deformation under
sudden or continuous pressure may ensue. Crosslinking co-
35 agente such as triallylcyanurate and the like may also be
11 117 5 5~ 8 3298
1 included to increase the effectiveness of the crosslinkingagent.
The tertiary organic peroxides, as with most
other chemical crosslinking agents, are activated by heating
5 to above their activation temperature whereupon decomposition
thereof occurs. Any of the known procedures can be used to
aCcomplish activation, e.g., high pressure steam application
to the composition.
The art of radiation crosslinking is so highly
lO developed that little need be said with respect to such
procedures. As higher total doses of radiation are used, the
degree of crosslinking generally increases, and for preferred
crosslinkings a total radiation dose of about 5-25 megarads
will be used.
Crosslinking is generally conducted at superatmos-
pheric pressures, e.g., on the order of 200 to 400 psi,
although higher or lower pressures may be used. Pressure is
employed to avoid uncontrolled porosity in the polymer, which
would be highly undesirable in electrical insulation.
In general, the higher the degree of crosslinking
the more resistant the polymeric composition is to moisture,
chemical reagents, etc., and the less resistant the polymeric
composition is to abrasion. At lower degrees of crosslinking
there is also some loss of heat resistance as well as pro-
25 nounced effect on percent elongation after aging. The exact
degree of crosslinking can, of course, be varied to take the
above factors and their effect on the final product into
account. Although higher or lower values can be used, for
wire and cable insulation a crosslinking percentage on the
3O order of about 95% for ethylene-vinyl acetate is generally
preferred, determined by extraction weight of soluble compo-
nents in the crosslinked polymer.
` ~ 17 S 58 8 3298
1 The Silane Component
One or more substituted silanes comprise the
second essential component of the polymeric compositions of
the present invention.
Any silane may be used in the present invention
which will not adversely affect the desired balance of
properties and which will help to bind the polymer and
inorganic filler of the present invention, provided that the
silane is not combustible, e.g., alkoxy and amine silanes,
10 and does not interfere with polymer crosslinking or degrade
during polymer processing.
The preferred silanes used in forming the insulating
compositions are the alkoxy silanes, e.g., lower alkyl-,
alkenyl-, alkynl- and aryl-alkoxysilanes as well as the lower
15 alkyl-, alkenyl-, alkynl- and aryl-alkoxyalkoxy or -aryloxy-
alkoxy silanes. Specific examples of such silanes are
methyltriethoxy-, methyltris (2 methoxyethoxy)-, dimethyl-
diethoxy-, alkyltrimethoxy-, vinyltris (2 - methoxyethoxy)-,
phenyl-tris (2 - methoxyethoxy), vinyltrimethoxy- and
20 vinyltriethoxy- silane.
It is preferred to use the vinyl silanes for best
results, and of the vinyl silanes the following are especially.
preferred:
gamma-Methacryloxypropyltrimethoxy-Silane
H C5C - -C - o(CH2)3Si(OCH3)3
30 and
Vinyl - Tris (2-Methoxyethoxy) Silane
H2C = CHSi (OCH2CH20CH3)3
~ 17 S 58 8 3298
1 The HYdrated Inorganic Filler Component
The fillers used in the present invention are the
hydrated inorganic fillers, e.g., hydrated aluminum oxides
(A12o3 3H20 or AlIOH)3), hydrated magnesia, hydrated calcium
silicate Of these compounds, the most preferred is hydrated
aluminum oxide.
To obtain the superior balance of properties
- described, it is mandatory that a hydrated inorganic filler
be used in formulating the polymeric compositions. It must
10 be emphasized that large proportions of another type of filler,
be it inert or not, cannot be added to the compositions and
still achieve the superior balance of properties.
The water of hydration in the inorganic filler must
be released during the application of heat sufficient to
15 cause combustion or ignition of the ethylene-vinyl acetate
copolymer. The water of hydration chemically bound to the
inorganic filler is released endothermically. It has been
found that the hydrated inorganic filler increased flame
retardance in a manner far superior to other fillers previously
20 used by the art to provide insulation with flame retardance,
e.g., carbon black, clays, titanium dioxide, etc. What is
even more surprising is that flame retardance is combined
- with excellent electrical insulation properties at the high
filler loadings used, since at these loadings the copolymeric
25 composition contains a large amount of bound water.
The filler size should be in accordance ~ith those
sizes used ~y the prior art.
The Antioxidant Component
An antioxidant composition comprises the fourth
30 component of the polymeric compositions of the present invention
and is the component which unexpectedly results in these
compositions passing the CSA varnish test. A diester of
thiodipropionic acid constitutes an essential ingredient of
this antioxidant. The preferred diester is distearyl - 3, 3'
35 thiodipropionate ~DSTDP). Although this material is a
-14- 1 175 58 8 3298
1 known antioxidant which functions as a peroxide decomposer,
its action in enabling the compositions of this invention to
pass the CSA varnish test is not entirely understood. The
action of this particular diester is all the more surprising
5 since a related diester, dilauryl - 3, 3' thiodipropionate
(DLTDP), although often used interchangeably with or in
combination with ~STDP in an antioxidant application, will
not produce a polymeric composition capable of passing the
CSA varnish test when it is substituted for DSTDP in the
10 compositions of the present invention.
In addition to DSTDP which constitutes an essential
component of the antioxidant composition, other antioxidants
may be used in combination therewith. It has been found that
the use of two different types of antioxidants provides
15 effective oxidation inhibition. Thus, a mixture of an
antioxidant of the chain breaking type and one which is a
peroxide decomposer provides a very effective antioxidant
composition. Therefore, with DSTDP, which is a known peroxide
decomposer, an amine or a hindered phenol may be effectively
20 employed as an antioxidant composition. Among these free
radical scavengers, the stearically hindered phenols are
especially effective. Useful phenols include the alkylated
phenols, the alkylidene - bis-alkylated phenols and the
polyphenols. Specific examples thereof include 2, 6 ditertiary
25 butyl-para-cresol, octadecyl 3, 5-di-t-butyl-4-hydroxy-
hydrocinnamate, 2, 2'-methylene bis~6-t-butyl-4-methyl phenol),
4, 4'-butylidene bis t6-t-butyl-3 methyl phenol), 1, 3, 5-
trimethyl-2, 4, 6-tris ~3, 5-di-t-butyl-4-hydroxybenzyl)
benæene and tetrakis (methylene (3, 5-di-t-butyl-4-hydroxy-
30 hydrocinnamate)) methane with the latter being particularlypreferred.
The CSA Varnish Test
This test developed by the Canadian Standards
Association evaluates the insulation of coil-lead wires
35 (Clause 6.7 of CSA Standard C22.2 No. 116) and electrical
~ 175 58 8 3298
1 wires and cables (Clause 4.25 of CSA Standard C22.2 No. 0.3).
The tests applied to coil-lead wires and electrical wires
and cables are essentially the same. Specimens of insulated
~ire are heated in an air oven at 104-106C. for 1/2 hour,
5 following which they are removed from the oven and immediately
immersed in insulating varnish for one hour at room temperature.
Upon removal from the varnish the specimen is suspended at
room temperature for one hour and then placed in an oven for
20 hours at either 149-151, 159-161 or 203-205C. depending
10 on the type of wire. Following the cooling of each specimen
at room temperature for 2 hours, it is bent once around a
small-diameter mandrel. An insulated wire fails this test if
the insulation on any one of three specimens of the wire under
test cracks through to the conductor.
The compositions of this invention unexpectedly pass
this stringent test whereas the prior art compositions
exemplified by North et al. although possessing properties
which make them useful as superior flame retardant wire and
cable insulation are unable to pass the CSA varnish test. Not
20 only do the compositions of this invention pass the CSA
varnish test they also exhibit the excellent fire retardance
and moisture and heat resistance of the North et al. poly-
meric compositions.
The Proportion of the Components
The amounts of the polymer and filler in the
composition of this invention can be varied within wide
proportions. However, the silane percentage should be in the
range of from about 0.5 to 5.0 parts per 100 parts of filler.
Lower amounts may be insufficient to provide adequate surface
30 treatment while larger quantities could have an adverse effect
on some of the physical properties, i.e., elongation, of an
extruded insulating compound after crosslinking.
Best results are obtained in coating, e.g.,
extruding, onto electrical wires and cabLes when from 80 to
35 400 or more weight parts of filler (most preferable at least
-16- 3298
1175588
1 125-150 weight parts), 0.5 to 5.0 weight parts of silane and
100 weight parts of polymer are present.
The antioxidant composition must be provided in a
amount which will provide effective oxidation inhibition
5 while also providing sufficient DSTDP to permit the polymeric
composition to pass the CSA varnish test. Where DSTDP is the
only component of the antioxidant composition, passing the
CSA varnish test constitutes no particular problems. When
other antioxidants are combined with the DSTDP, the DSTDP
10 should constitute at least 25% of the antioxidant composition.
The antioxidant composition in terms of a specific amount
should be in the range of 0.5 to 5.0, preferably 1.0 to 3.0,
parts per 100 parts of polymer.
The compositions of the present invention may be
15 formed in a number of ways. However, in every instance it is
necessary that the filler and silane be intimately contacted.
~or instance, the preferred method of filler treatment is by
direct addition of the silane to the polymer followed by
addition thereto of the filler, the antioxidant composition,
20 and other additives, if desired. This can be done in an
internal mixer, such as a Banbury or Werner & Pfleiderer
mixer. Alternatively, the silane may be added directly to
the filler, dispersed therein, and the polymer and the anti-
oxidant composition then added.
Any processing device known to the art which insures
an intimate mixture of the essential components may be used,
provided the silane is intimately and thoroughly dispersed onto
the surface of the hydrated inorganic filler.
It will be apparent that in addition to the essential
components of the compositions of this invention, other
additives may be present, e.g., pigments, stabilizers, so long
as they do not interfere with crosslinking, when desired, or
harm desired properties. Such materials are present in very
minor proportions, ranging from less than 10% of the polymer,
and usually in amounts of less than 5%. There are two reasons
` 11755~ 3298
1 amounts of other components are no~ desirable: firstly, the
present composition per se has such superior properties;
secondly, any signif icant amounts of other fillers for example,
serve only to degrade or upset the balance or properties.
For the formation of insulation on conductors by
extrusion, the most preferred embodiment of this invention,
another component is generally necessary, i.e., a lubricant
such as a fatty acid soap or metallic derivative thereof.
Such a material is also important to improve the stripping
10 properties of wire insulation and thereby to permit the
insulation to be easily stripped from the wire by the user to
facilitate splicing and to make terminations. It is necessary
to avoid, however, soaps which interfere with the crosslinking
reaction (free radical mechanism~ such as zinc stearate, which
15 will react with organic peroxides. Acceptable soaps are the
alkaline earth metal fatty acid soaps. A preferred soap is
calcium stearate. Additional representative examples of
useful lubricants include the alkaline earth metal salts and
aluminum salts of stearic acid, oleic acid, palmitic acid and
20 other fatty acids used by the art for this purpose, silicone
oil, long chain aliphatic amides, waxes, etc. One particularly
preferred lubricant is a mixture of 15-35% lauric acid and
85-65% ethylene-bis-stearamide.
The following example is provided to further
25 illustrate certain aspects of the invention.
A number of crosslinkable EVA copolymer compositions
were prepared and subjected to the CSA varnish test. Each of
the samples contained the same copolymer, hydrated alumina,
silane and crosslinking agent in the same proportions, viz:
3o
-18- 1175588 3298
Amount, Phr~l)
Ethylene-vinyl acetate copolymer 100
(17% Vinyl Acetate; Melt Index 1.5)
Hydrated Alumina 125
Silane ~vinyl-tris (2-methoxyethoxy)
silane) 2
Crosslinking agent ( ~ , ~ 'S bis
(t-butylperoxy) diisopropylbenzene) 4.25
(1) phr = pounds per 100 pounds of resin
Seventeen samples were prepared, each of which
contained, in addition to the above components, a one or two
15 component antioxidant composition, and a lubricant. Four
commercially available antioxidan's were evaluated including
two diesters of thiopropionic acid which are often used
interchangeably in the art because of their very similar
antioxidant properties. The other two antioxidants were
20 amine and phenol-type antioxidants. The two lubricants
evaluated wexe also commercially available products.
The silane, the filler and the other components were
added to the polymer and blended therewith. Care was taken
to control the temperature rise during the mixing so as to
25 not activate the peroxide prior to the completion of
blending. Following mixing, the polymer composition was
extruded onto a copper wire using a Brabender extruder and
raised to the peroxide activation temperature by vulcanization
in steam under high pressure.
The compositions of these samples and the results of
the CSA varnish test are presented in Table I below.
1175588
--19--
x o
o
u~) ~ ~1 H H a~ :~
~ H S e
s .,,
~q
~r I N _I I I --I tq ~ ~ ~ O
~ ~ ~ O
P. u~ ,: s
O D
H
` ~ X
~J H ~ ~1 0 C o
~1 ~'J ~1 1 1 11 _I U) H .C .~ ~ t~ U~
. ~ ~ I,a
H ~ ~ J.
~: S _l ~ `~
~ ~Q 14 ~i ~ ~ o ~
~ ~ I ~
~ ~ ~ U~ oS ~ ~ ~
¢ ~:
tq ~ ~ ~,1 0_~
2~ ~ ~: o~
,~ a) ~ o u~ .,, .,, ~
~ ~ s ~ ~-- 1 0 .,,
.C S-- ~ I ~ 0~Y
h ~ Q~ ~ ~1 ~ ~ t~
O ~ Q) ` ~2 U
t` ~ ~ ~ E~ ~ ` ~h
~ O ~I)-- I ~ O U~
--`-- h h ~ ~ ~ O .y N
~ S S h ~ ~ ~~1 0 ~ O ~,
--o ~ ~ o fd ~
.¢ o ~ ~ J- H E~ O ~ ~- E~ 0 h
0 ~ ~1 ~ ~ U~ rl ~ .,1 O
J~ * * ~ u~ N Sid O O .Y ~ ~ ~ 0 ~
~ a) x---- 0 E~rl U~ ~ U d O ~ o I
~ ~ O ~ ~ ~ ~ ~ ~ a ~ ~ ~ U H ~
~ -rl ~ r~ ~ ~ ~ !C ~ E~ :~
.,, s~ rd a a d u ~ ~ a~ u u c~
x a) ~ E~ E~ U ~ _I Id u~ _ _ _
o ~ ~ 1 ~ o :> ~ o 0 _ __
~ H a a ~ u ~ ~ u u z ~ ______
C: ~ U~ ~ o
~ ~ U Z;
~r$ ~
,, ~
~ 5~
1175S88
-20- 3298
N I I ~1 1 ~1 ~rl H H
~4 H O
~ ~ H H , ~I
~ .Y a~
o ¦ H ~ Ll 0
0 a~ H 1~1 U
_ a~ ¦ I I I I ~ I ~ H H a~ O ~ U
V . ~H`
15 _ u~ ~ o
~ ~ c~ x , . o
C~ P~ . P~ X , s~
20 ~ ~q X
~ ~ '`I ~ P, x ~.l o,~
N ~ o,. ,~ V
C.) R~ ~ O '1:5 d~ R '~
) rl O U~
~C~ ~ o ~ ~ UE~
~: ~ E~ ,,'4 V
~ O N ~
~ o ~ ~ ~ ~ o ~ 3 ~
U~ ~ ~ _ _ ~ H E- .,1 ~ ~rl
~ ~ X ~ ~ ~ O O ~ ~ E~ a a
,~ s~ ~ ~t) o
o ~¢H~ ~ ~ o ~ ~1 Z ~
~ ~ c~ zl
-21~ 5S8~ 329 8
o
H _I
I N I _I I ~I H O ~
P~ H S
~Q~
u~ X â) ~,o
~ x
_l ~-0
U) ~ H H . ~ U
O 1~ H ~ Ei
~ . ~ xa~
~ ~ ~1 ~ N _J I I _I 01U~ ,~ ,~ E~ O U~
~) ~ o
~: . .
H ~ ~
~ E~ er R ~J ~ I ~ h
~¢ C N I I I I ~ 1 H H ~ ~ ~
~ 3 ~ H ` ~ ~-1 o o E~ O U 3
,~ ~ , ~.,, ,, ~ .,,
> h ~o4
S ` ~ h~J~
u Q. ~ rOa ~
~ O U~
~D ~ ~ C ,C ~ r~
h h-- N ~ I ~ `~ rl
~: ~ h 5 ~ ) U E~ U
Q. ` ~ ~ ~ U O q) ~ ~ r~ U ~ U ~ ~
-- h h ~ 7 ~ ~ N r-l 1 .,1- h C.C
N S ~ ~ ~ ~ rl U~ ~1 h ~ 1:7) CJ~
_o Q, ~ ~ ~: o s~
--I ~ .C G) O ~ ~ a) .Y t~5 h a~ ~ U a.
~; o ~ ~ ~ HE~~ U C E~ ~ u~ U~
~q ~ cn ,~ 1
c a) x ~ ~ q ~4 ~ C U o a),1 ~ o
0 ~ O ~ ::~ 3 ~1 1~ l~ ~ ~ ~ N ~ U H U7 U~
~ ~ C ~1C~.~ 1 ::~
~/ S~ 11U ~ 1 u~ u u u
X o tn E~ t) ~ d u~ ~ _~,_
O ~ h u~ ~rl1~ O ~ 111 h h O u~ N ~
~¢ H C~ ~ O ~ ~3 ~ ~ U Z ~ _ _ _ _ __
~ ~ u z
-22- 1175S8~ 3298
1 Sample No. 1 is an exemplification of the compositions
of U.S. Patent Nos. 3,832,326 and 3,922,442 of North et al.
This sample did not pass the CSA varnish test; six other
samples also failed the test. Of the seven samples containing
5 DSTDP, six passed the test (Samples 3, 4, 7, 8, 14 and 16).
Of the 18 specimens comprising these six DSTDP samples, only
one specimen showed a deep crack in the insulation. Each of
the fifteen specimens of the samples containing the polymerized
quinoline antioxidant exhibited deep cracks ~Samples 1, 2, 11,
10 12 and 13) as did all nine specimens of the samples containing
the DLTDP antioxidant ~Samples 12, 15 and 17). It may also
be signif icant that the only DSTDP sample (Sample 11) which
failed the test also contained the polymerized quinoline
antioxidant and all three specimens showed deep cracks.
These tests show that DSTDP was not effective with
the polymerized quinoline antioxidant. Further, DLTDP cannot
be substituted for DSTDP where passing the CSA varnish test
is a requirement.
From these tests, it appears that, of those additives
20 evaluated, DSTDP is the most significant contributor to passing
the CSA varnish test. Further, the best antioxidant combination
was DSTDP plus the hydrocinnamate, while the most effective
system contained this antioxidant system plus the Mold Wiz
lubricant. Samples of this latter system ~Samples 4, 14 and
25 16) showed only slight cracks, if any.
3o
