Note: Descriptions are shown in the official language in which they were submitted.
FLAME RETARDANT POLYMERIC MAT~RIAI,S
This invention relates to polymeric flame retardant
compositions exhibiting enhanced properties, said compositions
being particularly adapted for coating electrical conductors.
Industry is continually searching for new fire resistant
polymeric compositions to improve the performance of existing
products and/or meet the needs of new applications. One of
the most important areas where fire resistant polymeric
compositions find use is in the electrical environment where
physical, insulating and fire resistant properties are
sought. A particularly important application in this area
is insulation used in automotive vehicle electrical wiring.
This type wiring also requires for many applications resistance
to oil. Typical applications include primary wiring, spark
plug cables, ignition wiring and battery cables. Another
important application is ror insulated wire suitable for use
as a fusible link in automotive wiring harnesses. Good
physical properties are extremely important in this application
to minimize insulation rupture due to short circuits which
may cause an explosion.
Materials presently in use for automotive applications
include Hypalon*, ethylene-propylene elastomers, chlorinated
polyethylene, silicon elastomer and flame retardant crosslinked
polyolefin insulation. Unfortunately, however, these materials
are unsuitable for use as, e.g., a fusible link in automotive
vehicle wiring, e.g., harnesses, because they do not provide
the combination of flame retardancy, physical strength,
resistance to oil, moisture, heat, gasoline and solvents and
insulation rupture due to a severe electrical overload.
Additionally, it is very important that the material be easily
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rocessed, e.g., by extrusion into its final form. Performance
of these ma-terials in automotive electrical insulation applications
is described in detail in the product brochures and applications
literature distributed by producing companies for these materials.
Reference books are replete with discussions of mechanisms
of fire retardancy and operative systems. "Flame Retardancy
of Polymeric Materials", Volume 1, by W.C. Kuryla and A.J. Papa,
Marcel Dekker, Inc., N.Y., 1973, Cahpter 1 and pages 171-181
and Lyons, "The Chemistry & Uses of Fire Retardants", John Wiley
and Sons, Inc., 1970, pages 330-332, are exemplary. A number of
U.S. patents show the wide variety of fire retardant additive
combinations known in the art. U.S. Patent No. 3,832,326 discloses
crosslinkable polymeric compositions based upon an ethylene-
vinyl acetate copolymer, preferably containing less than about
28% vinyl acetate by weight, having improved moisture, heat
resistance and flame retardance and is particularly adapted for
coating electrical wiring. The compositions are specifically
directed to a non-halogenated flame retardant system. Another
non-halogenated system is shown in U.S. Patent No. 3,741,929.
U.S. Patent No. 3,362,928 shows a thermoset system based on a
diallyl phthalate molding compound, a flame retardant organic
chlorine containing compound, antimony oxide and hydrated alumina.
The compositions are used for the manufacture of rigid type
electronic components and switches. U.S. Patent No. 3,694,305
discloses an emulsion type adhesive for laminating various plies
of a flame retardant fire barrier. U.S. Patent No. 3,720,643
discloses a first retardant polymeric material based on adding
talc, chlorinated polyethylene and anitomy trioxide to poly-
propylene, styrene-acrylonitrile copolymer or acrylonitrile-
butadiene-styrene resins.
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U.S. Patent No. 3,936,403 relates to synthetic resin
compositions having flameproofness and surface hardness
comprising an olefinic resin, vinyl chloride resins and alumina
trihydrate having a gibbsite crystal structure. Ethylene-vinyl
acetate copolymers are not disclosed and the preferred resin
is high density polyethylene, which, as shown hereinbelow,
cannot be extruded to make a coating for an electrical conductor.
Further, the disclosed vinyl chloride resin is polyvinyl chloride
which, again, cannot be employed in the claimed composition
since the coated wire does not pass the UL-FR-l flame test.
It has now been unexpectedly discovered that fire retardant
polymeric compositions exhibiting enhanced properties suitable
for use as insulation for automotive vehicle wiring, comprise
suitable preportions of a vinyl acetate-ethylene copolymer,
chlorinated polyethylene and hydrated alumina.
In general, the polymeric fire retardant composition
comprises a vinyl acetate-ethylene copolymer containing about
20% to 90% by weight vinyl acetate and, per hundred parts of the
copolymer, about 10 to 50 parts of chlorinated polyethylene and
about 70 to 300 parts of hydrated alumina. A preferred composition
comprises about 10 to 35 parts of chlorinated polyethylene and
about 100 to 250 parts of hydrated alumina. A composition
wherein the copolymer contains vinyl acetate in an amount of
about 40% to 70% is highly preferred.
Although not necessary to achieve the desired properties,
it is advantageous to employ antimony trioxide and/or silica to
further imporve the fire resistance and processability,
respectively, of the composition. In general, the antimony
oxide and silica each may be used in an amount, per hundred parts
of copolymer, of about 10 to 50 parts, preferably about 10 to
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, par-ts. A silane coupling agen-t as discussed hereinbelow is
necessary to provide a composition which may be used as a
coating for wire and cable.
Such polymeric fire retardant compositions find particular
utility in the insulation of automotive wire but are useful in
other applications where a unique combination of enhanced
properties are needed such as good processability, physical
properties, electrical properties, oil resistance, moisture
resistance, gasoline or solvent resistance and fire resistance.
The polymeric component of the present composition is
based upon a vinyl acetate-ethylene copolymer. The copolymer
contains vinyl acetate (VA), by weight, about 20% to about 90%
and is preferably about 40% to 70%, e.g., 50% to 65%. The
preferred copolymers have a unique combination of properties
which are mainly dependent on the vinyl acetate content. For
example, as the vinyl acetate content is increased, the oil and
solvent resistance is generally increased. A more detailed
description of the preferred copolymer is set forth in the
booklet entitled "Vynathene~ VAE Elastomers" by National
Distillers and Chemical Corporation. In general, the preferred
copolymers have a density of about 0.960 to 1.05 grams per cubic
centimeter (g/cc), a melt flow rate at 125C. of about .1 to
20 g/lO minutes of flow, vinyl acetate content of about 40%
to 70% by weight and inherent viscosities of 0.70 to l.10 for
0.15 g polymer per 100 ml. tetrahydrofuran at 40C. Three
preferred copolymers which are products of National Distillers
and Chemical Corporation are:
(a) VYNATHENE EY 904, a vinyl acetate-ethylene copolymer
having a VA content of from about 50% to about 54% by
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weight and a melt Elow rate (~FR) of from about 0.5 to
about 1.5 at 125C.;
(b) VYNATHENE EY 905, a vinyl acetate-ethylene copolymer
having a VA content of from about 50% to about 54% by
weight and an MFR of from about 1.5 to about 7.0 at
125~C.; and
(c) VYNATHENE EY 907, a vinyl acetate-ethylene copolymer
having a VA content of from about 58% to about 62% by
weight and an MFR of from 1.0 to about 2.2 at 125~C.
Although not necessary, to provide a special combination
of properties minor amounts of other polymers or copolymers or
mixtures thereof may be included in the composition of this
invention, e.g., polyethylene, polypropylene, ethylene propylene
elastomer, polybutylenne, ethylene-acrylate copolymer, ethylene-
vinyl chloride copolymer and the like. They may be present in
amounts, per hundred parts of vinyl acetate-ethylene copolymer,
up to about 25 parts or higher, and are preferably below about
15, e.g., 10 parts.
Chlorinated polyethylene (CPE) is a well-known material
and preferred materials are CPE X02242.46 and CPE 4814 manufactured
by Dow Chemical Co. Other chlorinated polymers include
chlorinated polypropylene, polyvinylidene chloride, chloro-
sulfonated polyethylene and the like. Other halogenated polymers
are useful, especially brominated polymers; such polymers may be
found in the text by W.C. Kuryla and A.J. Papa, supra. A
composition containing polyvinyl chloride has been found to be
unacceptable since it does not pass the UL - ER-l test for coated
wire. CPE is preferred because of its demonstrated effectiveness.
The hydrated alumina, or alumina trihydrate, is preferably
included in relatively fine particle sizes of about 0.3 to 2
.
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~. ~d. f~ 8
.icrons, although larger or smaller size particles may be employed.
Preferred materials are HYDRAL* 710 and P.G. Alumina manufactured
by Aluminum Co. of America.
An important feature of the invention comprises specially
correlating the CPE and hydrated alumina with the vinyl acetate-
ethylene copolymer as set forth hereinabove to provide a highly
preferred composition having an excellent combination of properties,
including passing the stringent requirements of flame tests
such as UL-FR-1.
It has been found, unexpectedly, that the combination of the
halogenated polymer and hydrated alumina provides a synergistic
flame retardancy effect in the polymer composition of the
invention. Thus, for example, other known halogenated fire
retardant additives do not exhibit such an increase in fire
resistance when combined with hydrated alumina and actually
decrease the fire resistance of the material. It has been
theorized in U.S. Patent No. 3,694,305, supra, that the
combination of a chlorinated paraffin, antimony oxide and
hydrated alumina provides a faster synergistic fire retardancy
effect. While not wishing to be bound by any theories, it is
hypothesized that the combination of the halogenated polymer
and hydrated alumina provides a synergistic fire retardancy
effect by both materials acting in concert to provide a very
effective sustained fire retardancy effect. This effect is
particularly important under stringent fire retardancy
requirements such as the UL-FR-l test and is achieved under the
combinations of the halogenated polymer and hydrated alumina
as discussed hereinabove. While the amounts of halogenated
polymer and hydrated alumina may be varied widely as set forth
hereinabove, to achieve a still more enhanced combination of
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proper~ies it is preEerred -that high amounts of both components
not be employed. Thus, as shown hereinbelow in the Examples,
increasing the amount of halogenated polymer at a high hydrated
alumina content, depresses the ~ elongation of the composition.
It is important therefore for some applications to correlate the
amount of halogenated polymer and hydxated alumina and it is
highly preferred that, per hundred parts of resin, when the
hydrated alumina is above about 150 parts, that the halogenated
polymer be up to about 15 parts.
Antimony trioxide is the preferred antimony compound;
although many other antimony compounds are suitable as known
in the art, such as antimony sulfide and sodium antimonite and
the organic antimony compounds such as antimony butyrate and
antimony caprylate.
The silica component may be any of the well-known materials
and preferred silicas include Hi-Sil* 233 and Hi-Sil* EP, both
of which are manufactured by PPG Industries, Inc. The particle
size of the silica is preferably about 0.01 to 0.05 microns,
although larger or smaller size particles may be employed.
The polymeric compositions of this invention may include
other ingredients, additives and agents, depending upon the
intended service of the products thereof, and the required or
desired properties. For example, other components may comprise
antioxidants, acid acceptors, preservatives, lubricants and
processing aids, mold release agents, pigments or coloring agents,
inorganic fillers, waterproofing agents, coupl~ing agents, etc.
The preferred antioxidants are the polyquinolines such
as polytrimethyl dihydroquinoline which is sold under the
trademark Agerite Resin D and Agerite MA (higher molecular weight)
by R. T . Vanderbilt Company, Inc. Other conventional antioxidants,
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.,
8~3
.g., useful in the prior art for the stabilization oE low
density polyethylene and ethylene copolymers, may also be
employed. The amount of antioxidan-t used is about 0.25 to
4% by weight of the total composition.
The preferred acid acceptor is tetrabasic lead fumarate
which is marketed under the trademark Lectro 78 by N.L. Industries,
Inc. Other acid acceptors such as magnesium oxide, litharge
and the like may be utilized. The concentration is about 0.5
to 4% by weight of the total composition or about 1 to 3% of
the total resin content.
Lubricants and processing aids, such as stearic acid
(Hystrene* 9718 sold by Humko-Sheffield Chemicals Co.) and
calcium stearate are preferred. Others well-known in the art
may also be employed. Amounts of about 1 to 3 parts, preferably
about 1.5 to 2.5 parts per hundred parts of resin are generally
employed.
A coupling agent is preferred in the compositions to
provide a composition suitable for coating wire or cable and
any coupling agent may be employed in the compositions, it
being important that it does not interfere with polymer cross-
linking or degrade during polymer processing. Silanes as
disclos d in U.S. Patent No. 3,832,326, supra, are preferred;
e.g., Silane* A-172 solud by Union Carbide Co. provides
excellent results. Amounts of about 0.2 to 4%, preferably 0.2
to 2% and most preferably 0.5 to 1.2% by weight of the
composition are generally employed.
An important feature of the invention is to crosslink
the above described compositions to provide their final product
form. Crosslinking may be accomplished by any of the known
crosslinking techniques, such as chemical crosslinking and
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:radiation.
Curing agents which can be used herein include such
peroxides as: t-butyl perbenzoate, dicumyl peroxide,
2,5-dimethyl-2,5-di(t-butyl peroxy) hexane, 2,5-dimethyl-2,5-
di(t-butyl peroxy) hexyne-3, 1,3,5-tris [~ dimethyl-~-(t-
butyl peroxy)]-methyl benzene,~,~'-bis(t-butyl peroxy) diisopropyl
benzene and N-butyl-4,4-bis (t-butyl peroxy) valerate. These
curing agents can be used alone or in combination with any of
several polyfunctional monomers such as triallyl cyanurate,
triallyl isocyanurate, triallyl phosphate, trimethylol propane
triacrylate, diallyl fumarate, pentaerythritol tetraacrylate,
trimethylol propane trimethacrylate, 1,3-butylene glycol
dimethacrylate, allyl methacrylate, ethylene glycol dimethacrylate
and 1,3-butylene glycol diacrylate. The preferred curing agents
for use herein include Vul-Cup* 40 KE alone [40% ~,~' bis(t-
butyl peroxy) diisopropyl benzene on Burgess KE obtained from
Hercules Inc.] and Vul-Cup 40 KE in combination with the
polyfunctional monomer triallyl isocyanurate (TAIC) obtained
from Allied Chemical Corporation.
The amount of peroxide curing agent can range from about
1.0 to about 10 parts, and preferably from about 3.0 parts to
about 6.0 parts per hundred parts of copolymer.
The polyfunctional monomer used as auxiliary curing agent
in combination with crosslinking peroxide can be used in the
range of from about 0.1 to about 3.0 parts per hudnred parts of
copolymer. The preferred amount of auxiliary curing agent can
range from about 0.5 to about 1.5 parts and the most preferred
amount about 1.0 part per hundred parts of copolymer.
The compositions of the invention may be prepared using
known compounding techniques. Mixing is preferably carried out
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_ g _
sing an intensive mixer such as the Banbury or Werner &
Pfleiderer mixers. A preferred method is to prepare a polyblend
of the resin components and the chlorinated polyethylene. Any
other ingredient, exclusing the crosslinking agents, may then be
added and mixed. If silica is employed, it is preferred to add
it before the hydrated alumina. After thorough mixing, the
temperature is raised to about 250F. and mixing continued for
about 1 to 2 minutes. The temperature is then lowered to below
about 235F. and the crosslinking agents added. Mixing is
continued untii the composition is uniform, usually about 4 to
5 minutes. The batch may then be further processed on a two-roll
mill or in a processing extruder.
The compositions of the present invention will now be more
fully illustrated by the following specific examples and are not
to be considered as constituting a limitation on the present
invention. All parts and percentages are by weight and
temperatures in degrees Fahrenheit unless otherwise indicated.
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EXAMPLE I
The following compositions as shown in Table 1 were
prepared as described hereinbelow in a Banbury mixer, Model
No. sR.
Composition 1 was prepared by mixing the resin and CPE
for about three minutes at 230 revolutions per minute (rpm.)
speed. Hi-Sil 233, Agerite and antimony trioxide were added to
the Banbury and mixing continued for about 3 minutes. The
temperature was raised to about 250F. and mixing continued
at his temperature for about one to two minutes. The temperature
was then lowered below about 235F. and the stearic acid and
Lectro 78 were added and mixed for about three minutes, followed
by adding the Vul-Cup 40 KE and continued mixing for about four
to five minutes. The batch was then mi:Lled on a 6" x 12"
Thropp 2 roll rubber mill at about 100F. and sheeted to 10-15
millimeter (mm.) crepe, which was diced to cubes of about 1/8
inch. Wire coated samples were prepared by extrusion onto 20
gauge stranded wire at 30 mil wall thic}cness using a 3/4 inch
Brabender Extruder, Type No. PL-V340. Curing was performed in
a vulcanizing tube at 400F for 6 minutes. The insulated wire
was cooled by quenching in cold water for two minutes under
pressure and then retained in water during slow removal of
pressure over ten minutes time.
Compositions 2, 3 and 4 were prepared by mixing the resin,
hydrated alumina, silane and Agerite for about 5 minutes. The
temperature was then raised to about 250F. and the same
procedure for composition 1 was then followed except that
calcium stearate replaced Lectro 78 and was omitted in
composition 4.
Compositions 5 and A were prepared by mixing the resin
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38
and CPE for about 3 minutes at 230 rpm. speed. Hi-Sil 233,
Agerite and the silane were added and mixing continued for
about 3 minutes, followed by addition of the alumina and
antimony trioxide and continued mixing for about 3 minutes.
The temperature was then raised to about 250F. and the
procedure set forth for Composition 1 was followed.
Compositions B and C were prepared by mixing the resin
and CPE for about 3 minutes at 230 rpm. speed. Alumina,
Agerite and the silane were then added and mixing continued
lQ for about 5 minutes. The temperature was then raised to about
250F. and the procedure set forth for Composition 1 was
followed except that calcium stearate replaced the Lectro 78.
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The cured compositions were tested using the Eollowing
standard techniques and the results are shown hereinbelow in
Table 2: Tensile and Elongation - ASTM D 638; Oxygen Index -
ASTM D 863; FR-l Flame Test - UL-FR-l; Shore A Hardness -
ASTM D 2240.
Table 2
C o m p o s i t i o n s
1 2 3 4 5 A B C
Unaged
Tensile, psi2850 1290 1820 1400 1890 1570 1980 1820
Elongation, %590 130 110 310 170 300 420 140
Oxygen, Index
(O.I.)30.3 33.0 44.6 31.2 52.2 49.0 37.4 58.4
FR-l Flame
Test Fail Fail Fail Fail Fail Pass Pass Pass
Shore A
Hardness - - - -~ 92 83 74 92
Compositions A, B and C were tested in the aged condition
(70 hours at 125C) and the results are shown hereinbelow in
Table 3. Volume Swell (%) was performed with ASTM #3 oil as
prescribed in SAE J 878a speci~ications for fusible link
insulation and ASTM Method D-471.
Table _
C o m p o s i t i o n s
_ A B C
Tensile, psi 1980 2050 2340
Elongation, % 220 350 110
Shore A Hardness85 79 93
Volume Swell (%)77.3 100 58.7
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Volume Swell (%) was performed on Compositions 1, 3 and 4
and the results are 166%, 74.4% and 96.8%, respectively.
A review of the results shown in Tables 2 and 3 shows
the unexpected and synergistic performance provided by the
compositions of the invention. A comparison of 1, 2, 5 and A
clearly shows the importance for flame resistance of using
chlorinated polyethylene in combination with hydrated alumina
and employing the hydrated alumina above about 70 parts per
hundred parts of copolymer. Composition A is particularly
preferred because of its good overall properties and its ease
of processability. A comparison of B and C shows the importance
of using correlated amounts of chlorinated polyethylene and
hydrated alumina to achieve enhanced % elongation properties.
~ 15 -
8~3
EXA~IPLE II
To further demonstrate the invention, the following
comparative compositions were prepared and tested in accordance
with the procedures set forth in Example I. Composition A was
repeated and is herein termed A'. Composition A' was repeated
replacing the vinyl acetate-ethylene copolymer (VAE) with high
density polyethylene (HDPE) (Petrothene* LB 830 manufactured by
National Distillers and Chemical Corp.) and is termed Composition
6. Composition A' was repeated by (1) replacing the CPE with
polyvinyl chloride (PVC) (B.F. Goodrich Geon* 103 EP) (Composition
7) and (2) replacing the CPE with PVC plasticized with 25% by
weight dioctyl phthalate (Composition 8) both at an equivalent
chlorine level based on weight. Composition A' was repeated
replacing the VAE with an ethylene-vinyl acetate copolymer
(Ultrathene* UE 630 made by National Distillers and Chemical
Corp.) containing about 18% by weight vinyl acetate and is termed
Composition 9. The test results in the unaged condition are
as follows:
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As is clearly shown by the test results, Compostion 6
containing HDPE and Composition 7 containing PVC could not be
extruded onto wire. Composition 8, containing plasticized PVC
failed the FR-l flame test. Composition 9 containing an
ethylene-vinyl acetate copolymer with only 18% VA also failed
the FR-l flame test.
Composition A', without the silane component, could not
be extruded onto wire and had an O.I. of 34.9.
While the invention has been directed to copolymers of
vinyl acetate and ethylene containing greater than about 20%
by weight vinyl acetate, it will be understood to those skilled
in the art that the disclosed combination of ingredients is
applicable to other polymer and/or copolymer systems which
provide the same results afforded by the preferred vinyl
acetate-ethylene copolymers, and that such other embodiments
are, therefore, also embraced within the scope of the present
invention.
3 ~;
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