Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LOW TOXICITY FIRE R~TARDAN~ THERNOP~A~TIC MATERIA~
FIELD OF THE INVENTION
This invention relates to very low toxicity, fire
retardant thermoplastic compositions which may be
processable into various products in which fire safety is
a consideration.
BACKGROUND OF THE INVENTION
Although flame retardant polymer compositions have
been in use for several decades, they have generally
relied upon the presence of halogens, mainly chlorine or
bromine containing chemicals, to yield flame retardancy.
Examples include polychloroprene ("neoprene"),
chlorosulphonated polyethylene ("Hypalon"), thermoplastic
PVC compounds, or compounds of polyethylene with
halogenated flame retardant additives. Matex-ials under
development over the last ten years, and even more
intensively in the last five years in Europe and the
United States have focused on halogen free, flame
retardant (HFFR) compounds, since halogens give off very
toxic and corrosive combustion products in fires.
Thermoset HFFR's have been developed based on
polyethylene and its copolymer.s, but these materials have
inherently high processing costs due to the need for
cross-linking. Thermoplastic HFFR's, usually classified
as thermoplastic polyolefins or TPO's since they are
typically based on polymers and copolymers of ethylene
and propylene, are the focus of much industrial materials
research at present for construction and transportation
because of their greater ease of use (fabrication into
end use products) and the recyclability of trim or scrap.
Development of a cost ef~ective and acceptable
performance HFFR/TPO is a challenging project. The
essence of the technical challenge is as ~ollows:
Conventional materials, namely PVC compounds, have shown
a good balance of properties in mechanical strength and
flexibility, chemical, aging resistance and low cost.
Unfortunately, burning PVC's release a great deal o~
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black smoke and their combustion fumes contain HCl gas,
which is highly corrosive, particularly in combination
with the water used to fight fires. This hydrochloric
acid is capable of destroying e~cpensive computer
equipment and even such rugged electrical fixtures as
fuse boxes which may not be directly destroyed by the
flame or heat of a fire.
~ alogen free systems of modest cost are restricted
ko polyolefins in terms of raw material. Polyole~ins do
not have inherently good flame resistance. Choice of
halogen free flame retardant additives is limited to
certain hydrated halogen free flame retardant additive
minerals such as alumina trihydrate ~ATH) or magnesium
hydroxide, which are relatively inexpensive.
These flame retardant additives function by
releasing their water of hydration, preferably at
temperatures above those required for processing but
below those of combustion of the flame retardant
composition. At relatively high concentrations, such
additives also impair combustion by conducting heat
relatively e~ficiently from burning surfaces. To
maximize these flame-retardant effects, it is preferable
that the flame retardant additives be present at maximum
levels.
However, these particular halogen free flame
retardant materials are relatively inefficient and must
be added in large amounts (>50% by weight). Because such
flame retardant materials are non reinforcing in the
final product, HFFR/TPO compounds using this conventional
technology normally have poor strength and flexibility,
poor processing characteristics (eg. ease of mixing and
extrusion) and only fair flame retardancy.
Approaches tried to avoid these difficulties include
the use of coupling agents (to compensate for the non-
reinforcing nature of ATH~, and intumescent additives~al~o called char formers).
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Silicone flame retardants for plastic compositions
have been extensively investigated in United States
patent 4,387,176. A composition which lends fire-
retardancy to a thermoplastics includes a silicone with a
group IIA metal organic salt and a silicone resin which
is soluble in the silicone to impart flame-retardancy to
the thermoplastic. The silicone is of the general
organopolysiloxane group, such as polydimethylsiloxane.
The silicone resin is generally represented by the
formula MQ where M is the monofunctional group of the
average formula R3Sioo5 and the tetrafunctional Q units of
the average formula SiO2 with the average ratio of
approximately 0.3:4 of M units per Q unit. The patent
teaches that this fire-retardant composition is useful
with a variety of thermoplastics including specifically
polypropylene, polyethylene~ polycarbonate, polystyrene,
acrylonitryl-butadiene-styrene terpolymer, polyphenylene
oxide-polystyrene blends, acrylic polymer, polyurethane
and polyamides. It is required that the group IIA metal
organic salts be included to ensure solubility of the
silicone resin in the polysiloxane base. Representative
salts include magnesium stearate, calcium stearate,
barium stearate, strontium stearate. It has been found,
however, that compositions of this type are not readily
processable particularly when high loadings of fire-
retardant additives are included.
More particularly, Frye, discloses a flame retardant
including three principal ingredients:
1. polysiloxanes which are organopolysiloxane
polymers;
2. Group IIA metal carboxylic acid salts; for
example, magnesium stearate, calcium stearate,
barium stearate and strontium stearate; and
3. silicone resins such as the General Electric
silicone sold under the trademark SR545.
Halides may be used to improve the fire retardancy
properties of this combination of components. The major
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components may be used with various thermoplastics, suchas poly~thylenes, polypropylenes, and polybutylenes as
well as copolymers and polycarbonates. Heat activated
cross-linkers, such as peroxides, may be used to initiate
cross linking in the composition in an attempt to improve
physical characteristics of the material. Based on a
review of the examples of this patent, generally Frye
requires the use of halogens to achieve a suitable flame
retardancy to meet commonly acceptable indexes for flame
retardancy.
SUMMARY OF THE INVENTION
According to an aspect of the invention, a ~ire-
retardant composition comprises:
~a) 5% to 60% by weight of an olefinic copolymer or
terpolymer wherein 3% to 20% by weight of the
copolymer or terpolymer is a carboxylic acid
comonomer;
~b) 1% to 15% by weight of an organopolysiloxane;
and
(c) 20% to ~5% by weight of a flame-retardant
additive comprising a group I or group II or
group III metal oxide hydrate.
According to another aspect of the invention, the
processability of the above composition is greatly
improved by including a dialdehyde in the composition.
According to another as~ect of the invention, the
formability of the composition is greatly improved by the
inclusion of polymers, such as low modulus ethylene
copolymers, polyethylene, polypropylene,
ethylenepropylene synthetic rubbers and ethylenepropylene
elastomers with a reactive monomer graft.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown in
the drawings, wherein:
Figures :L and 2 show weight and percent weight loss
of two compositions during heating.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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compositions of this invention provide
a series of very low toxicity, ~ire-retardant compounds
that comply with the requirements of a Class A
composition when tested in accordance with the procedures
of ASTM E-84. The preferred compositions include a
copolymer or terpolymer wherein 3% to 20% by weight of
the copolymer or terpolymer is a carboxylic acid
comonomer. These compounds are intended for use in the
construction, building and wire insulation industries.
lo ~ire-retardant plastics are commonly availa~leO
However to achieve their ratings, it has been essential
to use halogenated polymers or additives as flame
retardant agents. As already noted, those materials are
becoming unacceptable in respect to the toxicity and
corrosivity of the decomposition products when subjected
to heat and/or fire.
The flame retardant compositions of this invention
release combustion products of low optical density and
low levels of toxicity. These materials can be
manufactured without using harmful halogenated additives.
The flame retardant propertiPs of these compositions
are advantageous in the construction, building and wire
insulation industries in meeting the requirements of burn
tests in accordance with ASTM E-84 in addition to UL 94
V-O and UL wire and cable vertical flame tests.
These compositions perform particularly well in
characteristics of Flame Spread Index [FSI3 and Smoke
Density [SD~ These characteristics are now commonly
specified in government regulations and included in
specifications of other agencies i.e. Underwriters
Laboratories, and State, Provincial and Municipal
Building codes.
The composition, according to this invention, when
cross-linXed by irradiation or chemical methods has quite
surprisingly enhanced physical properties particularly
with respect to the elongation parameter. Although the
reasons are not readily understood, it appears that
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irradiation of the composition increases elongation
properties of the composition rather than the commonly
understood decraase in elongation. The composition o~
this invention is readily modified to permit processing
into various articles of manufacture which include
building materials, such as wallboards, ceiling panels,
pipe wrap, wire cladding and insulation and the like.
Such processability may be improved and enhanced by
various additives readily incorporated in the composition
to enable injection molding of the composition as well as
compression molding and blow molding.
The fire-retardant composition of this invention
comprises:
5% to 60~ by weight of an olefinic copolymer or
terpolymer wherein 3% to 20% by weight of the
copolymer or terpolymer is a carboxylic acid
comonomer.
According to a preferred embodiment of the
invention, the copolymer or terpolymer is selected from
the group consisting of a copolymer of ethylene and
ethylene acrylic acid and a copolymer of ethylene and
methacrylic acid. In each of these copolymers, there is
3~ to 20~ by weight of the copolymer of carboxylic acid
comonomer. Although the reactivity of the copolymer,
terpolymer with a carboxylic acid comonomer with other
components of the composition i5 not fully understood, it
is theorized that the carboxylic acid comonomer is
reactive with the other components o~ the composition to
improve processability, formability and fire retardancy.
In addition to the copolymer, terpolymer, another
component of the composition is 1% to 15% by weight o~ an
organopolysiloxane. The organopolysiloxane is a compound
selected from the group represented by the formulae:
R3sios/ R2Sio~ Rlsiol5, RIR2sioo5~ Sio, (Rl)2sio,
RSiol5 and SiO2,
wherein each R represents independently a saturated or
unsaturated monovalent hydrocarbon radical, R~ represents
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a radical such as R or a radical selected from the group
consisting of a hydrogen atom, hydrGxyl, alkoxyl, aryl,
vinyl, or allyl radicals; and wherein said
organopolysiloxane has a viscosity of approximately 600
to 300,000,000 centipoise at 25OC.
Organopolysiloxane acts as a plasticizer (or
internal lubricant), a low level linking agent and a
coupling agent between the hydrophobic polymer and the
hydrophilic flame retardant additive material. As a
result of this unexpected effect of the
organopolysiloxane, it is now possible to incorporate
larger amou~ts of the hydrophilic flame retardant
additive than in previous flame retardant compositions.
Surprisingly, compositions, in which an
organopolysiloxane is thus utilized, retain plasticity
and processability even at relatively low temperatures.
The fire retardancy of some of the compositions of
this invention may be improved by including active
silicone resin in the organopolysiloxane. The reactive
resin is represented by the formula:
MQ
wherein said reactive silicone resin is comprised of
monofunctional M units of the averagP formula R3Sioos and
tetrafunctivnal Q units of the average formula sio2, and
having an average ratio of approximately 0.3 to 4.0 M
units per Q unit.
From a solubility standpoint for the organosiloxane,
processing conditions may require the use of group II
metal organic salts. Appropriate amounts of the group II
metal organic salt, such as metal stearates, are added to
the composition as required to solubilize the reactive
silicone resin in the polysiloxane base.
It is believed that the reactivity o~ the
polysiloxane with the carboxyl moieties of the copolymer,
terpolymer aids in the incorporation of the hydrophilic
flame-retardant additives in the polymer composition.
Hence it is now possible to incorporate larger amounts of
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the flame-retardant additives than in previous flame-
retardant compositions while ret:aining processability and
subsequent formability into desired commercial products.
One organopolysiloxane useful in the compositions of
this invention is Dow Corning 200 Fluid. It is a
dimethylsiloxane polymer. This silicone polymer is
essentially non-reactive except for a small amount of
silanol (approximately 200 to 800 parts per million) left
over after processing. Dow Corning 200 Fluid can be made
reactive, if desired, through the addition of a secondary
hydroxyl functional silicone resin, such as Dow Corning
1248 Fluid.
Another useful organopolysiloxane is General
Electric's SFR 100, which is essentially a silicone fluid
similar to the Dow corning 200 Fluid with the difference
that is has been modified through the addition of group
II metal organic compound(s) and a reactive silicone
resin (specifically polytrimethyl-silylsilicate)
represented by the formula MQ, where said reactive
silicone resin is comprised of monofunctional M units of
the average formula ~3sio05 and tetrafunctional Q units of
the average formula SiO2 and having an average ratio of
approximately 0.3 to 4.0 M units per Q unit having a
ratio of approximately 0.3 to 4.0 M units per Q unit.
The hydrophilic fire-retardant additives, according
to this invention, are generally defined by group I and
group II metal oxide hydrates. There are a variety of
such hydrates available, although the preferred hydrates
are selected from the group consisting of alumina
trihydrate, magnesium hydroxide and hydrotalcite (sodium
aluminum hydroxy carbonate). Another hydrate, which is
useful in some compositions, is hydracarb, which is a
form of hydrated calcium carbonate. A preferred
concentration of the metal oxide hydrates is in the range
of 20 to 40% by weight.
The organopolysiloxane may have a viscosity in the
range of 0.6 centipoise to 300X106 centipoise, although in
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most situations the preferred viscosity range is lOx103
centipoise to 900X103. For the compositions which are
used in a variety of commercial products, such as
coverings for wire cable, the viscosity is normally in
the range of 30x103 centipoise to 600x~03 centipoise. The
preferred organopolysiloxane is polydimethylsiloxane.
Other significant additives for use in the composition of
this invention, which further enhance the fire retardancy
thereof, is the use of red amorphous phosphorous. It has
been found that the amount of red phosphorous used can
range from approximately 1~ to 10%, pre~erably in the
range of 1% to 4% and most preferred in the range of 1
to 2%.
In addition to the fire-retardant additive, other
suitable fillers may be included, such as talc, calcium
carbonate, mica, clay, zinc borate, wallastonite and
mixtures thereof. A preferred amount of zinc borate is
in the range of 5% to 30% by weight in the composition.
Zinc borate is particularly effective when used in
combination with red amorphous phosphorous.
It has been found that the addition of dialdshydes
surprisingly improves the processability and workability
of the compositions. Preferred dialdehydes are selected
from the group consisting of glyoxal and glutaraldehyde.
The dialdehydes are used in the range of 0.1% to 4%
by weight of the composition, although the preferred
range is from 0.5% to 3% by weight of the selected
dialdehyde in the composition.
Although the function of the dialdehyde in the
composition is not fully understood, it is believed that
the additional carboxyl groups of the dialdehyde react to
combine with the organopolysiloxane and the carboxyl
groups of the co- and terpolymers. A dialdehyde (such as
glyoxal) is believed to cross-link the polymeric units by
polycondensation reactive processing. In the field of
~ire retardant thermoplastics, free radical
polymerization had heretofore been the method or choice.
20~9075
The use of polycondensation is a novel approach which
gives unexpectedly good fire rel:ardancy and
processability. This approach causes cross-linking which
increases with the amount of dialdehyde used.
To further enhance this reactivity, it has also been
found that the addition of monorner grafts, such as maleic
anhydride, further enhance the composition. Furthermore,
maleic anhydride may be used with other additives to be
described. Such further uses include grafting of the
maleic anhydride onto polyolefins. Also, maleic
anhydride may be used as an alloying agent which
facilitates the combination of polyolefins with
copolymers thersof.
Formability of the composition, particularly in
sheet form, becomes important in forming a variety of
building products, such as ceiling tiles and the like.
To enhance the formability, the inclusion of up to 30% by
weight of a pol~mer selected from the group consisting of
low modulus ethylene copolymers, polyethylene,
polypropylene, ethylenepropylene synthetic rubbers and
ethylenepropylene elastomers with a reactive monomer
graft are particularly useful. The low modulus ethylene
copolymers may be selected from the group consisting of
ethylenevinylacetate, ethylene-methylacrylate,
ethyleneethylacrylate and ethylene-butylacrylate. As
previously noted, the properties of the ethylenepropylene
elastomer may be improved with a monomer graph,
particularly maleic hydride.
Further enhancements of the processability of this
composition may be achieved by the use of either short-
chain carboxylic acids, such as fumeric acid, citric
acid, formic acid, tartaric acid, lactic acid and short-
chain (Cl- C6) amino acids. Of this group, tartaric acid
is preferred. Also longer chain (C8 - C22)fatty acids are
used, particularly stearic acid. One or more of these
acids may be compounded into the mix or tumble blended
after pelletiæing. The use of either or both o~ these
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acids siynificantly reduces the pressures for extrusion
thereof and hence increases processability. Preferred
concentration for the tartaric acid in the composition is
0.1% to 5% by weight thereof. With stearic acid, the
prefarred concentration is in the range of 0.1% to 3% by
weight thereof. The acids can be incorporated directly
in the blend, or as already mentioned tumble blended
after pelletizing of the fire retardant composition so as
to be part o~ the composition during extrusion.
Although the composition of this invention is
intended to be halogen-free, in certain situations where
use of halogens is not of particular concern, the fire
retardancy of the composition can be enhanced by the
addition of organic halides, such as decabromo-
diphenyloxide. Normally when halogens are incorporated
into a composition, an antimony oxide synergist is
included with the composition up to approximately 10% by
weight to improve flame retardancy hy combininy the
halogens, thus preventing their loss to the atmosphere
during combustion.
According to a preferred embodiment of the
invention, a representative composition providing for
fire retardancy and processability and formability is the
following:
(a) 5% to 60% by weight of (i) a copolymer of
ethylene and acrylic acid containing from 3% to 9.0% of
the acrylic acid comonomer and (ii) with 2% to 10% by
weight of the mixture comprised of the organopoly-
siloxane coupling agent;
(b) 5% to 20% by weight of the composition of
at least one polymeric material selected from ethylene
copolymers, polyethylene and/or from a group of synthetic
hydrocarbon elastomers;
(c) 50% to ~5% by weight of the composition of
35 a filler comprising 40% to 100% by weight of at least one
of aluminum trihydrate and magnesium hydroxide and 0% to
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60% by weight of at le~st one of hydracarb, zinc borate,
mica and clay.
These compositions may be extruded into sheet
material having a Flame Spread Index [FSI] of less than
50 and a Smoke Density [SD] of less than 50.
Preferably the compositions of the present invention
also contain 5% to 20% of a polymeric material selected
from combinations of synthetic hydrocarbons elastomers
and low modulus polymers and mixtures thereof. In
embodiments of the composition the elastomer is defined
as a substance that is capable of being extended to twice
its length at 68C and on release of the applied stress
returns with force to approximately its original length.
Compatibility with polyethylene is a desirable feature in
order to improve product toughness. The use of high
ethylene elastomers is essential to provide the melt flow
properties required.
It has been found that the combined use of copolymer
of ethylene acrylic acid with the oryanic polysiloxane
provides a slight improvement in fire retardancy,
particularly when only 1% to 5% by weight of the
composition is the desired organopolysiloxane.
As already noted, the preferred elastomers are
ethylenepropylene copolymer or an ethylenepro-pylenediene
terpolymer or a terpolymer e.g. ethylenepropylenediene.
In combination the polymeric material may be a low
modulus polymer. This category includes such polymers as
polyethylene, ethylenevinylacetate, ethyleneethyl-
acrylate, and ethylenemethylacrylate copolymers as well
as branched polymers of the above having maleic anhydride
or other suitable carboxylic group grafted thereon.
The carboxylic acid copolymer, such as EAA, plus
other polymeric materials comprises 15% to 30% by weight
of the composition~ However for most methods o~
fabrication, the carboxylic acid copolymer, such as FAA,
plus other polymeric material should be at least 25% o~
the composition.
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The composition of the present invention also
contains 50% to 85%, especially 55% to 75% and more
particularly 55% to 65% by weight of the composition of
fire-retardant additive. Of this filler 40 to 100 parts
by weight is alumina trihydrate [ATH] viz, Al2033H20,
and/or magnesium hydroxide and/c)r sodium aluminum hydroxy
carbonate and hydrotalcite. According to an aspect o~
the invention all of the filler may be ATH or magnesium
hydroxide. The remainder of the filler, i.e. up to 60%
parts by weight is hydracarb, zinc borate, mica and/or
clay incorporating color pigments, lubricants and
stabilizers not to exceed 10 parts of the 0 to 60 parts
designated.
In order to facilitate processing of the
compositions of this invention, it is preferred that the
flame-retardant, additive material has a relatively broad
particle size distribution. This requires selection of a
mechanically ground flame-retardant, additive material or
a precipitated product. According to one embodiment of
the invention, the flame-retardant, additive material
will have a coarse and fine fraction with a distribution
of about o.5 to 60.0 mm and a median of about 2.5 mm.
The flame-retardant, additive material should have a
coarse fraction of about 60% by weight. High proportions
of fine particles may cause processing difficulties at
high flame-retardant, additive material levels but may
improve flame resistancy due to greater surface area.
The compositions of this invention should all be
compounded prior to fabrication. The equipment
recommended must be of the high intensity design. The
mixer must also incorporate adequate auxiliary equipment
including scales and finishing equipment with proper
drying facilities. The compounder [mixer] should be
computer controlled for optimum mixing cycle.
Recommended mixers are: Banbury, Moriyama, FCM ~Farrel
Continuous Mixer], Pomini Continuous Mixer and other high
intensity mixers, i.e. Berstorff, Werner Fleiderer etc.
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The compounding equipment should be operated at
temperatures below the decomposition temperature of the
filler, it being understood that if the material contains
more than one flame-retardant, additive material, the
temperature is lower than the lowest decomposition
temperature of such flame-retardant, additive material.
It is anticipated that the compositions will contain
at least one antioxidant and at least one ultraviolet
(W) absorber. It will be appreciated by those skilled
in the art that the amount and type of additive may
effect changes in and the rate of change of properties
over a period of time i.e. especially physical properties
of products derived therefrom. One property of
particular importance is the color of the composition.
Apart from matters like cigarette smoke and pollution the
aesthetic qualities of the product must remain as
installed.
In another embodiment of the present invention all
components are equivalent except for the elastomer
indicated. An elastomer may be substituted consisting of
an ethylene propylene elastomer to which reactive monomer
such as maleic anhydride has been grafted. As is
appreciated, the polyolefin back-bone, provides
outstanding environmental resistance, aging properties,
thermostability, chemical resistance as well as ease of
processing. The reactive group on the polyolefin back-
bone results in improved adhesion properties to various
substrate materials. It can be utilized directly as one
of the polymeric materials as all or part of 5 - 20% by
weight of the composition.
Optionally, a free radical acceptor (acrylic monomer
or dimer) or a chemical cross linking agent (i.e.,
peroxide) enhances irradiatable cross linkage or chemical
cross linkage respectively. Physical properties i.e.
tensile strength, tensile modulus, impact resistance and
flexibility will show definite improvement.
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Free radical linking bet-ween carhon atoms of the
formed composition, either through irradiation or
chemical bonding, as noted u~ually increases many
physical properties. However, it is generally understood
cross-linking in the polymeric composition reduces
elongation of the formed composition. This is due to the
cross-linking bonds normally reducing the elastomeric
properties in the composition. However, quite
surprisingly with this composition, cross-linking
increases elongation properties of the formed composition
when subjected to tensile forces. Irradiation then
provides increased tensile strength as well as increased
elongation. The reasons for such reversal in properties
of the composition are not readily understood. However,
as demonstrated in the examples, such properties are
readily repeatable with the composition of this
invention.
The preferred technique for inducing cross-linking
in the formed composition is the use of irradiation.
Normally irradiation takes place by the use of an
electron beam having an ionization energy which releases
radiation to encourage free radical cross-linking in the
composition. The irradiation energy is measured in
megarads where desired exposure is in the range of 2 to
15 megarads depending upon the rate of processing and the
thickness of material to be treated. As is understood,
gamma radiation from Colbat 60 has higher penetration
rates than the normal form of electron beam radiation, so
that lower dosages may be used in the range of one
megarad and higher. The choice of tha irradiation is to
some extent dependent upon the processing method and the
type of article manufacture to be treated.
With glyoxal (tha preferred dialdehyde), use of 0.1%
to 4% by weight of the total product provides the
preferred results. Concentrations of up to 10% by weight
may be used where processability of the other components
is a problem. Too high a concentration of dialdehyde,
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however, yields a thermoset rather than a thermoplastic.
Thermosets have very reduced flow characteristics
(compared to thermoplastics) and are extremely difficult,
if not impossible, to process, so they normally would not
be acceptable for formation into sheet, tiles, wire
coverings and the like.
The use of glyoxal and an organopolysiloxane enables
concentrations of flame retardant additives as high as
85% by weight to be practically processable using
conventional extrusion and molding techniques.
Other members of the homologous series of
dialdehydes will also aid processability such as
glutaraldehyde.
Maleic anhydride is useful with polyolefins, such as
PE, PP, EVA, etc. and with ethylene propylene synthetic
rubbers in this composition. Maleic anhydride increases
the flame retardancy as it produces a more viscous
intumescent foam or char during combustion. This more
viscous foam does not drip from the burning material and
serves to shield material that would otherwise be exposed
to combustion during burning.
Maleic anhydride is believed to aid in the formation
a viscous intumescent foam during combustion by cross-
linking the polymeric units as a result of its carboxylic
functionality. This is believed to be a process
analogous to the cross-linking that takes place with
olefinic copolymers or terpolymers used in this
invention, wherein 3% to 20% by weight of said copolymers
or terpolymers are carboxylic acid comonomers.
Processing of the compositions of this invention can
occur at relatively low temperatures. The haloyen free
flame retardant materials such as alumina trihydrate lose
their water of hydration at 420~F. The presence of this
water of hydration is essential for effective fire
retardancy. Formerly, processing had to take place at
350 to 410F, because old flame-retardant materials were
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so difficult to work with. This involved the risk of
ruining the flame retardant materials' efficacy.
With glyoxal and an organopolysiloxane, much lower
processing temperatures of 250 to 310F are possible,
and with much higher flame retardant material
concentrations. Also, the material is more fluid at the
same concentration of flame retardant material than
previous preparations. As a result, industrial
production can run faster, with more production per
person hour. The lower processing temperatures make for
faster cooling and therefore slightly lower processing
costs. With inclusion of tartaric acid, we have found
that the processing temperature can be further expanded
to range from 230F to 380F.
Several major developments are in progress in the
area of understanding of fire dynamics and the scientific
study of performance of materials in a fire. Work on
fire dynamics centers around the building of
mathematical, computer driven models of "compartment
fires" (models of single room fires) and the extension of
these fire models to multistory buildings. The objective
is to be able to determine how the choice of materials
and design of a building affect the fire death toll for a
hypothetical fire in a real building.
From a materials viewpoint, the main impact of the
fire science work is characterized by the following
parameters:
Ignitability;
flame spread rate;
heat release rate;
smoke toxicity (mainly inhalation toxicity to
humans);
smoke density (obscuration of visibility); and
smoke corrosivity (corrosive effects on electronic
equipment).
Conventional PVC compounds are inherently good in
the first three items but perform poorly in smoke
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.
~9~37~
18
density. Their smoke toxicity :is the subject of debate,
it may not be worse than that of other conventional
plastics in this regard. On the issue of corrosivity,
AT~T has publicly presented data on the serious building-
wide damage to telephone switch:ing equipment experiencedwith burning PvC insulated wire.
The compositions, according to this invention,
preform extremely well in the ignitability, flame spread
rate, heat release rate, smoke toxicity, smoke
corrosivity, and smoke density parameters.
In additionl success at maintaining good
manufacturing processability for the compositions of this
invention is maintained, which has been impossible with
prior approaches. Surprisingly, the compositions of this
invention are easily processed into end use products such
as wire and cable extrusions, and sheet extrusions for a
variety of construction products.
Further, addition of small amounts of zirconates,
titanates, zinc, and tin salts enhances physical
properties of the final product. These materials in
combination with dialdehydes raise the viscosity of the
burning material and thus improve flame retardancy by
contributing to the intumescent char that forms at
burning surfaces rather than dripping off ~nd leaving
more new material exposed for combustion.
In all the compositions of this invention, reactive
processing builds in a sufficient degree of cross-
linking among polymeric units, and between polymeric
units and particles of flame-retardant additives is such
that the composition is easily processable (extrudable
and moldable) at relatively low temperatures and
relatively high flame retardant additive levels.
Performance and flame retardancy of these
compositions could be enhanced by any of the
conventionally known halogen-containing fire retardant
additives such as decabromodiphenyloxide. Addition o~ an
antimony oxide syneryist to the halides in appropriate
~9~
19
amounts to combine with and prevent them from being lost
to the atmosphere considerably improves the flame
retardancy of compositions containing the halides.
The fire retardant composition, according ta this
invention, therefore has among others the following five
distinct features:
(1) processability over a broad range o~ component
concentrations in the composition;
(2) processability at considerably lower processing
temperatures compared to prior art
compositions;
(3) significant increase in the formability
properties of the composition when extruded in
sheet form due primarily to the presence of the
low modulus copolymers and/or elastomers;
(4) enhanced fire retardancy properties primarily
due to the incorporation o~ very high amounts
of fire-retardant additives facilitated
primarily by the use of the polysiloxanes which ..
react with the carboxylic acid comonomers of
the co- and terpolymers, and optionally the
inclusion of a dialdehyde and/or tartaric acid;
and
(5) enhanced slump stress cnaracteristics which
ease lamination.
Preferred embodiments of the invention are
demonstrated in the following Examples which are
understood to be enabling with respect to pre~erred
embodiments of the invention, but are not to be
interpreted as restrictive to the scope of the appended
set of claims.
EXAMPLE I
A number of samples of compositions of the invention
were prepared in a laboratory Type BR Banbury mixer and
compression molded into test specimens 25 to 35 mils
thick. Their flame retardant properties were then
compared with a commercially available competitive
.
.,, . ' . ::
,.
~ 7~
material as the standard. A simulated ASTM E-84 test was
used together with a much more severe vertical flame
test.
The T.V.I. Vertical Flame Test is defined as
follows:
Specimen: - 1" x 8" ex~ruded or pressed
- 25 to 35 mils thick
Flame Application: 30 seconds
After burn: seconds
Criteria: - Pass - self extinguishing
- Fail - destructive burn or heavy drip
.
~9~7~
o o o o ~ o o o
~1 In In O ~D O IS) N ~D O
o\ I ~1 1 ~1 1 ~1 ~ I I
In Ln
O U~ Ln O 1` 0 0 0 ~
O 1~ t~ D 0 10 ~ ~ O
~1 o\ I ~ I ~-1 I rl ~r I I
Ul 0 1~1 0 0 0 0 0
u~ r` In ~1 0 ~ In
\O I ~ I I Lt~
~n
O O O O O O O O
o~ O~o I ~ I I ~D I I I a
O O O O
In o . ~ o
1~ o\OI ~
O O ~ O
0 ~
o\ I ~ I ~ IIn
O ~ o , U~ O
ul 0\ ~ I ~ I
É~i .o In O m h
O N ~i a) t)
o\ I ~ I ~ ~r I u~ I u~ ,~ I I I ~ ,a
o u~ o
o ~ o
o In o
O u~ O
o\ I ~ I u~
o 1~ o o
0~
h 1::1
O O O ~0 0 O ~ ~ rl h
N O ~ a ~ ~
a cn ~ I I I ~I h ~1 ,1
O h h UCO ` ,4
~; o C ~ 1 gi .~ o ~ ~ -I
a) - t~ a~ O O O OO H ~ U~4 u~ ~-1 U
Q, 1--1 P~ tq (1~Ul ~rl 0 H E~ H Q)
U~ a l~ ~ ~ a t:r ~ O 0 ~ ~ ~ H ~
u~ P~; ~ '' ~ y ~ ~ '/ * O
~ ' ' ' ~ ' ' :
2~6~07~
22
The low modulus polymer is CIL's 1830, an 18% vinyl
acid copolymer.
The elastomer of all runs except sample 3 is ~psyn
DE 208 supplied by Copolymer Corp.
The elastomer in sample 3 is Exxon's Exxolor VA 1801
consisting of an ethylene propylene elastomer to which a
reactive monomer, such as maleic anhydride, has been
grafted.
The silicon coupler is General Electric's SFR-100.
This material has proven effective on test with or
without the addition of a metallic stearate.
Flame Evaluation:
Mortile Vertical Test_
Dupont 1 2 3 4 5 6 7
Std % % % % % % % %
AFTERBURN
Secs. 200 120 1.5 ~ 153 220 2.5
Criteria Fail Pass Pass Pass Pass Pass Pass Pass
Sample No No
Destroyed Ignition Ignition
The samples produced in accordance with this invention
exhibit superior flame resistance. The use of low
modulus polymers and elastomers provides improved tensile
and flexular strength making the finished product
suitable for vacuum forming.
. . . :
'': ' ~ ..:'
23 2`~ 9~7~
EXAMPLE II
SAMPLE STD. 1 2 3 4 5
No. ~ % % % % %
5 LLPDE 26.0
Carboxylic acid - 22.0 22.0 2~.0 22.0 23.5
Copolymer
. .
Low modulus - 5.05.0 5.0 5.0 5.0
Polymer
lo Elastomer 100.0 4.5 - 4.5 4.5
Grafter elastomer - - 4.5 - - 7.5
Polydimethyl - 5.0 5.0 5.0 5.0 5.0
Siloxane Filler
ATH 61.0 61.5 61.5 50.0 50.0 51.0
15 Zinc borate - - - - - 5.0
Mica - - - 11.5
Hydracarb - - - 11.5
Additives* 3.0 2.0 2.0 2.0 2.0 3.0
* Colors, antioxidants, lubricants, etc.
The elastomer used in Samples 3 and 4 is
ethylenepropylene, terpolymer. The grafted elastomer is
an ethylenepropylene terpolymer with a maleic anhydride
graft.
The acrylic acid ethylene copolymers used are market
ed under the trade name Primacor by Dow Chemical.
The reactive polydimethyl siloxane copolymer is SFR-
100 supplied by the General Electric Co.
Flame Evaluations Mortile Vertical Flame Test
30 SAMPLE STD. 1 2 3 4 5
NO.
Afterburn (secs) ~00 145 _ 153 220
Test criteria Fail Pass Pass Pass Pass Pass
Sample No No
Destroyed Ignition Ignition
All samples in this invention exhibit superior flame
retardancy. The use of low modulus polymers and
. . ,
.
24 ~9~7~
elastomers provide improved tensile and flexular strength
making the finished products suitable for vacuum forming.
EXAMPLE III
Laboratory compounds were mixed in a Type BR Banbury
and compression molded into test specimens 25 to 35 mils
thick. Their flame retardant properties were then compar
ed using a ~imulated vertical flame test against a commer
cially available UL approved ceiling tile material that
meets ASTM E-84.
Test Descriptlon:
Specimen - 1 x 8 x 0.025 to 0.035 inches
Flame application - 30 seconds
Criteria - pass - self extinguishing
Fail - destructive burn and heavy drip.
Table 1
Sample STD 1 2 3
RESIN % % ~ %
Polyethylene (grafted) 26.0 - - _
Acrylic acid copolymer - 15.015.0 15.0
20 Low modulus polymer - 8.05.0 5.0
Elastomer 10.0 7.0 5.05.0
Polydimethylsiloxane - 5.0 5.0 5.0
FILLER
ATH 61.0 53.0 58.050.0
Zinc borate - 8.0 8.08.0
Calcium carbonate - - - 8.0
Additives* 3.0 4.0 4.04.0
Flame test results FAI~ PASS PASS PASS
Destructive --self
extinguish
Burn ~ drip --no drip--
* Color, antioxidants, lubricants, etc.
The elastomer used in formulations 1 to 3 is an
ethylene, propylene tsrpolymer to which a reactive monome
r, such as maleic anhydride has been grafted. This
elastomer was supplied by Exxon Chemical co~pany.
The low modulus polymer was an ethylenevinyl acetate
copolymer obtained from Exxon Chemical Company.
,:
...
.
', ~ ' , :
~.
::
The acryli~ acid ethylene copolymers are obtained
from Dow Chemical USA and are marketed under the trade
name PRIMACOR.
The reactive polydimethylsiloxane copolymer is
supplied by Genaral Electric Company under the trade name
: SFR~100.
EXAMPLE IV
Biological, Physical and Chemical Data of Sample 8
of Example I.
AL Test #197, Sample #A-0028 Case # 010489-1
LC50~ 87.3 grams
95% Confidence interval~ 74.6 - 102.3 grams
LC50 sample dimensions/descriptionb chips
Furnace temperature at 1% weight lossb 299C
Furnace temperature range at most
rapid weight lossb 420 - 600C
Furnace temperature at apparent spon-
taneous flame (mean of 7 samples) 4S4C
Percent residue (mean of 6 samples) 50.6%
Maximal CO in exposure chamberb 0.08% 800 ppm
Furnace temperature at maximal cob 570C
Maximal C02 in exposure chamberb 2.11%
Furnace temperature at maximal CO2b 570C
Minimal 2 in exposure chamberb 19.8%
Furnace temperature at minimal o2b 570C
Number of times exposure chamber
exceeded 45OCb None
Duration exposure chamber
exceeded 45OCb 0 sac
30 Eye damage (corneal opacity)C None
Eye damage (severity) None (1)
Number of test runs on sample
material 7
a - calculated according to the method of C. Weil, 1952.
b - from single experiment using 87.3 gram test sample.
2~69~7~
26
c - from single experiment with animals using 78.1 gram
test sample; sample weight equal or closest to the LCso
value.
The results of this test demonstrate characteristics
which are approximately ten times better than
polyethylene pellets and better than most other known ole
fins from the standpoint of bio:Logical, physical and
chemical data in the fire retardancy field.
~XAMPLE V
Vertical Burning Test - UL 94 (specimens were tested
"as is", i.e. no conditioning).
Sample 9 of Example I (#0202-6, 125 to 130 mil)
Three specimens 5 inches x 1/2 inch were cut from a
sample. They were tested using the Vertical Burning Test
for 94-Vo classification.
The burner was adjusted to produce a five inch flame
with a one and a half inch inner blue cone (using natural
gas~. The test flame was applied to one of the lower cor
ners of the specimen at an angle of 20 from the
vertical, so that the tip of the inner cone touches the
specimen.
The flame was applied for 5 seconds and then removed
for 5 seconds. This was repeated until the specimen was
subjected to the test flame five times total.
Observa ons After Fifth Removal of Test Flame
1 2 3
Duration of flaming and
glowing, sec. 23 32 25
Affected length, in. 2.78" 2.50" 1.94"
30 Dripping None None None
Deformation curled slightly at exposed
end
EXAMPLE_VI
Vertical Bur lng Test - UL 94
Sample 9 of Example I (#0202-6, 78 mils) Thickness
was measured with a micrometer
: ' " ~ ' ,` '
27
Ten specimens 4 9/16 inches x 1/2 inch were tested.
Five specimens were tested for 5U classification, since
the burner was already adjusted for this test. It was
found that two out of five specimens passed the criteria.
~ natural gas flame was used.
1 2 3 4 5
Duration of flaming and
glowing, sec. 29 43 76 7a 102
10 Affected length, inchas 2.81 3.50 3.25 Burnt Burnt
to to
clump clump
(4") (4")
15 Dripping None None None None None
Deformation B e c a m e e l o n g a t e d
EXAMPLE VII
Vertical B rn Test - UL 94
Sample 9 of Example I (#0202-6, 78 mil)
Five specimens, 4 9/16 inches x one-half inch were
tested for 94U-o, 94U-1 or 94U-2 classification.
The specimens were held vertically 9.5 mm above the
orifice of the burner. The burner was adjusted to
produce a three-quarter inch ~19 mm) flame. The air
supply was increased until the yellow tip of the flame
disappeared. The specimens were exposed to the test
flame for 10 seconds. The burner was removed and any
flaming was noted. When the specimens stopped burning,
the burner was placed under the specimens for another 10
seconds.
Duration of flaming after 1st 55 40 70 26 l9
ten sec. exp. (in secs)
Duration of flaming after 2nd 25 0 70 3 40
ten sec. exp. (in secs)
Duration of glowing after 2nd None None None None None
application
~ .
~9~7~
28
Dripping None None None None None
Length of Affected Area - ~ 1 3~ 3h ~~ 1%
inches
Burnt to clump No No No No No
EXAMPLE VIII
Figures 1 and 2 show weigh~ and percent weight loss
of two compositions during heating. The composition
tested and results shown in Figure 1 is a polyethylene
composition of the invention of Sample 2 of Example 1 not
containing a dialdehyde. The composition tested and
results shown in Figure 2 is Sample 9 of Example 1 with
dialdehyde added.
The composition of Figure 2 lost the bulk of its
mass at a substantially higher temperature, 472.59C than
the composition of Figure 1, which lost the bulk of its
mass at 437.22C.
Loss of mass at substantially higher temperatures
indicates better flame retardancy or resistance. The
results of Figures 1 and 2 indicate a marked improvement
in flame retardancy characteristics with addition of a -
dialdehyde to the compositions of the invention.
; ', -~
, - ,;
,
~9~7~
29
EXAMPLE IX
Cable Physical Test Data
Sample A* Sample B**
Tensile Elongation Elonga1ion/ Elongation/
5 Unmodified Sample Ultimate Ultimate
Tensile Psi Tensile Psi
.030 inch wall 80%/2100 Psi 105%/1896 Psi
.008 inch wall 90%/221)0 Psi 110%/1817 Psi
Tensile Elongation
After B irradiation
.030 inch wall 133~/2614 Psi 173%/2430 Psi
Tensile Elongation After
7 Days Age Testing at
121C
.030 inch wall 20%/1589 Psi 20%/1532 Psi
UW-1 Test
.030 inch wall Pass Pass
Insulation Resistance 10,000 Meg n 5,000 Meg n
ShrinXage Test
.030 inch wall None None
* Sample A is Sample 10 of Example 1
** Sample B is Sample 11 of Example 1
During the testing of the various flame retardant
compositions o~ this invention, it is noted that the
compositions fail to drip when exposed to flame. This is
a significant development and is thought to be due to the
degree of cross-linking in the composition. At the stage
of processing, there appears to be a condensation-type
polymerization taking place in the reactivity of the
various components with the carboxyl groups. During
exposure, however, to a flame, it is believed that, due
to additional cross-linking, a solid charred substance is
formed which is inclined not to drip and thereby not
exposing fre~h polymer. This is a significant
development, particularly when it is considered that the
.. , , : ,
.
2~075
composition is particularly useful in the formation o~
ceiling tile. Ceiling tiles of this invention, when
exposed to a flame, are less likely to drop from the
ceiling and hence contain the fire for a longer period.
EXMAPLE X
Irradiation cross-linking has been investigated with
respect to samples of the composition identified as
follows:
SAMPLE A B C D E
Carboxylic Acid 24.0 24.0 24.0 24.0 24.0
Copolymer
Low Modules
Polymer 9.5 9.5 10.0 10.0 10.0
Grafter
20 Elastomer 9.5 9.5 10.0 10.0 10.0
Polydimethyl
Siloxane 5.8 5.8 6.0 6.0 6.0
Filler ATH 60.0 60.0 63.0 63.0 63.0
Zinc Borate 6.5 6.5 7.0 7.0 7.0
Red Phosphorous 4.7 4.7 - - -
* Additives *4.0 *4.0 *4.0 *4.0 *4.0
*Pigments, antioxidents, lubricants, etc.
*A. includes Carbon Black Pigment (2.6%)
*B. includes Tio2 pigment (2.6~)
*C. includes Tio2 pigment (2.6%)
*D. includes Magnesium Oxide (2.6%)
*E. contains ~ractional Melt Low Modules Polymer.
P~OCESSING NOTE: Materials excluding carboxylic acid
copolymer were master-batched and then 25% carboxylic
acid copolymer and 76% o~ the master-batch by weight were
'' ~ . ' .,' : ~
~ . ~ , i . . ,. ', ':'
'
'~
3~ 9 ~ 7 ~
mixed and compounded. Plaques were pressed and tested
according to ASTM D-412.
Radiation induced cross-linking is preferably
produced by high voltage linear accelerators which
generate beams of high energy electonsO These beams may
have energies in the range of 2 to 3 million electron
volts (MEV~ and are high current beams capable of
irradiating large volumes of materials in a short time.
Beam energies in excess of three MEV's are normally
required to irradiate thicknesses of the composition in
excess of 0.1 inches. For example, in wire and cable
applications, the cable may be passed through the beam at
a fairly high speed in a manner which ensures uniform
dosage over the entire circumference of the cable and at
a high enough dose rate to effect cross linkage. This
may be accomplished by having a cable make multiple
passes through the beam while rotating the cable so that
all sides are illuminated by electron beam. It is
appreciated that similar procedures may be used in
treating sheet material which has previously been
extruded and the like.
As a measure of the dosages in exposing the material
to the beam of high energy electrons, in this Example,
the dosage is in the range of 12 to 15 megarad. The
cross-linking occurs when high energy electrons ionize
the linear polymeric material so that adjacent chains may
form chemical bonds to each other. Quite surprisingly as
demonstrated by the ~ollowing data, such cross-linking
does not decrease elongation but increases elonyation
before failure at maximum tensile stress.
To test each of the above samples A through E, each
sample is stretched linearly while recording the
elongation of the sample during stretching and the
pressure appl:ied in stretching the sample before
breakage. Samples are tested be~ore they have been
irradiated and after irradiation to determine the impact
.
'
. -
2~6~75
32
o~ irradiation on elongation and tensile strength. Theresults are set out as follows:
SAMPLE PHYSICALSBEFORE AFTER ~ INCREAS
MEASURED RAD RAD
A) Elongation %118 155 31.36
Tensile PSI1425 1660 16.49
B) Elongation %130 182 40.00
Tensile PSI1525 1937 27.02
C) Elongation %150 200 33.30
Tensile PSI1635 2100 28.44
D) Elongation %164 190 15.85
Tensile PSI1650 2200 33.33
E) Elongation % 87 165 89.66
Tensile PSI1750 2500 42.86
:
EXAMPLE_XI
The use of red amorphous phosphorous has been
investigatad to determine its impact on fire retardancy
properties. From the following test results, it
becomes apparent that less not necessarily more of the
red amorphous phosphorous enhances the fire retardancy
properties of the composition.
Four samples of this invention were prepared as
followsO Each sample had a base formulation comprising:
40% EVA, EAA, EPD blend resins
55% by weight fillers - ATH zinc borate
:., . , ~:
: . .
2 ~ 7 ~
33
5% polydimethylsilicone
1% glyoxol
1% processing aids - stearic acid.
~he above base formulation was modified as follows
to prepare samples A, B, C and D.
A - base formulation
B - base formulation plus 1.5% by weight red
phosphorous
C - base formulation plus 3.5% by weight red
phosphorous
D - base formulation plus 7.5% by weight red
phosphorous
All samples were extruded to a 0.75 inch thick sheet
which was one-half inch wide and six inches long.
A flame was applied to each specimen and
ignitiontextinguishing times were recorded. The
procedure is that of other Examples where the sample was
held in a vertical orientation and the flame applied at
an angle to the bottom of each sample.
Sample A B C D
Sec. to ignition 35 sec 15 sec 20 sec 25 sec
Sec. to extinguish 35 sec 0 sec 5 sec 2 sec
It is apparent that red amorphous phosphorous
surprisingly reduced the time to ignition of each of the
samples, but in turn reduced the amount of time to self-
extinguish. It is also of note that a lesser
concentration of red amorphous phosphorous, as in sample
B, resulted in a self-extinguishing time of zero seconds,
whereas larger concentrations in sample C took longex to
self-extinguish and then in sample D with high
overloading, two seconds to self-extinguish. It i
therefore believed that this data predicts in the range
of 1% to 3~ o~ the red amorphous phosphorous is efective
in reducing extinguishing times and it is not necessary
.
,
,
2~
34
to use higher concentrations in the range of 7~ or
greater.
EXAMPLE XII
The impact on the carboxylic acid comonomer for
enhancing flame retardancy has been investigated. The
carboxylic acid comonomer used :in the following
formulations is ethylene acrylic acid. This was compared
to a linear, low density polyethylene where aluminum
trihydrate and the dimethylsiloxane polymer, SF~100 was
used. The samples had the following compositions prepare
d in accordance with the previous Examples.
SAMPLE ~
COMPONENTS (1) (2) t3) (4)
15 LLDPE 40.0%40.0% - -
EAA 1430 - - 40.0%40.0%
SFR 100 - 5.0% - 5.0%
ATH 60.0%55.0% 60.0%55.0%
Two strips of each sample were prepared having the
dimensions of the samples of Example XI. Flame was
applied to each of the duplicates of the four samples.
Once ignition occurred, the flame was removed. The time
to ignition was recorded. After removal of the flame
time to self-extinguish or consumed by flame was
recorded. The results are as follows:
SAMPLE Ignition Extinguish Consumed
(1) a 25 sec -- 9 minfailed
b 20 sec -- 8 minfailed
(2) a 15 sec -- 3.5 min failed
b 20 sec -- 4.0 min failed
(3) a 20 sec 10 sec - Pass
b 20 sec 0 -- Pass
40 (4) a 30 sec 0 -- Pass
b 35 sec 0 -- Pass
. 1 `, ~ ,`
.
`:
2 ~ 5
From the above results, it is apparent that samples
1 and 2 were total failures. Sample 1 did not contain
the carboxylic acid comonomer. Sample 2 similarly did
not contain the carboxylic acid comonomer, but did
contain SFR100. Obviously SFR100 by itself without the
metallic stearate and used with the polyolefin does not
provide desirable fire retardancy properties. If
anything, the rate of burn was increased since th~ sample
was consumed within three to four minutes. However,
lo samples 3 and 4, both of which contain the carboxylic
acid comonomer with no linear monomer polyolefin, self-
extinguished and readily passed the test. There is a
slight improvement in ~he fire retarding when the of the
carboxylic acid comonomer is used in combination with
SFR100 as observed by increased time to ignition and both
samples extinguishing in zero seconds, that is a non-
detectable time period.
As an adjunct to this test, we have also
demonstrated that the amount of SFR100 in the formulation
does not increase flame retardancy with higher
concentrations. With sample 4, 3% by weight SFR100 was
compared to sample 4 with 8% SFR100. The flame test
d~monstrated that sample 4 containing 3% SFR100 had a
significantly better LOI, (limited oxygen index - a value
indicating minimum oxygen needed for combustion) than the
sample with 8% SFR100. This further example and the
above examples demonstrata that fire retardancy is not
due alone to the presence of SFR100 or other forms of
dimethylsiloxane polymers.
It is thought that SFR functions primarily as a
coupling, cross-linking, anti-drip and processing
component and not essentially as a flame retardant.
Although preferred embodiments of the invention
have been described herein in detail, it will be
understood by those skilled in the art that variations
may be made thereto without departing from the spirit
of the invention or the scope of the appended claims.
