Note: Descriptions are shown in the official language in which they were submitted.
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SILICONE FOAM BACKED FLAME RETARDANT FABRICS
The present invention relates to foam backed fabrics. More
particularly, the present invention relates to flame retardant
- silicone foam backed fabrics.
Background of the Invention
Fabrics, both woven and nonwoven, are used in seating or
bedding, in rugs, in drapes, as wall covering, etc. Modern
fabrics are commonly polymeric materials which are particularly
prone to produce large cuantities of smoke, heat, and toxic
by-products during combustion. Even wool as a natural fabric,
used alone and in blends, is known to produce toxic by-products
of combustion. Much effort has been devoted to improving the
technology of fabric flame retardancy. Such technology
includes, for example, the use of flame retardant additives,
such as halogenated compounds, to prevent flame spread in the
fabric.
It is known to use silicone foam blocking layers adjacent
to fabric layers to prevent the spread of flames into
sublayers, such as polyurethane layers. The silicone foam
blocking layer has, in practice, been employed in the form of a
sleeve which envelopes a combustible material under a fabric or
as a simple layer which is glued to the surface of flameable
substructures under the fabric.
It is the object of the present invention to produce an
integral silicone foam/fabric combination.
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It is another object of the present invention to produce a
silicone foam/fabric combination which can be cut, sewn, and
otherwise utilized as a simple fabric.
It is another object of the present invention to produce a
flame retardant fabric which is self extinguishing and which
will also prevent flame propagation to adjacent and possibly
more readily combustible layers.
Detailed Description of the Invention
Briefly, according to the present invention, there is
provided a silicone foam faced fabric which comprises:
(a) a layer of fabric having adhered to at least one
face thereof, and
(b) at least one layer of silicone foam.
Fabrics suitable for use herein include woven and nonwoven
fabrics of both natural and synthetic materials. Woven fabrics
are usually produced by weaving, spinning, knitting or
knotting. Common woven fabrics are produced from cotton; flax;
wool; silk; rayon; Arnel triacetate; nylon 6; nylon 6,6; poly-
carbonamide; nylon 4; nylon ll; polyvinylcyanide and copolymers
thereof with acrylic acid, vinyl pyridine, acrylic acid amide,
vinyl chloride, etc; tetrafluoroethylene polymers; copolymers
of vinyl chloride and vinylidene; polyesters, including poly
(ethylene terephthalate), poly(cyclohexanedimethanol-tere-
phthalate), etc; and polypropylene. Non-woven fabrics are
produced from spunbonded or staple fibers. The basic materials
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for use in nonwoven fabrice are polyamide, including nylon-6
and nylon 6,6; polyester, including poly(ethylene terephtha-
late~; isotactic polypropylene, polyethylene, and viscose
rayon. The makeup and type of fabric are not critical to the
present invention except that the fabric be combustible.
The methods of manufacture and the materials of choice in
the production of fabrics are well known to persons skilled in
the art. Suitable fabrics are generally described in the
Encyclopedia of Chemical Technology, 3rd edition, Vol. 16,
pages 72-124, and Vol. 22, pages 762-833 .
Silicone foams for use herein are presently manufactured by
two principle methods. Each method depends upon the in situ
generation of hydrogen gas and simultaneous crosslinking of a
silicone elastomer. Less preferred methods of blowing silicone
elastomer include the use of a blowing agent.
One silicone foam composition suitable for use herein
comprises (a) 100 parts by weight of a base vinyl-containing
polymer of the formula:
Rl Rl Rl
R - SiO --SiO -- Si--R (I)
.
Rl Rl Rl
where R and Rl are selected from the class consisting of
alkyl radicals of 1 to 8 carbon atoms, aryl radicals, vinyl
radicals and fluoroalkyl radicals of 3 to 8 carbon atoms, such
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that the polymer contains from 0.0002 to 3% by weight vinyl,
and x varies such that the viscosity of the polymer varies from
100 to 1,000,000 centipoise at 25C; (b) from 0 to 200 parts by
weight of a filler; (c) from 100 parts per million to 1.5 parts
by weight water; (d) from 1 to 50 parts by weight of a hydride
polymer of the formula:
R3 R3 R3
.
R2 _ SiO SiO - Si R2 (2)
R3 Z H Y R3
where R2 is selected from the class consisting of hydrogen,
alkyl radicals of from 1 to 8 carbon atoms and aryl radicals,
and R3 is selected from alkyl and aryl radicals of up to 8
carbon atoms, where the hydride polymer has a hydrogen content
varying from 0.3 to 1.6~ by weight, where z and y vary such
that the polymer has a viscosity varying from 5 to 100
centipoise at 25C; and where there is at least 0.2 moles of
SiH per mole of water; and (e) from 1 to 250 parts per million
of a platinum catalyst. It is preferred that the base
vinyl-containing polymer only contain vinyl terminal units,
however, it can contain some vinyl on chain units. With
respect to the hydride polymer, such polymer must have a
hydrogen atom on the polymer chain to produce a suitable foam.
However, in addition to the chain hydrogen atoms, there may be
present terminal hydrogen atoms. A hydride polymer cannot be
. used as a cross-linking agent with only terminal hydrogen
atoms. As stated above, it is necessary that the composition
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have at least 0.2 moles of hydrogen in the hydride-containing
polysiloxane cross-linking agent for every mole of water to
release sufficient hydrogen to produce a suitable foam.
The above composition is utilized to produce a foam by
simply mixing the ingredients and allowing them to react in two
principle reactions. One reaction will produce hydrogen gas in
a reaction between water with hydride polymer and foam the
composition. The second reaction will cure the composition to
a silicone elastomer in a reaction between vinyl functional
groups and hydride polymer. If heat is applied, of course, the
reaction will proceed at a very fast rate. This silicone foam
composition is further described in United States
Patent Number 4, 18 9, 5 4 5 .
Another silicone foam composition suitable for use herein
comprises (a) an organohydrogensiloxane having an average of at
least three silicon-bonded hydrogen atoms per molecule, an
average of no more than one silicon-bonded hydrogen atom per
silicon atom and organic radicals selected from the group
consisting of alkyl radicals having l to 6 carbon atoms per
radical, phenyl and 3,3,3-trifluoropropyl; (b) a hydroxylated
organosiloxane having an average of from greater than l.O to
2.5 silicon bonded hydroxyl radicals per molecule and having an
average of at least one organic radical per silicon atom
selected from the grouP consisting of alkyl radicals having
from l to 6 carbon atoms per radical, phenyl and 3,3,3-tri-
fluoropropyl; and (c) a platinum catalyst in an amount of from
5 to about 200 parts by weight platinum per one million parts
by weight total composition. The organohydrogensiloxane and
the hydroxylated organosiloxane should be present in sufficient
amounts to provide a molar ratio of silicon-bonded hydrogen
atoms to silicon-bonded hydroxyl radicals of 2.5 to 40.
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This silicone composition is easily foamed by simply mixing
the ingredients and allowing them to react. The principle
reaction produces hydrogen gas to foam the composition and
simultaneously crosslinks the polymers to cure the composition.
The mechanism of the principle reaction is that the
hydrogen atom of a hydroxy group on the hydroxylated
organosilicone reacts with a hydrogen atom on the
organohydrogensiloxane producing a molecule of hydrogen and a
Si-O-Si bond. This silicone foam composition is
further d-escribed in United States~Patent
Number 4,189,545.
The ingredients of either of the above suggested silicone
foam compositions can be mixed according to common practices.
For instance, the hydride polymer or organohydrogensiloxane can
be mixed with the platinum catalyst and then mixed with the
base vinyl-containing polymer and water or with the hydroxy-
lated organosiloxane. In the alternative, the platinum
catalyst can first be mixed with the base vinyl-containing
polymer and water or with the hydroxylated organosiloxane and
then mixed with the hydride polymer or organohydrogensiloxane
as appropriate. Other methods of mixing are also appropriate,
for example, the vinyl-containing polymer and water or hydroxy-
lated organosiloxane can be divided into two portions, where
one portion is mixed with the platinum catalyst and the second
portion is mixed with the hydride polymer organohydrogen-
siloxane and then the two mixtures are combined to form a
foam. Various optional ingredients such as silica filler can
be mixed with one or more of the required ingredients as
suitable. These "packages" of ingredients can be formulated
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with any combination of ingredients so long as a premature
reaction does not take place before all ingredients are present
in the mixture. For purposes of storage, the hydride polymer
or organohydrogensiloxane should not be stored as a "package"
or mixture with the platinum catalyst because gassing may occur.
To control the foaming and curing reactions which are
taking place simultaneously, a platinum catalyst inhibitor,
such as polymethylvinylsiloxane cyclic compounds and acetylenic
alcohols can be added. The platinum catalyst inhibitors are
I0 known in the art and many varieties are available. These
inhibitors should however not interfere with the foaming and
curing in such a manner that destroys the foam product of this
invention. The mixture of ingredients should be placed in the
desired place where they are to be used as soon as they are
mixed because foaming begins immediately, unless a platinum
catalyst inhibitor is used to extend the pot life such that
they can be mixed and then put in the desired place of use.
The amounts of inhibitors are present in relatively small
amounts, such as up to 2 parts by weight polymethylvinyl-
siloxane cyclics can be used to control the initiation of the
foaming and curing. The polymethylvinylsiloxane cyclics are
known in the art and can be prepared by hydrolyzing
methylvinyldichlorosilane, for example.
The density of the above foams may be lowered where
necessary or desirable by the incorporation of MDQ
polyorganosiloxane resins. These resins comprise
R~SiOo 5 (M), R2SiO (D), and SiO2 (Q) units where
.R is selected from substituted and unsubstituted monovalent
hydrocarbon radicals. These resins and their use for the above
purpose are further described in U.S. Pat. No. 4,418,157.
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To produce articles of the present invention, the silicone
foam composition is applied to at least one face of fabric and
foamed. For best results, the silicone foam composition should
be formulated to 1,000,000 centipoise at 25C and should
preferably have a viscosity ranging between about 500 and
100,000 centipoise at 25C. The object of viscosity control is
to obtain a controlled penetration into the fabric along with
good cell formation in the foam. Penetration of the fabric may
be complete, resulting in foam on both sides, however, for most
uses, it is desirable to maintain one side of the fabric as
fabric so that only partial penetration is permitted, i.e.
sufficient penetration for adhesion to one face of the fabric.
Additionally, the formulation and conditions of foaming should
be such as to produce a foam having a density from about 0.08
to 0.4 g/cm3 and preferably from about 0.16 to 0.32g/cm3.
.
The silicone foam composition is applied to the fabric by
known methods, for example by roller, by blades, etc.
Generally, sufficient silicone foam composition should be
applied that the foam thickness on onse side of the fabric is
at least about 1.5 mm. Thicknesses less than this supply
almost no fire protection for light fabrics. The thickness
should increase depending upon the fabric thickness, fabric
weight, and the degree of fire protection sought. Ordinary
foam thickness for use in many fabric applications, i.e. for
example seat coverings, run from about 6 mm to about 51 mm.
The silicone foam composition is preferably mixed from
packages just prior to application to the fabric, but it is
understood that mixing could be accomplished on the fabric
surface, for example, where low viscosity silicone polymers are
employed.
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One preferred method of applying the silicone foam
composition to the fabric involves passing two sheets of
impermeable film, such as polyolefin film, through the nip
formed by two rollers and in the nip subsequently formed where
the sheets of polyolefin contact or are adjacent to one another
passing a layer of fabric with the silicone foam composition.
Of course, the resultant silicone foam will have a backing of
polyolefin. The use of the impermeable film controls hydrogen
gas escape and also prevents the silicone foam composition from
IO adhering to the roller.
Foaming of the composition may be accelerated by the
application of heat. Too vigorous a foaming action will
disrupt cell formation and lead to an irregular foam. However,
heat may be used to increase production rates as well as
control fabric penetration by the silicone foam composition.
The heat may be applied by convection or radiation. The
temperature within the foam mass should not exceed about 65C,
however, oven temperature or foam surface temperature may be
much higher.
Fillers may be added to the silicone foam composition which
are usually added in making such foams. These fillers include
fumed silica, diatomaceous earth, zinc oxide, calcium
carbonate, crushed quartz, and the like. The maximum amount of
filler to be added depends on the desired properties of the
foam. Generally, up to about 60% by weight filler may be
employed.
To enhance the burn resistance of the above silicone foams,
other burn resistant additives may be employed. For instance,
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1 334361 PATENTS
60SI-1073/~WH:mz/0279p
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per hundred parts of the resin portion of the silicone foam
composition, there may be added from 0.1 to 10 and preferably
from 0.5 to 2 parts by weight carbon black to enhance the burn
resistance of the foam. When carbon black is used, the foams
are self-extinguishing in shorter times.
The following examples are presented for illustrative
purposes only and should not be construed as limiting the
present invention which is properly delineated in the claims.
Examples
Example 1
A 9" x 9" piece of seating fabric, nylon/wool, used in
commercial aircraft was horizontally mounted in a high draft
hood. A Meeker burner was placed under the piece at a distance
of 2" and held there for two minutes. The burner quickly
burned a hole through the fabric and continued to consume a
large section of the fabric during the two minute period.
Example 2
Composition A contains 100 parts by weight 80,000
centipoise vinyl terminated polydimethylsiloxane fluid, 25
parts by weight a MD VinylQ resin, 1 part by weight water, 20
ppm platinum catalyst capable of gelling foam in 20 minutes,
and 50 parts -by weight ground silica filler. Composition B
contains 20 parts by weight 80,000 centipoise vinyl terminated
. polydimethylsiloxane fluid and 80 parts by weight 30 centipoise
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trimethyl terminated methylhydrogensiloxane fluid. Ten parts
by weight of Composition A was combined with one part by weight
of Composition B resulting in a 25,~00 to 40,000 centipoise
silicone foam composition. This silicone foam composition was
evenly applied to one side of the cloth of Example 1 using a
blade and applying sufficient pressure to insure that the
composition partially penetrated the fabric. The coated cloth
was allowed to stand at room temperature until foaming and
curing were complete, i.e. about 5 minutes to substantial
cure. The resultant foam backing thickness was 1/16" to 1/8".
The foam backed sample was subsequently subjected to the
same flame test as Example 1. The Meeker burner, after a
longer period, burned away the fabric in direct contact with
the flame but the combusted zone did not beyond the zone of
flame impingement. After two minutes the foam backing was not
penetrated and was still flexible.
Example 3
A 9" x 9" piece of seating fabric, wool/polyester, used in
subway seating, was tested in the same manner as Example 1.
The sample began to burn, melted, dripped, and was essentially
consumed by the fire.
Example 4
The silicone foam composition of Example 2 was evenly
applied to one side of the cloth of Example 3 using a blade and
applying sufficient pressure to insure that the composition
partially penetrated the fabric. The coated cloth was allowed
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to stand at room temperature until foaming and curing were
complete, i.e. about 5 minutes to substantial cure. The
resultant foam backing thickness was 3/8" to 1/2".
The foam backed sample was subsequently subjected to the
same flame test as Example 1. The Meeker burner, after a
longer period, burned away the fabric in direct contact with
the flame but did not allow the combusted zone to extend beyond
the zone of flame impingement. After two minutes the foam
backing was not penetrated and was still flexible.
