GB2199262A

GB2199262A - Reinforced silicone foam

Info

Publication number: GB2199262A
Application number: GB08720409A
Authority: GB
Inventors: John Simon Razzano
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1986-12-22
Filing date: 1987-08-28
Publication date: 1988-07-06
Anticipated expiration: 2007-08-28
Also published as: FR2608504A1; JPS63173629A; GB8720409D0; CA1295783C; GB2199262B; FR2608504B1; DE3742006A1; JPH0586749B2

Description

- 2 19 & 2Z U-,' MAT REINFORCED SILICONE FOAM The present invention

relates to fiber reinforced silicone fo am. More particularly, the present invention relates to silicone foam flame barriers containing non-combusting and non-melting fiber reinforcement.

Protective and insulating silicone foams are in demand for many applications which require flame-retardance. Silicone foams are effectively used today as fire proofing in electrical equipment, buildings, airplanes, automobiles and furniture.

Silicone foam will withstand some time of direct flame contact without flame penetration. These foams tend to char and form a protective ash at the point of flame or heat contact. The protective ash prevents flame spread into the body of the foam and as the ash builds in thickness will prevent further silicone foam from decomposing to ash.

Silicone foam may be used as a film or sheet. and due to the elastomeric nature of the foam, it can be bent or stressed to conform to various shapes. However, wheyle there is a sharp bend or angle in the silicone foam sheet, stress is created that will lead to cracks forming in the foam upon oxidation and pryollysis. Thus, where flame is applied to a bend or angle in silicone foam sheet, the surface will oxidize to brittle silica, acrack will form in the sheet due to the stress of the bend, and flames will penetrate the sheet.

1 t i 5 an object of the present invention to produce silicone foam sheet with improved resistance to flame penetration at a bend angle or other point of stress.

It is a further object of the present invention to produce a silicone foam sheet which has reduced tendency to crack when under stress in its oxidized state.

Detailed Description of the Invention

Briefly, according to the present invention there is provided a silicone foam sheet containing:

(a) a layer of silicone foam and (b) imbedded therein a continuous mat of non-combusting, non-melting fibers.

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:

R I I R - Sic - 01 R 1 - sic - 01 1 R a 01 (1) where R and R 1 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 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 25% (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:

R 3 A R 2 S10 9 R 3 lz R 3 4 10 R3 9 S1 R 2 Y ' R3 (2) 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 2SOC; 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 have at least 0.2 moles of hydrogen in the hydride-containing polysiloxane cross-linking agent for every mle 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 compo s i t io n. 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 U.S. Pat. No. 4,189,545, hereby incorporated by reference.

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 1 to 6 carbon atoms per radical, phenyl and 3,3,3-trifluoropropy]; (b) a hydroxylated organosiloxane having an average of from greater than 1.0 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 1 to 6 carbon atoms per radical, phenyl and 3,3,3-trifluoropropyl; and (c) a platinum catalyst in an amount of from 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.

This silicone composition is easily foamed by simply mixing the ingredients and allowing them to react. The principle reaction produc es hydrogen gas to foam the composition aInd 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 o rgano hydrogens i loxane producing a molecule of hydrogen and a Si-O-Si bond. This silicone foam composition is further described in U.S. Pat. No. 4,189,545, hereby incorporated by reference.

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 hydroxylated 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 hydroxylated organosiloxane can be divided into two portions, where one portion is mixed with the platinum catalyst and the second po rt io n is mixed with the hydride polymer organohydrogensiloxane and then the two mixtures are combined to form a fo am. 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 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 organo hydro gens i loxane 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 po lymethyl vinyl si loxane cyclic compounds and acetylenic alcohols can be added. The platinum catalyst inhibitors are 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 rel- atively small amounts, such as up to 2 parts by weight po lymethyl vinyl siloxane cyclics can be used to control the initiation of the foaming and curing. The po lymethyl vinyls i loxane 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 compr ise R 4 Si00. 5 (M) ' R 4 Sio- (D), and Sio (Q) units where 2 2 R is selected from substituted and unsubstituted monovalnt hydrocarbon radicals. These resins and their use for the above purpose are further described in U.S. Pat. No. 4,418,157, herein incorporated by reference.

Non-combusting, non-melting fiber mats suitable for use herein may contain inorganic fibers, for example, glass fibers, asbestos fibers, graphite fibers, etc., or even very heat resistant organic fibers such as polyimide fibers. It is essential to the instant invention that the fiber mat not burn or melt when exposed to ordinary flame temperatures, i.e. temperatures of at least about 3000C or greater, and preferably, temperatures of at least about 5000C or greater.

The term "mat" as used herein is a non-woven, woven, needled, or otherwise intertwined layer of fibers which will distribute an applied load over a large surface area. The mat may be comprised of, for example, parallel continuous fibers,-or bundles of continuous fibers intermittently joined by perpendicularly running cross fibers. Alternatively, the mat may be short fibers woven into a mat. The mat may be lofty, i.e. a loose weave allowing the fibers to loft out of the plane of the mat, or the mat may have no loft, i.e. the mat is tightly woven and the fibers are held closely to the place of the mat. Preferred inorganic non-melting fiber mats for use herein generally have a fiber content ranging from about lxlO-3 to about 5XIO -1 g/cm 2 and preferably from about 3 1 2 5xlO- to about lxlO- g/cm To produce the composite article of the present invention, the silicone foam composition is applied to at least one face of the inorganic non- melting mat and foamed.

For best results, the silicone foam composition should be formulated to 1, 000,000 centipoise at 25'C and should preferably have a viscosity ranging between about 500 and 100,000 centipoise at 250C. The object of viscosity control is to obtain a controlled penetration into the mat along with good cell formation in the foam. Penetration of the mat may 'be complete, resulting in foam on both sides and a completely imbedded mat. However, it may also so desirable to maintain one side of the mat as an external face of the composite; i.e. only partially imbed the mat. In this case only partial penetration is permitted, i.e. sufficient penetration for adhesion to one face of the mat. 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/cm 3 and preferably 3 from about 0.16 to 0.329/cm The silicone foam composition is applied to the mat by known methods, for example by roller, by blades, etc. Generally, sufficient silicone foam composition should be applied that the foam thickness on one side of the mat is at least about 1.5 mm. Thicknesses less than this supply almost no resistance to flame penetration. The thickness should increase depending upon the degree of fire protection sought. Ordinary foam thickness for use in many applications, run from about 6 mm to about 51 mm.

The silicone foam composition is preferably mixed from packages just prior to application to the mat, but it is -g- understood that mixing could be accomplished on the mat surface, for example, where low viscosity silicone polymers are employed.

k One preferred method of applying the silicone foam composition to the mat 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 mat with the silicone foam composition on one or both faces. Of course, the resultant silicone foam will have a backing of polyolefin which may be removed. The use of the impermeable film controls hydrogen gas escape and also prevents the silicone foam composition from 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 mat penetration by the silicone foam composition. The heat may be applied by convection 0 r radiation. The temperature within the foam mass should not exceed about 65% 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 f umed silica, diatomaceous earth, zfnc oxide, calcium carbonate, crushed quartz, and the like. The maximum amount of filler to be added depends on the desired properties- of the f o am. Generally, up to about 60% by weight filler may be To enhance the burn resistance of the above silicone foams, other burn resistant additives may be employed. For instance, 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 fo 1]owing 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

Compo s i t io n A contains 100 parts by weight 80,000 centipoise vinyl terminated polydimethylsiloxane fluid, 25 parts by weight a MDv inyl Q resin, 1 part by weight water, 20 ppm platinum catalyst capable of gelling foam in 20 minutes, 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 trimethyl terminated methyl hydro gens i loxane fluid. Ten parts by weight of Composition A was combined with one part by weight of Composition B resulting in a 25,000 to 40,000 centipoise silicone foam composition. The silicone foam composition immediately begins to react and cure.

Example 2

The silicone foam composition of Example I was mixed and continuously fed into the nip formed by two rollers having two continuous sheets of polyethylene running therebetween. The resultant foam sheet cures to a thickness of 1/16 in. in about 5 minutes and the polyethylene facing is peeled away.

Example 3

A section of the silicone foam sheet of Example 2 was vertically aligned and exposed on both faces. A gas flame having a temperature of about 2100F is applied to the center of one face of the vertical section and a silicon oxide layer immediately forms on the surface. With continued application of the flame, the area of flame impingement crabks and begins to fall away due to the simple impact force of the flame. The flame freely penetrates the silicone foam sheet.

Example 4

A section of the silicone foam sheet of Example 2 was stressed by loosely bending it at a 90 degree angle. A gas flame is applied to the outer face of the bend and a silicon oxide layer immediately forms on the surface. With continued application of the flame, the area of flame impingement cracks and begins to fall away due to the simple impact force of the flame. The flame freely penetrates the silicone foam sheet.

Example 5

Example 2 was repeated except there was further fed into the nip of the rollers a continous mat of glass manufactured by Clark Schweble Fiberglass Company, of White Plains, NY (style 1609, finish CS-210), having 30 x 10 fiber bundles per sq. in., and having a weight of 5.1 x 10- 3 grams/cm 2. The foam composition was fed to the nip on only one side of the glass mat so that the mat was partially exposed on one side.

Example 6

Experiment 3 was repeated by applying a gas flame to the silicone foam sheet of Example 5 on the foam face. With continued exposure, the area of flame impingement did crack but did not fall away. The flame did not penetrate the silicone foam sheet even after prolonged exposure.

Example 7

Experiment 4 was repeated by applying a gas flame to the silicone foam sheet of Example 5 on the foam face. With continued exposure, the area of flame impingement did crack but did not fall away. The flame did not penetrate the silicone foam sheet even after prolonged exposure.-

Claims

A silicone foam sheet pomprising:

(a) a layer of silicone foam, and (b) imbedded therein a continuous mat of non-combusting, non7melting fibers.
2. The silicone foam sheet of Claim 1 wherein said fibers do not burn or melt when exposed to temperatures of at least about 300C or greater.
3. The silicone foam sheet of Claim I wherein said fibers do not burn or melt when exposed to temperatures of at least about 400% or greater.
4. The silicone foam sheet of Claim 2 wherein said fibers are inorganic fibers.
5. The silicone foam sheet of Claim 2 wherein said fibers are heat resistant organic fibers.
6. The silicone foam sheet of Claim I wherein said continuous mat is partially imbedded.
7. The silicone foam sheet of Claim I wherein said continuous mat is completely imbedded.
8. The silicone foam sheet of Claim I wherein said continuous mat has a fiber content ranging from about 1 x 10 -3 to about 5 X 10- 1 g/cm 2.
9. The silicone foam sheet of Claim I wherein said continuous mat has a fiber content ranging from about 500- 3 to about 1 2 IX10- g/cm
10. The silicone foam sheet of Claim 1 wherein said fibers are continuous fibers.
11. The silicone foam sheet of Claim I wherein said fibers are short fibers -woven into continuous bundles.
12. The silicone foam sheetof Claim 1 wherein said silicone foam has a thickness of at least about 1.5 mm.
13. The silicone foamsheetof Claim 1 wherein said silicone foam has a thickness of from about 6mm to about 51 mm.
14. The silicone foamsheetof Claim 1 wherein said silicone 3 foam has a density of from about 0.08 to about 0.4 g/cm
15. The silicone foamsheetof Claim 1 which contains platinum cure catalyst residue.
16. A silicone foam sheet as claimed in claim 1, substantially as hereinbeCore described in any one of the examples.

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