CA2059162A1 - Silicone foams of improved fire resistance - Google Patents
Silicone foams of improved fire resistanceInfo
- Publication number
- CA2059162A1 CA2059162A1 CA002059162A CA2059162A CA2059162A1 CA 2059162 A1 CA2059162 A1 CA 2059162A1 CA 002059162 A CA002059162 A CA 002059162A CA 2059162 A CA2059162 A CA 2059162A CA 2059162 A1 CA2059162 A1 CA 2059162A1
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- CA
- Canada
- Prior art keywords
- foam
- composition
- silicon
- moulding cavity
- silicone
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/02—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by the reacting monomers or modifying agents during the preparation or modification of macromolecules
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
- B29C44/34—Auxiliary operations
- B29C44/60—Measuring, controlling or regulating
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
- B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
- B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
- B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
- B29C2035/0855—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using microwave
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2105/00—Condition, form or state of moulded material or of the material to be shaped
- B29K2105/24—Condition, form or state of moulded material or of the material to be shaped crosslinked or vulcanised
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2995/00—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds
- B29K2995/0012—Properties of moulding materials, reinforcements, fillers, preformed parts or moulds having particular thermal properties
- B29K2995/0016—Non-flammable or resistant to heat
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2383/00—Characterised by the use of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen, or carbon only; Derivatives of such polymers
- C08J2383/04—Polysiloxanes
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
Abstract
Abstract of the Disclosure The specification describes and claims a method of making silicone foam compositions comprising the steps of introducing into a moulding cavity a quantity of foamable silicone compositions which is curable at room, or slightly elevated, temperature and bring about curing in the cavity to produce a cured silicone foam. The moulding cavity is closed prior to foaming thereby restricting expansion of the foam. The volume of the closed moulding cavity is a minimum 10% less than that which would be occupied by the composition if it foamed and cured at room temperature without restriction. Lower density foams formed by the above procedure may be converted into rigid elastomeric low density materials by a heat or microwave post cure. For a given composition and foam density the fire resis-tance of a foam produced by a method according to the invention is greater than a foam which is allowed to foam freely.
Description
SILICONE FOAMS OF IMPROVED FI~E RESISTANCE
This invention is concerned with preparation of silicone foams of improved fire resistance.
Liquid, foam forming, curable silicone compositions are available which flow and foam readily at room or slightly elevated temperature to provide a cured foam product. It has been proposed to employ foamable silicone based room temperature curable compositions for various purposes, including applications where fire resistance is desirable. For example, U.S. Patent Specification 4,760,098 is directed to a composition of selected formu-lation which is curable and foamable at room temperature for preparation of flexible silicone foams of gaod fire resistance and low density which have good mechanical a~ld physical properties. The compositions may be cured in a mould; the moulds exemplified are generally open but there is mention of gelling the composition in a closed mould and opening the mould and placing it in an oven at 60 to 70C
for 15 minutes to cure the foam.
Whilst it is desirable to provide fire resistant foams of lower density than previously employed, it is generally accepted that the fire resistance of foams of lower density is lower than the fire resistance of foams of higher density. We have now found, surprisingly, that the fire resistance of a cured silicone foam may be enhanced by restricting the expansion of the foam as it cures.
The invention provides in one of its aspects a method of making a cured silicone foam comprising the steps of introducing to a moulding cavity a quantity of a silicone composition which is curable at room or slightly elevated temperature to provide a foam and bringing about curing of the composition in the moulding cavity to form the cured silicone foam characterised in that the moulding cavity is closed during foaming of the composition whereby to restrict expansion of the foam and in that the volume of the closed moulding cavity is at least 10% less than the volume which would be occupied by the foam produced by permitting that quantity of the composition to foam and cure at room temperature without restriction.
In a method according to the invention the selected silicone composition, which is curable at room or slightly elevated temperature to provide a foam, is introduced to a moulding cavity. The moulding cavity may be of any desired design and may be for the production of any article. If desired one or more surfaces of the moulding cavity may be provided by a surface of an element, for example a building element, to which the cured foam is intended to adhere with or without the use of a surface primer. The moulding cavity may be provided by a mould comprising for example a base and side walls and a moveable top which provides closure means for closing the cavity. Alternatively, the moulding cavity may be defined by two preformed elements for example panels of building board, stone, metal or glass spaced apart to provide a moulding cavity which is closed at its periphery by spacer elements, one or more of which provides closure means for the mould. We prefer that the moulding cavity is one designed for the production of building components, for example, separation wall panels, exterior cladding elements, ceiling panels, silicone foam blocks or automotive body panels. Prior to introduction to the moulding cavity the composition is mixed, care being taken that the cure does not progress significantly before the composition is introduced to the moulding cavity. The composition may be mixed and introduced to the mculding cavity by any suitable means for example by injection or pouring. Before or after introduction of the composition to the moulding cavity, the moulding cavity is closed for example by closure means which may take any suitable form, and the foaming of the composition occurs in the closed moulding cavity. It is important in respect of the fire retardant properties of the foam that the volume of the closed moulding cavity is less than the volume which would be occupied by the foam produced by permitting the same quantity of the composition as used in the method according to the invention to foam and cure at room temperature without restriction. When the moulding cavity was reduced in volume by up to 8% we observed that there was no increase in the fire resistance of the cured foam. For a reduction of 10% in t~e volume of the moulding cavity a significant increase in the fire resistance oE the cured foam was observed. Further reductions in the moulding cavity volume resulted in cured foams of increased fire resistance. However, there was an attendant rise in the densities of the cured foams. Curing may be brought about by maintaining the mould at a temperature of the order of 18 to 35C, although curing may be accelerated by heating the composition. After the moulding has formed and cured the closure means may be removed from the moulding cavity and the foam or laminate (comprising foam bonded to one or more panels) may be released Foams of any density, for example in the range 40 to 700 Kg/m3, may be prepared using many silicone compositions by a method according to the invention in which the compo-sition is foamed and cured at room or slightly elevatedtemperature. Many of the lower density foams formed are relatively soft and spongy products. However, by use of the most preferred compositions referred to hereinafter one may employ a method according to the invention to prepare somewhat rigidly elastomeric low density silicone foam mouldings having high flexural strength, low comp-ression set, and good self adhesion to panel substrates, leading to good resistance to compression, tension or deflection. Surprisingly we have also found that the cured mouldings may be converted to a more crosslinked form by subjecting the mouldings to heat in a post cure, after completion of the foaming process. This is especially useful with respect to the relatively soft and spongy lower density mouldings which thus may be converted to somewhat rigidly elastomeric low density silicone foam mouldings having some at least of the mentioned properties, particu-larly good rigidity. The post cure may be achieved, for example, by maintaining the foam at a temperature of from about 80C to about 120C for from 1 to 2~ hours in an oven. Mouldings which are difficult to heat sufficiently in an oven, for example due to their size or due to the heat sensitive nature of panels to which the foam has been caused to adhere, may alternatively be subjected to a post cure by microwave heating; this method is effective for those foams which contain sufficient ingredients which demonstrate a heating effect when subjected to microwaves.
These elastomeric properties of the foam cannot be achieved by aging the room temperature cured foam at room tempe-rature. Foam mouldings having these more elastomeric properties are useful, for example in producing somewhat rigid low density silicone foam mouldings having lips, grooves or the like which serve a mechanical purpose, for example building panels or blocks with interlocking recesses and tabs suitable for assembly as a continuous wall of interlocking panels or blocks with or without the additional use of adhesive or sealant.
, ' ', .
The foamable silicone composition used in a method according to the invention may be any of those which are commercially available which comprise an organosilicon polymer including siloxane units having a silicon-bonded hydrogen atom, a hydroxy bearing material, for example an organosilicon polymer includin~ siloxane units providing silicon-bonded hydroxyl groups and a ca~alyst, for example a tin compound or more preferably a noble metal compound or complex. They may (and where post cure by microwave heating is intended, should) also comprise finely divided filler. These compositions cure according to the scheme OH ~ -SiH --> 9si-o- + H2. A polymeric material reactive with the silicon-bonded hydrogen atoms is included in the compo-sition for example an organosilicon polymer having silicon-bonded hydroxyl and/or unsaturated e~g. vinyl groups so that a network of interconnected polysiloxane chains is produced and the hydrogen evolved as a gas serves to form cells within the developing network. Preferred foam forming, curable organosilicone polymer compositions comprise a polydiorganosiloxane having silicon-bonded unsaturated e.g. vinyl groups available for reaction with polysiloxanes having silicon-bonded hydrogPn atoms. The addition reaction which occurs is appropriate to yield chain extended or crosslin~ed elastomeric silicone products but does not generate volatile materials for causing foaming in the curing composition. The foaming may be achieved by chemical reaction of the silicon-bonded hydrogen atoms with silicon-bonded hydroxyl groups and/or water or an aliphatic alcohol as more fully described for example in U.S. 4,613,630, or by inclusion in the compo-sition of a volatile blowing agent. The polysiloxanes and other ingredients and the proportions thereof are selected so that the network is sufficiently developed and cured to produce a resilient foam of desired cellular structure within a short pexiod of time of the order of a few minutes or less.
Suitable polysiloxanes including siloxane units having a silicon-bonded hydrogen atom include polysiloxanes having units according to the general ~ormula RpHSiO(~
in which each R represents a monovalent hydrocarbon group containing 1 to 20 carbon atoms, for example a lower alkyl or phenyl group e.g. a methyl group, and ~ is 1 or 2. The polysiloxanes may also comprise units (i) RnSiO(~n~ in which R is as referred to above and n is 1, 2 or 3. Pre~e-rably, the polysiloxane has from 0.3% to 2.5% by weight of silicon-bonded hydrogen atoms. We pre~er that each R
represents a methyl group. Preferably, terminal groups of the polysiloxane have the formula R3Sio~ where each R
represents a methyl group. Suitable polysiloxanes include those comprising MeHSiO units with or without the presence of Me2SiO (where Me represents a methyl group) units and having viscosities of the order of from about 1 to about lOOO mm2/s more preferably from about 5 to about 50 mm2/s.
Suitable polysiloxanes having silicon-bonded unsatu-rated e.g. vinyl groups available for reaction with polydi-organosiloxanes having silicon-bonded hydrogen atoms include polysiloxanes having siloxane units according to the general formula RmRlSio(3 m) in which each R represents a monovalent hydrocarbon group having up to 20 carbon atoms, for example a lower alkyl or phenyl group e.g. a methyl radical, _ is 1 or 2 and R' represents an aliphati-cally unsaturated group for example cyclohexenyl or a group CH=CHR" linked to the silicon atom for example via a divalent aliphatic chain wherein R" represents a hydrogen atom or an alkyl group for example vinyl, allyl or hexenyl.
These polysiloxanes also comprise units (i) in which R and n are as referred to above. These materials are reactive with the silicon-bonded hydrogen atoms in presence of a noble metal catalyst by a hydrosilylation reaction and thus contribute to the polysiloxane matrix. Preferably these polysiloxanes have from 0.0002% to 3% by weight of alipha-tically unsaturated groups and _ is such that they have aviscosity of the order of about lOmmZ/s to about 500,000 mm2/s. Preferred compositions employ a polysiloxane having siloxane units according to the general Eormula RmR'Sio(3 m) in which R' represents a group CH=CH2 linked to the silicon atom via a divalent aliphatic chain and having a viscosity in the range lO0 mm2/s to 2000 mm2/s.
Suitable organosilicon polymers including siloxane units providing a silicon-bonded hydroxyl group include 0 polydiorganosiloxanes having at least two siloxane units of a RaQbSi(4-(a+b)) in which a has a value of 0 or 2, _ has a value of 1 or 2 and the sum of a + b is not greater than 3, Q represents a hydroxyl group for example silanol terminated polydioganosiloxanes according to the general formula Ho((R2)Sio)SH in which each R represents a methyl group and s has a value from about lO to about 1200.
Suitable materials have viscosities of the order of about 10 mm2/s to about 500,000 mm2/s. Preferred compositions which provide the more elastomeric foams employ polydi-organosiloxanes according to the general formula Ho((R2)Sio)sH as aforesaid which have viscosities of the ordar of about 2,500 mm2/s to about 20,500 mm2/s. The density of the silicone foam can be significantly reduced without degrading its structural strength by including a short-chain silanol terminated polydiorganosiloxane in the formulation. Preferred compositions employ polydiorgano-siloxanes according to the general formula HotR2sio)sH asaforesaid in which s has a value from about 2 to about 10.
Preferred materials have viscosities of the order of about 5 mm2/s to about 100 mm2/s. Polydiorganosiloxanes having at least two siloxane units of the formula RaQbSiO(4 (a~b~) in which Q is a hydroxyl bearing alkylene or oxyalkylene chain may also be used. The chain may be attached to the silicon atom in any convenient way but is preferably linked to the silicon atom by a carbon atom. Suitable hydroxyl bearing chains include those containing up to 50 chain atoms. Suitable alkylene chains are those having 1 to 15, more preferably ~ to 10 chain carbon atoms. Suitable oxyalkylene chains include those of the formula (CdH2dO)eH
in which d has the value 2, 3 or ~ and e has a value in the range 1 to 15 more preferably 1 to 10, i.e. having from 1 to 15, more preferably 1 to 10 oxyalkylene groups. The oxyalkylene groups may be for example oxyethylene, oxypro-pylene or oxybutylene or mixtures thereof, the most pref erred being the oxyethylene group. This polydiorgano-siloxane also comprises siloxane units (i) as aforesaid.
Other materials which may be included as crosslinking agents include materials having three or more functional e.g. hydroxy groups per molecule.
Compositions for use in the invention preferably include one or more alcohols. These materials influence the structure of foams formed by use of the composition and yield cured foams of low density. The alcohol is selected with a view to contributing not only generation of hydrogen gas but also with a view to achieving desired resilience of .
the foam. Suitable alcohols include the primary aliphatic and araliphatic alcohols for example the lower aliphatic mono functional alcohols having up to 8 carbon atoms, e.g.
ethanol, propanol, butanol and benzyl alcohol~ Foams of lowest density are formed by use of the aliphatic alcohols having from 2 to 12 chain carbon atoms. Preferred compo-sitions employ n-propanol.
Compositions suitable for use in the invention pr~fe-rably employ a foam stabiliser or surfactant. Suitable foam stabilising materials include fluorinated silicones, for example a polyorganosiloxane comprising (CF2)m(CH2)nOpSiO(4_p), R3Sio~, SiO4/2 units and silicon-bonded hydroxyl groups wherein each R represents a mono-valent hydrocarbon group containing from l to 20 ~arbon atoms, m is an integer having an averaye value of from 1 to 20, n has the value 1 or 2, ~ has the value 1, 2 or 3. The polysiloxane may also include from 0 to 10 percent, based on the weight of said polyorganosiloxane, of GSio3/2 units wherein G represents the residue obtained by removing the hydrogen atom from a hydroxyl group of a linear organic polymer selected from the group consisting of homopolymers of ethylenically unsaturated alcohols, copolymers of these alcohols with ethylenically unsaturated hydrocarbons, poly-ethers and polyoxyalkylene glycols, wherein said organic polymer contains an average of at least one terminal hydroxyl group per molecule. These materials may be prepared by treatment of hexamethyldisiloxane coated poly-silicates with the alcohol F(CF2)8CH2CH2OH, and are morefully described and claimed in European Patent Specification 179 598. They serve to stabilise the structure of the foam during its curing.
Suitable noble metal catalysts include rhodium and platinum containing materials. Platinum catalysts may take any of the known forms, ranging from platinum as deposited on carriers such as silica gel or powdered charcoal to platinic chloride, salts of platinum and chloroplatinic acids. A preferred form of platinum is chloroplatinic acid either as the commonly obtainable hexahydratQ or the anhydrous form, on account of its easy dispersibility in organosilicon systems and its non-effect on colour of the mixture. Platinum complexes may also be used e.g. those prepared from chloroplatinic acid hexahydrate and divinyl tetramethyldisiloxane. Compositions according to the invention foam and cure very rapidly when the component parts have been mixe~ together. If it is desired to prolong the cure time, for example if it is desir~d to mix the composition and then transfer it to the site where it is intended to foam and cure, one may include in the compo-sition one of the known platinum catalyst inhibitors such as a polymethylvinylsiloxane cyclic compound or an acety-lenic alcohol e.g. methyl butynol. Larger proportions of catalyst may be used when a faster cure is desired.
If desired other adjuvants may be included in a composition for use in the invention, for example fillers, colorants, coloured indicators and extenders. Fillers which may be used include, for example silica, glass beads or glass microspheres all of which may be treated to render them hydrophobic, calcium carbonates and carbon black.
Compositions for use in the invention may be formu-lated to cure within a short period of time. In order toachieve this it is important that the ratio of silicon-bonded hydrogen atoms to all carbon-bonded or silicon-bonded hydroxyl groups, together with other reactive hydroxyl, unsaturated and other groups present in the . .
composition is appropriate. This ratio may be in the range 2.0:1 to 35:1 and is preferably in the range 2.5:1 to 10:1.
The ratio of silicon-bonded hydrogen atoms to carbon-bonded hydroxyl groups and silicon-bonded hydroxyl groups is suit-ably in the range 2.0:1 to 40:1 more preferably 2.5:1 to 10:1. The ratio of aliphatically unsaturated groups to silicon-bonded hydroyen atoms is preferably in the range 1:20 to 1:150 more pre~erably in the range 1:20 to 1:90.
The ratio of aliphatically unsaturated groups to carbon-bonded hydroxyl groups and silicon-bonded hydroxyl groups may be in the range 1:2 to 1:60, more preferably 1:5 to 1:18. We have found that compositions in which the ingredients are present in the preferred ratios can be formulated to cure within 20 to 40 seconds of mixing of the composition at room temperature (i.e. of the order of 18C
to 20C) and humidity (i.e. about 30~ to 90% relative humidity) to provide cured foams of a density between about 40kg/m3 and 600kg/m3 or less when foamed freely or cured foams of a density between about 50 and 700kg/m3 when foamed by a method according to the invention. The foams formed according to the invention are fine pored foams of uniform cell size. They are hydrophobic and generally comprise from about 20% to about 80% closed cells and correspondingly about 80% to about 20% open cells, the more closed cell foams being produced when increased proportions of the foam stabiliser are present.
Compositions suitable for use in the invention foam and cure when mixed at room temperature and humidity.
Accordingly the reactive components are stored separated until required for use. In order to enable simplicity and ease of mixing the components at the application site, it is preferred to store the compositions in two-part form in which each of the parts is of substantially the same viscosity so that the first and second parts may be mixed together in a ratio of 1:1 by volume or 1:1 by weight as desired.
A method according to the present invention may be used to produce foams of various densities and combinations of properties by adjustment of the foam formulation. For any given foam density, the fire resistance of foams produced according to the invention is greater than the fire resistance of foams formed by permitting the foam to expand and cure freely without constraint on its foamed volume. The evaluation of fire resistance as meant in this specification involves exposing the foam to a flame; prior art foams tend to exhibit large cracks in the exposed foam surface very quickly upon exposure to the flame and these permit heat to penetrate quickly through the mass of the foam, whereas foams made according to the invention are more resistant to penetration of heat. We believe this is due to a more homogenous foam structure of foams made 2Q according to the invention coupled with a small average cell size.
In order that the invention may become more clear there now follows a description of example compositions according to the invention. All parts are by weight unless otherwise specified.
In the Examples the following materials were used:
The polysiloxane I having silicon-bonded hydrogen atoms was a trimethylsilyl end-blocked polymethylhydrogen-siloxane having a viscosity of about 30 mm2~s and 1.5 mole % hydrogen.
The polysi~oxane II having silicon-bonded hydrogen atoms was a trimethylsilyl end-blocked polysiloxane having methylhydrogensiloxane and dimethylsiloxane units having a viscosity of about 5 mm2/s and 0.76 mole % hydrogen.
The polysiloxane III having silicon-bonded hydroxyl groups was a dimethylhydroxysilyl endblocked polydimethyl-siloxane having a viscosity of about 13,500 mm2/s and a hydroxyl content of about 0.066 mole %.
The polysiloxane IV having silicon-bonded hydroxyl groups was a dimethylhydroxylsilyl endblocked polydimethyl~
siloxane having a viscosity of about 42 mm2/s and a hydroxyl content of 4 mole ~.
The polydiorganosiloxane V having silicon-bonded unsaturated groups was a dimethylvinylsilyl endblocked polydimethylsiloxane having a viscosity of about 450 mm2/s and 0.45 mole ~O vinyl groups.
The foam stabiliser was prepared by treatment of hexamethyldisiloxane coated polysilicates with the alcohol F(CF2)8CH2CH20H, as more fully described in European Patent Specification 179 598.
Cyclic polymethylvinylsiloxane compounds were used to adjust the speed of cure. N-propanol was used as a blowing agent for the low density foams. Chloroplatinic acid, complexed with vinyldisiloxane, was used as the catalyst.
Ground quartz of 5 micron particle size was used as filler 1. For the purpose of better microwave (RF) radiation absorbance ultra-fine carbon black with high dielectric loss was added as Filler 2.
Fire resistance of sample foam plates was evaluated by positioning the plate at an angle of 45 over a blue flame of a blow torch and spaced lOcm from the orifice of the torch with the tip of the blue flame just touching the plate. The time required for the flame to penetrate through the plate was measured. The values in seconds are recorded in the Tables as "fire resistance". As can be seen from the results, for any given foam density, the fire resistance of foams produced according to the invention is , greater than the fire resistance of foams formed by permitting the foam to expand and cure freely without constraint on its foamed volume.
ExamPle 1 Example compositions were prepared which comprised two parts A and B and contained ingredients in the amounts shown in Tables I(a) and I(b).
The value given in Table II for Molar Ratio 1 is the ratio of silicon-bonded hydrogen atoms of the polysiloxane to all carbon bonded hydroxyl groups together with other reactive hydroxyl, unsaturated and other groups present in the composition. Th~ value given for ~atio 2 is the ratio of silicon-bonded hydrogen atoms to silicon-bonded and carbon-bonded hydroxyl groups. The value given ~or ~atio 3 is the ratio of aliphatically unsaturated groups ~o silicon-bonded hydrogen atoms and the value given for Ratio 4 is the ratio of aliphatically unsaturated groups to carbon-bonded hydroxyl groups and silicon-bonded hydroxyl groups.
A mould was prepared comprising a base, four side walls normal to the base and a lid to close the mould and so define a closed moulding cavity capable of producing foam plates 270mm thick. The inner dimensions of the closed moulding cavity were 20 x 20 x 2.7cm corresponding to a volume of the closed moulding cavity 1080 cm3. Compo-sitions were prepared by mixing equal volumes of the Parts A1, A2, A3 and B1 or A4 and B2. Each of these example compositions was mixed to form a homogenous fluid and poured into the moulding cavity within 30 seconds of mixing. In a first group of experiments the composition was poured into the mould but the moulding cavity was not closed by the lid. It was found that the compositions each cured in 120 to 600 seconds or less to provide a fine pored foam of density as shown in Table II. The quantities of the compositions formed by mixing equal volumes ~f the Parts A and B required to produce a cured foam which just filled the mould are shown in Table II as l'Quan~ity Free Foam". In a second group of experiments, quantities as shown in Table II as "Quantity Constrained Foam " obtained by mixing equal volumes of the Parts A and B (principally approximately 10% more than the quantities required to produce a cured foam which just filled the mould) were mixed in the same way and introduced to the mould and the mould closed by the lid and clamped closed. Each compo-sition was allowed to foam and cure in the mould cavity at room temperature. The density of the foams was found to be as shown in Table II. These foam samples were removed from the moulding cavity and aged at room temperature for 24 hours. The foams formed in both groups of experiments were demoulded and post cured by heating in an oven maintained at 100C for a further 24 hours. The samples from the second group of experiments were found to have a much more regular and homogenous cell structure than those formed in the first group of experiments.
Example 2 Compositions were processed in a similar manner to that employed in Example 1 but the sample mouldings produc~d measured 10 x 10 x 2cm. The post cure was carried out during microwave radiation. The samples were placed between two plates of a capacitor in such a way that a distance of 3mm betwean the plates and the foam sample was maintained. The samples were then post cured with a radio wave signal of 35 MHz at 3 - 4 kV potential for 10 seconds.
The formulations employed are shown in Table III and the resultant properties are recorded in Table IV.
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TABLE I ( a) Formulations Al Bl A2 Polysiloxane I or II
having silicon-bonded hydrogen I - 23.8 II - 1.7 Polysiloxane III
or IV having silicon-bonded hydroxyl groups carbon-bonded hydroxyl groups III 39.9 49.3 40.2 IV - 9.4 N-propanol 2.0 ~ 1.7 Polysiloxane V having unsaturated groups V 30.6 1.7 30.8 Methylvinyl cyclics - 0.1 20 Foam stabiliser 6.5 - 6.0 Catalyst 0.5 - 0.5 Filler 1 15.3 13.6 15.5 Pigment (a) 5.2 5.3 (b) 0.4 TABLE I(b) Formulations A3 A4 B2 Polysiloxane I or II
having silicon-bonded hydrogen I - - 8.6 II - - 2.1 Polysiloxane III
or IV having silicon-bonded hydroxyl groups carbon-bonded hydroxyl groups III 41.4 43.6 59.5 IV - - 11.3 N-propanol 1.0 Polysiloxane V having unsaturated groups V 31.7 33.4 2.0 Methylvinyl cyclics - - 0.1 20 Foam stabiliser 4.0 Catalyst 0.5 0.5 Filler 1 16.0 16.8 16.4 Pigment (a) 5.4 5.7 (b) ' - , , ~ :.
.
TABLE II
Property Composition formed by mixing Parts Al~B1 A2+B1 A3~B1 A4+B2 (D) (C) (B) (A) Molar Ratio 1 2.9:1 7.1:1 6.3:1 6.0:1 2 3.5:1 8.4:1 7.3:1 6.9:1 3 1:24.6 1:66.3 1:68.1 1:68.7 4 1:7.1 1:7.9 1:9.4 1:10.1 Curing time (sec) 420 175 150 140 Quantity (ml) Free Foam 150 210 260 310 Constrained Foam 165 230 290 345 Density (Kg/m~) Free Foam 150 210 260 31Q
Constrained Foam 16S 230 290 345 Elastomer properties tYoung's modulus of Compression) Free Foam Before post cure 0.013 0.040 0.066 0.128 After post cure 0.062 0.080 G.155 0.178 Constrained Foam Before Post-Cure 0.043 0.051 0.190 0.290 After Post-Cure 0.057 0.105 0.390 0.315 Fire R~sistance Free Foam Before Post-Cure 300 420 540 1300 After Post-Cure 450 500 550 1800 Constrained Foam Before Post-Cure 420 540 720 3600 After Post-Cure 800 800 1200 3550 FormulationsA5 B3 A6 Polysiloxane I or II
having silicon-bonded hydrogen I - 26.7 II - 1.4 Polysiloxane III or IV having silicon-bonded hydroxyl groups III 41.4 39.9 40.1 IV - 19.6 N-propanol - - 1.0 Polysiloxane V having unsaturated groups V 31.7 1.3 30.7 Methylvinyl cyclics - 0.1 Foam stabiliser - - 2.0 Catalyst 0.5 - 0.5 Filler 1 16.0 11.0 15.2 Pigment (a~ 5.4 5.2 Filler 2 5.0 5.0 TABLE IV
Property Composition formed by mixing Parts A5+B3 A6+B3 (E) (F) Molar Ratio 1 5.5:1 4.g:1 2 6.1:1 5.3:1 3 1:74.5 1:76.8 4 1:12.3 1:14.5 Curing time (seconds) 350 290 Quantity ~ml) Free Foam 195 240 Density (Kg/m3) Free Foam 150 240 Elastomer properties (Young's modulus of Compression) Free Foam Before post cure 0.084 0.078 After post cure 0.342 0.355 Fire Resistance Free Foam Before Post-Cure 830 720 After Post Cure 720 670 The formulation E (A5+B3) results in a more friable foam upon post-cure whilst the higher density foam F (A6+B3) containing the profoamer shows better flexibility due to its more regular cell structure.
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This invention is concerned with preparation of silicone foams of improved fire resistance.
Liquid, foam forming, curable silicone compositions are available which flow and foam readily at room or slightly elevated temperature to provide a cured foam product. It has been proposed to employ foamable silicone based room temperature curable compositions for various purposes, including applications where fire resistance is desirable. For example, U.S. Patent Specification 4,760,098 is directed to a composition of selected formu-lation which is curable and foamable at room temperature for preparation of flexible silicone foams of gaod fire resistance and low density which have good mechanical a~ld physical properties. The compositions may be cured in a mould; the moulds exemplified are generally open but there is mention of gelling the composition in a closed mould and opening the mould and placing it in an oven at 60 to 70C
for 15 minutes to cure the foam.
Whilst it is desirable to provide fire resistant foams of lower density than previously employed, it is generally accepted that the fire resistance of foams of lower density is lower than the fire resistance of foams of higher density. We have now found, surprisingly, that the fire resistance of a cured silicone foam may be enhanced by restricting the expansion of the foam as it cures.
The invention provides in one of its aspects a method of making a cured silicone foam comprising the steps of introducing to a moulding cavity a quantity of a silicone composition which is curable at room or slightly elevated temperature to provide a foam and bringing about curing of the composition in the moulding cavity to form the cured silicone foam characterised in that the moulding cavity is closed during foaming of the composition whereby to restrict expansion of the foam and in that the volume of the closed moulding cavity is at least 10% less than the volume which would be occupied by the foam produced by permitting that quantity of the composition to foam and cure at room temperature without restriction.
In a method according to the invention the selected silicone composition, which is curable at room or slightly elevated temperature to provide a foam, is introduced to a moulding cavity. The moulding cavity may be of any desired design and may be for the production of any article. If desired one or more surfaces of the moulding cavity may be provided by a surface of an element, for example a building element, to which the cured foam is intended to adhere with or without the use of a surface primer. The moulding cavity may be provided by a mould comprising for example a base and side walls and a moveable top which provides closure means for closing the cavity. Alternatively, the moulding cavity may be defined by two preformed elements for example panels of building board, stone, metal or glass spaced apart to provide a moulding cavity which is closed at its periphery by spacer elements, one or more of which provides closure means for the mould. We prefer that the moulding cavity is one designed for the production of building components, for example, separation wall panels, exterior cladding elements, ceiling panels, silicone foam blocks or automotive body panels. Prior to introduction to the moulding cavity the composition is mixed, care being taken that the cure does not progress significantly before the composition is introduced to the moulding cavity. The composition may be mixed and introduced to the mculding cavity by any suitable means for example by injection or pouring. Before or after introduction of the composition to the moulding cavity, the moulding cavity is closed for example by closure means which may take any suitable form, and the foaming of the composition occurs in the closed moulding cavity. It is important in respect of the fire retardant properties of the foam that the volume of the closed moulding cavity is less than the volume which would be occupied by the foam produced by permitting the same quantity of the composition as used in the method according to the invention to foam and cure at room temperature without restriction. When the moulding cavity was reduced in volume by up to 8% we observed that there was no increase in the fire resistance of the cured foam. For a reduction of 10% in t~e volume of the moulding cavity a significant increase in the fire resistance oE the cured foam was observed. Further reductions in the moulding cavity volume resulted in cured foams of increased fire resistance. However, there was an attendant rise in the densities of the cured foams. Curing may be brought about by maintaining the mould at a temperature of the order of 18 to 35C, although curing may be accelerated by heating the composition. After the moulding has formed and cured the closure means may be removed from the moulding cavity and the foam or laminate (comprising foam bonded to one or more panels) may be released Foams of any density, for example in the range 40 to 700 Kg/m3, may be prepared using many silicone compositions by a method according to the invention in which the compo-sition is foamed and cured at room or slightly elevatedtemperature. Many of the lower density foams formed are relatively soft and spongy products. However, by use of the most preferred compositions referred to hereinafter one may employ a method according to the invention to prepare somewhat rigidly elastomeric low density silicone foam mouldings having high flexural strength, low comp-ression set, and good self adhesion to panel substrates, leading to good resistance to compression, tension or deflection. Surprisingly we have also found that the cured mouldings may be converted to a more crosslinked form by subjecting the mouldings to heat in a post cure, after completion of the foaming process. This is especially useful with respect to the relatively soft and spongy lower density mouldings which thus may be converted to somewhat rigidly elastomeric low density silicone foam mouldings having some at least of the mentioned properties, particu-larly good rigidity. The post cure may be achieved, for example, by maintaining the foam at a temperature of from about 80C to about 120C for from 1 to 2~ hours in an oven. Mouldings which are difficult to heat sufficiently in an oven, for example due to their size or due to the heat sensitive nature of panels to which the foam has been caused to adhere, may alternatively be subjected to a post cure by microwave heating; this method is effective for those foams which contain sufficient ingredients which demonstrate a heating effect when subjected to microwaves.
These elastomeric properties of the foam cannot be achieved by aging the room temperature cured foam at room tempe-rature. Foam mouldings having these more elastomeric properties are useful, for example in producing somewhat rigid low density silicone foam mouldings having lips, grooves or the like which serve a mechanical purpose, for example building panels or blocks with interlocking recesses and tabs suitable for assembly as a continuous wall of interlocking panels or blocks with or without the additional use of adhesive or sealant.
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The foamable silicone composition used in a method according to the invention may be any of those which are commercially available which comprise an organosilicon polymer including siloxane units having a silicon-bonded hydrogen atom, a hydroxy bearing material, for example an organosilicon polymer includin~ siloxane units providing silicon-bonded hydroxyl groups and a ca~alyst, for example a tin compound or more preferably a noble metal compound or complex. They may (and where post cure by microwave heating is intended, should) also comprise finely divided filler. These compositions cure according to the scheme OH ~ -SiH --> 9si-o- + H2. A polymeric material reactive with the silicon-bonded hydrogen atoms is included in the compo-sition for example an organosilicon polymer having silicon-bonded hydroxyl and/or unsaturated e~g. vinyl groups so that a network of interconnected polysiloxane chains is produced and the hydrogen evolved as a gas serves to form cells within the developing network. Preferred foam forming, curable organosilicone polymer compositions comprise a polydiorganosiloxane having silicon-bonded unsaturated e.g. vinyl groups available for reaction with polysiloxanes having silicon-bonded hydrogPn atoms. The addition reaction which occurs is appropriate to yield chain extended or crosslin~ed elastomeric silicone products but does not generate volatile materials for causing foaming in the curing composition. The foaming may be achieved by chemical reaction of the silicon-bonded hydrogen atoms with silicon-bonded hydroxyl groups and/or water or an aliphatic alcohol as more fully described for example in U.S. 4,613,630, or by inclusion in the compo-sition of a volatile blowing agent. The polysiloxanes and other ingredients and the proportions thereof are selected so that the network is sufficiently developed and cured to produce a resilient foam of desired cellular structure within a short pexiod of time of the order of a few minutes or less.
Suitable polysiloxanes including siloxane units having a silicon-bonded hydrogen atom include polysiloxanes having units according to the general ~ormula RpHSiO(~
in which each R represents a monovalent hydrocarbon group containing 1 to 20 carbon atoms, for example a lower alkyl or phenyl group e.g. a methyl group, and ~ is 1 or 2. The polysiloxanes may also comprise units (i) RnSiO(~n~ in which R is as referred to above and n is 1, 2 or 3. Pre~e-rably, the polysiloxane has from 0.3% to 2.5% by weight of silicon-bonded hydrogen atoms. We pre~er that each R
represents a methyl group. Preferably, terminal groups of the polysiloxane have the formula R3Sio~ where each R
represents a methyl group. Suitable polysiloxanes include those comprising MeHSiO units with or without the presence of Me2SiO (where Me represents a methyl group) units and having viscosities of the order of from about 1 to about lOOO mm2/s more preferably from about 5 to about 50 mm2/s.
Suitable polysiloxanes having silicon-bonded unsatu-rated e.g. vinyl groups available for reaction with polydi-organosiloxanes having silicon-bonded hydrogen atoms include polysiloxanes having siloxane units according to the general formula RmRlSio(3 m) in which each R represents a monovalent hydrocarbon group having up to 20 carbon atoms, for example a lower alkyl or phenyl group e.g. a methyl radical, _ is 1 or 2 and R' represents an aliphati-cally unsaturated group for example cyclohexenyl or a group CH=CHR" linked to the silicon atom for example via a divalent aliphatic chain wherein R" represents a hydrogen atom or an alkyl group for example vinyl, allyl or hexenyl.
These polysiloxanes also comprise units (i) in which R and n are as referred to above. These materials are reactive with the silicon-bonded hydrogen atoms in presence of a noble metal catalyst by a hydrosilylation reaction and thus contribute to the polysiloxane matrix. Preferably these polysiloxanes have from 0.0002% to 3% by weight of alipha-tically unsaturated groups and _ is such that they have aviscosity of the order of about lOmmZ/s to about 500,000 mm2/s. Preferred compositions employ a polysiloxane having siloxane units according to the general Eormula RmR'Sio(3 m) in which R' represents a group CH=CH2 linked to the silicon atom via a divalent aliphatic chain and having a viscosity in the range lO0 mm2/s to 2000 mm2/s.
Suitable organosilicon polymers including siloxane units providing a silicon-bonded hydroxyl group include 0 polydiorganosiloxanes having at least two siloxane units of a RaQbSi(4-(a+b)) in which a has a value of 0 or 2, _ has a value of 1 or 2 and the sum of a + b is not greater than 3, Q represents a hydroxyl group for example silanol terminated polydioganosiloxanes according to the general formula Ho((R2)Sio)SH in which each R represents a methyl group and s has a value from about lO to about 1200.
Suitable materials have viscosities of the order of about 10 mm2/s to about 500,000 mm2/s. Preferred compositions which provide the more elastomeric foams employ polydi-organosiloxanes according to the general formula Ho((R2)Sio)sH as aforesaid which have viscosities of the ordar of about 2,500 mm2/s to about 20,500 mm2/s. The density of the silicone foam can be significantly reduced without degrading its structural strength by including a short-chain silanol terminated polydiorganosiloxane in the formulation. Preferred compositions employ polydiorgano-siloxanes according to the general formula HotR2sio)sH asaforesaid in which s has a value from about 2 to about 10.
Preferred materials have viscosities of the order of about 5 mm2/s to about 100 mm2/s. Polydiorganosiloxanes having at least two siloxane units of the formula RaQbSiO(4 (a~b~) in which Q is a hydroxyl bearing alkylene or oxyalkylene chain may also be used. The chain may be attached to the silicon atom in any convenient way but is preferably linked to the silicon atom by a carbon atom. Suitable hydroxyl bearing chains include those containing up to 50 chain atoms. Suitable alkylene chains are those having 1 to 15, more preferably ~ to 10 chain carbon atoms. Suitable oxyalkylene chains include those of the formula (CdH2dO)eH
in which d has the value 2, 3 or ~ and e has a value in the range 1 to 15 more preferably 1 to 10, i.e. having from 1 to 15, more preferably 1 to 10 oxyalkylene groups. The oxyalkylene groups may be for example oxyethylene, oxypro-pylene or oxybutylene or mixtures thereof, the most pref erred being the oxyethylene group. This polydiorgano-siloxane also comprises siloxane units (i) as aforesaid.
Other materials which may be included as crosslinking agents include materials having three or more functional e.g. hydroxy groups per molecule.
Compositions for use in the invention preferably include one or more alcohols. These materials influence the structure of foams formed by use of the composition and yield cured foams of low density. The alcohol is selected with a view to contributing not only generation of hydrogen gas but also with a view to achieving desired resilience of .
the foam. Suitable alcohols include the primary aliphatic and araliphatic alcohols for example the lower aliphatic mono functional alcohols having up to 8 carbon atoms, e.g.
ethanol, propanol, butanol and benzyl alcohol~ Foams of lowest density are formed by use of the aliphatic alcohols having from 2 to 12 chain carbon atoms. Preferred compo-sitions employ n-propanol.
Compositions suitable for use in the invention pr~fe-rably employ a foam stabiliser or surfactant. Suitable foam stabilising materials include fluorinated silicones, for example a polyorganosiloxane comprising (CF2)m(CH2)nOpSiO(4_p), R3Sio~, SiO4/2 units and silicon-bonded hydroxyl groups wherein each R represents a mono-valent hydrocarbon group containing from l to 20 ~arbon atoms, m is an integer having an averaye value of from 1 to 20, n has the value 1 or 2, ~ has the value 1, 2 or 3. The polysiloxane may also include from 0 to 10 percent, based on the weight of said polyorganosiloxane, of GSio3/2 units wherein G represents the residue obtained by removing the hydrogen atom from a hydroxyl group of a linear organic polymer selected from the group consisting of homopolymers of ethylenically unsaturated alcohols, copolymers of these alcohols with ethylenically unsaturated hydrocarbons, poly-ethers and polyoxyalkylene glycols, wherein said organic polymer contains an average of at least one terminal hydroxyl group per molecule. These materials may be prepared by treatment of hexamethyldisiloxane coated poly-silicates with the alcohol F(CF2)8CH2CH2OH, and are morefully described and claimed in European Patent Specification 179 598. They serve to stabilise the structure of the foam during its curing.
Suitable noble metal catalysts include rhodium and platinum containing materials. Platinum catalysts may take any of the known forms, ranging from platinum as deposited on carriers such as silica gel or powdered charcoal to platinic chloride, salts of platinum and chloroplatinic acids. A preferred form of platinum is chloroplatinic acid either as the commonly obtainable hexahydratQ or the anhydrous form, on account of its easy dispersibility in organosilicon systems and its non-effect on colour of the mixture. Platinum complexes may also be used e.g. those prepared from chloroplatinic acid hexahydrate and divinyl tetramethyldisiloxane. Compositions according to the invention foam and cure very rapidly when the component parts have been mixe~ together. If it is desired to prolong the cure time, for example if it is desir~d to mix the composition and then transfer it to the site where it is intended to foam and cure, one may include in the compo-sition one of the known platinum catalyst inhibitors such as a polymethylvinylsiloxane cyclic compound or an acety-lenic alcohol e.g. methyl butynol. Larger proportions of catalyst may be used when a faster cure is desired.
If desired other adjuvants may be included in a composition for use in the invention, for example fillers, colorants, coloured indicators and extenders. Fillers which may be used include, for example silica, glass beads or glass microspheres all of which may be treated to render them hydrophobic, calcium carbonates and carbon black.
Compositions for use in the invention may be formu-lated to cure within a short period of time. In order toachieve this it is important that the ratio of silicon-bonded hydrogen atoms to all carbon-bonded or silicon-bonded hydroxyl groups, together with other reactive hydroxyl, unsaturated and other groups present in the . .
composition is appropriate. This ratio may be in the range 2.0:1 to 35:1 and is preferably in the range 2.5:1 to 10:1.
The ratio of silicon-bonded hydrogen atoms to carbon-bonded hydroxyl groups and silicon-bonded hydroxyl groups is suit-ably in the range 2.0:1 to 40:1 more preferably 2.5:1 to 10:1. The ratio of aliphatically unsaturated groups to silicon-bonded hydroyen atoms is preferably in the range 1:20 to 1:150 more pre~erably in the range 1:20 to 1:90.
The ratio of aliphatically unsaturated groups to carbon-bonded hydroxyl groups and silicon-bonded hydroxyl groups may be in the range 1:2 to 1:60, more preferably 1:5 to 1:18. We have found that compositions in which the ingredients are present in the preferred ratios can be formulated to cure within 20 to 40 seconds of mixing of the composition at room temperature (i.e. of the order of 18C
to 20C) and humidity (i.e. about 30~ to 90% relative humidity) to provide cured foams of a density between about 40kg/m3 and 600kg/m3 or less when foamed freely or cured foams of a density between about 50 and 700kg/m3 when foamed by a method according to the invention. The foams formed according to the invention are fine pored foams of uniform cell size. They are hydrophobic and generally comprise from about 20% to about 80% closed cells and correspondingly about 80% to about 20% open cells, the more closed cell foams being produced when increased proportions of the foam stabiliser are present.
Compositions suitable for use in the invention foam and cure when mixed at room temperature and humidity.
Accordingly the reactive components are stored separated until required for use. In order to enable simplicity and ease of mixing the components at the application site, it is preferred to store the compositions in two-part form in which each of the parts is of substantially the same viscosity so that the first and second parts may be mixed together in a ratio of 1:1 by volume or 1:1 by weight as desired.
A method according to the present invention may be used to produce foams of various densities and combinations of properties by adjustment of the foam formulation. For any given foam density, the fire resistance of foams produced according to the invention is greater than the fire resistance of foams formed by permitting the foam to expand and cure freely without constraint on its foamed volume. The evaluation of fire resistance as meant in this specification involves exposing the foam to a flame; prior art foams tend to exhibit large cracks in the exposed foam surface very quickly upon exposure to the flame and these permit heat to penetrate quickly through the mass of the foam, whereas foams made according to the invention are more resistant to penetration of heat. We believe this is due to a more homogenous foam structure of foams made 2Q according to the invention coupled with a small average cell size.
In order that the invention may become more clear there now follows a description of example compositions according to the invention. All parts are by weight unless otherwise specified.
In the Examples the following materials were used:
The polysiloxane I having silicon-bonded hydrogen atoms was a trimethylsilyl end-blocked polymethylhydrogen-siloxane having a viscosity of about 30 mm2~s and 1.5 mole % hydrogen.
The polysi~oxane II having silicon-bonded hydrogen atoms was a trimethylsilyl end-blocked polysiloxane having methylhydrogensiloxane and dimethylsiloxane units having a viscosity of about 5 mm2/s and 0.76 mole % hydrogen.
The polysiloxane III having silicon-bonded hydroxyl groups was a dimethylhydroxysilyl endblocked polydimethyl-siloxane having a viscosity of about 13,500 mm2/s and a hydroxyl content of about 0.066 mole %.
The polysiloxane IV having silicon-bonded hydroxyl groups was a dimethylhydroxylsilyl endblocked polydimethyl~
siloxane having a viscosity of about 42 mm2/s and a hydroxyl content of 4 mole ~.
The polydiorganosiloxane V having silicon-bonded unsaturated groups was a dimethylvinylsilyl endblocked polydimethylsiloxane having a viscosity of about 450 mm2/s and 0.45 mole ~O vinyl groups.
The foam stabiliser was prepared by treatment of hexamethyldisiloxane coated polysilicates with the alcohol F(CF2)8CH2CH20H, as more fully described in European Patent Specification 179 598.
Cyclic polymethylvinylsiloxane compounds were used to adjust the speed of cure. N-propanol was used as a blowing agent for the low density foams. Chloroplatinic acid, complexed with vinyldisiloxane, was used as the catalyst.
Ground quartz of 5 micron particle size was used as filler 1. For the purpose of better microwave (RF) radiation absorbance ultra-fine carbon black with high dielectric loss was added as Filler 2.
Fire resistance of sample foam plates was evaluated by positioning the plate at an angle of 45 over a blue flame of a blow torch and spaced lOcm from the orifice of the torch with the tip of the blue flame just touching the plate. The time required for the flame to penetrate through the plate was measured. The values in seconds are recorded in the Tables as "fire resistance". As can be seen from the results, for any given foam density, the fire resistance of foams produced according to the invention is , greater than the fire resistance of foams formed by permitting the foam to expand and cure freely without constraint on its foamed volume.
ExamPle 1 Example compositions were prepared which comprised two parts A and B and contained ingredients in the amounts shown in Tables I(a) and I(b).
The value given in Table II for Molar Ratio 1 is the ratio of silicon-bonded hydrogen atoms of the polysiloxane to all carbon bonded hydroxyl groups together with other reactive hydroxyl, unsaturated and other groups present in the composition. Th~ value given for ~atio 2 is the ratio of silicon-bonded hydrogen atoms to silicon-bonded and carbon-bonded hydroxyl groups. The value given ~or ~atio 3 is the ratio of aliphatically unsaturated groups ~o silicon-bonded hydrogen atoms and the value given for Ratio 4 is the ratio of aliphatically unsaturated groups to carbon-bonded hydroxyl groups and silicon-bonded hydroxyl groups.
A mould was prepared comprising a base, four side walls normal to the base and a lid to close the mould and so define a closed moulding cavity capable of producing foam plates 270mm thick. The inner dimensions of the closed moulding cavity were 20 x 20 x 2.7cm corresponding to a volume of the closed moulding cavity 1080 cm3. Compo-sitions were prepared by mixing equal volumes of the Parts A1, A2, A3 and B1 or A4 and B2. Each of these example compositions was mixed to form a homogenous fluid and poured into the moulding cavity within 30 seconds of mixing. In a first group of experiments the composition was poured into the mould but the moulding cavity was not closed by the lid. It was found that the compositions each cured in 120 to 600 seconds or less to provide a fine pored foam of density as shown in Table II. The quantities of the compositions formed by mixing equal volumes ~f the Parts A and B required to produce a cured foam which just filled the mould are shown in Table II as l'Quan~ity Free Foam". In a second group of experiments, quantities as shown in Table II as "Quantity Constrained Foam " obtained by mixing equal volumes of the Parts A and B (principally approximately 10% more than the quantities required to produce a cured foam which just filled the mould) were mixed in the same way and introduced to the mould and the mould closed by the lid and clamped closed. Each compo-sition was allowed to foam and cure in the mould cavity at room temperature. The density of the foams was found to be as shown in Table II. These foam samples were removed from the moulding cavity and aged at room temperature for 24 hours. The foams formed in both groups of experiments were demoulded and post cured by heating in an oven maintained at 100C for a further 24 hours. The samples from the second group of experiments were found to have a much more regular and homogenous cell structure than those formed in the first group of experiments.
Example 2 Compositions were processed in a similar manner to that employed in Example 1 but the sample mouldings produc~d measured 10 x 10 x 2cm. The post cure was carried out during microwave radiation. The samples were placed between two plates of a capacitor in such a way that a distance of 3mm betwean the plates and the foam sample was maintained. The samples were then post cured with a radio wave signal of 35 MHz at 3 - 4 kV potential for 10 seconds.
The formulations employed are shown in Table III and the resultant properties are recorded in Table IV.
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TABLE I ( a) Formulations Al Bl A2 Polysiloxane I or II
having silicon-bonded hydrogen I - 23.8 II - 1.7 Polysiloxane III
or IV having silicon-bonded hydroxyl groups carbon-bonded hydroxyl groups III 39.9 49.3 40.2 IV - 9.4 N-propanol 2.0 ~ 1.7 Polysiloxane V having unsaturated groups V 30.6 1.7 30.8 Methylvinyl cyclics - 0.1 20 Foam stabiliser 6.5 - 6.0 Catalyst 0.5 - 0.5 Filler 1 15.3 13.6 15.5 Pigment (a) 5.2 5.3 (b) 0.4 TABLE I(b) Formulations A3 A4 B2 Polysiloxane I or II
having silicon-bonded hydrogen I - - 8.6 II - - 2.1 Polysiloxane III
or IV having silicon-bonded hydroxyl groups carbon-bonded hydroxyl groups III 41.4 43.6 59.5 IV - - 11.3 N-propanol 1.0 Polysiloxane V having unsaturated groups V 31.7 33.4 2.0 Methylvinyl cyclics - - 0.1 20 Foam stabiliser 4.0 Catalyst 0.5 0.5 Filler 1 16.0 16.8 16.4 Pigment (a) 5.4 5.7 (b) ' - , , ~ :.
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TABLE II
Property Composition formed by mixing Parts Al~B1 A2+B1 A3~B1 A4+B2 (D) (C) (B) (A) Molar Ratio 1 2.9:1 7.1:1 6.3:1 6.0:1 2 3.5:1 8.4:1 7.3:1 6.9:1 3 1:24.6 1:66.3 1:68.1 1:68.7 4 1:7.1 1:7.9 1:9.4 1:10.1 Curing time (sec) 420 175 150 140 Quantity (ml) Free Foam 150 210 260 310 Constrained Foam 165 230 290 345 Density (Kg/m~) Free Foam 150 210 260 31Q
Constrained Foam 16S 230 290 345 Elastomer properties tYoung's modulus of Compression) Free Foam Before post cure 0.013 0.040 0.066 0.128 After post cure 0.062 0.080 G.155 0.178 Constrained Foam Before Post-Cure 0.043 0.051 0.190 0.290 After Post-Cure 0.057 0.105 0.390 0.315 Fire R~sistance Free Foam Before Post-Cure 300 420 540 1300 After Post-Cure 450 500 550 1800 Constrained Foam Before Post-Cure 420 540 720 3600 After Post-Cure 800 800 1200 3550 FormulationsA5 B3 A6 Polysiloxane I or II
having silicon-bonded hydrogen I - 26.7 II - 1.4 Polysiloxane III or IV having silicon-bonded hydroxyl groups III 41.4 39.9 40.1 IV - 19.6 N-propanol - - 1.0 Polysiloxane V having unsaturated groups V 31.7 1.3 30.7 Methylvinyl cyclics - 0.1 Foam stabiliser - - 2.0 Catalyst 0.5 - 0.5 Filler 1 16.0 11.0 15.2 Pigment (a~ 5.4 5.2 Filler 2 5.0 5.0 TABLE IV
Property Composition formed by mixing Parts A5+B3 A6+B3 (E) (F) Molar Ratio 1 5.5:1 4.g:1 2 6.1:1 5.3:1 3 1:74.5 1:76.8 4 1:12.3 1:14.5 Curing time (seconds) 350 290 Quantity ~ml) Free Foam 195 240 Density (Kg/m3) Free Foam 150 240 Elastomer properties (Young's modulus of Compression) Free Foam Before post cure 0.084 0.078 After post cure 0.342 0.355 Fire Resistance Free Foam Before Post-Cure 830 720 After Post Cure 720 670 The formulation E (A5+B3) results in a more friable foam upon post-cure whilst the higher density foam F (A6+B3) containing the profoamer shows better flexibility due to its more regular cell structure.
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Claims (16)
1. A method of making a cured silicone foam the steps of introducing to a moulding cavity a quantity of a silicone composition which is curable at room or slightly elevated temperature to provide a foam and bringing about curing of the composition in the moulding cavity to form the cured silicone foam in which the moulding cavity is closed during foaming of the composition whereby to restrict expansion of the foam and wherein the volume of the closed moulding cavity is at least 10%
less than the volume which would be occupied by the foam produced by permitting that quantity of the composition to foam and cure at room temperature without restriction.
less than the volume which would be occupied by the foam produced by permitting that quantity of the composition to foam and cure at room temperature without restriction.
2. A method according to Claim 1 wherein the moulding cavity is provided by a mould comprising a base and side walls and a moveable top which provides closure means for closing the cavity.
3. A method according to Claim 1 wherein the moulding cavity is defined by two preformed elements spaced apart to provide the moulding cavity which is closed at its periphery by spacer elements.
4. A method according to Claim 1 wherein at least one surface of the moulding cavity is provided by a surface of an element of building board, stone, metal or glass, to which the cured foam is intended to adhere with or without the use of a surface primer.
5. A method according to Claim 4 wherein the moulding cavity is designed for the production of building components, for example separation wall panels, exterior cladding elements, ceiling panels, silicone foam blocks or automotive body panels.
6. A method according to Claim 1 wherein the composition is foamed and cured in the moulding cavity at a temperature of the order of 18 to 35°C.
7. A method according to Claim 6 wherein after completion of the foaming process the moulding is heated to effect a post cure.
8. A method according to Claim 7 wherein the post cure is effected by microwave heating.
9. A method according to Claim 1 wherein the silicone compo-sition comprises a polysiloxane having alkylhydrogensiloxane units according to the general formula RpHSio(3-p) with or without the presence of R2 SiO units in which each R represents a methyl group, and p is 1 or 2, and having a viscosity of about 5 to about 50 mm2/s, an organosilicon polymer including silicon-bonded hydroxyl groups and one or more polysiloxanes having not less than two silicon-bonded aliphatically unsaturated groups per molecule and having a viscosity in the range 10 to 25000 mm2/s.
10. A method according to Claim 9 wherein the silicone compo-sition also comprises an alcohol.
11. A method according to Claim 10 wherein the alcohol is n-propanol.
12. A method according to Claim 9 wherein the composition also comprises a fluorosilicon surfactant.
13. A method according to Claim 9 wherein the proportions of the ingredients of the silicone composition is such that the ratio of silicon-bonded hydrogen atoms of the polysiloxane (A) to all silicon-bonded hydroxyl groups and carbon-bonded hydroxyl groups together with other reactive hydroxyl, unsaturated and other groups present in the composition is in the range 2.0:1 to 35.0:1, preferably 2.5:1 to 10.0:1.
14. A method according to Claim 9 wherein the proportions of the ingredients of the silicon composition is such that the ratio of silicon-bonded hydrogen atoms to carbon-bonded hydroxyl groups and silicon-bonded hydroxyl groups is in the range 2.1:1 to 40.0:1, preferably 2.5:1 to 10.0:1.
15. A method according to Claim 9 wherein the proportions of the ingredients of the silicone composition is such that the ratio of aliphatically unsaturated groups to silicon-bonded hydrogen atoms is in the range 1:6.9 to 1:800, preferably 1:20 to 1:150.
16. A composition according to Claim 9 wherein the proportions of the ingredients of the silicone composition is such that the ratio of aliphatically unsaturated groups to carbon-bonded hydroxyl groups and silicon bonded hydroxyl groups is in the range 1:30 to 1:350, preferably 1:2 to 1:60.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| BE9100707.0 | 1991-01-12 | ||
| GB919100707A GB9100707D0 (en) | 1991-01-12 | 1991-01-12 | Silicone foams of improved fire resistance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2059162A1 true CA2059162A1 (en) | 1992-07-13 |
Family
ID=10688368
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002059162A Abandoned CA2059162A1 (en) | 1991-01-12 | 1992-01-10 | Silicone foams of improved fire resistance |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5126083A (en) |
| EP (1) | EP0495566B1 (en) |
| CA (1) | CA2059162A1 (en) |
| DE (1) | DE69203733T2 (en) |
| GB (1) | GB9100707D0 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4235639A1 (en) * | 1992-10-22 | 1994-04-28 | Sonderhoff Ernst Fa | Process for the production of silicone foam molded parts by injection molding |
| USRE35771E (en) * | 1992-10-22 | 1998-04-14 | H. B. Fuller Licensing & Financing, Inc. | Process for producing a fine pored silicone foam |
| JP3501487B2 (en) * | 1993-12-28 | 2004-03-02 | ジーイー東芝シリコーン株式会社 | Foamable polyorganosiloxane composition |
| WO2023111405A1 (en) | 2021-12-17 | 2023-06-22 | Elkem Silicones France Sas | Method for preparing silicone foam |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1000566A (en) * | 1963-04-16 | 1965-08-04 | Ici Ltd | Improvements in or relating to the manufacture of polyurethane foams |
| US4550125A (en) * | 1985-03-25 | 1985-10-29 | Dow Corning Corporation | Foamable polyorganosiloxane compositions |
| US4760098A (en) * | 1985-07-12 | 1988-07-26 | Alexander Miutel | Low density foams |
| CA1267750A (en) * | 1985-07-12 | 1990-04-10 | Alexander Miutel | Low density foams |
| US4599367A (en) * | 1985-10-16 | 1986-07-08 | Dow Corning Corporation | Water-blown silicone foam |
| US4686244A (en) * | 1986-12-17 | 1987-08-11 | Dow Corning Corporation | Intumescent foamable compositions |
| GB8809293D0 (en) * | 1988-04-20 | 1988-05-25 | Dow Corning Ltd | Silicone foams |
-
1991
- 1991-01-12 GB GB919100707A patent/GB9100707D0/en active Pending
-
1992
- 1992-01-03 DE DE69203733T patent/DE69203733T2/en not_active Expired - Fee Related
- 1992-01-03 EP EP92300051A patent/EP0495566B1/en not_active Expired - Lifetime
- 1992-01-09 US US07/819,155 patent/US5126083A/en not_active Expired - Fee Related
- 1992-01-10 CA CA002059162A patent/CA2059162A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| DE69203733T2 (en) | 1996-01-18 |
| GB9100707D0 (en) | 1991-02-27 |
| DE69203733D1 (en) | 1995-09-07 |
| US5126083A (en) | 1992-06-30 |
| EP0495566A3 (en) | 1992-08-19 |
| EP0495566B1 (en) | 1995-08-02 |
| EP0495566A2 (en) | 1992-07-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |