Fire-retardant additives and their uses

Abstract: A composition is provided comprising two or more frits capable of melting progressively as the temperature rises in a fire situation, one of the said frits being a relatively high- melting frit which is a defitrifying frit. The composition may be added to a variety of materials to provide or enhance fire resistance; such materials include phenolic and polyester resins and sodium silicate.

Description: This invention concerns additive compositions for use in providing or enhancing fire resistance of materials and compositions and a method of providing or enhancing fire resistance properties for materials and compositions. If alumina trihydrate is used as an additive to plastics materials, as a fire retardant, several difficulties emerge. Alumina trihydrate produces water, up to 30% of its weight, at temperatures of 200 degrees C. This water turns to steam and blankets burning action. It follows therefore, that alumina trihydrate cannot be used in plastics materials which are processed at temperatures above 185 degrees C (to leave a safety margin). Such plastics materials include polypropylene and polyethylene. Secondly, to be effective, levels of 60% by weight and even 64% by weight of alumina trihydrate have been used in urethane methacrylate and polyesters. Such high amounts of a filling make the resin very difficult to work. Thirdly, alumina trihydrate is supplied in various grades priced according to their micron size. The cheapest is at 25 micron particle size, the dearest at about 10 micron. The larger particles are in plate form which makes them difficult to disperse in high concentrations, and that can also have an adverse effect on surface finish. The smaller particles are rounded during processing and disperse more easily but are more expensive by a factor of three compared to the larger particles. Another popular fire retardant additive is antimony oxide. This material contains 3% arsenic and consequently renders any product containing it toxic. Antimony oxide works by combining with free halogen but is only partially effective, in that it improves existing fire retardant properties rather than making materials conform to rigorous tests. Antimony oxide is usally used in amounts of 3% by weight, although higher amounts may be used in some materials. In European Patent Application No. 88303176.7 (EP-A-0 287 293) the parent of the present application, there are described fire retardant compositions comprising two or more frits melting progressively as the temperature rises under fire conditions. According to one aspect of this invention there is provided a fire-retardant composition comprising a polymer or sodium silicate and further comprising two or more frits capable of melting progressively as the temperature rises under fire conditions, whereby one of said frits melts at a lower temperature than another of said frits, the higher melting frit being a devitrifying frit, subject to the provisos that (a) the composition does not include a foamed filler, and that (b) if the composition contains ceramic fibres or powder then the lower melting frit melts at a temperature of at least 450°C. According to another aspect of this invention there is provided a method of providing or enhancing fire-retardant properties of a material or composition characterised by incorporation therein of two or more frits capable of melting progressively as the temperature rises under fire conditions, whereby one of said frits melts at a lower temperature than another of said frits, the higher melting frit being a devitrifying frit, subject to the provisos that (a) the composition or material does not include a foamed filler, and that (b) if the composition or material contains ceramic fibres or powder then the lower melting frit melts at a temperature of at least 450°C. The devitrifying frit tends to solidify after melting to provide strength. The frits under fire conditions will melt progressively to provide a fused protective layer. A preferred frit combination comprises a low melting frit e.g. that starts to melt at about 450 degrees C and a devitrifying frit that starts to melt at about 700 degrees C. The preferred weight ratio of low melt frit to high melt frit is in the range 1:9 to 1:1, especially 3:7. A typical selection of frits may be from those that melt at or about the following temperatures: 450 degrees C, 650 degrees C, 850 degrees C and 1000 degrees 6. The frits used are preferably oven dried, water washed and ground prior to inclusion in the compositions of the invention. The inclusion of ceramic in fibre or powder form can be used to bind the melting frits and also to remain unchanged at temperatures above 1000 degrees 6. Basalt fibre or chopped fibre or powder can also be used in place of or in addition to the ceramic material. The compositions of the invention may also comprise one or more other fire retardant additives. For example an intumescent substance or substances may be included in the compositions of the invention, such as alumina trihydrate which releases most of its chemically combined water between 200 and 330 degrees C to dampen burning and reduce smoke emission or hydrated magnesium calcium carbonate which releases its chemically combined water and carbon dioxide from 230 degrees C upwards. For some purposes hydrated magnesium calcium carbonate may be preferable to alumina trihydrate because it is less expensive to obtain in very finely divided form say of the order to 2 to 3 µ particle size. A preferred composition of frits and intumescent substance or substances comprises from 15-50, especially 20-30, % by weight of frits and 85 to 50, especially 80-70, % by weight of intumescent substance(s). Another example of fire retardant additives may be antimony oxide usually used in combination with halogenated hydrocarbon, whereby halogen free radicals are produced that suppress burning. The proportion of frits to ceramic or basalt in a preferred embodiment of the invention is about 7:3. Suitable polymers for incorporation in compositions in accordance with the invention include polyesters, phenolic resins, polyurethanes and other thermosetting resins and thermoplastics. If, however, alumina trihydrate is to be included, the composition cannot be used on materials processed at 200 degrees C or more preferably at 185 dgrees C or more. In a phenolic resin, for example, the proportion of an additive composition comprising the frits and ceramic or basalt to resin may be from 3:7 to 1:4. The frits additive with intumescent substance, such as hydrated magnesium calcium carbonate or alumina trihydrate or a mixture thereof, may be added to dough moulding compounds, such as of the phenolic or polyester type to be used with glass reinforcement. Preferably the ratio of frits to intumescent is about 1:4. For addition to phenolic resin frit/intumescent substance mix ratio in the range of from 7:3 to5:5 may be used, the preferred ratio of that mix to phenolic resin being in the range of 3:7 to 4:6. The action of heat on a resin which contains the frits has the following effect. The resin or plastic materials burns and the frit in the first temperature band melts and combines with the char. The second frits then melts and so on. The substrate and burning material are encapsulated by the molten frits thus starving the fire of oxygen. The ceramic or basalt or both, if present, insulate and stiffen the molten mass to prevent excessive running. They also contribute greatly to stability at high temperatures. Since the particle size of the frits and ceramic can be controlled they are suitable for use with alumina trihydrate in its coarse form. The particles fill the gaps between the alumina trihydrate plates to give a better finish. The plates of alumina trihydrate act as a suspension agent for the frits/ceramic mix. The water produced in the form of steam has a beneficial effect on the frits, which are water soluble, aiding in the coating action. The addition of mixes to sodium silicate has a beneficial effect, in that the frits tend to plasticise the sodium silicate under increasing temperature conditions, this counteracts the embrittlement and powdering of the sodium silicate normally encountered in these conditions. The inclusion of frits in an intumescent seal or paint formula would constitute an improvement. It is preferred to use a mix of frits and intumescent substance, such as hydrated magnesium calcium carbonate or alumina trihydrate or a mixture thereof, say in the ratio of 3:7 to 1:1, preferably 4:6, with sodium silicate and by varying the ratio of the frit mix to sodium silicate materials suitable for different uses may be obtained. At a ratio about 1:1 the resultant mixture has a paint consistency at a ratio of aboiut 7:13 the mixture has adhesive properties and at a ratio of about 1:4 the mixture is in a gel form. Compositions of the invention may be used as a sealant say for around fire doors or windows. The preferred sealant will swell when heated and stop any gaps around say doors or windows. For a sealant paste a frit combination containing intumescent with sodium silicate say in the ratio of 3:7 to 4:6, preferably 7:13 by weight may be used as a base to which is added a char agent, such as mica, ammonium polyphosphate and an inorganic gelling agent. The resultant paste is one which will harden in situ. By using polyvinylacetate in place of the sodium silicate, a resilient sealant may be produced that will swell and harden when heated. The composition of the invention may be a sheet or board made by compression of chips of wood with a binder. Thus, the binder may be a composition comprising phenolic resin or sodium silicate solution containing ceramics such as carborundum, and frits, preferably three frits having different melt temperatures. Alternatively the composition of the invention may be an adhesive. The preferred adhesive will be based on sodium silicate solution containing a catalyst of phenolic resin and the composition of the invention. Such an adhesive may be used in circumstances where fire resistance is important. For example, the adhesive may be used for bonding facing sheets, such as of melamine, to a base material, such as chipboard. Then under fire conditions, the adhesive can provide a protective shield for the base material even when the facing sheet has been burnt off. Another particular use is as an adhesive for attaching a brake lining to its carrier. Indeed brake linings may be made from the same composition, the ceramic material preferably being slag fibre and shot, such as produced as waste from power stations. The brake linings material may comprise additional strengthening components, such as carbon fibre or thermoplastics material e.g. KEVLAR (trade name). Another example of using frits is in the construction of a laminate comprising an outer skin formed by heat and pressure where a glass cloth has been impregnated with a liquid settable resin, such as phenolic, containing frits of different melt temperatures together with a binding heat stable, fibre, such as ceramic mullite fibre, and optionally alumina trihydrate. The skins of impregnated cloth are place on either side of a ceramic paper, combination basalt, ceramic and glass fibre paper, glass cloth treated with vermiculite or indeed any heat resistance barrier material. When this laminate is pressed under heat and with any number of interleaved sheets the settable resin migrates into the barrier material to produce a solid sheet. When flame is applied to the laminate the settable resin burns to protect the substrate, the barrier material providing stability. The surface of the laminate may be covered with melamine sheet either plain or patterned or real wood veneer when flamne is applied, the frits/ceramic help to form a char and prevent spread of flame. This moulded laminate, flat or three dimensional, can then be adhered to a substrate, such as a door, using sodium silicate containing the same frits, ceramic fibre and optionally alumina trihydrate previously mentioned to make a high heat performance adhesive. The substrate can be a rigidized sheet of ceramic fibre which is in turn adhered with the adhesive described, to a heat resistance sound deadening core made from say basalt fibre or rockwool rigidized or non-rigidized. The construction may be repeated about the centre line. For thirty minute rating the pressed laminates adhered and/or mechanically fixed to a basalt or rockwool core is sufficient. For sixty minute rating the rigidized ceramic board may be introduced, and for extended times the ceramic board can be increased in thickness and a ceramic non-rigid blanket can be used instead of the rockwool/basalt core. For light weight constructions a phenolic foam core or a foam made from the adhesive mentioned can be used. A foamed vermiculite clay can be included in the adhesive to produce a lightweight, highly insulating core. Alternatively a core can be made by using woodchip as a filler to the adhesive to make a high heat resistance chipboard core to a door, building panel or partition. This invention will now be further described by means of the following examples. Example 1 A basic powder mix was produced from 40% by weight of a combination of a low melting frit (450 degrees C) and a high melting (devitrifying) frit (700 degrees C) in the weight ratio of 3:7 and 60% of hydrated magnesiums calcium carbonate. An adhesive composition was produced by adding 35% by weight of the powder mix to 65% by weight of sodium silicate. Example 2 A paint-like composition was produced by adding 50% by weight of the powder mix of Example 1 to 50% by weight of sodium silicate. Example 3 A gel-like composition was produced by adding 20% by weight of the basic powder mix of Example 1 to 80% by weight of sodium silicate. Example 4 A powder mix of 70% by weight of low melting frit (450 degrees C) and devitrifying frit (700 degrees C) in the ratio of 3:7 and 30% by weight of hydrated magnesium calcium carbonate was prepared and then added to phenolic resin in the weight ratio of 3:7 to produce a mouldable material. Example 5 A sealant paste was produced from the following ingredients in the amounts stated: Mica powder (char agent) 10% by weight Ammonium polyphosphate 10% by weight Composition of Example 1 70% by weight Inorganic gelling agent 10% by weight Example 6 A resilient sealant was produced in the same way as in Example 5 except that polyvinyl acetate was used instead of sodium silicate.

Claims: A fire-retardant composition comprising a polymer or sodium silicate and further comprising two or more frits capable of melting progressively as the temperature rises under fire conditions, whereby one of said frits melts at a lower temperature than another of said frits, the higher melting frit being a devitrifying frit, subject to the provisos that (a) the composition does not include a foamed filler, and that (b) if the composition contains ceramic fibres or powder then the lower melting frit melts at a temperature of at least 450°C. A composition according to Claim 1 wherein the frits melt within the range from about 450 degrees C to about 1000 degrees C. A composition according to Claim 2 comprising (i) a frit that starts to melt at about 450 degrees C and (ii) a devitrifying frit that starts to melt at about 700 degrees C. A composition according to any of the preceding claims wherein the weight ratio of lower melting frit to higher melting frit is in the range of from 1:9 to 1:1. A composition according to Claim 4 wherein the weight ratio of lower melting frit to higher melting frit is about 3:7. A composition according to any of the preceding claims further comprising an intumescent substance. A composition according to Claim 6 wherein the intumescent substance is alumina trihydrate or hydrated magnesium calcium carbonate. A composition according to Claim 6 or 7 wherein the proportion of frits is from 15% to 50% by weight of the total of frits and intumescent substance. A composition according to any of the preceding claims further comprising ceramic fibre or powder. A composition according to any of the preceding claims further comprising basalt fibre or powder. A composition according to any of Claims 1 to 10 containing a phenolic or polyester resin as a said polymer. A composition according to any of Claims 1 to 10 containing polyvinyl acetate as a said polymer. A method of providing or enhancing fire-retardant properties of a material or composition characterised by incorporation therein of two or more frits capable of melting progressively as the temperature rises under fire conditions, whereby one of said frits melts at a lower temperature than another of said frits, the higher melting frit being a devitrifying frit, subject to the provisos that (a) the composition or material does not include a foamed filler, and that (b) if the composition or material contains ceramic fibres or powder then the lower melting frit melts at a temperature of at least 450°C.

Inventors: CROMPTON GEOFFREY, CROMPTON, GEOFFREY
Applicants: BRUNNER MOND & CO LTD, BRUNNER MOND & COMPANY LIMITED
Application year: 1988
Main classification: C09K21
IPC codes: C08K3, C09K21