INTUMESCENT FIRE PROTECTION COMPOSITIONS

Abstract: The combination of comparatively small amounts (e.g. 3-20 wt %) of exfoliable laminar minerals such as expandable graphite with one or more binders and one or more of a range of intumescent char-forming materials such as carbonifics, acids and acid-yielding catalysts, blowing agents, char-formers and stabilisers gives novel fireproofing materials having beneficial properties such as ease of application and enhanced weathering properties of coatings formed therefrom, together with improved expansive pressure, degree of expansion and char strength under fire conditions.

Description: Intumescent fire protection compositions This invention is concerned with compositions of use in fire protection, more especially with fireproofing compositions which expand under fire conditions to form a substantially stable and protective carbonaceous char. A range of methods of treating inflammable or heat sensitive substrates, for example building materials such as structural timbers or steelwork, interior- decorative materials such as plywood or fibrous panels, or insulated electrical wiring, are known. One such method comprises the application of intumescent coatings or paints to the materials in question. Generally such coatings comprise materials selected from a number of the following categories of ingredients:- i) inorganic acids and/or acid-yielding catalysts, ii) polyhydric carbonific materials and/or other char sources, iii) spumific or blowing agents, and iv) binders. Various such coatings are described in, for example, GB-A-0862569, GB-A-2151237, US-A-3102821, US-A-3663464, US-A-3702841, US-A-3969291, US-A-3983082, US-A-4035315 and US-A-4061579. A typical mechanism of operation for such a coating is essentially that, in the event of a fire, acid from the catalyst reacts with and dehydrates the carbonific to form a char which is expanded by the action of the spumific and stabilised by the binder, which melts to form a skin over the resulting carbonaceous foam. Char foams so produced protect an underlying substrate by virtue of their thermal insulating properties and by excluding oxygen (in cases where the substrate is inflammable) . Intumescent coatings are of considerable potential advantage compared to other forms of fire protection, having many of the desirable features of traditional decorative paints and in some instances being applicable to existing structures without loss of structural or architectural detail; moreover they occupy minimal floor space and have an insignificant effect on the overall weight of the structure. Disadvantages of such coatings, however, include their relatively poor stability on exposure to external conditions and._ weathering, in particular the tendency of water soluble components to be leached out of the coatings. The use of a variety of water-insoluble ingredients and/or the use of water-proof resins to encapsulate the ingredients have been proposed, but none of these proposals have proved wholly satisfactory. Thus, for example, no thin film external grade intumescent paint is currently commercially available; such thick film grades as are available may be used only in limited external exposure situations and are expensive and require specialist application. A particular problem is that commercially available intumescent materials exert only a low expansive pressure under fire conditions so that the use of water- resistant encapsulating binders such as epoxy resins and silicones is limited by their constraining effect on char formation. Similarly it is not possible to paint over intumescent coatings with conventional paints or other polymeric coating materials since these will again inhibit expansion and char formation and thus the fire protective performance of the intumescent material. A further category of materials used in fire protection, particularly in lightweight protective materials of use in buildings and in marine structures such as oil or gas production platforms, comprises exfoliated (i.e. expanded) laminar minerals such as vermiculite. These exfoliated minerals may be used in plasters and renderings, e.g. applied wet with gypsum plaster or Portland cement, or may be combined with appropriate binders to form flat slabs for ceiling panels or for column or b_eam encasement. The use of materials such as vermiculite as fillers or pigments in the preparation of opaque or enamel-like intumescent compositions has been proposed in the above-mentioned reference GB-A-0862569; this disclosure does not specify that the materials are to-.be in exfoliated form but this would be understood from the reference to their_use as fillers and the generally known utility of, for example, expanded vermiculite as a "loose fill insulating, filler and packing material" (Merck Index, 1983) . Yet another category of fireproofing compositions comprises materials incorporating "expandable graphite" and a binder (e.g. as disclosed in GB-A-1497118, GB-A-2012296, WO 88/02019, WO 89/09808 and US-A- 4277532) , these relying on the expansive properties of the graphite under fire conditions to generate an expanded and insulating carbon matrix. The majority of such compositions are presented in solid form, e.g. as cured mouldings or as impregnated fibrous arrays; "paint"-type compositions are described in GB-A-1497118 and GB-A-2012296, but only as multilayer coatings in which the graphite-containing layer is trowelled or sprayed onto a primer layer and is thereafter covered with a further, protective coating layer. In view of the high graphite content of such compositions (typically of the order of 20-90% of the overall weight) it has not been proposed to formulate compositions capable of thin layer applications, for example by brushing. We have now found that by combining comparatively small quantities of expandable graphite and/or a number of other exfoliable laminar minerals with a wide range of intumescent char-forming materials it is possible to obtain novel fireproofing materials having unexpected and surprisingly beneficial properties, including ease of application and enhanced weathering properties of coatings formed from the materials, combined with substantially improved expansive pressure, degree of expansion and char strength under fire conditions. In particular, we have found that intumescent materials as previously used, which as indicated above exert relatively low expansive pressure (and are thus rendered comparatively ineffective when formulated with relatively tough binders such as thermosetting resins or when overpainted, e.g. with paints based on thermosetting resins) , can be made markedly more effective by incorporation of small quantities of such exfoliable laminar materials. It would appear that the expansion of the latter is capable of overcoming the constrictive forces of the binder or overpainted layers, thereby allowing the less powerfully expansive char- forming intumescents to expand and produce the required insulating carbonaceous layer. Thus according to one aspect of the present invention we provide a fireproofing composition comprising effective amounts of one or more exfoliable laminar minerals and one or more intumescent char- forming materials in combination with at least one binder. Exfoliable laminar minerals which may be used include natural phyllosilicates such as vermiculite, chlorite and kaolinite. These layer-structured hydrated polymeric silicates exfoliate when subjected to sufficient heat as a result of the generation of interlaminar steam; thus, for example, vermiculite may expand by 2 to 20 times the original layer thickness depending on the temperature and duration of exposure and the initial degree of hydration. The above-mentioned expandable graphite is a particularly useful exfoliable laminar mineral of use in the compositions of the invention. Natural graphite, which does not have any water between the structural layers t does not expand on heating. It may, however, be treated with, for example, mineral acids such as hydrochloric acid or oxidising agents such as nitric acid, potassium chlorate, chromic acid, potassium permanganate, potassium chromate, potassium dichromate, perchloric acid and mixtures thereof, e.g. as described in US-A-3404061, to effect chemical/structural modifications, possibly whereby water may be entrapped interlaminarly, so that the resulting intercalated and thereby expandable graphite is a water-resistant, self- contained exfoliant. Since the material is man-made it is possible to control the degree of expansion and the expansive force generated by selection of appropriate conditions during the intercalation stage. In general, intercalated, expandable graphite begins to expand at about 200°C and continues to expand over a relatively large temperature range; expansion to as much as 800 times the original volume may be attainable, generating a low density, fire resistant carbon matrix. Mica is a further example of a material which may be pretreated in a similar ^ manner to produce an exfoliable laminar mineral of use in compositions according to the invention. Intumescent char-forming materials of use in compositions according to the invention include, for example, acids such as phosphoric acid or sulphamic acid and acid-generating catalysts such as monoammonium phosphate, diammonium phosphate, ammonium phosphate, ammonium polyphosphate, melamine phosphate, potassium phosphate, ammonium sulphate, ammonium sulphamate, nitroaniline bisulphate, 4-nitroaniline-2-sulphonic acid, and 4,4•-dinitrosulphanilide; carbonifics, e.g. amylaceous materials such as starch or modified starch, and/or polyhydric alcohols such as saccharides and polysaccharides (for example hexitols, pentitols and tetritols such as erythritol, pentaerythritol and di- and tri-pentaerythritol) ; char-formers and stabilisers such as melamine phosphate and melamine borate; organic blowing agents such as melamine, dicyanodiamide, methylolmelamine, chlorinated paraffin hydrocarbon waxes, azobiscarbonamide and nitrosoamines (e.g. dinitrosopenta ethylenetetramine) ; and/or inorganic blowing agents such as carbonates, bicarbonates and carbamates (e.g. alkali metal salts such as the sodium salt) . Binders which may be employed in compositions according to the invention include polyurethane, polyester, phenolic resin, polycarbonate, polyvinyl chloride, polyvinylidene chloride, chlorinated rubber, polysulphide, urea/formaldehyde, phenol/formaldehyde, urea/phenol/formaldehyde, acrylonitrile/butadiene/ phenol, optionally methylated melamine, melamine/formaldehyde, melamine/urea, polyvinyl acetate, polyacrylonitrile, nitrocellulose, epoxy, nylon, silicone, aerylate/vinyl acetate and optionally chlorinated ethylene/vinyl acetate polymer systems. In general, substantially any thermoplastic polymer may be employed as binder, but in certain applications, e.g. where high resistance to weathering is required, it may be particularly advantageous to employ a substantially water-resistant thermosetting resin as binder, examples including ureaformaldehyde resins, phenol resins, epoxy resins, unsaturated polyester resins (e.g. vinyl toluene acrylic copolymer) , melamine- formaldehyde resins, urea-melamine resins, methylated melamine resins, nylon and silicone resins. In such applications it may be advantageous for all the ingredients of the coatings to be hydrophobic or adapted to a hydrophobic form. Fireproofing compositions as generally described above may, for example, contain 3-20 wt % of the exfoliable laminar mineral (all percentages are relative to the overall composition) , the precise amount used depending in part on the nature of the binder. Thus where a thermoplastic binder is used it may be convenient to employ 3-ip wt % of exfoliable laminar mineral, while amounts of 10-20 wt % may be appropriate where a thermosetting binder is used. Binders and any associated curing agent may conveniently be used in amounts of up to 60 wt %, e.g. 10-40 wt % of a vinyl toluene/butadiene or vinyl toluene/acrylic copolymer or a chlorinated rubber, or 20-40 wt % of an epoxy resin (which may, for example, ultimately be combined with 10-15 wt % of curing agent) . Carbonifics may for example be present in amounts in the range 15-25 wt. %, while 15-35 wt % of catalyst and 15-30 wt % of blowing agent may conveniently be used. Compositions accords-fig to the invention may optionally also contain one or more solvents (e.g. in an amount of up to 20 wt %) as a vehicle to assist application and so may be formulated as coating compositions such as paints. Suitable solvents include hydrocarbons such as benzene, toluene, xylene, solvent naphtha or white spirit; ketones such as acetone, methyl ethyl ketone or methyl isobutyl ketone; and esters such as ethyl acetate or butyl-.acetate. Other optional components of fireproofing compositions of the invention include pigments (e.g. titanium dioxide, magnesium silicate or red, yellow or black ferric oxide) , for example in amounts of up to 20 wt %, plasticisers (e.g. in amounts of 2-5 wt %) , sticking agents (e.g. in amounts of. , 5-10 wt %) , and flame retardants (e.g. in amounts of up to 10 wt %) . It may also be advantageous to incorporate glass microspheres and/or fibres into the ' compositions of the invention. Advantageously a combination of low temperature (e.g. melting at 300-600°C) and high temperature (e.g. melting at 600-900°C) glasses is used, the softer low temperature glass enhancing the adhesion of the char to the substrate after intumescence and the harder glass assisting the production of a hard ablative-type foam with good resistance to crushing. If desired, ceramic fibres and/or powders (e.g. melting at temperatures in excess of 900°C) may also be used to improve the high temperature stability of the char. In general, the glasses may, for example, conveniently be used in overall quantities of 5-10 wt %. Such glasses and ceramics may be regarded as high temperature sticking agents. Further useful components of the compositions of the invention are oxides of cerium and/or molybdenum, by virtue of their smoke inhibiting effect, this being particularly useful where interior applications of the compositions are intended. Typically such oxides are used in quantities of 3-10 wt %, e.g. about 5 wt %, and are believed to operate by reacting with carbon particles in any smoke to yield the corresponding cerium or molybdenum carbonate. One advantage of compositions containing exfoliable laminar minerals in accordance with the invention is that these materials exfoliate cleanly, with virtually no emission of fumes or toxic vapour. The expansion is endothermic and therefore absorbs heat so as to moderate the temperature of a substrate during intumescence of a coating thereon. Furthermore, the expansive pressure from the exfoliable laminar minerals is significantly greater than that developed by known intumescent systems, permitting the use of strong weather-resistant binders such as epoxy, silicone or nylon type resins to encapsulate the ingredients (especially the catalyst, which is often particularly water sensitive) and also permitting overpainting of the intumescent coatings, for example with conventional outdoor grade paints, in contrast to the prior art discussed above. Known intumescents fail under such conditions of encapsulation by virtue of the hardness of the encapsulant and its high softening temperature; the exfoliable laminar minerals used according to the present invention, however, can generate sufficient expansive pressure to break through such polymeric binding or overcovering whereafter the intumescent char-forming agent or agents present may also operate. The use of expandable graphite in combination with conventional intumescent materials is also of advantage in that the exfoliated graphite immediately provides a basic insulating vermiform carbon structure which expands through and strengthens the binder and which may subsequently be consolidated by additional char formation by the conventional intumescents. The stabilising effect of the vermiform carbon structure also reduces any tendency of the intumesced char to shrink and separate from Hhe substrate to which the composition is applied, thereby minimising insulation breakdown. A further advantage of the use of expandable graphite is that it appears, even at levels as low as 3 wt % overall, to render the binder blend more hydrophobic, thereby enhancing the weathering properties of the compositions. Furthermore, the compositions of the invention, e.g. in the form of paints, may easily be applied to give thin coating films, for example having a thickness of 0.5-lmm, which nonetheless have a very marked fireproofing effect. This ability to produce thin coating films is clearly of economic benefit and may also be advantageous cosmetically in that decorative features of the coated surface are not obscured. Where the coating compositions are prepared in the form of paints we have found that these may be particularly effectively applied by brushing, using brush strokes in one direction only. This appears to have the effect of causing the lamina of the exfoliable mineral to line up, producing a more stable and coherent water resistant expandable structure than may be achieved by, for example, spray application of the paint. The present invention therefore permits the production of fireproofing compositions having advantageous features such as good flexibility and adhesion, negligible smoke generation, absence of toxic fumes, controllable degree of expansion and effectiveness at temperatures of up to 1100"C. Compositions in accordance with the invention thus find a wide variety of applications in the building and construction industries (both land-based and offshore) , including use in the protection of structural steelwork, and structural and decorative timber; as pipe and cable coverings or coatings; as void fillers; as putties and caulking materials; as coatable decorative finishes; as components of plaster mouldings or finishes e.g. gypsum type plaster coatings which can be applied very thinly but which will provide good fire resistance properties upon intumescence; and as door seals (positioned on door edges or frames so that in the event of a fire the expanding intumescent material firmly seals the door, thus preventing ingress of oxygen to the fire via the doorway) . Other applications include protection of filters, including both filter bodies and support structures therefor, such as header frames; aircraft engine components and mountings; and heat shields e.g. for re-entrant satellites. The following non-limitative examples serve to illustrate the invention. All percentages and ratios are by weight. Example 1 Composition employing thermoplastic binder and expandable graphite The following components were blended together in the stated proportions:- Chlorinated rubber (Alloprene RIO - I.C.I.) 12 Chlorinated paraffin wax (Chlorowax - I.C.I.) 7 Pentaerythritol 7 Ammonium polyphosphate 22 Melamine . 8 Titanium dioxide (R522 - Hombitan) 15 Expandable graphite (Cellotek - BDH) 4 Solvents (SBP5:MIAK 83:17 - Samuel Banner) 24 Bentone 38 - Steetly 0.25 Airex 900 - Tegochemie AG 0.25 Airex 115 - Tegochemie AG 0.5 100.00 Example 2 Composition employing thermosetting binder and expandable graphite The following components were blended together in the stated preportions:- Epoxy base resin (Epikote 235 - Shell) 35 Brominated epoxy resin (F 2001 P - Croxton and Garry) 8 Polysulphide (LP3 - Morton Thiokol) 13 Melamine borate 5 Melamine phosphate 4 Titanium dioxide (R522 - Hombitan) 15 Expandable graphite (Cellotek - BDH) 4 Solvents (Aromosol:MIBK:Buglylol 7:2:1 - - Samuel Banner) 12.3 Bentone SDI - Steetly 1.5 Cabosil EH5 - Cabot G.m.b.H. 1.4 Airex 900 - Tegochemie AG 0.8 100.0 The resulting composition was used in conjunction with a hardener comprising 75 wt % Ancamine 1618 and 25 wt % of an Aromosol, MIBK and Buglylol solvent mixture as above, in the proportion 4 parts base resin composition to 1 part hardener. 13 Example 3 Composition employing thermosetting binder and expandable vermiculite The composition was prepared and used in a similar manner to that of Example 2 except that the expandable graphite was replaced by expandable vermiculite (Mando 125 EV - 7 wt %) , the proportion of solvent mixture being reduced to 9.3 wt %.

Claims: CLAIMS 1. A fireproofing composition comprising effective amounts of one or more exfoliable laminar minerals and one or more intumescent char-forming materials in combination with at least one binder. 2. A composition as claimed in claim 1 wherein the exfoliable laminar mineral or minerals are selected from expandable vermiculite, chlorite, kaolinite and mica. 3. A composition as claimed in claim 1 wherein_the exfoliable laminar mineral is expandable graphite. 4. A composition as claimed in any of the preceding claims wherein the intumescent char-forming material or materials comprise one or more materials selected from acids, acid-forming catalysts, carbonifics, char formers/stabilisers and blowing agents. 5. A composition as claimed in any of the preceding claims wherein the binder or binders are selected from polyurethane, polyester, phenolic resin, polycarbonate, polyvinyl chloride, polyvinylidene chloride, chlorinated rubber, polysulphide, urea/formaldehyde, phenol/formaldehyde, urea/phenol/formaldehyde, acrylonitrile/butadiene/phenol, optionally methylated melamine, melamine/formaldehyde, melamine/urea, polyvinyl acetate, polyacrylonitrile, nitrocellulose, epoxy, nylon, silicone, aerylate/vinyl acetate and optionally chlorinated ethylene/vinyl acetate polymer systems. 6. A composition as claimed in any of the preceding claims further containing glass microspheres, fibres and/or powders. 7. A composition as claimed in claim 6 containing a combination of low temperature and high temperature glasses. 8. A composition as claimed in any of the preceding claims further containing one or more oxides of cerium and/or molybdenum. 9. A coating composition comprising a composition as claimed in any of the preceding claims in admixture with one or more solvents and/or other vehicles. 10. A composition as claimed in claim 9 formulated for brush application. 11. A composition as claimed in any of the preceding claims in which the binder is a thermoplastic material and which contains 3-10 wt % relative to the total weight of the composition of exfoliable laminar mineral, 12. A composition as claimed in any of claims 1 to 10 in which the binder is a thermosetting material and which contains 10-20 wt % relative to the total weight of the composition of exfoliable laminar mineral. 13. A composition as claimed in any of the preceding claims in the form of a pack also containing any necessary curing agent for the binder.

Inventors: DEOGON MALKIT SINGH, DEOGON, MALKIT, SINGH
Applicants: HIGH POINT RENDEL PROJECTS LIM, HIGH-POINT RENDEL PROJECTS LIMITED
Application year: 1991
Main classification: C09K21
IPC codes: C09K21