GB2359308A - Expandable graphite as a flame retardant in unsaturated polyester resins - Google Patents

Abstract

Flame retardant compositions, useful for providing protection from fire to a substrate, such as fibreboard or strandboard, comprise an unsaturated polyester resin and particles of expandable graphite.

Description

2359308

Description

EXPANDABLE GRAPHITE AS A FLAMEE RETARDANT IN UNSATURATED POLYESTER RESINS Technical Field

The present invention relates to flame retardant compositions, useful for providing protection from fire to a substrate, such as fibreboard or strandboard. Mlore g)ecifically, the present invention relates to unsaturated polyester resin intumescent compost-ti,..)ns containing particles of expandable graphite. The flammability of the crosslinked polyester resin is reduced by the addition of particles of expandable: graphite, even at levels as low as 7 pph. The expandable graphite is particularly effective when used in conjunction with ammonium polyphosphate or a halogen compound as a synergist.

Background Art

Chemical intumescent systems have been used as flame retardants for over 50 years. Typically based on phosphates, melamine, and pentaerythritol, these intumescents rely on heat-induced decomposition to agenerate: a char layer that insulates the substrate from the heat source. As such, they are most useful as coatings for flammable materials. en added into inany materials, however, the expansive force of chemical intumescents is often insufficient to generate an effective char layer. For example, it has been found that many thermoset phenolic or unsaturated polyester resins cannot be protected by the incorporation of chemical intumescents.

Expandable graphite flake is now being used in a growing number of applications as an intumescent fire retardant additive, as an expansive ag gent, and as a smoke suppressant. Ford et al. describe the use of expandable graphite in oriented strandboard panels to reduce the flame spread in U.S. Patent 5,443,894. Hutchings et al. developed an especially effective 0 intumescent coating containing expandable graphite that reduced the flame spread and smoke -2 of highly combustible fibreboard panels, as described in a paper titled "Expandable Graphite Flake As An Additive For A New Flame Retardant Resill,- presented at the Fire Retardant Chemicals Association Fall Meeting, Naples, Florida, pp. 137-146 (October 1996). N1any intumescent putties, caulks and firestop systems rely on expandable graphize te. provide the expansive force necessary to close off gaps and holes during the course of a fire. Expandable grapWte is also used in various polyurethane foams to pass the rigorous tests required of aircraft seating and construction insulation, as described in U.& Patent Application 2,168,706.

The fire retardant properties of a number of thermoplastic polymers with expandable graphite and synergists was described by Okisaki in "Fl. amectit GREP Series New NonHalogenated Flame Retardant Systems," presented at the Fire Retardant Chemicals Association Sprina, Meeting, San Francisco, Califomia, pp. 11-24 (March 1997).

1.1 For many applications, there is a need for unsaturated polyester resins, rupRs) to be fire retardant or self-extinguishing. Fibre-reinforced plastic (FRP) materials cont i i Z> 1 aining UPRs are of particular concern, since this material is often used in critical applications such as aircraft, shipbuilding, and building construction.

The fire retardancy of UPRs has been recognized in the past. Chlonine and bromine compounds (e.g. HET acid, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, dibromoneopentyl glycol) can be built into the UPR molecule, or added to the U-PR directly as pentabromoethylbenzene or various chloroparaffins. The mechanism of fire retardancy involves the formation of Cl or Br radicals that terminate the zadical chain reaction of flame propaggadon. Antimony trioxide is often used to enhance the fire retardant efficiency of halogen compounds- However, the use of halogenated compounds and antimony oxide has come under some criticism due to the possible formation of toxic or corrosive: combustion products.

Aluminurn trihydroxide AI(O11)3 and magnesium hydroxide MIC(OH)z exhibit a p different mechanism of fire retardancy- Both materials evolve water at high temperatures, thus decreasing the temperature of the substrate and diluting the combustible pyrolysis gases.

-3 The primary disadvantage of these fire retardants is that they require relatively high loadings to be effective. This makes impregnation of the fiber reinforced composite more difficult while reducing its final physical properties- The metal hydroxides do have an important advJhtage in that they can significantly decrease the evolution of smoke.

A still different mechanism of fire retardancy is observed when red phosphorus and phosphorus compounds (e.g. triethyl phosphate or ammonium polyphosphate) are used. The oxidation and pyrolysis of these compounds result in the formation of polyphosphoric acid. The acids tend to promote charring of the plastic during heating which acts to reduce burning. Moreover, the char formation decreases the concentration of gaseous hydrocarbons due to pyrolysis. The concentration of phosphorus is usually much less than that required for the AI or Mg hydroxides. In fact, if the amount of the phosphorous-containling fire retardants is too large some properries of the UPRs may be adversely affected and processing problems may arise.

There have been many acidic metal compounds suggested for use as flame retardants. The fiTe retardant mechanism of these compounds maybe similar to that of phosphoruscontaining compounds- In addition to the well-known zinc borates, tin compounds (zinc stannate, ZnSti03 and zinc hydroxystannate, ZnSn(OR)r,) have also been suggested as possible fire retardants and smoke suppressants- As mentioned above, a flame retardant system must reduce the generation of smoke as well as suppress the flame propaggation. In addition to AI and Mg hydroxides and the borates and stannates,'molybdenum trioxide (MioO3) is an efficient smoke suppressantThe effect of the various smoke suppressants depends on the temperature of pyrrolysis.

Combinations of various fire retardants can exhibit an elevated efficiency when the mechanism of fire retardancy is different.' For example, halogen cornpounds:Corin synergi 1 0 g stic systems with AI(OHh or phosphorus compounds. Halogen-free systems containing AI(OH)3 1 with red phosphorus or ammonium polyphosphate can be somewhat effective- Phosphorusphosphorus synergisrn was found when triethyl phosphate was added together with melamine polyphosphate.

What is desired, therefore, is an additive effective to increase the fire retardancy of compositions basied on crosslinked polymers (e.g. unsaturated polyester resins). The additive should be capable of improving fire retardancy and related properties at relatively low levels, and act synergistically with other fire retardant compositions to improve the fire retardancy g achieved.

Summary of the Invention

It is an object of the present invention to provide an unsaturated polyester resin having improved fire retardancy.

It is another object of the invention to provide an unsaturated resin having particles of expandable graphite as an intutnescent additive.

It is yet another object of the present invention to provide a fire retardant composition comprising an unsaturated polyester resin having particles of expandable graphite and a synergistic fire retardancyenhancing compound mixed therein.

These objects and others which will become apparent to the artisan upon review of the following description can be accomplished by providin a a fire retardant composition which comprises an unsaturated polyester resin which includes as an additive particles of expandable graphite. The particles of expandable graphite are present in the polyester resin at levels of.at least about 7.5 parts by weight of expandable graphite particles per 100 parts resin (phr) when the particles of expandable graphite are the only additive, and at least 5 phr when the expandable graphite particles are used in combination with a synergistic additional fire retardant compound.

Graphites are made up of layer planes of hexagonal arrays or nehyorks of carbon atoms. These layer planes of hexagonally arrangged carbon atoms are sbstant"tally flat and are oriented or ordered so as to be substantially parallel and equidistant to one another. The substantially fla parallel equidistant sheets or layers of carbon atoms, usually. referred to as basal planes, are linked or bonded together and groups thereof are arnmeed in crystallites. Highly ordered graphites consist of crystallites of considerable size. the crystal lites being highly aligned or oriented with respect to each other and having well ordered carbon layers. In other words, highly ordered _graphites have a high degree of preferred crystallite orientation. Briefly, _graphites may be characterized as laminated structures of carbon, that is, structures consisting of superposed layers or laminae of carbon atoms joined together by weak van der Waals forces. In considering the graphite structure, two axes or direct' 0 1 ions are usually noted, to wit the 'c" axis or direction and the "a' axes or directions- For simplicity, the -c- axis or direction may be considered as the direction perpendicular to the carbon layers. The 'V' axes or directions may be considered as the directions parallel to the carbon layers (parallel to the planar direction of the crystal structure of the graphite) or the directions perpendicular to the "c" direction.

As noted above, the bonding forces holding the parallel layers of carbon atoms together are only weak van der Waals forces. Graphites can be treated so that upon the application of heat, the spacing between the superposed carbon layers or laminae can be appreciably opened up so as to provide a marked expansion in the direction perpendicular to the layers, that is, in the "c" direction and thus form an expanded graphite structure (also referred to as exfoliated or intumesced graphite) in which the laminar character of the carbon layers is substantially retained. Upon exposure to a flarne, the graphite particles expand (or exfoliate) to form a mechanical and Misulative barrier to fire- Brief Description of the Drawings

Th.e present invention will be better understood and its advantages more apparent in view of the following, detailed description, especially when read with reference to the appended Figure, which is a photornicrograph of a particle of expanded graphite.

Detailed Description of the Invention

Expandable graphite is manufactured usina natural crystalline graphite flake. Deposits of crystalline graphite are numerous and fouiid around the world, usually as inclusions in metamorphic rock, or in the silts and clays that result fto.m their erosion.

Graphite is recovered from the ore by crushing and flotation, and is usually berieficiated to give graphite flake that is 95-98% carbon.

As discussed above, graphite is a crystalline form of carbon comprising atoms covalently bonded in flat layered planes with weaker bonds between the planes. By treating particles of graphite, such as natural graphite flake, with an intercalant of, e.g. a solution of sulfun'c and nitric acid, the crystal structure of the graphite reacts to form a compound of graphite and the intercalant. The treated particles of graphite are referred to as -particles of intercalated graphite." Upon exposure to high temperature, the particles of intercalated graphite expand in dimension as much as 80 or more times their original volume in an accord- lon-like fashion in the "c'.' direction, i.e. in the direction perpendicular to the crystalline pI anes of the graphite, thus the particles of intercalated graphite can also be referred to as particles of expandable graphite." Exfoliated graphite particles are vermiform in appearance, and are therefore commonly referred to as worms. The worms act as a barrier to fire, both mechanically and because of their insulative value.

A common method for manufacturing particles of expandable graphite is described by Shane et aL in U.S. Pat. No. 3,404,061, the disclosure of which is incorporated herein by reference. In the typical practice of the Shane et a]. method, natural graphite flakes are intercalated by dispersing the flakes in a solution containing e.g., a mixture of nitric and sulfliric acid. The intercalation solution contains oxidizing and other intercalating agents known in the art. Examples include those containing oxidizing agents and oxidizing r7 mixtures, such as solutions containing nitric acid, potassium chlorate, chromic acid, potassium permanganate, potassium chromate, potassium dichromate, perchloric acid, and the like, or mixtures, such as for example, concentrated nitric acid and chlorate, chromic acid and phosphoric acid, sulftific acid and nitric acid, or mixtures of a strong organic acid, e.g. trifluoroacetic acid, and a strong oxidizing agent soluble in the organic acid.

0 0 Z> In a preferred embodiment, the intercalating agent is a solution of a mixture of sulfc acid, or sulfuric acid and phosphoric acid, and an oxidizing agent suc; acid = g h as nitric perchlonic acid, chromic acid, potassium permanganate, hydrogen peroxide, iodic or periodic acids, or the like. Although less preferred, the intercalation solution may contain metal -7 halides such as ferric chlofide, and ferric chloride niixed with sulfilric: acid, or a halide, such as bromine as a solution of bromine and sulfuric acid or bromine in an organic solvent, After the flakes are intercalated, any excess solution is drained from the flakes and the flakes are water-washed. The quantity of intercalation solution retained on the flakes after draining may range from 20 to 150 parts 0Esolution by weight per 100 parts by weight of graphite flakes (pph) and more typically about 50 to 120 pph. Alternatively, the quantity of the intercalation solution may be limited to between 10 to 50 parts of solution per hundred parts of 1 graphite by weight (pph) which permits the washing step to be eliminated as taught and described in U.S. Pat- No. 4,895,7 131, the disclosure of which is also herein incorporated by reference.

When the intercalated graphite is exposed to heat or flame, such as in a fire, the inserted molecules decompose to generate gas. The 0-as forces apart the carbon layers and the graphite expands- The expandedgraphite is a low density, non-burnable, thermal insulation, often referred to as a "worm" because of its curved shape (Figure). For use in the inventive composition, the particles of expandable graphite should preferably expand at temperatures no higher than about 30CC, preferably no higher than about 25WC. Suitable expandable graphites are commercially available from UCAR Graph-Tech, Inc- of Lakewood, Ohio and include UCAR Grraph- Tech's GRAFGUARD0 Grade 220 expandable graphite flake and GRAFGUARDO Grade 160 expandable graphite flake. The principal functional difference between the two grades is onset temperature, that is, the temperature at which expansion begins. For the GRAFGUARDC Grade 220 expandable graphite flake, expansion begins at 22WC, whereas for GRAFGUARD0 Grade 160 expandable graphite flake, expansion begins at 16WC.

The unsaturated polyester resin "R) into which the particles of expandable graphite can bemicorporated to fortn the inventive intumescent composition compnise solutions of unsaturated polyesters "s) and similar products in unsaturated monomers that can be cured by radical copolymerization. UPs are composed of glycol and dicarboxylic acid units which include unsaturated copolymerizable acid units and saturated or unsaturated noncopolymerizable acid units. The unsaturated copolymerizable acid tinhs are primarily -8-.

derived ftom maleic acid and kmaric acid residues. The saturated or unsaturated acid units are priman ly derived ftorn orthophthalic acid, acid, terephthalic acid-- tetrahydrophthalic acid, endomethylenctetrahydrophthatic acid, hexachlora endomethylenetetrahydrophthalic acid, adipic acid, sebacic acid and tenbromophthalic acid.

A variety of glycol units can also form a part of the structure of Ups, narnely ethylene alycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, dipropyleneglycol, 1,3)propylene glycol, 1,4-butylene glycol, neopentyl glycol, dibromoneopentyl gglycol, 2-methyl1,3-propanediol, chloromethylethylenc glycol, 2),4-trimethyl-l,-"1-pentanediol, ethoxylated bisphenol,A, propoxylated bisphenol A, and 1,4- eyclohexanedimethanol.

The UP molecules contain terminal hydroxyl and carboxylic groups. They can also be terrrinated with dicyclopentadiene, i.e. with dihydrodicyclopentadienyl ester groups. The UPs that are chain terminated with brominated monofunctional units, e.g. dibromopropyl residues, are included also. Additionally, oligo (ethylene terephthalate) segments can be incorporated.

lj'PRs commonly contain mostly styrene as the monomer, although thestyrene can be partially or entirely replaced by vinyl monomers, e.g. vinyltoluene or p-t-butylstyrene, acrylic monomers, e.g. methyl methacrylate, ethyl acrylate, 2-hydroxyethyl methacrylate, 2hydroxypropyl methacrylate, ethylene glycol dirnethacrylate, diethylene glycol dimethacrylate or triethylene glycol dimethacrylate, and allyl esters, e. a. diallyt phthalate, isophthalate or terephthaIate. Allyl ethers, e.g. trimethylolpropane monoallyl ether or trimethylolpropane diallyl ether, can also be used as one of die monomers or built into the molecule of an UP.

So-called vinyl ester resins are also UPRs and are cured and processed in the same way. Vinyl ester resins are solutions of unsaturated esters in the above listed unsaturated inonomers, mostly styrene. The unsaturated esters are addition products of methacrylic acid to epoxy groups in epoxy resint, mostly bispheriol A dialycidyl ether type, tetrabromobisphenol A diglycidyl ether and epoxynovolak resin. UPRs, comprising vinyl ester resins, are also used in urethanized forin. The urethanization consists of the reaction of -g- a diisocyanate with a part of hydroxyl groups contained in an UP ivith the rnaleatelfumarate unsaturation or in the vinYl esters with the methacrylate unsaturation.

The above described UPRs are cured at ambient temperature using an initiatoraccelerator system, such as a hydroperoxide or a ketone peroxide with a cobalt salt or a vanadium compound, or benzoyl peroxide with a tetiary aromatic amine (e.g. N,Ndimethylaniline or XiN-dimethyl-ptoluidiiie); or at elevated temperatures using peroxy W Z? compounds with an elevated decomposition temperature, e... benzoyl peroxide or dicurnyl peroxide.

Fillers containing UPRs can also be used In the compositions according to this invention, together with expandable graphite and optionally other fire retardants. Powdered fillers, e.g. chalk and talc, and fibrous reinforcing fillers, e.g. glass fiber, juta and sizal can also be included.

In formina the inventive flame retardant compositions, particles of expandable 0 graphite are incorporated into the UPR prior to curing- The gra 0 g phite particles are included in an amount sufficient to exhibit flame retardancy as compared with the UPR wtthout graphite. When incorporated without a synergistic agent, the particles of expandable gn,.phite should be incorporated into the resin at a level of at least about 7 parts by weight graphite per 100 parts by weight of UPR (pph), rnore preferably at least about 7.5 pph. Most preferably, the particles of expandable graphite are included in the resin composition at a level of at least about 10 pph. Although there is no strict upper limit of the amount of graphite particles to be included, generally, no more than about 25 pph should be included, in order to maintain the mechanical strength of the cured resin composition- In addition to the particles of expandable graphite and UPRs, the Inventive flarne retardant compositions can also include other components that act synergistically with the graphite particles to create flirther flame retardancy for the inventive composition. Such sy nergistic compositions include ammonium phosphate type composit' ns like ammonium polyphosphate, which tends to form polyphosphonic acid on oxidation and pyTolysis, and promote charring which redu= burning, and halogen compounds such as cblorine 0 compounds and bromine compounds like pentabromoethylberizene, optionally with an antimony compound like antimony trioxide or antimony pentoxide. These synergistic compounds can be included at levels of at least about 2 pph, and generally not more than about 15 pph. When the synerclistic compounds are included the minimum level of graphite 0 particles can be reduced to about 4 pph in the inventive composition.

In use, the compositions of the present invention can be incorporated in or coated on the surface of the substrate to be protected, and then curedFor instance, the inventive compositions can be coated on strandboard or fibreboard, and provide enhanced fire retardancy to the surfaces. or, the particles of expandable graphite can be incorporated in glass fiber reinforced polyester resin (GRP) products, such as GRP products made by the hand-lay-tip method, by spraying etc.

1 In another embodiment of die invention, particles of expandable "hite can also be added to unsaturated polyester-based resin binders with fibrous and powdered fillers. The best example of these are sheet molding compounds (SMCs) which consist of UPP, chalk, cut glass fibers, a thickener, peroxide initiators, pigments arid, optionally, a lowprofile additive. Expandable graphite, (optionally with other fire retardant adffives) may be used to make the compression molded pans fire resistant. In such applications, the expandable graphite can be included at lower levels, as low as 5 parts by weig per 100 parts ht by weight of UPR or even as low as 3 parts by weight if used in conjunction Mlith a synergistic agent like an ammonium phosphate type compound. An exemplary formulation, in parts by weight: general purpose UPR 100, chalk 120, tert-butyl perbenzoate 1.5, MgO (thickener) 4.5, zinc stearate 4.5, cut glass fiber 9.14, expandable graphite particles 5 or, when arnmonium polyphosphate is present at 5 parts by weight, then expandable gr-1phite particles can be present at 3 parts by weight.

The following examples are presented to further illustrate and explain the present invention and should not be viewed as limiting in any regard. Unless otherwise indicated, all 0 parts and percentages are by weight, and are based on the weight of the product at the particular stage in processing indicated.

Example I

The resin employed was Polimal 109 unsaturated polyester resin obtained from Chem. Works "or,-,anika-Sarzytia", Nowa Sarzyna Poland- The resin is a genenal-purpose, halogen-free system made of maleic anhydride, phthalic anhydnide, 1,2-propylene glycol and styrene. The cold curing systern consisted of methytethylketone peroxide and cobalt octoate.

The expandable graphite employed was GPLA1GUARD0 220-80N Expandable Graph. ite Flake, obtained from UCAR Graph-Tech, Inc. of Lakewood, Ohio. As noted above, in the grade nomenclature, 220 refers to the temperatwe (in 'C) at which the gaphite begins to expand; in addition 80 refers to the mesh size of the particles (177 micron or larger), and N refers to a neutral flakeThe liquid UPR was mixed with the expandable graphite paxticles (denoted G), at differing levels, and 1 pph Aerosil 200 (to avoid sedimentation)The components of the curing system consisting of 1.5 pph methylethylketone peroxide (40%) and 0-4 pph cobalt octoate solution (1 % Co) were added, and the compositions were cast into 4 r= x 10 min x 100 nim steel molds. The curing was carried out by holding the cast pieces at 2 O'C for 24 hours, followed by a postcuring treatment at WC for 2 hours.

The fire performance of the bars was tested by heating the samples in a horizontal position using a gas flame for 60 seconds, the self-extinguishing (afterflame) then monitorin- C? 0 time (and time to extinguish after application of flame) and the remaining non-burnt length of the bar (up to 80 mm). This test corresponds to the Polish Standard PN-82/C-89023 [see ISO 1210:1992 (E) "Plastic s-detennination of the buming behaviour of horizontal and vertical specimens in contact with a small-flame ignition source"]. In addition, the Limiting Oxygen Index (LOI) was also determined.

The results are shown in Table L Table 1

Sample G, pph Behavior in fire IN 0. Afterflame Non-burnt Selfextinguishing time, sec length, mm L01, 1 - 1 0 No 280 0 19.5 21 5 NO 365 0 21.6 7.5 Yes 7 78 4-1 10 Yes 0 80 23.3 5-1 15 Yes 80 2 3. 3 6-1 25 yes 0 80 7-1 25 Yes 0 80 8-1 Yes 0 79 1 At some of the lower loading levels of G there was observed some "sparkin. 'of the graphite during expansionPresumably, this was the result of the graphite expanding through the rigid polyester, causingsome small particles of the resin to be C-lected from the sample. In a few cases, the sparks were hot enough to ignite a sheet of filter paper placed 20 cm below the burnina bar.

Example II

Phosphorus in the form of ammonium polyphosphate (APP) was also included in the UPR composition, along with expandable graphite, in the amounts indicated.

The results are shown in Table 11.

Table 11

Fire retardant, Behavior in fire pph Sample No. A-PP Self- Afterflame Non exdnguishin time, see burnt lenath, MM 2-1 5 0 No 365 0 1 -iv 5 5 No 13 73 2-1V 5 10 Yes 10 75 3-rV 5 is Yes 0 80 4-rV 10 0 Yes 0 80 4 - rV 10 5 Yes 0 80 - TV 10 10 Yes 0 80 6 - IV 10 is Yes 0 so 7-1V 0 15 NO 40 55 Whereas APP by itself at 1.5 phr was not self-extinguishill- and had an afterflarne time of 40 seconds, the addition of 5 phr 0 gaye immediate self-extinguishing. No sparks 0 an were observed at this concentration of additives. In addition, at a loadin- level of 10 phr G + 15 phr APP, the amount of smoke produced was reduced significantly. Thus, the combination of G and APP is distinctly synergistic in this unsaturated polyester resin system.

Example Ill pentabromoethylbenzene [PBEB] with antimony trioxide (Sb203, ATO) were also included in the UPR/expandable _graphite composition in the amounts shown below.

The results are shown in Table 111.

Table 111

Fire retardant, pph Behavior in Fire Sample G PBEB ATO Self- Afterflame Non-burnt No. exduguishing time, see length, Z> mm 1 -1 5 0 0 No 365 0 1 v 5 3 2 Yes 0 74 3V 5 10 3 Yes 7 80 It is apparent that the self-extinguishing properties appear at a relatively low concentration of the fire retardants. Zero burning tirae was found at loadings as low as 5 phr G and 3 phr PBEB with 2 phr ATO.

Expandable graphite flake added to unsaturated polyester resin in the amount of 7 pph or more makes the resin self-extinguishing. The use of expandable graphite with ammonium polyphosphate further improves the fire retardant behaviour of UPR- G added at 5 phr with 15 phr APP inhibits burning of the sample while eliminating any afterflarne (immediate selfextinguishing). Moreover, G and APP together suppress the formation of smoke. Good fire retardaDey can also be obtained by adding expandable graphite to a brominated fire retardant and antimony trioxide. Sparks generated by pieces of the rigid resin ejected by the expansion of the graphite are eliminated with APP or (PBEB + ATO) when applied in a proper ratio.

The above description is intended to enable the person skilled in the art to practice the invention. It is not intended to detail all of the possible variations and modificaetons which will become apparent to the skilled work-er upon reading the description. It is intended, however, that all such modifications and variations be included within the scope of the -Isinvention which is defmed by the following claims- The claims are intended to cover the indicated elements and steps in any arrangement or sequence which is effective to meet the 0 objectives intended for the invention, unless the context specifically indicates the contrary.

Claims (29)

1. An intumescent composition wbich comprises a cross-linkable unsaturated polyester resin having particles of expandable graphite incorporated therzin.

2. The composition of claim 1 wherein the particles of expandable grdphite comprise particles of intercalated graphite which expand when exposed to a temperature of no higher than about J31 00 "C.

The composition of claim 1 or 2 wherein the particles of expandable graphite are present in the composition at a level of at least about 5 parts by weight of graphite per 100 parts by weight of resin.

4. The composition of any of claims 1 to 3 wherein the cross-Linkable unsaturated polyester resin is selected from the group consisting of glycol and dicarboxyLic acid units wbich include unsaturated copolymerizable acid units and saturated or unsaturated noncopolymerizable acid units.

5. The composition of claim 4 wherein the unsaturated copolymerable acid units comprise maleic acid and fumaric acid residues.

6. The composition of claim 4 or claim 5 wherein the saturated or unsaturated noil-copolymerizable acid units comprise derivatives of orthophthalic acid, isophthalic acid, tereplithalic acid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, hexachloroendomethylenetetrahydrophthalic acid adipic acid, sebacic acid and tetrabromophthalic acid.

7. The composition of any one of claims 1 to 6 wherein the cross-linkable unsaturated polyester resin comprises a vinyl ester resin.

8. The composition of any one of claims 1 to 7 wherein the cross-linkable umaturated polyester rcsin comprises styrene monomers.

9. The composition of any one of claims 1 to 8 wherein the cross-linkable unsaturated polyester resin can bc cured using an initiator-accelerator system.

10. The composition of any one of claims 1 to 9 which further comprises an ammonium phosphate type composition,

11. The composition of claim 10 wherein the ammonium phosphate type composition comprises ammonium polyphosphate.

12. The composition of claim 11 wherein the particles of expandable graphite are present in the composition at a level of at least about 3 parts by weightof graphite per 100 parts by weight of resin and the ammonium polyphosphate is present in the composition ai a level of at least about 2 parts by weight per 100 parts by. weight of resin.

13. Mic composition of any one of claims 1 to 12 which further comprises a halogen compound.

14. The composition of claim 13 wherein the halogen compound comprises pentabromoethylbenzene.

15. The composition of claim 14 wherein the particles of expandable graphite are present in the composition at a level of at least about 3 parts by weight of graphite per 100 parts by weight of resin and the pentabromoethylbenzene is present in the composition at a level of at least about 2 parts by weight per 100 parts by weight of resin.

16. A method for providing flame retardancy to a substrate, the method comprising coating the substrate with an intumescent composition which comprises a cross-linkable unsatuiated polyester resin having particles of expand;ble graphite incorporated therein, and curing the cross- linkable unsaturated polyester resh

17. The method of claim 16 wherein the particles of expandable grapbite are present in the composition at a level of at least about 7 parts by weight of graphite per 100 parts by weight of resin.

18. The method of claim 16 or claim 17 wherein the cioss-linkable unsaturated polyester resin is selected from the group consisting of glycol. and dicarboxylic acid units which include unsaturated copolymerizable acid units and saturated or unsaturated noncopolymerizable acid units.

19. The method of claim 18 wherein the unsaturated copolyrmerizable acid units comprises maleic acid and fumaric acid residiis-

20. The method of claim 18 or claim 19 wherein the saturated or unsaturated rion-copolymerizable acid units comphse derivatives of ohop!Athalic acid, isophthalic ' acid, terephthalic acid, tetrahydrophthalic acid, eadomethyIenetetrahydrophthalic acid, hexachloroendomethylenetetmhydrophtbalic acid, adipic acid, sebacie acid and tetrabromophthalic acid.

2 1. The method of any one of claims 16 to 20 wherein the cross-linkable unsaturated polyester resin comprises a vinyl ester resin.

22. The method of any one of claims 16 to 21 wherein the cross-linkable unsaturated polyester resin comprises styrene monomers.

23). The method of any one of claims 16 to 22 wherein the cross-linkable unsaturated polyester resin can be cured using an initiator-accelerator system.

24. The method of any one of claims 16 to 23 which further comprises an ammonium phosphate type composition.

25. The method of claim 24 wherein the particles of expandable graphite are present in the composition at a level of at least about 4 parts by weight of graphite per 100 parts by weiglit of resin and the ammonium phosphate type composition is present in the intumesceDt composition at a level of at least about 2 parts by weight per 100 parts by weight of resin.

26. The method of any one of claims 16 to 25 which flirtber comprises a bromine compound.

27- The method of claim 26 wherein the particles of expandable graphite are present in the composition at a level of at least about 4 parts by weight of graphite per 100 parts by weight of resin and the bromine compound is present in the composition at a level of at least about 2 parts by weight per 100 parts by weight of resin.

28. An intumescent composition substantially as hereinbefore. described.

29. A method substantiaUy as hereinbefore described for providing flame retardaDcy to a substrate.

j