GB1570482A - Flame retardant resin compositions - Google Patents

Description

(54) FLAME RETARDANT RESIN COMPOSITIONS (71) We, ALRIGHT & WILSON LIMITED, a British Company of Albright and Wilson House, Hagley Road West, Oldbury, Warley, West Midlands, England, formerly of P.O. Box 3, Oldbury, Warley, West Midlands, England9 do hereby declare the invention, for which we pray that a Patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to resin compositions and the cured products obtainable therefrom.

British Patent Specification No. 1150203 describes the production of resins having repeating units of the formula

wherein R' is an aromatic hydrocarbon or aromatic hydrocarbon-oxy-aromatic hydrocarbon group, which optionally has inert substituents and Ar is the residue of a phenolic compound hereinafter defined and n is 0 or 1. British Patent Specification No. 1305551 describes the curing of these resins with epoxides having 2 or more epoxy groups per molecule to form cured products.

Solutions of the above resins can be used for the production of surface coatings and laminates having good chemical and high temperature ageing resistance and electrical properties.

German Published Patent Application No. P22479 17 (British Patent Specification No. 1365936) describes the curing of the resins with epoxides, especially cycloaliphatic epoxides, in the presence of a compound containing a tertiary nitrogen atom and a secondary or tertiary nitrogen atom, both in a heterocyclic ring. German Published Patent Application No. 2402928 further describes the incorporation in mixtures of resin and curing agents e.g. epoxides of fine particle inorganic dispersing agents such as fumed silica and particulate material such as flame retardants, lubricants or metal powders. The flame retardants described are organic compounds containing halogen and/or phosphorus atoms such as polyhalogenated organic compounds, preferably those in which the halogen is chlorine or bromine, and especially those in which the organic nucleus is an aromatic nucleus, e.g. decachlorobiphenyl, hexabromobenzene, hexachlorobenzene and tetrabromobisphenol A, and tris (bromophenyl). phosphate, tris (pentabromophenyl) phosphate and tris (dichloropropyl) phosphate. These compounds, which may be soluble in the resin solution, are used in conjunction with antimony oxide, which is insoluble. Other flame retardants are metal borates e.g. borates of metal of Gp. 2 (of the Periodic Table published in Bull. Soc. Chim France January 1966) such as zinc. calcium or barium. Antimony oxide may also be present in admixture with the borates.

USP 3280216 describes curing a mixture of an epoxy novolac resin, and a halogenated phenol or halogenated novolac, with a curing or cross linking agent, the proportion of equivalents of phenolic hydroxy groups to equivaients of epoxide groups being not more than 0.45:1. The Examples show that much lower heat distribution temperatures for the cured products are achieved if the epoxy novolac is replaced by another epoxide or if the proportion of phenolic groups is higher than 0.45:1 e.g. 0.89:1.

The laminates prepared by curing the resin of British Patent No. 1150203 with epoxides can be used as insulation for high temperature use or as the base board for printed circuits. However, if the printed circuit is to be flame retardant, it is not desirable to use any flame retardant which contains antimony oxide, as this tends to contaminate plating baths need d during the manufacture of the complete printed circuit.

While some halogenated organic compounds are suitable alone or in a synergistic mixture with antimony oxide as flame retardants for some resins, we have found that alone they are not suitable for use with mixtures of the above resin and epoxides, either because the compounds are incompatible with the mixture before or after curing or and/or hardly affect the flame retardancy over that of the cured mixture of resin and epoxide without the flame retardants and/or give blistered cured products, and/or drastically reduce the strength of the cured products at high temperatures.

We have now found a class of halogenated organic flame retardants which are compatible with the mixture of resin and epoxide, give a surprisingly high degree of flame retardance to the cured product containing them, tend not to give blistered cured products, and give cured products with high strength at high temperatures and good retention of that strength.

The present invention provides a resin composition which comprises (a) a resin having repeating units of the formula:

with terminal ArH(OH)2 groups and preferably consists essentially of such repeating units especially 2 or 3 of such units, wherein R' is a divalent aromatic mononuclear hydrocarbyl group and Ar(OH)2 is a residue formed by removal of 2 nuclear hydrogen atoms from a dihydric phenol with at least 2 nuclear hydrogen atoms, (b) a cycloaliphatic epoxide containing at least 2 epoxy groups per molecule and (c) a brominated phenol e.g. one containing at least two hydroxyl groups, the molar proportion of epoxy groups in the epoxide to the total of phenolic hydroxyl groups in the resin and in the brominated phenol being in the range 0.5:1 to 2:1 and the percentage of brominated phenol is 324% (expressed as a percentage of the weight of bromine to the total weight of resin, epoxide and brominated phenol), the resin composition being in the absence of antimony oxide.

The brominated phenol has at least one aromatic ring with at least one bromine atom and at least one but preferably at least two hydroxyl groups attached directly to the aromatic ring or rings. Preferably the one or each aromatic ring has 1, 2 or 3 or 2 bromine atom and the molecule contains a total of two hydroxy groups, especially one hydroxyl group per aromatic ring in a phenol having two aromatic rings.

Preferably, the brominated phenol is of formula

where b is an integer of I to 3, c is 0 or preferably an integer of I to 3, d is 0 or 1, each of e and f isO or an integer of I to 3, g is0, 1 or 2, his 0 or I andj isO or an integer of 1 to 5, subject to it containing at least 1 and preferably at least 2 hydroxyl groups and the maximum of 6 substituents on each benzene ring, each of R2, R4 and R5, which are the same or different, is an alkyl group of 1 to 4 carbon atoms and R3 is an oxygen atom or sulphur atom or a CH2 or -C(CH3)2- group, subject to the proviso that R3 is a CH2 group and d and h are 1 when j is an integer of 1 to 5.

Preferably b is 2 or 3, especially 3 when h and j are 0, preferably c is 2 or 3, especially 2, d is 0 or 1, e and f preferably 0 or 1, especially 0, g is preferably 0 or 1, especially 0 (unless j and h are both 0 when g is 0 or 1), h is 0 or I and j is 0 or an integer of I to 5, preferably 0. Most preferably g is 0, j is 0, h is 1, d is I, e and fare 0 and b is 1 or 2, especially 2.

Examples of the halogenated phenol are bis (hydroxy bromo phenyls), bis (hydroxybromophenyl) oxides and sulphides, bis (hydroxy bromophenyl)methanes and -2,2-propylidenes; the latter 5 classes of compound preferably have 2 or 4 bromine atoms e.g. tetra bromo bis phenyl A i.e. bis (4-hydroxy-3,5dibromophenyl) 2,2-propylidene. Further examples of the halogenated phenol are brominated phenol formaldehyde novolac resins i.e. novolac resins formed by reaction of formaldehyde and a bromophenol or reaction product of a phenol formaldehyde resin and bromine. Another example is 2,4,6-tribromophenol. The halogenated phenol may also be an aralkylene phenol resin of a similar type to the phenolic resin used in the compositions of the invention but is an aralkylene phenol resin having repeating units of formula -CH-R'-CH2-Ar'- and terminal Ar' (H) groups wherein R' is as defined above and Ar' represents a residue formed by removal of two nuclear hydrogen atoms from a monomeric brominated phenol having at least 2 nuclear hydrogen atoms and at least 1 hydroxyl group. These aralkylene phenol resins may be made by reaction of an aralkylene compound, in particular the ether or halide as described in British Patent No. 1150203 and hereafter, with a molar excess of a monomeric brominated phenol having at least two nuclear hydrogen atoms and at least 1, and preferably 2 hydroxyl groups, e.g. dibromophenol or tetrabromobisphenol A.

The halogenated phenol is present in the resin composition of the invention in an amount of 325% e.g. 618% (expressed as a percentage of the weight of bromine to the total weight of resin, epoxide and halogenated phenol), preferably the percentage of bromine is 10-18% e.g. 12-18% and especially 12-15%. Thus for tetra bromobisphenol A the preferred weight of the compound is 10-30% e.g.

16-30% and especially 20-25% (based on the weight of the tetra bromo bis phenol A as a percentage of the total weight of resin, epoxide and bromophenol).

The resin composition of the invention is substantially free of antimony oxide, is preferably substantially free of other particulate materials of particle size 0.2 -2 mm, which are stable to at least 150 C and also preferably substantially free of inorganic dispersing agents such as those described in said German published Patent Application 2402928.

The The resin is preferably prepared as described in British Patent Specification No. 1150203 or Japanese Patent Application 120362/75 (Japanese Published App.

63899/76, British Patent Specification No. 1528748) by reacting (1) an aralkyl ether of the general formula R' (-CH2OR)2 and/or an aralkyl halide or ester of the general formula R'-(CH2X)2, wherein R' is a divalent aromatic mononuclear hydrocarbyl group, R is an alkyl radical containing 1-5 carbon atoms, X is chlorine, bromine or iodine, alkanoate group or an alkane suiphonate group each of 2 to 6 carbon atoms e.g. acetate or methane sulphonate group, or aryl sulphonate- group of 6-13 carbon atoms, e.g. benzene-toluene- or xylene-sulphonate group with (2) molar excess of at least 1.3:1, preferably in the range of 1.4:1 to 2.5:1 e.g.

1.4-2.0:1 and especially 1.4-1.7:1 of a dihydric phenolic compound of formula Ar(OH)2.

In these general formula R' represents any divalent mononuclear aromatic hydrocarbon radical, for example the m- or p-phenylene radical. The resin is preferably prepared from the aralkyl ether, especially ones in which R is an alkyl radical of less than 4 carbon atoms e.g. a methyl radical. The preferred compounds for a reaction with the phenol compound are particularly the p-xylylene dihalides, for example p-xylylene dichloride and the p-xylylene dialkyl ethers, for example p-xylylene-glycol di methylether If desired the R' radical may contain at least one substituent which is a phenyl, or alkyl group.of I to 4 carbon atoms.

The aralkyl compounds are preferably at least 90% pure, though technical grade products with 6590% of the expected compound may be used. Thus technical grade p-xylylene glycol dimethyl ether can contain 6590% e.g. 65-75% of the expected compound, 1035% e.g. 2035% of the p-methoxy methyl benzal dimethyl acetal, up to 5% of p-methoxy methyl toluene and up to 10% of the ptolualdehyde dimethyl acetal; the amount of acetal includes any free aldehyde present.

The phenolic compound includes any compound or mixture of compounds derived from benzene and containing 2 hydroxyl radicals joined to the aromatic nucleus, there being a total of not more than 3 substituents attached to ring carbon atoms of the benzene nucleus apart from the two essential hydroxyl groups. Thus subject to the above provisos the phenolic compounds may be of formula:

where each R, is hydrogen, alkyl of I to 8 carbon atoms e.g. methyl, ethyl, isopropyl, tert. butyl or tert. octyl, or phenyl. Examples of these phenolic compounds are resorcinol, catechol, hydroquinone, 4-methylcatechol and isopropyl catechol. Mixtures of the phenols can be used such as mixtures of diphenols e.g. 4-methyl catechol and catechol and/or resorcinol such as that sold as a phenolic coal tar fraction.

The curing agent for the resin is cycloaliphatic epoxide with two or more epoxy groups per molecule and is usually the sole curing agent present so that non phenolic hydroxyl curing agents such as diprimary amines and anhydrides are usually absent. The epoxide preferably contains just 2 epoxy groups per molecule.

The amount of epoxide used depends on the total phenolic hydroxyl group content of the resin and brominated phenol, and the epoxy group content of the epoxide, and is such that the molar proportion of epoxy to total phenolic groups is 0.5:1 to 2:1, preferably 0.8:1 to 1.25:1 and especially about 1:1. The epoxide is mixed with the resin and cured with or without a cure accelerator. Alternatively, the epoxide and resin can be partially reacted first and then the partially cured product cured by further heating, addition of more epoxide or some cure accelerator.

The epoxides are cycloaliphatic with at least one and preferably at least two epoxy groups, each of which is fused to a cycloaliphatic nucleus, other epoxy group or groups (if present) being cyclic epoxides which are preferably not part of a glycidyl group.

The cycloaliphatic epoxides preferably have a maximum of 4 carbon atoms joining the cycloaliphatic nuclei, if more than I such nucleus is present and especially not more than 3 bridging chain atoms, but advantageously the epoxide only contains cyclic groups between the epoxy groups. Examples of cycloaliphatic epoxides are dicyciopentadiene dioxide and vinyl cyclohex-2-ene dioxide but preferably those of formula

wherein R7 is a hydrogen or methyl, and

The cure accelerator, which is advantageously used with the epoxides, is preferably a tertiary amine or salt thereof e.g. morpholinium p-toluenesulphonate, a phenol containing 1, 2 or 3 dimethylaminomethyl groups such as dimethylaminomethyl phenol and 2,4,6-tris (dimethylaminomethyl) phenol or benzyl dimethylamine, or a compound having a tertiary nitrogen atom and a secondary or tertiary nitrogen atom both in a heterocyclic ring e.g. imidazoles such as N-butylimidazole. The latter class of accelerators are further described in our West German OLS P2247917, while the use of epoxides for curing the resin with details of the other cure accelerators are described in our British Patent 1305551. 2 Ethyl-4-methyl imidazole is the preferred accelerator.

The compositions of this invention may also contain inorganic fillers, e.g. asbestos flour, mica or chopped glass strands, especially when used as moulding compositions. The inorganic filler and resin will normally be present in a weight ratio of 0.05:1 to 4.0:1. Other ingredients such as pigments, accelerators, and antistaining agents e.g. magnesium oxide, or titanium dioxide may also be present if desired.

The compositions of the invention can be made by mixing the various components in any order, but it is convenient to add the curing agent last. The mixing can be carried out in any convenient method such as dry blending to form a powder for moulding (optionally with subsequent addition of organic solvent to make the desired liquid for coating and impregnating purposes) or blending in solutions in an organic solvent to prepare the liquid directly. The solvent may be a dialkyl ketone of 3-8 carbon atoms e.g. methyl isobutyl ketone, methyl ethyl ketone, or methylisoamyl ketone, isophorone, diacetone alcohol, a cycloalkyl ketone of 5-7 carbon atoms e.g. cyclohexanone, an alkoxy alkanol with 1-6 carbon atoms in the alkoxy group and 2-7 carbon atoms in the alkanol group such as 2-ethoxyethanol, alkyl ethers thereof with 1-6 carbon atoms in the alkyl group e.g. the methyl ether, esters of the alkoxy alkanols with alkanoic acids of 2-6 carbon atoms e.g. the acetate, any of which solvents can be (in an amount sufficient to maintain the resin in solution) mixed with an aromatic hydrocarbon preferably a monocyclic one of 6-12 carbon atoms such as benzene, toluene or xylene or an aliphatic hydrocarbon such as white spirit or solvent naphtha or and alkanol e.g. of 1 to 6 carbon atoms, such as methanol, ethanol or n-butanol. The resin is usually present in the organic solvent solutions in an amount of 5-90% preferably 2065 e.g. 2050% by weight. The mixing can be carried out at a low temperature e.g. 2O300C and this mixture stored until required, but the mixing of the curing agent with the remainder of the components is usually carried out at a higher temperature e.g. about 60"C for several hours e.g. 1 hours and then the mixture cooled to room temperature and stored until required.

The liquid mixture of resin, solvent, epoxide and halogenated phenol (and other additives if present) can be used as a coating solution or as an impregnant for the production of laminates. The solvent from the liquid mixture can also be evaporated and the residual product used as a moulding powder. This technique is preferred for the production of moulding powders containing long fibres, which may be broken in the dry mixing method. However preferably the liquid mixture ready for use as a coating or impregnant is a solution, free of any insoluble materials, such as undissolved flame retardant.

The liquid mixture, with or without solvent may be used as an encapsulant with heating if necessary if the solvent is absent.

The compositions of the invention are cured by heating usually at above 700C and preferably over 1000C e.g. 100--2500C such as lSO-1750C. Post curing if needed is usually carried out at l600C-2200C. The time needed for post-curing varies according to the properties of the desired product, and the temperature of use of that product.

For the use of the compositions of the invention for coating, the liquid mixture can be applied by any means to the surface to be coated e.g. by painting, spraying or immersion. Normally the surface will be of metal e.g. ferrous metal such as mild steel but other substrates such as wood, plastic material or inorganic material such as porcelain or cement can be coated, if desired. After coating the solvent is evaporated and the layer cured.

In the use of the compositions of the invention for making laminates, the liquid mixture is applied to the laminate base. Suitable laminate bases are glass cloth or carbon fibre agglomerates although other fibrous materials such as asbestos cloth may also be employed if desired. Such materials are impregnated with the mixture as described above and then dried. Typically the fibrous base is passed through a bath of the resin dispersion.

The fibrous material into which the resin has been impregnated is then usually subjected to a precure heat treatment at 100--1500C e.g. about 140"C, often for about 10 minutes. The laminates are then usually pressed at a temperature above 160"C often in the range 170 to 1900C at a pressure of from 7 to 105 kg/cm2, although pressures above 35 kg/cm2, often of about 70 kg/cm2 are normally employed. Normally pressing will be carned out for a period of at least 0.5 hours, e.g. 0.5--4 hours often for about an hour, depending upon the conditions of temperature and pressure employed.

For optimum results the laminates are subsequently post cured. The temperature and time employed for the post cure operations are dependent upon each other. For example a post cure in the temperature range 140-190 C may take at least 7 hours whereas one in the range 200-220 C may be accomplished in 1--5 hours. However, it is normally desirable that the material is heated to a temperature at least in the range 190--220"C e.g. at about 200"C.

The laminates may just comprise the fibrous base and the cured resin, but this invention is of particular use for preparing metal clad laminates e.g. copper clad laminates for use in making printed circuits. Especially important are multi-layer printed circuits with a layer of fibrous base and cured resin sandwiched between 2 layers of copper, and also laminate systems produced from such 3 layer laminates with further layers of copper and cured resin impregnated fibrous base.

The invention is illustrated in the following examples:- EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLES 1 ".

An aralkylene-phenol resin was prepared by heating together a molar proportion of 38% p-xylylene glycol dimethyl ether (about 65-70% pure) and 62% technical 4-methylcatechol (containing about 65-75% 4-methylcatechol and the rest substantially other dihydric phenols) in the presence of diethyl sulphate catalyst, as described in British Patent Specification No. 1305551. The analysis of the technical ether was (by weight) 70% p-xylylene glycol dimethyl ether; 5% pmethoxymethyl benzaldehyde; 10% p-methoxymethyl benzaldehyde dimethylacetal; 5% p-tolualdehyde; 2.5% p-methoxymethyl toluene; 2.5% ptolualdehyde dimethylacetal and 5% unknown.

286g of the above resin were mixed with 464g of a cycloaliphatic epoxide known as Araldite CY175 sold by Ciba Geigy Limited and of formula:

and 13g of 2-ethyl-4-methylimidazole, and an amount of methyl ethyl ketone as given below to give a resin solution. In some of the solutions flame retardant was also present in amount as given below.

Glasscloth ("Marglass" 116T with a P705 finish) ("Marglass" is a Registered Trade Mark) was impregnated with the above solution and the excess solvent evaporated. The impregnated glasscloth was cut into 25.4 cm squares which were precured at 160 C for 10 minutes. Laminates were prepared in each case by pressing 11 of the prepregs for 1 hour at 1750C under 35kg/cm2 pressure. The resin contents of the prepregs and the laminates were determined. In some cases the laminates were post cured in an oven at 2000C or 250"C. The flexural strength of the laminates were measured at 250C and 200"C. The degree of flame retardance in the laminate was found by measuring the oxygen index according to the method of ASTM 02863. The results were as follows: Fire Retardant (a) Ugine Diol 111 weight g % based on resin and epoxide and retardant weight (b) Tetrabromobis phenol A.g % based on resin and epoxide and retardant weight - % Br in total (c) Tris (di-bromopropyl) phosphate g % based on resin and epoxide and retardant weight Methyl ethyl ketone g % Resin in prepreg in laminate Oxygen index on laminate before post curing Post curing conditions Oxygen Index on laminate after post curing Flexural strength of laminate after post curing (if performed) Comparative Examples Examples

1 2 3 4 1 2 61 92 8% 12% 76 152 10% 20% 6% 12% 38 5% 385 430 385 385 465 600 43 41 44 43 47 42 36 22 41 39 37 41 36% 38% 5 hr at 200 C 5 hr at 200 C 30 hr at 30 hr at 5 hr at 200 C 5 hr at 200 C 200 C (a) 200 C (a) and up to and up to 250 C over 250 C over 10 hr (b) 10 hr (b) 30% (a) 26% (a) 28% 36% 41% (b) 29% (b) 30.5% laminate softened and relaxed when post cured Comparative Examples Examples

1 2 3 4 1 2 Measured at 25 C 85,000 psi 80,900psi 69,100 psi (6,000kg/cm) (5,690 kg/cm) (4,860 kg/cm) at 200 C 58,400 psi 60,300 42,900 (4,100kg/cm (4,240kg/cm (3,020 kg/cm) Notes:- A. In Comparative Examples 3 and 4, the laminates after post curing to stage (a) blistered when heated at 250 C.

B. Ugine Diol 111 sold by Ugine Kuhlmann has the formula

C. The tris (di-bromopropyl) phosphate was the low volatility grade LVT-T23P sold by Michigan Chemical Corp.

These results show that addition of flame retardant (a) did not alter the flame retardancy of the cured product over that without fire retardant, and gave a cured product without blisters only with difficulty. Addition of fire retardant (c) gave a laminate without strength at high temperature. Addition of flame retardant (b) of the invention gave cured laminates with high flame retardancy and substantial retention of the strength of the cured products at 25 C and 200 C.

EXAMPLES 3,4.

The experiments were carried out as in the previous Examples but with the following amounts: Example 3 Example 4 Example 5 Resin as in previous Examples g. 286 286 286 Epoxide as in previous Examples g. 599 704 464 246 tribromo phenol g. - 145 Tetrabromobisphenol A g. 225 330 2 Ethyl 4 methyl imidazole g. 19 24 12 Bromine in total 12 15 11 Methylethyl ketone g. 740 780 450 Oo Resin in Prepreg 35 39 44 % Resin in Laminate 32 35 29 Oxygen index on Laminate before post curing 41 46 35 Post curing conditions 2 Hours at 2000C 5Hours at 200 C 5 hours at 2000C Oxygen index on Laminate after post curing 42 46 40 Flexural strength of laminate after post curing measured at: 25 C 84,900 psi (5,970 kg/cm2) 86,700 psi (6,100 kg/cm2j 200"C 63,000 psi (4,430 kg/cm2) 61,900 psi (4,350 kg/cm2) 25 C - - 99,400 psi 200 C - - 63,100 psi EXAMPLE 5.

(a) Preparation of Resins A mixture of two aralkylene-phenol resins was prepared from tetrabromo bisphenol A (136g., 0.5 mole), technical 4-methyl catechol (124, 1.0 mole) and technical grade p-xylylene glycol dimethyl ether of the purity given above (166g., 1.0 mole) in the presence of diethyl sulphate (1.3 mole) as catalyst. The tetra bromobisphenol A and 0.28 mile of the ether were reacted first at 90-130 C over 1 hour to give a bromine containing resin and then the rest of the ether and the 4methyl catechol were added with reaction at 130180 over a further 30 minutes to make the other resin. At the end of the reaction, the resin mixture was allowed to cool whereupon it solidified.

(b) A solution was prepared containing the above resin mixture (200 g), the cycloaliphatic epoxide (200g), sold under the Registered Trade Mark "Araldite" CY175 2-ethyl-4-methyl imidazole (6.8g) and methyl ethyl ketone (267g). A sheet of glass cloth, sold under the trade name "Marglass" 116T/P705, was impregnated with the solution and the excess solvent evaporated. The impregnated glasscloth was cut into squares which were precured for 10 minutes at 1600C. A laminate was prepared by pressing 12 of the precured prepregs for 1 hour at 1750C under 35 kg/cm2 pressure. The resin content of the prepreg before pressing was 39.9% and of the laminate after pressing 38.9%. The laminate was postcured for 5 hours at 200 C. Its flexural strength after postcuring was 76,900 psi measured at 250C and 53,300 psi measured at 2000 C. The oxygen index of the postcured laminate was 41.5.

Claims (18)

WHAT WE CLAIM IS:

1. A resin composition which comprises (a) a resin having repeating units of the formula:

with terminal ArH (OH)2 groups wherein R' is a divalent mononuclear aromatic hydrocarbyl group, and Ar (OH)2 is a residue formed by removal of two nuclear hydrogen atoms from a dihydric phenol having at least two nuclear hydrogen atoms, (b) a cycloaliphatic epoxide containing at least two epoxy groups per molecule and (c) a brominated phenol, the molar proportion of epoxy groups in the epoxide to the total of phenolic hydroxyl groups in the resin and brominated phenol being in the range 0.5:1 and 2:1 and the percentage of brominated phenol is 324% (expressed as a percentage of the weight of bromine to the total weight of resin, epoxide and brominated phenol), the resin composition being in the absence of antimony oxide.

2. A composition according to Claim 1 wherein the brominated phenol contains 2--4 bromine atoms per atomic ring.

3. A composition according to Claim 2 wherein the brominated phenol is bis (4-hydroxy 3,5-dibromo phenyl) 2,2-propylidene.

4. A composition according to Claim 2 wherein the brominated phenol is a novolac resin formed by reaction of formaldehyde and a bromophenol.

5. A composition according to Claim 1 or 2 wherein the brominated phenol is an aralkylene phenol resin having repeating units of formula -CH2-R'-CH2-Ar'- and terminal Ar'(H) groups wherein R' is as defined in Claim 1 and Ar' represents a residue formed by removal of two nuclear hydrogen atoms from a monomeric brominated phenol having at least 2 nuclear hydrogen atoms and at least 1 hydroxyl group.

6. A composition according to any one of Claims 1-5 wherein the percentage of bromine is 6-18%.

7 A composition according to Claim 6 wherein the percentage of bromine is 12-15%.

8. A composition according to any one of Claims 1-7 wherein the epoxide is a cycloaliphatic epoxide having two epoxy groups, each fused to a cycloaliphatic ring.

9. A composition according to Claim 8 wherein the epoxide is of formula

10. A composition according to any one of Claims 1-9 wherein the resin is prepared by reacting one molar proportion of an aromatic diether or dihalide of formula R'(CH2OR)2 or R'(CH2X)2 wherein R is an alkyl group of 1-5 carbon atoms and X is a chlorine or bromine atom, with 1.42.0 molar proportions of a phenol of formula H2Ar(OH)2 which contains two phenolic hydroxyl groups.

11. A composition according to Claim 10 wherein the R' group is a pphenylene group.

12. A composition according to Claim 10 wherein the R' group is a phenylene group with at least one substituent selected from the group consisting of alkyl and phenyl.

13. A composition according to any of Claims 1-12 in solution in an organic solvent selected from ketones and mixtures thereof with alcohols.

14. A moulding composition according to any one of Claims 1-12 which contains a filler selected from the group consisting of asbestos flour, mica and chopped glass strands.

15. A method of producing a cured product which comprises heating a composition as claimed in any one of Claims 1-14 at 100-250 C.

16. A cured product obtained by curing a composition as claimed in any one of Claims 1-1 4.

17. A composition according to any one of Claims 2 and 5-14 wherein the bromophenol contains at least 2 hydroxyl groups per molecule.

18. A composition according to Claim I substantially a hereinbefore described in any one of Examples 1--5.