GB1591324A

GB1591324A - Phenolaldehyde resin-impregnated composites

Info

Publication number: GB1591324A
Application number: GB28140/77A
Authority: GB
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1978-05-30
Filing date: 1978-05-30
Publication date: 1981-06-17

Description

(54) PHENOL-ALDEHYDE RESIN-IMPREGNATED COMPOSITES (71) We, CIBA-GEIGY AG, a Swiss Body Corporate of Basle, Switzerland, 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 a method for the production of reinforced composites from compositions which are photopolymerisable and thermosettable and from fibrous reinforcing materials, and to the composites obtained by this method. It is an improvement in, or a modification of, the invention described and claimed in our Patent Application No. 6527/76 (Specification No. 1522441).

Composite structures are commonly made by impregnating fibrous materials, such as fibres of paper, glass, an aromatic polyamide, or carbon, or metal filaments, or whiskers, usually in the form of layers, with a solution of a solid thermosettable resin in a volatile solvent and with a heat-activated curing agent for the resin, causing the resin to solidify by evaporation of the solvent, and, when desired, curing the resin composition in the resultant so-called "prepreg" by the action of heat. Frequently, the prepregs are stacked before heat-curing, so that a multilayer laminate is formed.

Composite structures may also be prepared from films of a thermosettable resin composition by the method described in British Patent Specification No.

1 299 177, which comprises laying a film of the resin composition on a fibrous reinforcement and applying heat and pressure so that the resin composition flows about the fibres but remains curable, and then heating further when desired so that the resin is cured by the heat-activated curing agent. This procedure is particularly convenient when unidirectional fibrous reinforcement is to be used, especially if the fibres are short and/or light, because there is less tendency for the fibres to become displaced and the reinforcing effect thereby become irregularly distributed.

Both these methods, however, suffer from certain drawbacks. If a solvent is used to dissolve components of the thermosettable resin composition it is not always possible to remove all traces of the solvent before heat-curing takes place, and in consequence the cured composite may contain voids caused by evaporation of residual solvent. Solvents may cause difficulties due to their toxicity or flammability or to pollution. If a film adhesive is used, it usually cast from a liquid thermosettable resin composition and this is then advanced to the solid state; such a process adds considerably to the cost of the composite. Both methods also require a considerable expenditure of heat energy, either to evaporate the solvent or to advance the resin.

In our aforesaid Application No. 6527/76 we describe a method by which fibrous reinforced composites containing a heat-curable resin ("prepregs") may be made without the inconveniences just mentioned of the prior art methods. The invention described and claimed in the aforesaid Application is a method for the preparation of prepregs which comprises i) impregnating a fibrous reinforcing material with a liquid composition containing both a thermosettable phenol-aldehyde resin and at least one photopolymerisable component (other than a phenol-aldehyde resin) and, if required, a heat-curing agent for the phenol-aldehyde resin, and ii) exposing the impregnated material to actinic radiation such that the said composition solidifies due to photopolymerisation of the said photopolymerisable component while the phenol-aldehyde resin remains substantially in the thermosettable state.

Composites prepared by that method are also described and claimed.

We have now found that fibrous reinforced composites containing a heatcurable resin may be made by another procedure and also without the inconveniences mentioned of the prior art. In this novel method, a liquid composition, comprising a thermally-curable phenolic resin and a photopolymerisable compound, is photopolymerised to form an essentially solid continuous film by exposure to actinic radiation, optionally in the presence of a catalyst for the photopolymerisation, but without thermally crosslinking it; the film so obtained is then contacted with fibrous reinforcing material, usually with the application of heat and/or pressure, such that a coherent structure is formed. The period of heating can be very short, as there need be no solvent to evaporate and the film need not be thick. It is not necessary to convert immediately the photopolymerised composition distributed on the fibrous reinforcing material into the fully cured, insoluble, and infusible C-stage; often, it can be changed into the still fusible B-stage, or remain in the A-stage, and, when desired, e.g., after the prepreg has been formed into some desired configuration, fully cured by heating to form the reinforced composite.

The present invention accordingly provides a method for the preparation of prepregs which comprises i) in the absence of a substance which gives rise to a substantial degree of photoinduced polymerisation of thermally curable phenolaldehyde resins, exposing to actinic radiation a layer of a liquid composition containing a thermally curable phenol-aldehyde resin, a photopolymerisable compound, and, if required, a heatactivated curing agent for the phenol-aldehyde resin, until the said composition solidifies to form an essentially solid continuous film due to photopolymerisation of the said photopolymerisable compound while the phenol-aldehyde resin remains substantially in the thermosettable state, and ii) bringing together the film so formed and fibrous reinforcing material under conditions such that the said film flows about the fibres, and the components of the said film and the fibres form a coherent structure but the phenol-aldehyde resin remains substantially thermally curable.

There are also provided prepregs prepared by the method of this invention.

Other aspects of this invention provide a method of preparing a reinforced composite which comprises heat-curing a photopolymerised, but still thermosettable, prepreg of this invention, and reinforced composites prepared by that method.

The reinforcement may be in the form of woven or non-woven cloth, unidirectional lengths, or chopped strands, and may be of natural or synthetic fibres, including strands and filaments, especially glass, boron, stainless steel, tungsten, silicone carbide, asbestos, an aromatic polyamide such as poly(mphenylene isophthalamide) or poly(p-phenylene terephthalamide), or carbon, or it may be whiskers of, e.g., potassium titanate.

Compositions used to prepare the films of the present invention must be liquid under the conditions used in making the films but are preferably solvent-free.

The phenol-aldehyde resins which are used may be any thermally curable resol or novolak prepared from a phenol and an aldehyde under acid or alkaline conditions. Suitable phenols include phenol itself, resorcinol, p-chlorophenol, alkyl-substituted phenols, such as cresols, xylenols, and tertiary butyl phenols, and aryl-substituted phenols, especially p-phenylphenol. The aldehyde which is condensed with the phenol is preferably formaldehyde, but other aldehydes such as acetaldehyde and furfuraldehyde may also be used. Novolaks are the preferred phenolic resins, especially those made from phenol itself and formaldehyde. If desired, a mixture of thermally curable phenol-aldehyde resins may be used.

The photopolymerisable compound used may be of any chemical type known to polymerise under the influence of actinic radiation. Such materials are described in, for example, Kosar, "Light-sensitive Systems: Chemistry and Applications of Non-Silver Halide Photographic Processes", Wiley, New York, 1965.

As is well known, these materials fall into two main classes (a) those which are polymerised through a free-radical chain reaction (photoinitiated polymerisation) and (b) those in which polymerisation is effected by reaction of an excited molecule of the monomer with an unexcited molecule of the monomer.

The first type require only one photopolymerisable group per molecule to form long chains on polymerisation while the second type must have at least two photopolymerisable groups per molecule, since if they have only one such group per molecule they will merely dimerise, not polymerise, on irradiation.

Photopolymerisable substances of the first type preferred for use in this invention have one ethylenic linkage, or more than one providing they are unconjugated. Examples of these substances are styrene and crotonic acid and, preferably, acrylic esters containing at least one group of the general formulae I, II, or III CH2=C(R)COO- I [CH2=C(R)CONH-]2-CHCOO- II CH2=C(R)CONHCH(OH)CH2COO- III where R is a hydrogen, chlorine, or bromine atom, or an alkyl hydrocarbon group of 1 to 4 carbon atoms, especially a hydrogen atom or a methyl group. More specific examples of preferred acrylates are neopentyl glycol diacrylate and those given below under formulae XVI to XX.

Photopolymerisable materials of the second type include those having at least two, and preferably three or more, groups which are azido, coumarin, stilbene, maleimide, pyridinone, chalcone, propenone, or pentadienone groups, or acrylic acid groups which are substituted in their 3-position by groups having ethylenic unsaturation or aromaticity in conjugation with the ethylenic double bond of the acrylic group.

Examples of suitable photopolymerisable azides are those containing at least two groups of the formula N3-R1- IV or N3-S02-R1- V where R' denotes a mononuclear or dinuclear divalent aromatic radical containing from 6 to at most 12 carbon atoms, especially a phenylene or naphthylene group.

Examples of suitable photopolymerisable coumarins are those containing at least two groups of the formula

where R2 is an oxygen atom, a carbonyloxy group (-COO-), a sulphonyl group, or a sulphonyloxy group.

Examples of photopolymerisable materials containing stilbene groups are those having at least two groups of the formula

where R3 is the residue, containing up to 8 carbon atoms in all, of a five or sixmembered nitrogen-containing heterocyclic ring, fused to a benzene or naphthalene nucleus, and linked through a carbon atom of the said heterocyclic ring adjacent to a nitrogen hetero atom thereof to the indicated benzene nucleus, such as a benzimidazolyl, benzoxazolyl, benzotriazolyl, benzothiazolyl, or a naphthotriazolyl residue.

Examples of photopolymerisable substances containing maleimide units are those having at least two groups of the formula

directly attached to a carbon atom or atoms, where each R4 is an alkyl group of 1 to 4 carbon atoms, a chlorine atom, or a phenyl group, and especially a methyl group.

Examples of photopolymerisable substances containing pyridinone units are those having, directly attached to carbon atoms, at least two groups of the formula

where R5 is an aliphatic or cycloaliphatic radical of 1 to 8 carbon atoms and a is zero or an integer of 1 to 4.

Examples of photopolymerisable compounds containing chalcone, propenone, or pentadienone groups are those containing groups of formula

where each R6 is a halogen atom, or an alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkoxy, cycloalkoxy, alkenoxy, cycloalkenoxy, carbalkoxy, carbocycloalkoxy, carbalkenoxy, or carbocycloalkenoxy group, such organic groups containing 1 to 9 carbon atoms, or is a nitro group, or a carboxyl, sulphonic, or phosphoric acid group in the form of a salt, a has the meaning previously assigned, R7 represents a grouping of formula

where R10 and R" are each individually a hydrogen atom, an alkyl group, e.g., of I to 4 carbon atoms, or an aryl group, e.g., of up to 12 carbon atoms, preferably a mononuclear group such as a phenyl group, or R'O and R" conjointly denote a polymethylene chain of 2 to 4 methylene groups, R12 and R'3 are each a hydrogen atom, an alkyl group, e.g., of 1 to 4 carbon atoms, or an aryl group, e.g., of up to 12 carbon atoms, which is preferably a mononuclear group such as a phenyl group, b and c are each zero, 1, or 2, with the proviso that they are not both zero, R8 represents a valency bond or a hydrogen atom, and R9 is an oxygen or sulphur atom.

Suitable 3-substituted acrylates contain at least two groups of the formula R'4CH=C(R)COO-- XV where R'4 is an aliphatic or mononuclear aromatic, araliphatic, or heterocyclic group, preferably of not more than 12 carbon atoms, which, as already indicated, has ethylenic unsaturation or aromaticity in conjugation with the ethylenic double bond shown, such as a phenyl, 2-furyl, 2- or 3-pyridyl, prop-2-enyl, or styryl group, and R has the meaning previously assigned.

Specific examples are disorbates and bis(2-furylacrylates) of poly(oxyethylene) glycols and poly(oxypropylene) glycols.

If desired, a mixture of photopolymerisable compounds may be used.

Especially preferred photopolymerisable compounds used in the process of this invention are, as already mentioned, neopentyl glycol diacrylate and esters of acrylic acid which are of any of the following general formulae XVI to XX.

Formula XVI is where

d is an integer of 1 to 8, e is an integer of 1 to 20, f is zero or 1, R15 denotes -H, -OH, or -OOCCH=CH2, and R16 denotes -H, -CH3, -C2H5, -CH2OH, or -CH2OOCCH=CH2.

Examples of compounds of formula XVI are triethylene glycol diacrylate and tetraethylene glycol. diacrylate.

Formula XVII is where

e, f, and R'5 have the meanings assigned above, g is zero or a positive integer, preferably of not more than 8, provided that f and g are not both zero, h is 1, 2, 3, or 4, R'7 denotes -H, -Cl, -CH3, or -C2, and R18 denotes an organic radical of valency h, linked through a carbon atom or carbon atoms thereof to the indicated h terminal oxygen atoms, preferably the hydrocarbon residue of an aliphatic alcohol containing from 1 to 6 carbon atoms, such as a methyl group or a pentaerythrityl group.

A specific example of a compound of formula XVII is 2-methoxyethyl acrylate.

Formula XVIII is

where f and h have the meanings previously assigned and R'9 denotes an organic radical of valency h, linked through a carbon atom thereof, other than the carbon atom of a carbonyl group.

More particularly, when fis zero, R'9 may denote the residue, containing from 1 to 18 carbon atoms, of an alcohol or phenol having h hydroxyl groups.

R'9 may thus represent, for example an aromatic group (which may be substituted in the ring by alkyl groups), an araliphatic, cycloaliphatic, heterocyclic, or heterocycloaliphatic group, such as an aromatic group containing only one benzene ring, optionally substituted by chlorine or by alkyl groups each of from 1 to 9 carbon atoms, or an aromatic group comprising a chain of two benzene rings, optionally interrupted by an ether oxygen atom, an aliphatic hydrocarbon group of 1 to 4 carbon atoms, or a sulphone group, each benzene ring being optionally substituted by chlorine or by an alkyl group of from 1 to 6 carbon atoms, or, preferably, a saturated or unsaturated, straight or branched-chain aliphatic group, which may contain one or more ether oxygen atoms and which may be substituted by one or more hydroxyl groups, especially a saturated or monoethylenically-unsaturated straight chain aliphatic hydrocarbon group of up to 8 carbon atoms.

Specific examples of such groups are the aromatic groups of the formulae -C6H5 and -C6H4CH3, in which case h is I, -C6H4C(CH3)2C6H4, and -C5H4C112C5H4-, in which case h is 2, and -C6H4(CM2C6H3-\-CH2C6H4- where i is 1 or 2, in which case h is 3 or 4, and the aliphatic groups of formula -CH2CHCH2- or -CH2CH(CH2)3C112-, in which case h is 3, of formula -(CH2)4-, -ClI2CH=CHCH2-, -CH2CH2OCH2CH2-, or -(CH2CH2O)2CH2CH2-, in which case h is 2, or of the formula -(CH2)3CM3, -(CH2)4OH, --CH,CH=CH,, -(CH2)2OH, -CH2CH(CH3)OII, or -CH2CH--CHCH2OH, in which case h is 1.

When fis 1, R'9 may represent the residue, containing from I to 60 carbon atoms of an acid having h carboxyl groups, preferably a saturated or ethylenicallyunsaturated, straight chain or branched aliphatic hydrocarbon group of from 1 to 20 carbon atoms, which may be substituted by one or more chlorine atoms or interrupted by one or more ether oxygen atoms and/or one or more carbonyloxy groups, or a saturated or ethylenically-unsaturated cycloaliphatic or aliphaticcycloaliphatic hydrocarbon group of at least 4 carbon atoms, which mav be substituted by one or more chlorine atoms, or an aromatic hydrocarbon group of from 6 to 12 carbon atoms, which may be substituted by one or more chlorine atoms.

Further preferred are such compounds in which R'9 represents a saturated or ethylenically-unsaturated straight chain or branched aliphatic hydrocarbon group of from 1 to 8 carbon atoms, optionally substituted by a hydroxyl group, or a saturated or ethylenically-unsaturated straight chain or branched aliphatic hydrocarbon group of from 4 to 50 carbon atoms and interrupted in the chain by one or more carbonyloxy groups, or a saturated or ethylenically-unsaturated monocyclic or dicyclic cycloaliphatic hydrocarbon group of 6 to 8 carbon atoms. or an ethylenically-unsaturated cycloaliphatic-aliphatic hydrocarbon group of from 10 to 51 carbon atoms, or a mononuclear aromatic hydrocarbon group of from 6 to 8 carbon atoms.

Specific examples of these residues of carboxylic acids are those of the formula -CH3, -CH2CH,, -CH2CH(OH)CH3, -CH2Cl, and -C6H6, in which case his 1, and -CH2CII2-, -CH=CH- and -C6H4-, in which case h is 2.

Specific examples of suitable compounds of formula XVIII are 1,4 - bis(2 hydroxy - 3 - (acryloxy)propoxy)butane, a poly(2-hydroxy-3-(acryloxy)propyl) ether of a phenol-formaldehyde novolak, l-(2-hydroxy-3-acryloxypropoxy)-butane, -n-octane, and -n-decane, bis(2-hydroxy-3-acryloxypropyl) adipate, 2-hydroxy-3 (acryloxy)propyl propionate, and 3-phenoxy-2-hydroxypropyl acrylate.

Formula XIX is R20C[CH2OOCCH=CHz] 3 where R20 denotes C113-, C2H5-, or CH2=CHCOOCH2-.

Examples of such acrylates are pentaerythritol tetra-acrylate and 1,1,1- trimethylolpropane triacrylate.

Formula XX is CH2=CHCOOR21 where R2' denotes either an alkyl group of 1 to 6 carbon atoms, optionally substituted by one hydroxyl group, such as an ethyl, n-propyl, n-butyl, 2hydroxyethyl, or 2-hydroxypropyl group, or a dialkylaminoalkyl group containing in all 3 to 12 carbon atoms, such as a diethylaminoethyl group.

The molar ratio of the phenol-aldehyde resin to the photopolymerisable compound is such that there is sufficient of each present to form both a satisfactory heat-curable prepreg and a satisfactory heat-cured composite. Usually the molar ratio is from 10:1 to 1:10, and especially from 5:1 to 1:5.

Preferably the photopolymerisable compound is irradiated in the presence of a photopolymerisation catalyst. Suitable catalysts are well known and are described in, for example, the book by Kosar cited above.

Like the photopolymerisable compounds, the catalysts fall into two main classes (a) those which, on irradiation, give an excited state that leads to formation of free radicals which then initiate polymerisation of the monomer (photoinitiators) and (b) those which, on irradiation, give an-.excited state which in turn transfers its excitation energy to a molecule of the monomer, giving rise to an excited molecule of the monomer which then crosslinks with an unexcited molecule of the monomer (photosensitisers).

The first class includes organic peroxides and hydroperoxides, a-halogen substituted acetophenones such as trichloromethyl 4'-tert. -butylphenyl ketone, benzoin and its alkyl ethers, e.g., the n-butyl ether, benzophenones, 0alkoxycarbonyl derivatives of an oxime of benzil or of 1 -phenylpropane- 1 ,2-dione, such as benzil (O-ethoxycarbonyl)a-monoxime and l-phenylpropane- 1,2-dione-2 (O-ethoxycarbonyl)oxime, benzil acetals, e.g. its dimethyl acetal, substituted thioxanthones, e.g., 2-chlorothioxanthone, anthraquinones, and mixtures of a phenothiazine dye (e.g., methylene blue) or a quinoxaline (e.g., metal salts of 2- (mor p-methoxyphenyl)quinoxaline-6'- or 7'-sulphonic acids) with an electron donor such as benzene sulphinic acid, toluene-p-sulphinic acid, or other sulphinic acid or a salt thereof, such as the sodium salt, an arsine, a phosphine, or thiourea (photoredox systems), these initiators being used with unsaturated esters, especially acrylates and methacrylates, and also acrylamides.

The second class includes 5 - nitroacenaphthene, 4 - nitroaniline, 2,4,7 trinitro - 9 - fluorenone, 3 - methyl - 1,3 - diaza - 1,9 - benzanthrone, and bis(dialkylamino)benzophenones, especially Michler's ketone i.e., bis(pdimethylamino)benzophenone.

Suitable photopolymerisation catalysts are readily found by routine experimentation. The catalyst must not, of course, give rise to a substantial degree of photoinduced polymerisation of the phenol-aldehyde resin, nor should any other substance present: further, it must not cause curing of the phenol-aldehyde resin such that the phenol-aldehyde resin is not substantially thermosettable after photopolymerisation.

Generally, 0.1 to 20%, and preferably 0.5 to 150/:,, by weight of the photopolymerisation catalyst is incorporated, based on the weight of the photopolymerisable compound.

In the photopolymerising step actinic radiation of wavelength 200--600 nm is preferably used. Suitable sources of actinic radiation include carbon arcs, mercury vapour arcs, fluorescent lamps with phosphors emitting ultraviolet light, argon and xenon glow lamps, tungsten lamps, and photographic flood lamps. Of these, mercury vapour arcs, particularly sun lamps, fluorescent sun lamps, and metal halide lamps are most suitable. The time required for the exposure of the photopolymerisable compound will depend upon a variety of factors which include, for example, the individual compound used, the type of light source, and its distance from the film. Suitable times may readily be determined by those familiar with polymerisation techniques, but in all cases the product after photopolymerisation must still be curable by heating: for this reason, photopolymerisation is carried out at temperatures below those at which heatcuring of the phenol-aldehyde resin becomes substantial.

Phenol-aldehyde novolaks are used, for preference, with as heat-activated curing agent, a substance liberating formaldehyde under the action of heat, such as paraform but usually hexamethylenetetramine. Resols may, if desired, be applied with a latent acid catalyst. Heat-activated curing agents are usually dissolved or suspended in the liquid composition before impregnation of the reinforcement.

Temperatures, and the amount of formaldehyde-liberator or latent acid catalyst, required for thermal curing are readily found by routine experimentation and are easily derivable by those skilled in the art from what is already well known concerning the heat-curing of phenolic resins.

The photopolymerisable, thermally curable compositions, including any heatcuring agent for the phenol-aldehyde resin and any photopolymerisation catalyst for the photopolymerisable component, are preferably applied to the reinforcing material so that the prepreg contains 20 to 80% by weight of the said composition and, correspondingly, 80 to 20% by weight of the reinforcement. More preferably, 30 to 50% by weight of the composition and 70 to 50% by weight of the reinforcement are employed.

Products made in accordance with the present invention may be in the form of flat sheets or shaped articles.

As already indicated, the components of the film are caused to flow about the fibrous reinforcing material by applying heat and/or pressure. Heated platens or pairs of rollers may be used, for example, and in the latter case, when unidirectional fibres are used, a rolling pressure may be applied in the direction of the fibre alignment. In place of pairs of rollers, the assembly may be passed under tension around part of the periphery of a single roller.

The film may be provided with a strippable backing sheet, e.g., of a polyolefin or a polyester, or of cellulosic paper having a coating of a silicone as release agent, on the face opposite to that brought into contact with the fibrous reinforcement.

Manipulation of the assembly is often easier if the film has a tacky surface. This may be produced by coating the film with a substance which is tacky at room temperature but which cures to a hard, insoluble, infusible resin under the conditions of heat employed to cure the phenol-aldehyde resin component of the film. However, an adequate degree of tackiness often exists without additional treatment.

Prepregs may be made by a batch process, the fibrous reinforcing material being laid on the film of the photopolymerised composition, which is advantageously under slight tension, when a second such film may, if desired, be laid on top and then the assembly is pressed while being heated.

Prepregs may alternatively be made continuously, such as by contacting the fibrous reinforcing material with the film of the photopolymerised composition then, if desired, placing a second such film on the reverse face of the fibrous reinforcing material, and applying heat and pressure. More conveniently, two such films, preferably supported on the reverse sides by belts or strippable sheets, are applied simultaneously to the fibrous reinforcing material so as to contact each exposed face. When two such films are applied, they may be the same or different.

Multilayer prepregs may be made by heating under pressure interleaved films and layers of one or more fibrous reinforcing materials.

When unidirectional fibres are used as the reinforcement material, successive layers of them may be oriented to form cross-ply prepregs.

With the fibrous reinforcing material there may be used additional (non fibrous) types of reinforcement, such as a foil of a metal (e.g., aluminium, steel, or titanium) or a sheet of a plastics material (e.g., an aromatic or aliphatic polyamide, a polyimide, a polysulphone, or a polycarbonate) or of a rubber (e.g., a neoprene or acrylonitrile rubber).

The following Examples illustrate the invention. Temperatures are in degrees Celsius and, unless otherwise indicated, parts are by weight. Epoxide contents were determined by titration against a 0.1N solution of perchloric acid in glacial acetic acid in the presence of excess of tetraethylammonium bromide, crystal violet being used as the indicator. All flexural strengths are the mean of three results and were determined according to BS 2782, Method 304B. "Resin-forming content" denotes the percentage of residue left after a 1 g sample of the material has been heated in a 5 cm diameter dish in an oven at 1200 for 3 hours at atmospheric pressure.

EXAMPLE 1 To 3,000 g of phenyl glycidyl ether (epoxide content 6.16 equiv./kg) containing 9 g of tetramethylammonium chloride and 6 g of 2,6-di-t-butyl-p-cresol, stirred at 100",was added 1,332 g of acrylic acid over one hour. The mixture was stirred at 100" for a further 4 hours, by which time the epoxide content had fallen to 0.91 equiv./kg, to yield substantially 3-phenoxy-2-hydroxypropyl acrylate.

This acrylate (30 parts) was mixed with 70 parts of a phenol-formaldehyde resol and 1 part of benzil dimethyl acetal. The resol had a resin-forming content of 90 /" and the molar ratio of phenol:formaldehyde was 1:1.43.

A film was made from this liquid composition by applying it as a coating 36 ssm thick on siliconised paper and irradiating for 5 minutes with a 400w high pressure metal halide quartz arc lamp providing radiation primarily in the 365 nm waveband.

The film was then used to glass cloth (epoxysilane finish, plain weave, 200 g/m2) at 1000 for 10 minutes under an applied pressure of 0.07 MN/m2.

A six-ply laminate was then prepared by pressing six 10cm-square pieces of the prepreg at 1700 for 1 hour at an applied pressure of 1.4 MN/m2. The laminate, which consisted of 60.5 /" by weight of glass fibres, had a flexural strength of 357 MN/m2.

WHAT WE CLAIM IS:- 1. A method for the preparation of prepregs which comprises i) in the absence of a substance which gives rise to a substantial degree of photoinduced polymerisation of thermally curable phenol-aldehyde resins, exposing to actinic radiation a layer of a liquid composition containing a thermally curable phenol-aldehyde resin, a photopolymerisable compound, and, if required, a heat-activated curing agent for the phenol-aldehyde resin, until the said composition solidifies to form an essentially solid continuous film due to photopolymerisation of the said photopolymerisable compound while the phenolaldehyde resin remains substantially in the thermosettable state, and ii) bringing together the film so formed and fibrous reinforcing material under conditions such that the said film flows about the fibres, and the components of the said film and the fibres form a coherent structure but the phenol-aldehyde resin remains substantially thermally curable.

2. A method according to claim 1, in which the phenol-aldehyde resin is a resol or a novolak from phenol, resorcinol, p-chlorophenol, an alkylsubstituted phenol or an aryl-substituted phenol.

3. A method according to claim 2, in which the alkylrsubstituted phenol is a cresol, a xylenol, or a tertiary butyl phenol, and the aryl-substituted phenol is pphenylphenol.

4. A method according to any preceding claim, in which the phenol-aldehyde resin is made from formaldehyde.

5. A method according to any preceding claim, in which the phenolaldehyde resin is a novolak employed in the presence of, as heat-activated curing agent therefor, a substance liberating formaldehyde under the action of heat.

6. A method according to claim 5, in which the formaldehyde-liberating substance is hexamethylenetetramine.

7. A method according to any preceding claim, in which the photopolymerisable compound is photopolymerised through a free-radical chain reaction.

8. A method according to claim 7, in which the photopolymerisable compound has one ethylenic linkage or, providing they are unconjugated, more than one.

9. A method according to claim 8, in which the photopolymerisable compound is an acrylic ester containing at least one group of formula CH2=C(R)COO- 1 or [CH2=C(R)CONH-]2-CHCOO- 11 or CH2=C(R)CONHCH(OH)CH2COO- 111 where R is hydrogen, chlorine, or bromine atom, or an alkyl hydrocarbon group of I to 4 carbon atoms.

10. A method according to claim 9, in which the photopolymerisable compound is neopentyl glycol diacrylate or of the formula

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. glass cloth (epoxysilane finish, plain weave, 200 g/m2) at 1000 for 10 minutes under an applied pressure of 0.07 MN/m2. A six-ply laminate was then prepared by pressing six 10cm-square pieces of the prepreg at 1700 for 1 hour at an applied pressure of 1.4 MN/m2. The laminate, which consisted of 60.5 /" by weight of glass fibres, had a flexural strength of 357 MN/m2. WHAT WE CLAIM IS:-

1. A method for the preparation of prepregs which comprises i) in the absence of a substance which gives rise to a substantial degree of photoinduced polymerisation of thermally curable phenol-aldehyde resins, exposing to actinic radiation a layer of a liquid composition containing a thermally curable phenol-aldehyde resin, a photopolymerisable compound, and, if required, a heat-activated curing agent for the phenol-aldehyde resin, until the said composition solidifies to form an essentially solid continuous film due to photopolymerisation of the said photopolymerisable compound while the phenolaldehyde resin remains substantially in the thermosettable state, and ii) bringing together the film so formed and fibrous reinforcing material under conditions such that the said film flows about the fibres, and the components of the said film and the fibres form a coherent structure but the phenol-aldehyde resin remains substantially thermally curable.

or R20CCHOOCCH-CH XIX R20C-[-CH,OOCCH=CH,]3 XIX or CH2=CHCOOR21 XX where d is an integer of 1 to 8, e is an integer of 1 to 20, fis zero or 1, g is zero or a positive integer, provided that f and g are not both zero, h is 1, 2, 3, or 4, R'5 denotes -H, -OH, or -OOCCH--CH2, R16 denotes -H, -CH3, -C2H5, -CH2OH, or -CH2OOCCH=CH2, R'7 denotes -H, -Cl, -CR3, or -C2H5, R18 denotes an organic radical of valency h, linked through a carbon atom or carbon atoms thereof to the indicated h terminal oxygen atoms, R'9 denotes an organic radical of valency h, linked through a carbon atom thereof other than the carbon atom of a carbonyl group, R20 denotes CH3-, C2H5-, or CH2=CHCOOCH2-, and R2' denotes either an alkyl group of 1 to 6 carbon atoms, optionally substituted by one hydroxyl group, or a dialkylaminoalkyl group containing in all 3 to 12 carbon atoms.

11. A method according to claim 10, in which R15 denotes the hydrocarbon residue of an aliphatic alcohol containing from I to 6 carbon atoms; and either fis zero and R19 denotes the residue, containing from 1 to 18 carbon atoms, of an alcohol or phenol, or fis 1 and R15 represents the residue, containing from 1 to 60 carbon atoms, of an acid having h carboxyl groups.

12. A method according to any of claims 1 to 6, in which the photopolymerisable component is photopolymerised by reaction of an excited molecule of the monomer with an unexcited molecule of the monomer.

13. A method according to claim 12, in which the photopolymerisable compound contains at least two groups which are azido, coumarin, stilbene, maleimide, pyridinone, chalcone, propenone, or pentadienone groups, or acrylic acid groups which are substituted in their 3-position by groups having ethylenic unsaturation or aromaticity in conjugation with the ethylenic double bond of the acrylic group.

14. A method according to claim 13, in which the photopolymerisable compound contains at least two groups of the formula N3-R1- IV or N3-SO2-R1- V where R' denotes a mononuclear or dinuclear divalent aromatic radical containing from 6 to at most 12 carbon atoms.

15. A method according to claim 13, in which the photopolymerisable compound contains at least two groups of the formula

where R2 is an oxygen atom, a carbonyloxy group, a sulphonyl group, or a sulphonyloxy group.

16. A method according to claim 13, in which the photopolymerisable compound contains at least two groups of the formula

where R3 is the residue, containing up to 8 carbon atoms in all, of a five or sixmembered nitrogen-containing heterocyclic ring, fused to a benzene or naphthalene nucleus and linked through a carbon atom of the said heterocyclic ring adjacent to a nitrogen hetero atom thereof to the indicated benzene nucleus.

17. A method according to claim 13, in which the photopolymerisable compound contains at least two groups of the formula

directly attached to a carbon atom or atoms, where each R4 is an alkyl group of 1 to 4 carbon atoms, a chlorine atom, or a phenyl group.

18. A method according to claim 13, in which the photopolymerisable compound contains, directly attached to carbon atoms, at least two groups of the formula

where R5 is an aliphatic or cycloaliphatic radical of 1 to 8 carbon atoms and a is zero or an integer of I to 4.

19. A method according to claim 13, in which the photopolymerisable compound contains, directly attached to carbon atoms, groups of the formula

where each R6 is a halogen atom, or an alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkoxy, cycloalkoxy, alkenoxy, cycloalkenoxy, carbalkoxy, carbocycloalkoxy, carbalkenoxy, or carbocycloalkenoxy group, such organic groups containing 1 to 9 carbon atoms, or is a nitro group, or a carboxyl, sulphonic, or phosphoric acid group in the form of a salt, a has the meaning assigned in claim 18, R7 represents a grouping of formula

where R'O and R" are each individually a hydrogen atom, an alkyl group, or an aryl group, or R'O and R11 conjointly denote a polymethylene chain of 2 to 4 methylene groups, R12 and R13 are each a hydrogen atom, an alkyl group, or an aryl group, and b and c are each zero, 1, or 2, with the proviso that they are not both zero, R8 represents a valency bond or a hydrogen atom, and R9 is an oxygen or sulphur atom.

20. A method according to claim 13, in which the photopolymerisable compound contains at least two groups of the formula R14CH=C(R)COO- XV where R14 is an aliphatic or mononuclear aromatic, araliphatic, or heterocyclic group, having ethylenic unsaturation or aromaticity in conjugation with the indicated double bond and R has the meaning assigned in claim 9.

21. A method according to claim 20, in which R14 denotes a phenyl, 2-furyl, 2or 3-pyridyl, prop-2-enyl, or styryl group.

22. A method according to any of claims 7 to 11, in which there is employed, as photopolymerisation catalyst for the photopolymerisable compound, one which, on irradiation, gives an excited state that leads to the formation of free radicals which then initiate polymerisation of the photopolymerisable compound.

23. A method according to claim 22, in which the photopolymerisation catalyst is an organic peroxide or hydroperoxide, an halogen substituted acetophenone, benzoin or an alkyl ether thereof, a benzophenone, an O-alkoxycarbonyl derivative of an oxime of benzil or of l-phenylpropane-l,2-dione, a substituted thioxanthone, an anthraquinone, a benzil acetal, or a mixture of a phenothiazine dye or of a quinoxaline with an electron donor.

24. A method according to any'of claims 12 to 21, in which there is employed, as photopolymerisation catalyst for the photopolymerisable compound, one which, on irradiation, gives an excited state which in turn transfers its energy to a molecule of the monomer giving rise to an excited molecule of the monomer which then crosslinks with an unexcited molecule of the monomer.

25. A method according to claim 24, in which the photopolymerisation catalyst is 5-nitroacenaphthene, 4-nitroaniline, 2,4,7-trinitro-9-fluorenone, 3-methyl- 1,3 diaza- 1 ,9-benzanthrone, or a bis(dialkylamino)benzophenone.

26. A method according to any preceding claim, in which the molar ratio of the phenol-aldehyde resin to the photopolymerisable compound in the composition is from 10:1 to 1:10.

27. A method according to claim 26, in which the said molar ratio is from 5:1 to 1:5.

28. A method according to any preceding claim, in which the fibrous reinforcing material comprises glass, boron, stainless steel, tungsten silicon carbide, asbestos, an aromatic polyamide, carbon, or whiskers of potassium titanate.

29. A method according to any preceding claim, in which the phendl-aldehyde resin and the photopolymerisable compound, together with any heat-curing agent for the phenol-aldehyde resin and any photopolymerisation catalyst for the photopolymerisable compound, constitute from 20 to 80 /" by weight of the prepreg.

30. A method according to any preceding claim, in which actinic radiation of wavelength 200-600 nm is used.

31. A method according to claim 1, substantially as described herein.

32. A method according to claim 1, substantially as described in the Examples.

33. Prepregs made by a method as claimed in any preceding claim.

34. A method of making a reinforced composite which comprises heat-curing a prepreg as claimed in claim 33.

35. Reinforced composites made by the method of claim 34.