The present invention relates to fibre reinforced polymer composites and to a method for making such composites.

Fibre reinforced polymer composites are conveniently prepared by an in-mould polymerisation process in which a fibre filled polymerisable composition is polymerised/cured in-mould to yield the composite.

In one example of such a process, the fibrous reinforcement (which may be chopped strand mat, continuous filament mat, woven continuous filament mat or any other variation of mat) is placed in the open mould, the mould is closed and the polymerisable composition (resin) charged to the mould by applying a vacuum to the closed mould cavity to draw the composition into the mould, or by pumping the resin through, or by a combination of vacuum assisted pumping, or by applying a positive pressure to the reservoir from which the resin is transferred to the mould. The polymerisable composition then polymerises/cures in-mould under the action of a suitable catalyst system which initiates the polymerisation reaction, and after a suitable period of time (the cure time) the fibre reinforced polymer composite can be removed from the mould (demoulded). Alternatively, the fibrous reinforcement and the polymerisable composition may be placed in the open mould and the act of mould closure itself causes the composition to flow through the fibres. Where the above described techniques are used to make fibre reinforced composites it is, of course, necessary that the polymerisable composition has a viscosity which is low enough to enable it to flow through and wet out the fibres before any substantial polymerisation thereof has occurred.

Where loose, short fibres are to be employed as the reinforcement a further useful in-mould technique for preparing fibre reinforced composites involves first dispersing the fibres in the polymerisable composition and then charging the resulting dispersion to the closed mould cavity where the polymerisable composition cures.

Hitherto, the preparation of fibre reinforced polymer composites by in-mould processes has tended to result in composites having an unsatisfactory surface finish. In particular, the surface tends to be highly pitted, i.e. contains numerous holes. The presence of the holes is particularly noticeable when the surface of the fibrous composite is painted, as is sometimes required, and as a result it has proved necessary to fill in the holes before applying the top-coat paint layer. In practice, this has been achieved by first coating the fibre reinforced composite with a polymer based primer paint containing an inorganic filler which fills in the holes, and which after smoothing, e.g. by sanding, provides a surface which is suitable for application of the top-coat paint layer. However, this approach to preparing fibre reinforced composites having a painted finish of acceptable quality is far from ideal since it requires additional processing steps.

Further problems arise, particularly when the fibrous composite is not to be painted, in that the presence of the holes can lead to an increased retention of stains and also a reduction in the structural integrity of the fibrous composite due to the easier ingress of water or other fluids.

In view of these problems, there is a need for an in-mould polymerisation process which yields fibre reinforced polymer composites having an improved surface quality.

The present applicant has discovered an in-mould polymerisation technique for preparing fibre reinforced polymer composites which yields products having a markedly improved surface as characterised by substantially reduced pitting. The surfaces of the fibre reinforced composites prepared using this method often require little or no pre-treatment with a primer paint before application of the top-coat, furthermore their susceptibility to staining and/or fluid ingress may be also much reduced.

According to one aspect of the present invention there is provided a method for preparing a fibre reinforced polymer

composite which method comprises curing in-mould a fibre filled, fluid polymerisable composition having a polymerisable liquid component, characterised in that at least one of the mould parts defining the mould cavity in which the polymerisable composition is cured is movably located and during the curing process is pressed against the polymerisable composition which is thereby subjected to a mould pressure as it cures within the mould cavity.

The process of the present invention is particularly suitable for the fabrication of planar sheets and non-planar shaped articles, i.e. shaped articles such as moulded chair seats or kitchen sinks in which the thickness of the fibre reinforced polymer composite forming the article is small compared to the areal extent thereof.

The process of the present invention requires the use of a mould in which at least one of the mould parts defining the mould cavity is movably located. During the curing process the movable mould part is acted upon by mould part movement means which operates to press the said movable mould part against the polymerisable composition contained in the mould cavity. As a result, the polymerisable composition is subjected to a mould pressure and so a compressive force as it cures within the mould. The operation of the movable mould part also enables the mould to compensate for the shrinkage which occurs on curing the polymerisable composition, since the movable mould part will move under the action of the mould part movement means to take up the shrinkage. A typical moulding device comprises male and female mould halves which are separated by a compressible gasket. At least one of the mould halves is movably located and under the action of mould part movement means will press against the compressible gasket which allows for the transfer of a compressive force to the polymerising composition contained in the mould cavity provided by the mould halves and the gasket. The means for moving the movable mould part may be a hydraulic system, e.g. a hydraulic ram, or an inflatable gas bag. A particular type of moulding device is described hereinafter.

The polymerisable composition is typically subjected to a mould pressure in the range of from 130 KPa to 7000 KPa, and preferably in the range of from 300 KPa to 1400 KPa, as it cures within the mould. A convenient maximum for the mould pressure is around 500 KPa. The mould pressure is generally applied in the thickness direction of the article being moulded.

Various techniques may be employed to introduce the polymerisable composition and the fibrous reinforcement to the mould cavity. For example, where short loose fibres are to be employed as the reinforcement they may be blended into the polymerisable composition to form a fibre filled polymerisable composition which is then transferred to the closed mould cavity, e.g. by injection under pressure. The polymerisable composition should have a viscosity which is low enough to enable the fibres to be efficiently dispersed therein and to enable the resulting fibre filled composition to be transferred to the mould. Dispersion of the fibres in the polymerisable composition may be achieved using vigorous mixing techniques, e.g. by means of a high shear mixer.

However, the preferred fibrous reinforcement is a premade multi-fibre structure such as a mat, blanket or felt in which the fibres may be held together, for example, by weaving, knitting or merely by virtue of entanglement. Either continuous or discontinuous (short) fibres may form the premade multi-fibre structure. Where such a fibrous reinforcement is employed, it should be placed in the open mould. The mould may then be closed and the polymerisable composition transferred to the closed mould cavity via an entrance port, either by applying a vacuum to the said cavity to draw the composition into the mould or by pumping the resin through, or by a combination of vacuum assisted pumping, or by applying a positive pressure to the reservoir from which the resin is transferred to the mould. As stated hereinbefore, the polymerisable composition should have a viscosity which is low enough to enable it to flow through and wet out the fibres before any substantial polymerisation thereof has occurred. This means

that the polymerisable composition should preferably have a viscosity in the range of from 50 to 10,000 centipoise and preferably in the range of from 50 to 5000 centipoise, for example 50 to 1000 centipoise as measured at 20°C on a Brookfield viscometer.

The fibrous reinforcement may constitute from 0.5 to 60 Z by volume of the total volume of the fibre reinforced polymer composite. Any fibrous reinforcement may in principle be used, but the preferred fibres are inorganic fibres, especially glass fibres.

The polymerisable composition comprises a polymerisable liquid component. The preferred polymerisable liquids are the ethylenically unsaturated, addition polymerisable liquids comprising at least one ethylenically unsaturated, addition polymerisable monomer and optionally at least one other ethylenically unsaturated, addition polymerisable compound, such as an unsaturated oligomer and/or polymer species.

The at least one addition polymerisable, ethylenically unsaturated monomer may be selected from those monoethylenically and/or polyethylenically unsaturated monomers known in the art. Preferably, the at least one addition polymerisable, ethylenically unsaturated monomer is at least one monoethylenically unsaturated monomer or a mixture of such a monomer with at least one polyethylenically unsaturated monomers.

Preferred monoethylenically unsaturated monomers are the esters of acrylic and methacrylic acid with alcohols and phenols having the formula CH2"C(R)C0.0R ¹ where R is H or methyl and R ¹ is an optionally substituted alkyl, aryl, aralkyl or cycloalkyl group. Suitable substituents include halo and hydroxy substituents. Preferred monomers therefore include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, benzyl methacrylate, phenyl methacrylate, isobornyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. Particularly preferred monomers are the optionally substituted

alkyl methacrylates having the formula CH2=C(CH3)C0.0R ² where R ² is an optionally substituted, but preferably unsubstituted Cτ__ιo alkyl group.

Other suitable monoethylenically unsaturated monomers may be selected from the vinyl aromatic monomers such as styrene and the substituted derivatives thereof, e.g. the halo substituted styrenes and vinyl toluene.

Preferred polyethylenically unsaturated monomers are the polyethylenically unsaturated monomers having two or more acrylic or methacrylic double bonds such as ethylene glycol dimethacrylate, ethylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, 1,3-butylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, tri ethylolpropane trimethacrylate and trimethylolpropane triacrylate.

Examples of ethylenically unsaturated, addition polymerisable polymer species include the ethylenically unsaturated polyester resins.

A particularly preferred polymerisable liquid is an unsaturated urethane containing resin comprising: (i) an ethylenically unsaturated urethane composition containing at least one unsaturated urethane compound having an average double bond functionality (i.e. an average number of double bonds per molecule) of greater than 1.0; and (ii) at least one ethylenically unsaturated monomer which is a solvent for, and is copolymerisable with the unsaturated urethane composition.

The unsaturated urethane composition is preferably the product obtained from the reaction of a reactant mixture containing at least one hydroxyl containing vinyl monomer, at least one organic polyisocyanate or isocyanate functional derivative thereof having an average isocyanate functionality of at least 2.0 and optionally at least one saturated compound containing a plurality of isocyanate reactive groups.

In a preferred embodiment, the unsaturated urethane composition is a polyurethane polyacrylate and/or polymethacrylate

composition which is the reaction product of:

(1) at least one hydroxyalkyl acrylate and/or methacrylate compound;

(2) at least one polyisocyanate or isocyanate functional derivative thereof having an average isocyanate functionality of at least 2.0 and preferably greater than 2.0; and

(3) optionally at least one saturated polyol.

Where the polyurethane polyacrylate and/or polymethacrylate composition is derived from reactants (1) and (2), the proportions of the reactants can be varied within a wide range providing the final product has the requisite amount of ethylenic unsaturation. However, it is generally preferred to react all or essentially all the isocyanate groups to form urethane groups, which means that the amount of the hydroxyalkyl (meth)acrylate relative to the polyisocyanate or isocyanate functional derivative thereof should be such as to provide at least one mole of hydroxyl groups per mole of isocyanate groups. Excess (unreacted) hydroxyalkyl (meth)acrylate in the final product is in general not objectionable, since any such excess may be incorporated in the copolymer produced in the subsequent addition polymerisation reaction. In effect, any excess hydroxyalkyl (meth)acrylate will form at least a part of the copolymerisable solvent monomer.

Where the polyurethane polyacrylate and/or polymethacrylate composition is derived from reactants (1), (2) and (3), it is desirable to avoid the presence of unreacted polyol in the final product. Accordingly, it is preferred to employ the reactants in such amounts that the polyisocyanate or isocyanate functional derivative provides at least one mole of isocyanate groups per mole of hydroxyl groups provided by the hydroxyalkyl (meth)acrylate and the saturated polyol. Of course, the amount of the hydroxyalkyl (meth)acrylate employed in the urethanation reaction should be such as to provide the requisite amount of ethylenic unsaturation in the final product.

The hydroxyalkyl acrylate(s) and/or methacrylate(s) preferably contains from 2 to 4 carbon atoms in the hydroxyalkyl

group; 2-hydroxyethyl and 2-hydroxypropyl acrylates and methacrylates are especially preferred. Mixtures of two or more hydroxyalkyl acrylates and/or methacrylates may be used if desired.

Suitable saturated polyols for the manufacture of the polyurethane poly(meth)acrylate include those conventionally used in the art for producing polyurethanes by reaction of a polyol with a polyisocyanate. Preferably the polyol is a diol or triol, although we do not exclude the possibility that the polyol may contain more hydroxyl groups. Mixtures of two or more polyols may be used if desired.

Representative examples of suitable polyols are the glycols of formula HO-R-OH, where R represents, for example, an alkylene or polyalkylene ether chain, e.g. ethylene glycol, propylene glycol, butan-l,4-diol, pentan-1,5-diol, hexan-l,6-diol, diethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol and polytetrahydrofuran; dihydric phenols and bisphenols, for example, 2,2-bis(4-hydroxyphenyl) propane (Bisphenol A) and bis(4-hydroxyphenyl) sulphone (Bisphenol S), and alkoxylated derivatives of the bisphenols, for example the ethoxylated and propoxylated derivatives thereof.

Further suitable polyols include the triols such as glycerol, pentaerythritol, and trialkylolalkanes, for example trimethylolpropane, triethylolpropane and tributylolpropane, and alkoxylated derivatives of the trialkylolalkanes, for example the ethoxylated and propoxylated derivatives thereof.

The average isocyanate functionality of the polyisocyanate or derivative thereof (i.e. the average number of isocyanate groups per molecule) is at least 2.0 and preferably is greater than 2.0. In a more preferred embodiment, the average isocyanate functionality of the polyisocyanate or derivative thereof is at least 2.2 and preferably is in the range 2.5 to 3.0. A mixture of polyisocyanates or derivatives thereof having an average isocyanate functionality as specified herein may also be used.

The polyisocyanates may be of the aliphatic, alicyclic or aromatic type and may be selected from any of those polyisocyanates that are conventionally used in the art for the preparation of polyurethane polymers. Examples of aliphatic polyisocyanates include ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate and hexamethylene diisocyanate. Examples of alicyclic polyisocyanates include isophorone diisocyanate and 4,4-(di-isocyanato)-dicyclohexyl- methane. However, the preferred polyisocyanates are the aromatic type polyisocyanates in which the isocyanate groups are bonded to aromatic groups. Examples of aromatic polyisocyanates include, inter alia, 4,4'-diphenylmethane and 2, '-diphenylmethane diisocyanates, 2,4-tolylene and 2,6-tolylene diisocyanates and polymethylene polyphenyl polyisocyanates. Of these 4,4*-diphenylmethane diisocyanate, 2,4*-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanates and the commercially available mixtures thereof are preferred. Preferably the polyisocyanate is or includes a polymethylene polyphenyl polyisocyanate.

Polyisocyanate derivatives which may be used in the preparation of the unsaturated urethane composition include polyisocyanate functional compositions containing urethane, allophanate, urea, biuret, carbodiimi.de, uretonimine or isocyanurate groups. Such derivatives and methods for their preparation have been fully described in the prior art, such as the derivatives obtained from 4,4'-diphenylmethane and 2,4'-diphenylmethane diisocyanates and their mixtures with polymethylene polyphenyl polyisocyanates, for example the uretonimine modified polyisocyanates.

Particularly preferred polyisocyanate derivatives are the urethane-modified polyisocyanates, or prepolymers (hereinafter urethane polyisocyanates), having an average isocyanate functionality as defined above, and obtained by reacting an organic polyisocyanate(s) with the hydroxyl groups of a saturated polyol(s). An excess of the polyisocyanate is normally employed

so that the isocyanate functionality of the urethane polyisocyanate will be the same as or greater than the isocyanate functionality of the polyisocyanate used as starting material. Whichever particular polyol is used, the relative proportions of the polyol and polyisocyanate and/or the isocyanate functionality of the polyisocyanate are chosen so as to yield the required isocyanate functionality in the urethane polyisocyanate. If the urethane polyisocyanate is to be obtained from a diisocyanate and where it is desired that the urethane polyisocyanate has an isocyanate functionality of greater than 2.0, reaction of the diisocyanate with a polyol containing more than two hydroxyl groups will be necessary in order to yield a urethane polyisocyanate having the desired isocyanate functionality of greater than 2.0. The urethane polyisocyanate is preferably obtained by reaction of a polyol with a polyisocyanate having an average isocyanate functionality of greater than 2.0. The polyisocyanates and especially the preferred polyisocyanates mentioned above will generally be employed for the manufacture of the urethane polyisocyanate.

Suitable saturated polyols for the manufacture of the urethane polyisocyanate include those described above as being suitable for reactant (3) .

In preferred embodiments, the at least one unsaturated urethane compound has an average double bond functionality of at least 2.0, more preferably at least 2.2, and especially in the range of from 2.5 to 3.0. Preferably, the unsaturated urethane composition comprises from 0.05 to 0.5 moles, preferably from 0.1 to 0.5 moles, and more preferably from 0.2 to 0.5 moles of ethylenic double bonds per 100 g thereof. Unsaturated urethane compounds having the desired amounts of ethylenic unsaturation can be obtained by appropriate selection of the amounts and types of precursors which are used in the preparation thereof.

The unsaturated urethane resin also comprises at least one ethylenically unsaturated monomer which is a vehicle for, and is copolymerisable with the unsaturated urethane composition. The at

least one copolymerisable monomer may be selected from the ethylenically unsaturated, addition polymerisable monomers known in the art.

Suitable ethylenically unsaturated copolymerisable monomers include the acrylic and methacrylic acid ester monomers, the vinyl aromatic monomers and the poly(meth)acrylate monomers discussed supra.

Alkyl methacrylates, in particular methyl methacrylate, and mixtures thereof with styrene provide a particularly suitable copolymerisable solvent vehicle for the unsaturated urethane composition.

The unsaturated urethane composition preferably constitutes from 10 to 90 1 by weight, more preferably from 25 to 75 % by weight of the total weight of the unsaturated urethane composition and the copolymerisable monomer(s).

The at least one copolymerisable monomer may be simply added to the unsaturated urethane composition in order to form the unsaturated urethane resin. However, if the copolymerisable monomer is of a type which is inert in the conditions used to from the urethane composition, it is most desirable to utilise such as a liquid vehicle in which the unsaturated urethane composition is formed.

The unsaturated urethane resin may also comprise a co-reactive, ethylenically unsaturated polymer resin. For example, ethylenically unsaturated polyester resins may be incorporated into the unsaturated urethane resin in an amount up to 50 1 by weight, e.g. 10 to 50 2 by weight, based on the total weight of the unsaturated urethane composition, the copolymerisable monomer(s) and the polyester resin.

The unsaturated urethane composition may be prepared using techniques conventional in the art for the preparation of polyurethanes.

The preparation of the unsaturated urethane composition is preferably carried out in the presence of an inert liquid diluent. A wide range of diluents may be used, but most conveniently, in

order to avoid the need for separation of the unsaturated urethane composition, the diluent is a monomer which does not comprise any isocyanate reactive groups and which can therefore, after reaction of the urethane precursors, form at least a part of the copolymerisable solvent monomer(s). Examples of such monomers for use as the liquid diluent are the alkyl methacrylates, e.g. methyl methacrylate.

Where it is desired to include in the unsaturated urethane containing resin, an ethylenically unsaturated monomer(s) which contains an isocyanate reactive group(s), such monomer may be added after the reaction to form the unsaturated urethane composition is complete.

Catalysts which may be used in the reaction of the urethane precursors may be those known in the art of polyurethane production, for example tertiary amines and metal salts, e.g. tin (II) octoate and di-n-butyltin dilaurate.

A preferred unsaturated urethane resin is one which polymerises/cures to form a solid polymer matrix having a glass transition temperature (tan delta max) of at least 60°C, preferably of at least 80°C and more preferably of at least 100°C, e.g. 100 to 180°C.

The preferred polymerisable liquids have a viscosity, as measured at 20°C on a Brookfield viscometer, in the range of from 50 to 500 centipoise, since such liquids may be readily transferred to the mould and caused to flow through and wet out the fibrous reinforcement. Furthermore, polymerisable liquids having a viscosity within this range have the ability to contain large amounts of a particulate inorganic filler and still retain a viscosity which is workable in the process of the present invention. More preferably the polymerisable liquid has a viscosity in the range of from 50 to 400 centipoise and especially in the range of from 50 to 300 centipoise.

In addition to containing the fibre reinforcement, the polymer composite may also comprise a finely divided inorganic filler material. Appropriate combinations of filler material,

polymeriable liquids and other additives are as disclosed in British Patent Specification No 1493393, which is incorporated herein by reference.

Suitable fillers may include amphoteric, basic and silicaceous fillers, and may be of natural or synthetic origin. The filler, if amphoteric, may, for example, be an oxide of this type. Suitable such fillers include oxides and hydroxides of aluminium, including hydrated alumina. The filler, if basic, may, for example, be an oxide, a hydroxide, a carbonate or a basic carbonate. Suitable fillers of this type include, inter alia, the oxides, hydroxides, carbonates and basic carbonates of alkaline earth metals and of zinc. Suitable silicaceous fillers include, inter alia, substantially pure silica, for example sand, quartz, cristobalite and precipitated or fused silica, or the metal silicates or aluminosilicates. Further useful fillers may be selected from the metal aluminates, phosphates, sulphates, sulphides and carbides.

Preferably, the finely divided fillers for use in the invention have a mean particle size in the range of from 0.1 to . 250 microns and more preferably in the range of from 0.1 to 100 microns. In talking about the size of the particles we are referring to the size thereof across their largest dimension. The filler particles for use in the invention may have any form suitable for a filler, e.g. they may be of granular, fibrillar or laminar form.

In order to attain high filler loadings the filler may also consist of two or more sets of particles having widely differing mean sizes such that one set of particles can fit in the interstices of the other within the polymer matrix.

The polymerisable compositions may contain from 1 Z to 90 2 by volume of a finely divided filler material. Preferably, the amount of the filler (if included) is from 20 2 to 75 2 by volume, more preferably from 40 2 to 70 2 by volume, of the total volume of the polymerisable composition.

Where the filler is already available in the required

particle size, the filler particles can be dispersed in the polymerisable liquid using techniques such as roll milling or high shear mixing. A further suitable mixing technique involves dispersing the filler in a liquid component of the polymerisable liquid, e.g. in a portion of the liquid monomeric component, and then mixing the resultant dispersion with the remaining components of the polymerisable liquid. Alternatively, the finely divided particles may be produced directly in the presence of the polymerisable liquid, or in a liquid component thereof, by comminution of coarse particles. Comminution of coarse material to yield smaller size particles can be readily carried out using conventional ball mills, stirred ball mills or vibratory mills.

When the polymerisable composition comprises a finely divided inorganic filler it may also comprise a polymeric dispersant to assist the dispersion of the filler in the polymerisable liquid. Suitable polymeric dispersants include copolymers of methyl methacrylate with comonomers such as methacrylic acid or a metal salt thereof, dimethylaminoethyl methacrylate and quaternary ions or acid salts thereof, methacylamide, gamma-methacryloxypropyl trimethoxy silane, adducts of glycidyl methacrylate with polar-substituted aromatic acids such as p-aminobenzoic acid, and adducts of glycidyl methacrylate with gamma-aminopropyl trimethoxysilane.

Furthermore, the filled polymerisable compositions of the invention may comprise a coupling agent having active groupings to promote polymer matrix/filler particle bonding. Suitable coupling agents comprise one or more groups capable of interacting with groups in the particulate inorganic filler, and also one or more ethylenically unsaturated, addition polymerisable groups which can copolymerise with the constituents of the polymerisable liquid. Examples of such bonding agents are as follows: gamma-methacryloxypropyl trimethoxysilane gamma-aminopropyl trimethoxysilane gamma-glycidyloxypropyl trimethoxysilane vinyl triethoxysilane

vinyl triacetoxysilane vinyl trichlorosilane acrylic and methacrylic acids and their metal salts methacrylatochromic acid maleimidopropionic acid succinimidopropionic acid

4-aminomethylpiperidine tetraisopropyl and tetrabutyl titanates.

The polymerisable compositions may comprise one or more preformed polymers, for example one or more poly(alkyl)methacrylates such as polymethylmethacrylate, which may be in solution in the polymerisable liquid component or in a state of dispersion therein. Preformed polymers which function as low profile additives to reduce the shrinkage which accompanies the curing reaction, or which function as rubber modifiers to improve the impact resistance of the finally cured composites may be particularly useful additions to the polymerisable compositions. Where low profiling and/or impact modifying preformed polymers are incorporated in the polymerisable compositions, they may be added in amounts which are conventional in the art. Preformed polymers may also be incorporated in the polymerisable compositions as a thickening aid to increase the viscosity thereof.

The preformed polymer may be dispersed or dissolved in the polymerisable liquid component using vigorous mixing, e.g. as is provided by a high shear mixer. A further suitable technique involves mixing the preformed polymer in a liquid component of the polymerisable liquid, e.g. in a portion of the liquid monomeric component, and then adding the resulting monomer/preformed polymer dispersion or solution, with mixing, to the remaining components of the polymerisable liquid.

The polymerisable compositions may also incorporate other additives conventional in the art such as pigments, dyestuffs, internal mould release agents and polymerisation inhibitors.

The polymerisation/curing reaction may be initiated using polymerisation catalysts known in the art. The catalyst is

preferably added immedia.tely prior to curing the polymerisable compositions in the mould; this is particularly important where the catalyst is activated at temperatures below or around ambient. Where the polymerisable liquid comprises ethylenically unsaturated, addition polymerisable species, suitable catalysts may be selected from the organic peroxides, such as dioctanoyl peroxide and dibenzoyl peroxide which may be used in conjunction with an amine accelerator, e.g. N,N-dimethylaniline or N,N-dimethyl-para-toluidine; the hydroperoxides, such as t-butyl hydroperoxid ; the peroxydicarbonates, such as diisopropyl-peroxydicarbonate, and the peresters. In the case of the unsaturated urethane resins discussed supra, a particularly suitable catalyst system comprises an organic peroxide catalyst, in particular dibenzoyl peroxide, and an amine accelerator, in particular N,N-dimethylaniline or N,N-dimethyl-para- toluidine. The organic peroxide and amine accelerator may be added to separate portions of the unsaturated urethane resin which are then combined prior to the moulding process. Particular unsaturated urethane resins have been found to be stable in the presence of the organic peroxide catalyst or amine accelerator, which enables two urethane resins respectively containing the catalyst and accelerator to be formulated in advance and mixed immediately prior to moulding.

Where heat activated polymerisation catalysts are employed the mould should be heated, e.g. by a heat transfer fluid circulating within the mould parts defining the mould cavity, in order to activate the catalyst and initiate the curing reaction. The mould may also be heated where it is desired to subject the fibre reinforced polymer article prepared in the mould to an in-mould post-cure reaction.

It may be desirable during the filling of the mould to maintain the temperature of the mould surfaces below the temperature at which the catalyst is activated, so as to prevent premature polymerisation and gelation.

Prior to moulding, the internal mould surfaces may be coated

with a release agent to prevent adhesion of the cured article to the mould and to obtain a good surface finish. These techniques are well known in the art. Examples of suitable external mould release agents include, inter alia, polytetrafluoroethylene, silicone and polyvinylalcohol.

After the in-mould cure is complete, the fibre reinforced polymer article thus prepared may optionally be subjected to an in-mould post-cure, after which it is demoulded, or, alternatively, it may be demoulded immediately and then optionally subjected to a post-cure.

A preferred moulding apparatus for effecting the process of the present invention is now described in detail below in relation to the enclosed drawing.

Fig 1 is a schematic, cross-sectional view of the moulding apparatus.

The moulding apparatus depicted in Figure 1 comprises mould halves (1) and (2) which are separated by a compressible gasket (3). The mould halves and the compressible gasket together provide a mould cavity (4). Mould half (1) comprises an entrance port (5) for injection of a polymerisable composition into the mould cavity (4), and is retained in position by clamp arms (6) and (7) which are fixed to the base (8). Mould half (2) rests (without fixing) on set blocks (9) and (10) which are attached to the base (8). An inflatable gas bag (11) located between the mould half (2) and the base (8) provides for movement of the mould half (2) against a polymerisable composition contained in the mould cavity (4) and enables the mould to subject the said composition to a mould pressure and so a compressive force as it cures within the mould.

The internal profile of the mould halves and so the shape of the mould cavity will, of course, vary in accordance with the shape of the article to be moulded.

In one mode of operation a premade multi-fibre reinforcement is placed in the open mould, the mould is closed and the clamp arms (6) and (7) located in order to prevent upward movement of

the mould half (1). The gas bag is inflated by means of a gas pump (not shown) to a sufficient pressure to effect a seal between the mould halves (1) and (2) and gasket (3). The polymerisable composition is then injected into the mould cavity via entrance port (5) using a pump (not shown) so that it quickly flows through and wets out the fibrous reinforcement. The entrance port is then closed and the gas bag (11) further inflated to increase the mould pressure on the polymerisable composition curing within the mould. The shrinkage of the polymerisable composition during the cure is taken up by the mould half (2) which is lifted off the set blocks (9) and (10) by the pressure of the inflated gas bag. After a certain period of time, normally a few minutes, the cure is essentially complete and by deflating the gas bag (11) and removing the clamp arms (6) and (7), the mould half (1) may be lifted away and the cured fibre reinforced polymer article demoulded.

It will be appreciated that during the injection of the polymerisable composition into the mould cavity, means must be provided to allow for the expulsion of air from the mould cavity. Conveniently, such means comprises a plurality of fine diameter tubes which are laid lengthwise across the gasket (3) prior to closing the mould. It has been found that the presence of such tubes does not prevent the formation of the seal between the mould parts (1) and (2) and the gasket (3). The polymerisable composition is injected into the mould until it begins to exude from the tubes showing the mould cavity to be full. After the injection is complete, the tubes may then be removed and the curing process continued.

The invention is now illustrated, but not limited, by the following Example. Example

In the Example:- "Modar" (TM) 836S is an unsaturated urethane containing resin as described hereinbefore available from Imperial Chemical Industries PLC (ICI) .

Example 1

The moulding apparatus of the type depicted in Fig 1 was used to prepare a glass fibre reinforced plastic stadium seat having a nominal thickness of 4 mm and containing 18 2 by volume of the glass fibres. The internal mould surfaces were treated with a mould release agent (Freekote 44, ex Rotec Chemicals).

Four layers of continuous filament, glass fibre mat having a density of 450 g.m" ² were laid in the open mould and these layers were overlaid with a single layer of a continuous filament, glass fibre surface veil having a density of 60 g. ^-2 . Fine diameter tubes were place over the compressible gasket (a 12 mm diameter silicone tube) in order to provide for the expulsion of air from the mould cavity to the atmosphere during injection. The mould was then closed and prepared for injection of the polymerisable composition by inflating the air bag to a pressure of 20 lb.in" ² (about 138 KPa).

The polymerisable composition was formulated from Modar 836S unsaturated urethane resin and calcium carbonate filler (75 2 by weight on the weight of the Modar resin). A catalyst system comprising dibenzoyl peroxide (1.4 2 by weight on the weight of the Modar resin) and N,N-dimethylaniline (0.5 2 by weight on the weight of the Modar resin) was then added to the polymerisable composition, and the resulting composition was immediately injected into the mould using a pump pressure of 45 lb.in ^-2 (about 310 KPa). The injection was continued until the composition began to exude from the fine diameter tubes (about 1 minute). The tubes were then removed, the injection port closed and the air bag further inflated to a pressure of 70 lb.in" ² (about 483 KPa). One mould half was heated to a temperature of 30°C by means of a heat transfer fluid circulating around the inside thereof. The other mould half was similarly heated, but to a temperature of 50°C. As a result, the polymerisable composition cured more rapidly in the region adjacent the hotter mould half. 5 minutes after injecting the polymerisable composition into the mould, the fibre reinforced plastic seat was demoulded.

The seat had one particularly good face (i.e. the upper show face of the seat) which was then painted. A 600 cm ² (30 cm x 20 cm) sample was cut from the seat and the painted show face thereof examined for pin-holes using the naked eye. The show face of the 600 cm ² sample had between 100 and 150 pin-holes. Comparative Example

The polymerisable composition and glass fibre reinforcement described in Example 1 was used to make a glass fibre reinforced stadium seat by a standard casting technique. The polymerisable composition was not subjected to a mould pressure during the curing process. The seat was demoulded and the upper show face painted as before. A 600 cm ² sample was cut from the seat and examined for pin-holes using the naked eye. Many thousands of pin-holes were visible on the show face.