| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | January 11, 2000 |
| PATENT TITLE |
At least trifunctional epoxy resin reacted with solid rubber mixed with epoxy resin and curing agent |
| PATENT ABSTRACT |
A curable composition and a method of making it comprises reacting in the presence of a catalyst epoxy resin(s) having at least 0.05% by weight of epoxy resin oligomer with a solid rubber which is swellable or soluble in the reaction mixture and possessing at least 1% by weight of reactive groups, in a rubber:epoxy resin(s) weight ratio of between 1:1 and 1:20, wherein said epoxy resin(s) comprises (a) at least one epoxy resin having an epoxy functionality of greater than three and (b) at least one second epoxy resin having a functionality of greater than one but not more than three; heating to effect the reaction, cooling to substantially ambient temperature, and adding any remaining portion of epoxy resin and curing agent(s). |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | July 28, 1997 |
| PATENT CT FILE DATE | June 6, 1995 |
| PATENT CT NUMBER | This data is not available for free |
| PATENT CT PUB NUMBER | This data is not available for free |
| PATENT CT PUB DATE | December 14, 1995 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT CLAIMS |
We claim: 1. A curable composition comprising an epoxy resin system, wherein said epoxy resin system comprises: an epoxy resin comprising at least one first epoxy resin component and at least one second epoxy resin component, at least one curing agent for said epoxy resin, and a reaction product formed in situ by prereaction between a solid rubber and at least a proportion of said at least one first epoxy resin component in a rubber to first epoxy resin component weight ratio of between 1:1 and 1:20, wherein each of said at least one first epoxy resin component comprises monomers having an epoxy functionality of greater than 3 and at least 0.05 wt % of oligomers of said monomers, and wherein each of said at least one first epoxy resin component is independently a polyglycidyl derivative or an oligomer of a polyglycidyl derivative of at least one compound selected from the group consisting of aromatic diamines, aromatic monoprimary amines and aminophenols, wherein each of said at least one second epoxy resin component has an epoxy functionality of greater than 1 but no more than 3, and wherein said solid rubber has at least 1 wt % of reactive groups, and wherein said solid rubber is swellable or soluble in a reaction mixture in which said reaction product is formed. 2. A curable composition according to claim 1 wherein said rubber to first epoxy resin component weight ratio is between 1:2.5 and 1:17. 3. A curable composition according to claim 2 wherein said rubber to first epoxy resin component weight ratio is between 1:2.5 and 1:16.5. 4. A curable composition according to claim 1 wherein said second epoxy resin component is a polyglycidyl derivative or an oligomer of a polyglycidyl derivative of at least one compound selected from the group consisting of aromatic diamines, aromatic monoprimary amines, aminophenols, polyhydric phenols, polyhydric alcohols, and polycarboxylic acids. 5. A curable composition according to claim 1 wherein said first epoxy resin component is selected from the group consisting of monomers and oligomers of N,N,N.sup.1,N.sup.1 -tetraglycidyl diaminodiphenylmethane and N,N,N.sup.1,N.sup.1 -tetraglycidyl-bis (4-amino-3,5-dimethylphenyl)-1, 4-diisopropylbenzene, and combinations thereof. 6. A curable composition according to claim 5, wherein said first epoxy resin component is selected from the group consisting of monomers and oligomers of N,N,N.sup.1,N.sup.1 -tetraglycidyl diaminodiphenylmethane. 7. A curable composition according to claim 1, wherein said at least one curing agent comprises 4-4'-diaminodiphenylsulphone as a first curing agent, and said solid rubber comprises a solid acrylonitrile/butadiene/methacrylic acid rubber. 8. A curable composition according to claim 5, wherein said at least one curing agent further comprises dicyanodiamide as a second curing agent. 9. A curable composition according to claim 1, further comprising reinforcement fibers impregnated by said epoxy resin system. 10. A curable composition according to claim 9, wherein said reinforcement fibers comprise at least 20% by volume of the curable composition. 11. A curable composition according to claim 7, further comprising reinforcement fibers impregnated by said epoxy resin system. 12. A curable composition according to claim 11, wherein said reinforcement fibers comprise at least 20% by volume of the curable composition. 13. A curable composition according to claim 8, further comprising reinforcement fibers impregnated by said epoxy resin system. 14. A curable composition according to claim 13, wherein said reinforcement fibers comprise at least 20% by volume of the curable composition. 15. A prepreg comprising a curable composition according to claim 9. 16. A prepreg comprising a curable composition according to claim 10. 17. A prepreg comprising a curable composition according to claim 11. 18. A prepreg comprising a curable composition according to claim 12. 19. A prepreg comprising a curable composition according to claim 13. 20. A prepreg comprising a curable composition according to claim 14. 21. A process for making a curable composition according to claim 1 comprising forming a reaction mixture of said rubber, at least a proportion of said at least one first epoxy resin component, a catalyst capable of promoting a reaction between epoxy groups and the reactive groups of said rubber, and a polar solvent, wherein said rubber, said first epoxy resin component, and said catalyst comprise between 25 and 75 wt % of the reaction mixture, heating the reaction mixture to effect said reaction, cooling the resultant mixture to substantially ambient temperature and adding said second epoxy resin component, any remaining proportion of said first epoxy resin component, and said at least one curing agent to the resultant mixture and substantially removing the solvent therefrom. 22. A process according to claim 21 in which said rubber, said first epoxy resin component and said catalyst comprise between 35 and 65 wt % of the reaction mixture. 23. A process according to claim 21 in which said rubber, said first epoxy resin component and said catalyst comprise between 40 and 50 wt % of the reaction mixture. 24. A process according to claim 21 in which the mixture is heated to a temperature in the range 40.degree. C. to 80.degree. C., optionally under reflux. 25. A process according to claim 21 in which the catalyst is selected from the group consisting of alkyl triphenyl phosphonium iodide, bromide and chloride, wherein the alkyl is selected from the group consisting of methyl, ethyl, propyl, n-butyl, isobutyl, n-pentyl and n-decyl, triphenyl phosphine, stannous octoate, boron trifluoride. 26. A process according to claim 25 wherein the catalyst is ethyl triphenyl phosphonium iodide. 27. A process for making a curable composition according to claim 1 comprising forming a reaction mixture of said rubber, at least a proportion of said at least one first epoxy resin component, a catalyst capable of promoting a reaction between epoxy groups and the reactive groups of said rubber, and a polar solvent, wherein said rubber, said first epoxy resin component, and said catalyst comprise between 25 and 75 wt % of the reaction mixture, heating the reaction mixture to effect said reaction, adding to the reaction mixture said second epoxy resin component and any remaining proportion of said first epoxy resin component, cooling the resultant mixture to substantially ambient temperature, and adding said at least one curing agents to the resultant mixture and substantially removing the solvent therefrom. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
This invention relates to curable compositions. The use of curable compositions such as epoxy, cyanate, phenolic and like resins, both reinforced and unreinforced, has been known for a long time in a wide variety of commercial and military applications. Of particular importance is the use of such resins reinforced with continuous fibres, both unidirectional and woven, for structural applications such as aerospace vehicle parts such as aircraft tail assemblies and wing structures. Many such applications involve the use of multifunctional epoxy resins such as tetraglycidyl compounds cured using diamine hardeners. However, whilst composite materials made from these resins have a relatively high modulus and Tg, they are usually brittle. A number of approaches have been used to improve the mechanical properties of the resin systems both in the bulk resin system and in the interlaminar regions in laminated fibre-reinforced composite materials. Typically, to improve toughness, for example, these include the addition of rubbers, thermoplastics, particulate fillers, interlaminar tougheners etc, often in combination. Examples of toughened resin systems are to be found in U.S. Pat. No. 4,482,660, U.S. Pat. No. 4,500,660, U.S. Pat. No. 4,680,076, U.S. Pat. No. 4,783,506, U.S. Pat. No. 4,863,787, U.S. Pat. No. 4,977,215, U.S. Pat. No. 4,977,218, EP-A-71197 and EP-A-559437. Brief details of the disclosures of these documents is given below. U.S. Pat. No. 4,482,660 and U.S. Pat. No. 4,500,660 both disclose epoxy resin systems which are derived from epoxy resins, a reaction product of an epoxy resin and a butadiene/acrylonitrile copolymer having carboxylic groups and a curing agent such as dicyandiamide or 4,4-diaminodipnenylsulphone. Whilst there are no specific details disclosed, both documents suggest that using a reaction product of an epoxy resin and a solid rubber does not give rise to useful properties either in the curable composition or in the cured articles made therefrom. It is suggested that the viscosity of the curable composition can be adjusted by the addition of solid rubber particles, eg nitrile rubbers having carboxylic groups, thereto. U.S. Pat. No. 4,680,076 discloses a tough cured resin system having a phase-inverted morphology derived from a polyepoxy resin, an aromatic oligomer (ie thermoplastic), an aromatic diamine hardener and a reactive liquid rubber. U.S. Pat. No. 4,783,506 and U.S. Pat. No. 4,863,787 disclose a curable composition based on a polyepoxy resin, an aromatic oligomer, a diamine hardener for the epoxy resin and a reactive (eg carboxyl functionality) solid rubber, the latter being present as infusible particles having a median size between 10 .mu. and 75 .mu.. The conversion of the rubber into infusible particles is preferably achieved in situ by removing solvent from the epoxy/oligomer/rubber mixture whilst heating it. In using the composition to form fibre-reinforced composite materials, a large proportion of the particles are filtered by the fibres and remain on the prepreg surface to act as interlaminar toughening agents. Alternatively, the particles, presumably preformed, may be applied directly to the surface of the prepregs. U.S. Pat. No. 4,977,215 and U.S. Pat. No. 4,977,218 disclose similar resin systems to U.S. Pat. No. 4,783,506 and U.S. Pat. No. 4,863,787 but in which the infusible rubber particles are preformed, have a Tg above 15.degree. C., a size in the range 1 to 75 .mu. and comprise cross-linked carboxylated diene rubbers or carboxylated acrylic rubbers. Again, in using the composition to form fibre-reinforced composite materials, a large proportion, if not all, of the particles remain on the prepreg surface to act as interlaminar toughening agents. EP-A-71197 is primarily concerned with novel diamine hardeners for curable compositions but again discloses the use of what is termed flexibilizing agents or elastomeric compounds such as rubbers and thermoplastics. EP-A-559437 is concerned with a particular problem arising when fabricating honeycomb reinforcing structures which are covered with resin-impregnated fabrics; that is porosity in the fabrics which it solves by crushing the impregnated fabric to achieve a certain cover factor K.sub.p as defined therein. As EP-A-559437 discloses, the liquid rubber systems, whether present as added or as a reaction product or alone or together with a solid rubber, or solid rubber systems do not adequately overcome the problem of porosity. EP-A-559437 discloses crushing fabrics impregnated with a composition of epoxy resin, pre-curing agent and solid rubber either without reactive groups or with reactive groups. The preferred composition adds the solid rubber in a lightly cross-linked state. In these known resin systems, the toughening effect is achieved by the generation of relatively large, infusible rubber particles which phase separated from the epoxy resin during curing. When curable compositions which have pre-formed rubber particles, eg U.S. Pat. No. 4,977,215 and U.S. Pat. No. 4,977,218, are used to make prepreg materials, the fibres have a filtering effect on the particles which effectively limits the toughening effect of the rubber to the interlaminar regions of the composite materials. Consequently, the intralaminar properties of such composite materials are enhanced, as a result of the presence of the rubber toughening agent, to a considerably lesser extent. Furthermore, as discussed in relation to EP-A-559437, the fabrication of honeycomb and like load-bearing structures present particular difficulties. One such proposed application of honeycomb structures involves aerospace vehicle components, eg aircraft tail units, in which prepregs will be used to form a continuous skin over a honeycomb reinforcing member. Such structural components are required inter alia to have high low temperature tensile strength. As discussed above, EP-A-559437 proposes to overcome the problem of porosity by crushing the fabric. However, in all instances, it is necessary to use relatively low moulding pressures, eg approximately 0.3 MPa, to avoid crushing the honeycomb material. Consequently, the rheological properties of the curable compositions considered for such use are critical since too high a viscosity will prevent resin flow into air pockets under the applied pressure, and thus will entrap volatile vapour which will nucleate to form voids, and too low a viscosity will cause the resin to flow out of the fibres even under the modest pressure applied. The known proposed curable compositions discussed above have serious disadvantages when considered for such applications. For example, the use of thermoplastic tougheners results in a significant increase in the viscosity, and hence the elasticity, of the composition. The use of liquid rubbers alone does not significantly affect the viscosity, and hence the elasticity, of the compositions including them. The use of infusible particles alone has no significant effect on the viscosity of the composition and thus the elasticity is too low. The use of solid rubbers which are capable of cross-linking, ie when the infusible particles are formed in situ, results again in relatively high viscosity as the composition is heated sufficiently for the rubber to react. The use of lightly cross-linked solid rubbers, eg as in EP-A-559437, also gives rise to high viscosity compositions, hence the need to crush the fabric under high pressure to achieve high coverage. Additionally, in EP-A-559437, the use of non-reactive solid rubbers requires the use of special closely-woven fabrics and, again, hence the need to crush the fabric to achieve impregnation. Furthermore, in the crushed fabrics of EP-A-559437, the low pressures may result in poor bonding of the fabrics to the honeycomb structures by preventing sufficient flow of the composition to form adhesive fillets with the honeycomb walls. It is a primary object of the invention to provide curable compositions utilising a solid rubber wherein said compositions give rise to cured polymer matrices throughout which the rubber is substantially dispersed to give homogeneous or fine particulate morphology. It is also an object of the invention to provide such curable compositions in which the requisite rheological properties are generated for selected applications. The objects of the invention are achieved by the provision of a curable composition in which a solid rubber has been pre-reacted in situ with at least a proportion of an epoxy resin present in the composition. In particular, in accordance with the invention, a curable composition comprises epoxy resin having at least 0.05% by weight (based on said epoxy resin) of oligomeric epoxy species, at least one curing agent for said epoxy resin and a reaction product formed in situ between a solid rubber, which has at least 1 wt % of reactive groups and which is swellable by or soluble in a reaction mixture in which said reaction product is formed, and at least a proportion of said epoxy resin which includes said oligomeric species in rubber to epoxy resin weight of ratios between 1:1 and 1:20, wherein said epoxy resin comprises: (a) at least one first epoxy resin monomeric component having an epoxy functionality of greater than three, preferably at least four; (b) at least one second epoxy resin monomeric component having an epoxy functionality of greater than one but not more than three. By reacting the rubber with the epoxy resin components prior to the addition of the remaining components of the curable composition, it has been found that the resultant curable composition is substantially homogeneous to look at, ie the rubber is not visibly detectable. In matrices obtained by curing the compositions according to the invention, the morphology is generally homogeneous but, if the rubber is detectable, ie particulate morphology, it is as very fine particles, ie substantially less than 5 .mu. and, more especially, not more than 1 .mu.. Additionally, as will be discussed in greater detail below, the viscoelastic properties of the curable composition are controllable to enable impregnation and subsequent fabrication of structures such as fabric-reinforced honeycomb structures to occur. It has been found that the reaction producing the reaction product occurs primarily between the rubber and oligomeric epoxy species present in the epoxy resin. Provided such oligomeric species are present, the reaction product comprises either rubber reacted with at least a proportion of a mixture of both of said epoxy resin components; or, alternatively, rubber reacted with at least a proportion of one or other of said epoxy resin components. In a particularly preferred form of the invention, the reaction product comprises rubber reacted only with at least a proportion of said first epoxy resin component. The amount of such oligomeric species present in the epoxy resin is at least 0.05% by weight, preferably at least 0.5%. In practice, however, epoxy resin systems contain significant quantities of oligomeric species which are created during the manufacture of said resins. The minimum quantities of such oligomeric species quoted above are derived from consideration of stoichiometric requirements based on potential reaction mechanisms. However, the types of oligomeric species present in the epoxy resin may differ from resin to resin depending upon the manufacturing route and, consequently, higher quantities of oligomeric species (to ensure the presence of sufficient quantities of appropriate reactive species) may be required. Thus, in practice, based on commercially-available epoxy resins, it is preferred that the epoxy resin has at least 5% by weight, preferably at least 7.5% by weight and especially at least 15% by weight of oligomeric species. In making the reaction product, the rubber to epoxy resin weight ratios are between 1:1 and 1:20, preferably between 1:2.5 and 1:17 and especially between 1:2.5 and 1:16.5. Preferably, the epoxy resin components comprise glycidyl derivative of one or more of: aromatic diamines aromatic monoprimary amines aminophenols polyhydric phenols polyhydric alcohols polycarboxylic acids. Examples of such compounds, which are useful as said first epoxy resin component, are as follows: N, N, N', N'-tetraglycidyldiaminodiphenylmethane, eg "MY 9663" sold by Ciba-Geigy; N, N, N', N'-tetraglycidyl-bis(4-aminophenyl)-1,4-diiso- propylbenzene, eg Epon 1071 sold by Shell Chemical Co, viscosity 18-22 Poise at 110.degree. C.; N, N, N', N'-tetraglycidyl-bis(4-amino-3,5-dimethylphenyl)-1,4-diisopropylbenzene, eg Epon 1072 sold by Shell Chemical Co, viscosity 30-40 Poise at 110.degree. C.; gylcidyl ethers of phenol novolak resins, eg "DEN 438" sold by Dow, varieties in the low viscosity class of which are preferred in making compositions according to the invention and which are typically of formula: ##STR1## and gylcidyl ethers of bisphenol A novolak resins which are typically of formula: ##STR2## Particularly preferred for said first epoxy component is N, N, N', N'-tetraglycidyl diaminodiphenylmethane with an epoxide equivalent weight of 112 to 125.5. Examples of gylcidyl derivatives which are useful as said second epoxy resin component are as follows: digylcidyl ethers of bisphenol A based materials, eg DER 661 sold by Dow, which have the formula: ##STR3## triglycidyl ethers of 4-aminophenol (eg "MY 0510" sold by Ciba-Geigy), viscosity 0.55-0.85 Pa s at 25.degree. C.; diglycidyl ether of bisphenol A (eg "Epikote 828" sold by Shell), which has a viscosity 8-20 Pa s at 25.degree. C.; digylcidyl 1,2-phthalate, eg GLY CEL A-100. Particularly preferred for said second epoxy component are digylcidyl ethers of bisphenol A based materials having the formula given in the preceding paragraph and having an epoxide equivalent weight of 188 to 500. Preferably, at least two curing agents are used, the first of the curing agents being capable of reacting with epoxy groups and of promoting reaction between hydroxyl groups and epoxy groups. The curing agents are preferably an amino compound having a molecular weight up to 500 per amino group, for example an aromatic amine or a guanidine derivative. Particular examples suitable for use as the second curing agent are: dicyanodiamide, ie: ##STR4## available as Amicure CG 1200 from Pacific Anchor Chemical; 4-chlorophenyl-N,N-dimethyl-urea, eg Monuron; 3,4-dichlorophenyl-N,N-dimethyl-urea, eg Diuron. Preferably, said second curing agent is dicyanodiamide. Particular examples suitable for use as the first curing agent are: 3,3'- and 4,4'-diaminodiphenylsulphone; methylenedianiline; bis(4-amino-3,5-dimethylphenyl)-1,4-diisopropylbenzene available as EPON 1062 from Shell Chemical Co; and bis(4-aminophenyl)-1,4-diisopropylbenzene available as EPON 1061 from Shell Chemical Co. Preferably, said first curing agent is 4,4'-diaminodiphenylsulphone. The total amine content of the curing agent is in the range 70-110% of the stoichiometric requirement of the epoxy resin component. If desired, a catalyst for the epoxy resin component/curing agent reaction may also be used. If such a catalyst is used, it is typically a Lewis acid, for example boron trifluoride, conveniently as a derivative with an amine such as piperidine or methyl ethylamine. Alternatively it can be basic, for example an imidazole or amine. The rubber used to prepare the reaction product is selected from olefin, diene and nitrile rubbers and copolymers and terpolymers thereof which have pendant reactive groups, especially carboxylic groups. Particularly preferred are diene-nitrile copolymers having carboxylic groups. A particular preferred rubber is acrylonitrile/butadiene rubber having carboxylic groups. Preferably, the carboxylic groups are provided by a termonomer such as methacrylic acid. Preferably, the rubber contains at least 1 wt % preferably at least 2 wt % and more especially at least 2.25 wt % of carboxylic groups; and preferably upto 5 wt % carboxylic groups. The carboxylic group content is expressed as a weight % derived from the molecular weight of a carboxyl group divided by the molecular weight of the length of polymer chain to which it is attached expressed as a percentage. This translates as follows: 1 wt % is equivalent to 1 carboxylic group per 4500 M.sub.w (M.sub.w =weight average molecular weight of the polymer chain); 2 wt % is equivalent to 1 per 2250 M.sub.w ; 2.25 wt % is equivalent to 1 per 2000 M.sub.w. Particularly preferred rubbers are the acrylonitrile/butadiene/methacrylic acid rubbers available from Nippon Zeon under the trade name Hycar, especially Hycar 1472 (now available under the trade name NIPOL 1472) which has 3.75 wt % of carboxylic groups (ie 1 per 1200 M.sub.w). Preferably, the rubber has an M.sub.w of at least 30,000, preferably at least 100,000 and especially at least 150,000. Preferably, the rubber is soluble or at least highly swellable in the epoxy resin. Preferably, the curable composition comprises 1 to 20 wt %, preferably 1 to 10 wt %, and more especially 3 to 6 wt %, of rubber based on the total weight of epoxy resin, curing agent and reaction product in said composition. In the preferred curable composition according to the invention wherein said reaction product is rubber reacted with said first epoxy component, the curable composition comprises 4.0 to 8.0 wt %, more especially 4.5 to 7.0 wt %, of rubber based on the total weight rubber and said first epoxy resin component. In this instance, said reaction product may contain all of said first epoxy resin: alternatively, said reaction product may contain only a proportion of said first epoxy resin. The prereaction of the rubber with at least a proportion of said epoxy resin in situ enables a significant degree of control over the viscoelastic properties of the resultant curable composition to be exercised. The viscoelastic properties can be varied by varying the ratio of rubber to epoxy resin. As previously mentioned, the rubber to epoxy resin weight ratios of between 1:1 and 1:20, preferably between 1:2.5 and 1:17 and especially between 1:2.5 and 1:16.5 are to be used. Surprisingly, small variations in the rubber to epoxy resin ratio have a significant effect on the viscoelastic properties of the resultant curable composition. A measure of the viscoelastic properties of the curable composition is possible by determining the Theological properties of the composition especially the storage or elastic modulus, G'. This is determined as described below in the Examples. In the curable compositions used for those applications in which significant moulding pressure cannot be used, the G' minimum of the curable composition is controlled within the range 20 Pa to 200 Pa, preferably within the range 40 Pa to 160 Pa and, more especially, within the range 80 Pa to 110 Pa. The curable composition according to the invention may also contain other toughening agents such as thermoplastics optionally having reactive groups; other fillers such as fumed silica: aggregates, eg glass beads: polytetrafluoroethylene; graphite: boron nitride; mica; talc; vermiculite; nucleating agents; and stabilisers. However, such additional components will have an effect on the viscoelastic properties of the composition which has to be taken into account when formulating the reaction product. Preferably, the invention includes composite material comprising the curable composition according to the invention and fibre reinforcement. Although the fibres may be any suitable fibres such as glass, carbon or organic polymers, preferably, the fibres are carbon fibres, especially graphite fibres. Graphite fibres which have been found to be especially useful in the invention are those supplied by Amoco under the trade designations T650-35, T650-42 and T300; those supplied by Toray under the trade designation T800-HB; and those supplied by Hercules under the trade designations AS4, AU4, IM 8 and IM 7. The fibres may be short or chopped fibres, typically of mean fibre length not more than 20 mm, for example about 6 mm. Alternatively, and preferably, the fibres are continuous and may, for example, be unidirectionally-disposed fibres or a woven fabric, ie the composite material comprises a prepreg. Combinations of both short and/or chopped fibres and continuous fibres may be utilised. The fibres may be sized or unsized. The total of the aforementioned other toughening agents, fillers, aggregates etc in the curable composition and the fibre reinforcement of any composite material comprising said curable composition should be such that the curable composition or composite material contains at least 20% by volume of such materials and/or reinforcing fibres. The percentages of fibres and such other materials are calculated on the total composition after curing. The invention also includes composite materials comprising prepregs according to the invention laminated together by heat and pressure, for example by autoclave, compression moulding or by heated milers, at a temperature above the curing temperature of the curable composition. When the fibres of the reinforcement are continuous and unidirectional, the resulting multi-ply laminated composite material may be anisotropic in which the fibres are oriented essentially parallel to one another or quasi-isotropic in each ply of which the fibres are oriented at an angle, conveniently 45.degree. as in most quasi-isotropic laminates but possibly for example 30.degree. or 60.degree. or 90.degree. or intermediately, to those in the plies above and below. Orientations which are between anisotropic and quasi-isotropic, and combination laminates, may be used. Suitable laminated composite materials contain at least four, preferably at least eight, plies. The number of plies is dependent on the application for the laminated composite material, for example the strength required, and laminated composite materials containing thirty-two or even more, for example several hundred, plies may be desirable. There may be aggregates, as mentioned above, in interlaminar regions. When the prepreg comprises woven fabric, structures may be quasi-isotropic or between anisotropic and quasi-isotropic. The invention also includes a composite material comprising prepreg according to the invention laid up on at least one side, and preferably with both opposed sides, of a honeycomb reinforcing component such as Nomex honeycomb available from Hexel, optionally with an adhesive layer interposed between the prepreg and the honeycomb component. Also according to the invention, a process for making a curable composition as hereinbefore defined comprises forming a reaction mixture of said rubber, at least a proportion of said epoxy resin, a catalyst capable of promoting a reaction between epoxy groups and the reactive groups of said rubber and a polar solvent , said rubber, said epoxy resin and said catalyst comprising between 25 and 75 wt %, preferably between 35 and 65 wt %, more especially between 40 and 50 wt %, of the reaction mixture, heating the mixture to effect said reaction, cooling the resultant mixture to substantially ambient temperature and adding the remaining proportion, if any, of said epoxy resin and said first and second curing agents to the mixture and substantially removing the solvent therefrom. Preferably, the mixture is heated to a temperature in the range 40.degree. C. to 80.degree. C., preferably under reflux. The catalyst is preferably selected from the group consisting of alkyl triphenyl phosphonium iodide, bromide or chloride, wherein alkyl is methyl, ethyl, propyl, n-butyl, iso-butyl, n-pentyl or n-decyl, triphenyl phosphine, stannous octoate, chromium octoate, boron trifluoride, boron trifluoride monoalkyl (eg monoethyl) amine, especially ethyl triphenyl phosphonium iodide. Composite materials according to the invention which comprise continuous fibres are made by preimpregnating the continuous fibres with the curable composition prior to removal of the solvent to form prepregs and removing the solvent from the prepreg, said prepreg optionally being consolidated between nip rollers. The invention will now be illustrated by reference to the accompanying drawings and the following Examples. In the accompanying drawings: FIG. 1 is a graphical representation of resin viscosity for a number of epoxy resin samples; FIG. 2 is a graphical representation of G' minimum against resin viscosity of formulations using the resins shown in FIG. 1; FIG. 3 is a schematic drawing of a drumwinding mechanism used to prepare prepregs; FIG. 4 is a schematic cross-sectional drawing of a layup and tool used to prepare consolidated samples for testing; FIG. 5 is a schematic drawing of prepregging equipment used to prepare pregpregs; FIG. 6 is a schematic perspective drawing of a layup used to prepare consolidated honeycomb-reinforced samples for testing; and FIG. 7 is a schematic cross-sectional drawing of a layup and tool used to prepare the samples shown in FIG. 6. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
|
Want more information ? Interested in the hidden information ? Click here and do your request. |