GB2207675A - Curable epoxy resin compositions containing a dihydroxynaphthalene and optionally a diphenol as curing agent - Google Patents

Description

Curable epoxy resin compositions containing-a.diphenol andlor a

dihydroxynaphthalene 2 2 07 V? 5 The invention relates to hot-curable compositions of matter which are stable on storage and contain certain diand polyfunctiona 1 epoxy resins, diphenols and/or dihydroxynaphthalenes as curing agents and accelerators and to the use thereof for the production of moulded articles. in particular of prepregs for fibre-reinforced composite materials and of adhesive films.

Many curable epoxy resin compositions which, interalia, also contain phenolic curing agents are known. Thus, for example, Japanese published application 76/129,498 describes compositions of matter containing polyfunctional epoxy resins, phenolic curing agents and accelerators and also the use thereof for the production of prepregs for special electrical insulating materials. US 4,322,456 disclosesmixtures of epoxy resins, phenolic curing agents and accelerators for which the functionality of the epoxy resins and/or of the curing agents is preferably greater than 2 and which are suitable for the production of curable coatings, especially in the form of powder coatings. US.4,288,565 describes mixtures consisting of epoxy resins having high and low epoxy equivalent weights and of phenolic curing agents containing at least 30% of compounds having 3 or more hydroxyl groups per molecule.

US 4,216,304 describes liquid, curable epoxy resin compositions containing a glycidyl ether of a phenol novolak, said ether being liquid at room temperature and free of ester groups, 2,6-dihydroxytoluene as curing agent and curing accelerators.

German Offenlegungsschrift 2,807,666 describes liquid polymer mixtures containing a terminal carboxyl group-containing polymer, an epoxy resin, a plasticizer, a dihydroxy compound as curing agent for the epoxy resin and 2-ethyl-4-methylimidazole as curing accelerator. Bisphenols and dihydroxynaphthalene are, inter alia, also mentioned as dihydroxy k compounds. The terminal carboxyl group-containing polymer is preferably an elastomer and the polymer mixtures are employed for the production of rubber bladders-for balls.

US 3.661.828 describes moulding compositions containing a copolymer of glycidyl methacrylate, (meth)acrylonitrile and methyl methacrylate having an average molecular weight of about 1,500 to 16,000 and a diphenol as curing agent. The moulding compositions can also contain low molecular weight diepoxides as reactive diluents. Bisphenols and 2,7dihydroxynaphthalene are also mentioned as suitable diphenol curing agents.

The present invention relates to curable compositions of matter which are stable on storage containing a) 10 to 80 parts by weight of an epoxy resin having a functionality of at least 3, b) 90-20 parts by weight of an epoxy resin having a functionality of 2-2.5, c) a diphenol, the amount of the diphenol being chosen in such a way that 0.7-1.2 hydroxyl equivalents of the diphenol (c) are used per epoxy equivalent of the epoxy resins (a) and (b), and the diphenol consisting of (cl) 0-80% by weight of a compound of the formula 1 or II K" OH /-R (II) HO/ X\OH ' 1 in which T is the direct bond, methylene, isopropylidene. 0, S$ CO or SO 2 and R is hydrogen or C 1-C 4 alkyl, and (c2) 100-20% by weight of a dihydroxynaphthalene, and also d) 0.05-5% by weight, based on the epoxy resins (a) and (b), of an accelerator.

The compositions according to the invention are suitable for the production of moulded articles, prepregs and adhesive films, and the cured products are distinguished by outstanding thermal and mechanical properties, in particular by a high heat distortion resistance and a high flexural strength.

Furthermore,.the compositions have very good processing properties, for example a high homogeneity, a long pot life and a favourable tack, which is maintained even after relatively long storage at room temperature.

In addition, they are distinguished in particular by a low viscosity even at room temperature, so that they are particularly suitable for solventfree applications.

Possible epoxy resins (a) and (b) for the present compositions are all. those which have a functionality of at least 3 or of 2-2.5 and which can be cured by means of diphenols (c) in the presence of accelerators (d).

Epoxy resins having a functionality of 3 are to be understood as meaning, for example those resins which have, on average, 3 epoxy groups per molecule.

Suitable epoxy resins (a) and (b) are, for example di- or polyglycidyl ethers of cycloaliphatic polyols such as 2,2-bis(4'hydroxycyclohexyl)propane, di- or polyglycidyl ethers of polyhydric phenols such as resorcinol, bis(41-hydroxyphenyl)methane (bisphenol F), 2, 2-bis-(4'-hydroxyphenyl)propane (bisphenol A), 2,2-bis-(41-hydroxy-31,51dibromophenyl)propane, 1,1,2,2,-tetrakis(41-hydroxyphenyl)ethane, or condensation products of phenols with formaldehyde such as phenol novolaks and cresol novolaks; furthermore, di- or poly(o-methylglycidyl) ethers of the abovementioned polyalcohols and polyphenols; Polyglycidyl esters and poly(o-methylglycidyl) esters of polybasic carboxylic acids such as phthalic acid, terephthalic acid, tetrahydrophthalic acid and hexahydrophthalic acid; Glycidyl derivatives of amino phenols, for example triglycidyl p-amino phenol; N-Glycidyl derivatives of amines, amides and heterocyclic nitrogen bases such as N,N-diglycidylaniline, N,Ndiglycidyltoluidine, N,N,W,W- tetraglycidyl-bis(4-aminophenyl)methane, triglycidyl isocyanurate, N,N- diglycidyl-N,NI-ethyleneurea, N,N'-diglycidyl-S,S-dimethylhydantoin, N,NIdiglycidyl-5-isopropylhydantoin, N,N'-diglycidyl-5,5-dimethyl-6isopropyl5,6-dihydrouracil; Multifunctional epoxy resins such as the 2,6-disubstituted 4- epoxypropylpheny1glycidyl ethers and adducts thereof described in EP 205, 409 and EP 204,659; Bisphenols which are substituted by two glycidyloxy and-2,3-epoxypropyl groups each, for example 2,2-bis(3'-epoxypropyl-41-epoxypropylphenyl)- propane described in GB 828,364; Glycidyl derivatives of tetramethylol-substituted cyclohexanols, cyclo- hexanones, cyclopentanols and cyclopentanones such as the compounds described in US 4,549,008; Glycidyloxy-sub ' stituted benzophenones and glycidyloxy diketones such as the compounds described in US 4,649,181.

in general, mixtures of two or more epoxy resins can also be used as component (a) andlor as component (b) in the materials according to the invention.

Particularly suitable epoxy resins (a) and (b) are compounds which have an epoxide content of 5-11 equivalents/kg and are glycidyl ethers, glycidyl esters or N-glycidyl derivatives of'a cycloaliphatic, aromatic or heterocyclic compound. Particularly preferred epoxy resins (a) and (b) are epoxy novolaks or glycidyl derivatives of a bisphenol, a hydantoin or of a tetramethylolcyclohexane.

Suitable epoxy resins (a) are preferably glycidyl derivatives of hydantoins and in particular epoxy phenol novolaks or glycidyl derivatives of tetramethylolcyclohexanes. These compounds preferably have a functionality of 3 to 4. Suitable epoxy resins (b) are in particular epoxy f 1 phenol novolaks or glycidyl derivatives of bisphenol A or of bisphenol F. Preferably, these compounds have a functionality of 2 to 2.2.

Preferred compositions according to the invention are those in which the hydroxyl substituents of the compound of the formula 1 are in the 4, 4'position and the symbol T is 0, S, methylene or isopropylidene.- Further preferred compositions according to the invention are those in which the compound of the formula II is a dihydroxytoluene, in particular 2,6-dihydroxytoluene.

Component (c2) of the compositions of matter according to the invention is a dihydroxynaphthalene, for example 1,5-, 1,7-, 2,6- or 2,7dihydroxynaphthalene. Component (c2) is preferably 2, 6dihydroxynaphthalene and in particular 2,7-dihydroxynaphthalene.

Preferred compositions are those in which the diphenol (c) consists of 2060% by weight of component (cl) and 80-40% by weight of component (c2), and in particular those in which the diphenol (c) consists of 50% by weight of each of components (cl) and (c2). Particularly preferred compositions are those in which the diphenol (c) consists of 2,6dihydroxytoluene and 2,7-dihydroxynaphtlialene.

Particularly good results are obtained by mixing equal amounts by weight of these compounds in the melt at about 1800C, grinding the product obtained after solidification of the melt to a fine powder and then using this powder as the curing agent.

The present invention also relates to a curing agent for epoxy resins containing a compound of the formula I or II and a dihydroxynaphthalene.

If desired. the compositions of matter according to the invention can contain as curing agents also a certain amount of one or more tri- or polyphenols such as, for example 2,4,6-tris[21-(p-hydroxyphenyl)2'propyllbenzene ("tris-TC" from Mitsui Petrochemical) in addition to the diphenols (c). However, in general not more than 30% of the phenolic hydroxyl groups should come from-a tri- or polyphenol and the remainder of the hydroxyl groups should belong to a diphenol. In general, phenol or cresol novolaks are not suitable as phenolic curing agents of the compositions according to the invention. It goes without saying that in the case where not only diphenols but also tri- or polyphenols are used, the total amount of phenolic curing agent (c) is chosen in such a way that overall 0.7-1.2 hydroxyl equivalents of the phenols used per epoxy equivalent of the epoxy resins used are contained the composition according to the invention.

Suitable accelerators (d) of the curable compositions of-matter are all compounds which are known to a person skilled in the art for the acceleration of the crosslinking reaction of epoxy resins by means of phenolic curing agents, for example tertiary amines, salts thereof or quaternary ammonium compounds such as tetramethylammonium chloride, phosphonium salts, alkali metal alcoholates, for example sodium hexanetriolate, Lewis acids, for example BF3 or SnC14, and nitzogencontaining heterocycles such as pyridines, imidazoles and derivatives thereof. Particularly suitable accelerators (d) are imidazoles and Nacylimidazoles (imidazolides).

Examples of suitable imidazoles are compounds of the formula III R 3 /R2 HN \. /> 11 (III) in which Rl, R2 and R3 independently of one another are hydrogen, C,- C12alkyl, CS-Clocycloalkyl or C6-Cloaryl '. Preference is given in particular to 2-methyl-, 2-ethyl-, 2-phenyl- and 2-ethyl-4methylimidazole.

Suitable N-acylimidazoles (imidazolides) are, for example the compounds described in US 4,436,892, US 4,587,311 and Japanese published application 74/7,599. Particularly suitable compounds are those of the formula IV 3 2 Rs /R4 PK=C/11 R7 (IV), in which Rl to R3 are as defined above and R4 to R8 independently of one another are hydrogen, Cl-C12alkyl, halogen, nitro or trifluoromethyl. Examples of suitable imidazolides are 1-(21,41,6'-trimethylbenzoyl)- 2ethyllmidazole, 1-(21,61-dichlorobenzoyl)-2-methyl:Lmidazole, 1-(21,41, 61trimethylbenzoyl)-2-methylimidazole and 1-(214161-trimethylbenzoyl)2phenylimidazole.

In addition to components (a) to (d), the curable compositions of matter according to the invention can, if advantageous, also contain (e) 10-140, preferably 20-130, in particular 80-120 parts by weight, based on 100 parts by weight of components (a) to (c), of a thermoplastic having a glass transition temperature of at least 1800C. The cured products produced using the thermoplastic-containing compositions are distinguished by outstanding thermal and mechanical properties, in particular by a high heat distortion resistance, a high fracture toughness, flexural and impact flexural strength and also a very high extensibility.

Thermoplastics (e) which can be used in the curable compositions of matter according to the invention are all the known polymers which have a sufficiently high glass transition temperature, that is 1 1800C, and are miscible with the epoxy resin/curing agent system according to the application.

Based on their properties, thermoplastics employed are in particular polyamide imides, polysulfones or polyether sulfones and especially polyimides and polyether imides. Of these, preference is given in particular to thermoplastics having a glass transition temperature of 180 to 350, in particular from 190 to 250, OC. In the case where polyether imides are used, preference is given in particular to polymers having a Tg of 220 to 2500C and, where polyimides are used, preference is given to those having 1 a Tg from 280 to 3400C.

In the case where a polysulfone is used as the thermoplastic, suitable compounds are, in particular, those described in EP-A 194,232 as polysulfone component (c). These compounds are available, for example, under the name "Polysulfone Udel P1800", "Polysulfone 230W' or "Polysulfone 35OW' (from Union Carbide Corporation).

According to the invention, mixtures of two or more thermoplastics can also be used as component (e).

Particularly suitable thermoplastics (e) are polyimides'such as polyimides having phenylindane units such as have been described, for example in US 3,856,752 and in EP-A 92,524, in particular those having a glass transition temperature of about 3050C and an average molecular weight of about 65,000 such as, for example Matrimidw 5218 from CibaGeigy, - homopolyimides and copolyimides consisting of at least one aromatic tetracarboxylic acid and at least one aromatic diamine such as have been disclosed, for example, in US 4,629,777 and homopolyimides and copolyimides such as have been described, for example in EP-A 162,017, EPA 181,837 and US 4,629,685.

Preferred thermoplastics (e) are polyether imides, for example the products from General Electric which are available under the name UltemO (for example Ultem01000). Further preferred thermoplastics are polyether sulfones, for example Victrex PES 100 P from ICI or Udel P1800 from Union Carbide.

Suitable polyamide imides are, for example the compounds described in US 3,894,114, US 3,948,835, US 3,926,911 and US 3,950,408.

Components (a) to (e) used in the Compositions according to the invention are all known compounds and can be prepared by known methods.

Particularly preferred curable compositions according to the invention are those which contain 10 to 60 parts by weight of the epoxy resin (a), 90 to 40 parts by weight of the epoxy resin (b), an amount of the diphenol (c) such that 0.8-1.1, preferably 03-1.0, hydroxyl equivalents of the diphenol are used per epoxide equivalent of the resins (a) and (b), and 0.1-1% by weight of the accelerator (d), based on the amount of (a) and (b).

The compositions according to the invention can be made available by thorough mixing or dissolution of all components in one another, it being possible for the individual components to be added in different sequences. If the compositions also contain a thermoplastic, this can, for example, be dissolved in the epoxy resin and in the phenolic curing agent with heating and after cooling the accelerator and, if desired, more additives can be added. However. a solution of the thermoplastic in an inert solvent, for example methylene chloride, can be prepared and then mixed with the epoxy resin/curing agent composition.

The compositions according to the invendon can be used for many purposes and are suitable, for example as casting resins, laminating or impre ' gnating resins, moulding compositions, sealants, embedding and insulating compositions for electrical engineering and preferably as adhesives and as matrix resins for composite materials, in particular for the production of fibre-reinforced plastics.

If desired, in particular in the case where modifying agents are also used, the compositions according to the invention can be dissolved in an organic solvent such as toluene, xylene, methyl ethyl ketone, methylene chloride or a similar solvent or solvent mixture which is customary in the coatings industry. Such solutions are suitable in particular as impregnating agents or coating agents.

Before curing, the curable mixtures according to the invention can also be admixed at any time with customary modifying agents such as extenders, fillers, reinforcing agents, pigments, dyes, organic solvents, softeners, flow-improving agents, thixotropic agents, flame retardents or mould release agents. Extenders, reinforcing agents, fillers and pigments which can be used in the curable mixtures according to the invention are for example: - liquid cumarone/indene resins, textile fibres, glass fibres, asbestos fibres, boron fibres, carbon fibres, polyethylene powder, polypropylene powder, quartz powder, mineral silicates such as mica, asbestos powder, slate powder, kaolin, chalk powder, antimony trioxide, bentone, lithopone, heavy spar, titanium dioxide, soot, graphite, oxide colours such as iron oxide or metal powders such as aluminium powder or iron powder. In the case where the mixtures according to the invention are used for the production of prepregs, the addition of short fibres is particularly desirable.

For the practical use of the curable mixtures, especially in surface protection, it is possible to add as flow-improving agents, for example silicones, liquid acrylic resins, cellulose acetobutyrate, polyvinylbutyral, waxes, stearates and the like (which in some cases are also used as mould release agents).

Plasticizers which can be used for modifying the curable mixtures are, for example, dibutyl, dioctyl and dinonyl phthalate, tricresyl phosphate, trixylenyl phosphate and diphenoxyethyl formal.

The mixtures according to the invention are preferably cured by heating them to a temperature within the range from 120 to 2500C, in particular 160 to 2200C. The curing can be carried out in a known manner also in two or more stages, the first curing stage being carried'81ut at low temperature and the post-curing at a higher temperature.

if desiredy active diluents, for example neopentyl glycol ether, butane diol diglycidyl ether or hexanediol diglycidyl ether can be added to the curable mixtures to reduce their viscosity.

The present invention also relates to the use of the compositions according to the invention for the production of cured mouldings and also to the use for the production of prepregs for fibre-reinforced composite materials or for the preparation of adhesive films. The prepegs and the adhesive films can be prepared in a manner known per se, for example by 1 the impregnation process in the presence of one of the abovementioned solvents, of a halogenated solvent, for example methylene chloride, or by the so-called "hot-melt" process.

The moulding materials are in general distinguished by high glass transition temperatures in combination with high mechanical strength.

The Examples which follow illustrate the invention in more detail.

Components (a)-(e) used in the Examples which follow are the following:

Epoxy resin al: An epoxy phenol novolak of a functionality of 3.6 having an epoxide content of 5.6 equivalents/kg and a viscosity at 500C of about Pa.s.

Epoxy resin a2: Tetraglycidyl ether of 2,2,6,6-tetramethylolcyclohexanol (prepared according to Example 2 of US 4,549,008) having an epoxide equivalent weight of 129.

Epoxy resin a3: A triglycidylbishydantoin of the formula VI having an epoxide content of 5.6 equivalents/kg and a viscosity at 800C of about 13 Pa. s.

1 0\ H3 CH3 CH.3----CH-CH2-N./ I;N--CH.., H-CH2-N/ >-CH?-Ce 0 /CH? H3C \H,/0 1 (VI) HZ 0 / H \ HZ Epoxy resin bl: An epoxy phenol novolak liquid at room temperature of a functionality of 2.2 having an epoxide content of 5.7 equivalents/kg and a viscosity at 500C of 1.4 Pa.s.

Epoxy resin b2: A bisphenol F diglycidyl ether having an epoxide content of 6.1 equivalents/kg and a viscosity at 250C of 6.0 Pa.s.

Polyimide 1: A polyimide containing phenylindane units having a glass transition temperature of 3050C and an average molecular weight of about 65,000 (Matrimid05218, Ciba-Geigy).

Polyether imide 1: A polyether imide having repeating units of the f ormula k / - -Nl 1 p' \i 1 -0 3 Q__ J n and a glass transition temperature of 2190C (Ultem01000 from General Electric).

Polysulfone 1: Polysulfone Udel P18000 (Union Carbide Corporation) having a melting point in the range from 350 to 3700C, a heat distortion resistance (according to ASTM D 648),of 1751C, a glass transition temperature of 2000C and a molecular weight range of about 22)000-35,000.

Example 1:

a) 15 g of epoxy resin al and 85 g of epoxy resin bl are mixed at 1200C. At this temperature, 17.7 g of 2,6-dihydroxytoluene and 17.7 g of 2, 7dihydroxynaphthalene are added and dissolved with stirring. After cooling of the mixture to 800C, 0.1 g of 2-phenylimidazole is added. After cooling to room temperature, a solution of 81.2 g of polyimide 1 in 82 g of methylene chloride is added to the mixture, which is thoroughly stirred until a homogeneous mixture is obtained. The mixture is used to cast a film, 0.1 mm in thickness, on silicone-treated paper by means of a doctor blade, and the solvent Is evaporated at room temperature. Several film cuts, 30 x 30 mm, are placed on top of each other, compressed to a 1 mm thick moulding in a press at 1800C and cured at 1800C for 1 hour. The moulding has a T 9 (measured by means of thermomechanical analysis) of 1420C and a secondary transition at 1600C.

i b) Example la) is repeated except that 135.4 g of the polyimide 1 is used as the thermoplastic to give, after curing, a material having a measured T 9 of 153 and 1820C.

Example 2: Example la is repeated except that 44.7 g of polysulfone 1 are used as the thermoplastic to give, after curing, a material having a measured T 9 of 1640C and a presoftening at 960C.

Example 3:

a) 35 g of epoxy"resin C and 65 g of epoxy resin W are mixed at 1200C with 20.5 g of 2,6-dihydroxytoluene and 20.5 g of 2,7- dihydroxynaphthalene. 0.1 g of 2-phenyllmidazole is added to the mixture which is cooled to room temperature and to which are then added as described in Example 1 84.5 g of polyimide 1 in methylene chloride, after which the mixture is processed. After curing, the material has a measured T of 1940C and a 9 slight presoftening at 1040C.

b) Example 3a) is repeated except that 60.4 g of polyimide 1 are used to give a film moulding having a T 9 of 210 and 1050C. One portion of the film is used to bond together 2 Al sheets at 18o0C and the product is postcured at 2000C for 1 hour. The cured resin has a fracture toughness (GIC) of 794 i/m2, measured by the double-torsion experiment according to "Journal of Materials Science, 10, 1334 (1975) and 14, 776 (1979)". In this procedure, two aluminium sheets Extrudal 050 (AlMgSi 0.5), dimensions 200 x 20 x 5 mm. which have been treated with chromic sulfuric acid, are bonded using the curable mixture, and the bonded product is cured by applying a little pressure. This method measures the crack propagation in the bonded product, that is, the fracture energy in J/J is calculated from the maximum load for the crack propagation.

Example 4: 50 g of epoxy resin a3 and 30 g of epoxy resin U are mixed with 19 g of 2,6-dihydroxytoluene, 19 g of 2,7-dihydroxynaphthalene, 0.1 g of 2-phenyllmidazole and 138 g of polyether imide 1 as described in Example 1 and processed. After curing, the material has a measured T 9 of 1880C and slight presoftening at 1000C.

Example 5:

a) 35 g of epoxy resin a2, 65 g of epoxy resin b2, 22 g of 2, 6dihydroxytoluene, 22 g of 2,7-dihydroxynaphthalene, 0.1 g of 1-(21,41, 61trimethylbenzoyl)-2-phenylimidazole and 96 g of polyimide 1 are processed according to Example 3a. After curing for 1 hour at 1800C and for 1 hour at 2000C, the material has a measured T 9 of 2120C.

b) The experiment is repeated using 71 g of polyimide 1 to give a material having a measured T 9 of 2220C (slight presoftening at 100OC) and a fracture toughness GIC (double-torsion experiment) of 976 i/m2.

Example 6:

a) 15 g of epoxy resin al, 85 g of epoxy resin bl, 17.7 g of 2,6dihydroxytoluene, 17.7 g of 2,7-dihydroxynaphthalene and a solution of 0. 1 g of 2-phenylimidazole and 44.7 g of polysulfone 1 are processed as described in Example 1 and cured for 2 hours at 1800C. The cured moulding has a T 9 of 1640C and a presoftening at 960C.

b) The experiment is repeated using 80.4 g of polyimide 1 instead of the polysulfone to give a cured moulding having a T 9 of 1420C.

Example 7: 100 g of a mixture consisting of 35 parts by weight of epoxy resin al, 65 parts by weight of epoxy resin bl, 20.5 parts by weight of 2, 6-dihydroxytoluene, 20.5 parts by weight of 2,7-dihydroxynaphthalene, 0.2 parts by weight of 1-(21,41,61-trimethylbenzoyl)-2-phenylimidazole and 80. 4 g of polyimide 1 are processed as described in Example 1 and cured. The cured moulding has a T 9 of 1940C and a slight presoftening a t 1010C.

Example 8: 33.3 g of epoxy resin a2, 33.3 g of epoxy resin bl, 33.3 g of epoxy resin b2, 45.9 g of 2,7-dihydroxynaphthalene and 0.1 g of 2phenylimidazole are processed according to Example 1. The cured mouldings have the following properties:

Tg (TMA) Flexural strength (ISO 178) = 1220C 152 MPa Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) = 6-9 % = 38 kJ/M2 Example 9: a) 50 g of epoxy resin C, 50 g of epoxy resin b2, 21 g of 2,6dihydroxytoluene, 21 g of 2,7-dihydroxynaphthalene and 0.1 g of 2phenylimidazole are processed according to Example 1. The cured mouldings have the following properties:

T. (TMA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) = 1130C = 140 MPa = 12. 1 % = 68 M/M2 b) The experiment is repeated using 17.5 g of 2,6-dihydroxytoluene and 17. 5 g of 2,7-dihydroxynaphthalene as phenolic curing agent to give cured mouldings having the following properties:

T 9 (7MA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) 960c MPa >14 % 67 kJ/M2 Example 10:

a) 35 g of epoxy resin a2, 65 g of epoxy resin b2, 20.5 g of 2,6dihydroxytoluene and 20.5 g of 2,7-dihydroxynaphthalene are processed as described in Example 1. The cured mouldings have the following properties:

T 9 (TKA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) Fracture toughness (double-torsion experiment) = 1060C = 151 MPa = > 13 % = 91 M/M2 = 454 j/M2 Example ll: 15 g of epoxy resin al and 85 g of epoxy resin bl are heated to 1200C, a mixture of 17.7 g of 2,6-dihydroxytoluene and 17.7 g of 2, 7dihydroxynaphthalene is added and thoroughly mixed to form a homogeneous composition. After cooling to 800C 0.1 g of 2-phenylimidazole is added, and the composition is briefly evacuated to remove the air bubbles. The mixture has a viscosity at 700C of T1 310 mPa.s. A part of the mixture is used for the measurement of the fracture toughness by the double-torsion experiment. The larger part of the mixture is poured into moulds made from Extrudal 050 WM9Si 0.5), dimensions 80 x 60 x 4 mm and cured for 2 hours at 1400C and for 2 hours at 1800C. The following results were obtained:

T 9 (TMA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) Fracture toughness (double-torsion experiment) 1050C 128 MPa >14 % 8 6 kj/M2 = 726 jIM2 After storing the resin mixture for 2 weeks at room temperature, the resin still has a good tack.

Example 12:

a) Example 11 is repeated using 40.3 g of 2,7-dihydroxynaphthalene as curing agent to give mouldings having the following properties:

T 9 (THA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) = 1200C m 14 5 MPa = 13 % = 86 kj1m2 b) Example 11 is repeated using 20.3 g of bisphenol A and 20.3 g of 2,7dihydroxynaphthalene as curing agent to give mouldings having the following properties:

T 9 (TMA) 1 = 940C 1.

Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) Fraction toughness (double-torsion experiment) 12 5 MPa >14 % 83 kJ1m2 = 783 j/M2 Example 13: 50g of epoxy resin a3, 50 g ofepoxy resin bl, 42.1 g of 2,7- dihydroxynaphthalene and 0.1 g of 2-phenyllmidazole are processed according to Example 11 to give mouldings having th e following properties:

T 9 (TRA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexutal strength (ISO R 179) 1330C 158 MPa 12 % 5 3 M/M2 Example 14: 20 g of epoxy resin al, 20 g of epoxy resin a3, 60 g of epoxy resin b2, 19.5 g of 2,6-dihydroxytoluene, 19.5 g of 2,7- dihydroxynaphthalene and 0.1 g of 2-phenylimidazole are processed according to Example 11 to give mouldings having the following properties:

T 9 (TMA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) = 1070C = 153 MPa = > 14 % = 44 kJ/J Example 15: 15 g of epoxy resin al and 85 g of epoxy resin bl are heated to 1400C and mixed thoroughly. To this resin mixture are added with stirring 45 g of a mixture of 22.5 g of 4,41-dihydroxydiphenyl sulfone, 11.25 g of 2,6-dihydroxytoluene and 11.25 g of 2,7-dihydroxynaphthalene (cooled melt of the three diphenols). After cooling the mixture to 900C 0. 1 g of 2-phenylimidazole is added, and the mixture is poured into moulds of dimensions 80 x 60 x 4 mm. After curing for 16 hours at 1600C the following properties are measured on the mouldings:

T 9 (TMA) = 1130C 11 - 18 Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) = 14 8 MPa = 8.9 % = 2 7 kJ/m2 1 Example 16: Example 15 is repeated using the following mixture: a resin mixture of 35 g of epoxy resin a2 and 65 g of epoxy resin U and a mixture of 25.5 g of 4,4'-dihydroxydphenyl sulfone, 12.75 g of 2,6dihydroxytoluene and 12.75 g of 2,7-dihydroxynaphthalene. The cured mouldings have the following properties:

Tg (TMA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) = 1080C = 15 3 MPa = 8.1 % = 2 6 kj/m2 Example 17: To the resin mixture of Example 15 is added a mixture (solidified melt) of 20.25 g of 4,41-dihdroxybiphenyl, 10.125 g of 2, 6dihydroxytoluene and 10.125 g of 2,7-dihydroxynaphthalene. Processing according to Example 15 gives mouldings having the following properties:

T 9 (TMA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) = 1090C = 154 MPa = 12. 9 % = 72 kJ1m2 Example 18: To the resin mixture of Example 16 is added a mixture of 23. 25 g of 4,41-dihydroxybiphenyl, 11.625 g of 2,6dihydroxytoluene and 11. 625 g of 2,7-dihydroxynaphthalene. Processing according to Example 15 gives mouldings having the following properties:

T 9 (TMA) Flexural strength (ISO 178) Flexural elongation (ISO 178) Impact flexural strength (ISO R 179) m 1090C = 15 3 MPa 11. 2 % 7 8 kJ/m2 cl i Examples 19 - 20: Preparation of laminates Example 19:. 146.3 g of polyimide 1 are dissolved in 300 g of methylene chloride and t hen 40 g of epoxy resin a2 and 60 g of epoxy resin b-1 are added. To the homogeneous mixture is added dropwise a solution of 46.3 g of 2,7-dihydroxynaphthalene and 0.1 g of 2-ethyl-4-methylimidazole in 50 g of methyl ethyl ketone. This solution is used to impregnate a quasi unidirectional carbon fibre fabric (G 827, Brochier SA) with 3% by weight of glass fibres in the weft direction followed by drying at 500C for 16 hours. After treatment at 900C in a vacuum for 30 minutes, the prepregs (11 layers) are placed on top of each other and compressed at 2000C for 2 hours at 8 bar to give a laminate. The following results are obtained:

T 9 (TMA) Fibre content Interlaminar shear strength (ASTM 2344) = 2260C = 80.6% by weight = 60 MPa Example 20: Using the same solution as in Example 19, a unidirectional prepreg is prepared (resin content 37% by weight) from the carbon fibre T300 (Toray) by winding on a drum winder. After treatment at 900C and 50 mbar In a vacuum for 30 minutes, the prepregs (10 layers) are placed on top of each other and compressed for 1 hour at 2000 and 10 bar to give a unidirectional laminate. The laminate is postcured for 1 hour at 2000 and 1 hour at 2100C. The following values are measured:

T 9 (IRA) =2250C Flexural strength (parallel to the fibre) (ISO 178) = 1350 MPa Flexural strength (transverse to the fibre) (ISO 178) = 85 MPa Flexural elongation (parallel to the fibre) (ISO 178) = 1.3 % Flexural elongation (transverse to the fibre) (ISO 178) = 1.3 % Example 21: 149 g of polyether imide 1 are dissolved in 250 g of methylene chloride and then 50 g of epoxy resin a2 and 50 g of epoxy resin b2 k are added and the mixture is thoroughly mixed. After evaporation of the solvent down to about 10%, 49 g of 2,7-dihydroxynaphthalene and 0.1 g of 2-ethyl-4-methylimidazol dissolved in methyl ethyl ketone (50%) are added dropwise with vigorous stirring. This mixture is used to prepare a film on silicone paper which is dried for 12 hours at 500C (without vacuum) and 30 minutes at 900C in a vacuum. The film is then cut and compressed on a laboratory press at a compressing temperature of 2000C for 2 minutes to give a pure resin platelet. After complete curing in an oven at 2000C for 2 hours, the moulding has a T 9 (IRA) of 1600C.

1

Claims (17)

What is claimed is:

1. A curable composition of matter which is stable on storage containing a) 10 to 80 parts by weight of an epoxy resin having a functionality of at least 3, b) 90-20 parts by weight of an epoxy resin having a functionality of 2-2.5, a diphenol, the amount-of the diphenol being chosen in such a way that 03-1.2 hydroxyl equivalents of the diphenol (c) are used per epoxy equivalent of the epoxy resins (a) and (b), and the diphenol consisting of (cl) 0-80% by weight of a compound of the formula I or II OH H0/X =0/ \.X\ OH in which T is the direct bond, methylene, isopropylidene, 0, S, CO or SO 2 and R is hydrogen or C 1-C 4 alkyl, and (c2) 100-20% by weight of a dihydroxynaphthalene, and also d) 0.05-5% by weight, based on the epoxy resins (a) and (b), of an accelerator.

2. A composition according to claim 1 in which the epoxy resins (a) and (b) have an epoxide content of 5-11 equivalents/kg and are glycidyl ethers, glycidyl esters or N-glycidyl derivatives of a cycloaliphatic, an aromatic or a heterocyclic compound.

3. A composition according to claim 1 in which the epoxy resins (a) and (b) are epoxy novolaks or glycidyl derivatives of a bisphenol, a hydantoin or of a tetramethylolcyclohexane.

4. A composition according to claim 1 in which epoxy resin (a) has a functionality of 3 to 4 and is an epoxy phenol novolak or a glycidyl derivative of a hydantoin or of a tetramethylolcyclohexane.

5. A composition according to claim 1 in which epoxy resin (b) has a functionality of 2 to 2.2 and is-an epoxy phenol novolak or a glycidyl derivative of bisphenol Aor of bisphenol F.

6. A composition according to claim 1 in which the hydroxyl substituents of the compound of the formula I are in the 4,41-position and the symbol T is 0, S, methylene or isopropylidene.

7. A composition according to claim 1 in which the compound of.the formula II is a dihydroxytoluene.

8. A composition according to claim 1 in which component (c2) is 2, 6dihydroxynaphthalene or 2,7-dihydroxynaphthalene.

9. A composition according to claim 1 in which diphenol (c) consists of 50% by weight of each of components (cl) and (c2).

10. A composition according to claim 1 in which diphenol (c) consists of 2,6-dihydroxytoluene and 2,7-dihydroxynaphthalene.

11. A composition according to claim 1 in which accelerator (d) is an imidazole or an N-acylimidazole.

12. A composition according to claim 1 which in addition to components (a) to (d) also contains (e) 10-140 parts by weight, based on 100 parts by weight of components (a) to (c), of a thermoplastic having a glass transition temperature of at least 1800C.

13. A composition according to claim 12 in which thermoplastic (e) is a polyllnide, a polyether imide, a polyamide imide, a polysulfone or is a polyether sulfone and has a glass transition temperature of 180 -3500C.

14. A composition according to claim 1 containing 10 to 60 parts by weight of the epoxy resin (a), 90 to 40 parts by weight of the epoxy resin (b), an amount of the diphenol (c) such that 0.8-1.1 hydroxyl equivalents of the diphenol are used per epoxide equivalent of the resins (a) and (b), and 0.1-1% by weight of the accelerator (d), based on the S k amount of (a) and (b).

15. Use of a composition according to claim 1 for the production of cured mouldings.

16. Use of a composition according to claim 1 for the production of prepregs for fibre-reinforced composite materials or for the prepar ation of adhesive films.

17. Curing agents for epoxy resins containing a compound of the formula I or II according to claim 1 and a dihydroxynaphthalene.

Published 1988 at The Patent Office, State House. 66171 High Holborn, London WC1R 4TP. Further copies may be obtained frOM The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.