CA2065181C

CA2065181C - Epoxy resin mixtures, in particular for the production of prepregs with a long shelf life

Info

Publication number: CA2065181C
Application number: CA002065181A
Authority: CA
Inventors: Theobald Haug; Beat Muller; Martin Roth
Original assignee: Vantico GmbH
Current assignee: Huntsman Advanced Materials Switzerland GmbH
Priority date: 1991-04-08
Filing date: 1992-04-06
Publication date: 2002-12-03
Anticipated expiration: 2012-04-06
Also published as: KR920019867A; EP0508952A3; DE59205890D1; KR100218590B1; JP3163387B2; EP0508952A2; CA2065181A1; EP0508952B1; ES2085605T3; JPH06228283A

Abstract

Epoxy resin mixtures, in particular for the production of prepregs with a long shelf life Curable mixtures comprising (a) an epoxy resin, (b) a sulfonium salt of the formula (I), (II), (III) or (IV) (see formula I,II,III,IV) in which, in the formulae (I) to (IV), A is C1-C12alkyl, C3-C8cycloalkyl, C4-C10cycloalkylalkyl, or unsubstituted or substituted phenyl, Ar, Ar1 and Ar2, independently of one another, are each unsubstituted or substituted phenyl or naphthyl, arylene is in each case unsubstituted or substituted phenylene or naphthylene, and Q- is SbF6-, AsF6- or SbF5OH-, and (c) a stabiliser selected from certain aromatic amines having one to four NH2 groups with certain substituents in the ortho-position to each amino group, with the proviso that no amino group is substituted in both ortho-positions by halogen, or with a selected ortho- or para-substituent to each amino group, or selected from bipyridines, where 0.1-10% by weight of component (b) and 0.02-5% by weight of component (c), based on the epoxy resin (a), are present in the mixtures.

They are particularly suitable for the production of prepregs which have a long shelf life, are rapidly thermocurable and can be pressed to give laminates having excellent properties.

Description

Epox~resin mixtures, in yarticular for the production of prepregs with a long shelf life The invention relates to curable mixtures which comprise an epoxy resin, certain araliphatic sulfonium salts as initiators and certain amines as stabilisers, to prepregs and laminates obtainable using the mixtures, and to a process for the production of the laminates.
Epoxide-based laminates are generally produced using selected curing agent/acclerator combinations, for example the combination dicyandiamide/imidazole. The resin formulations must satisfy a number of requirements, some of which are difficult to combine with one another. Thus, for example, the prepreg should have a satisfactory shelf life and the matrix resin should cure rapidly in the compression mould.
Cationically curable mixtures containing sulfonium salts of the formulae (I) to (IV) mentioned below as initiators, and the use of the mixtures, inter alia, as impregnation, lamination and matrix resins are disclosed in EP-A-0 379 464. According to the teaching presented therein, the mixtures must not contain any amines so as to avoid interfering with the cationic curing with the sulfonium salts.
Although these mixtures enable rapid thermal curing of the matrix resin to give laminates having good properties, they do, however, have disadvantages. Thus, prepregs produced using solutions of these mixtures can only be dried at temperatures up to about 125°C if it is then desired to press the prepregs to give laminates. However, there is a risk at such low drying temperatures of any residual solvent which has not been removed from the prepreg material forming bubbles in the laminates during pressing and/or acting as a plasticises to lower the glass transition temperature (Tg) of the cured laminates in a disadvantageous manner. If, by contrast, the mixtures are applied without solvents at elevated temperature in the form of a melt, there is likewise a risk of such dense precrosslinking occurring that further processing to laminates of the prepregs produced in this way is no longer possible.
In addition, the shelf life of the matrix resin or of the prepregs produced using these resins may not be entirely satisfactory.

Surprisingly, it has now been found that the addition of small amounts of certain amines to the previously known epoxy resin mixtures has a stabilising action on the mixture, so that the temperature of the mixtures during the production of prepregs can be greatly increased.
The above-outlined disadvantages do not occur or only occur to an extremely small extent when the novel mixtures are used, and a rapid curing of the laminate material takes place during thermal pressing of the prepregs to give laminates. Furthermore, the addition improves the shelf life of the mixture and of prepregs produced therefrom.
The invention therefore relates to curable mixtures comprising (a) an epoxy resin, (b) a sulfonium salt of the formula (I), (II), (III) or (IV) Ar2 A

S ~ Q (I)~ , S~' Q~ (II)s CH2 CI-I2 CHZ ~ CHI
r r Ar Ir t Ar Ar Q (III) and A, S+- CH2 arylene CH2 S ~ A

Ar Ar CH2 S'~ CH2 arylene CHI- S'~' ~ 2 Q-Ar in which A is Gt-C~2alkyl, C3-Cgcycloalkyl, C4-Clpcycloalkylalkyl, phenyl which is unsubstituted or monosubsdtuted or polysubstituted by Cg-CBalkyl, Cl-C4alkoxy, halogen, hydroxyl, nitro, phenyl, phenoxy, alkoxycarbonyl having 1-4 carbon atoms in the aIkoxy radical or acyl having 1-12 carbon atoms, Ar, Arl arid Ar2, independently of one another, are each phenyl or naphthyl which is unsubstituted ar monosubstituted or polysubstituted by Ct-C8alkyl, Ct-C4alkoxy, halogen, hydroxyl; vitro, phenyl, phenoxy, alkoxycarbonyl having 1-4 carbon atoms in the alkoxy radical or aryl having 1-12 carbon atoms, arylene is in each case phenylene or naphthylene which is unsubstiW ted or monosubstituted or polysubstituted by Ct-CBalkyl; Cl-C4alkoxy, halogen, hydroxyl, vitro, phenyl;
phenoxy, alkoxycarbonyl having 1-4 carbon atoms in the alkoxy radical or acyl having I-12 carbon atoms, and Q- is SbF~~, AsFs or SbF50H-, and (c) a stabiliser selected from the group comprising (c1) aromatic amines having a pKa value of 2-5 and having one to four NH2 groups with at least one substituent in the ortho-position to each amino group, the substituent being Ct-Ctpalkyl, Ct-Ctpalkoxy, CS-Cbcycloalkyl, C6-Ctparyl or halogen, with the proviso that the amine is not substituted in both ortho-positions to an amino group by halogen, or (c2) aromatic amines having a pKa value of 2-S and having 1 to ~1 NH2 groups with an ortho- or para-substituent to each amino group, the substituent being -COOH, -COOK, -COR, -S02R or -SOR where R is Ct-Ctpalkyl, CS-C6cycloalkyl, C6-Ctovyl, aminoaryl or -R'-OOC-C~H4-NH2 where R' is alkylene, or (c3) bipyridines, where 0.1-10% by weight of component (b) and 0.02-5% by weight of component (c), based on the epoxy resin (a); are present in the mixture.
The mixtures according to the invention are particularly suitable for the production of prepregs which have a long shelf life, are rapidly thermocurable and can be pressed to give laminates having excellent properties.

The invention therefore also relates to prepregs comprising a fibrous support material and a mixture according to the invention, and to laminates obtained by thermal curing of the prepregs.
Suitable support materials are in principle all fibres which are able to form a composite with the epoxide matrix and reinforce the matrix material. Examples of fibre materials are natural polymers, such as cellulose; metals, such as steel, Ti, W, Ta and Mo;
organic fibre-forming polymers, in particular aromatic polyamides, such as Nomex or Kevlar;
carbon, such as materials prepared by carbonisation of cellulose, polyacrylonitrile or pitch, and in particular glass.
The fibre materials may be employed as supports in a wide variety of forms.
They can be used, for example, as continuous filaments (individual filaments or spun filaments), continuous yarn, parallel rovings, woven continuous yarn, spun rovings, woven roving material, short fibres, continuous mats, cut mats, nonwovens or felts (papers). Particularly preferred materials are woven glass materials and paper.
The contacting of the fibrous support material with the curable mixture varies depending on the fibre type and form and on the properties of the matrix material.
Examples of such processes are the impregnation of woven fabrics, nonwovens or continuous fibres with the liquid resin/curing agent mixture or with a solution of the mixture of a solid and/or liquid resin and the sulfonium salt curing agent in an inert solvent.
Layers containing short fibres can be produced, for example, by applying the curable mixture together with cut fibres to a woven material or a metal foil.
The contacting of the fibrous support material with the curable mixture is preferably effected by impregnation. To this end, woven webs of said support material are passed through, for example, a resin bath comprising the epoxy resin, the initiator, the stabiliser and, if desired, a solvent, are dried if necessary, and are subsequently wound onto a storage reel.
The invention also relates to a process for the production of a laminate, which comprises the steps i) production of a layer by contacting a fibrous support material with a curable mixture according to the invention in flowable form, *Trade-mark ii) production of a layer sequence comprising at least two layer materials to be bonded to one another, of which at least one is a layer obtainable in accordance with step i) and, if desired, this being stored in the interim, and in which the cuxable material is essentially in unmodified form, and iii) pressing said layer sequence at elevated temperature and under pressure.
If the mixture according to the invention employed in step i) contains a solvent, this must generally be removed at elevated temperature. This temperature is preferably sufficiently high that as much solvent as possible is removed from the material, for example to a solvent content of the material of less than 0.5% by weight. Temperatures of up to about 200°C are possible here.
In a specific embodiment of the above-described process, the fibrous support material in step i) is therefore contacted with a solution of the curable mixture according to the invention in order to produce the layer. The solvent is removed at a temperature of up to 200°C. This can be done, for example, in a drying oven or in a tunnel oven (speed, for example, 2 to 25 metres per minute). The heating time is preferably 1 to 10 minutes.
In step ii), individual layers of the previously obtained material are laid on one another in the desired number. The layers here may be idenrical or layers of Further materials may be present. Examples of layers of further materials are metal foils, such as copper foils or aluminium foils, or further reinforcing agents, such as mats or nonwovens of fibrous reinforcing material.
In step iii), the arrangement obtained in ii) is cured by pressing and heating. 'The process conditions in step ii) can be kept constant or varied. Thus, for example, the pressure and temperature in a first step can be prespecified so that essentially no curing takes place or the curing rate is so slow that the viscosity of the resin drops to the desired extent as a consequence of the increase in temperature. The pressure and/or temperature can subsequently be increased so that the desired rate of viscosity increase is achieved. These increases can be effected continuously or in steps. For example, the pressure can be increased in steps in accardance with the increase in viscosity, while the temperature is increased continuously.
However, the pressure and temperature can be fixed at the beginning of step iii) so that the crosslinking reaction commences virtually immediately.

_6_ Step iii) can be carried out batchwise in a mufti-daylight press or continuously in a twin-belt press, if desired under reduced pressure.
In a preferred embodiment of the process, steps ii) and iii) are carried out continuously. To this end, webs of the material obtainable in accordance with step t), if desired together with webs of further layered materials to be banded to one another, are simultaneously passed between heated twin-belt presses in the layer sequence desired in each case.
In this embodiment, step t) can be carried oat separately by contacting the fibrous support material with the curable mixture and winding the resultant webs onto storage reels.
However, step t) can also be carried out continuously together with steps ii) and iii) by, for example, passing webs of the fibrous support material through a resin bath immediately before step ii).
The pressing pressure in step iii) is generally 1-60 bar, preferably 10-50 bar; the curing temperature is generally 50-250°C, preferably 80-200°C, most preferably 100-200°C. The pressing duration, depending on the particular curable mixture, is generally 0.1-120 minutes, preferably 0.1-60 minutes, in particular 0.1-20 minutes.
The fibrous support material used in step t) is preferably woven glass material or paper.
T'he pressing pressure and temperature generally depend on the curable mixture used in each case. When selecting the experimental parameters, the reactivity and state of aggregation of the particular xesin/curing agent mixture, far example, are tlken into account.
The conditions necessary in the individual case can be selected and optimised by a parson skilled in the art depending on the abovementioned criteria.
The stabiliser component (c) suitable for the mixtures according to the invention are the above-defined aromatic amines (cl) and (c2), which contain 1 to 4 NH2 groups.
Such compounds containing 2, 3 or 4 NH2 groups can be prepared, for example, by condensation of an appropriately substituted aniline with an aldehyde or ketone, for example with formaldehyde [component (c1)], or by reaction of an amino acid with a _7_ compound containing 2-4 OH groups capable of ester condensation [component (c2)].
The aromatic amines used as components (c1) and (c2) may be monocyclic ox bicyclic.
The bicyclic compounds may contain both fused and unfused rings.
The alkyl substituents and the alkyl groups of the alkoxy substituents of component (c1}
may be straight-chain or branched. Examples of suitable alkyl groups are methyl, ethyl, n-and isopropyl, butyl, pentyl, hexyl, octyl and decyl. Examples of suitable alkoxy groups are the alkoxy radicals corresponding to these alkyl radicals. Examples of suitable cycloalkyl groups are cyclopentyl and cyclohexyl. Examples of suitable aryl groups are phenyl and naphthyl. Suitable halogen substituents are iodine, bromine and in particular chlorine.
Preferred components (c1) have one or two NH2 groups and a pK$ value of 3-4.5 and contain at least one alkyl substituent in the ortho-position to each amino group.
Particularly preferred components (c1) are 2,6-dialkylanilines and compounds of the formula (V) R,s R3 H2N ~ ~ CI-t2 ~ ~ NH2 (V), Fiq R4 in which R3 is chlorine or Ct-C3alkyl, and R4 is hydrogen or Ct-C3alkyl; in particular 2,6-diisopropylaniline and compounds of the formula (V) in which R3 and R4, independently of one another, are Ct-C3alkyl, preferably ethyl or isopropyl.
Examples of particularly suitable stabilisers (c1) are 2,6-diisopropylaniline, bis(4-amino-3,5-diethylphenyl)methane, bis(4-amino-3-methyl-5-isopropylphenyl)-methane, bis(4-amino-3,5-diisopropylphenyl}methane, bis(4-amino-3-ethyl-5-methylphenyl)methane, bis(4-amino-3,5-diethylphenyI)methane, bis(4-amino-3-methylphenyl)methane and bis(4-amino-3-chlorophenyl)methane.
The ortho- or para-substituents relative to the amino groups of stabiliser component (c2) are electron-withdrawing groups.

_g_ If the radical R in the definition of the amines (c2) is Ct-Ctpalkyl, Cs-C6cycloalkyl or C6-Ctoaryl, the comments made above for the corresponding substituents of component (c1) apply to this radical.
Aminoaryl R is preferably aminoaryl having 6 to 10 ring carbon atoms, for example aminonaphthyl or arninophenyl, such as 1-amino-4-naphthyl, 2-amino-6-naphthyl, 2-amino-7-naphthyl or 2-, 3- or, in particular, 4-aminophenyl.
If R is an -R'-OOC-C6H4NH2 group, R' is preferably C2-CtQalkylene and the amino group is preferably in the para-position on the phenyl ring.
Preferred components (c2) are compounds containing one or two NH2 groups and having a pKa value of 2-3.5. Examples of preferred compounds are anthranilic acid or compounds of the formula (VI) H2N ~ ~ T ~ ~ NH2 (VI), in which T is CO, SO or in particular S02 or -COO(CI-IZ)n()OC- where n = 2-6, preferably 2or3.
Examples of suitable components (c2) are 4-aminobenzoic acid, anthranilic acid, bis(4-aminophenyl) sulfone, bis(4-aminophenyl) sulfoxide, bis(4-aminophenyl) ketone and 1,3-propaneciiol bis(4-aminobenzoate).
Examples of suitable bipyridines used as component (c3) are 2,3'-, 2,4'-, 3,3'-, 4,4'- and in particular 2,2'-bipyridine. These components (c3) are less preferred as stabilisers than the above-described amine components (c1) and (c2).
The stabiliser components (c1) and (c2) may be present in the curable mixture as such or, if desired, can be partially or fully reacted with the epoxy resin (a) before addition of the sulfonium initiator (b). This prereaction is preferably carried out at elevated temperature, for example at 100-200°C. However, the preferred embodiment according to the invention involves employing components (c1) and (c2) without prereaction with the epoxy resin.

-c~-The amine is preferably present in an amount of from 0.~5 to 3% by weight, based on the epoxy resin.
As stated above, the stabilisers (c) significantly extend the shelf life of the mixtures according to the invention without impairing the thermal crosslinking reaction to be carried out after storage. The crosslinking is still carried out quickly and completely at elevated temperature and results in cured products having excellent properties.
Suitable epoxy resins (a) of the mixtures according to the invention are virtually all epoxy resins. Examples of these are:
I) Folyglyeidyl and poly((3-methylglycidyl) esters derived from compounds containing at least two carboxyl groups in the molecule, and epichlorohydrin or glycerol dichlorohydrin or ~3-methylepichlorohydrin.
The compounds containing at least two carboxyl groups in the molecule may be aliphatic polycarboxylic acids. Examples of these polycarboxylic acids are oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and dimerised or trimerised linoleic acid.
I-Iowever, it is also possible to employ cycloaliphatic polycarboxylic acids, for example tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid and 4-methylhexahydrophthalic acid.
It is furthermore possible to use aromatic polycarboxylic acids, for example phthalic acid, isophthalic acid and terephthalic acid.
II) Polyglycidyl or poly((3-methylglycidyl) ethers derived from compounds captaining at least two free alcoholic hydroxyl groups and/or phenolie hydroxyl groups, and epichlorohydrin or (3-methylepichlorohydrin.
Examples of compounds c<3ntaining at least two alcoholic hydroxyl groups are acyclic alcohols, such as ethylene glycol, diethylene glycol and higher poly{oxyethylene) glycols, propane-1,2-diol and poly(oxypropylene) glycols, propane-1,3-diol, butane-1,4-diol, poly(oxytetramethylene) glycols, pentane-1,5-diol, hexane-1,6-diol, hexane-2,4,6-triol, glycerol, 1,1,1-trimethylolpropane, pentaerythritol, sorbitol and polyepichlorohydrins.
These ethers may also be derived from cycloaliphatic alcohols, such as from 1,3- or 1,4-dihydroxycyclohexane, bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)pxopane or 1,1-bis(hydroxymethyl)cyclohex-3-ene.
The epoxide compounds may also be derived from rnonocyclic phenols, for example from resorcinol or hydroquinone; or they are based on polycyclic phenols, for example on bis(4-hydroxyphenyl)methane, 4,4'-dihydroxydiphenyl, bis(4-hydroxyphenyl) sulfone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyI)propane, 2,2-bis-(3,5-dibromo-4-hydroxyphenyl)propane or on novolaks obtainable by condensation of aldehydes, for example formaldehyde, acetaldehyde, chloral or fiufuraldehyde, with phenols, such as phenol or with phenols which are substituted in the ring by chlorine atoms or Cl-C9alkyl groups, for example 4-chlorophenol, 2-methylphenol or 4-tert-butylphenol, or obtainable by condensation with bisphenois, as described above.
These epoxy resins also include higher-molecular-weight and higher-melting epoxy resins obtainable by preextension, ie. by reaction of relatively low-molecular-weight and low-melting or liquid epoxy resins with polyfunctional compounds. Examples of starting materials for such preextension reactions are low-molecular-weight diglycidyl ethers based on bisphenol, such as based on bisphenol A, which are reacted with an excess of a bisphenol, such as bisphenol A or tetrabromobisphenol A, in a manner known per se to give higher-molecular-weight compounds.
These reactions are known per se and are described, for example, in Kirk-Othmer "Encyclopedia of Chemical Technology", Volume 9, pp. 275-276 (J. Wiley ~c Sons, New Cork, 1980).
III) Poly(S-glycidyl) compounds, in particular di-S-glycidyl derivatives derived from dithiols, for example ethane-1,2-dithiol or bis(4-mercaptomethylphenyl) ether.
IV) Cycloaliphatic epoxy resins, such as bis(2,3-epoxycyclopentyl) ether, 2,3-epoxycyclopentyl glycidyl ether and 1,2-bis(2,3-epoxycyclopentyloxy)ethane, and 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate.
However, it is also possible to use epoxy resins in which the 1,2-epoxide groups are bonded to different hetero atoms or functional groups; these compounds include, for example, the glycidyl ether glycidyl esters of salicylic acid.
If desired, a mixture of epoxy resins can be used in the curable mixtures.
The change in viscosity in step iii) of the process according to the invention can be controlled by employing a modified epoxy resin in step i) in order to achieve a relatively high initial viscosity and a faster increase in viscosity during the pressing step.
To this end, the epoxy resin can be modified, for example, by partial reaction with an epoxide curing agent which is effective at elevated temperature, for example with an anhydride curing agent; or the epoxy resin is combined with a small amount of a polyphenol, in particular a novolak.
The amount of modifier can be selected so that an increase in viscosity of the resin to be modified takes place, but this is not so great that an initial decrease in viscosity of the epoxy resin in step iii) is prevented.
In this embodiment, a polyglycidyl ether, in particular a diglycidyl ether based on bisphenol, which may also have been pre-extended, is preferably partially reacted with a cyclic anhydride of a polycarboxylic acid, in particular an anhydride of a cycloaliphatic dicarboxylic acid; in a further preferred embodiment of this variant, a polyglycidyl ether, in particular a diglycidyl ether based on bisphenol, which may, if desired, also have been pre-extended, is combined with a small amount of a novolak, in particular a phenol-formaldehyde novolak or a cresol-formaldehyde novolak.
The curing initiators of the formula (I) to (IV) are described in El'-A-0 379 464; disclosure thereof is intended to form part of the present description. The definitions given therein for the various radicals of the formulae (I) to (1V) also apply to the present invention.
Particularly suitable initiators for the mixtures according to the invention are sulfonium salts of the formula (I) or (II) in which A is Ct-Ct2alkyl, C3-Cgcycloalkyl or phenyl which is unsubstituted or substituted by halogen or Ct-C4alkyl, Ar, Arl and Ar2, independently of one another, are each phenyl which is unsubstituted or rnonosubstituted or polysubstituted by Ct-CBalkyl, Ct-C4alkoxy, Cl or Br, and Q~ is SbFb or SbF50H-, for example dibenzylethylsulfonium hexafluoroantimonate or dibenzylcyclohexylsulfonium hexafluoroantimonate.
The curable mixtures may also contain further additives.
These may be additives by means of which the end properties of the cured products and/or the processing properties of the mixture are modified.
Examples of such additives are fillers or extenders, such as chalk, talc, kaolin, mica, plaster, titanium dioxide, quartz sand; aluminium oxide, cellulose, clay, ground dolomite, woilastonite, silicious earth having a large specific surface area (obtainable under the tradename Aerosil), powdered polyvinyl chloride, polyolefins and metal powders, such as copper, silver, aluminium or iron powders, flameproofng agents, such as antimony trioxide; colorants, such as pigments or dyes; light stabilisers for improving the U~V
stability of the finished laminate; release agents for, for example, interim release of the individual layers produced in step i), such as release films, film-forming coatings or waxes; thixotropic agents, such as highly disperse silicic acid; reactive diluents, such as phenyl glycidyl ether, cresyl glycidyl ether, butanediol diglycidyl ether or diglycidyl hexahydrophthalate, or inert diluents for, for example, preparing impregnation solutions of high-viscosity or solid epoxy resin mixtures, such as chlorinated aliphatic or aromatic hydrocarbons, for example dichloromethane, trichloroethane, tetrachloroethane, chlorobenzene, or such as aromatic hydrocarbons, such as toluene or xylene, or such as aliphatic ketones, such as acetone or methyl ethyl ketone.
Particular preference is also given to mixtures according to the invention in which component (b) is a sulfonium salt of the formula (I) in which A is Cl-Cl2alkyl or C3-C8cycloalkyl, Ar and Art, independently of one another, are each phenyl which is unsubstituted or monosubstituted or polysubstituted by Cl-CBalkyl, C~-C4alkoxy, Cl or Br, and Q- is AsF6 or SbF6 , and component (c) is a compound of the formula (~) in which R3 and R4, independently of one another, are Ct-C3alkyl, in particular ethyl or isopropyl.
The laminates according to the invention can be employed, in particular, for the production of circuit boards and insulating materials.
Example 1: 571 g of a brorninated technical-grade diglycidyl ether based on bisphenol A
(epoxide content 1.85 equivalents/kg) dissolved in methyl ethyl ketone are mixed homogeneously with 4.0 g of tribenzylsulfoniurn hexafluoroantimonate (1°lo by weight, ~~~5~.8~.

based on solid epoxy resin) and 1.2 g of bis(4-amino-3,5-diethyIphenyl)methane (0.3°lo by weight, based on the solid resin). This solution is used to impregnate a woven glass material (200 g/m2 basis weight). The resin solution-impregnated material is dried for 3 minutes at 140°C in a drying oven, giving a tack-free, stackable prepreg. 8 layers of this prepreg (15 x 15 cm) are laid one on top of the other and pressed for 15 minutes at 170°C
to give a bubble-free laminate. Its glass transition temperature Tg, determined by differential scanning calorimetry (DSC), is 136°C ("Tg 1"). The same sample is then subjected to a further DSC measurement. This time a glass transition temperature of 138°C ("Tg 2") is obtained. 'The very small difference between Tg 1 and Tg 2 shows that in 15 minutes, a relatively short time, a cured laminate was obtained.
Example 2: An impregnating solution of 571 g of the epoxy resin solution used in Example l, 1.2 g of bis(4-amino-3,5-diethylphenyl)methane and 4.0 g of dibenzylethylsulfonium hexafluoroantimonate is prepared as in Example 1.
Prepregs are produced as in Example 1 by drying for 3 minutes at 145°C and pressed to give an 8-layer laminate. Tg 1 and T~ 2 are 146 and 148°C respectively, i.e. the laminates have cured after the short pressing time.
Without addition of the amine, drying can only be carried out at much lower temperatures and only for very short times; at higher temperatures, as used in the examples, the epoxide polymerisation has proceeded so far that only inadequate bonding of the individual pre.pregs to one another is achieved on the pressing. T~ 1 and Tg 2 are therefore about 20°C if a mixture without amine is used.
Example 3: An impregnating solution of 571 g of the epoxy resin solution used in Example 1, 1.2 g of bis(4-amino-3,5-diethylphenyl)methane and 4.0 g of dibenzylcyclohexylsulfonium hexafluoroantimonate is prepared as in Example 1.
Prepregs are produced as in Example 1 by drying for 3 minutes at 145°C arid are pressed to give an 8-layer laminate. T~ 1 and Tg 2 are 144 and 143°C respectively.
In addition, prepregs are tested for shelf life. To this end, the gelling time of the prepregs is measured at 130°C immediately after production of the prepregs and after storage for 30 days at room temperature. The following values are obtained:

~~~~~.8~.
_14_ Storage time [days) 0 30 Gelling time at 130°C [s) 270 245 The decrease in the gelling time after storage for 30 days is accordingly less than 10%.
Without addition of amine, the gelling time after 30 days is more than three times as long under otherwise identical conditions.
Examples 4-6: 3 impregnating solutions are prepared as in Example 1 in each case from 571 g of the epoxy resin solution used in Example 1. Sulfonium salts and amines are added to the solutions in accordance with the table below. Prepregs are produced as in Example 1 by drying the impregnated woven glass material for 3-4 minutes at 130-150°C.
In each case, 8 of the resultant prepregs are pressed for 15 minutes at 170°C to give laminates. The glass transition temperatures and the gelling times of the prepreg resins before and after storage for 30 days at room temperature are given in said table. It can be seen from the values that the laminates are fully cured and the prepregs have an adequate shelf life.
Sulfonium salt/ Tgl/T~2 Prepreg gelling time amine at 130 °C after 0 days 30 days f°~:1 f5) fs) 4.00 g Dibenzylcyclohexyl-sulfonium hexafluoroantimonate/
0.68 g Diaminodiphenyl sulfone 134/133 i04 86 4.00 g Tribenzylsulfonium hexafluoroantimonate/
0.78 g 2,6-Diisopropylaniline 140/139 145 140 ~~~~.8~.

3.00 g 1,4-Bis(benzylethyl-sulfoniummethyl)benzene bis-hexafluoroantimonate/
0.35 g Trimethyleneglycol di-p-aminobenzoate 130/132 165 15I

Claims

1. A curable mixture comprising (a) an epoxy resin, (b) a sulfonium salt of the formula (I), (II), (III) or (IV) in which A is C1-C12alkyl, C3-C8cycloalkyl, C4-C10cycloalkylalkyl, phenyl which is unsubstituted or monosubstituted or polysubstituted by C1-C8alkyl, C1-C4alkoxy, halogen, hydroxyl, nitro, phenyl, phenoxy, alkoxycarbonyl having 1-4 carbon atoms in the alkoxy radical or acyl having 1-12 carbon atoms, Ar, Ar1 and Ar2, independently of one another, are each phenyl or naphthyl which is unsubstituted or monosubstituted or polysubstituted by C1-C8alkyl, C1-C4alkoxy, halogen, hydroxyl, nitro, phenyl, phenoxy, alkoxycarbonyl having 1-4 carbon atoms in the alkoxy radical or acyl having 1-12 carbon atoms, arylene is in each case phenylene or naphthylene which is unsubstituted or monosubstituted or polysubstituted by C1-C8alkyl, C1-C4alkoxy, halogen, hydroxyl, nitro, phenyl, phenoxy, alkoxycarbonyl having 1-4 carbon atoms in the alkoxy radical or acyl having 1-12 carbon atoms, and Q- is SbF6-, AsF6- or SbF5OH-, and (c) a stabiliser selected from the group comprising (c1) aromatic amines having a pKa value of 2-5 and having one to four NH2 groups with at least one substituent in the ortho-position to each amino group, the substituent being C1-C10alkyl, C1-C10alkoxy, C5-C6cycloalkyl, C6-C10aryl or halogen, with the proviso that the amine is not substituted in both ortho-positions to an amino group by halogen, or (c2) aromatic amines having a pK a value of 2-5 and having 1 to 4 NH2 groups with an ortho- or para-substituent to each amino group, the substituent being -COOH, -COOR, -COR, -SO2R or -SOR where R is C1-C10alkyl, C5-C6cycloalkyl, C6-C10aryl, aminoaryl or -R1-OOC-C6H4-NH2 where R' is alkylene, or (c3) bipyridines, where 0.1-10% by weight of component (b) and 0.02-5% by weight of component (c), based on the epoxy resin (a), are present in the mixture.

2. A mixture according to claim 1, in which component (c1) has one or two NH2 groups and a pK a value of 3-4.5 and contains at least one alkyl group in the ortho-position to each amino group.

3. A mixture according to claim 1, in which component (c1) is a 2,6-dialkylaniline or a compound of the formula (V) in which R3 is chlorine or C1-C3alkyl, and R4 is hydrogen or C1-C3alkyl.

4. A mixture according to claim 3, in which component (c1) is 2,6-diisopropylaniline or a compound of the formula (V) in which R3 and R4, independently of one another, are C1-C3alkyl.

5. A mixture according to claim 4, wherein R3 and R4, independently of one another, are ethyl or isopropyl.

6. A mixture according to claim 1, in which component (c2) has one or two NH2 groups and a pK a value of 2-3.5.

7. A mixture according to claim 1, in which component (c2) is anthranilic acid or a compound of the formula (VI) in which T is CO, SO, SO2 or -COO(CH2)nOOC- where n=2-6.

8. A mixture according to claim 7, wherein T is SO2 or -COO (CH2) nOOC- where n is 2 or 3.

9. A mixture according to claim 1, in which component (c3) is 2,3'-, 2,4'-, 3,3'-, 4,4'- or 2,2'-bipyridine.

10. A mixture according to claim 9, wherein component (c3) is 2,2'-bipyridine.

11. A curable mixture according to claim 1, in which component (b) is a sulfonium salt of the formula (I) or (II) according to claim 1 in which A is C1-C12alkyl, C3-C8cycloalkyl or phenyl which is unsubstituted or substituted by halogen or C1-C4alkyl, Ar, Ar1 and Ar2, independently of one another, are each phenyl which is unsubstituted or monosubstituted or polysubstituted by C1-C8alkyl, C1-C4alkoxy, Cl or Br, and Q- is SbF6- or SbF5OH-.

12. A curable mixture according to claim 3, in which component (b) is a sulfonium salt of the formula (I) according to claim 1 in which A is C1-C12alkyl or C3-C8cycloalkyl, Ar and Ar1, independently of one another, are each phenyl which is unsubstituted or monosubstituted or polysubstituted by C1-C8alkyl, C1-C4alkoxy, C1 or Br, and Q-is AsF6- or SbF6- and component (c) is a compound of the formula (V) according to claim 3 in which R3 and R4, independently of one another, are C1-C3alkyl.

13. A curable mixture according to claim 12, wherein R3 and R4, independently of one another, are ethyl or isopropyl.

14. A prepreg comprising a fibrous support material and a mixture according to any one of claims 1 to 13.

15. A laminate obtainable by thermal curing of a prepreg according to claim 14.

16. A process for the production of a laminate, which comprises the steps i) production of a layer by contacting a fibrous support material with a curable mixture according to any one of claims 1 to 13 in flowable form, ii) production of a layer sequence comprising at least two layer materials to be bonded to one another, of which at least one is a layer obtainable in accordance with step i) and, if desired, this being stored in the interim, and in which the curable material is essentially in unmodified form, and iii) pressing said layer sequence at elevated temperature and under pressure.

17. A process according to claim 16, in which the fibrous support material is contacted in step i) with a solution of the curable mixture in order to produce the layer, and the solvent is removed at a temperature of up to 200°C.