CA2040010A1 - Epoxy resin compositions comprising iron-arene complexes and specific amines - Google Patents

Abstract

Epoxy resin compositions comprising iron-arene complexes and specific amines Abstract of the Disclosure Curable compositions comprising (a) an epoxy resin, (b) an iron-arene complex of formula I

(I), wherein a and b are each independently of the other 1 or 2, R1 is isopropylbenzene, R2 is a cyclopentadienyl anion, and X- is SbF6-, and c) an amine stabiliser, such as a 2,6-dialkylaniline, said composition comprising 0.1-10 %
by weight of component (b) and 0.02-5 % by weight of component (c), based on the epoxy resin (a), are particularly suitable for the preparation of storage stable prepregs which, after irradiation with UV light, are rapidly heat-curable and can be compressed to laminates having excellent fastness properties.

Description

~ ~3 ~

Epoxy resin compositions comprisin~ iron-arene complexes and speci~lc amines The present inve~tion relates to curable compositions comprising an epoxy Iesin, specific iron-arene complexes as initiators and specific amines as stabilisers, to the prepregs and laminates obtainable by using said compositions, and to a process for the preparation of said laminates.

Cationically curable mixtures containing metallocene complex salts, including iron-arene complexes, are disclosed as initiators in EP-A-94 91~.

To prepare epoxy resin-based laminates it is common to use selected hardener/accelator combinations, for example the combination of dicyandiamide/benzyldimethylamine. The resin formulations must meet a number of requirements, some of which are difficult to reconcile with one another. Thus, for example, the prepreg should have a sufficient storage stability and a rapid full cure of the matrix resin in the compression mould should take place. In addition, the matrix resin should have a reduced viscosity at the start of the moulding procedure, so that trapped gases may be removed from the material to bemoulded. However, the fall in viscosity should only be such that no more than a minor amount of resin flows out of the fibre matrix.

A process for the preparation of epoxy resin-based laminates using specific iron-arene complexes as initiators is disclosed in EP-A-323 584. In this process, the iron-arene complexes are activated by irradiation to form the corresponding Lewis acids which initiate a cationic polymerisation of the epoxy resin. Although this prior art process makes it possible to effect a rapid thermal cure of the matrix resin to give laminates having excellent properties, the storage stability of the matTix resin after iTradiation does not fully meet all requirements. These epoxy resins which contain the irradiated, i.e. activated, photoinitiator have to be thermally cured a comparatively short time after irradiation because their melt viscosity at room temperature increases rapidly and the moulding conditions change. It has therefore only been possible to store such irradiated epoxy resin systems, for example the prepregs obtained with these resins, at low temperature, for example at temperatures below 0C.

, .
: ` ~

Surprisingly, it has now been found that the addition of minor amounts of specific amines to the epoxy resin mixtures of the prior art has a stabilising effect, such that the compositions so obtained are storage-stable even after iIradiation at room temperature over a considerable period of time (for example 30 days), yet can still be cured rapidly at elevated temperature.

Accordingly, the invention relates to curable compositions comprising (a) an epoxy resin, (b) an iron-arene complex of formula I

[Rl (FeIIR2)alab~3 ab~

wherein a and b are each independently of the other 1 or 2, Rl is a ~-arene, R2 is a ~-arene or an indenyl or cyclopentadienyl anion, X~ is an anion ~Qm]~3 or an anion of a partially fluorinated or perfluorinated aliphatic or aromatic sulfonic acid, L is B, P, As or Sb, Q is fluoro or some of the radicals Q may also be hydroxyl groups, and m is the valency of L
increased by one, and (c) a stabiliser selected from the group consisting of (cl) aromatic amines having a pKa value of 2-5 and containing 1 to 4 NH2 groups and a$
least one substituent in ortho-position to each amino group, said substituent being Cl-ClOaLt~yl, Cl-ClOalkoxy, Cs-C6cycloalkyl, C6-ClOaryl or halogen, with the proviso that no halogen is present in both ortho-positions to the amino group, or (c2) aromatic amines having a pKa value of 2-5 and containing 1 to 4 NH2 groups and one substituent in ortho- or para-position to each amino group, said substituent being -COOH, -COOR, -COR, -SO2R or -SOR, and R is -H, alkyl, cycloaL~yl, aryl, arninoaryl or -R5-OOC-C6H4-NH2, where R5 is alkylene, or (c3) bipyridines, which compositions contain 0.1-10 % by weight of component (b) and 0.02-5 % by weight of component (c), based on the epoxy resin (a).

The compositions of this invention are particularly suitable for the preparation of storage-stable prepregs which are rapidly heat-curable and can be compressed to larninates having excellent properties.

The invention therefore also relates to prepregs comprising a fibrous substrate and a ~ , .
, ~

composition of the invention which is achvated by iIradiation, and to the larninates obtained by the thermal curing of the prepregs.

Suitable substrates are generally all fibres which are able to form a composite structure with the epoxy resin matrix and to effect a reinforcement of the matrix material. Fibre materials are typically natural polymers such as cellulose, and metals such as steel, Ti, W, Ta or Mo, organic fibre forming polymers, especially aromatic polyamides such as Nomex or Kevlar, as well as carbon, for example matelials obtained by carbonising cellulose, polyacrylonitrile or bitumen, and, preferably, glass.

The fibre materials may be used in a wide v aIiety of forms as substrates. Thus, for example, they can be used as continuous filaments (ends or fibre strands), continuous filament yarns, rovings, woven continuous filament yarns, multistrand rovings, roving cloth, ground fibres, continuous strand mats, chopped strand mats, nonwovens or felts (papers).

Contacting the fibrous substrates with the curable mixture can be performed by a wide range of methods, depending on the type of fibre and its form or depending on the properties of the matrix material. Typical examples of such methods are the impregnation of fabrics, nonwovens or continuous filaments with the liquid resin/photoinitiator/stabiliser composition or with a solution of a solid resin/photoinitiator/stabiliser composition in an inert solvent.

Layers containing chopped strands can be prepared, for example, by applying the curable composition, together with chopped fibres, to a fabric or a metal foil.

Contacting the fibrous substrate with the curable composition is preferably effected by impregnation. Webs of said substrate pass through a resin bath containing the epoxy resin, the initiator, the stabiliser and, if required, a solvent. After optional drying they are wound on a spool.

The invention further relates to a process for the preparation of a laminate comprising the steps:
I) preparing a layer by contacting a fibrous substrate with a curable composition of the mvention, ii) preparing a sequence of layers of at least two layered materials to be bonded together, at least one of which is a layer obtainable in step i) in which the curable material is substantially in unchanged form, and iii) compressing said sequence of layers at elevated temperature, the pressure and temperature being so chosen that a liquid matrix resin is formed at the start of this step, the viscosity of said resin initially falling so that trapped gases are able to escape almost completely from the sequence of layers and that the increase in viscosity during the subsequent crosslinking reaction is so rapid that the resin flowing from the compression mould does not glueing of the mould.

Before step ii) it is advisable to subject the impregnated layers to irradiation, whereby the hardener of formula I is converted into an activated form. The subsequent heat-activated curing can be carried out by this treatment at lower tempe}atures than in directheat-activated curing.

EIence a preferred process is that comprising the steps i), ii) and iii) as defined above, wherein an additional iIradiation step ia) is carried out prior to step ii) ~y irradiating the hardener of formula I with actinic light to activate said hardener: This additional step can be carried out by irradiating the prepreg prepared in step i) or by impregnating a fibrous substrate with a previo-lsly i}radiated mixture of epoxy resin and initiator of formula I.
The intensity and wavelength of the radiation used will depend on the nature of the initiator. Depending on the structure of the arene ligand Rl, the absorption of the initiator may be in th~ UV range or in the visible range, for example in the range from 250-600 nm.

Depending on the nature of the latent hardener, the curable composition may additionally contain a sensitiser for said hardener.

After impregnation and irradiation, it may be expedient to heat the material briefly, for example to 70-120C, in order to increase the viscosity of the resin before carrying out step ii).

In step ii), the desired number of individual layers of the previously obtained material are stacked. The layers may each be of the same material or additional layers of further materials may be present. Layers of further materials are typically metal foils, such as copper foils or aluminium foils, or further reinforcing materials such as mats or nonwovens made from fibrous reinforcing material.

.

In step ii;), the assembly obtained in ii) is cured by compression moulding and heating.
The process conditions in step iii) may be kept constant or varied. Thus, for example, in a fîrst step pressure and temperature may be applied such that substantially no cure yet takes place or the curing rate is so slow that the viscosity of the resin falls to the desired extent as a result of the increase in temperature. Pressure and/or temperature can be increased so as to produce the desired rate of increase in viscosity. These increases can be made continuously or stepwise. For example, the pressure can be increased stepwise commensurate with the increase in viscosity, whereas the temperature is increased continuously.

Pressure and temperature can, however, also be preset at the start of step iii), so that crosslinking begins almost immediately. This procedure is expedient in the case of liquid matrix resins of low viscosity. Initial compression normally suffices in this case to remove trapped gases from the laminate. In such systems there is usually only a brief fall in viscosity before the cure leads to an increase in viscosity.

Step iii) can be carried out discontinuously in multi-daylight presses or continuously in continuous laminators.

In a preferred embodiment of the process, steps ii) and iii) are carried out continuously. In this procedure, webs of the material obtainable in step i), if desired together with webs of further layered materials for bonding together, are passed in each the desired layer sequence simultaneously between heatable continuous laminators.

Step i) can be carried out separately in this embodiment of the process by contacting the fibrous substrate with the curable composition and the webs so obtained are wound on spools.

Step i) can, however, also be carried out continuously with steps ii) and iii) by passing webs of the ~lbrous substrate through a resin bath immediately before step ii).

In the continuous procedure, it is preferred to use particularly rapid-acting initiators of formula I. Such initiators are preferably compounds of formula I, wherein X~3 is AsF~-and, most preferably, SbF6-.

The webs of impregnated material are normally irradiated in this embodiment of the 2 ~

process with actinic light before passage through the continuous larninator. Irradiation can be effected before or immediately after impregnation or shortly before the actual contact step.

The compression moulding pressure in step iii) is normally 1-60 bar, preferably 10-50 bar.
The curing temperature is generally in the range from 50-250C, preferably 80-200C, most preferably 10~-20~C. The compression time, depending on the respective curable composition, is 0.1-120 minutes, preferably 0.1-60 minutes and, most preferably, 0.1-20 minutes.

The preferred fibrous substrate in step i) is glass cloth or paper.

Compression moulding pressures and temperatures normally depend on the curable composition used. Governing factors in the choice of the experimental parameters are typically reactivity and aggregate condition of the respective resinllhardener mixture.

The conditions necessary for the individual case can be chosen and optimised on the basis of the criteria referred to above.

Suitable stabiliser components (c) of the compositions of this invention are the above defined aromatic arnines (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 condensing a suitably substituted aniline [component (cl)] with an aldehyde or ketone, for example with formaldehyde, or by reacting an amino acid [component (c2)] with a compound which contains two to four OH groups capable of ester condensation.

The amines used as components (cl) and (c2) may be mononuclear or binuclear. Thebinuclear compounds may contain fused as well as non-fused rings.

The aL~yl substituents or aL~cyl moieties of the aLIcoxy substituents of component (cl) may be straight chain or branched. Suitable aL~cyl groups are typically methyl, ethyl, n-propyl and isopropyl, butyl, pentyl, hexyl, octyl and decyl. Suitable cycloalkyl groups are typically cyclopentyl and cyclohexyl. Suitable aryl groups are typically phenyl and naphthyl. Suitable halogen substituents are iodo, bromo and, preferably, chloro.
Preferred components (cl) contain one or two NH2 groups and have a pKa value of 3-4.5 ' , .

and car~y at least one alkyl substituent in ortho-position to each amino group. Particularly preferred components (cl) are 2,6-diaL1cylanilines or compounds of formula R R

H2N ~3 CH2~ NH2 (II), wherein R3 is chloro or aLl~yl and R4 is hydrogen or aL~cyl, but preferably 2,6-diisopropylaniline or compounds of formula II, wherein R3 and R4 are each independently of the other Cl-C3aLkyl, preferably methyl, ethyl or isopropyl.

Representative examples of particularly suitable stabilisers 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-~liethylphenyl)methane, bis(4-arnino-3-methylphenyl)methane and bis(4-arnino-3-chlorophenyl)methane.

The substituents in ortho- or para-position to the amino group of ~he stabiliser component (c2) are electron-repelling groups such as carboxyl, ester, carbonyl, sulforle or sulfoxide groups.

If the radical R in these groups is aL~cyl, cycloalkyl or aryl, then what has been said in respect of the corresponding substituents of component (cl) applies to said radical.

R as aminoaryl is typically aminonaphthyl or am.inophenyl, such as l-amino-4-naphthyl, 2-amino-6-naphthyl, 2-amino-7-naphthyl or 2-, 3- and, preferably, 4-aminophenyl.
Where R is a -R5-OOC-C6H4NH2 group, R5 is preferably C2-CIOaL~cylene, and the amino group is preferably para-positioned at the phenyl ring. -Preferred components (c2) aue compounds containing one or two NH2 groups and having a pKa ~alue of 2-3.5. Exemplary of preferred compounds are anthranilic acid or compounds of formula III

, H2N ~3T ~ 3NH2 ~III), wherein T is CO, SO and, preferably, SO2, -COO(CI-I~CH2O)nOC- or -COO(CH2)nOOC-,where n is 2-6, preferably 2.

Suitable components (c2~ are typically 4-aminobenzoic acid, anthranilic acid, bis(4-aminophenyl)sulfone, bis(4-aminophenyl)sulfoxide, bis(4-aminophenyl)ketone, 1,3-propanediol-bis(4-aminobenzoate) or di-, tri- or tetraethylene glycol bis(4-amino-benzoate).

Illustrative examples of bipyridines suitable for use as component (c3) are preferably 2,3'-, 2,4'-, 3,3'-, 4,4'- and, preferably, 2,2'-bipyridine. These components (c3) are less preferred stabilisers than the amine components tcl) and (c2) described above.

The stabiliser components (cl) and (c2) may be used by themselves in the curablecomposition or, if appropriate, partially or completely prereacted with the epoxy resin (a) before the addition of the iron-arene complex (b). This preliminary reaction is preferably carried out at elevated temperature, for example in the range from 100-200C. In the practice of this invention, however, the preferred embodiment is that in which the components (cl) and (c2) are used without a preliminary reaction.

As stated above, the stabilisers ~c) substantially improve the storage stability of the compositions of this invention after activation of the photoinitiator (b) by irradiation without thereby impairing the heat-activated crosslinking reaction to be carried out after storage. The crosslinking still takes place rapidly and completely at elevated temperature and gives cured products having excellent properties.

This feature is all the more surprising, as a contrary behaviour of spec;fic amines in conjunction with iron-arene complexes for curing epoxy resins is disclosed in EP-A 29~ 211. This publication discloses positive photoresist compositions on the basis of epoxy resins, which compositions, in addition to containing a latent urea or imidazole hardener for the epoxy resin, con;ain an iron-arene complex as photoinitiator. The irradiated areas of the positive resist differ in their curability markedly from the non-irradiated areas. After heat treatment, the non-irradiated areas are so completely cured .

2 ~

that they are substantially insoluble in conventional developers, whereas the irradiated areas are still largely uncured and thus soluble in the same developer. This feature is attributable to the interaction of the iron-arene complex initiator, which is activated in the irradiated areas, with the urea or imidazole hardener, so that in the heat treatment neither the amine hardener nor the activated photoinitiator is an effec~ive hardener.

Surprisingly, the stabilisers (c) of this invention are able to improve the storability of the irradiated compositions without impairing the processing and final properties.

Almost all epoxy resins are suitable for use as epoxy resin (a) of ~e composition of this invention. Illustrative examples of such epoxy resins are:
I) polyglycidyl and poly-(~-methylglycidyl) esters which can be obtained by reacting a compound containing at least two carboxyl groups in the molecule with epichlorohydrin or glycerol dichlorohydrin or ~-methylepichlorohydrin.

Aiiphatic polycarboxylic acids may be used as compounds containing at least two carboxyl groups in the molecule. Illustrative of these polycarboxylic acids are oxalic acid, succinic acid, glutalic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid or dimerised or trimerised linoleic acid.

Cycloaliphatic carboxylic acids can also be used, such as tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid or 4-methylhexahydrophthalic acid.

It is also possible to use aromatic polycarboxylic acids such as phthalic acid, isophtalic acid or terephthalic acid.

II) Polyglycidyl or poly-(~-methylglycidyl) ethers which are derived from compounds which contain at least two alcoholic hydroxyl groups and/or phenolic hydroxyl ~,roups and epichlorohydrin or ~3-methylepichlorohydrin.

Exemplary of compounds containing at least two alcoholic hydroxyl groups are acyclic alcohols such as ethylene glycol, diethylene glycol and higher poly(oxyethylene) glycols, 1,2-propanediol or poly(oxypropylene) glycols, 1,3-propanediol, 1,4-butanediol, poly(oxytetramethylene) glycols, 1,5-pentanediol, 1,6-hexanediol, 2,4,6-hexanetriol, glycerol, l,l,l-trimethylolpropane, pentaerythritol, sorbitol, as well as polyepichlorohydrins .

Such ethers may also be derived from cycloaliphatic alcohols, such as from 1,4-dihydroxycyclohexane, bis(4-hydroxycyclohexyl)methane, 2,2-bis~4-hydroxycyclo-hexyl)propane or 1 ,1-bis(hydroxymethyl)cyclohex-3-ene.

The epoxy compounds may also be derived from mononuclear phenols such as from resorcinol or hydroquinone; or they are based on polynuclear phenols, for example bis(4-hydroxyphenyl)methane, 4,4'-dihydroxydiphenyl, bis(4-hydroxyphenyl)sulfone, 1,1,2,2-tetrakis~4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane as well as on novolaks obtainable bycondensation of aldehydest such as formaldehyde, acetaldehyde, chloral or furfuraldehyde, with phenols such as phenol, or with phenols which are substituted in the nucleus by chlorine atoms or Cl-CgaLIcyl groups, for example 4-chlorophenol, 2-methylphenol or 4-tert-butylphenol, or obtainable by condensation with bisphenols, as described above.

These epoxy resins also include the higher molecular weight and higher melting epoxy resins obtainable by advancement, for example by reacting relatively low molecular weight and low melting or liquid epoxy resins with polyfunctional compounds. Starting materials for such advancement products are typically low molecular weight diglycidyl ethers based on bisphenols, for example based on bisphenol A, which are reacted with a less than equivalent amount of a bisphenol, such as bisphenol A or tetra-bromobisphenol A, in a manner known per se, to higher molecular weight compounds.

Such reactions are known per se and described, for example, in Kirk-Othmer "Encyclopedia of Chemical Technology", Volume 9, pp. 275-276 (J. Wiley ~ Sons, New York 1980).

III) Poly (S-glycidyl) compounds, preferably di-S-glycidyl derivatives which are derived from dithiols, such as 1,2-ethanedithiol or bis(4-mercaptomethylphenyl) ether.

IV) Cycloaliphatic epoxy resins such as bis~2,3-epoxycyclopentyl) ether, 2,3-epoxycyclo-pentylglycidyl ether or 1,2-bis(2,3-epoxycyclopentyloxy)ethane or 3,4-epoxycyclo-hexylmethyl-3 ' ,4 ' -epoxycyclohexanecarboxylate.

It is, however, also possible to use epoxy resins in which the 1,2-epoxy groups are . ~ . .

s~

attached to different hetero atoms or functional groups. Such compounds include, ior example, the glycidyl ether/glycidyl ester of salicylic acid.

If desired, a mixture of epoxy resins can be used in the curable mixtures.

To control the viscosity gradient in step iii) of the process of this invention it may be expedient to use in step i) a modified epoxy resin in order to ensure a higher initial viscosity and a more rapid increase in viscosity in the compression step.

This can be accomplished, for example, by modifying the epoxy resin by partial reaction with an epoxy hardener which acts at elevated temperature, typicaUy an anhydridehardener, or by combining the epoxy resin with a minor amount of a polyphenol, preferably a novolak.

The amount of modi~ler is chosen such that the viscosity of the resin to be modifled is increased, but not to such a degree that the initial fall in viscosity of the epoxy resin in step iii) does not take place.

In this embodiment of the process of the invention, it is preferred to react partially a polyglycidyl ether, preferably a diglycidyl ether of a bisphenol which may also be advanced, with a cyclic anhydride of a polycarboxylic acid~ especially an anhydride of a cycloaliphatic dicarboxylic acid. In a further preferred embodiment of this process variant, a polyglycidyl ether, preferably a diglycidyl ether of a bisphenol which may also be advanced, with a minor amount of a novolak, preferably a phenol-formaldehyde novolak or a cresol-formaldehyde novolak.

A 7~-arene Rl or R2 of the iron-arene comple~c tb) is normally a nonbasic heterocyclic-aromatic or, preferably, a carbocyclic-aromatic radical which is mononuclear or polynuclear and which, if polynuclear, may be uncondensed or condensed. Theseradicals may be unsubstituted or they are substituted by non-basic radicals.

A ~-arene Rl or R2 is suitably a carbocyclic-aromatic hydrocarbon radical s)f ~ to 24 carbon atoms, preferably of 6 to 12 carbon atoms, or a heterocyclic-aromatic hydrocarbon radical of 4 to 11 carbon atoms and containing 1 to 2 O- or S-atoms, which groups may be substituted by one or more identical or different monovalent radicals, such as haloge atoms, preferably chlorine or bromine atoms, or Cl-C8aLkyl, Cl-C8aLkoxy or phenyl 2 ~

groups. Non-fused polynuclear 7~-arene groups may be linked direct or through linking groups such as -CH2-. -C(CH3)2-, -CH=C~I-, -O-, -S-, -SO2- oder-CO-.

The alkyl or alkoxy groups may be straight chain or branched. Typical alkyl or aL~coxy groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl and n-octyl; methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, n-hexyloxy and n-octyloxy. Alkyl or aL~oxy groups of 1 to 4 carbon atoms are preferred. Preferred substituted ~-arenes are those which contain one or two of the above mentioned substituents, preferably methyl, ethyl, n-propyl, isopIopyl, methoxy or ethoxy groups.

R2 may additionally be an indenyl anion and, preferably, a cyclopentadienyl anion, which anions may be substituted by one or more identical or different monovalent radicals, typically by Cl-C8alkyl and Cl-C8alkoxy groups. R2 is preferably an unsubstituted indenyl anion and, most preferably, an unsubstituted cyclopentadienyl anion.

Illustrative examples of suitable ~-arenes Rl or R2 are benzene, toluene, xylenes, ethyl benzene, cumene, methoxybenzene, ethoxybenzene, dimethoxybenzene, p-chlorotoluene, m-chlorotoluene, chlorbenzene, bromobenzene, dichlorobenzene, trimethylbenzene, ~imethoxybenzene, naphthalene, 1,2-dihydronaphthalene, 1,2,3,4-tetrahydronaphthalene, methylnaphthalene, methoxynaphthalene, ethoxynaphthalene, chloronaphthalene, bromonaphthalene, biphenyl, stilbene, indene, 4,4'-dimethylbiphenyl, fluorene, phenanthrene, anthracene, 9,10-dihydroanthracene, triphenyl, pyrene, perylene, naphthacene, coronene, thiophene, chromene, xanthene, thioxanthene, benzofuran, benzothiophene, naphthothiophene, thianthrene, diphenylene oxide and diphenylenesulfide.

Illustrative examples of anions of substituted cyclopentadiene are the anions ofmethylcyclopentadiene, ethylcyclopentadiene, n-propylcyclopentadiene and n-butylcyclopentadiene, or the anions of dimethylcyclopentadiene.

When a is 2, R2 is preferably the substituted indenyl anion or, preferably, the cyclopentadienyl anion.

The index a is preferably 1. The index b is preferably 1.

X~3 is preferably an anion of forrnula [LQm]~

,i .
`

2 ~

Q is preferably fluoro.
L is preferably As or Sb and, most preferably, Sb.

The anion X~ may also, however, be an anion of a partially fluorinated or perfluorinated aliphatic or aromatic sulfonic acid.

Preferably the anion X~ is an anion of a perfluorinated aliphatic or perfluorinated aromatic organic sulfonic acid.

Exemplary of such anions are anions of Cl-CgperfluoroaLkanemonosulfonic acids or of perfluorobenzene- or perfluortoluenemonosulfonic acid, such as CF3S03-, C2FsSO3-, C2F7S03, C4FgS03, C6Fl3S03-, C8Fl7S03-, C6FsS03- and CF3-C6F4S03-All these anions are very weak nucleophiles.

Preferred anions X9 are BF4-, PF6-, AsF6-, SbF6- or SbFs(OH)- and CF3S03-.

Among these anions, it is especially preferred to use AsF6- and SbF6- . Initiators containing these last mentioned anions, preferably containing the SbF6- anion, result in particularly rapidly curing epoxy resin mixtures.

The compounds of forrnula I can be prepared by processes analogous to known ones. The preparation of metallocene complexes of this type containing complex halide anions is described, for exarnple, in EP-A-94 915 cited above.

Compounds of formula I containing other anions can be prepared by a modification of the process disclosed therein by introducing, in a manner known per se, in place of an anion of a complex acid an anion of the acid HX, wherein X~ is as defined above.

Especially preferred compounds of formula I are those wherein a and b are 1, Rl is a stilbene radical or a benzene or naphthalene radical which is substituted by one or two Cl-C4alkyl or Cl-C4aLI~oxy groups, R2 is an unsubstituted cyclopentadienyl anion, and X~
is BF4-, PF6-, AsF6-, CF3S03- and, preferablyl SbF6-, including especially thosecompounds of formula I, wherein Rl is isopropylbenæne or methylnaphthalene, and X~ is SbF6- .

Typical examples of suitable compounds of formula I are (~6-isopropylbenzene)(~5-cyclo-pentadienyl)iron(II)hexafluoroantimonate, (~6-isopropylben~ene)(~5-cyclopentadienyl)-iron(II)trifluoromethanesulfonate or (~6-isopropylbenzene)(~5-cyclopentadienyl)-iron(II)hexafluorophosphate, (~6-stilbene)(~s-cyclopentadienyl)iron(II)hexafluoro-antimonate or ~llfi-stilbene)(~S-cyclopentadienyl)iron(ll)hexafluorophosphate, (ll6-methylnaphthalene)(~5-cyclopentadienyl)iron(I~hexafluoroanti nonate or (~6-methyl-naph~lhalene)(~s-cyclopentadienyl)iron(II)hexafluoroarsenate and (7l6-naphthalene)(~-cyclopentadienyl)iron(II)tetrafluorborate. Most preferred compounds of formula I are (1l5-methylnaphthalene)(~s-cyclopentadienyl)iron(II)hexafluoroantimonate, ar~d, most particularly, (ll6-isopropylbenzene)(~s-cyclopentadienyl)iron(II)hexafluoroantimonate.

The compositions of this invention comprise preferably 0.2-5 % by weight, preferably 0~5-2 % by weight, of component (b) and 0.05-2 by weight, preferably 0.1-1 % by weight, of component (c), based on the epoxy resin (a) The curable compositions may additionally comprise filrther additives. These additives are substances with which the properties of the cured products and/or the processingproperties of the compositions are modified.

Typical exarnples of such modifiers are fillers or extenders such as chaL~, talcum, kaolin, mica, gypsum, titanium dioxide, quartz powder, alumina, cellulose, ground dolomite, wollastonite, silica having a large specific surface area (sold under the registered trademark Aerosil), bentonites, powdered polyvinyl chloride, polyolefins, also metal powders such as copper, silver, aluminium or iron powder, flame retardants such as antimony trioxide, colourants such as dyes and pigments, light stabilisers for improving the resistance of the final composition to UV light, release agents for separating at an intermediate stage the layers individually prepared in step i), for example release liners, film-forming varnishes or waxes, thixotropic agents such as highly dispersed silicic acid, reactive diluents such as phenyl or cresyl glycidyl ethers, butanediol diglycidyl ethers or hexahydrophthalic acid diglycidyl ethers, or inert diluents for preparing impregnating solutions of highly viscous or solid epoxy resin mixtures, such as chlorinated aliphatic or aromatic hydrocarbons such as dichloromethane, trichloroethane, tetrachloroethane, chlorobenzene, or aromatic hydrocarbons such as toluene or xylene, or aliphatic ketones such as acetone oe methyl ethyl ketone.

As further modifiers it is also possible to ue sensitisers and/or oxidising agents such as anthracene or cumene hydroperoxide.

The laminates of this invention can be used in particular for making printed circuit boards and insulating materials.

The invention is illustrated by the following Examples.

Example 1: A solution is prepared from 1000 g of a brominated technical grade diglycidyl ether, dissol~ed in methyl ethyl ketone, based on bisphenol A (epoxy value 1.85 eq/kg), 3.5 g of (~6-isopropylbenzene)(~s-cyclopentadienyl)iron(II)hexafluoroantimonate (abbreviated to "photoinitiator I") and 5.6 g of 2,6-diisopropylaniline. The concentration of the photoinitiator and of the aromatic amine is, respectively, 0.5 and 0.8 percent b~
weight, based on solid epoxy resin.

Webs of glass cloth are impregnated with this solution (weight per unit area 200 g/m2).
The impregnated glass cloth is allowed to drip for several minutes at room temperature before it is freed from solvent for 2 minutes at 150C in a circulating air oven. The solvent-free webs are passed under a W lamp (Fusion D-lamp, 80 W/cm) at a speed of 2.7 m/min, and then the solid resin is rippled out of a dried web and the other webs are cut into pieces measuring 15 x 15 crn.

The lowest melt viscosity of the rippled resin is measured at 100C with a conical-plate viscosimeter and is indicated in Table 2. Eight each of the 15 x 15 cm pieces are processed together in a heatable press to a laminate, applying first a pressure of 1-5 b~Lr for 20 seconds at 170C, then of 30 bar for 15 minutes at 170C. The glass transition temperature of the finished laminate is given in Table 2.

A portion of the dried and ilradiated web is stored at room temperature and after 28 days processed again as described above. Resin is rippled out of the dried web and a laminate is prepared under the same compression moulding conditions. The melt viscosity of the resin and the glass transition temperature Tg are reported in Table 2.

Examples 2-7 and 9-15: A solution of the resin used in Example 1 is prepared. To this resin solution are added the photoinitiators (designated as I) and ms)difiers listed in Table 1, the amounts indicated therein being parts by weight, based on solid resin. These solutions are processed as described in Exarnple 1. The melt viscosities and glass :: :
. , . .~ .

transition points Tg in the storable state and after storage are indicated in Table 2.

Table 1: Chemical structure and arnount of photoinitiator and stabiliser in Examples 1-7 and 9-15 Example Photoinitiator Stabiliser ( % by wt. ) ( % by wt. ) , 1 I; 0.5 % 2,6-diisopropylaniline; 0.8 %
2 I; 1.0 % bis(4-amino-3,5-diethylphenyl)methane; 0.5 %
3 I; 0.5 % bis(4-amino-3-isopropyl-5-methylphenyl)methane; 0.5 %
4 I; 0.5 % bis(4-amino-3,5-diisopropylphenyl)methane; 0.5 %
I; 0.5 % bis(4-amino-3-ethyl-5-methylphenyl)methane; 0.5 %
6 I; 0.5 % 4,4'-diarninodiphenylsulfone; 0.8 %
7 I; 0.5 5b 1,3-propanediolbis(4-aminobenzoate); 0.4 %
9 I; 0.5 % 2,2'-bipyridine; 0.5 % ~
10 I; 1.0 % anthranilic acid; 0.5 %
11 I; 0.5 % anthranilic acid; 0.5 %
12 I; 1.0 % diethyltoluylenediamine; 0.2 %
13 I; 0.5 % Mixture [Detda-80; I,onza Basel] of 2,4-diamino-3,5-diethyltoluene (ca. 20 %) and 2,6-diamino-3,5-diethyltoluene (ca. 80 %); 0.5 %
14 I; 1.0 % 3-dimethylaminobenzoic acid; 0.2 %
I; 1.0 % 4-dimethylarninobenzaldehyde; 0.7 %

Exarnple 8: In a flask, 1524 g of a technical grade diglycidyl ether based on bisphenol A
(epoxy value 5.27 eq,~cg) and 79û g of tetrabromobisphenol A are mixed and heated to 170C until the tetrabromobisphenol A has reacted completely with the diglycidyl ether.
The epoxy value is then 2.22 eq/kg.

Then 9.0 g of bis(4-amino-3,5-diethylphenyl)methane are added and the mixture is kept at ca. 170C until the amine has reacted completely with the epoxy resin. Then, with cooling, 583 g of methyl ethyl ketone are added dropwise to the reaction mixture.

" . ~, To 450 g of this epoxy resin are added 1.8 g of photoinitiator I of Example 1: its concentration is 0.5 %, based on solid epoxy resin. This solution is processed as in Example 1, except that the impregnated, solvent-free glass cloth is treated under the U~
larnp at a speed of 2.0 m/min. The lowest melt viscosity and glass transition temperature are measured in the storable state and after storage ~q.v. Table 2).

-Table 2: Melt viscosity and Tg of compositions of Examples 1-15 Storage ome Melt viscosity O
Exampl Tg ( C) at RT (days) at 100C (poise) 28 2070 13~

12 0 11~0 143 13 0 79~ 130 The melt viscosities shown in Table 2 illustrate the good storage stability of the compositions of the invention after irradiation. Even after storage for 28 days or longer at room temperature, the increase in viscosity of the compositions is insignificant, in~icating that the cure has not taken place at all or has not substantially taken place. The same conclusion can be inferred from the glass transition temperature. This temperature is measured in the fully cured system, the heat-activated cure being carried out after varying length of storage of the irradiated mixtures. ~s is evident, the Tg values measured scarcely change even after prolonged storage. The differences are in the mean error range in view of the accuracy of the measurement.

Comparison Example (without stabiliser): ~ solution of 700 g of the epoxy resin used in Example 1 and 2.45 of photoinitiator I is prepared. As in Example 1~ the concentration of the photoinitiator is 0.50 %, based on solid epoxy resin~ but no stabiliser is used. This solution is processed as in Example 1. The lowest melt viscosity is measured at 100C, and the glass transition temperature is measured at room temperature as a function of the storage at room temperature.

Viscosity (poise) Tg (C) in the storable state after 0 days 1335 141 after 1 day 1610 139 after4 days 187~) 136 Compared with Exarnples 1-9, the viscosity increases very rapidly (by 40 % in only 4 days); the Tg has fallen to 5C after this time.

This comparison shows that the irradiated resin is not storage stable in the absence of the amine and essential properties alter substantially over the short period of 4 days.

. .

Claims (16)

1. A curable composition comprising (a) an epoxy resin, (b) an iron-arene complex of formula I
(I), wherein a and b are each independently of the other 1 or 2, R1 is a .pi.-arene, R2 is a .pi.-arene or an indenyl or cyclopentadienyl anion, X? is an anion [LQm]? or an anion of a partially fluorinated or perfluorinated aliphatic or aromatic sulfonic acid, L is B, P, As or Sb, Q is fluoro or some of the radicals Q may also be hydroxyl groups, and m is the valency of L
increased by one, and (c) a stabiliser selected from the group consisting of (c1) aromatic amines having a pKa value of 2-5 and containing 1 to 4 NH2 groups and at least one substituent in ortho-position to each amino group, said substituent being C1-C10alkyl, C1-C10alkoxy, C5-C6cycloalkyl, C6-C10aryl or halogen, with the proviso that no halogen is present in both ortho-positions to the amino group, or (c2) aromatic amines having a pKa value of 2-5 and containing 1 to 4 NH2 groups and one substituent in ortho- or para-position to each amino group, said substituent being -COOH, -COOR, -COR, -SO2R or -SOR, and R is -H, alkyl, cycloalkyl, aryl, aminoaryl or -R5-OOC-C6H4-NH2, where R5 is alkylene, or (c3) bipyridines, which composition contains 0.1-10 % by weight of component (b) and 0.02-5 % by weight of component (c), based on the epoxy resin (a).

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

3. A composition according to claim 1, wherein component (c1) is a 2,6-dialkylaniline or a compound of formula II

(II), wherein R3 is chloro or alkyl and R4 is hydrogen or alkyl.

4. A composition according to claim 3, wherein component (c1) is 2,6-diisopropylaniline or a compound of formula II, wherein R3 and R4 are each independently of the other C1-C3alkyl, preferably methyl, ethyl or isopropyl.

5. A composition according to claim 1, wherein component (c2) contains ane or two NH2 groups and has a pKa value of 2-3.5.

6. A composition according to claim 1, wherein component (c2) is anthranilic acid or a compound of formula III
;
(III), wherein T is CO, SO and, preferably, SO2, -COO(CH2CH2O)nOC- or -COO(CH2)nOOC-, where n is 2-6, preferably 2.

7. A composition according to claim 1, wherein component (c3) is 2,3'-, 2,4'-, 3,3'-, 4,4'-and, preferably, 2,2'-bipyridine.

8. A composition according to claim 1, wherein the iron-arene complex (b) is a compound of formula I, wherein a and b are 1, R1 is a stilbene radical or a benzene or naphthalene radical which is substituted by one or two C1-C4alkyl or C1-C4alkoxy groups, R2 is an unsubstituted cyclopentadienyl anion, and X? is BF4-, PF6-, AsF6-, CF3SO3- and, preferably, SbF6-.

9. A composition according to claim 8, wherein R1 is isopropylbenzene or methyl-naphthalene, and X- is SbF6-.

10. A composition according to claim 1, comprising 0.2-5 % by weight, preferably0.5-2 % by weight, of component (b) and 0.05-2 by weight, preferably 0.01-1 % by weight of component (c), based on the epoxy resin (a).

11. A composition according to claim 1 comprising in addition to components (a), (b) and (c) an electron acceptor as oxidising agent and/or a sensitiser for the compound of formula I.

12. A prepreg comprising a fibrous substrate and a composition according to claim 1.

13. A prepreg comprising a fibrous substrate and an activated composition obtainable by irradiating the composition according to claim 1.

14. A laminate obtainable by subjecting the prepreg as claimed in either claim 12 or claim 13 to heat-activated curing.

15. A process for the preparation of a laminate comprising the steps:
i) preparing a layer by contacting a fibrous substrate with a curable composition according to claim 1, ii) preparing a sequence of layers of at least two layered materials to be bonded together, at least one of which is a layer obtainable in step i) in which the curable material is substantially in unchanged form, and iii) compressing said sequence of layers at elevated temperature, the pressure and temperature being so chosen that a liquid matrix resin is formed at the start of this step, the viscosity of said resin initially falling so that trapped gases are able to escape almost completely from the sequence of layers and that the increase in viscosity during the subsequent crosslinking reaction is so rapid that the resin flowing from the compression mould does not cause glueing of the mould.

16. A process according to claim 15, which comprises carrying the steps ii) and iii) continuously, such that a web of material obtainable according to step i), if desired together with webs of another layered material to be bonded together, is passed in each desired layer sequence simultaneously between heatable continuous laminators.