GB2099825A - Photopolymerisable mixtures, and processes for the photopolymerisation of cationically polymerisable compounds - Google Patents

Abstract

Cationically polymerisable compounds, particularly epoxide compounds, can be polymerised by UV irradiation when the catalyst used is a quaternary ammonium salt of an aromatic-heterocyclic compound which contains 1 or 2 N atoms, with an anion from the series comprising BF4<->, PF6<->, SbF6<->, SbF5(OH)<-> or AsF6<->, in combination with a photoinitiator from the series comprising the photolytically cleavable carbonyl compounds, as the co-catalyst.

Description

SPECIFICATION Photopolymerisable mixtures, and processes for the photopolymerisation of cationically polymerisable compounds The invention relates to photopolymerisable mixtures of cationically polymerisable compounds and a special catalyst-combination, and also to the corresponding process for the photopolymerisation of cationically polymerisable compounds by means of such catalyst-combinations.

Cationically polymerisable compounds cannot in general be polymerised by irradiation with shortwave light. Only by the addition of such catalysts that with UV irradiation form Lewis acids, which act as cationic polymerisation initiators, can cationically polymerisable compounds be also photochemically polymerised. Known examples of photocatalysts of this type are the tetrafluoroborates, hexafluorophosphates or similar complex salts of aromatic diazonium cations (US 3,708,296). Complex salts of this kind form, on exposure to UV light, BF3, PF5 or similar Lewis acids, which serve as cationic polymerisation initiators.

Also Lewis-acid complex salts of aromatic ammonium salts have been suggested as catalysts for a photopolymerisation of epoxides. In the German Offenlegungsschrift No. 2,518,656, there have been suggested for example the following aromatic ammonium salts as photoinitiators:

With the addition of 3% of ammonium salts of this type to 4-vinylcyclohexane dioxide or limonene dioxide, films formed therefrom cure on exposure to UV irradiation in times of about one minute. For many commercial applications, however, these exposure times are still too long. For example, for photographic printing, for coil coating or for other continuous processes, exposure times of 1-5 seconds are desired.

It has now been found that the exposure times necessary for curing can be considerabiy reduced by using aromatic-heterocyclic ammonium salts in combination with specific co-catalysts as photoinitiators.

The invention relates to photopolymerisable mixtures containing A) at least one cationically polymerisable compound, B) a quaternary ammonium salt of an aromatic-heterocyclic compound which contains 1 or 2 N atoms, with an anion from the series comprising BF4-, PF6-, SbF6-, SbFs(OH)- and Ass6~, as catalyst, C) at least one photoinitiator from the series comprising photolytically cleavable carbonyl compounds, as co-catalyst, and D) optionally further additives.

Further subject matter of the present invention is a process for the photopolymerisation of cationically polymerisable compounds or mixtures of compounds by irradiation with short-wave light in the presence of an aromatic heterocyclic ammonium salt as catalyst, as well as in the presence of a photoinitiator, as co-catalyst, from the series comprising photolytically cleavable carbonyl compounds.

It was not to be expected that photoinitiators from the series of photolytically cleavable carbonyl compounds would in any way influence the photopolymerisation of cationically polymerisable compounds, since such carbonyl compounds are indeed khown as being effective photoinitiators for radically polymerisable compounds, but on their own have no effect on cationically polymerisable compounds.

Compounds cationically polymerisable according to the invention are saturated heterocycles containing 0 or S, especially those with 3, 4 or 5 ring members, and derivatives thereof. Examples thereof are oxiranes, such as ethylene oxide, propylene oxide, epichlorohydrin, styrene oxide, phenyl glycidyl ether or butyl glycidyl ether; oxetanes, such as trimethylene oxide, 3,3-dimethyloxetane or 3,3di(chloromethyl)-oxetane; oxolanes, such as tetrahydrofuran or 2,3-dimethyltetrahydrofuran; cyclic acetals, such as trioxane, 1 ,3-dioxolane or 1 ,3,6-trioxyacyclooctane; cyclic lactones, such as propiolactone, E-caprolactone and alkyl derivatives thereof; thiiranes, such as ethylene sulfide, 1,2 propylene sulfide or thioepichlorohydrin; thietanes, such as 1,3-propylene sulfide or 3,3dimethylthietane.

Compounds polymerisable according to the invention are also those ethylenically unsaturated compounds which are polymerisable by a cationic mechanism. These include mono- and diolefins, for example isobutylene, 1 -octene, butadiene or isoprene; styrene, allylbenzene or vinylcyclohexane; vinyl ethers, such as vinyl methyl ether, vinylisobutyl ether or ethylene glycol divinyl ether; vinyl esters, such as vinyl acetate or vinyl stearate; N-vinyl compounds, such as N-vinyl pyrrolidone or N-vinyl carbazole, and dihydropyrane derivatives, for example the 3,4-dihydro-2H-pyrane-2-carboxylic acid ester of 2 hydroxymethyl-3,4-dihydro-2i-i-pyrane.

Compounds polymerisable according to the invention are moreover the pre-polymers of phenolformaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins and similar aminoplasts, as well as mixtures of such aminoplasts with functional acrylic resins, alkyd resins or polyester resins.

Compounds polymerisable according to the invention are also N-methylol derivatives of polycarboxylic acid amides, for example polyacrylamide.

Of particular importance among these polymerisable compounds mentioned are the epoxide compounds, especially the di- and polyeppxides and epoxide resin prepolymers, such as are used fpr producing epoxide resins. This is effected usually by chemical curing with amines, phenols, dicarboxylic acid anhydrides, and so forth, either at room temperature or with heating. When the catalyst combinations according to the invention are used, the epoxides can be cured photochemically without the addition of chemical reactants, that is to say, a single-component system can be used.

The di- and polyepoxides used for this purpose can be aliphatic, cycloaliphatic or aromatic compounds. Examples thereof are the glycidyl ethers of aliphatic or cycloaliphatic diols or polyols, for example those of ethylene glycol, propanediol-1,2, propanediol-1,3, butanediol-1,4, diethylene glycol, glycerol, trimethylol propane, 1 ,4-dimethylol-cyclohexane or of 2,2-bis(4-hydroxycyclohexyl)-propane, the glycidyl ethers of di- and polyphenols, such as of resorcinol, 4,4'-dihydroxydiphenylmethane, 2,2di(4-hydroxyphenyl)-propane or novolaks. Further examples are the N-glycidyl compounds, for example the digylcidyl compounds of ethylene urea, 1,3-propylene urea, 5-dimethylhydantoin, or of 4,4'methylene-5,5'-tetramethyl-dihydantoin, or such as triglycidylisocyanurate.

Further glycidyl compounds of commercial importance are the glycidyl esters of carboxylic acids, especially of di- and polycarboxylic acids. Examples of these are the glycidyl esters of adipic acid, phthalic acid, terephthalic acid, tetra- or hexahydrophthalic acid, isophthalic acid or of trimellitic acid.

Examples of polyepoxides which are not glycidyl compounds are the diepoxides of vinylcyclohexene, dicyclopentadiene, 3-(3',4'-epoxycyclohexyl)-8,9-epoxy-2,4-dioxaspiro[5,5]- undecane, 3,4-epoxycyclohexanecarboxylic acid-3' ,4'-epoxycyclohexylmethyl ester, butadiene- or isoprene diepoxide, epoxidised linoleic acid derivatives or epoxidised polybutadiene.

Ethylenically unsaturated epoxide compounds which are capable under the reaction conditions of reacting polyfunctionally and hence of forming crosslinked resins can also be used. Examples thereof are allyl-glycidyl ethers, acrylic acid- or methacrylic acid glycidyl esters or unsaturated polyepoxides, such as partially (meth)-acrylated epoxide resins.

The epoxide compounds can be used in admixture with one another or in admixture with other cationically polymerisable compounds, in order for example to modify the physical properties of the resins obtainable therefrom. An example of this are mixtures of polyglycidyl ethers with epoxidised soybean oil, which exhibit after cooling high elasticity and flexibility. The mixtures according to the invention can also contain additions of hydroxyl-containing compounds, such as are described in the German Offenlegungschrift No. 2,639,395. The epoxide compounds can also be pre-cured by chemical means, for example by reaction with diols or with dicarboxylic acid anhydrides.The use of prepolymers of this kind for producing articles made from epoxide resins can have certain advantages compared with the use of di- and polyepoxides, for example easier storage and handling, more rapid processing into shapes, as well as the possibility of incorporating additives, such as glass fibres or pigments, into the prepolymers, for example in the production of prepegs.

Such prepolymers can also be produced by thermal polymerisation when a thermal radical former is added as a second co-catalyst to the mixtures to be polymerised. Suitable thermal radical formers are for example organic peroxy compounds or azo compounds, especially however dibenzyl derivatives of benzopinacol and derivatives thereof.

The ammonium salts used as component B) according to the invention are salts of aromaticheterocyclic nitrogen bases. Examples of these are in particular six-membered nitrogen heterocycles, such as pyridine, pyrazine, pyrimidine and pyridazine, and the alkyl, aryl, benzo and naphtho derivatives thereof, for example picoline, lutidine, quinoline, benzopyrazine or benzopyridazine, but also fivemembered hetero rings, such as benzimidazole or benzothiazole and derivatives thereof.

Preferred as component B) are ammonium salts of the formulae I, II, Ill and IV,

wherein R1 is C1-C12-alkyl, C3-C15-alkoxyalkyl or benzoylmethyl, R2, R3, R4, R5 and R6 independently of one another are each hydrogen, C1-C4-alkyl or phenyl, or R2 and R3 or r3 and R4 or R4 and R5 or R5 and R, together with the two C atoms to which they are bound, form an annularly-linked benzo, naphtho, pyridino or quinoline group, R7 is C1-C12-alkyl or phenyl, X is BF4, PF6, SbF6, SbF5(OH) or AsF6, and Y is oxygen, sulfur or a direct bond.

Some of these ammonium salts are known compounds, whilst some are novel compounds which can however be produced by methods analogous to known methods. They can be produced in particular by quaternisation of the heterocyclic bases by means of a halogen compound B1 Hal, and subsequent exchange of the halide anion for an anion of the formula X by means of the alkali salts of X.

Examples of individual ammonium salts usable according to the invention are: 1 -methyl-quinolinium-hexafluorophosphate, 1 -methyl-quinolinium-hexafluoroantimonate, 1 -methyl-quinolinium-hexafluoroarsenate, 1 -methyl-quinolinium-pentafluorohydroxyantimonate, 1 -methyl-quinolinium-tetrafluoroborate, 1 ,2-dimethyl-quinolinium-hexafluorophosphate, 1 -ethyl-quinolinium-hexafluorophosphate, 1 -butyl-quinolinium-hexafluorophosphate, 1 -benzoyl methyl-quinoliniu m-hexafluorophosphate, 1 -benzoylmethyl-quinolinium-hexafluoroantimonate, 1 -methyl-2,3-diphenyl-pyridinium-hexafluornphosphate, 1 ,2-dimethyl-3-phenyl-pyridiniu m-hexafluorophosphate, 1 -benzoylmethyl-pyridinium-hexafluorophosphate, 1 -ethoxyethyl-quinoliniu m-hexafluorophosphate, 2-methyl-isoquinolinium-hexafluorophosphate, 1 0-methyl-acridinium-hexafluorophosphate, 1 O-benzoylmethyl-acridinium-hexafluorophosphate, 1 0-butyl-acridinium-hexafluoroarsenate, 5-methyl-phenanthridinium-hexafluorophosphate, 5-benzoylmethyl-phenanthridinium-hexafluorophosphate, 1 -methyl-naphthyridinium-hexafluorophosphate, 1 -methyl-2,3-diphenylquinoxalinium-hexafluorophosphate, 1 ,2,3-trimethyl-quinoxalinium-hexafluorophosphate, 1 -methyl-quinazolinium-hexafluorophosphate, 1 -methyl-quinoxalinium-hexafluorophosphate, 1 ,2,4,6-tetramethylpyrimidinium-hexafluorophosphate, 1 -methyl-2,4-diphenylpyrimidinium-hexafluorophosphate, 1 -methyl-3-phenyl-pyridazinium-hexafluorophosphate, 1 -methyl-2,5-diphenyl-pyridaziniu m-hexafluorophosphate, 1 -methyl-phenanthrolinium-hexafluorophosphate, 5-butyl-phenaziniu m-hexafluorophosphate, 1 -methyl-cinnoliniu m-hexafluorophosphate, 1 -benzoyl methyl-quinoxaliniu m-hexafluorophosphate, 1 ,2-dimethylbenzthiazolium-hexafluorophosphate, 1 -methyl-2-methylthio-benzthiazolium-hexafluorophosphate, 1-methyl-2-methoxy-benzthiazolium-hexafluorophosphate, and 1 -benzoylmethyl-2-methylbenzthiazolium-hexafluorophosphate.

A photolytically cleavable carbonyl compound, of the type known as initiators for radical photopolymerisation, is used as the co-catalyst (component C). Examples of there are benzoin and derivatives thereof, benzil and derivatives thereof and a-di- and trisubstituted acetophenones. When exposed to short-wave light, compounds of this kind split into two radical fragments, of which one is an acyl radical. These radicals are able to initiate radical chain reactions; such compounds are therefore generally applicable as radical photoinitiators.

There is preferably used as co-catalyst (component C) a compound of the formula V, VI, VII or VIII

wherein Ar is phenyl, or phenyl substituted by C1-C4-alkyl, halogen, C1-C4-alkoxy, phenoxy, C1-C4- alkylthio or phenylthio, R'O is hydrogen, C1412-alkyl, C3-C15-alkoxyalkyl or phenyl, or phenyl substituted by C1-C4-alkyl or halogen, R" is hydrogen, C1-C4-alkyl, allyl, benzyl or phenyl, R12 is hydrogen or it is Ar, R'3 is C 1-C4-alkyl which can be substituted by halogen or C1-C12-alkoxy, R14 and R15 independently of one another are each C1-C8-alkyl which can be substituted by OH, C1-C4-alkoxy or phenyl, or R'4 and R15 together are C4-C7-alkylene, R16 is hydrogen, C1-C4-alkyl, benzyl, allyl, 2-cyanoethyl, phenyl or-Si(R20)2R21, and R20 and R21 are identical or different radicals and are methyl or phenyl, R17 is tertiary C4-C12-alkyl or phenyl which is substituted at least in both ortho-positions by C1-C4-alkyl, C1-C4-alkoxy or halogen, and R18 and R'9 independently of one another are each C1-C4-alkyl, C1-C4-alkoxy or phenyl, or phenyl substituted by C1-C4-alkyl, C1-C4-alkoxy or halogen.

Examples of compounds of the formula V are: benzoin, 4,4'-dichlorobenzoin, a-methylbenzoin, benzoin-methyl ether, -ethyl ether, -isopropyl ether, -sec-butyl ether, -isobutyl ether, -amyl ether, -hexyl ether, -octyl ether or -dodecyl ether, abenzylbenzoin-butyl ether and 4,4'-dimethoxybenzoin-isopropyl ether.

Examples of compounds of the formula VI are: a-dimethoxyacetophenone, a-diethoxyacetophenone, benzil-dimethyl ketal, benzil-diethyl ketal, benzil-di(2-chloroethyl) ketal, benzil-di(2-butoxyethyl) ketal, benzil-dibutyl ketal, 4,4'-dichlorobenzil- diethyl ketal and 4,4'-dimethylbenzil-dimethyl ketal.

Examples of compounds of the formula VII are: 2-benzoyl-propanol-2, 2-(4-isopropylbenzoyl)-propanol-2, 2-(4-tert-butylbenzoyl)-propanol-2, 2 (4-chlorobenzoyl)-propanol-2, 2-(4-methylbenzoyl)-butanol-2, 2-benzoyl-butanediol- 1,2, 1 -benzoyl- cyclopentanol, 1 -benzoyl-cyclohexanol, 1 -(4-isopropylbenzoyl)-cyclohexanol, 1-(4-chlorobenzoyl)cyclooctanol, a-methoxy-isobutyrophenone, a-cyanoethoxy-isobutyrophenone, a-phenoxy-4chloroisobutyrophenone and ct-trimethylsiloxy-isobutyrophenone.

Examples of compounds of the formula Villi are: 1 ,3,5-trimethylbenzoyl-diphenyl-phosphine oxide, 2,6-dichlorobenzoyl-diphenylphosphine oxide, 2 ,6-dimethoxy-benzoyl-diphenyl-phosphine oxide, methyl- 1 ,3,5-trimethyl-benzoyl-phenylphosphinate, pivaloyl-diphenylphosphine oxide and methyl-pivaloyl-phenylphosphinate.

The amount of ammonium salt as component B) required for the process according to the invention is 0.1 to 5% by weight, preferably 1 to 3% by weight, relative to component A).

The amount of co-catalyst (component C) required for the process according to the invention is 0.1 to 5% by weight, preferably 2 to 4% by weight, relative to the component A).

The photopolymerisable mixtures according to the invention can contain further additives of the types known and customarily used in the technology of photocurable compositions. Examples of additives of this kind are pigments, dyes, fillers and reinforcing materials, glass fibres and other fibres, flameproofing agents, antistatic agents or levelling agents. Further examples are photosensitisers, which shift the spectral sensitivity of the photopolymerisable mixtures into specific ranges, for example perylene, derivatives of anthracene and of thioxanthone, or organic dyes. Further examples are antioxidants and light stabilisers, which stabilise the cured compositions against ageing.

With the exclusion of short-wave light, the mixtures according to the invention can be stored at room temperature for a long time without undergoing change. Polymerisation of the mixture is effected by irradiation with short-wave light, for example by means of medium pressure, high pressure or low pressure mercury vapour lamps, or by means of superactinic fluoroescent tubes, the emission spectrum of which is in the range of 250-400 my. When suitable photosensitisers are present, it is also possible to effect curing in daylight. Such sensitisers are described for example in U.S. Patent Specification No.

3,729,313. it is not necessary to add to the mixture according to the invention any catalyst or other additive prior to polymerisation. The mixtures are therefore single-component systems free from solvents.

The process is suitable in particular for curing films and coatings based on epoxide compounds.

These coatings can be applied and cured on any material, for example on metal, wood, paper, glass ceramic compositions or plastics, and serve in most cases to protect or to decorate the articles concerned.

The process is also suitable for curing printing inks, since the drying time of the binder plays an important part with respect to the rate of production of graphical products.

The process is also suitable for producing laminates, mouldings and printing plates, for example those made from epoxide resins. The photopolymerisable mixtures are in this case largely used in combination with glass fibres and other fibres. Examples are the production of sheets or tubes, or the production of sports articles or of components for automobile bodies. In the case of such relatively thick-walled laminates and mouldings, the superiority of the photopolymerisation obtained using the catalyst combination according to the invention compared with that obtained using ammonium salts as the sole catalyst in the known manner is partiularly clear.

One variant of the process comprises carrying out curing in two stages. In this case, the substrate is firstly irradiated with a radiation dosage that indeed effects an activation of the catalyst but still no curing. In a second stage, the substrate is heated, whereupon the actual cationic polymerisation occurs and curing is completed. It applies to this two-stage process too that satisfactory results are not obtained either with the catalyst alone or with the co-catalyst alone. Only when the two components are combined is a satisfactory curing effected.

This two-stage process is of interest especially with regard to those applications whereby a purely radiation curing is not possible, for instance in the bonding of nontransparent materials (for example, metals, wood or ceramic compositions) with epoxide resins.

Mixtures and photopolymerisation thereof according to the present invention are further illustrated in the Examples which follow. The term 'parts' therein denotes parts by weight, and percentage values are given as per cent by weight.

EXAMPLE 1 20 g of an epoxide resin based on bisphenol-A glycidyl ether and having an epoxide equivalent of 1 85-1 96 g/equiv. (Araldit GY 250, Ciba-Geigy AG) are mixed together with the catalyst and cocatalyst in the amounts shown in Table 1, and the mixture is stirred at 50-600C until a clear solution has formed (about 1 0 minutes). This solution is then applied, by means cf a coating knife, in a layer thickness of 300 ym to glass plates 9x 12 cm in size, and the specimens thus obtained are irradiated, in a PPG irradiation apparatus with 2 lamps each of 80 W/cm, at a transport speed of 10 m/minute in up to 20 passes, after which the drying of the film is assessed.In the following Table 1 is given the number of passes required until-the lacquer film is free from tackiness (tack-free).

Table 1

Passes Catalyst Amount Co-catalyst Amount until tack - free 0 5% - - > 20 PF6 CH3 2% C1 5% 2 25% C1 2,5 % 1 2% C2 5% 2 2,5 % C2 2,5% 1 pFO S% )20 CH 6 5% - - > 20 2% 2% C2 5% 8 CH3 2 % C2 5 25% 15 3 2,5% C2 2,5% 15 ::X PF6&commat; 5% - - > 20 2,5% 2,5 C2 C 2 35% 1 CH3 PF0 5% - > 20 N 2% Ci 5% 2 CtI2 2% C2 5% 7 Table I (continuation)

Passes Catalyst Amount Co-catalyst Amount until tack- free 0 PF6 5% - - > 20 2% Ci 5% 5 % 11 CH3 2% C2 SW 9 GC , 3 PF6 ~ ~ > 20 CH3 2,5 % C1 25 % 2 25% C2 2,5% 2 PF60 S% > 20 CHs 2 % C1 5 3 3 CH 2% Cl 5% 3 2% C2 5% 3 Employed co-catalysts: C1 = benzil-dimethyl ketal C2 = 1 -benzoylcyclohexanol EXAMPLE 2 Combined photo-curing and thermal curing Onto glass plates (9x 13 cm) are applied, by means of a coating knife, 200 ,um thick films of the following composition: 95.0 parts of Araldit GY 250, epoxide resin based on bisphenol-A diglycidyl ether having an epoxide equivalent of 185-196 glequivalent, 2.5 parts of catalyst according to Table 2, and 2.5 parts of 1 -benzoylcyclohexanol as co-catalyst.

The specimens are irradiated in a PPG irradiation apparatus with 2 lamps each of 80 W/cm at a transport speed of 10 m/minute in 4 passes. The specimens are subsequently heated in a drying cabinet at 1 600C for 30 minutes. After a conditioning time of several hours at room temperature, the pendulum hardness of the epoxide resin films is determined according to DIN 53 1 57. It is shown that the specimens with a co-catalyst are excellently cured throughout, whereas the specimens without the cocatalyst remain so soft that the pendulum hardness cannot be measured.

Table 2

Pendulum Catalyst Co-catalyst hardness jNp PF69 1- I-benzoyl- 98 sec.

N',',, F6 cyclohexanone not 3 without measurable I- benzoyl- 190 sec.

cyclohexanone CH3 without measurable EXAMPLE 3 Bonding ofmetal Test strips (1 5x2,5 cm) from a 1.5 mm thick aluminium sheet (Anticorodal) are used in the test.

The ends of the strips have been mechanically roughened on one side, and are coated with a film which is about 200 ,um thick and has the following composition: 95 parts of AralditB GY 250, 2.5 parts of catalyst: N-methylquinoxalinium-hexafluorophosphate, and 2.5 parts of co-catalyst: 1 -benzoylcyclohexanol.

The coated test strips are irradiated in a PPG irradiation apparatus with 2 lamps each of 80 W/cm in 4 passes with a transport speed of 10 m/minute. The coated ends of two test strips are then pressed together with 12 mm overlap, which corresponds to a bonding area of 300 mm2. The bonded areas are secured with a spring clip and the specimens are heated in the drying cabinet for 30 minutes at various temperatures. The strength of the bond is afterwards tested by determining the tensile strength. The results are shown in Table 3. Corresponding comparative tests without the co-catalyst show that no bonding occurs under these conditions.

TABLE 3

Curing Tensile strength in temperature N/mm 60 C 14,3 80 C 14,5 120 C 11,6

Claims (9)

1. A photopolymerisable mixture containing A) at least one cationically polymerisable compound, B) a quaternary ammonium salt of an aromatic-heterocyclic compound which contains 1 or 2 N atoms, with an anion from the series comprising BF4-, PF6-, SbF6-, SbFs(OH)- and AsF6~, as catalyst, C) at least one photoinitiator from the series comprising photolytically cleavable carbonyl compounds, as co-catalyst, and D) optionally further additives.

2. A photopolymerisable mixture according to Claim 1, which contains at least one epoxide compound as component A).

3. A photopolymerisable mixture according to Claim 1, which contains, as component B), an ammonium salt of the formula I, II, Ill or IV

wherein B1 is C1-C12-alkyl, C2-C16-alkoxyalkyl or benzoylmethyl, R2, R3, R4, B5 and R6 independently of one another are each hydrogen, C1-C4-alkyl or phenyl, or R2 and R3 or R3 and R4 or R4 and R5 or R5 and R6, together with the two C atoms to which they are bound, form an annularly-linked benzo, naphtho, pyridino or quinoline group, R7 is C1-C12-alkyl or phenyl, X is BF4, PF6, SbF6 SbF5(OH) or AsF6, and Y is oxygen, sulfur or a direct bond.

4. A photopolymerisable mixture according to Claim 1, which contains, as component C), at least one photoinitiator of the formula V, VI, VII or VIII

wherein Ar is phenyl, or phenyl substituted by C1-C4-alkyl, halogen, C1-C4-alkoxy, phenoxy, C1-C4- alkylthio or phenylthio, R10 is hydrogen, C1-C 12-alkyl, C3-C15-alkoxyalkyl or phenyl, or phenyl substituted by C1-C4-alkyl or halogen, R11 is hydrogen, C1-C4-alkyl, allyl, benzyl or phenyl, R12 is hydrogen or it is Ar, R'3 is C1-C4-alkyl which can be substituted by halogen or C1-C12-alkoxy, R14 and R15 independently of one another are each C1-C8-alkyl which can be substituted by OH, C1-C4-alkoxy or phenyl, or R'4 and R15 together are C4 t'C7-alkylene, R15 is hydrogen, C1-C4-alkyl, benzyl, allyl, 2-cyanoethyl, phenyl or -Si(R20)2R21, and R20 and R21 are identical or different radicals and are methyl or phenyl, R'7 is tertiary C4-C12-alkyl or phenyl which is substituted at least in both ortho-positions by C1-C4-alkyl, C1-C4-alkoxy or halogen, and B18 and R'9 independently of one another are each C1-C4-alkyl, C1-C4-alkoxy or phenyl, or phenyl substituted by C1-C4-alkyl, C1-C4-alkoxy or halogen.

5. A photopolymerisable mixture according to claim 1 substantially as described with reference to Example 1.

6. A process for the photopolymerisation of cationically polymerisable compounds or mixtures of compounds by irradiation with short-wave light in the presence of a catalyst and a co-catalyst, wherein the catalyst used is a quaternary ammonium salt of an aromatic-heterocyclic compound which contains 1 or 2 N atoms, with an anion from the series comprising BF4-, PF8-, SbF6-, SbFs(OH)- or AsF6-; and the co-catalyst used is a photoinitiator from the series comprising photolytically cleavable carbonyl compounds.

7. A process according to Claim 6, wherein the cationically polymerisable compounds or mixtures of compounds are firstly irradiated with short-wave light and subsequently heated.

8. A process according to Claim 6 substantially as described with reference to Example 2 or 3.

9. Polymerised compounds or mixtures of compounds when photopolymerised by a process claimed in any of claims 6 to 8.