GB2089818A - Photocurable compositions containing a photoinitiator and an azo compound or peroxide - Google Patents

Abstract

This invention provides a UV radiation curable composition consisting essentially of: (1) a liquid, ethylenically unsaturated compound of the formula: <IMAGE> wherein R is H or CH3, R1 is an organic moiety with the valence of n, and n is at least 2, (2) a non-nitrogen containing photoinitiator, and (3) a synergistic agent which is either an azo compound or an organic peroxide of the formula: R-O-O-1R1-O-O)n-R2 wherein n is 0 or 1, R and R2 are each hydrogen, aryl, alkyl, aryl carbonyl alkaryl carbonyl, aralkyl carbonyl or alkyl carbonyl, and R1 is alkyl or aryl, said alkyl groups containing 1 to 20 carbon atoms each. On exposure of such compositions to UV radiation, very rapid cures are obtained.

Description

SPECIFICATION Photocurable compositions containing a photoinitiator and an azo compound or peroxide 1. Field of the Invention This invention is directed to a radiation curable composition. More particularly, this invention relates to a radiation activated composition comprising liquid di-and polyacrylic terminated monomers, obligomers or prepolymers hereinafter referred to as the ethylenically unsaturated compound in combination with a non-nitrogen containing photoiniator and a synergistic agent from the group consisting of an azo compound and an organic peroxide.

The invention also relates to a process for forming cured materials from the aforesaid composition which can be utilized as coatings. gaskets, sealants, resists and the like.

2. Description of the Prior Art Curable coatings containing peroxides are known in the art.

U.S. 3,662,023 teaches a composition consisting essentially of an allylic terminates polyene and a polthiol in combination with an organic peroxide or hydroperoxide which on exposure to heat forms cured polythioethers.

U.S. 4.222,835 teaches a UV curable composition comprising a liquid vinyl monomer, a UV activated photoinitiator, a thermal initiator such as a peroxide or hydroperoxide and an accelerator capable of lowering the temperature at which said thermal initiator is activated comprising an amine or an amide.

Canadian Patent 1,076,296 teaches a photopolymerizable composition suitable for tooth coating purposes comprising a diacrylate terminated oligomer, an aliphatic acrylate monomer diluent, an organic peroxide free radical initiator and a photosensitizer comprising 4, 4'-bis-(dimethylamino)-benzophenone.

It is to be noted that in the latter two prior art UV curable compositions an amine is present either per se as an accelerator or as a moiety portion in the photo-sensitizer in order to obtain a tack-free surface on curing of the composition.

The present invention provides a composition which on exposure to UV radiation results in a through-cured material with a tack-free surface, and which has an accelerated curing rate.

This invention provides a UV radiation curable composition consisting essentially of: (1) a liquid, ethylenically unsaturated compound of the formula:

wherein R is H or CH, R, is an organic moiety with the valence of n, and n is at least 2, (2) a non-nitrogen containing photoinitiator, and (3) a synergistic agent which is either an azo compound or an organic peroxide of the formula: R-O-O-(R,-O-O),-R, wherein n is O or 1, R and R2 are each hydrogen, aryl, alkyl, aryl carbonyl, alkaryl carbonyl, aralkyl carbonyl, of alkyl carbonyl, and R, is alkyl or aryl, said alkyl groups containing 1 to 20 carbon atoms each.On exposure of such compositions to UV radiation, very rapid cures are obtained, and the invention includes within its scope a process for forming a cured solid product which comprises exposing a composition as aforesaid to UV radiation.

Although the aforesaid compositions, per se, are operable herein to form useful products, they may also be used in combination with conventional copolymerizable monomeric compounds or reactive diluents. The admixture of the composition of the instant invention with other monomers is employed usually to control viscosity and other application variables such as rate of cure as well as final film or coating properties such as hardness and flexibility. These reactive diluents cocure with the ethylenically unsaturated compound on exposure to UV radiation and heat.Examples of conventional copolymerizable compounds useful as reactive diluents include, but are not limited to, monofunctional acrylic esters, monofunctional methacrylic esters, styrene, vinyl-toluene, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl pyrrolidone, vinyl chloride, vinylidene chloride, butadiene, isoprene, chloroprene, divinyl benzene, di(vinyl-phenyl) carbonate, diallyl phthalate, diallyl carbonate, di-(allylphenyl) carbonate, diallyl furmarate, triallyl isocyanurate, triallyl cyanurate, diallyl chlorendate, diallyl maleate and unsaturated polyesters and mixtures threof.By the term unsaturated polyesters herein is meant the usual polycondensation products which consist of ester-like linked residues of polyvalent, especially divalent, alcohols, as well as possibly also residues of monovalent alcohols and/or of monovalent carboxylic acids, whereby the residues must contain at least partially unsaturated groups.

Examples of acids include maleic acid, fumaric acid, itaconic acid, mesaconic cid, citraconic acid, succinic acid, glutaric acid, adipic acid, phthalic acid, tetrachlorophthalic acid, hexachloroendomethylenetetrahydrophthalic acid, trimellitic acid, benzoic acid, linseed oil fatty acid and ricinoleic fatty acid and mixtures thereof. Examples of alcohols include ethylene glycol, diethylene glycol, propane, butane and hexane diols, trimethylolpropane, pentaerythritol, buta nol and tetrahydrofurfuryl alcohol.

The reactive diluents can be added to the system in amounts ranging up to 90% by weight of the ethylenically unsaturated compound, preferably 20 to 50% by weight on the same basis.

One class of non-nitrogen containing photoinitiators are the carbonyl compounds having at least one aromatic nucleus attached directly to the

group with any substituents on either the aromatic nucleus or the carbonyl group being limited to atoms selected from the group consisting of carbon, oxygen, hydrogen, chlorine, phosphorous, sulfur and combinations thereof.Various photoinitiators of this type include, but are not limited to, bezophenone, acetophenone, o-methoxy-benzophenone, dibenzosuberone, 4'-methoxy-acetophenone, benzaldehyde, 1 0-thioxanthen-9-one, xanthrene-9-one, 7-H-ben[dejanthra- cen-7-one, 1-naphthaldehyde, 2'-acetonaphthone, acetonaphthone, benz[a]anthracene 7.1 2 dione, 2,2,2-trichloro-4-t-butyl-acetophenone; 2-hydroxy-2-methyl- 1 -phenyl-propane-1 -one; benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin tretrahydropyranyl ether, 2, 2-dimethoxy-2-phenyl-acetophenone and benzil dimethyl ketal.

Mixtures of photoinitiators are operable herein. The photoinitiator or mixtures thereof are usually added in an amount ranging from 0.0005 to 30% by weight of the ethylenically unsaturated compound.

The organic peroxides operable as synergistic agents are of the general formula: R-O-O-(R,-O-O),-Rp wherein n = O or 1, R and R2 are is independently selected from hydrogen, aryl, alkyl, aryl carbonyl, alkaryl carbonyl, aralkyl carbonyl and alkyl carbonyl and R1 is alkyl or aryl, said alkyl groups containing 1 to 20 carbon atoms.

Examples of operable organic peroxides include, but are not limited to, 2,5-dimethyl-2, 5-di(tbutylperoxy)- hexane, 1, 3-bis(t-butylperoxyisopropyl) benzene, 1, 3-bis-(cumylperoxyisopropyl)benzene, 2, 4-dichlorobenzoyl peroxide, caprylyl peroxide, lauroyl peroxide, t-butyl peroxyisobutyrate, benzoyl peroxide, p-chlorobenzoyl peroxide, hydroxyheptyl peroxide, di-t-butyl diperphthalate, t-butyl peracetate, t-butyl perbenzoate, dicumyl peroxide, t-butyl hydroperoxide and di-t-butyl peroxide.

The organic peroxide is added to the composition in an amount ranging from 0.001-5.0%, preferably 0.01-2%, by weight based on the weight of the ethylenically unsaturated compound.

Examples of azo compounds operable as synergistic agents herein include, but are not limited to, commercially available compounds such as 2-t-butylazo-2-cyanopropane; 2, 2'-azobis(2, 4-dimethyl-4-methoxy-valeronitrile); 2,2'-azobis(isobutyronitrile); 2, 2'-azobis (2, 4-dimethylvaleronitrile) and 1 , 1 '-azobis-(cyclohexanecarbonitrile).

The azo compound is added to the composition in an amount ranging from 0.001-5%, preferably 0.01-2% by weight based on the weight of the ethylenically unsaturated compound.

The synergistic agent can be added to the system in various ways. That is, the synergistic agent, per se, can be admixed with the ethylenically unsaturated compound. Additionally, it can be admixed with a photoinitiator and added to the ethylenically unsaturated compound.

Furthermore, the organic peroxide can be dissolved or suspended in well known commercially available solvents such as dibutyl phthalate; Ketones, e.g., acetone and methylethyl ketone or chlorinated hydrocarbons such as methylene chloride, and then added to the system.

In practicing the instant invention it is sometimes desirable to add a polythiol to the composition prior to curing. Such addition of a polythiol to the system helps preclude the occurrence of a tacky surface due to air inhibition of the curing.

As used herein, the term polythiols refers to simple or complex organic compounds having a multiplicity of pendant or terminally positioned -SH functional groups per average molecule.

On the average the polythiols must contain 2 or more -SH groups/molecule and usually have a viscosity range of slightly above 0 to 20 million centipoises (cps) at 70"C, as measured by a Brookfield viscometer. Included in the term "polythiols" as used herein are those materials which in the presence of an inert solvent, aqueous dispersion or plasticizer fall within the viscosity range set out above at 70 C. Operable polythiols in the instant invention usually have molecular weights in the range 94-20,000, preferably 100-10,000.

The polythiols operable in the instant invention can be exemplified by the general formula: R8 (SH)n where n is at least 2 and R8 is a polyvalent organic moiety free from reactive carbon-tocarbon unsaturation. Thus, Rs may contain cyclic groupings and minor amounts of hetero atoms such as S, P or 0 but primarily contains carbon-hydrogen, carbon-oxygen or silicon-oxygen containing chain linkages free of any reactive carbon-to-carbon unsaturation.

One class of polythiols operable in the instant invention to obtain essentially odorless polythioether products are esters of thiol-containing acids of the general formula HS-R 9-COO H, where R9 is an organic moiety containing no "reactive" carbon-to-carbon unsaturation, with polyhydroxy compounds of the general structure R10-(OH))n, where R10 is an organic moiety containing no "reactive" carbon-to-carbon unsaturation and n is 2 or greater. These components will react under suitable conditions to give a polythiol having the general structure

wherein R9 and R10 are organic moieties containing no "reactive" carbon-to-carbon unsaturation and n is 2 or greater.

Certain polythiols such as the aliphatic monomeric polythiols (ethane dithiol, hexamethylene dithiol, decamethylene dithiol, tolylene-2, 4-dithiol, etc.) and some polymeric polythiols such as a thiol-terminated ethylcyclohexyl dimercaptan polymer, etc., and similar polythiols which are conveniently and ordinarily synthesized on a commerical basis, although having obnoxiuos odors, are operable in this invention but many of the end products are not widely accepted from a practical, commercial point of view.Examples of the polythiol compounds preferred for this invention because of their relatively low odor level include, but are not limited to, esters of thioglycolic acid (HS-CH2COOH), alpha-mercaptopropionic acid (HS-CH(CHa)-COOH) and betamercaptopropionic acid (HS-CH2CH2COOH) with polyhydroxy compounds such as glycols, triols, tetraols, pentaols, hexaols, etc. Specific examples of the preferred polythiols include, but are not limited to, ethylene glycol bis-(thioglycolate), ethylene glycol bis-(bate-mercaptopropionate), trimethylolpropane tris(thio-glycolate), trimethylolpropane tris(beta-mercapto-propionate), pentaerythritol tetrakis-(thiog lycolate) and pentaerythritol tetrakis-(beta-mercaptopropionate), all of which are commerically available.A specific example of a preferred polymeric polythiol is polypropylene ether glycol bis(beta-mercaptopropionate) which is prepared from polypropylene ether glycol (e.g., Pluracol P2010, Wyandotte Chemical Corp.) and beta-mercaptopropionic acid by esterification.

Additionally, polythiols operable herein to give cured solid polythioether products with the ehtylenically unsaturated compound (polyene) include the mercaptoester derivatives of styreneallyl alcohol copolymers set out in U.S. Patent No. 3,904,499 and the isocyanurate containing polythiols disclosed in U.S. Patent No. 3,676,440 and liquid thiol-terminated polymers made in accord with U.S. Patent No. 3,258,495, all incorporated hereby by reference. An example of the aforesaid latter type liquid thiol-terminated polymer is CAPCURE 3-800, commercially available from Diamond Shamrock Chemical Company.

The preferred polythiol compounds are characterized by a low level of mercaptan-like odor initially and, after reaction, give essentially odorless polythioether and products which are commercially attractive and practically useful resins or elastomers for both indoor and outdoor applications.

It should be understood that in order to obtain the maximum strength, solvent resistance, creep resistance, heat resistance and freedom from tackiness, the reaction components consisting of the polyene and polythiol of this invention are formulated in such a manner as to give solid, crosslinked, three dimensional network polythio-ether polymer systems on curing. In order to achieve such infinite network formation, the individual polyenes and polythiols must have a functionality of at least 2 and the sum of the functionalities of the polyene and polythiol components must always be greater than 4. Blends and mixtures of the polyenes and the polythiols containing said functionality are also operable herein.

When a polythiol is used in combination with the ethylenically unsaturated compound, the amount of polythiol used for preparing the curable composition can vary up to a stoichiometric amount required to react with all the ethylenically unsaturated groups present in the compound.

Prior to curing, the polyene and polythiol components are admixed in a suitable manner so as to form a homogeneous liquid curable mixture. Thus, the polyene and polythiol reactants can be admixed without the necessity of using a solvent at room temperature or slightly elevated temperatures up to about 40"C when one of the components is a solid or, if desired, the reactants may be dissolved in a suitable solvent and, thereafter, the solvent can be removed by suitable means such as evaporation.

The compositions of the present invention may, if desired, include such additives as antioxidants, dyes, inhibitors, fillers, pigments, antistatic agents, flame-retardant agents, thickeners, thixotropic agents, surface-active agents, viscosity modifiers, extending oils, plasticizers, tackifiers and the like within the scope of this invention. Such additives are usually preblended with the ethylenically unsaturated compound prior to or during the compounding step. Operable fillers include natural and synthetic resins, glass fibers, wood flour, clay, silica, alumina, carbonates, oxides, hydroxides, silicates, glass flakes, berates, phosphates, diatomaceous earth, talc, kaolin, barium surfate, calcium sulfate, calcium carbonate, antimony oxide and the like.The aforesaid additives may be present in quantities up to 500 parts or more per 100 parts of the ethylenically unsaturated compound by weight and preferably about 0.005 to about 300 parts on the same basis.

Additionally, conventional UV stabilizers and antioxidants such as hydroquione, tert-butyl hydroquinone, tert-butyl catechol, p-benzoquione, 2, 5-diphenylbenzoquinone, 2, 6-di-tert-butylp-cresol, substituted acrylonitriles such as ethyl-2-cyano-2, 3-diphenyl acrylate, 2-ethylhexyl-2cyano-3, 3-diphenyl acrylate, etc., are added to the system.

A type of radiation useful herein for curing is ultraviolet light and other forms of actinic radiation which are normally found in radiation emitted from the sum or from artifice31 sources such as Type RS Sunlamps, carbon arc lamps, xenon arc lamps, mercury vapor lamps, tungsten halide lamps and the like. Ultraviolet radiation may be used most efficiently if the photocurable composition contains a suitable photoinitiator. Curing periods may be adjusted to be very short and hence commercially economical by proper choice of ultraviolet source, photoinitiator and concentration thereof, organic peroxide or azo compound and concentration thereof, temperature and molecular weight and reactive group functionality of the ethylenically unsaturated compound. Curing periods of about 1-80 seconds duration are possible, especially in film and coating applications.

When UV radiation is used, an intensity of 0.0004 to 60.0 watts/cm2 in the 200-400 nanometer region is usually employed.

In practice the instant invention the UV curable composition is admixed in any order and applied to the substrate by various conventional means such as spraying roller coating or dipping. Following application the composition is exposed to UV radiation for a short period of time, e.g., about 1 second to 10 minutes.

The following examples will aid to explain, but specifically not limit, the instant invention.

Unless otherwise noted, all parts and percentages are by weight.

Example 1 100 parts of commerically available trimethylol-propane triacrylate was admixed with 1 part of 2, 2-dimethoxy-2-phenylacetophenone, commercially available from Ciba-Geigy under the tradename "IRGACURE"-651, in an aluminium weighing dish. The admixture was exposed to UV light from a medium pressure Hg lamp; Ascor Addalux Model 1415-42 situated 24" from the admixture. A total cure through the approximately 80 mil thick mixture was obtained in 9 seconds.

Example 2 100 parts of commercially available trimethylol-propane triacrylate were admixed with 0.5 parts of benzoyl peroxide in an aluminium weighing dish. The admixture was exposed as in Example 1 to UV radiation. A through-cure of the 80 mil thick mixture was obtained in 66 seconds.

Example 3 100 parts of trimethylolpropane triacrylate was admixed with 1 part of "IRGACURE"-65 1 and 0.5 parts of benzoyl peroxide in an aluminium weighing dish. After exposure to UV radiation as in Example 1 a through-cure of the 80 mil thick mixture was obtained in 2 seconds.

Example 4 100 parts of commercially available trimethylol-propane triacrylate was admixed with 1 part of "IRGACURE"-651 and 5 parts of pentaerythritol tetrakis-beta-mercaptopropionate, commercially available from Cincinnati Milacron under the tradename "Q-43" in an aluminium weighing dish. The admixture was exposed to UV light from a medium pressure Hg lamp; Ascor Addalux Model 1415-42 at a distance of 24" from the admixture. A through-cure was obtained in 7 seconds.

Example 5 100 parts of commercially available trimethylol-propane triacrylate was admixed with 0.5 parts of benzoyl peroxide and 5 parts of "Q-43". After exposure as in Example 4 the admixture cured clear through in 1 8 seconds.

Example 6 100 parts of commercially available trimethylol-propane triacrylate was admixed in an aluminium weighing dish with 1 part "IRGACURE"-651, 5 parts "Q-43" and 0.5 parts benzoyl peroxide. After exposure as in Example 4 a through-cure was obtained in 1.5 seconds.

As shown in TABLE 1, trimethylolpropane triacrylate with or without a polythiol was admixed with either a photoinitiator or a synergistic agent or both in an aluminum weighing dish. The various admixtures were each exposed to UV light at a distance of 24" from a medium pressure Hg lamp (Ascor Addalux Model 1415-42). The various combinations and the UV exposure times are shown in TABLE I.

SYNERGISTIC EFFECT WITH MIXED PHOTOINITIATORS AND SYNERGISTIC AGENTS IN ACRYLATE AND THIOL ACRYLATE FORMULATIONS TABLE I Exposure Ex. Time to No. Formulation UV (sec) Comments 7 TMOP-TA(a)/1% Irgacure 651(b) 9 Cure 8 w/o.5t Benzoyl Peroxide 2 Cure & Exotherm (C) 9 w/0.1% Benzoyl Peroxide 3 Cure & Exotherm 10 w/0.01% Benzoyl Peroxide 7 Cure 11 TMOP-TA/0.58 Benzoyl Peroxide 66 Cure & Exotherm 12 TMOP-TA/18 IrXacure 651/ 5% 0-43 a) 7 Cure 13 w/0.5% Benzoyl Peroxide 1.5 Cure & Exotherm 14 w/0.1$ Benzoyl Peroxide 1.5 Cure & Exotherm 15 w/0.01% Benzoyl Peroxide 5 Cure 16 w/0.005% Benzoyl Peroxide 5 Cure 17 TMOP-TA/0.5% Benzoyl Peroxide/5% Q-43 18 Cure & Exotherm 18 TMOP-TA/1% Benzophenone/5% Q-43 42 Cure 19 w/0.5% Benzoyl Peroxide 14 Cure & Exotherm 20 TMOP-TA/0.5% Benzoyl Peroxide/5% Q-43 18 Cure & Exotherm 21 TMOP-TA/1% Irgacure 651 9 Cure 22 w/1% CADOX-TDP(e) 2.5 Cure & Exotherm 23 w/0.2% CADOX-TDP 3 Cure & Exotherm 24 TMOP-TA/1% CADOX-TDP 13 Cure & Exotherm 25 TMOP-TA/1% Irgacure 651 9 Cure 26 w/0.5% t-Butyl Perbenzoate 3 Cure & Exotherm 27 w/0.1% t-Butyl Perbenzoate 4 Cure & Exotherm 28 w/0.01% t-Butyl Perbenzoate 7 Cure & Exotherm 29 TMOP-TA/0.5% t-Butyl Perbenzoate 110 Cure & Exotherm 30 TMOP-TA/1% Irgacure 651/ 5% Q-43 7 Cure 31 w/0.5% t-Butyl Perbenzoate 1.5 Cure & Exotherm 32 w/0.1% t-Butyl Perbenzoate 2 Cure & Exotherm 33 w/0.01%-Butyl Perbenzoate 5 Cure Exposure Ex. Time to No.Formulation UV (sec) Comments 34 w/0.005% t-Butyl Perbenzoate 5 Cure 35 TMOP-TA/0.58 t-Butyl Perbenzoate 38 Cure & Exotherm 36 TMOP-TA/1$ Benzophenone/5% Q-43 42 Cure 37 w/0.5% t-Butyl Perbenzoate 24 Cure & Exotherm 38 w/0.l% t-Butyl Perbenzoate 27 Cure & Exotherm 39 w/0.01% t-Butyl Perbenzoate 31 Cure 40 TMOP-TA/0.5% t-Butyl Perbenzoate/5% Q-43 38 Cure & Exotherm 41 TMOP-TA/1% Irgacure 651 9 Cure 42 w/0.5% di-t-Butyl Peroxide 4.5 Cure & Exotherm 43 w/0.1$ di-t-Butyl Peroxide 7 Cure & Exotherm 44 TMOP-TA/0.5% di-t-Butyl Peroxide 420 Partial Cure 45 TMOP-TA/1% Irgacure 651/5% Q-43 7 Cure 46 w/0.5% di-t-Butyl Peroxide 2 Cure & Exotherm 47 w/0.1% di-t-Butyl Peroxide 2 Cure & Exotherm 48 TMOP-TA/0.5% di-t-Butyl Peroxide/5% Q-43 65 Cure & Exotherm 49 TMOP-TA/1% Irgacure 651 9 Cure 50 w/0.5% Lupersol 231(f) 2.5 Cure & Exotherm 51 w/0.1% Lupersol 231 3.5 Cure & Exotherm 52 TMOP-TA/0.5% Lupersol 231 196 Cure & Exotherm 53 TMOP-TA/1% Irgacure 651/5% 0-43 7 Cure 54 w/0.5% Lupersol 231 1.4 Cure & Exotherm 55 w/0.1% Lupersol 231 1.8 Cure & Exotherm 56 TMOP-TA/0.5% Lupersol 231/ 5% 0-43 58 Cure & Ex6therm 57 TMOP-TA/1% Benzophenone 240 Partial Cure 58 w/0.5% Lupersol 231 183 Cure & Exotherm 59 TMOP-TA/0.5% Lupersol 231 196 Cure & Exotherm 60 TMOP-TA/1B Irgacure 651 9 Cure 61 w/0.5% t-Butyl Hydroperoxide 8 Cure 6 Exotherm Exposure Ex. Time to No. Formulation UV (sec) Comments 62 TMOP-TA/0.5% t-Butyl Hydroperoxide 300 Some Gelation 63 TMOP-TA/1% Irgacure 651/5% Q-43 7 Cure 64 w/0.5% t-Butyl Hydroperoxide 5 Cure & Exotherm 65 TMOP-TA/0.5% t-Butyl Hydroperoxide/5% Q-43 71 Cure & Exotherm 66 TMOP-TA/1% Benzophenone/5% Q-43 42 Cure 67 w/0.5% t-Butyl Hydroperoxide 28 Cure & Exotherm 68 0.1% t-Butyl Hydroperoxide 35 Cure 69 TMOP-TA/0.5% t-Butyl Hydroperoxide 71 Cure & Exotherm 70 TMOP-TA/1% Benzophenone/5% Q-43 42 Cure 71 w/0.5% Lupersol 231 25 Cure & Exotherm 72 w/0.1% Lupersol 231 27 Cure & Exotherm 73 TMOP-TA/0.5% Lupersol 231/ 5% Q-43 58 Cure & Exotherm 74 TMOP-TA/1% Irgacure 651 9 Cure 75 w/0.5% Luazo 79(g) 2.5 Cure & Exotherm 76 w/0.1% Luazo 79 4 Cure & Exotherm 77 TMOP-TA/0,5% Luazo 79 149 Cure & Exotherm 78 TMOP-TA/1% Irgacure 651/5% Q-43 7 Cure 79 w/0.5% Luazo 79 1.5 Cure & Exotherm 80 w/0.1% Luazo 79 2 Cure & Exotherm 81 TMOP-TA/0.5% Luazo 79/5% Q-43 33 Cure & Exotherm 82 TMOP-TA/1% Benzophenone 240 Partial Cure 83 w/0.5% Luazo 79 74 Cure & Exotherm 84 TMOP- TA/0.5% Luazo 79 149 Cure & Exotherm 85 TMOP-TA/1% Benzophenone/5% Q-43 42 Cure 86 w/0.58 Luazo 79 16 Cure & Exotherm 87 w/0.1% Luazo 79 26 Cure & Exotherm 88 TMOP-TA/0.5% Luazo 79/5% Q-43 33 Cure & Exotherm 89 TMOP-TA/1% Irgacure.651 9 Cure 90 w/0.5% VAZO-64(h) 2 Cure & Exotherm Exposure Ex. Time to No.Formulation Cure (sec) Comments 91 TMOP-TA/0.5% VAZO-64 99 Cure & Exotherm 92 75% TMOP-TA/25% TAIC(i)/ 1% Irgacure 651 12 Cure 93 w/5% Q-43 6.5 Cure 94 w/0.5% VAZO-64 3 Cure & Exotherm 95 w/0.5% VAZO-64/5% Q-43 2 Cure & Exotherm 96 50% TMOP-TA/50% TAIC/ 1% Irgacure 651 25 Cure 97 w/5% Q-43 10 Cure 98 w/0.5% VAZO-64 8 Cure 99 w/0.5% VAZO-64/5% Q-43 6.5 Cure / FOOTNOTES (a) TMOP-TA = Trimethylolpropane triacrylate (b) Irgacure 651 = 2,2-Dimethoxy-2-phenyl acetophenone, commercially available from Ciba-Geigy (c) Material started to surface cure normally but then exothermed vigorously at which point light was turned off and material continued to exotherm and cure (d) Q-43 = Pentaerythritol tetrakis (beta-mercapto propionate), commercially available from Cincinnati Milacron (e) CADOX-TDP = 50% 2,4-Dichlorobenzoyl peroxide in dibutyl phthalate, commercially available from Noury Chemical Co.

(f) LUPERSOL 231 = 1,1-Bis(t-butylperoxy)3,3,5 trimethyl-cyclohexane, commercially available from Pennwalt Corp.

(g) LUAZO-79 = 2-t-Butylazo-2-cyanopropane, commercially available from Pennwalt Corp.

(h) VAZO-64 = 2,2'-azobis(isobutyronitrile), commercially available from DuPont Company (i) TAIC = Triallyl isocyanurate As is readily seen from the results in TABLE I, a synergistic effect of a reduced curing time occurs when the non-nitrogen containing photoinitiator is used in combination with either an organix peroxide or an azo compound as compared to either member of the combination, per se.

Claims (7)

1. A UV radiation curable composition essentially of: (1) a liquid, ethylenically unsaturated compound of the formula:

wherein R is H or CH3, R1 is an organic moiety with the valence of n, and n is at least 2, (2) a non-nitrogen containing photoinitiator, and (3) a synergistic agent which is either an azo compound or an organic peroxide of the formula: R~O~O~(R1~0~C))n~R2 wherein n is O or 1, R and R2 are each hydrogen, aryl, alkyl, aryl carbonyl, alkaryl carbonyl, aralkyl carbonyl, or alkyl carbonyl and R1 is alkyl or aryl, said alkyl groups containing 1 to 20 carbon atoms each.

2. A composition according to Claim 1, containing in addition up to a stoichiometric amount of a polythiol required to react with the liquid ethylenically unsaturated compound.

3. A composition according to Claim 1 or 2, containing in addition a reactive diluent.

4. A composition according to any of Claims 1 to 3 wherein the non-nitrogen containing photoinitiator is a carbonyl compound having at least one aromatic nucleus attached directly to the

group with any substituents on either the aromatic nucleus or the carbonyl group being limited to atoms selected from the group consisting of carbon, oxygen, hydrogen, chlorine, phosphorus, sulfur and combinations thereof.

5. A composition according to Claim 1 substantially as described in any one of the Examples.

6. A process for forming a cured solid product which comprises exposing a composition as claimed in any one of Claims 1 to 5 to UV radiation.

7. A cured solid product produced by the process of Claim 6.