CA1301394C - Uv curable epoxy resin compositions with delayed cure - Google Patents

Abstract

UV CURABLE EPOXY RESIN COMPOSITIONS WITH
DELAYED CURE
Abstract of the Disclosure A fixing agent comprising Poly(alkylene oxide) moieties is used to fix a delayed cure of UV curable epoxy compositions exposed to UV radiation.

Description

UV CURABLE EPOXY RESIN
COMPOSITION WITH
DELAYED CURE

The present invention relates to UY curable epoxy resin compositions having delayed cure upon UV radiation exposure.
Mbre particularly, the present invention relates to the addition of a fixing agent to UV curable epoxy resin compositions to fix a period of delayed cure and create open time in which the composition may be worked.

Background of the Invention UY curable epoxy resin compositions and their uses are well known in the art. Such compositions are used, for example, in printing inks, protective, decorative, and insulating coatings, pitting compounds, sealants, adhesives, molding compositions, wire insulation, textile coatings, laminates, impregnated tapes, varnishes, etc.

One problem with expanding the use of UV curable epoxy resins is that they may only be utilized where UV light can penetrate for curing. Further, upon exposure, cure begins immediately on the exposed surface and progresses into the resin with continued exposure. Thus, there is no opportunity to work the resin after exposure begins. Although, it is possible to çure many of these compositions by heating to temperatures of greater than about 150C. This is simply impractical in most situations. As a consequence of the above, uses which require a composition to bond two opaque surfaces, to cure in a shaded area, or to be worked after W exposure are , , .

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60SI-1069/~WH:`mz/0320p not suitable for the application of UV curable epoxy compositions.

U.S. Pat. No.4,308,118 discloses the combination of a UY
activated and thermally activated catalyst to produce deep section cure epoxy resin compositions. These compositions may contain UV opaque fillers yet cure quickly upon the application of heat and UY radiation.

U.S. Pat. No~ 39960,979 discloses the use of polyether polyols, including polyethylene glycol and polypropylene glycol as flexibilizing agents in heat cured epoxy resins. These epoxy resins utilize an acid catalyst and a bake cycle at temperatures of from 80C to about 210C.

U.S. Pat. No. 4,434,286 discloses the use of polyether polyols as a flexibilizing agent in cycloaliphatic epoxide resins having ~ood electrical properties. These epoxy resin compositions utilize organic acids to catalyze the cure at temperatures of from about 100C to about 200C.

It is an object of the present invention to produce a UV
curable epoxy composition that can be worked in an open time following exposure to UV radiation.

It is another object of the present invention to provide a UV curable epoxy composition with a fixed period of cure delay following exposure to UY radiation.

PATENTS
60S1-1069/JWH.mz/0~20p Description of the Invention :
Briefly, according to the present invention, there is provided a curable epoxy composition, fixed for delayed cure, comprising:

(a) an epoxy resin, (b) a sufficient amount of UV catalyst to render the composition UV curable, and (c) a sufficient amount of fixing agent comprising poly(alkylene oxide) n~ieties to prevent immediate skinning upon UV exposure.

The term "epoxy resin" as utilized in the description of the curable compositions of the present invention, includes any monomeric, dimeric, oligomeric or polymeric epoxy material containing one or a plurality of epoxy functional groups. For example, those resins which result from the reaction of bisphenol-A (4,4'-isopropylidenediphenol) and epichlorohydrin, or by the reaction of low molecular weight phenol-formaldehyde resins (Novolak resins) with epichlorohydrin, can be used alone or in combination with an epoxy containing compound as a reactive diluent. Such diluents as phenyl glycidyl ether9 4-vinylcyclohexene dioxide, limonene dioxide, 1,2-cyolohexene oxide, glycidyl acrylate, glycidyl methacrylate, styrene oxide, allyl glycidyl ether, etc., may be added as viscosity nodifying agents.

In addition, the range of these compounds can be extended to include polymeric materials containing terminal or pendant . . :.
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60SI-1069/JWH:mz/0320p epoxy groups. Examples of these compounds are vinyl copolymers containing glycidyl acrylate or methacrylate as one of the comonomers. Other classes of epoxy containing polymers amenable to cure using UV catalysts are epoxy-siloxane resins, epoxy-polyurethanes and epoxy-polyesters. Such polymers usually have epoxy functional groups at ~he ends of their chains. Epoxy-siloxane resins and method for making are more particularly shown by E.P. Plueddemann and G~ Franger, J. Am.
Chem. Soc. 81 632-5 (1959). As described in the literature, epoxy resins can also be modified in a number of standard ways such as reactions with amines, carboxylic acids, thiols, phenols, alcohols, etc. as shown in U.S. Pat. Nos. 2,935,488;

3,235,620; 3,369,055; 3,379,653; 3,398,211; 3,403,199,-3,563,850; 3,567,797; 3,677,995; etc. Further examples of epoxy resins which can be used are shown in the Encyclopedia of Polymer Science and Technology, Vol~ 6, 1967; Interscience Publishers, New York, pp 209-271.

The function of the fixing agent herein is to delay cure of the UV curable epoxy resin upon exposure to UV light. 8y adjusting fixing agent amount and composition, the cure may be fixed at some set time after UV exposure or may be entirely delayed until a very mild heating, for example 70C for 5 minutes.

The fixing agents herein are compounds which have poly(alkylene oxide) moieties. Preferred such compounds have the general formula:
R7 ( oR6 ~ n oR7 wherein R6 is independently a divalent substituted or unsubstituted hydrocarbon radical~ having from 2 to about 8 PATENTS
60SI-1069/JWH:mz/0320p carbon atoms, R7 is independently selected from the group consisting of hydrogen, substituted or unsubstituted hydrocarbon of 1 to 8 carbon atoms, and n is at least 2.
Preferably R6 has 1 to 5 carbon atoms, R7 is hydrogen, methyl or epoxy hydrocarbon and n has a value of from 2 to 50.
Particularly good properties are obtained in the UV curable epoxy resin composition where the fixing agent is epoxy functional. Thus, most preferably, R is aliphatic or cycloaliphatic epoxy and n has a value of from 2 to 10.

Suitable UV catalysts for curing epoxy resins are well known to persons skilled in the art. The instant inventors are most familiar with the onium photoinitiators of the general formula:

~Y]c ~MQd] (d e) where Y is a cationic group selected from the class consisting of:

(R)d (R )bD (i), (R)f (R2)9 (R3)h E (ii), and (R)j (R4)k (R5)m G (iii), M is selected from a metal or metalloid, Q is a halogen radical, R is a monovalent aromatic orgdnic radical, Rl is a divalent aromatic organic radical, R2 and R4 are monovalent organic aliphatic radicals selected from alkyl, cyclo alkyl and substituted alkyl, R3 and R5 are polyvalent organic radicals forming a heterocyclic or fused ring structure with E
or G, D is a halogen radical, such a I, E is a group Va element selected from S, Se and Te, "d" is a whole number equal to 0 or ,,, -, ~

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60SI-1069/JWH:mz/0320p 2, "b" is a whole number equal to 0 or 1 and the sum of "d" ~
"b" is equal to 2 or the valence of D, "f" is a whole number equal to 0 to 4 inclusive, "9" is a whole number equal to 0 to 2 inclusive, "h" is a whole number equal to 0 to 2 inclusive and the sum of "f" ~ ~g~ + ~h~i is a value equal to 4 or the valence of E, "j" is a whole number equal to 0 to 3 inclusive, "k" is a whole number equal to 0 to 2, inclusive and "m" is a whole number equal to 0 or 1, where the sum of "j" + "k" + "m"
is a value equal to 3 or the valence of G, c = d - e, e is I0 equal to the valence of M and is an integer equal to 2-7 inclusive and d is greater than e and is an integer having a value up to 8.

Radicals included by R can be the same or different, aromatic carbocyclic or heterocyclic radicals having from 6 to 20 carbon atoms, which can be substituted with from 1 to 4 monovalent radicals selected from C(l 8) alkoxy9 C(l 8 alkyl, nitro, chloro, etc., R is more particularly phenyl, chlorophenyl, nitrophenyl, methoxyphenyl, pyridyl, etc.
Radicals included by Rl are divalent radicals, such as ~a~

R and R radicals include C(l 8) alkyl, such as methyl, ethyl, etc., substituted alkyl, such as -C2H40CH3, -CH2COOC2H5, -CH2COCH3, etc. R and R radicals include a structure such as PATENTS
605I-1069/JWH:mz/0320p where Q' is selected from 0, CH2, NR', C0, CH2CH2 and S
and R' is a monovalent radical selected from hydrogen and hydrocarbon.

Metal or metalloids included by M of formula 1 are transition metals such as Sb, Fe, Sn, Bi, Al, ga, In, ti, ~r, Sc~ Y, Cr, Mn, Cs, rare earth elements such as the lanthanides, for example, Cd, pr, nd, etc., actinides, such as Th, Ta, U, Np, etc., an~ metalloids such as B, P, As, etc. complex anions la included by MDd(d e) are, for example, BF4, PF6, ASF6, FeC14, SnC16, SbC16, BiC15, etc.

Halonium salts included by formula 1 above include 4,4'-dimethyldiphenyliodonium hexafluoroarsenate, 4,4-dichlorodi-phenyliodonium hexafluoroarsenate, 4-methoxydiphenyliodonium lS hexafluoroborate, etc. Further halonium salts and methods to make are disclosed in United States Patent Number 4,026,705.

Group Ya onium salts included by formula 1 are, for example, triphenylphenacyltetrafluoroborate, triphenylcarbethy-2a oxymethyl phosphonium tetrafluoroborate, diphenylmethylphenyl-acyl arsonium bromide, N-phenylacylpyridinium bromide, etc.
Further group Va onium salts and methods to make are disclosed by U.S. Pat. No. 4~069~055 r , , .

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60SI-1069/JWH:mz/0320p Group VIa cnium salts included by formula 1 are, for example~ triphenylsulfonium hexafluorophosphate, 3,5-dimethyl-4 hydroxyphenyl dimethyl sulfonium fluorsborate, triphenyl-sulfonium hexafluoroarsenate, phenacyltetramethyl sulfonium 5fluoroborate, etc. Further Group VIa onium salts and methods to make are disclosed by United States Patent Number 4,058,400.

The fixed curable compositions of the present invention can be made by simply blending the epoxy resin, which includes 10epoxy monomer, epoxy prepolymer, or mixture thereof with the fixing agent and UV cure catalyst. The resulting curable composition can be in the form of a varnish having a viscosity of from 10 centipoise at 25C up to the form of a free flowing powder.

15Experience has shown that the proportion of UV cure catalyst to curable composition can vary widely in as much as the salt is substantially inert, unless activated. Effective results can be achieved if the proportion of from O.lX to 15X
by weight of UV cure catalyst is employed, based on the weight 20of curable composition.

The amount of fixing agen~ employed depends upon the desired delay sought, the particular epoxy resins employed, the ultraviolet light exposure, and the particular fixing agent.
By manipulating the above variables properly, the delay in cure 25or skinning (surface cure to a tack free state) may be fixed anywhere from less than 1 minute up to a day or two in the absence of mild heating. Persons skilled in the art may find certain fixing agents to be effective at from as little as ~31)~

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60SI-l069/JWH:mz/0320p g_ about l part by weight up to lO0 parts by weight fixing agent per lU0 parts by weight total epoxy resin content. Of course, where the fixing agent is epoxy functional then it must be counted into the bulk of the epoxy resin in forming the stated ratios. Thus, the fixing agent may be both fixing agent (c) and epoxy resin (a~. Preferably, from abDut 5 to about 50 parts by weight fixing agent are present for each lO0 parts by weight epoxy resin. Most preferably, this ra~io should be from aoout lO to about 50 parts by weight fixing agent per lO0 parts by weight epoxy resin.

The fixed curable compositions may be applied to a variety of substrates by conventional means and delay cured to a tack free state by either UV exposure alone or a combination of UY
exposure and subsequent mild heating. At a minimum, the composition should receive enough exposure to UV radiation to activate the catalyst. Further exposure will spend and diminish the period of delayed cure~ that is open time, by high yields of activated catalyst and by radiant heat energy from the UV radiation source. Of course, further exposure may be used as a variable to control open time~ however, the composition must be removed from exposure before skinning or cure. After exposure and during the open time, the epoxy composition may be worked for instance, to act as an adhesive, to make contact with other substrates, etc.

The UY radiation should have a wavelength of from about 1849 A to 4000 A and an intensity of at least 5,000 - 80,000 microwatts/cm . Intensity should be linked with exposure time to insure sufficient exposure. Following UV exposure, the curable composition may require mild heating for final cure.
Such heating should be carried out at as low a temperaute as is effective given time constraints. Where heatin~ is~ necessary, temperatures of from about 40C to about 150C a~e useful.
This heating may be done in an oven, by exposing the composition to the radiated or conductive heat of a hot object, or by exposing the composition to an infrared radiation source.
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605I-1069/~WH:mz/0320p EXAMPLES
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In order that those skilled in the art will be better able to practice the invention, the following examples are given by : way of illustration and not by way of limitation. All parts are by weight.
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Ingredlents BPA epoxy - diglycidyl ether of bisphenol-A, EponTM
828 resin, Shell Chemical Corporation.
Cyclo epoxy - 3,4 epoxycyclohexylmethyl-3,4- epoxy-cyclohexane carboxylate, ERLTM 4 2 21 resin, Union Carbide Corporation.
Novolac epoxy - polyglycidyl ether of phenol-formal-dehyde novolac, DENTM 43g resin, Dow Chemical Company.
Fixing agent A - propylene glycol di(2,3-epoxypropyl)-ether, epoxy equiv~ wght = 305 - 335, Epon 502 resin, Shell Chemical Corporation, DERTM 732 resin, Dow Chemical Company.
Fixing agent B - propylene glycol di(2,3-epoxypropyl) -ether, epoxy equiv. wght. = 175 - 205, DER 8736 resin, Dow Chemical Company.
Fixing agent C - poly(ethyleneglycol), CarboxwaxTM 400 resin.
Catalyst A 5096 solids in carrier triarylsulfonium hexafluoroantimonate, General Electric Company.
Catalyst B - 50% solids in carrier triarylsulfonium hexafluorophosphate, General Electric Company.
Catalyst C - 50~6 solids in carrier di(dodecylphenyl) iodonium hexafluoroarsenate, General Electric Company.

Key to Tables s = non-tacky film formed on polymer surface w = no visible curing; polymer is wet g = polymer notably gelled t = polymer cured but tacky c = polymer solidly cured; non-tacky ~.~

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60SI-1069iJaH:mz/0320p ~12-All examples are 10 mil ~ilms on cold rolled steel.
Separate coated samples of each formulation were passed one and two times at a belt speed of 20 ft/min under 2-300 watt/in2 medium pressure, mercury vapor, lamps wi~h IR filter in place.
Each sample, following UV exposure, was placed in an oven at 70C or at 150C if indicated.

Examples 1-6 These examples demonstrate the effect of increasing fixing PATENTS
60SI-l069/J-WH mz/0320p -l3-Composition Time after UY Time of and exposure, min oven exp.
Expl. ExposureAm~unt 0 l 2 3 4 5 lOl5 5 30 5 ~ ~ l BPA epoxylo Cat B 2 l pass s c*
2 pass s c*
2 BPA epoxy95 Fix A 5 Cat B 2 l pass w t t c 2 pass s s c 3 BPA epoxy75 Fix A 25 Cat B 2 l pass w w w t t c 2 pass w 9 t t t c 4 BPA epoxy20 Fix A 80 Cat B 2 l pass w w c 2 pass w w c BPA epoxy5 Fix A 95 Cat B 2 l pass w w c 2 pass w w c 6 BPA epoxy0 B0 Fix A lO0 Cat 8 2 l pass w - w c 2 pass w w c * 150C oven : .

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60SI-1069/JWH:mz/0320p Examples 7-8 These examples dem~nstrate glycidyl functional fixing agent response to oven exposure without UV exposure.

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60SI-1069/JWH:mz/0320p Composition Time after UY Time of and exposure, min oven exp.
Expl. ExposureAmount O 1 2 3_ 4 5 10 15 5 30 7 BPA epoxy 0 Fix A 100 Cat B 2 1 pass --- no UV exposure --- w 2 pass 8 BPA epcxy 0 Fix A 100 Cat B 2 1 pass --- no UV exposure -- w*
2 pass * 150C oven :~ `

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60SI-10697J~H:mz/0320p Examples 9-10 These examples demonstrate the response of cycloaliphatic epoxy resins to fixing agent addition.

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60SI-1069/JWH:mz/0320p Composition Time after UV Time of and exposure, min oven exp.
Expl. Exposure Am?unt 0 _1 2 3_ 4 5 _10 15 5 30 9 Cyclo epoxy 100 Fix A
Cat B 2 1 pass s c : 2 pass s c Cyclo epoxy50 Fix A 50 Cat B 2 1 pass w t c 2 pass c c .__ __ _ . .
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605I -1 069/JWH :mz/0320p Examples 11 -1 ?
These examples demonstrate novolac epoxy response to 39~

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60SI-1069/JWH:mz/0320p _l g Composi~ion Time after UV Time of and exposure, min oven exp.
Expl. ExposureAmount 0 1 2 3 4 5 10 15 5 30 11 Novolac epoxy 100 Fix A O
Cat B 2 1 pass s c 2 pass s c 12 Novolac epoxy 75 Fix A 25 Cat B 2 1 pass w t t c 2 pass t c c :
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60SI-1069/JWH:mz/0320p Examples 13 -14 These examples demonstra~e the use of low molecular weight fixing agent addition.

13~ 4 PATENTS
60SI-1069TJWH:mz/0320p Composition Time after UV Time of and exposure, min oven exp.
Expl. ExposureAnount 0 1 2 3 4 5 1015 5 30 . ~ . . . _ 13 BPA epoxy100 Fix B 0 Cat B 2 1 pass s c 2 pass s c 14 BPA epoxy75 Fix B 25 Cat B 2 1 pass w w c 2 pass w t t c .. . _ _ .. . .. .. .. . _ 3L3~3g'~

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60SI-10697JWH:mz/0320p Examples 15 - 16 . . . _ These examples demonstrate the use of a halonium salt catalyst in combination with a ~ixing agent.

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605I-1069/JWH:mz/0320p Composition Tirne after UV Time of and exposure, min oven exp.
Expl. ExposureArr~unt 0 1 2 3 4 5 10 15 5 30 BPA epoxy 100 Fix A 0 Cat C 2 1 pass s c 2 pass s c 16 BPA epoxy 75 Fix A 25 Cat C 2 1 pass w w c 2 pass w w c 1~3~`4 PATENTS
60SI-1069/JWH:mz/0320p Examples 17 -18 These examples compare the use o~ low molecular weight and high molecular weight fixing agent.
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60SI ~1 069/JWH :mz/0320p -2~-Composition Time after UV Time of and exposure, min oven exp.
Expl. Exposure Anount 0 1 2 3 4 5 1015 5 30 17 BPA epoxy 75 Fix A 25 Cat B 2 1 pass w t c 2 pass w t t c 18 BPA epoxy 75 Fix B 25 Cat B 2 1 pass w w c 2 pass w t t c L3~ '3~

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60SI-10697Jh~r-ztO320p Example 19 This example demonstrates the use of a fixing agent having no expoxy functionality.

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60SI -1 069/JWH :~z/0320p Composition Time after UV Time of and exposure, min oven exp.
Expl. Exposure Amount O ~ 2 3 4 5 10lS 5 30 19 BPA epoxy 75 Fix C 25 Cat B 2 1 pass w w c 2 pass _ w t c \

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Claims (22)

1. A curable composition consisting essentially of:
(a) a bisphenol-A epoxy resin, (b) a sufficient amount of UV catalyst to render the composition UV curable, and (c) a sufficient amount of fixing agent capable of delaying the cure of the composition for a fixed period of time after exposure to UV radiation, the fixing agent having the general formula:

R7?OR6?nOR7 wherein R6 is selected from the group consisting of -CH2CH2- and -CH2CH(CH3)-, R7 is epoxy hydrocarbon and n is at least 2.

2. The composition of claim 1 wherein said UV
catalyst is an onium photoinitiator.

3. The composition of claim 1 wherein said fixing agent is present in an amount of from about 1 to about 100 parts by weight per 100 parts by weight total epoxy resin content.

4. The composition of claim 1 wherein said fixing agent is present in an amount of from about 5 to about 50 parts by weight per 100 parts by weight total epoxy resin content.

5. The composition of claim 1 wherein said R7 is selected from the group consisting of aliphatic and cycloaliphatic epoxy.

6. The composition of claim 1 wherein said fixing agent is a digylcidyl ether.

7. A composition not skinned and not fully cured that has been exposed to UV radiation sufficient to activate a UV catalyst consisting essentially of:
(a) a bisphenol-A epoxy resin, (b) a sufficient amount of UV catalyst to render the composition UV curable, and (c) a sufficient amount of fixing agent capable of delaying the cure of the composition for a fixed period of time after exposure to UV radiation, the fixing agent having the general formula:

R7?OR6?nOR7 wherein R6 is selected from the group consisting of -CH2CH2- and -CH2CH(CH3)-, R7 is epoxy hydrocarbon and n is at least 2.

8. The composition of claim 7 wherein said UV
catalyst is an onium photo initiator.

9. The composition of claim 7 wherein said fixing agent is present in an amount of from about 1 to about 100 parts by weight total epoxy resin content.

10. The composition of claim 7 wherein said fixing agent is present in an amount of from about 5 to about 50 parts by weight per 100 parts by weight total epoxy resin content.

11. The composition of claim 7 wherein said R7 is selected from the group consisting of aliphatic and cycloaliphatic epoxy.

12. The composition of claim 7 wherein said fixing agent is a diglycidyl ether.

13. A method for employing an epoxy resin composition comprising the steps:
(a) exposing a composition to sufficient UV
radiation to activate a UV catalyst, said composition comprising:
(i) an epoxy resin, (ii) a sufficient amount of said UV catalyst to render the composition UV curable, and (iii) a sufficient amount of fixing agent having the general formula:

R7?OR6?nOR7 wherein R6 is selected from the group consisting of -CH2CH2- and -CH2CH(CH3)-, R7 is epoxy hydrocarbon and n is at least 2, to prevent immediate skinning upon UV exposure;
and (b) removing said composition from exposure before skinning or cure.

14. The method of claim 13 wherein there is a step:
(c) working said epoxy resin composition during open time until cure.

15. The method of claim 13 wherein said cure is effected by a step:
(d) heating said epoxy resin composition to a temperature of between about 40°C and 150°C.

16. The method of claim 13 wherein said UV
catalyst is an onium photo initiator.

17. The method of claim 13 wherein said fixing agent is present in an amount of from about 1 to about 100 parts by weight total epoxy resin content.

18. The method of claim 13 wherein said fixing agent is present in an amount of from about 5 to about 50 parts by weight per 100 parts by weight total epoxy resin content.

19. The method of claim 13 wherein said R7 is selected from the group consisting of aliphatic and cycloaliphatic epoxy.

20. The method of claim 13 wherein said fixing agent is a digylcidyl ether of poly(alkylene oxide).

21. The method of claim 13 wherein epoxy resin includes at least one resin selected from the group consisting of bisphenol-A epoxy resin, epoxy novolac resin, and cycloaliphatic epoxy resin.

22. A method for employing an epoxy resin composition comprising the steps:
(a) exposing a composition to sufficient UV
radiation to activate a UV catalyst, said composition comprising:
(i) an epoxy resin, (ii) a sufficient amount of said UV catalyst to render the composition UV curable, and (ii) a sufficient amount of fixing agent having the general formula:

R7?OR6?nOR7 wherein R6 is selected from the group consisting of -CH2CH2- and -CH2CH(CH3)-, R7 is epoxy hydrocarbon and n is at least 2, to prevent immediate skinning upon UV exposure;
and (b) removing said composition from exposure before skinning or cure, (c) shading said composition, and (d) curing said epoxy composition by heating to a temperature between 40°C and 150°C.