Photoinitiated cationic epoxy compositions and articles exhibiting low color

1. A photoinitiated cationically curable composition, comprising:

(a) at least one substantially saturated epoxy component comprising at least two glycidyl ether groups;

(b) at least one functionalized acrylonitrile/butadiene copolymer in liquid form; and

(c) at least one cationic photoinitiator,

wherein the cationic photoinitiator comprises a mixture of triarylsulfonium hexafluoroantimonate salts in propylene carbonate, the triarylsulfonium hexafluoroantimonate salts being selected from the group consisting of:

2. The composition according to claim 1 , wherein the at least one functionalized acrylonitrile/butadiene copolymer is present in an amount from about 0.1 to about 25 weight percent on a basis of total weight of the composition.

3. The composition according to claim 1 , wherein the substantially saturated epoxy component is a diglycidyl ether epoxy compound having a saturated backbone selected from the group consisting of hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol S and hydrogenated biphenyl.

4. The composition according to claim 1 , wherein the substantially saturated epoxy component comprises:

5. The composition according to claim 1 , wherein the functionalized acrylonitrile/butadiene copolymer in liquid form has at least one functional group which is a hydroxyl functional group, a vinyl functional group, a carboxyl functional group, an epoxy functional group, or an acrylate functional group.

6. The composition according to claim 1 , wherein the mole percentage of acrylonitrile in the copolymer is from about 10 to 26% and the mole percentage of butadiene in the copolymer is from about 74 to 90%.

7. The composition according to claim 1 , wherein the cationic photoinitiator is selected from the group consisting of triarylsulfonium, diaryliodonium and aryl diazonium salts containing non-nucleophilic counterions, 4-methoxybenzenediazonium hexafluorophosphate, benzenediazonium tetrafluoroborate, diphenyl iodonium chloride, diphenyl iodonium hexafluorophosphate, 4,4-dioctyloxydiphenyl iodonium hexafluorophosphate, triphenylsulfonium tetrafluoroborate, diphenyltolylsulfonium hexafluorophosphate, phenylditolylsulfonium hexafluoroarsenate, diphenylthiophenoxyphenylsulfonium hexafluoroantimonate, triaryl sulfonium hexafluoroantimonate, triaryl sulfonium hexafluorophosphate and diaryl iodonium hexafluoroantimonate.

8. The composition according to claim 7 , wherein the cationic photoinitiator is selected from the group consisting of triarylsulfonium, diaryliodonium and aryl diazonium salts containing non-nucleophilic counterions.

9. The composition according to claim 1 , wherein the cationic photoinitiator comprises a cationic counter ion within the following structure:

wherein R 1 , R 2 , R 3 , R 4 , R 5 and R 5′ are each independently selected from the group consisting of H, C 1-6 alkyl, C 2-6 alkenyl, halo, hydroxyl and carboxyl, n is 0-3 and m is 0-1.

10. The composition according to claim 1 , wherein the cationic photoinitiator comprises tolylcumyl iodonium tetrakis(pentafluorophenyl)borate.

11. The composition according to claim 1 , wherein cationic photoinitiator is used in an amount within the range of about 0.1 to about 3 percent by weight of the total composition.

12. The composition according to claim 1 , further comprising a free radical initiator.

13. The composition according to claim 12 , wherein the free radical initiator comprises a phenone initiator.

14. The composition according to claim 12 , wherein the free radical initiator is selected from the group consisting of 1-hydroxy cyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenyl acetophenone, 1-hydroxy cyclohexyl phenyl ketone, benzophenone, 2-benzyl-2-N,N-dimethlamino-1-(4-morpholino phenyl)-1-butane, 2-methyl-1-[-4(methylthio)phenyl]-2-morpholino propane-1-one, 2-hydroxyl-2-methyl-1-phenyl-propane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenyl acetophenone, 4-(2-hydroxyethyoxy)phenyl-(2-hydroxy-2-methylpropyl)ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and combinations thereof.

15. The composition according to claim 1 , further comprising an oxetane-containing component.

16. The composition according to claim 1 , wherein the photoinitiator is triggered by exposure to radiation in the visible range of the electromagnetic spectrum.

17. A method of bonding substrates, comprising the steps of:

(a) providing a first substrate;

(b) providing a second substrate;

(c) providing a composition according to claim 1 on at least one of the first or second substrates;

(d) mating the first and second substrates; and

(e) exposing the composition to conditions sufficient to initiate cure thereof.

18. The method of claim 17 , wherein the conditions comprise exposure to ultraviolet radiation within a wavelength of from about 254 to 405 nm.

19. The method of claim 17 , wherein the conditions comprise exposure to temperatures of from about 60 to 140° C.

20. A method of curing a composition comprising:

(a) providing a composition according to claim 1 ;

(b) exposing the composition to ultraviolet radiation to initiate curing of the composition; and

(c) exposing the composition to temperatures of from about 60 to 140° C.;

wherein the cured composition exhibits little to no color change after said thermal exposure of step (c).

21. The method of claim 20 , wherein the cured composition exhibits less color than a color of a composition formed by the same curing process and thermal exposure, and from the same components in the same amounts, except for the absence of at least one acrylonitrile/butadiene copolymer.

22. The method of claim 20 , wherein the cured composition exhibits improved impact strength when compared with a composition formed by the same curing process and thermal exposure, and from the same components in the same amounts, except for the absence of at least one acrylonitrile/butadiene copolymer.

23. A method of preventing color formation in a cationically curable composition including at least one epoxy component and a cationic photoinitiator, wherein the cationic photoinitiator comprises a mixture of triarylsulfonium hexafluoroantimonate salts in propylene carbonate, the triarylsulfonium hexafluoroantimonate salts being selected from the group consisting of:

subjected to ultraviolet curing followed by thermal exposure, the method comprising incorporating at least one acrylonitrile/butadiene copolymer into the curable composition prior to subjecting the composition to ultraviolet curing and thermal exposure.

24. A method of preventing color formation during thermal treatment of a cationically cured composition, comprising:

(a) providing a cationically cured composition according to claim 1 ; and

(b) heating the cationically cured composition to form a fully cured composition;

such that a resulting color of the fully cured composition exhibits little to no color change from a color of the cationically cured composition prior to the heating step.

25. The method of claim 24 , wherein the resulting color of the thermally cured composition exhibits less color than a color of a composition formed by the same curing process and heating step, and from the same components in the same amounts, except for the absence of at least one acrylonitrile/butadiene copolymer.

26. The composition of claim 1 , wherein when cured by exposure to UV light the cured composition exhibits a significantly reduced color when measured on the Yellowness Index.

27. A photoinitiated cationically curable composition, comprising:

(a) at least one substantially saturated epoxy component comprising at least two glycidyl ether groups;

(b) at least one functionalized acrylonitrile/butadiene copolymer in liquid form; and

(c) at least one cationic photoinitiator, wherein the functionalized acrylonitrile/butadiene copolymer in liquid form has at least one functional group which is a vinyl functional group.

28. A photoinitiated cationically curable composition, comprising:

(a) at least one substantially saturated epoxy component comprising at least two glycidyl ether groups;

(b) at least one functionalized acrylonitrile/butadiene copolymer in liquid form; and

(c) at least one cationic photoinitiator, wherein the functionalized acrylonitrile/butadiene copolymer in liquid form has at least one functional group which is an epoxy functional group.

29. A photoinitiated cationically curable composition comprising:

(a) at least one substantially saturated epoxy component comprising at least two glycidyl ether groups;

(b) at least one functionalized acrylonitrile/butadiene copolymer in liquid form; and

(c) at least one cationic photoinitiator, wherein the functionalized acrylonitrile/butadiene copolymer in liquid form has at least one functional group which is an acrylate functional group.

30. The composition according to claim 27 , further comprising a free radical initiator.

31. The composition according to claim 28 , further comprising a free radical initiator.

32. The composition according to claim 29 , further comprising a free radical initiator.

33. A method of bonding substrates, comprising the steps of:

(a) providing a first substrate;

(b) providing a second substrate;

(c) providing a composition according to claim 27 on at least one of the first or second substrates;

(d) mating the first and second substrates; and

(e) exposing the composition to conditions sufficient to initiate cure thereof.

34. A method of bonding substrates, comprising the steps of:

(a) providing a first substrate;

(b) providing a second substrate;

(c) providing a composition according to claim 28 on at least one of the first or second substrates;

(d) mating the first and second substrates; and

(e) exposing the composition to conditions sufficient to initiate cure thereof.

35. A method of bonding substrates, comprising the steps of:

(a) providing a first substrate;

(b) providing a second substrate;

(c) providing a composition according to claim 29 on at least one of the first or second substrates;

(d) mating the first and second substrates; and

(e) exposing the composition to conditions sufficient to initiate cure thereof.

36. A method of curing a composition comprising the steps of:

(a) providing a composition according to claim 27 ;

(b) exposing the composition to ultraviolet radiation to initiate curing of the composition; and

(c) exposing the composition to temperatures of from about 60 to 140° C.;

wherein the cured composition exhibits little to no color change after said thermal exposure of step (c).

37. A method of curing a composition comprising the steps of:

(a) providing a composition according to claim 28 ;

(b) exposing the composition to ultraviolet radiation to initiate curing of the composition; and

(c) exposing the composition to temperatures of from about 60 to 140° C.;

wherein the cured composition exhibits little to no color change after said thermal exposure of step (c).

38. A method of curing a composition comprising the steps of:

(a) providing a composition according to claim 29 ;

(b) exposing the composition to ultraviolet radiation to initiate curing of the composition; and

(c) exposing the composition to temperatures of from about 60 to 140° C.;

wherein the cured composition exhibits little to no color change after said thermal exposure of step (c).

39. A method of preventing color formation during thermal treatment of a cationically cured composition, comprising:

(a) providing a cationically cured composition according to claim 27 ; and

(b) heating the cationically cured composition to form a fully cured composition;

such that a resulting color of the fully cured composition exhibits little to no color change from a color of the cationically cured composition prior to the heating step.

40. A method of preventing color formation during thermal treatment of a cationically cured composition, comprising:

(a) providing a cationically cured composition according to claim 28 ; and

(b) heating the cationically cured composition to form a fully cured composition;

such that a resulting color of the fully cured composition exhibits little to no color change from a color of the cationically cured composition prior to the heating step.

41. A method of preventing color formation during thermal treatment of a cationically cured composition, comprising:

(a) providing a cationically cured composition according to claim 29 ; and

(b) heating the cationically cured composition to form a fully cured composition;

such that a resulting color of the fully cured composition exhibits little to no color change from a color of the cationically cured composition prior to the heating step.