High energy electron beam curing of epoxy resin systems incorporating cationic photoinitiators

• US 5,877,229 A
• Filed: 07/26/1995
• Issued: 03/02/1999
• Est. Priority Date: 07/26/1995
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Energy Systems, Inc. (AES Corporation), Applied Poleramic, Inc. (Kaneka Corporation)
• Original Assignee: Lockheed Martin Energy Systems, Inc. (AES Corporation)
• Inventors: Janke, Christopher J., Dorsey, George F., Moulton, Richard J., Lopata, Vincent J., Havens, Stephen J.
• Primary Examiner(s): Berman, Susan W.
• Application Number:
  US08/507,569
• Time in Patent Office: 1,315 Days
• Field of Search: 522/25, 522/31, 522/170, 522/129, 522/146
• US Class Current: 522/31
• CPC Class Codes: C08G 59/38 together with di-epoxy compounds
• CPC Class Codes: C08G 59/68 characterised by the catalysts used
• CPC Class Codes: C08G 59/687 containing sulfur
• CPC Class Codes: C08L 2666/02 Organic macromolecular compounds, natural resins, waxes or and bituminous materials
• CPC Class Codes: C08L 63/00 Compositions of epoxy resins; Compositions of derivatives of epoxy resins

Abstract

A mixture of epoxy resins such as a semi-solid triglycidyl ether of tris (hydroxyphenyl) methane and a low viscosity bisphenol A glycidyl ether and a cationic photoinitiator such as a diaryliodonium salt is cured by irradiating with a dosage of electron beams from about 50 to about 150 kGy, forming a cross-linked epoxy resin polymer.

Claims

1. A non-thermal curing method characterized as not using external heat for curing an epoxy resin system comprising the following steps:

Step 1. providing a blend of an epoxy resin system, said epoxy resin system comprising an epoxy resin and a cationic photoinitiator, said cationic photoinitiator being a diaryliodonium salt; and

Step 2. irradiating said blend with high energy electron beam ionizing radiation for a period of time sufficient to effectuate an efficient cross-linking and an essentially complete and uniform non-thermal curing of said epoxy resin system thereby forming a non-thermally cured epoxy resin system having a glass transition temperature essentially the same or greater than a glass transition temperature obtained by thermally curing said epoxy resin system.

2. A non-thermally cured epoxy resin system made by a method in accordance with claim 1.

3. The method according to claim 1, wherein said epoxy resin is selected from the group consisting of:

bisphenol F epoxies;

tetraglycidyl ether of tetrakis (4-hydroxyphenyl)ethane;

diglycidyl ether of 9,9-bis(4-hydroxyphenyl)fluorene;

glycidyl ethers of the product of condensation of dicyclopentadiene and phenol;

triglycidyl ether of tris(hydroxyphenyl)methane;

diglycidyl ester of hexahydrophthalic anhydride; and

mixtures of the above.

4. The method according to claim 3, wherein said epoxy resin is selected from the group consisting of:

bisphenol F epoxies;

tetraglycidyl ether of tetrakis (4-hydroxyphenyl)ethane;

diglycidyl ether of 9,9-bis(4-hydroxyphenyl)fluorene;

glycidyl ethers of the product of condensation of dicyclopentadiene and phenol;

triglycidyl ether of tris(hydroxyphenyl)methane; and

mixtures thereof.

5. A non-thermal curing method characterized as not using external heat for curing an epoxy resin in accordance with claim 1 where in said epoxy resin system consists essentially of an epoxy resin and a cationic photoinitiator, said epoxy resin being selected from the group consisting of:

glycidyl ethers of bisphenol A, epoxy phenolic novolacs, epoxy cresol novolacs, bisphenol F epoxies, tetraglycidyl ether of tetrakis (4-hydroxyphenyl) ethane, diglycidyl ether of 9,9-bis (4-hydroxyphenyl) fluorene, glycidyl ether of the condensation product of dicyclopentadiene and phenol, triglycidyl ether of tris (hydroxyphenyl) methane, 3'"'"',4'"'"'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, diglycidylester of hexahydrophthalic anhydride, bis (3,4-epoxycyclohexylmethyl) adipate, isomeric mixture of bis (2,3-epoxycyclopentyl) ether, isomeric mixture of bis (2,3-epoxycyclopentyl) ether reacted with ethylene glycol, isomeric mixture of bis (2,3-epoxycyclopentyl) ether blended with glycidyl ethers of bisphenol A, and mixtures thereof, said cationic photoinitiator is a diaryliodonium salt, said diaryliodonium salt has the following formula;

##STR10## where R₁ and R₂ are selected from the group consisting of;

H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, Cl, Br, OC_n H_2n+1, OCH₂ CH(CH₃)C_n H_2n+1, OCH₂ CH(C₂ H₅)C_n H_2n+1, OCH₂ CH(OH)C_n H_2n+1, OCH₂ CO₂ C_n H_2n+1, OCH(CH₃)CO₂ C_n H_2n+1, OCH(C₂ H₅)CO₂ C_n H_2n+1, and mixtures thereof, where n is an integer between 0 and 18 and An^- is an anion selected from the group consisting of;

hexafluoroarsenate (AsF₆^-), hexafluoroantimonate (SbF₆^-), hexafluorophosphate (PF₆^-), boron tetrafluoride (BF₄^-), trifluoromethane sulfonate (CF₃ SO₃^-), and tetrakis (pentafluorophenylborate) (B C₆ F₅ !)₄^-), and mixtures thereof.

6. The method according to claim 1, wherein said cationic photoinitiator is said diaryliodonium salt having formula ##STR11## wherein An^- is tetrakis(pentafluorophenyl) borate B(C₆ F₅)₄^-).

7. The method according to claim 1, wherein said epoxy resin is 3'"'"',4'"'"'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate and said cationic photoinitiator is one or more diaryliodonium salts having the following formula:

##STR12## wherein R₁ and R₂ are independently selected from the group consisting of H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, Cl, Br, OC_n H_2n+1, OCH₂ CH(CH₃)C_n H_2n+1, OCH₂ CH(C₂ H₅)C_n H_2n+1, OCH₂ CH(OH)C_n H_2n+1, OCH₂ CO₂ C_n H_2n-1, OCH(CH₃)CO₂ C_n H_2n+1, OCH(C₂ H₅)CO₂ C_n H_2n+1, wherein n is an integer between 0 and 18; and

An^- is tetrakis(pentafluorophenyl) borate) (B(C₆ F₅)₄^-).

8. The method according to claim 1, wherein said epoxy resin is a glycidyl ether of bisphenol A having formula:

##STR13## wherein n ranges from 0 to 12; and

said cationic photoinitiator is one or more diaryliodonium salts having the following formula;

##STR14## wherein R₁ and R₂ are independently selected from the group consisting of H, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, Cl, Br, OC_n H_2n+1, OCH₂ CH(CH₃)C_n H_2n+1, OCH₂ CH(C₂ H₅)C_n H_2n+1, OCH₂ CH(OH)C_n H_2n+1, OCH₂ CO₂ C_n H_2n+1, OCH(CH₃)CO₂ C_n H_2n+1, OCH(C₂ H₅)CO₂ C_n H_2n+1, wherein n is an integer between 0 and 18; and

An^- is tetrakis(pentafluorophenylborate) (B(C₆ F₅)₄^-).

9. The method according to claim 1, wherein said epoxy resin is an epoxy phenolic novolac or epoxy cresol novolac having formula:

##STR15## wherein n ranges from 0 to 5, and R is H or CH₃ ; and

said cationic photoinitiator is one or more diaryliodonium salts having the following formula;

##STR16## and An^- is tetrakis(pentafluorophenyl) borate (B(C₆ F₅)₄^-).

10. The method according to claim 1, wherein said epoxy resin is bis(3,4-epoxycyclohexylmethyl)adipate and said cationic photoinitiator is one or more diaryliodonium salts having the following formula:

##STR17## and An^- is tetrakis(pentafluorophenyl) borate (B(C₆ F₅)₄^-).

11. The method according to claim 1, wherein said epoxy resin comprises one or more resins selected from the group consisting of an isomeric mixture of bis(2,3-epoxycyclopentyl)ether, an isomeric mixture of bis(2,3-epoxycyclopentyl) ether reacted with ethylene glycol, and an isomeric mixture of bis(2,3-epoxycyclopentyl)ether blended with a bisphenol A based glycidyl ether and said cationic photoinitiator is one or more diaryliodonium salts having the following formula:

##STR18## and An^- is tetrakis(pentafluorophenyl) borate (B(C₆ F₅)₄^-).

12. A method in accordance with claim 1 wherein said epoxy resin consists essentially of triglycidly ether of tris (4-hydroxyphenyl)methane-based epoxy, said cationic photoinitiator consists essentially of about 3 parts of (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate per hundred parts of said epoxy resin, and said glass transition temperature being about 362°

C. tan delta.

13. A method in accordance with claim 1 wherein said epoxy resin consists essentially of a fifty-fifty blend of bis(2,3-epoxycyclopentyl) ether and diglycidyl ether of bisphenol A, said cationic photoinitiator consists essentially of about 1 part to about 5 parts of (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate per 100 parts of said epoxy resin, and said glass transition temperature being from about 147°

C. to about 205°

C. tan delta.

14. The method according to claim 1, wherein said non-thermally cured epoxy resin system has a glass transition temperature (tan δ

) of about 105°

C. or higher.

16. The method according to claim 14, wherein said glass transition temperature (tan δ

) is about 128°

C. or higher.

17. The method according to claim 16, wherein said glass transition temperature (tan δ

) is about 147°

C. or higher.

18. The method according to claim 17, wherein said glass transition temperature (tan δ

) is about 166°

C. or higher.

19. The method according to claim 18, wherein said glass transition temperature (tan δ

) is about 186°

C. or higher.

20. The method according to claim 19, wherein said glass transition temperature (tan δ

) is about 206°

C. or higher.

15. A non-thermal curing method characterized as not using external heat for curing an epoxy resin system comprising the following steps:

Step 1. providing a blend of an epoxy resin system, said epoxy resin system consisting essentially of an epoxy resin and a cationic photoinitiator, said epoxy resin being a diglycidyl ether of bisphenol A and said cationic photoinitiator being from about 0.5 to about 4 parts of (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate per hundred parts of said epoxy resin, and

Step 2. irradiating said blend with high energy electron beam radiation for a period of time sufficient to effectuate an efficient cross-linking and an essentially complete and uniform non-thermal curing of said epoxy resin system thereby forming a non-thermally cured epoxy resin system having a glass transition temperature from about 124°

C. to about 207°

C. tan delta.

21. A epoxy resin system consisting essentially of an epoxy resin and a cationic photoinitiator, said epoxy resin consists essentially of a fifty-fifty blend of bis(2,3-epoxycyclopentyl) ether and diglycidyl ether of bisphenol A and said cationic photoinitiator consists essentially of from about 1 part to about 5 parts of (4-octyloxyphenyl) phenyliodonium hexafluoroantimonate per 100 parts of said epoxy resin;

said epoxy system being characterized as producing a non-thermally cured epoxy resin system having a glass transition temperature from about 147°

C. to about 205°

C. tan delta when exposed to high energy ionizing radiation generated by an electron beam accelerator having an energy of 10 MeV and a power of 1 kW.

22. A epoxy resin system where in the epoxy resin consists essentially of diglycidyl ether of bisphenol A and the cationic photoinitiator consists essentially of from about 0.5 to about 4 parts of (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate per 100 parts of said epoxy resin;

said epoxy system being characterized as producing a non-thermally cured epoxy resin system having a glass transition temperature from about 124°

C. to about 207°

C. tan delta when exposed to high energy ionizing radiation generated by an electron beam accelerator having an energy of 10 MeV and a power of 1 kW.

23. A epoxy resin system wherein the epoxy resin consists essentially of a epoxy phenolic novalac and the cationic photoinitiator consists essentially of about one part to about 5 parts of (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate per 100 parts of said epoxy resin;

said epoxy system being characterized as producing a non-thermally cured epoxy resin system having a glass transition temperature from about 128°

C. to about 197°

C. Tan delta when exposed to high energy ionizing radiation generated by an electron beam accelerator having an energy of 10 MeV and a power of 1 kW.

24. A epoxy resin system wherein the epoxy resin consists essentially of a triglycidyl ether of tris(4-hydroxyphenyl)methane-based epoxy and the cationic photoinitiator consists essentially of about 3 parts of (4-Octyloxyphenyl) phenyliodonium hexafluoroantimonate per 100 parts of said epoxy resin;

said epoxy system being characterized as producing a non-thermally cured epoxy resin system having a glass transition temperature being 362°

C. tan delta when exposed to high energy ionizing radiation generated by an electron beam accelerator having an energy of 10 MeV and a power of 1 kW.