Anhydride accelerators for epoxy resin systems
View Patent ↗Carboxylic acid salts of tertiary amines for use as an accelerator for an anhydride based epoxy curing agents are disclosed. The disclosed carboxylic acid salts of certain tertiary amines are latent anhydride accelerators and enable epoxy resin curing when heated to an elevated temperature (e.g., an onset temperature of greater than about 50° C.).
1. An epoxy resin curing agent composition comprising at least one tertiary amine salt and at least one anhydride; wherein the tertiary amine salt comprises at least one member selected from the group of salts represented by the structure of Structure 1:
wherein A is CH 2 , O, NH, or NR; R is an alkylene chain of 1-6 carbon atoms; X − is a carboxylate anion of 1-40 carbon atoms, and the group of salts represented by the structure of Structure 2:
wherein R 1 and R 2 are H or alkyl and R 3 and R 4 are alkyl.
2. The composition of claim 1 wherein the tertiary amine salt is represented by the structure of Structure 1:
wherein A is CH 2 , O, NH, or NR; R is an alkylene chain of 1-6 carbon atoms; X − is a carboxylate anion of 1-40 carbon atoms.
3. The composition of claim 2 wherein the tertiary amine salt comprises at least one member selected from the group consisting of N-hydroxyalkylpiperidinyl, N-hydroxyalkylmorpholinyl, N-hydroxypiperazinyl, 1-hydroxyethylpiperazinyl, and combinations thereof.
4. The composition of claim 1 wherein the tertiary amine salt is represented by the structure of Structure 2:
wherein R 1 and R 2 are H or alkyl and R 3 and R 4 are alkyl.
5. The composition of claim 4 wherein the tertiary salt comprises N-cyclohexyl-N,N-dimethylamine contacted with at least one acid selected from the group consisting of acetic acid, hexanoic acid and tall oil fatty acid.
6. The composition of claim 1 wherein the tertiary salt comprises the contact product of at least one carboxylic acid and at least one tertiary amine.
7. The composition of claim 6 wherein the tertiary amine comprises at least one member selected from the group consisting of N-hydroxyethylpiperidine, N-hydroxypropylpiperidine, 2-methyl-N-hydroxyethylpiperidine, N-hydroxymethylpiperidine, N-hydroxyethylmorpholine, 1,4-bis(2-hydroxyethyl)piperazine, 1,4-dimethylpiperazine, N-cyclohexyl-N,N-dimethylamine, N-cyclohexyl-N,N-diethylamine, N-cyclohexyl-N-ethyl-N-methylamine, N,N-dimethyl-N-(2-methylcyclohexyl)amine, N,N-dicyclohexyl-N-methylamine, N-hydroxyethyl-N-cyclohexyl-N-methylamine, N-cyclohexyl-N,N-dipropylamine, N-cyclohexyl-N,N-dioctylamine and combinations thereof.
8. The composition of claim 6 wherein the carboxylic acid comprises at least one member selected from the group consisting of acetic acid, propanoic acid, hexanoic acid, 2-ethylhexanoic acid, decanoic acid, tall oil fatty acid (TOFA), dimer acid and mixtures thereof.
9. The composition of claim 1 wherein the tertiary amine salt comprises N-hydroxyalkylpiperidinyl.
10. The composition of claim 6 wherein the tertiary amine comprises N-hydroxyethylpiperidine.
11. The composition of claim 10 wherein the carboxylic acid comprises tall oil fatty oil.
12. The composition of claim 6 wherein the tertiary amine comprises N-cyclohexyl-N,N-dimethylamine.
13. The composition of claim 11 wherein the carboxylic acid comprises tall oil fatty oil.
14. The composition of claim 1 wherein the anhydride comprises at least one member selected from the group consisting of polysebacic and polyazelaic anhydride; methyltetrahydrophthalic anhydride, tetrahydro phthalic anhydride, methyl nadic anhydride, hexahydro phthalicanhydride, and methylhexahydro phthalic anhydride; succinic anhydride, substituted succinic anhydride, citric acid anhydride, maleic anhydride, adducts of maleic anhydride, dodecyl succinic anhydride, maleic anhydride vinyl and styrene copolymers of maleic anhydride, multi-ring alicyclic anhydrides, phthalic anhydride, and trimellitic anhydride.
15. The composition of claim 1 further comprising at least one epoxy resin.
16. The composition of claim 15 further comprising fiberglass.
17. A heat curable composition comprising at least one tertiary amine salt, at least one anhydride, and at least one epoxy resin wherein the composition is curable at a temperature ranging from about 100 to about 150 C; and has an ΔH of about 150 to about 400 J/g and the cured composition has a Tg ranging from about 60 to about 175 as measured by differential scanning calorimetry; wherein the tertiary amine salt comprises at least one member selected from the group of salts represented by the structure of Structure 1:
wherein A is CH 2 , O, NH, or NR; R is an alkylene chain of 1-6 carbon atoms; X − is a carboxylate anion of 1-40 carbon atoms, and the group of salts represented by the structure of Structure 2:
wherein R 1 and R 2 are H or alkyl and R 3 and R 4 are alkyl.
18. The composition of claim 17 further comprising fiberglass.
19. The composition of claim 17 wherein the composition comprises less than about 2 wt % tertiary amines.
20. The composition of claim 17 wherein the composition comprises less than about 2 wt % water.
21. The composition of claim 17 wherein the composition comprises about 0.8 to about 1.1 equivalents of anhydride.
22. The composition of claim 1 wherein the composition comprises about 1 to about 20 parts of tertiary amine salt.
23. A curing agent consisting essentially of at least one tertiary amine salt and at least one anhydride; wherein the curing agent has a AH of greater than 120 J/g and the tertiary amine salt comprises at least one member selected from the group of salts represented by the structure of Structure 1:
wherein A is CH 2 , O, NH, or NR; R is an alkylene chain of 1-6 carbon atoms; X − is a carboxylate anion of 1-40 carbon atoms and the group of salts represented by the structure of Structure 2:
wherein R 1 and R 2 are H or alkyl and R 3 and R 4 are alkyl.