One component epoxy curing agents comprising hydroxyalkylamino cycloalkanes
Liquid epoxy curing agents that have improved latency over conventional liquid curing agents while retaining the physical properties of the cured material are disclosed. These liquid curing agents can be used for curing epoxy resins, or in combination with dicyandiamide (DICY) based curing agents in order to accelerate DICY curing.
1. A latent curing and heat activated composition comprising: i) dicyandiamide, ii) at least one liquid tertiary amine salt curing agent accelerator having a viscosity of about 150 to about 200 cP, and iii) at least one epoxy resin; wherein the tertiary amine salt comprises a salt of at least one carboxylic acid and 1,4-bis(2-hydroxyethyl)piperazine, wherein the carboxylic acid comprises at least one member selected from the group consisting of acetic acid, propanoic acid, decanoic acid, dimer acid and mixtures thereof, wherein the amount of the curing agent accelerator ranges from about 1 phr to about 2 phr and wherein the composition is at least 85% cured when exposed to a temperature of 80° C. for 2 hours.
2. The composition of claim 1 wherein a cured composition has a Tg of about 90 to about 130° C.
3. The composition of claim 2 wherein the composition is substantially free of anhydrides and styrene and styrene containing compounds.
4. The composition of claim 1 wherein a cured composition has a flexural modulus when measured in accordance with ASTM C881 of about 14,000 to about 450,000 psi.
5. A cured epoxy resin obtained from the composition of claim 1 .
6. A latent heat curable composition consisting of: i) at least one epoxy resin, and ii) a curing agent consisting of dicyandiamide and a liquid carboxylic acid salt of 1,4-bis(2-hydroxyethyl)piperazine.
7. The composition of claim 6 wherein the composition is substantially free of anhydrides.
8. The composition of claim 6 wherein the ratio of amine to acid is about 1.0 to about 1.1.
9. The composition of claim 8 wherein the composition is at least 85% cured when exposed to a temperature of 80° C. for 2 hours.
10. The composition of claim 9 wherein the curing agent is between 5 weight percent and 7.4 weight percent of the composition.
11. The composition of claim 9 wherein the composition has a viscosity from about 6000 cp to about 20,000 cp for a period of about 2 days to about 8 days when measured at a temperature of 25° C.
12. The composition of claim 6 wherein the epoxy resin comprises bisphenol A diglycidyl ether.
13. The composition of claim 11 wherein the composition is cured when heated to a temperature of about 50 to about 150° C.