Storage-stable heat-activated tertiary amine catalysts for epoxy resins
View Patent ↗Epoxy adhesive compositions contain a heat-activatable catalyst. The heat-activatable catalyst includes a tertiary amine catalyst and a novolac resin that has a weight average molecular weight of at least 3000. One-component epoxy adhesive formulations that contain the heat-activatable catalyst have unexpectedly good storage stability.
1. A process for making a heat-activatable catalyst composition comprising a mixture of 2-(dimethylaminomethyl)phenol, 2,6-bis(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol or 2,4,6-tris(dimethylaminomethyl)phenol and a novolac resin that has a weight average molecular weight of at least about 5000, wherein the weight ratio of the 2-(dimethylaminomethyl)phenol, 2,6-bis(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol or 2,4,6-tris(dimethylaminomethyl)phenol and the novolac resin is from 40:60 to 70:30, which process includes the steps of:
a) mixing the 2-(dimethylaminomethyl)phenol, 2,6-bis(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol or 2,4,6-tris(dimethylaminomethyl)phenol with a liquid solution of a novolac resin having a weight average molecular weight of at least 5000 in a lower alcohol, at a temperature above the melting temperature of the 2-(dimethylaminomethyl)phenol, 2,6-bis(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol or 2,4,6-tris(dimethylaminomethyl)phenol but not greater than 80° C. and not greater than the boiling temperature of the lower alcohol and at proportions such that from 0.1 to 10 equivalents of phenol groups are provided by the novolac resin per equivalent of tertiary amine groups provided by the 2-(dimethylaminomethyl)phenol, 2,6-bis(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol or 2,4,6-tris(dimethylaminomethyl)phenol, whereby the reaction mixture separates into a liquid phase containing mainly the lower alcohol and a precipitate of the 2-(dimethylaminomethyl)phenol, 2,6-bis(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol or 2,4,6-tris(dimethylaminomethyl)phenol and the novolac resin;
b) separating the precipitate from the liquid phase by decanting, filtering or centrifugation while maintaining the temperature of the precipitate at no greater than 80° C. and
c) drying the separated precipitate at a temperature of no greater than 80° C. to remove residual lower alcohol from the precipitate.
2. The heat-activatable catalyst composition of claim 1 wherein the novolac resin has a weight average molecular weight of from 5000 to 20,000.
3. The heat-activatable catalyst composition of claim 1 wherein the novolac resin is a phenol novolac resin.