PURPOSE: To obtain at low cost the subject prepolymer good in impregnability into glass base materials, unnecessary for dealing with offensive odor, useful as e.g. an electrical insulation material, by prepolymerizing a specific epoxy resin in an alcohol-based solvent.
CONSTITUTION: This prepolymer is obtained by reaction between (A) a bifunctional epoxy resin selected from bifunctional epoxy resins having ≤250 of epoxy equivalent and brominated bifunctional epoxy resins having η500 of epoxy equivalent and (B) a polyfunctional phenolic compound having in one molecule >2 in phenolic OH groups in the presence of (C) a catalyst in (D) an alcohol-based solvent at the equivalent ratio B/A of 0.05-0.6, with a solid concentration of 30-95wt.% at 50-130°C. It is preferable that the component B be a phenol novolak resin having 50-120°C of softening point, cresol novolak resin having 60-130°C of softening point or bisphenol novolak resin, and the component C an alicyclic amine.
SHIBATA KATSUJI
KOBAYASHI KAZUHITO
