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 an epoxy resin in an alcohol-based solvent in the presence of dicyandiamide.
CONSTITUTION: This prepolymer is obtained by reaction between (A) a bifunctional epoxy resin selected from bifumctional epoxy resins having ≤250 of epoxy equivalent and brominated bifunctional epoxy resins having ≤500 of epoxy equivalent, (B) a polyfunctional phenolic compound having in one molecule >2 in phenolic OH groups and (C) dicyandiamide in the presence of (D) a catalyst in (E) 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.
SHIBATA KATSUJI
KOBAYASHI KAZUHITO
