PURPOSE: To efficiently carry out purification of a methylene-cross-linked- polyphenylene polyisocyanate useful for coating, etc., without changing condensation conditions of a polyamine by separating an isocyanate mixture being a prescribed value or above in a ratio of trinucleic body/tetra or more nucleic body from a specific polyisocyanate mixture in specific conditions.
CONSTITUTION: A polyisocyanate mixture of the formula (n is integer of 0 or positive) containing ≤50% diphenylmethane diisocyanate is extracted with a >5C aliphatic and/or alicyclic hydrocarbon at <40°C. Thereby, an isocyanate mixture having ≥1.5 ratio of 3 nucleic body/≥4 nucleic body is separated to carry out purification of methylene-cross-linked polyphenylene polyisocyanate.
ISHIDA NORITOSHI
TAJIMA JUNJI
KURODA KAZUMOTO
NITTA KAZUNARI
