METHOD FOR PRODUCING METHYLENE-CROSSLINKED POLYPHENYL POLYISOCYANATE

摘要

A method for producing a methylene-crosslinked polyphenyl polyisocyanate, wherein sufficient hue improvement can be achieved while suppressing the amount of hydrogen chloride used therein. The method for producing a methylene-crosslinked polyphenyl polyisocyanate is characterized by comprising: a phosgenation step wherein a polymethylene polyphenyl polyamine and phosgene are reacted in the presence of an inert solvent; a solvent removal step wherein the inert solvent is removed from the reaction liquid obtained in the phosgenation step until the concentration of the solvent becomes 5-35% by mass; and a hydrogen chloride introduction step wherein hydrogen chloride is introduced into the reaction liquid after the solvent removal step.  The method is also characterized in that the temperature of the reaction liquid is kept within the range of 60-130°C in the phosgenation step, the solvent removal step and the hydrogen chloride introduction step.  As a result, sufficient hue improvement can be achieved, while suppressing the amount of hydrogen chloride used therein.