BLEACHING OF POLYMERIC DIPHENYLMETHANE DIISOCYANATE AND USE OF BLEACHED DIPHENYLMETHANE DIISOCYANATE IN PRODUCING POLYURETHANE PLASTIC

摘要

PROBLEM TO BE SOLVED: To obtain a polymethylene poly(phenyl isocyanate) having a color value as low as possible without changing the other physical properties by a technically simple method having high reliability by treatment with light rays at a specific wavelength. SOLUTION: A polymethylene poly(phenyl isocyanate) (PMDI) is treated with light rays at 250-2,500 nm, preferably 300-450 nm wavelength. For example, PMDI is transported to a reactor 5 in a loop system by a peristaltic pump 2 and is irradiated with ultraviolet rays by an ultraviolet lamp 3. The reactor for the treatment is preferably made of a quartz glass or another type of glass not absorbing light rays of application wavelength. The irradiation time is preferably 5 seconds to 10 minutes. An industrial mixture of 4,4'-diphenylmethane diisocyanate containing =10 wt.% 2,4'-diphenylmethane diisocyanate is preferable as the PMDI.