process for the production of lagerstabilen, liquid urea formaldehyde leimharzen.

摘要

A process is claimed for the prodn. of urea-formaldehyde resins (I) with U:F ratio from 1:1.0 to 1:2.1 and a solids content of 58-75 wt.% (opt. contg. melamine, phenol, etc.), by concn. of a condensate soln. (II), followed opt. by reaction with urea. (II) contains 38-55 wt.% dry matter, and is conc. by thin-layer evapn. to 58-72 wt.%, with recycling of 10-60 wt.% of the prod. soln. to the thin layer evaporator. Evapn. is performed in falling-film evaporator(s) in series or in parallel, pref. in two or three stages with recycling at each stage; evaporator is operated with film thickness about 1.5 mm and dwell-time 1-10 mins., pref. with steam at 2-6 bar, and at 48-100 deg.C; recycled soln. is treated with 60-70 wt.% aq. urea soln. before re-entering the evaporator; evapn. is performed at 850-100 mbar; pref., (II) contains 40-50 wt.% dry matter, and is conc. to 60-68 wt.%.