PROCEDEU DE PREPARAREA A CLEIURILOR DE RASINI UREOFORMALDEHIDICE UTILIZATE LA FABRICAREA PLACILOR AGLOMERATE

摘要

Urea-formaldehyde binders for wood chipboard having reduced emission are made by (a) condensing urea (U) with formaldehyde (F) in the presence of ammonia at >100 degrees C in aq. soln. using a mol ratio U/F of 1:1.8-1:2.5 and a mol ratio U/NH3 of 1:0.04-1:0.2 with backflowing mixing for 10-60 mins. at 100-140 degrees C and a pressure of 1-4 atm., (b) in a second stage, condensing at 40-80 degrees C with the pH adjusted to 7-8 with an alkali and using a U/F ratio of 1:1.4-4:1.6, opt. with backflow mixing and (c) concentrating the condensate at 40-80 degrees C under a pressure of 40-600 mm Hg. Prod. gives very low concn. of free formaldehyde in the atmos. in use to comply with pollution and toxicity requirements.