Process for the preparation of thermosetting melamine-modified urea formaldehyde resins and their use as impregnating resins

摘要

Method for making urea-formaldehyde resin doped with melamine involves adjusting pH at least with aid of an alkanolamine. Method for making urea-formaldehyde resin doped with melamine involves: (a) adding melamine to a urea-formaldehyde mixture of formaldehyde/NH2 ≥ 1.5, in aqueous medium of pH = 6-8, at 20-90 degrees C; melamine content in final product = 1-5 wt.%; (b) keeping the reaction medium at 80-103 degrees C and pH = 6.5-7.8 for 5-15 mins., and then at a lower pH to obtain a resin with required degree of condensation; and (c) adjusting pH to 7.2-7.5, and cooling mixture to 40-60 degrees C, and if necessary adding urea and water, for up to 30 mins. Ratio formaldehyde/NH2 is 0.45-0.85, and after cooling, pH is further adjusted to 8-10, using, at least, an alkanolamine. An Independent claim is also included for use of urea-formaldehyde resin as an impregnation resin.