METHOD OF OBTAINING A CARBAMIDE-FORMALDEHYDE RESIN AND A CONDENSATE FOR THE MANUFACTURE OF THE SAME

摘要

The invention relates to the chemical and wood processing industries and facilitates the production of a carbamide-formaldehyde resin of low toxicity and with the highly developed adhesive and industrially useful properties of a binder, and of a carbamide-formaldehyde condensate which is stable in storage, of low toxicity and frost-resistant, and has an enhanced dry residue content. The proposed carbamide-formaldehyde resin is obtained by carrying out a condensation reaction of carbamide and formaldehyde. The aqueous carbamide solution used for this reaction in the first stage of the process is a carbamide-formaldehyde condensate or a mixture of individual substances containing (in wt %): carbamide - 11.4-20.9; monomethylol urea - 24.9-33.1; dimethylol urea - 4.2-9.2; formaldehyde 1.9-2.4; water - the remainder. Formaldehyde is introduced until the molar ratio of carbamide to formaldehyde is 1.0:(1.75-2.1) at a pH of 6.0-8.5. The second stage of the condensation is carried out at a pH of 3.9-5.1 and a temperature of 82-98 DEG C. The condensation product is cooled and evaporated and an additional quantity of carbamide is added until a molar ratio (carbamide to formaldehyde) of 1.0:(1.0-2.0) is reached at a pH of 7.5-8.5 and a temperature of 40-65 DEG C, the resin being subsequently cooled and stabilized. The proposed carbamide-formaldehyde condensate is obtained by mixing the excess carbamide and the aqueous formaldehyde solution in the presence of an alkali agent at a pH of 8.2-8.8, the molar ratio of carbamide to formaldehyde being (0.8-2.0):1.0. The solution thus obtained is then condensed at a temperature of 5-45 DEG C, and the condensation product is stabilized by being left to stand for not less than three hours. An alkaline environment is created with the aid of aqueous solutions of alkali metal hydroxides, amino compounds or mixtures of the two.