A PROCESS FOR PREPARING A UREA-FORMALDEHYDE RESIN HAVING A VERY LOW MOLE RATIO OF FORMALDEHYDE TO UREA.

摘要

UREA AND FORMALDEHYDE ARE MIXED IN A MOLE RATIO OF ABOUT 1: 2. THE MIXTURE IS CONDENSED FOR 30 MINUTES AT A PH OF 7.0 TO 7.4 AND A TEMPERATURE BETWEEN 80 AND 85°C. THE CONDENSATION IS CONTINUED AT A PH OF 5.8 AT THE SAME TEMPERATURE UNTIL THE VISCOSITY REACHES VALUES BETWEEN 15 AND 50 MPA.S. THE MOLE RATIO OF UREA TO FORMALDEHYDE IS ADJUSTED TO A VALUE OF 1:1.80 TO 1:1.90 BY ADDING UREA.THE CONDENSATION IS CONTINUED UNDER ACIDIC CONDITIONS AT THE SAME TEMPERATURE, UNTIL THE VISCOSITY REACHES VALUES OF 35 TO 80 MPA.S. AT A PH OF 5.8 TO 6.5, THE MOLE RATIO OF UREA TO FORMALDEHYDE IS ADJUSTED TO A VALUE BETWEEN 1.0:1.0 AND 1.0:1.30 BY ADDING UREA. THE TEMPERATURE IS ALLOWED TO DROP FREELY. WHEN THE TEMPERATURE HAS DROPPED TO BELOW 50°C THE PH IS ADJUSTED TO A VALUE OF 7.0 TO 8.0.