Verfahren zur Herstellung von Harnstoff-Formaldehyd-Harzen

摘要

The invention concerns a urea-formaldehyde resin which sets highly exothermically and is prepared by: a) heating paraformaldehyde in solid form to between 60 and 120 DEG C, preferably to between 80 and 100 DEG C; b) adding urea and optionally dicyandiamide and melamine in appropriate molar amounts to the heated paraformaldehyde, mixing the substances intensively dryly and heating them until, after approximately 15 minutes, a temperature of between 80 and 110 DEG C, preferably of between 85 and 100 DEG C, is reached; c) adding 32 % methanolic guanidine base in an appropriate molar ratio to the heated mixture which is further heated, the mixture liquefying within 10 minutes and, in spite of the increased thermal energy, cooling to 65 DEG C; heating the mixture to the boiling range of between approximately 103 and 110 DEG C by the further addition of thermal energy, and condensing it in a first condensation stage, the beginning of condensation stage I being set arbitrarily as from a temperature of 90 DEG C, and condensation stage I lasting for between 30 and 100 minutes, preferably for between 50 and 85 minutes; d) at the end of condensation stage I, adding a second amount of urea, dicyandiamide, etc. in appropriate molar ratios to the boiling mixture and condensing it in a second condensation stage for between 90 and 180 minutes at a condensation temperature of between 105 and 120 DEG C; and e) at the end of condensation stage II, buffering off the mixture with lactic acid in the boiling heat and cooling the resin to approximately 25 DEG C for approximately 120 minutes.