| 摘要 |
The invention relates to strongly exothermally setting urea-formaldehyde resin, obtained by condensation of urea with formaldehyde under alkaline conditions, wherein it is obtained by a) condensation in a first condensation stage I of 0.2 to 0.7, preferably 0.5 moles of urea with 1.2 to 3 moles, preferably with 1.7 to 2.2 moles of formaldehyde in the form of solid paraformaldehyde, under exclusively alkaline conditions, at a spontaneously establishing initial pH of 8 to 12, preferably 9 to 11, b) in the presence of 1 to 10 mmoles of NaCH and 10 to 80 mmoles or NH3 or in the presence of 2.5 to 50 mmoles of guanidine base and 0 to 80 mmoles of NH3 per 1 mole of formaldehyde c) at a condensation temperature (I) of 90 to 110.degree.C, d) for a condensation time (I) of 10 to 100 minutes, preferably 15 to 70 minutes, and e) subsequent addition, in a second condensation stage II, of a further 0.2 to 0.7, preferably 0.5 moles of urea, f) at a condensation temperature (II) of 105 to 120.degree.C, g) for a further condensation time (II) of 1.5 to 5 hours. It offers advantages due to freedom from pollution, freedom from waste water, reduced energy and plant costs, improved drying of the expanded materials and increase economy. |
