| 摘要 |
1. Method for preparing urea-formaldehyde resin based adhesives for gaining wood material having an extremely low formaldehyde emission, by an intermediate product forming condensation of urea and formaldehyde in the molar ratio of 1:1,8 to 1:2,1 at temperatures of 373 to 414 degrees K and conversion of these condensates, in manner known per se, into adhesive resins, characterized in that one condenses urea and formaldehyde in aqueous solution in presence of 0,05 to 0,5% organic or anorganic acids, related to the amount of urea used, in maintaining a carbon dioxide pressure of 2 to 4.10**5 Pa that long until at least 40% of the formaldehyde used is bound in form of methylene bridges, and one further condenses this intermediate product in the neutral or low alkalic range after addition of urea up to a molar ratio of urea related to formaldehyde of 1:0,9 to 1:1,3 and, if desired, concentrates simultaneously. |
