| 摘要 |
1. A process for the preparation of aqueous urea/formaldehyde wood glues containing less than 1.4 moles of formaldehyde per mole of urea, wherein, after an optional hydroxymethylating reaction, in a first stage aqueous formaldehyde or a formaldehyde-donating compound and urea in a molar ratio of >= 1.8:1 are condensed in the presence of an effective amount of up to 0.3 mole of a monohydric or polyhydric alcohol, with reference to the total amount of urea envisaged, at a pH of less than 6, to a viscosity of at least 600 mPas, measured at 20 degrees C on a solution having a condensate content of 66.5%, the condensation is interrupted and concentration is optionally carried out, and, in a second stage, urea is added to give a molar ratio of formaldehyde to urea of less than 1.4:1, and, if concentration is carried out, at least part of the urea is added after the concentration step. |
