| 摘要 |
<p>1. A process for producing carbamide bonding materials, containing, for 1 mole of urea, 0.2 to 0.8 moles melamine, 2 to 5 moles of formol, 0.05 to 0.5 moles of phenol, characterised in that in the first stage all the phenol is condensed with a precondensate of urea and formol having the molar ratio F/U between 3 and 6, or with formol in an aqueous solution, in the presence of urea so that the proportion of urea present at this stage, either between 33 and 100%, relative to the final total urea contained in the final resin, condensation being carried out at a temperature of between 40 and 100 degrees C, at first with a neutral pH value, then with an acidic pH value equal to 5.5 at most for at least 30 minutes and in that in a second stage after neutralising all the melamine, and if necessary a new amount of urea is added, so that the proportion of urea present at this stage is equal to 100% at most, relative to the total urea contained in the finished resin, the condensation being carried out at a basic pH value, at least equal to 8, at a temperature of between 40 and 100 degrees C, until the viscosity of the reactive mixture is between 200 and 1500 mPa.s at 20 degrees C, a dried extract of 60% and that in a third stage the remaining urea is added after being cooled to a temperature of between 40 and 80 degrees C.</p> |
