| 摘要 |
Aqueous urea-formaldehyde resins solutions are prepared by (a) forming a first aqueous solution containing urea and formaldehyde in a molecular ratio in the range urea:formaldehyde=1:3 to 1:1.5, (b) reacting the first aqueous solution under neutral or alkaline conditions to form a reaction mixture containing substantial amounts of methylol urea products, (c) vacuum evaporating the reaction mixture to produce a concentrated mixture having a solids content of 55% to 80% by weight, and (d) further condensing the concentrated mixture under acid conditions to produce a resinous material. The urea may be wholly or partially replaced by melamine. |
