PROCEDEU PENTRU OBTINEREA UNOR CLEIURI PE BAZA DE RASINI UREOFORMALDEHIDICE CU CAPACITATE IMBUNATATITA DE LIPIRE LA RECE,PENTRU FABRICAREAPLACILOR AGLOMERATE

摘要

Prodn. of urea-formaldehyde resin adhesives comprises first precondensing urea and HCHO in a molar ratio of 1:1.8-2.2 at 100-140 degrees C and elevated pressure in the presence of 0.5-5 wt.% (based on urea) of an acid (esp. HCOOH) for 10-100 min. to form a precondensate with a predetermined viscosity. The precondensate is neutralised or made weakly basic and condensn. is continued at 40-80 degrees C while adding urea until the final urea-HCHO molar ratio is 1:1.3-1.8. Water is opt. removed to obtain the required solids content. The adhesives are esp. useful for the mfr. of wood chipboard. They have good cold bonding properties, allowing continuous board prodn. by cold pressing to form a self-supporting rough board, which can then be passed for hot pressing without a support.