Production of alkali-condensed phenol-urea-formaldehyde resin used e.g. for lignocellulosic material

摘要

A process for the production of an alkali-condensed phenol-urea-formaldehyde (PUF) resin with a mol ratio of P:F:U = 1:(1.5-3.5):(0.3-2.5), comprising: (a) preparation of a PF condensate by alkaline condensation of P and F up to a viscosity of 100-5000 mPa.s; (b) production of a PF resin by further condensation to a viscosity of more than 5000 mPa.s; and (c) reaction of the PF resin with urea. The novelty is that stage (b) is carried out in an extruder. Also claimed is a PUF resin obtained by this process. Preferably stage (b) is carried out in an extruder at 90-150 deg C, preferably in a continuous single- or twin-screw mixer, a twin-screw continuous kneader or a continuous multi-screw kneader. Stages (a)-(c) may be carried out continuously. The PF resin is produced in stages (a) and (b) by starting with 60-90% of the total amount of formaldehyde required, and then reacted in stage (c) with the remaining 10-40% F and the urea, possibly in the form of a UF precondensate. The PF resin obtained in stage (b) has a viscosity of more than 5000 to 100,000 mPa.s. The final PUF resin has a solid content of 40-70 wt% and a mol ratio of (phenol):(alkali hydroxide) = 1:(0.4-1.2), which may be reduced to 1:(0.9-1.5) before processing by adding more alkali hydroxide.