GB1513409A - Process for the manufacture of solutions of curable urea-formaldehyde resins - Google Patents

Abstract

1513409 Laminates TH GOLDSCHMIDT AG 10 Oct 1975 [11 Oct 1974] 41702/75 Heading B5N [Also in Division C3] Sheets of wood-based materials are surfacefinished by lamination thereto of a carrier web impregnated with a solution of a curable ureaformaldehyde resin prepared by (a) reacting urea and formaldehyde together in an aqueous solution in a molar ratio of 1:1À5 to 1:2À5 in the presence of 0À2 to 1À0 mmol of an aminosulphonic acid and 20 to 100 mmols of ammonia (relative to 1 mol of urea in each case) at a temperature of 70 to 95‹C for 10 to 30 minutes until a 50% w/v solution thereof has a viscosity at 20‹C of 55 to 65 cP, (b) 0À8 to 1 mmols of an aminosulphonic acid (relative to 1 mol of urea in stage (a)) is added to the first reaction product and a pH of 4À0 to 4À5 is maintained using ammonia for a reaction time of 10 to 25 minutes at 70 to 95‹C until a 50% w/v solution thereof has a viscosity at 20‹C of 80 to 110 cP, and finally (c) 40 to 200 mmols of ammonia and 0À1 to 0À3 mol of urea (relative to 1 mol of urea in stage (a) in each case) are added to the second reaction product and the reaction mixture is reacted at 70 to 95‹C for 15 to 45 minutes until a 50% w/v solution thereof has a viscosity at 20‹C of 85 to 125 cP. In examples a paper carrier web is impregnated with a solution of the urea-formaldehyde resin and is then pressed to a pressboard sheet at high temperature.