A method for the preparation of aqueous urea, melamine formaldehyde - - - aminoplast resins, their use as adhesives for the production of wood materials and resulting wood materials

摘要

Is prepared in such a resin with a melamine-formaldehyde resin in the final 10 - 40% by weight, by condensing urea and formaldehyde and melamine, and by addition of urea in order to obtain a final molar ratio f / nh2 of 0, 25 - 0, 85. (a) is heated at reflux, up to 15 min at ph 7 - 8, 5, a mixture in aqueous medium of urea, melamine formol and f / nh2 = 0, 85 - 1, 15; (b) the 1ère step of condensation to ph 5 - 6, 5 and 70degrec - 100degrec, until a degree of condensation, corresponding to a viscosity at 25degrec whose value depends on the active material, and it stops the condensation by bringing the ph at 7 - 8, and the temperature to 60 - 80degrec; (c) is carried out by adding 2ème step of condensation of formaldehyde, urea, melamine for an f / nh2 of 0, 6 - 0, 9, and it is condensed at ph 8 - 10 and 70 - 100 grade c, until a degree of condensation, corresponding to a viscosity at 25degrec whose value depends on the active material, and (d) is carried out, a post - addition of urea, nh2 group comprising the moles of urea and melamine.