GB1420017A - Aminoplastic binder for wood-base materials - Google Patents

Abstract

1420017 Uron-containing urea-formaldehyde resins BADISCHE ANILIN- & SODAFABRIK AG 16 Feb 1973 [19 Feb 1972 7 Sept 1972] 7639/73 Heading C3R A urea-formaldehyde resin of F : U ratio 1 to 2À75 : 1 is obtained by (i) condensing urea and formaldehyde, or a precondensate thereof, of F : U ratio at least 3 : 1 in squeous solution at pH not above 3 until at least 1% of the urea present is in the form of uron groups, (ii) adding urea, still at pH not above 3 to an F : U ratio of 2À75 to 2 : 1, and optionally (iii) adding urea at pH 5-6À5 or 8-10 to an F : U ratio not less than 1 : 1, the condensation being continued until the solution is no longer dilutable with water in all proportions at room temperature, and the product, if desired, being concentrated or dried. The urea is preferably added continuously. In Examples 1-3 and 5-8, 470-552 p.b.w. of 68À3% aqueous urea is added over 4.5 to 79 minutes to 1000 p.b.w. of 40% formalin at 95‹ C., adjusted with H 2 SO 4 to pH 0À5-1; the pH is then adjusted with NaOH to 8À5-9 and 61-639 p.b.w. of the urea solution are added over 3-60 minutes (this stage is omitted in Example 6). In Examples 4 and 11-15, 1000 p.b.w. of a 60% solution of a precondensate of F : U ratio 4 : 1 is held at 95‹ C. for up to 33 minutes at pH 1À4-2À4, then 182-490 p.b.w. of the urea solution is added over 0-20 minutes (total time 6-53 minutes), the solution is neutralized with NaOH and a further 232-363 p.b.w. of the urea solution is added and the pH brought to 6À5. In all the examples the solution is neutralized with NaOH and concentrated to 65% solids: these solutions have F : U ratios of 1 to 2À15 : 1 and viscosities of 190-1272 cP./20‹ C. Uses.-Binders for chipboard, plywood, fibreboard.