GB819044A - Methylol melamine phenol-formaldehyde adhesives - Google Patents

Abstract

An adhesive composition comprises an aqueous dispersion of (i) a condensation product of a monohydric phenol with 1.2-3 mols. of formaldehyde per mol. of phenol, said condensation product having been prepared in the presence of 0.4-1 mol. of analkali metal hydroxide per mol. of phenol, the alkali metal being retained in solution; (ii) 3-25 per cent by weight of (i) of a water-soluble alkali metal silicate having an alkali metal to silica ratio of 1 : 3 to 1 : 3.4; and (iii) 2.5-25 per cent by weight of (i) of a separately prepared monomeric and/or dimeric condensation product of melamine with 2-4 mols. of formaldehyde per mol. of melamine produced under alkaline conditions. The phenol condensation product (i) may be prepared from phenol, a cresol, a xylenol or mixtures thereof and the catalyst, preferably NaOH, may be added at the beginning of the reaction or incrementally. The silicate (ii) is preferably added as a 38 per cent by weight aqueous solution to a 35-50 per cent by weight aqueous solution of (i). This mixture of (i) and (ii) may then be aged at 20-35 DEG C. for 8-24 hours. The melamine condensation product (iii) is normally a mixture of di-, tri-, and tetra-methylolmelamines and may be added either at the same time as the silicate, or after the ageing. Optional ingredients include asbestos, a -cellulose, wood flour, nutshell flour, Douglas Fir bark flour, oathulls, clays, anti-foaming agents (Diesel oil), NaOH and Na2CO3. Use.-Plywood glue.