GB1028394A - Bonding porous particles - Google Patents

Abstract

Water-penetrable cellulosic particles or fibres or sheets are bonded by applying to them an aqueous solution of an acid or acid salt of pKa less than 5.5, followed by an aqueous solution of a urea-formaldehyde resin, then forming, pressing and heat-curing the mass in the desired shape. The resin amounts to 3-15% by weight of the particles, and the catalyst, usually, to 0.1-1%. The resin may comprise 5-50% by weight of a melamine-formaldehyde resin, and usually contains a part of the catalyst, preferably 0.5 to 1.5 parts per 100 of resin of an acidic salt, e.g. NH4Cl, (NH4)2SO4. The remainder of the catalyst is applied to the particles as the pretreatment. Suitable acids and salts are acetic, phosphoric, hydrochloric, sulphuric, nitric, chloracetic, and oxalic acids, and ammonium nitrate, chloride, sulphate, and silicofluoride. The preferred particles are wood flakes, but may be paper stock, veneers-for plywood, wood flour-for moulding compositions, or rag fibres. In examples, catalysts are sprayed as 10% solutions in amounts of 0.1 or 0.2 parts per 100 of wood on to wood chips, followed by a urea-formaldehyde resin solution in amount 7 parts per 100 of wood, and from the mixture board is made by pressing at 375 p.s.i., followed by cure at 290 DEG C. and 350 p.s.i.