GB809662A - Stable solutions of water-soluble amino-aldehyde resins - Google Patents

Abstract

Stable aqueous solutions of modified melamine-formaldehyde resins are prepared by reacting in aqueous medium (i) one mol. of melamine with (ii) 2.5-6.0 mols. of formaldehyde and (iii) such amounts of water-soluble polyhydric aliphatic alcohols containing more than one primary hydroxy group, as to give the ratio of 0.2-1.0 primary hydroxy groups per hydroxymethyl group of the melamine-formaldehyde addition product, and continuing the reaction until one volume of the resin solution is precipitable by not less than 2 and not more than 4 volumes of water at 25 DEG C., the concentration of the reactants being such as to yield in the solution a solids content of 50-60 per cent by weight, and storing the resin solution at pH 8.5-9.5. In a modification up to 0.5 mol. of melamine may be replaced by an equivalent molecular amount of urea, the amount of formaldehyde being made up of an amount relative to urea in the molar ratio of 1:2 plus an amount relative to melamine as in (ii) above, and the amount of polyhydric alcohol being such as to give 0.2-1.0 primary hydroxyl groups per hydroxy methyl group of the combined addition product. Polyhydric alcohols specified are ethylene-, diethylene-, propylene- and dipropylene-glycols, pentaerythritol, dipentaerythritol, trimethylol-propane, glycerol, erythritol and mannitol. The reaction pH is 4-10, preferably 8-9, it may be adjusted by the use of NaOH, KOH, NH4OH, amines, HCl, H2SO4, formic or acetic acids. The reaction temperature is 50-100 DEG C. The storage temperature is 25 DEG C. Examples are given. Uses.-Laminates, plywood adhesives, coating, binding rock wool to glass fibres, impregnating fabrics.