GB498043A - Urea formaldehyde resins - Google Patents

Abstract

Hydrocarbon-soluble condensation products are obtained by heating urea and formaldehyde in an alcoholic solvent in the presence of a volatile acidic catalyst and in the absence of water until the product becomes soluble in hydrocarbons, the amount of catalyst being insufficient to cause gelling of the reaction mass when heated to 117 DEG C. for approximately 10 hours and the water formed by the reaction together with the acidic catalyst being distilled from the solution as the reaction proceeds. The preferred alcoholic solvent is n-butyl alcohol; ethyl and propyl alcohols may be used with pressure and amyl alcohol with vacuum; alcoholic solvents boiling between 78-137 DEG C. may be employed at boiling temperatures, but with higher-boiling alcohols, e.g. cyclohexanol and the mono ethers of ethylene and diethylene glycols, the temperature is preferably kept below 120 DEG C. and removal of water assisted by blowing with an inert gas. Specified volatile acids are formic, hydrochloric and acetic acids. Preferably 2,5 mols of formaldehyde per mol of urea is employed and the acid catalyst is not added until the dimethylol-urea stage has been reached; alternatively, dimethylol urea may be employed as starting material. In an example, urea is added to a 40 per cent solution of formaldehyde in butanol, prepared by refluxing butanol with paraformaldehyde in the presence of a small amount of hexamethylenetetramine, and the mixture is heated and then refluxed for 15-30 minutes; formic acid is then added and distillation begun and continued, the temperature gradually rising to 115-117 DEG C.; water and butanol distilled off are condensed, the butanol being returned to the reaction mixture; after 12-14 hours removal of water and resinification are complete, the resinous product being miscible with monohydric alcohols and esters and almost completely miscible with aromatic hydrocarbons and tolerating dilution with aliphatic hydrocarbons. Urea may be partly replaced by thiourea or other urea derivative, and formaldehyde may be partly replaced by other aldehydes, e.g. acetaldehyde and benzaldehyde. The resin solutions may be employed as coating-compositions, alone or blended with other resins, e.g. alkyds, or with nitrocellulose or cellulose acetate. Hardening of films may be accelerated by addition of an acidic catalyst just prior to application. The resin may be plasticized, e.g. with raw or blown castor oil, phthalic acid esters, tricresylphosphates, and esters of sebacic acid, e.g. glyceryl and p butyl modified or not with oils or their fatty acids. The resin may be employed as a binding material for moulded or laminated products and as an adhesive, e.g. for plywood.