GB641703A - Manufacture of unpolymerized urea-formaldehyde reaction products - Google Patents

Abstract

Liquid urea-formaldehyde compositions are made by admixing a liquid mixture of formaldehyde and water containing from 50-70 per cent of formaldehyde by weight, the temperature of said liquid having been maintained above 45 DEG C. since its preparation, with urea at a pH of 7-9, in the proportion of one molecule of urea per 3.9-10 molecules of formaldehyde and maintaining the temperature of the resulting liquid at least momentarily at from 70-90 DEG C. The proportion of formaldehyde to urea is preferably from 4.5 : 1 to 7.0 : 1, and most preferred at 6.0 : 1. Additional amounts of urea may be added subsequently to reduce the formaldehyde-urea ratio to not less than 3.9 : 1, the temperature being preferably lowered below 50 DEG C. prior to the second addition of urea. The formaldehyde solution may be prepared by liquefying a gaseous formaldehyde-watervapour mixture of corresponding composition having a temperature above 90 by cooling to 60-90 DEG C. The compositions obtained may be used for impregnating lignocellulosic and cellulosic materials, e.g. wood, and in the manufacture of lacquers, moulded products and finishes. Further additions of urea may be made immediately before such use. The pH is preferably adjusted by the use of buffer mixtures, e.g. phosphoric acid or boric acid and sodium hydroxide. Examples are given, giving details of procedures carried out in accordance with the above.ALSO:Liquid urea-formaldehyde compositions are made by admixing a liquid mixture of formaldehyde and water containing from 50-70 per cent of formaldehyde by weight, the temperature of said liquid having been maintained above 45 DEG C. since its preparation, with urea at a pH of 7-9, in the proportion of one molecule of urea per 3.9-10 molecules of formaldehyde and maintaining the temperature of the resulting liquid at least momentarily at from 70-90 DEG C. The proportion of formaldehyde to urea is preferably from 4.5 : 1 to 7.0 : 1, and most preferred at 6.0 : 1. Additional amounts of urea may be added subsequently to reduce the formaldehyde-urea ratio to not less than 3.9 : 1, the temperature being preferably lowered below 50 DEG C. prior to the second addition of urea. The formaldehyde solution may be prepared by liquefying a gaseous formaldehyde-water-vapour mixture of corresponding composition having a temperature above 90 by cooling to 60-90 DEG C. The compositions obtained may be used for impregnating lignocellulosic and cellulosic materials, e.g. wood, and in the manufacture of lacquers, moulded products, and finishes. Further additions of urea may be made immediately before such use. The pH is preferably adjusted by the use of buffer mixtures, e.g. phosphoric acid or boric acid and sodium hydroxide. Examples are given, giving details of procedures carried out in accordance with the above.