GB703426A - Improvements in or relating to urea-melamine-formaldehyde resins - Google Patents

Abstract

Resin syrups are made by condensing a mixture of melamine and urea, the urea being present in an amount from 5 to 35 per cent. by weight of melamine, with aqueous formaldehyde at pH 3 to 10 and in an amount to provide 0.9 to 2 mols. of formaldehyde for each amino and amido group, until the condensate has a water tolerance of not less than 1:1 at 20 DEG C.; the reaction being performed in presence of methyl or ethyl alcohol and the weight ratio of water/alcohol before reaction being 5:1 to 1:2. The formaldehyde may be formalin and/or aqueous paraformaldehyde. After condensation water and alcohol may be distilled off, preferably under vacuum at less than 50 DEG C. and at a pH greater than 7, and additional methyl or ethyl alcohol added to the syrup. Unspecified curing catalysts, fillers and plasticizers may be added to the syrup. The Provisional Specification refers also to the use of propyl, butyl and amyl alcohols. In example (1) a mixture of formalin (pH-8.9), melamine, and urea in m.w. ratio 13.2/3/1 dissolved in methylated spirits was reacted at reflux temperatures until the syrup formed had a water tolerance of 6:1. After cooling to 50 DEG C. water and alcohol were distilled off under reduced pressure to reduce the water content to 27.5 per cent. of the syrup. Further alcohol was then added to make the resin/alcohol (free and combined)/water ratio 45/27.5/27.5. The syrup had a stoved solids content of 48 per cent., a viscosity of 40.3 cs. at 25 DEG C. and a shelf life of four months. Specification 683,630 is referred to.