Preparation of urea-formaldehyde condensates, and the use thereof

摘要

The invention relates to a process for the preparation of water-dilutable, low-formaldehyde urea-formaldehyde condensates which have a low viscosity and a long shelf life by condensing urea and formaldehyde in a molar ratio of from 1:2.0 to 2.25 in the presence of alkali metal sulphite at a pH of from 9.0 to 10.5 and a temperature of from 80 DEG C to the reflux temperature, and subsequently continuing the condensation at a pH of from 4.0 to 6.0 and at from 70 to 95 DEG C, where from 0.01 to 0.03 mol of alkali metal sulphite are employed per mol of formaldehyde, the condensation at pH 4.0 to 6.0 is carried out with addition of from 0 to 0.2 mol of a water-soluble alkanol per mol of formaldehyde until infinite water-dilutability is just achieved, urea is subsequently added until the overall urea:formaldehyde molar ratio is from 1:1.60 to 1.95, and then from 0.01 to 0.04 mol of glyoxal are added per mol of formaldehyde, and to the use of the urea-formaldehyde condensates as binders for fibre nonwovens made from organic and/or mineral fibres.