Process for the preparation of a modified amino-formaldehyde resin; modified amino-formaldehyde resin thus obtainable and use thereof

The invention relates to a process for the preparation of a modified amino-formaldehyde resin, comprising: a) a mixing step, in which a liquid phase, an amino-formaldehyde resin and free formaldehyde are brought together to form a mixture, -whereby the amino- formaldehyde resin has a molar formaldehyde to (NH2)2 ratio (F/(NH2)2 ratio) lying between 0.5 and 3 and has a weight average molecular weight lying between 500 and 50,000, and whereby the overall molar F/(NH2)2 ratio in the mixture is higher than the molar F/(NH2)2 ratio of the amino-formaldehyde resin and lies between 2 and 6; b) an F-binding step, in which the mixture is brought to conditions whereby at least part of the free formaldehyde reacts with the amino-formaldehyde resin to form a_ formaldehyde-enriched amino-formaldehyde resin, such that the F/(NH2)2 ratio of the formaldehyde-enriched amino-formaldehyde resin is at least 1 higher than that of the amino-formaldehyde resin; c) an alkylation step, in which an alcohol and an acid having a pKa lower than 6 are added to the mixture, the mixture then being brought to conditions whereby at least part of the alcohol reacts with the formaldehyde-enriched amino-formaldehyde resin to form the modified amino-formaldehyde resin, whereby steps a) and b) may be executed either consecutively or simultaneously, The invention further relates to a modified amino-formaldehyde resin, obtainable by the said process, as well as to use of the said resin, in particular in coating compositions.