PROCESS FOR PREPARATION OF AMINOPLAST SOLUTIONS

摘要

The present invention relates to processes for discontinuously or continuously preparing aminoplast solutions by condensation of aminoplast formers with formaldehyde in a serial cascade of at least three stirred tank apparatus A, B, and C, which involves a) in apparatus A, reacting a mixture comprising formaldehyde and urea in a molar ratio of 2.3:1 to 2.9:1 and water at a pH of 6 to 8, set by means of a base, at a temperature of 80 to 85°C, where apparatus A consists of one or more, i.e., one to ten, preferably one to five, more preferably one to three, more particularly one or two stirred tanks in parallel or in series, very preferably of one stirred tank, b) in apparatus B, reacting said mixture at a molar ratio of formaldehyde to urea of 1.9:1 to 2.6:1, where apparatus B consists of one or more stirred tanks, wherein the molar ratio of formaldehyde to urea is lowered, optionally by further addition of urea, in stages to not less than 1.9:1, at a pH of 3.5 to 5.5, which is kept virtually constant, at a temperature of 100 to 105°C, and with a mean residence time of 10 to 90 minutes in the entire apparatus B, c) in apparatus C, at a temperature of 90 to 100°C, raising the pH to at least 5.9 and lowering the molar ratio of formaldehyde to urea to 1.7:1 to 1.4:1, where apparatus C consists of one or more stirred tanks, and d) by adding urea, at temperatures of 15 to 100°C, setting a final molar ratio of formaldehyde to urea of 0.7.1 to 1.28:1 and a pH of at least 7.