Process for the production of foamed plastics with improved combustion characteristics

Claim 1

In a process for the production of foamed plastics with improved combustion characteristics by a condensation reaction of aminoplast precondensates with organic isocyanates which are at least bifunctional in the presence of an acid curing catalyst and an accelerator for polyurethane formation selected from the group consisting of tertiary amines and tin salts containing metal organic bonds, whereby an aqueous solution of a water soluble precondensate of formaldehyde and an aminoplast forming compound selected from the group consisting of urea and melamine, the solution having a water content of 13 to 40% by weight, is added to the organic isocyanate which is already mixed with the accelerator for polyurethane formation, being used in an amount of 0.5 to 5% by weight relative to the foamable mixture and at the same time as the aqueous solution of the aminoplast precondensate but separately from it the acid curing catalyst is added, which is also used in an amount of 0.5 to 5% by weight, relative to the foamable mixture, whereby the ratio of water to organic isocyanate prior to the start of the reaction is 0.14 to 1.5 parts by weight of water to 1 part by weight of organic isocyanate the improvement wherein the water soluble aminoplast precondensate employed is a precondensate of this type in the form of an aqueous solution which has been obtained by reacting formaldehyde with the aminoplast-forming compound in a molar ratio of 1.80 to 4.5:1 at elevated temperature, the maximum temperature being the boiling point, and at pH values of 4 to 9.5, subsequently cooling the reaction mixture, adjusting the pH value to 7.0 to 8.0 and dissolving urea in an amount such that the molar ratio of formaldehyde to the total amount of aminoplast forming compound present in the solution is 1.0-2.1:1.