| 摘要 |
FIELD: polymer production. ^ SUBSTANCE: object of invention is to obtain urea-formaldehyde foamed plastics with low formaldehyde emission and improved physicochemical properties. Essence if invention resides in that raw material, formalin or urea-formaldehyde concentrate, is neutralized with aqueous ammonia solution and urea-formaldehyde condensation is carried out at ratio 1:(1.9-2.2) in medium with variable acidity at heating until required water number (solubility in distilled water) is attained. Reaction mixture is then neutralized to pH 7.0-8.5 using aqueous solutions of alkali metal silicates or water-alcohol solutions of sodium alkylsiliconate and cooled to 65-75. Thereafter, plasticizing modifier and more urea are added and post-condensation at 65-70 is performed followed by cooling to temperature no higher than 35, said plasticizing modifier being dispersions of polymers (thermoplastics, elastomers), which may contain polyacrylamide as thickener. ^ EFFECT: increased hardening velocity, reduced water absorption of foamed plastic, and retained low formaldehyde emission. ^ 2 cl, 1 tbl, 4 ex |
