Лако-красочные материалы — производство

An introduction to the typical resin synthesis of a UF resin used as an adhesive for wood products and in industrial applications is given below. It constitutes a handy formulation for those who want to work in this field. It is not a low-formaldehyde-emission formula­tion. To 1000 parts by mass of 42% formaldehyde solution (methanol <1%) are added 22% NaOH solution to pH 8.3 to 8.5, 497 parts by mass of 99% urea, and the temperature raised in ± 50 min from ambient to 90°C while maintaining pH in the range 7.3 to 7.6 by small additions of 22% NaOH. The temperature is maintained at 90 to 91 °C until the turbidity point is reached (generally another 15 to 20 min). The pH is then corrected to 4.8 to 5.1 by addition of 30% formic acid, and the temperature is raised to 98°C. The water tolerance point is reached in ± 18 min and the pH is then adjusted to 8.7. Vacuum dis­tillation of the reaction water with concomitant cooling is then initiated. After distillation of the wanted amount of water to reach a resin content of 60 to 65%, the resin is cooled to 40°C, 169 parts by mass of second urea is added, the pH is adjusted to 8.5 to 8.7, and the resin is allowed to mature at 30°C for 24 to 48 h; resin characteristics: solids content, 60%; density, 1.268 g/cm3; free HCHO, 0.4%; viscosity, 200cP; pH, 8.