| 摘要 |
A method of obtaining a urea-phenol-formaldehyde binding agent for mould materials whereby urea and formaldehyde taken at a mole ratio of 1:(1.9-2.1) are heated at a pH of 6.5-8.0 up to a temperature of 80-100` C and kept at that temperature for 20-40 minutes, then an acidic catalyst is introduced until the pH value of 4.2-4.7 is reached, after which, following a pause of 15-30 minutes, the pH value is raised to 6.5-8.0 and phenol and formaldehyde are introduced until the mole ratio of (0.25-0.4):1:(2.5-2.7) between phenol, urea and formaldehyde, respectively, is reached and then, after a pause of 40-60 minutes at a temperature of 85-90` C and at a pH of 7.5-9.0 the reaction mass is vacuum dried up to the index of refraction of 1.468-1.472, urea is added until the mole ratio of (0.2-0.3):1:(1.8-2.2) between phenol, urea and formaldehyde, respectively, is reached and, finally after being kept for 20-40 minutes at a temperature of 55-65` C the reaction mass is cooled.
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