Method for preparing high mole ratio and low free formaldehyde concentration

A process for preparing the urea-formaldehyde resin with high mole ration and low content of free formaldehyde includes such steps as proportionally providing urea and formaldehyde, proportionally adding modifier chosen from ammonia, ammonium dicarbonate and ammonium carbonate to formaldehyde solution, and adding urea to it step by step. 一种高摩尔比低游离甲醛含量的脲醛树脂的制备方法，其特征是按尿素与甲醛摩尔比1∶1.4～2.2备料；先将甲醛溶液加入反应釜中，在常温条件下向甲醛中加入作为改性剂的氨或碳酸氢铵或碳酸铵，改性剂氨或碳酸氢铵与甲醛的摩尔比为0.02～0.4∶1，改性剂碳酸铵与甲醛的摩尔比为0.01～0.2∶1，制得改性甲醛；然后按常规生产方法将上述所备尿素分次加入所说的的改性甲醛中，制得低游离甲醛含量的脲醛树脂。