| 摘要 |
PURPOSE:To produce a filler for paper, which can give paper improved in whiteness, opacity, opacity after printing, etc., by grinding an aqueous slurry containing a solid crosslinked urea/formaldehyde resin prepared by a specified process with an ultrasonic dispersion type polymer. CONSTITUTION:A solid crosslinked urea/formaldehyde resin is produced by agitating a mixture mainly consisting of a precondensate obtained by reacting urea with formaldehyde at a molar ratio of formaldehyde to urea of 1:1.9-1:2.4 in a neutral to weakly alkaline aqueous medium, carboxymethyl-cellulose or its salt, water in amount 5-15 times the weight of the precondensate and an acidic catalyst so that the entire may be uniform, keeping agitation stopped for at least 5min and thereafter reacting this mixture at 35-65 deg.C. The obtained resin-containing aqueous slurry is ground with an ultrasonic dispersion type grinder to produce a filler for paper. By performing paper-making by adding this filler to a pulp material, it is possible to give paper improved in optical properties such as whiteness, opacity and opacity after printing. |
