Recently large changes in newsprint are observed. That is, the changes are promotion of lightweight, accelerated increase of web offset printing, increase of multi-colored printing and increase of the rate of using of recycled paper.
The feature of web offset printing in newsprint is to use cold set type ink. Accordingly the drying after printing is done by absorption in newsprint without oven.
One of important property of the newsprint is fast ink setting. Also higher picking resistance is required for good print quality at high speed printing of newsprint.
For this purpose coated newsprints by starch and polyvinylalchol are generally used today.
High brightness newsprint and pigment coated newsprint are mainly used in sports newspaper. They have clear print qualities.
The rate of ultra lightweight newsprint is about 81.8% today. The rate of web offset printing in newsprint is over 86% today.
In recent Japanese public patents many applications of improvement for newsprint is observed. There are the improvement by the change of pulp composition, the improvement by surface sizing agents, the improvement by starch, PVA and latex, the improvement by pigment coating with latex, the improvement by calendering condition and so on.
In Japan there are many different newsprints in paper weight, brightness, opacity, absorption degrees of oil, picking resistance, ink receptivity and ink set.
Today in Japanese coated newsprints by gate roll coater with starch are increasing. This trend will continue in future.
Our test results of coated newsprint by starch, starch/latex blend and plastic pigment showed possibility of improvement (brightness, picking resistance, especially wet pick resistance, and ink receptivity).