A method for increasing filler retention of cellulosic fiber sheets is disclosed. In the method, cellulosic fibers with increased anionic sites are treated with either positively charged filler particles and/or amphoteric filler particles or a cationic retention aid and negatively charged filler particles...http://www.google.ca/patents/US6514384?utm_source=gb-gplus-sharePatent US6514384 - Method for increasing filler retention of cellulosic fiber sheets
