A novel filler treatment comprising the preparation of swollen
starch-latex compositions, prepared in the presence or absence of co-additives, and the addition of the said composition to a filler suspension, has been developed. Use of the treated filler during
papermaking improves filler retention and produces filled papers where addition of the filler has only a minimal negative effect on strength properties. The swollen
starch-latex compositions can be prepared in a batch or jet
cooker, or by mixing with hot water under controlled conditions (i.e., temperature, pH, mixing, mixing time) in order to make the
starch granules swell sufficiently to improve their properties as a filler additive but avoiding excess swelling leading to their rupture. The swollen starch-latex composition is then rapidly mixed with the filler
slurry, preferably in a
static mixer, and added to the
papermaking furnish at a point prior to the headbox of the
paper machine. The starch-latex composition can be used with wood-free or wood-containing furnishes. The treated filler is easily retained in the web during
papermaking, improves drainage, and gives sheets having good formation. Sheets made with the treated fillers have higher bonding and tensile strengths than sheets produced using filler treated with either swollen starch alone or latex alone. Retention and drainage are further improved when conventional retention aid chemicals are added to the furnish containing the treated filler. The use of swollen starch-latex compositions could allow the papermaker to increase the filler content of the paper without sacrificing dry strength properties or increasing the amount, and hence the cost, of the retention aid added. The combination of swollen starch and latex could be used as furnish additives in the manufacture of both filled grades and grades that contain no filler such as sack papers and
paperboard products.