High Opacity Fillers: A New PCC Morphology and its Properties in Wood Free and Wood Containing Paper, 1991 Papermakers Conference Proceedings

To achieve high brightness and opacity with precipitated calcium carbonate, PCC, alkaline papermakers have been using a scalenohedral calcite. However, the papermaking objectives in wood containing and wood free papermaking are for even higher brightness and opaque sheets. This has led to the development of a new cost effective, high opacifying, high brightness PCC which competitive with current high opacity fillers such as calcined clay and titanium dioxide. As such, this product represents a new generation of PCC filler pigments.

The new precipitated calcium carbonate has a unique morphology which when utilized as a filler imparts high opacity to the sheet. At the 8% filler level the new PCC produces a pigment scattering coefficient mid way between titanium dioxide and the most effective scalenohedral PCC. The particle size and distribution of the new PCC morphology is similar to titanium dioxide. The new PCC, made at commercial scale, has been evaluated in the laboratory for both wood free and groundwood applications.

The results indicate that the new high opacity PCC exhibits scattering coefficients 500 cm2/g greater than the most efficient scalenohedral PCC. Sheets filled with this product display up to 1.5 points higher opacity than sheets utilizing a 1.2 micron scalenohedral PCC. The new PCC also produces a much more closed sheet than scalenohedral PCC. For groundwood applications, a dramatic improvement in brightness can be achieved over calcined clay at alkaline pH.