A Little on Fillers
In the mid-1980s the United States paper industry began converting mill operations to support alkaline papermaking processes, although the possibility to convert had been around for a quarter of a decade before that. Prior to the 1980s the US paper industry didn’t have enough incentive to make the conversion. The 80s brought an increase in the production of precipitated calcium carbonate as paper filler, which coincided with the rise in cost of the fiber supply (up 100% from 1985 to 1989) and a tightened supply of the preferred filler of the time, titanium dioxide.
Besides higher costs from suppliers, the paper industry was facing a change in demand from customers who now wanted a brighter and more opaque paper. Mills realized that in order to compete with these new cost restraints they would have to sacrifice the quality they could achieve with acid paper making but also save in cost when replacing fiber in their paper with fillers, primarily ground calcium carbonate. The conversion rate was substantial. Only 50 mills were operating using alkaline processes in 1989. In 1990, 50% of North American paper output was a result of alkaline processes. Papers produced in acidic conditions have a lifespan of around 50 years while alkaline produced papers can last for over a century.
Calcium carbonate has many advantages as a filler material. It produces brighter and more opaque results than other fillers. It also improves on printability. Printing and writing grades can be upwards to 30% fillers, providing substantial savings in fiber content. Calcium carbonate is restricted to use in alkaline paper processes because it dissolves in acid. The widely used forms are precipitated calcium carbonate (PCC) and ground calcium carbonate (GCC). PCC results in greater opacity (related to its light scattering capacity) than GCC. On the negative side, PCC use results in a decrease in strength of the sheet. GCC increases reel speed due to better drainage than PCC. Combinations of the two can be used to achieve desired results. Several other industrial pigments are available for use as filler material including titanium dioxide, kaolin and clay.
Synovec, M. (1991): “Alkaline conversions in North America gain momentum as mills take advantage of high-quality, lower-cost paper making.” TAPPI J. April, 95-99.
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