Fiber Extension
By using PCC, papermakers are able to reduce their operating costs in various ways. In mills that produce woodfree copy papers, filler-for-fiber substitution usually offers the biggest economic gain. That is, by increasing the amount of mineral filler in the sheet, less cellulose pulp fiber, a more costly component, is used. By selecting the PCC morphology that is best suited to providing the particular balance of properties that are important to the end user, paper makers can raise the amount of mineral filler in their paper without degrading the performance of the paper. The savings that are realized will depend on each manufacturer’s particular cost structure for fiber. Market pulp—pulp that is delivered to a mill from a remote location—is the most expensive. For mills that purchase market pulp, the savings from even a small increase in filler content can be substantial. Integrated paper mills have a pulp mill on site that produces the raw material for their papermaking operation. Integrated mills produce pulp at a substantially lower cost than market pulp. In these mills, the direct savings that are realized when PCC content in the sheet is increased are not as great as for mills that use market pulp. However, an integrated mill with the capacity to sell market pulp will have a financial incentive to replace fiber with filler and sell their excess fiber capacity, usually at a substantial profit.
A second way that paper mills can extend their cellulose fiber is by taking advantage of the bulking effect of certain PCC morphologies. When papermakers use large scalenohedral rosette structures, or large clusters of needle-shaped aragonite as fillers, the paper tends to be thicker (bulkier) than for other mineral fillers. Since cut-size copy paper is produced to meet specifications for both area and thickness, a filler that bulks the paper requires that less material be used in order for the thickness specification to be met. This basis weight (weight per unit area) reduction means that less raw material is being used, thereby leading to lower cost.
Bleaching & Optical Brighteners
Groundwood (or wood-containing) papers are usually produced at a lower brightness specification than fine, woodfree copy papers. When PCC is used as the filler in groundwood papers, such as supercalendered (SC) grades, paper mills usually find that less bleaching is required, because the brightness of the PCC offsets the need for bleaching. This significantly reduces cost and reduces the environmental burden as well. However, to use PCC, groundwood paper mills must almost always use the AT® PCC process. Sometimes, woodfree mills can also take advantage of PCC’s inherent brightness to reduce cost. Optical brightening agents (OBA) are often used in these papers, and woodfree paper mills often find PCC reduces the amount of OBA that is required to achieve a specified level of brightness. This can have both cost and environmental benefits.
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