Volume 2, Number 1
Apr 1989

Alkaline Paper-Making Conversion Rate Accelerates

The rate at which paper mills are converting from acid to alkaline papermaking has accelerated in recent years. At the begriming of 1988, about four million tons per year of coated and uncoated printing and writing paper were made at an alkaline pH in North America. This is about 25% of all fine (groundwood-free) paper produced in the continent. By the end of 1988 alkaline fine paper was made at a rate in excess of 4.6 million tons per year, and an additional 900,000 tons per year will be added in the first half of 1989, with much more to follow. Why the sudden interest in alkaline papermaking, which had been growing at a leisurely pace since neutral or alkaline papermaking was first adopted by U.S. papermakers before 1970?

Quality is highly important in the very competitive fine paper segment of the paper industry. Its leaders have found in recent decades that by replacing the traditional kaolin clay, titanium dioxide and calcined clay with precipitated calcium carbonate (PCC) they are able to improve the brightness, opacity and printability of their product, and significantly improve its quality. Heightened quality consciousness has combined in recent years with improved alkaline papermaking technology and low-cost PCC from satellite plants to speed the rate of alkaline conversions.

PCC has long been recognized as a low-abrasive, high-brightness pigment, but in the past, before its on-site manufacture was widely practiced, its high cost relative to ground carbonate and kaolin clay limited its use, and in any event there was insufficient manufacturing capacity to support widespread alkaline conversions by the paper industry. Satellite PCC plants have positively impacted both of these concerns and helped to improve product quality as well. When PCC is manufactured at an off-site plant it is usually dewatered by the merchant plant before it is shipped to the paper mills, and the combined cost of dewatering and transporting is typically 45%, of its delivered cost. By building a satellite PCC plant on site and using local lime and carbon dioxide, which mills normally discharge to the atmosphere, this cost is eliminated. Further economies are often made possible by sharing other elements in the manufacturing process (such as process water and waste treatment) with the host mill.

All calcium carbonates impart permanence and brightness to paper. Beyond that, the quality improvements imparted to the paper are specific to the type of PCC chosen. All precipitated calcium carbonate is not alike. It can be precipitates in three distinct crystalline forms and with a wide range of particle size and particle size distribution. All of these factors affect paper quality in various ways. Although PCC generally has more opacifying power than ground calcium carbonate, some grades of PCC have been significantly improved in this respect. Another feature that is not widely recognized, except among those papermakers who have used it, is that if you replace clay or titanium dioxide with an equal amount of some grades of PCC, the bulk of the paper will increase. This allows the papermaker to improve sheet smoothness for better printability, or to make a sheet with similar physical and optical properties but with a lower basis weight--an obvious advantage for anything to be mailed. Since any kind of PCC can be made as needed in the satellite plant, this gives the paper mill m unusual amount of flexibility in its operations.

Pfizer Inc. first started making PCC over 50 years ago and is now the largest manufacturer of PCC in the world. The first Pfizer-owned and operated on-site plant was constructed in Wisconsin Rapids, Wisconsin, in 1985, followed by on-site plants at Ticonderoga, New York (1986); Erie, Pennsylvania (1988); Cloquet, Minnesota (1988); Chillicothe, Ohio (1988); Lock Haven, Pennsylvania (1989); and Longview, Washington (1989). Pfizer currently has contracts for two additional plants. Weyerhaeuser's new paper machine in Prime Albert, Saskatchewan (1988), the only alkaline mill in Canada, uses PCC produced on site. Canadian Pacific Forest Products is scheduled to convert its Dryden, Ontario, mill in May with a Pfizer PCC satellite. Paper companies like these, which have encouraged their suppliers to invest capital in PCC plant construction and operation, have obviously made a major long-term commitment to alkaline papermaking, and can be expected to continue making alkaline paper indefinitely.

The transition from acid to alkaline papermaking must be carefully considered by paper manufacturers. Although capital requirements are minimal, operating changes are numerous. Because of today's high dm" for fine papers, any losses in production during the transition will be felt and must be minimized. Fortunately, alkaline papermaking technology has made significant advances as the practice has heroine more widespread. The time it takes to climb the "learning curve" of alkaline papermaking appears to shorten with each successful conversion, to the point where some talented papermakers now report on-budget production from Day One of conversion.

The consumer's search for archival quality paper is now being aided by the papermaker's never -ending desire to improve the quality of their product. It is a fortunate coincidence that the same process which allows the paper industry to make better quality paper also provides an alkaline reserve that will assure preservation of printed and written records far into the future. We can expect the alkaline process to be adopted at an increasing rate as a result of developments like satellite PCC plants and the increasing sophistication of papermakers and their suppliers in alkaline papermaking technology.