Volume 26, Number 5
Jul 2003

Acid-Tolerant PCC: Changing the Way Paper is Made

Reprinted from the 2002 Annual Report of Minerals Technologies Inc.

The problem: In conventional groundwood papermaking, calcium carbonate filler can cause pulp to yellow or darken. The solution: An innovative product, conceived and patented more than a decade ago, that overcomes the usual limitations of papermaking.

As much as any current MTI product line, AT® PCC (acid-tolerant precipitated calcium carbonate), the patented acid-tolerant technology, embodies the company's response to meet the needs of the marketplace, as well as the shift from straightforward product marketing to a more synergistic involvement in the end-user's lines of business.

AT®PCC permits the use of alkaline PCC in the acid environment of groundwood-papermaking. "Groundwood papers are 45 percent lignin, and lignin is very pH-sensitive," said Bruce Evans, Technical Manager of Groundwood Research. "Typically those mills are running at pH5. When you add ordinary calcium carbonate, that level rises to 7.5 or 8.5. The higher the pH rises, the darker the lignin gets. However, MTI's AT®PCC is designed to minimize 'alkaline darkening,' thereby providing the full benefits of greater brightness and opacity over kaolin or other calcium carbonate."

Because PCC can replace expensive bleached wood fiber and pigments, AT®PCC technology delivers to groundwood mills cost efficiencies long available to free-sheet manufacturers. "While the papermaker is always interested in quality, the real driver in changing technology is cost savings," said Kenneth L. Massimine, Senior Vice President and Managing Director, Paper PCC. "The beauty is that AT®PCC accomplishes both goals."

For the Company, the potential payoff is equally clear. Groundwood, used chiefly in magazines and catalogs, accounts for 40 to 50 percent of all paper produced.

Work on AT®PCC began with a special research unit in 1989, and trials began a year later. The Company's penetration of the groundwood sector has increased dramatically since 1997, when Myllykoski Paper of Finland and Madison Paper Industries of Maine became the first producers of uncoated groundwood with fully dedicated AT®PCC satellite plants on-site. Today about 20 groundwood mills use MTI's PCC. Feedback from end-users has been excellent. At Myllykoski Paper, the initial customer was furniture maker IKEA, one of the world's largest distributors of catalogs. "Appearance is very important to them," said Ari-Pekka Laakso, Technical Manager, Specialty Minerals. "They now feel that their catalogs have a better look, a better 'touch.'"

If the amount of savings is linked to the amount of filler, a clear opportunity exists for anyone who can increase the amount of filler without causing incidental quality-related problems. That objective has spawned a second-generation groundwood product called VELACARB™ PCC. "Normally," said Massimine, "as you increase the filler content, you weaken the sheet. With VELACARB™ PCC the sheet does not weaken. Thus you increase the cost savings without sacrificing quality."

The VELACARB™ PCC project symbolizes the distinct advantage of working with synthesized materials over ground calcium carbonate. "If you're grinding, there is only so much you can accomplish. With PCC, which has uniform crystal morphologies, or shapes that impart distinct characteristics to a sheet of paper, you can leverage the desired end result," said Massimine.

The next frontier is the vast European market for supercalendered (SC) rotogravure and offset papers. "This is the biggest groundwood market in the world," said Evans. "There's probably an opportunity of close to a million tons of filler." Today, the SC rotogravure market almost universally uses water-washed clay as a filler. Evans feels that eventually, there will be pressure on the market to improve the brightness and opacity of this paper. "When it happens," he said, "we will be positioned to take advantage of it."

Note This new development in the manufacture of higher quality groundwood paper may affect the methods used to assess permanence of paper in libraries around the world. Apart from accelerated aging, there may be no way to assess the correlation between brightness/opacity and retention of physical properties over time.
The address of Minerals Technologies, Inc., is The Chrysler Building, 405 Lexington Ave., New York, NY 10174-1901, and the Website is www.mineralstech.comi.