The Alkaline Paper Advocate

Volume 10, Number 4


Mechanical Grades of Paper

"The main trends in production of mechanical grades of paper are: increased filler contents, higher brightness, lower basis weight, increased content of recycled pulp and the introduction of calcium carbonate as a filler with the necessary move to neutral pH conditions." --from "Controlling Filler Retention in Mechanical Grades," by T. Tomney et al., presented at the 83rd Annual Meeting, Technical Section, CPPA, 1997.


Donald Meadows, editor of the Tappi Journal, devoted his column in the July 1998 issue to the mergers taking place in the paper industry. He quotes a consultant to the pulp and paper industry, who says he believes the industry "will consolidate to some very large players and some very tiny niche players. The existing middle-sized companies, especially those not fully integrated to end users, will be absorbed or driven out of the business.... [Small companies] will survive because they exist to service a specialized customer base that they know very well and have had very long-term relationships with."

Increased Machine Speeds

The pressure felt by paper companies to get more production out of their machines is described in "The Role of Paper Chemicals in Increasing Machine Speeds," by Glen Swistra et al. in the July 1998 Tappi Journal. Most of it has to do with return on investment, since the paper industry is so capital-intensive. In the old days (five or ten years ago) the way to increase production during good times would have been to add a machine; today they lower basis weight, improve paper grades, minimize deposits by eliminating internal sizing agents and applying size instead at the size press--and speed up the paper machine. Hercules has introduced new AKD-based sizing products designed to improve machine speed in many alkaline board grades, with the addition of other additives.

Some twin-wire paper machines can run over a mile a minute.

Conversions to Alkaline Will Continue

Ken Patrick, in "New Papermaking Technologies Pave Way to Higher Quality and Efficiency" (Pulp & Paper, April 1998, p. 91-92), says that almost all fine paper machines in Europe now operate alkaline and some 80%+ have also converted from acid to alkaline in the US. and Canada.

Union Camp's Eastover mill, which is about the tenth largest fine paper mill in the U.S., converted to alkaline recently. Westvaco's Luke mill still had two acid machines, last time they were contacted from this office. Champion has signed an agreement with Specialty Minerals for construction of a PCC plant at its immense Courtland mill.

New Equipment, New Methods

Ken Patrick also says, in his Pulp & Paper article, "Today, more than 85% of North America's printing and writing paper is made on twin-wire machines, and gap formers are claiming an increasing share of that capacity."

He sees a possibility of layered or stratified headboxes being used in fine paper production soon, so that recycled paper could be put in an inner layer and premium fibers used on the outside. There are many other ways in which many-layered paper is being developed and used, including the use of the size press instead of internal sizing agents.

Growing Use of the Size Press

Surface sizing used to be mainly with starch; now synthetic surface sizes are taking its place. Most used is SMA, styrene maleic anhydride (64%). Others, in decreasing order of popularity, are styrene acrylic emulsions (SAE), ethylene acrylic acid (EAA), styrene acrylonitrile acrylics (SAA), polyacrylamides (PAM) and polyurethane resins (PUR). They are used to help the papermaker meet more demanding print requirements (e.g., for colored ink jet images), and to decrease production problems associated with use of recycled fiber, internal size and increased filler loading. These synthetic surface sizes do more than hydrophobize the paper surface; they modify sheet characteristics like surface strength, to make the paper run better on specific machines.

Since filler loading is growing, and finer grinds of CaCO3 are being used, internal sizes have much more surface to cover. They have to be added in increasing amounts, and complemented with surface size.

Coating Pigments and Fillers

Although calcium carbonate was used as a filler long before onsite PCC plants were built, it has not been used for coating until recently. Ken Patrick (Pulp & Paper, April 1998) says that some lightweight coated mills began using carbonate in their coating formulations in the early 1990s.

High filler levels attract attention in the paper industry press, and will probably grow over the years as the world's fiber supply dwindles. An article by J. Weidenmuller in Internationale Papwirtschaft no. 6, 1997, is entitled "Does 'Inorganic Paper' have a Future? The Spotlight." The abstract (PBA #3542, 1998) says, "A figure of almost 50% inorganic material in the dry mass of paper has now been reached."

New Tests for Permanence Will Be Necessary

Non-homogeneous and multilayer papers will be hard to test for pH and calcium carbonate content, either from a slurry or with a surface electrode, if the purpose is to test conformity to a permanence standard. The hot and cold extraction tests will give an average pH for the paper--but what if there is an acid layer of paper on the inside? This is not unusual. (Victor Laties, in his paper in the last issue of APA, quotes a publisher as saying, around 1981, that they were using "neutral paper," which was really acidic paper with an alkaline coating. In fact, most base stock is still acid.)

There will be a greater reliance on oven aging to compensate for the growing unreliability of pH tests and alkaline filler measurements. Aging ovens cost thousands of dollars, so there can never be one in every home or office, but perhaps they can be installed as a central facility and rented to companies, organizations and individuals that have paper to test. Dr. Chandru Shahani, Preservation Research Officer at the Library of Congress, is developing an economical rapid aging method that can be used by more people.

Future Trends Seen in Recent Research

Chemical and Engineering News for March 25, 1998, ran an article on p. 39-42, 44-47, "New Age Paper and Textiles," by Mairin B. Brennan. (The first four pages are on paper, the rest on textiles, mainly on economic processing of flax fiber; accelerated biodegradation; and permanent-press processing without formaldehyde.) The editor's subtitle/introduction reads, "Fungi, enzymes, and closed-loop catalysis offer environmental, economic gains in manufacturing and recycling."

In the section on paper, the author interviews researchers at the Forest Products Lab, University of Georgia and other research centers, and covers three of the topics previously reported in the Alkaline Paper Advocate: Biopulping, bleaching with enzymes and delignification with polyoxometalate. These developments are covered in the author's easy-to-read style, with a gratifying amount of detail to fill in the big picture which is often hard to put together from news reports. All three developments are just coming into use now, and promise benefits to fiber permanence as well as to papermaking and the environment.

An announcement of a different kind of research was published in the May issue of Tappi Journal on p. 49. A biochemist at Purdue University has identified genes that affect the production of lignin. They cause plants to make only easy-to-degrade syringyl lignin. This should make it possible to get more pulp out of a tree, and to minimize damage to cellulose fibers during the pulping process. The biochemist, Clint Chapple, was in the process of patenting the gene when this notice was published.

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