Papermaking

Mills in Europe and North America have progressively converted to advanced paper machine and paper chemistry technologies in recent years

New Papermaking Technologies Pave Way to Higher Quality

BY KEN L. PATRICK, Senior Editorial Consultant

Continuing globalization of the pulp and paper industry has created new arenas for advanced technology applications in recent years, in both chemical pulping and papermaking. But while pulping developments have been driven extensively by environmental forces during the past couple of decades, papermaking has advanced to the beat of a different drum.

Primarily, the relentless push for higher efficiency and quality has driven new developments in papermaking technology, more so during the past quarter century than any other period in the industry’ history. This push has resulted in higher speeds, wider machines, and dramatic advances in former technologies, as well as new developments in wet-end chemistry, pressing, drying, and paper machine control strategies.

A two-part special series on advanced papermaking technologies in the May and June 1998 issues of Pulp & Paper will explore some of these new technologies and the driving forces that will continue to accelerate their implementation well into the next century. It will focus on printing and writing papers, but will also examine developments in the coated board sector.

In particular, the series will look at trends in Europe and North America, in terms of how and why papermaking in these two regions of the world seems to have evolved along somewhat different lines, and what can be expected in the near future. The impact of recent expansions in Asia and South America will also be analyzed, as producers in these areas respond to rising domestic demand and begin to literally elbow their way into established world marketplaces.

WET-END DEVELOPMENTS. The wet end of the paper machine, including the headbox and former/forming zone as well as papermaking chemistry in general, has received a lion’ share of attention since the mid-1970s.

With the full commercial application of gap formers beginning in the early 1970s, the science of papermaking changed dramatically and permanently. Today, more than 85% of North America’ printing and writing paper is made on twin-wire machines, and gap formers are claiming an increasing share of that capacity.

With twin-wire machines, mills have been able to approach speeds of 6,000 fpm on printing and writing grades, and could break that barrier in a few years. The progressive closing of open draws and increasing use of metering or film size presses will continue to play an important role in that regard.

The number of traditional fourdrinier paper machines has declined rapidly in recent years. But while some industry observers do foresee a continuation of this mainstay design into the next century, others believe the last fourdrinier printing and writing papers machine might have already been built.

Layered or stratified headboxes have allowed highly efficient ply-building on tissue and some board grades, and could find their way into fine paper production in the not too distant future. These units would permit better “” of the sheet, where recycled and premium fibers, as well as minerals and other agents, are placed in specific layers of the web. Available fiber furnishes are maximized in a well-engineered sheet and quality characteristics are more effectively controlled.

The special May and June series tracks the evolution of wet-end design and explores where the technology currently is and what is on the drawing boards for implementation during the next decade. The application of some of these newer technologies at mills in Europe and North America is examined and compared.

The conversion to alkaline papermaking that began in Europe more than 20 years ago spread rapidly through North America during the 1980s and 1990s. Almost all fine paper machines in Europe now operate alkaline and some 80%+ have also converted from acid to alkaline in the U.S. and Canada.

In general, recent advances in alkaline papermaking have been fueled by developments in the calcium carbonate and synthetic sizing areas. The prime wet-end filler ingredient in alkaline systems, calcium carbonate has undergone a virtual renaissance in processing technologies, and today is a highly cost effective chemistry for improving brightness, opacity, bulk, and general printing quality of fine papers. Recent developments in calcium carbonate technologies, especially ultrafine-ground grades, are examined in detail in the two-part series.

As furnish streams have changed considerably in recent years, the need for improved retention and drainage technologies has increased. With higher filler contents and more recycled fiber in almost all printing and writing grades, keeping these minerals and “ trash” moving through the sheet has become essential. This report details some of the latest developments and mill applications in the wet-end retention and drainage chemistry area.

Forming fabrics have also played a key role in new paper machine developments during the past quarter century, especially in regard to multi-wire/gap former applications. As machines continue to run even faster in the future, demands on these critical fabrics will necessitate further design evolutions and application modifications, which are analyzed in the report. Recent developments in starch and specialized/ engineered premium pigments such as calcined clay are also examined.

PRESSING/DRYING TECHNOLOGIES. Press section developments in recent years have been concentrated mainly on extending the time that the sheet is resident in the press nip. These wide-nip or shoe technologies have taken several routes, and most recently have been applied to fine paper production as well as board machines.

The advanced papermaking report takes a close-up look at mill experiences with these types of presses in the white papers sector, and examines recent and planned evolutions in design and operation of these units. The continuing development of press felts for these units is also analyzed in regard to increased operating life and reduced sheet marking problems with fine papers.

Under development for almost two decades, impulse or impact drying still holds some promise for application on today’ and especially tomorrow’ faster fine paper machines. The report will update the status of this technology, and will look at the current usage of single-tier dryer runs in both Europe and North America.

COATING TRENDS. Multiple coating of board and paper grades has been practiced in Europe for many years, beginning in the 1970s and earlier. The trend slowly caught on in North America during the past decade, particularly on board grades, but also in some fine paper areas.

Multiple coating allows further engineering of the sheet, with selected placement of pigments in two or more coating layers. Using coarser, heavier pigments and other coating ingredients in the inside and middle coating layers to maximize opacity, stiffness, etc, allows finer, more expensive materials to be used in the outside layer for maximum gloss, smoothness, brightness, etc.-in a highly cost effective manner.

Pigmented size pressing with high speed film press units is proving to be very effective as a pre-coat or even a first coating stage. In fact, these units are more or less the center piece in the development of newer printing and writing grades such as film-coated offset (FCO).

Some industry experts see FCO, which employs on-line soft-nip calendering and pigmented film presses to produce a “ quality” groundwood specialty grade, possibly replacing supercalendered (SC) grades in the near future. Some of the top-of-the-line SC grades, such as SC-A and SCA-plus, use pigmentation in the size press, but employ off-line supercalendering.

Although the use of clay as a paper filler has declined dramatically in recent years as more precipitated and ground carbonates have been used in the wet end, kaolin clay still holds the major share in world coating formulations. But carbonate has gained significant ground on kaolin clay. Offering higher brightness and improved runnability, as well as significant cost benefits, carbonate’ share of the world coating pigment market has now increased to 30%+ and is expected to pass the half-way mark in just a few years. Beginning in the early 1990s, some lightweight coated mills also began using carbonate in their coating formulations, allowing the wet ends of these machines to “” toward neutral or even slightly alkaline conditions. This trend with LWC and other groundwood grades is explored in the special report.

KEN L. PATRICK, senior editorial consultant for Pulp & Paper, is president of Paper Industry Communications, Inc., Atlanta, GA.

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