Coated paper and board: grades in transition.

May is TAPPI Coating Conference month--a good time to look at market and technical trends in the coated paper and paperboard industry segments. U.S. demand for coated groundwood papers increased 7.4% in 2003. On the other hand, demand for coated free sheet was down 5.7% in 2003. The difference in performance of the two major segments was due to end users switching from coated free sheet to coated groundwood to save money. This economizing was facilitated by increased brightness of coated groundwood grades. Several producers have introduced new grades with a mixed furnish that are competing as woodfree but statistically classified as groundwood because more than 10% mechanical pulp is used in the furnish. Acceptance of these newer grades caused a swing of over 300,000 tons of end user demand from coated free sheet to coated groundwood in 2003.

Even though demand remains healthy, limited supply of high brightness coated groundwood papers may impede further grade switching in 2004. Coated groundwood mills are operating near capacity. The suspension of work on the Papiers Gaspesia SEC project at Chandler, Quebec, Canada means that coated groundwood paper supply will remain tight. The slippage of the U.S. dollar vs. the Euro--combined with improving demand in Europe--will limit imports of coated groundwood. This combination of circumstances could produce a modest recovery for coated free sheet. Most forecasters expect coated groundwood demand to grow by about 2-3% over the next two years. Coated free sheet demand is expected to grow about 4% per year for the next two years. U.S. coated free sheet mills ran at only 84% of capacity in 2003-a decline from the 89% operating rate in 2002. The strong Euro is likely to inhibit imports of coated free sheet from Europe. Imports from Asia-particularly China with its currency pegged to the dollar-are likely to increase.

INK JET & DIGITAL PRINTING PAPERS

There is continued interest in coated ink jet and coated papers for digital printing. At present, most coated ink jet papers are made with silica pigments coated at low solids off machine--which results in high price. The real market need is for quality better than synthetic surface sized uncoated free sheet but significantly lower cost than silica coated papers. For these larger volume markets, it is desirable to coat on-machine at higher solids using a metered size press. Recent advances in coating materials to be discussed later in this article may provide the key.

COATED BOARD

Coated folding carton board demand in the U.S. was depressed in 2003 but is recovering. The challenge to U.S. producers from imports of coated board is increasing. Total U.S. imports of folding cartonboard are expected to increase from about 650,000 tons in 2003 to almost 800,000 tons in 2005. China added over one million tons of new coated board capacity in 2003, and another 2.5 million tons of capacity is scheduled to come on line by 2005 from large, state-of-the-art multi-fourdrinier machines equipped for triple coating and on-machine finishing. The biggest impact on U.S. board makers is likely to be displacement of tonnage that had been exported to China. The planned increase in capacity is so large that it is likely that a significant amount of it will be targeted for export to North America and perhaps Europe. The past year has also witnessed initial imports to North America of Brazilian coated multi-ply SBS board. The Brazilian board is made from eucalyptus pulp, which does not have the bulking and strength of southern U.S. species. However, it is formed on multi-fourdrinier machines and has excellent smoothness.

Coated SUS producers have also witnessed some decline in export markets. Some Asian producers are starting to make both carrier stock and folding carton grades by triple coating heavy weight kraft liner and wet strength kraft liner.

Coated recycled multi-ply paperboard production in the North America is different than in most other world regions. With one exception, North American mills use cylinder or modified cylinder formers. The machines do not have size presses. In most cases, the coating section consists of a rod precoated and air knife top coater followed by a conventional gloss calender. In Europe, Asia and Latin America, most of the machines are multi-fourdrinier machines with size presses and double or triple blade coating plus modern calendering technology. Top liner furnish is a key difference. Most North American mills run non-deinked recycled fiber as top liner. The rest of the world runs bleached kraft pulp as top liner. North American mills run higher cost coating formulations--usually with a significant amount of titanium dioxide in the topcoat. Mills outside of North America coat over a brighter base sheet and don't need the high refractive index pigment to obscure the darker base. There is an economic tradeoff between furnish and coating costs.

The threat to North American coated multi-ply recycled board makers is not likely to be from imports but rather from advances in micro-flute corrugated. In calipers from 28 to 32 points, N-flute corrugated can be 40% lower in weight than recycled multi-ply board and yet provide higher stacking strength. Use of N-flute in this application requires a coated linerboard surface printable by offset.

IMPACT OF "BIG BOD" STORES

Retailing trends are having a dramatic effect on the corrugated container segment. Total North American consumption of corrugated containers is declining about 1% per year. A prime driver of this is Wal-Mart's requirement to switch to returnable plastic containers. However, in big box stores the package is the sales person. The high graphic quality container business is increasing 7-8% per year. There is also a trend toward lighter basis weights and the use of high performance linerboard. The amount of bleached kraft pulp needed to make white top is constant regardless of total basis weight. Bleached pulp is not as strong as unbleached kraft; as total basis weight goes down, percentage of bleached pulp in white top liner increases, sacrificing strength. These trends combine to create a need for coated linerboard that can be printed by direct print flexo without drying. Coating is more efficient than bleached pulp in covering the dark base sheet and can help to reduce strength loss.

Digital printing can be a key to reducing systems cost in short and medium length box runs. A growing number of Belcom digital presses are being installed in corrugated plants. This new printing technology is creating a need for coated linerboard designed for digital printing.

PROCESS AND EQUIPMENT TRENDS

At the past several Coating Conferences there have been papers presented and a lot of discussion of new non-impact coating methods including spray coating and curtain coating. However, commercialization has been slow. There is only one commercial installation of a spray coater and no curtain coaters for regular printing grades. There are several curtain coaters making carbonless and other specialty papers.

There is continued interest in metered size press coating--especially when combined with on-machine soft nip or supercalendering. The new higher brightness coated groundwood grades discussed above are being made using this technology. The most expensive component of LWC or ULWC is bleached kraft pulp--especially in a non-integrated mill. One of the major advantages of metered size press coating-compared to blade coating--is the ability to significantly reduce kraft pulp content. Base stock can either approach a newsprint furnish or include higher levels of filler while maintaining the internal bond strength required for offset printing.

The development of acid tolerant calcium carbonate pigments--both precipitated calcium carbonate (PCC) and ground calcium carbonate (GCC)--has been another key to making higher brightness coated groundwood papers. Problems with heatset offset printing of uncoated SC papers are likely to make this trend continue. SC papers do not have binder to hold the pigment together on the surface and they are water sensitive and prone to milking in heatset offset printing. As the SC producers have pointed out, it is practical to heatset offset print their products, but special care must be taken. The new emerging higher brightness coated groundwood grades run well on heatset offset presses using the same ink tacks and fountain solutions used for blade coated LWC.

Gravure is another matter. It hasn't proven practical to make LWC or ULWC gravure via metered size press coating. It may be practical to do so using a metered size press and on-machine supercalendering, but why do so? Supercalendered (SC) technology came from Europe--a market dominated by gravure. The premium SCA+ papers have high brightness and gloss. They run very well in gravure, where the sheet surface is not stressed as in offset.

There have been no significant advances in conventional coating methods since the development of the low angle jet blade coater.

One significant trend in U.S. coated multiply board mills is the installation of backside coaters--usually air-tube-loaded rod coaters. Backside coating solves the problem of linting and offsetting of debris in the reel, producing a cleaner and better printing coated side. Market developments are likely to make the backside coaters valuable in application of barrier coating materials.

COATING MATERIALS

Binder suppliers have responded to the trends noted above by developing new specialty latices for metered size press coating. They have also developed new specialty latices for coating linerboard to provide more open coating structure to prevent smudging in direct post print flexo.

Pigment suppliers continue development of engineering and structured kaolin clay, GCC and PCC pigments. Aragonite PCC is of particular note. It has a tightly controlled particle size distribution and can provide improved gloss in coated free sheet and coated board. When combined with acid resistant treatment, this new type of PCC could facilitate further growth in high brightness coated groundwood.

The importation of Brazilian clays is increasing. The Brazilian clays are high brightness and platy, providing easier glossing that results in less opacity loss in super-calendering.

Another trend worth noting is the use of high aspect ratio clays to plug pores in barrier coatings. This application of nano technology is still new but a great deal of progress is expected in the next several years.

[ILLUSTRATION OMITTED]

One of the most interesting recent developments is a high brightness purified natural zeolite pigment that could provide keys to several of the opportunities discussed above. This zeolite pigment has a cage-like structure that makes it absorptive. It can be dispersed at solids twice as high as silica pigments. Ink jet coatings formulated with the zeolite pigment have good rheology and can be coated via metered size press or blade. The zeolite pigment is low in abrasion. Addition of the zeolite pigment to linerboard coating formulations not only improves flexo print quality but also prevents smudging in direct post print and eliminates metal marking. This pigment could be the key to widespread commercialization of coated linerboard. The zeolite pigment can also be used as a wet end additive. It is easy to retain and reduces print-through in ULWC and uncoated groundwood grades. It is effective in reducing print-through at lower levels of addition than calcined clays.

WHAT YOU WILL LEARN

* Market changes for U.S. coated paper and board.

* Key coating technology trends.

* How specific processes and materials are affecting production.

ADDITIONAL RESOURCES

The following articles are available for download at www.tappi.org. Access is free for TAPPI and PIMA members. To access an article, enter the product code in the search engine:

* "TAPPI Coating Conference: A technology update," Charles Klass, Solutions!, September 2003. Product Code: 03SEPS037.

* "Improving the quality and printability of coated paperboard," Charles Klass, Solutions!, December 2003. Product Code 03DECS042.

* "Formulating coatings for direct print flexo without drying," Solutions!, Charles Klass February 2003. Product code: 03FEBS037.

ABOUT THE AUTHOR

Charles P. (Chuck) Klass heads a consulting firm, Klass Associates, Radnor, Pennsylvania, USA. He has been active in TAPPI for many years and is a member of the Solutions! Editorial Board. Contact him at [e-mail]