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Practical applications for pigments and fillers.

The following is a Solutions! magazine roundtable. Participants in the roundtable are:

* Rajan Iyer, technical manager, coated papers, IMERYS Pigments for Paper Business Group, Sandersville, Georgia, USA

* Charles Klass, principal, Klass & Associates, Redington Beach, Florida

* Tony Lyons, director of research, IMERYS Pigments for Paper Business Group

* Prakash Malla, manager of research and development, Thiele, Sandersville, Georgia.

* Kurt Rank, global marketing manager, uncoated paper, Specialty Minerals Inc., Bethlehem, Pennsylvania

* Stephen O. Stueck, director of marketing, Omya Inc., Alpharetta, Georgia

* Eric Tillirson, Vice President, Sales and Marketing, Thiele

* Eddy Turner, director of business development, IMERYS Pigments for Paper Business Group

SOLUTIONS! How are engineered pigments and fillers being applied in practical papermaking applications?

KLASS: Engineered pigments are being used to optimize quality and cost in both filling and coating applications. Thermally structured (calcined) kaolin has been in use for decades as an extender for titanium dioxide in both filling and coating applications. They have also seen limited use to reduce print-through in newsprint.

There have been developments in both ground (GCC) and precipitated (PCC) calcium carbonate to facilitate increased use in both filling and coating. The use of dual addition points--part in the thick stock and part in the thin stock--has facilitated not only better retention but also higher levels of PCC addition in both uncoated free sheet and coating base stock. Recently developed aragonite PCC products have facilitated increased gloss in both gloss-calendered coated paperboard and coated papers. This allows the papermaker to achieve a target gloss level with less intense calendering--resulting in better bulk and opacity.


IYER: More precise control of ink penetration for maximum print gloss results from the synergy between EFP (engineered fine platy) kaolins and engineered carbonates.

LYONS: They are being used when ink setting rates need to be controlled, when coverage is very important, and for high brightness and opacity applications.

TILLIRSON: Tailored kaolin products have allowed paper producers to reduce or eliminate the use of higher cost products such as plastic pigments or titanium dioxide in coating formulations. Hydrous clays and hydrous/calcined blends can be tailored for individual mill requirements, resulting in significant economic advantages for the mills. Hybrid grades can eliminate the need for multiple clay products at the individual mill site. Certain supply chain efficiencies can be realized when one clay product can meet the needs of several grade applications at an individual mill.

Also, the different shapes and sizes of different pigments can be exploited to maximize performance synergy in the coating. For example, the platy kaolin particles with rounded or blocky carbonate particles yield a highly disorganized open coating structure creating more pore volume and bulkier coating for higher light scattering and opacity. This synergy can be realized only when the right shape and size of kaolin particles are blended with carbonate, indicating the importance of shape and size engineering of kaolin.

RANK: Engineered fillers are being applied in the sheet under more traditional methods, albeit at increasing filler levels. Surface application of pigments at the size press has met with some success in the North American market and interest is growing. More so than ever, the goal is higher filler loading levels for cost reduction. Technologies ranging from wet end additives to filler/fiber composites are being pursued to achieve these higher filling targets. The uncoated mechanical sector has stepped up its efforts in evaluating ground and precipitated carbonates and carbonate/clay blends. These mechanical papers could be the future benchmarks for quality performance minerals. Manufactured precipitated carbonates present future opportunities to significantly advance particle properties with subsequent paper benefits, whereas natural carbonates probably have reached the limit of their ability to improve paper characteristics.

STUECK: The use of engineered pigments continues to grow in coating applications as paper manufacturers strive to improve coating coverage and opacity. Several trends stand out:

* Predominance of single coating in North America leads the drive to improved coverage

* Ever increasing imports of European double and triple coated papers also drive improved coverage and brightness

* Upcoming increases in postal rates will start another round of basis weight reductions that will require higher opacity pigments. Engineered pigments have demonstrated success in improving scatter and opacity

* The need to cut costs to compete globally necessitates reducing high cost pigments such as titanium dioxide and calcined clays. The higher scattering power of engineered pigments enables greater substitution.

* Costs have led some paper manufacturers to return to broader distribution coating pigments in an effort to save material costs. Higher coat weights and higher ratios of carbonates have helped them achieve their results

* Coating formulations with engineered and conventional pigments are focusing more and more on pore structure and the coating's ability to control ink set, dot formation and print gloss

* Smaller particle sized engineered pigments are gaining wider acceptance as some producers push for higher gloss

The use of engineered pigments in filling applications has slowed as papermakers focus more on reducing costs and improving printing properties through fiber replacement and higher filler loadings. Optical properties, however, are still very important, and engineered pigments provide higher light scattering for lightweight paper applications.

SOLUTIONS! How are current trends in the price of wood fiber affecting the use of pigments and fillers?

KLASS: Pigments have always been lower in cost than pulp--the reason we refer to them as "fillers." Papermakers have tried to maximize filler levels for decades. The advent of alkaline papermaking allowed significantly increased use of fillers, especially calcium carbonate--which also improves brightness. As pulp costs go up, there is increased pressure to control costs. However, I don't believe that trends in pulp costs per se have affected the use of pigments.

An exception to this is in the area of white top linerboard. Board makers have always been reluctant to use filler due to its adverse impact on strength and bulk. However, as the market for graphic quality corrugated increased due to trends in retailing, there was a need to move from mottled white to white top linerboard. Developments in paper machinery such as high intensity pressing have facilitated production of high performance linerboard. White top producers have found that they can include some calcium carbonate filler in the white top furnish and still meet the strength requirements. Since white pigment is more effective than bleached kraft pulp in obscuring the dark brown base sheet, it can be practical to reduce top liner basis weight--further reducing costs. The next likely step in this area is coated linerboard. There are a few small conversion coaters producing coated linerboard, but none of the major North America producers have followed the lead of their global competitors in Europe and Asia. The benchmark standard in this area is a product imported from Finland. There are plans moving forward to install coated linerboard capacity in China.

LYONS: I don't think price trends are having that much of an effect according to what I am reading and hearing. Having a much larger effect are the cutbacks on total fiber being allowed to be used for forest stewardship reasons. The pressure on fiber cutbacks means that pigments that provide higher bulk are being favored more these days Structuring of the coating by use of engineered pigments will help to do this.

MALLA: We have noted an increase in interest and demand for coarse, platy filler clays to displace fiber while maintaining sheet optical and strength properties. Also, coat weight in the coated grades is being increased to offset the increase in fiber cost or even reduce the cost of the paper while keeping the same final basis weight and without adversely affecting performance. As fiber prices increase, papermakers attempt to substitute less costly fillers and coating pigments in the sheet to reduce total cost.

RANK: Increases in wood fiber cost, as well as availability of supply, continue to create opportunities for optimizing filler use. As mills evaluate the composition and cost of their fiber furnish, they uncover avenues for increasing the use of fillers, which are less expensive than fiber. Cost reduction continues to be a strong driver for paper mills.

STUECK: Price and availability of fiber has pushed the move to higher and higher ash levels. There are several trends in this area:

* Higher ash levels are achieved through higher coat weights and higher filler loadings

* GCC in the wet end enables papermakers to run at higher ash levels with faster drying and less strength loss than conventional PCC

* Blending GCC with PCC in the wet end is growing at a very fast rate as papermakers maintain their bulk and optical properties while increasing fiber substitution without killing sheet strength

* Perhaps the biggest development in fiber substitution is the use of GCC with starch at the size press in the manufacturing of uncoated freesheet grades ("size press filling"). The addition of GCC at a rate of up to 2.5% fiber substitution produces a sheet with improved porosity, equal strength at higher ash levels, improved stiffness, better formation (through improved ash distribution) and lower energy costs (through reduced steam in the dryers). The application has settled on a conventional filling GCC because PCC and clays tend to dust.

* The legislated reduction of wood use in Quebec is leading to new filling applications for standard newsprint and directory grades

SOLUTIONS! How are pigments and fillers being used to help create new, branded paper products?

KLASS: See the comments above about coated linerboard. New types of pigments could be the keys to producing more economical coated ink jet and digital printing papers. These grades were among the hottest of topics at the 2005 TAPPI Coating Conference Top quality ink jet papers are coated with silica pigments--which are not only very expensive but also cannot be coated at high solids. This makes producing coated ink jet papers on machine impractical. There has been considerable effort to find alternatives to silica pigment, but they have achieved only marginal commercial application. Included in this area are specialty heat treated PCC and combinations of engineered kaolin and synthetic zeolite. One of the kaolin producers has just introduced an engineered kaolin product that shows promise of good performance. There is also a modified natural zeolite product that shows promise of meeting the market need moving toward commercialization.

LYONS: Mostly, pigments and fillers are being used to increase the blue-white shade of publication papers.

MALLA: An excellent example of this process is the development of low abrasion, high brightness, calcined clay. Producers of converting-sensitive grades can deliver a quality product at a competitive price that offers the additional benefit of low abrasion. The result is less wear on slitter knives and converting dies which translates to lower ultimate costs for the end user.

RANK: Given the general paper quality improvements in the last decade, cost reduction has now superseded product differentiation to a large extent. Recent filler modifications have focused on reducing the total cost of producing paper while maintaining key physical and optical properties of the sheet. Improvements in the quality of some mechanical grades of paper have created competition with woodfree paper grades, and this grade substitution will become increasingly common. Where true grade differentiation has been merited, the effort has focused on the introduction of carbonates into mechanical grades for better optical properties, and the application of specialty coating pigments for improved printability or significantly enhanced brightness, gloss or other improvements in coated grades. In uncoated freesheet paper grades, there is a trend toward grade consolidation to control costs.

STUECK: Applications of new modified calcium carbonates have led to numerous advancements in paper coating and filling. The high surface area and unique morphologies of the modified calcium carbonate pigments have demonstrated success in the development of: higher brightness and glossing SC filler pigments; higher bulking filler and coating pigments; lower cost, high performance inkjet pigments; improved coverage pre-coat pigments; and applications to reduce print through and show-through in ultra-lightweight papers. Additional uses for these structures are under development.

Also, developments with GCC as a high-brightness rotogravure coating pigment are gaining global acceptance.

TURNER: Engineered fine platy (EFP) kaolins were developed for evolving and new brands, matching the ever-increasing performance demands of high-end coated papers and packaging. Engineered for synergy with carbonates, fine platy pigments notably improves print quality, while increasing light scatter, brightness and opacity in the coating.


* How engineered pigments and fillers are being applied in practical papermaking applications.

* How current trends in the price of wood fiber is affecting the use of pigments and fillers.

* How pigments and fillers are being used to help create new paper products with brand differentiation.


* "Pigments & fillers: New technology for new markets," by Alan Rooks, Solutions!, July 2004. To access this article, enter the following Product Code in the search field at 04JULSO28.

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Author:Rooks, Alan
Publication:Solutions - for People, Processes and Paper
Date:Jul 1, 2005
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