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Nanotechnology Supports Grade Evolution


January 1, 2003
By Pulp & Paper Canada

In recent years, the evolution of grades is happening increasingly as a result of understanding paper on a nanoparticle level. Nano knowledge of the process, and the products that influence the proces…

In recent years, the evolution of grades is happening increasingly as a result of understanding paper on a nanoparticle level. Nano knowledge of the process, and the products that influence the process, allow papermakers to create higher value in a wide range of end products from fast filling cement bags to bold printability potential on formerly low level grades. High performance chemistry and additives for the wet end and coating, and even paper machine clothing are producing surface enhancements, and providing more flexible and effective use of valuable raw materials.

Composing the sheet to match market needs

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Benefits well beyond the mill tell the story best. Eurocan, a producer of high quality sackkraft for two-ply cement and similar sacks, saw the potential in helping their customer solve productivity problems in their packaging facility. When the cement maker filled bags, the level of dust in the air was very high. They were using traditional sacks, consisting of a conventional kraft paper grade with perforations at the top of the bag (or within the body of the bag) to facilitate the filling process, allowing air to escape.

Now, they produce a highly open sheet, which allows for the bags to be filled without any perforations, avoiding the dust in the air or on the surface of the sack. The new sheet design was made possible with the application of silica nanoparticle technology.

As Eurocan’s technical management sees it, silica nanoparticle technology has played an essential part in the development of highly porous sackkraft. Sackkraft grades have gone through a substantial evolution in last 15 years. First, there was a development of two-ply sackkraft for high strength applications like cement sacks. Mostly during last five years highly porous paper grade has been developed among leading producers like Eurocan. Strong northern virgin kraft fibre in combination with high consistency refining and nanoparticle technology enabled the development of this new product.

Eurocan is also testing anionic trash collectors, as well, to boost wet end performance, and run with fewer breaks.

Responding to requirements from printers, Ken Calder, paper machine superintendent at Domtar Vancouver says,” Printers are getting more and more demanding, and we are delivering a sheet, which prints better and runs better. Our more uniform sheet is notable for its improved surface characteristics.” He points out that they are always trying to lower costs, and will continue to explore options to do so.

A process engineer at Weyerhaeuser, Dryden, Ontario sees silica nanoparticle retention as being the key to ongoing improvements and efficiency. He says, “Silica nanoparticle allows for a low hassle system, which is more stable. Our experience with polymers has shown a greater sensitivity to dirt and deposition in the pipelines. A recent trial confirmed this.”

Runway to innovation

As Greg Bengtson, product leader for Compozil from Eka Chemicals, Akzo Nobel, puts it, “papermaking is becoming a runway for innovation thanks to nano developments. Paper producers can evolve grades or make entirely new ones by adjusting the process and the ingredients to a degree of precision unthinkable just a few years ago. Papermakers are now able to manipulate fibre and additives to optimize the surface or the base sheet in real time, gently tweaking the process. In addition to quality gains, expensive OBAs and Ti02 can be reduced, while at the same time applying nano-chemistry at lower dosage levels.”

Adds Sebastien Ricchi, sales manager of Eastern Canada with Eka Chemicals, “It’s kind of remarkable the ways papermakers can now alter the ratios of raw materials, and have the freedom to substitute. Higher value and higher quality paper, utilizing fibre, water, energy, chemistry, minerals and other additives more efficiently is quite an achievement. With on-line monitoring and control we are able to see the unseen work of nanotechnology in action, and make subtle adjustments.”

New role for clothing

Interesting developments in sheet enhancements are also coming from innovations in press fabric composition, which are designed to increase sheet smoothness and reduce fiber requirements.

These high performance composite fabrics utilize a unique manufacturing process to engineer the fabric’s surface characteristics in a manner to reflect the sheet’s microscopic attributes.

Sophisticated manufacturing methods and material innovations allow design engineers to manipulate and precisely customize fabric pore size and structure to emulate the sheet surface.

This advanced technology, often combined to other recently developed sub-systems, e.g., tri-axially oriented microfilaments, provides enhanced dewatering, better sheet control and superior sheet finish.

Several mills have reported fewer complaints from printers following the application of these technically advanced press fabrics.

Eric Arseneault, application specialist, Voith Fabrics, says it this way, “We are all looking into the nano window to figure out ways to improve the sheet or do a better job with raw materials or clothing composition. The nano breakthrough changes everything we do around the sheet, including the use of non-traditional innovative materials. You could say that we are beginning to get into the gene structure of a sheet and the surfaces that touch it. When you know the DNA, you can dramatically improve manufacturing tools, including clothing, and therefore improve performance of the final product.”

Digging into the structure of additives

Progress in adding greater value to paper also comes from advances in scientific instruments to observe the components of paper.

On the minerals and chemicals front atomic force microscopy, filed emission scanning and electron microscopy, mercury porosmetry and microcalomitry are all being employed.

According to Bomi Bilimoria, director of new product development for Imerys, “We now utilize electron microscopes, chemical analysis, and advanced particle geometry techniques to grasp why a particular kaolin or carbonate has a certain behavior. Minerals are poised to deliver value far beyond what was possible only a few years ago.”

One noteworthy development in minerals, resulting from greater scientific understanding, is referred to as shape engineered kaolins. This concept offers a new paper coating formulation tool to change the contour of the coating basestock for a smooth surface with exceptional print properties.

This means surface gloss and superior print properties, ideal for lightweight publication grades and coated board.

According to John Manasso, head of R & D at Imerys, a key factor contributing to the success of all minerals, and especially Capim clays from Brazil and the new shape-engineered offerings from Middle Georgia, is the leap in understanding of particle shape, its measurements and size. He notes that knowledge on the nano and micro levels is allowing not only for better coating performance, but new ways for minerals to combine with fibre, additives and chemicals to produce better formulations at lower costs. Says Manasso, “Capim kaolins and new shape-engineered kaolins deliver a unique coating layer, which maximizes printability and optics.”

Nano beyond the mill

Tony Lyons, director of technology platforms for Imerys, stresses the importance of cooperation beyond the mill with ink makers, who need to be kept in mind when changes are made in coating formulations.

He says, “Offset printing has requirements for high ink gloss, good ink holdout, avoidance of mottle and ink set off. Gravure demands excellent dot transfer and definition, as well as ink holdout and gloss. Digital printing, both ink jet and electrophotography, also has special needs. With ink jet color intensity, ink dot definition, light fastness and water fastness are most important.”

Lyons notes that the dimensions of shapes and pores dictate print properties, such as ink holdout, blister resistance, dot shape, water uptake in ink jet and thermal barrier for electrophotographic grades
.

Nano synergy as an investment tool

Before the development of tools like advanced silica nanoparticle formulations, designed to work in concert with sizing and coating combinations, coating interactions between latexes and pigments were less predictable. Bulk properties are no longer the dominant factor in determining the outcome of the sheet.

Adds Bengtson, “Better retention and dewatering, resulting from the application of silica nanoparticle technology, provides better formation for smoothness, and/or hole reduction, and also savings in OBA (optical brighteners and Ti02. It’s important for wet end, sizing and coating specialists to work together, especially when the savings from base sheet gains are more than enough to pay the surface enhancements achieved through sizing and coating.”

Synergy of chemical systems from the wet end through coating is a sure way to reduce headaches for those involved in optimizing the process. When the system runs cleaner, boil outs are less frequent. Zirconium crosslinkers are noted by some papermakers as a vehicle to allow coated broke to re-enter the papermaking system more easily.

Depositing value into the sheet

Even more important for some producers is the opportunity to run cleaner because of the reduction of deposits thanks to even better retention, resulting from the application of proprietary anionic trash collectors in conjunction with retention/drainage aids.

Says Richard Urbantas, senior applications scientist and deposit control team leader for Eka Chemicals, “a well formed base sheet can be a superb vehicle for “deposition” of various raw materials, even trash into the sheet. The result is cleaner, flexible papermaking, more efficient production, and a reduction of costly deposit treatments and frequent boilouts.”

Proof is always in the paper, of course. One coated fine paper producer recently changed to a novel polymeric ATC, and reduce broke treatment costs by 55%. There was such a degree of synergy between the ATC chemistry and colloidal silica and the silica requirements decreased by 30%. Filler retention increased by 3%. The mill managed to eliminate latex/acetate deposits and improve sheet quality in a higher basis weight range.

Looking to the future, expect to see nanotechnology play a continued role in advances in quality, grade development, and process flexibility, while at the same time contributing to dramatic changes in the raw material mix and products which come in contact with the sheet.

Martin Koepenick of Innova International has been writing about paper industry innovation for over twenty years. Innova provides creative concepts and global editorial programs to industry suppliers and producers. Contact him at brandsmiths@aol.com


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