Trends in papermaking: ideas from the experts.
Respondents to this Solutions! roundtable are:
* Katherine Buckman Davis, chairman, Bulab Holdings (parent company of Buckman operations worldwide), Memphis, Tennessee, USA
* Bob Kinstrey, director, process technology, Jacobs, Greenville, South Carolina
* Ted McDermott, McDermott Consulting Services, Schaumburg, Illinois, and member of the Solutions! Editorial Board
* Jim Atkins, Atkins Inc., Flemington, New Jersey, and member of the Solutions! Editorial Board
* Jyrki Jaakkola, senior product manager, Metso Paper, Norcross, Georgia
* Kenneth Mueller, business development manager, Specialty Minerals Inc., Bethlehem, Pennsylvania
* Mark Meixner, director, business development, Hercules Pulp and Paper Division, Jacksonville, Florida
* Prakash Malla, manager, paper research and applications laboratory, Thiele Kaolin Co., Sandersville, Georgia
* Kasy King, Papermaking Process Consulting, Appleton, Wisconsin, and member of the Solutions! Editorial Board
* Brine Ranson, printing and writing marketing manager, Hercules Pulp and Paper Division, Jacksonville, Florida
1. Paper and paperboard mills are beginning to move operations that have typically been off-machine, such as coating and converting, to on-machine operations. What areas are most active in the trend toward on-machine operations, and what are the pros and cons?
DAVIS: The most active sectors moving toward on-machine operations are light-weight coated, coated paper, and coated board. Mills are moving toward on-machine coating and converting to increase manpower efficiencies, decrease the need for extra machinery, eliminate the logistical problems of moving and storing paper and board, and reduce the maintenance involved in conducting the various steps.
The push to on-machine operations exists because the technology is available and the cost savings are substantial. Although these production enhancements have benefits, cautions are also necessary. Product quality and converting characteristics are vital. On-machine operations must be absolutely correct the first time the paper comes off the machine. Recent technological advancements make the efficiency of new on-machine operations possible.
MCDERMOTT: Coating and finishing continue to be the most active areas. The "pros" of converting to on-line are typically cost advantages. They can also include quality uniformity because the controls and measurements around on-line coating and finishing on a paper machine can be more uniform.
A negative aspect of going on-line is the need to do the product development and try to match the sheet properties of off-line created processes. For extremely flat-surfaced papers or extremely high gloss coated papers, on-line processes cannot achieve the off-line quality level.
ATKINS: A recent success story has been moving the supercalender from off-machine to on-machine. This has allowed making such grades as SC [supercalendered] and LWC [light-weight coated] with no off-machine operation. The obvious advantage is that manufacturing costs decrease significantly. On the downside, it makes operation of the paper machine that much more difficult. Some quality issues may also exist. For example, gloss and surface roughness for LWC made totally on-machine might not yet match LWC made with off-machine operations. The plusses nevertheless far out-weigh the negatives.
JAAKKOLA: A trend truly exists toward on-line concepts. This approach often requires less initial investment and lower operating costs. Final product quality control is immediate. The potential exists for less off-quality product produced than can occur when reels go through different production steps. One drawback to an on-line approach is that the broke has a coating and is therefore more difficult to handle.
MUELLER: Today, virtually all newly installed coaters have an on-machine configuration. Some technical advances helped drive the shift to on-machine coating, such as reduced web breaks with the short dwell time applicator. Another advance was the move to a one-station, pre-metered size press to coat two sides simultaneously rather than a two-coating station with a blade coating system.
Most recent installations call for on-machine, multi-nip hot soft calendering. Significant advancements in areas such as the temperature tolerance of roll coverings and the vibration control of the stack were necessary to enable the move to on-machine.
The paperboard industry, in stark contrast with the coated paper industry, has been operating with both on-machine coating and calendering for many years. For coaters and calenders, the advantage of on-machine operations is decreased cost. Additionally, less manpower is necessary because fewer rolls require handling between stations.
On-machine operations also avoid uncoated roll inventory accumulation. This is a constant challenge for some mills. An additional area supporting the shift to on-machine operation is reduced trim waste.
On-machine systems do have some disadvantages. Specifically, increased interconnectivity can lead to a lower total operating efficiency. On-line machine runnability is a critical component of the total equation.
MEIXNER: The most significant move toward on-machine operations is in the surface effects area. Size presses are now more common in grades that were previously untreated. On-machine coaters are now normal for coated papers and board. The advent of hot, soft nip calendering has virtually eliminated off-machine supercalender operations. In addition, surface treatments are no longer simply starch applications. They include treatments for sheet charge control, ink absorption, and functionality in security-based papers.
The movement to more on-machine operations places a significant premium on wet-end stability and performance. Little time is available to respond to defects and variations when these processes are on-machine. That is why companies are continuously working on more robust chemistries.
2. More paper mills are adopting and refining wet end additive control and monitoring. How is this changing papermaking?
DAVIS: Various types of monitoring and control equipment exist for different functions. All these systems ensure that sheet quality is on target as it comes off the machine, that broke and downgrading are minimal, and that the mill can increase production efficiency. Mill and vendor personnel can now focus on papermaking and grade development goals rather than testing, retesting, or adjusting settings and parameters. These changes have given papermakers the freedom to focus on how to develop and--more importantly--how to maintain a strategic competitive advantage in the marketplace.
MALLA: Adopting and refining wet end additive control and monitoring simply has contributed to improved paper quality and productivity. A better wet end additive control system delivers improved paper formation, filler and fines retention, and drainage. This has helped to replace expensive fibers with less expensive fillers. It has also allowed the use of increased level of recycled papers, including coated broke, without deteriorating final quality and productivity.
RANSON: Papermakers are working with various equipment manufacturers to install closed loop control in their wet end. This provides better quality on a more consistent basis and lower costs. Some specialty chemical suppliers also have proprietary control and monitoring devices as part of their service package. These are generally specific to their programs and technologies. A key benefit of these monitoring devices is less hands-on time by operators to adjust chemicals.
KINSTREY: Our European counterparts report that the modern European gap formers have highly instrumented and automated wet ends that control the ash distribution within the sheet.
KING: Wet end additive control has changed papermaking for the better. Variation in the papermaking process is a huge source of poor runnability and off-quality product. By monitoring and controlling wet end additives, the variability decreases. As we gain a larger number of on-line, real-time monitoring instruments, more information is available to use for troubleshooting and problem solving. With more automation, machine operation and product quality are more easily attainable with fewer resources.
MCDERMOTT: The shift to on-line has driven the need for new additives in the wet end. Costs vs. fiber and the continued trends to lighter basis weights with similar print properties are other factors. Controls and monitors are necessary, but the lack of resources--people and money--makes implementation of these systems impossible.
JAAKKOLA: Machine direction product and operation stability is key for high quality and high operating efficiency. Wet end additive control is one of the contributing factors, but definitely not the only one.
3. Due to cost and quality issues, mills in North America are moving to higher filler levels already achieved in European mills. How does this trend affect papermaking operations?
DAVIS: Fillers contribute to a brighter sheet, higher opacity, printability, and other end sheet qualities. These attributes are part of the drive toward higher filler levels. Fiber costs are a driver too. Challenges do exist when increasing the percentage of filler. Higher filler levels will affect runnability, deposits, retention issues, water clarification, paper strength, water balance, wet-end chemistries, and related control issues. This development requires an even closer relationship between suppliers and a mill to manage the papermaking process effectively.
MALLA: A principal drawback of higher filler loadings is the reduction in strength properties of paper due to reduced inter-fiber bonding. If the paper is undergoing coating, paper mills may need to consider coating on coaters that are less demanding on paper strength such as metering size press (film coating) and curtain coating (non-impact coating). This could require major capital investments for many paper mills.
Paper mills will also need better control and refining of their wet-end chemistry strategies to account for increased filler loading. Potentially, a higher filler loading increases the chance of forming large flocs with heterogeneous distributions that are detrimental to good paper formation. A higher filler loading can also contribute to poor filler retention and drainage. These shortcomings may be overcome with the right choice of retention system and filler pigment. For example, new microparticle retention systems will improve paper formation, retention, and drainage. A coarse filler pigment with a low level of fines (engineered filler) would also retain better and improve drainage. The industry needs to develop filler pigments with functionality that would strongly bond with fiber the same way a fiber would bond with another fiber and not deteriorate strength properties, including stiffness.
RANSON: In North America, a desire exists to increase the total filler level in a sheet similar to the European papers today. To do this, paper producers must carefully review their processes. Immediate changes are not always necessary, but people must thoroughly understand system limitations before starting to use higher loading levels. Typically, increased filler loading in the wet end will have an immediate impact on the retention system and often force a step change in this technology.
Increased wet end filler loading also affects other aspects of the papermaking process such as runnability, wet web strength, dryer dusting, sheet dusting, and printability issues. While retention on a macro scale is important, so is filler distribution, refining, machine cleanliness, etc. Conditions that yield good machine runnability for filler loading today may not work for higher filler loading tomorrow.
The paper producer must look at each area of the machine to see if adjustments are necessary to meet the new conditions. These areas include felt conditioning, microbiological control, sizing, and even the type of PCC [precipitated calcium carbonate] in use. It may take a combination of two PCC shapes/sizes, a different MB strategy and/or a surface treatment program to effectively produce a sheet that looks, feels, and prints like the old sheet.
KINSTREY: A key question exists. Why has North America taken so long to attempt to achieve the filler levels Europe has been using for many years? Perhaps our reliance on cheap fiber and energy--or our perceived notion that our fiber and energy were cheap and would always remain that way--made us complacent.
KING: This question is complex. Many years of alkaline conversion experience have demonstrated the advantages and disadvantages of higher filler content including the following:
* Cost decreases because filler is cheaper than fiber.
* Sheet strength decreases because bonding and tear are fiber generated.
* Brightness and opacity increase, because filler is brighter and more opaque.
* Dye consumption increases resulting from the high surface area of the filler.
* Picking may increase when the filler is difficult to bond into the sheet.
* Internal size consumption increases because of the high surface area.
* Retention is critical to good operation and may require changes.
* Sheet formation generally improves as the filler fills in voids.
* Sheet dryness may be better or worse since filler holds water, but the vacuum seal may be enhanced.
* Sheet dimensional stability is better because the sheet is more relaxed.
* Breaks may increase until the strength and filler balance is found.
* Additional wet end starch may be necessary to offset the strength loss.
* Since filler goes into the sewer, treatment plant changes may be necessary.
* Clothing cleanliness is more difficult--especially felt filling.
MCDERMOTT: Without wet-end controls on retention and other wet-end factors, filler levels in water loops increase and cause scaling issues. The felt cleaning requirements also experience greater impacts. With higher filler levels, felt plugging occurs sooner. The need for dramatically improved felt cleaning systems often is not recognized sufficiently soon.
JAAKKOLA: We can hope that the trend toward higher filler levels will lead to more machine modernizations. Mills will most likely elect to increase filler content only enough to achieve runnability and paper property targets without major machine modernizations.
RELATED ARTICLE: IN THIS ARTICLE, YOU WILL LEARN:
* Which grades will most likely move toward on-machine operations.
* How wet end additive control is changing papermaking.
* The effects on papermaking of higher filler levels.
* "Taking wet end chemistry to the next level," Jan Bottiglieri, Solutions!, June 2003
* "A marriage for performance sake," C.A. "Kasy" King, Solutions!, April 2003
* Go to www.tappi.org and enter "papermaking" in search engine. Also, on home page click on link to "divisions" and then "Paper and Board Division."
BY JANICE BOTTIGLIERI, SENIOR EDITOR
ABOUT THE AUTHOR
Edited by Janice Bottiglieri, senior editor of Solutions! and editor of TAPPI JOURNAL Contact her at firstname.lastname@example.org.
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|Publication:||Solutions - for People, Processes and Paper|
|Date:||Dec 1, 2003|
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