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European Conference Draws Large Audience

European Conference Draws Large Audience

by David A. Markgraf

The Eighth European Polymers, Films, Laminations, and Extrusion Coatings Conference sponsored by the Polymers, Laminations and Coatings Division of TAPPI on May 28-30, 2001, attracted 208 attendees. The conference at the Barcelona Hilton in Barcelona, Spain had five technical sessions:

  • Polymers/Raw Materials I
  • Polymers/Raw Materials II
  • Process/Converting
  • End Applications/Environment
  • Machinery/Equipment.

Erkki Laiho, Borealis Polymers Oy, was the technical program chairman for the meeting. He assembled 34 technical papers. Most papers reflected serious research and provided an extension of current state-of-the art knowledge. These included “Processing And Converting Of Plastic Films Vacuum Coated With Inorganic Barriers” by Hans-Rudolf Naegeli and Wolfgang Lohwaser of Lawson Mardon Packaging Services Ltd.; “Enhanced Products And Structures With 14 Layer Feedblock” by Andrew W. Christie and Timothy Watson of Black Clawson Converting Machinery, L.L.C.; and “Flame Treatment Meets Quality Management” by Manfred Hill of H. O. T. Oberflachentechnik.

As a finale to the conference, Comexi, SA, a manufacturer of flexographic printing presses and laminating and coating lines, sponsored a tour of their nearby facility. Fifty registrants visited the plant in Girona that opened in 1999. The highlight of the tour was a demonstration of their new flexographic “gearless” press.

A CD-ROM published by TAPPI PRESS contains the proceedings of this meeting. Order “2001 Eighth European Polymers, Films, Laminations and Extrusion Coatings Conference Proceedings,” EPLCCD-01, from TAPPI PRESS at www.tappi.org. The Ninth European Polymers, Films, Laminations, and Extrusion Coatings Conference will be in Italy in 2003. Details will be available in this publication and from TAPPI as they become available.

“Web Words” Book Review

by Dante F. Ferrari

“Web Words” is a compilation of the popular Web Works columns written by David R. Roisum from 1994 to January 2000. The book offers more than 100 pages of useful advice on web handling principles and troubleshooting tips. Roisum clearly indicates the scope and mandate of his column in his inaugural article, “I will answer questions on web handling and converting in subject areas such as roller design; calendering, embossing and laminating; slitting; spreading; winding and unwinding; as well as drive, nip, and draw/tension controls. I will explain the underlying mechanics and draw conclusions as to what options are available for improved performance.” The information that follows in the book is simple, clear, and highly informative.

Readers who are familiar with Roisum's monthly column will be happy to know that all his information is now available in one handy reference book published by TAPPI PRESS. For those unfamiliar with the column, you have been missing a valuable resource for the converting industry. This is your opportunity to gain access to this wealth of information.

Roisum received an MS in engineering at the University of Wisconsin in Madison and a Ph.D. from the Web Handling Research Center. His column covers more than 20 years of industrial experience. What makes this a truly valuable reference is his ability to combine his extensive technical knowledge with a practical, easy to understand approach. Using the Socratic method, the title of each article poses a practical converting question that the column proceeds to answer. Roisum provides all the necessary information without any unnecessary jargon. The columns reproduced in his new book allow anyone to apply complex engineering principles in a quick and straightforward manner on the production floor. This obviously makes them truly useful tools.

“Web Words” is available for purchase from TAPPI PRESS online at www.tappi.org. It is also available by calling the TAPPI Service Line at 1-800-332-8686 in the United States, 1-800-446-9431 in Canada, and +1-770-446-1400 from other locations. Other publications available from TAPPI PRESS of interest to those in the converting and flexible packaging industries include “Extrusion Coating Manual,” edited by Thomas Bezigian; Film Extrusion Manual-Process, Materials, Properties,” edited by Thomas I. Butler and Earl W. Veazy; and “1995-1999 Polymers, Laminations and Coatings Conference Proceedings CD-ROM.”

Secrets Of A Level Process And Product

by David R. Roisum Finishing Technologies, Inc. email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Application: A level profile can be difficult to obtain partly because some processes object to variations below the threshold of common measurement techniques such as scanners and laboratory bench tests. A wound roll is a very sensitive customer and a very sensitive measure of profile variations.

The meaning of profile depends upon whom you ask. Perhaps the most common definition is the variation of gauge — caliper or thickness — across the width of a web. A papermaker will also include basis weight and moisture with caliper as a measure of profile. Some say that a web with baggy lanes has a poor profile. Bagginess is a variation of machine direction (MD) tension across the width that may result from variations of manufacturing, converting, or uneven yielding during web handling. Profile could therefore mean variation of any measurable property across width. Profiles sometimes connect. An example is when gauge variations stack up during winding to create ridges that stretch the web into baggy lanes. Another example occurs on paper where wet streaks are baggy. For these reasons, one must be precise by specifying a particular property when communicating with others.

Profile Sampling

Another complication is that sampling of profile measurements can occur in many ways. The most common method involves cutting evenly spaced samples across the width of a roll immediately after winding as Fig. 1 shows. These samples then go to a testing laboratory for measurement. The intent here is that the samples on the outside tail of the roll somehow represent the entire roll, series of rolls, or lot. This common sampling technique requires many assumptions:

  • The number of samples at any point or cross machine (CD) position is sufficient to resolve variations at a sufficiently fine level for the need. The resolution of the test method is something that only statistics may determine. If no independent measurement method of the same variable exists that has even greater resolution, determining whether variation belongs with the material, sensor, or both may be difficult.
  • The number of sampling points is sufficient to capture features as narrow as the application requires. For example, samples 6 in. apart will have little to say about a defect that is 1 in. wide.
  • The magnitude of MD variation is small and stable compared with the CD variation over the course of one roll. Although this is often true, the assumption also requires verification for each specific application.

Another approach is use of on-machine sensors that sample as Fig. 2 shows. The first technique in the figure employs a fixed, single-point sensor. While the sensor might move sideways, it is obviously more capable of capturing MD variation than CD variation. The second technique in the figure involves a traversing, single-point sensor. This is the most common type of scanner used in web industries. The path of the sensor is a zigzag. A computer manipulates the raw data from this sensor using filters, averaging, etc. The display may show profile across the width on a single scan, a fixed time interval average, or a roll average. The time interval allows heavy averaging to minimize the effects of variation in product and sensor so that patterns begin to emerge from the noise. Another sampling technique uses a sensor that can scan the entire width simultaneously. This sensor will also have a minimum resolution at any point and a minimum spatial resolution in both directions. MD resolution involves processing time and machine speed.

Importance Of Level Caliper Profile

This paper will focus on detecting caliper variations although the principles can also extend to include basis weight, density, and occasionally other properties such as bagginess. This may not be as limiting as it might seem. If caliper varies, other factors will undoubtedly also vary. The root cause of caliper variation sometimes also causes an additional factor to vary. In other cases, the caliper variation itself causes variation of other properties. In paper making for example, a thick or heavy lane will usually also be a wet streak because it has more total water to dry than neighboring positions. A relatively thick lane entering a calender will leave the calender relatively smoother, denser, or more highly bonded than neighboring positions. In film, the thick lane will often have different optical properties such as being less transparent or having different gloss characteristics. In coating, a variation of raw material caliper on the entering side will usually result in variation of coating on the exit side. Coating variations may likewise cause lanes that do not dry as completely. This can increase the risk of blocking on a winder.

Caliper is a commonly measured web property. Many suppliers and customers will reject using average caliper or variation of caliper. The intense interest in this particular property is due to processing and use characteristics. An uncountable number of problems occur due to poor control of caliper.

Width rather than MD position or time is the primary focus of this paper for two practical reasons. Adding information about the second dimension increases costs and efforts by orders of magnitude. In addition, many machines are more stable with time than across their width. The basic profile or fingerprint of a machine is recognizable for hours, days, or years. An example is a baggy edge that tends to be a permanent feature of many machines.

The premise of this paper is that a level caliper profile is necessary for a successful product. Without a level caliper profile, internal rejections and waste will increase. Customers will complain, return material, and seek another supplier. The fussiest customer is not always the one to whom we sell. It is often the wound roll. Many times the final customer can process caliper varying material provided it did not experience additional damage during winding.

Caliper Measurement

The most common laboratory measure of thickness in film, paper, and many other web industries is TAPPI Test Method T 411 om-97. It defines thickness as the distance between a flat pressure foot of 5/8-in. diameter and a parallel anvil with a single ply of the web sandwiched between. An effective pressure of 7.3 psi applies for 3 s before taking a reading. The test unit is a small laboratory bench device available commercially from several sources.

Measuring caliper in a laboratory has many obvious disadvantages. The most serious may be delay. Because of the limitations of laboratory testing, online caliper measurement may be useful. The paper industry has measured basis weight on a machine for many decades using absorption of nuclear products.

Wound Roll As A Measure Of Caliper Profile Variations

Hundreds, thousands, and sometimes even tens of thousands of layers accumulate to make a wound roll. If the caliper is higher at one CD position, microscopic differences can add to huge results. The wound roll has a substantial advantage in sample size compared with the laboratory and online caliper measurements. This is because the outside of the roll may reflect the stacking of caliper variations of many, many layers. Thick areas will build larger or stiffer because the material has nowhere to go. Due to the stacking of caliper variations, a wound roll can be a very sensitive measure of profile. It is often far more sensitive than the laboratory or online scanners.

A common misconception is that the stacking of layers is proportional — 1000 layers of 0.0001 in. thick caliper would cause the radius to be 0.1 in. larger. In reality, it is less because the relatively thick area also winds tighter and more compactly. In this sense, a roll has a built-in tendency to level itself. In materials with a very stiff stack modulus such as some films and densely coated or calendered paper, the buildup is nearly proportional. A stiff stack modulus is easy to detect by striking the roll with a stick.

Three primary measurements of a wound roll can detect basis weight, caliper variations, or both. These are variation of diameter, hardness, or density across the width. Several techniques for making each of these primary measurements is possible. The best alternative will depend on a particular situation.

Selection Of Caliper Measurement Method

In order of decreasing frequency of use, the three fundamental methods for determining if a process is level are laboratory test, scanner, and wound roll. The best technique is the subject of heated debate. Many people like the simplicity of the laboratory test and the fact that standards support it. Others like the scanner because it provides much more information with less labor. I often prefer the wound roll because it is usually the most sensitive. A sensitive reader may detect some bias in these preferences. A quality assurance manager will favor standardized measurements. Those who love instrumentation and technology will favor the scanner. The wound roll will obviously be the favorite for a winder guru.

Some people become so attached and vested in their instruments that they do not see the obvious. A paper client had a hard time believing that his million-dollar scanner was incorrectly showing a level profile when the wound roll set had a 1-in. diameter variation. The rolls looked like footballs! Manufacturing or gauge variations are subtle. A classic example is the wound roll corrugation that occurs at an abrupt change in caliper. Testing laboratories and scanners usually do not have the sensitivity or CD resolution to pick up the errors in gauge that are the root cause of this common defect.

Classifying Caliper Profiles

Classifying the shape of the more common types of gauge profile variation is useful. It allows communication with a few words. Equally important, shape is a useful tool in problem solving. The shape tool states that the “shape of the problem must match the shape of the cause.” This allows elimination of machine misalignment as a cause of ridges because misalignment has the shape of an even taper from front to back. The shape of ridges varies abruptly with CD position. Ridges could be the result of tiny nicks in a die lip.

On a coarse scale, caliper profile could be a taper, smile, or frown as Fig. 3 shows. The corresponding wound roll shape is barreled, belled, or coned, respectively. In some cases, a coarse scale is the most important consideration. A winding example is telescoping that a tapered profile can greatly exaggerate. In most cases, a level profile is preferable. With wound roll wrinkles, a bell-shaped roll acts like a concave spreader roll. This could be advantageous in unusual circumstances. With air entrainment in a wound roll, a football-shaped roll can sometimes allow air to escape from the edges gracefully rather than becoming trapped inside the roll.

Few profiles are as simple as these discussed in this paper. In many cases, profiles are usually the superposition of two or more features. Each requires separation for problem solving purposes. For example, you might have a ridge-containing, barrel-shaped roller. In this case, causes for ridges are possibly entirely different than the cause of the barrel. They merely have the same outcome — caliper variation. This is like having a headache that can be due to any number of root causes singly or combined.

Oscillators And Randomizers

Gauge will never be dead level. Thickness variation can be a problem for the next unit operation or a customer. The most serious influence of gauge variation will sometimes be on the wound roll. For example, the thicker position will wind larger. This may stretch the material into a baggy lane. This problem is common on many grades of film and paper. The thicker position will also wind tighter and cause increased interlayer pressure that increases the risk of blocking on some materials. This problem is common with grades that are coated, printed, or perhaps have surfaces that have an affinity for each other. If a roll has a bulge, the web may gather there due to the concave spreader principle. This causes the bulge to build larger with a greater gathering force in a vicious snowballing pattern that is common on thin film. A bulge on the edge such as raised edges on slitting can sometimes destabilize a roll because it prevents the remainder of the roll from winding sufficiently tight. Oscillators or randomizers can accommodate these gauge variations.

Shifting any forming element sideways in a reciprocating fashion keeps a pattern from building. A classic example is doctor blade oscillation. Oscillating an unwind or winder can keep narrow gage variations from exacerbating wound roll problems. The two parameters to control are stroke and speed. A randomizer is generally only for tubular products such as blown film. The extrusion die may rotate 360 degrees in one direction and then reverse in a reciprocating pattern. A more effective approach is to randomize a web after the collapsing nip by using a pair of rotating turn bars.

Conclusion

Everyone desires a uniform product. To achieve this, we must have basis weight, coating weight, caliper, etc., level across the width of a roll. Although we can measure these with laboratory instruments and scanners, I propose that you also consider the wound roll as a profile indicator. If the roll is not uniform, the manufactured web is probably not uniform too. Your challenge is to find a method for checking profile that is easy to use and not prohibitively expensive. You must also be certain that the method you use is sufficiently sensitive to satisfy the requirements of all customers including the wound roll.

For information about the Polymers, Laminations and Coatings Division of TAPPI, see the web page at www.tappi.org/public/divisions/polymers_laminations_coatings.asp or access the TAPPI web site at www.tappi.org. For the complete papers whose expanded summaries appear in this section, go to the TAPPI web site at www.tappi.org/public/library.asp and click on the logo displayed here.

Telephone inquiries are welcome at the TAPPI Service Line by calling 1-800-332-8686 in the United States, 1-800-446-9431 in Canada, or +1-770-446-1400 in other countries. Send FAX to 1-770-446-6947. Address mail to TAPPI, Box 105113, Atlanta, GA, 30348-5113. Contact “the PLACE” editor using e-mail at This email address is being protected from spambots. You need JavaScript enabled to view it..

PEER-REVIEWED TECHNICAL PAPERS: Following are expanded summaries of complete papers that are available on the TAPPI web site at www.tappi.org/public/library.asp


 

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