Polymers/Laminations/Adhesives/Coatings/Extrusions

Division Announces Honors

The Polymers, Laminations and Coatings Division honors two people each year with prestigious division awards. In 2001, the winner of the Division Leadership and Service Award with the accompanying Andreas Ahlbrandt Prize endowed by Enercon Industries, Inc. is Louis W. Piffer of Egan Davis-Standard Corporation. He has been very active in the Extrusion Coating Committee of the Polymers, Laminations and Coatings Division. In this capacity, he has presented numerous papers, led the extrusion primer sessions, and participated in panel discussions at division conferences.

Piffer chaired the Extrusion Coating Short Course offered by the division in 2001. In earlier years, he was a speaker at this short course. He was also the Extrusion Coating Committee secretary during 2000 and chaired the International Planning Subcommittee of the division from 1997 to 1999. Piffer conceived the idea for a CD-ROM for the proceedings of the Polymers, Laminations and Coatings Conferences for 1995-1999 and implemented the idea.

Piffer received a BS degree in chemical engineering from Drexel University in 1985. He has been with Egan Davis-Standard since 1989 as senior sales engineer. In 1998, he received the President's Award from his employer.

Robert Moeller of Black Clawson Converting Machinery LLC is the winner of the Division Technical Award and Sam Zweig Prize originally endowed by Morton International. Moeller is product manager of cast film systems. He has been with this organization for 22 years and was vice president of technology for a start-up converting company, Great Lakes Technology.

Moeller received a BS degree in Engineering Technology from Rochester Institute of Technology. While at Black Clawson, he received three patents for his innovative work. Two involved winding technology and the other concerned chill roll technology. Assisting cast film and extrusion coating companies in designing the equipment that provides a competitive edge is Moeller's niche.

As a product manager, Moeller has been involved in the design and startup of more than 125 machine lines for cast film and extrusion coating. While most people have an area of expertise such as screw design, winding, or controls, Bob Moeller has an immense understanding of how the entire process system works. Many leaders in the production of flexible packaging, stretch film, packaging films, and similar areas rely on Moeller's knowledge and expertise to apply machinery to make higher quality products faster and more economically. People know his creative problem solving techniques from Wisconsin to Malaysia to Chile to

In his spare time, Moeller is an avid snowmobiler. He also enjoys fishing, boating, and camping at a location in the Thousand Islands.

Piffer and Moeller join a distinguished list of previous winners. Earlier winners of the Leadership and Service Award were as follows:

1987 Walter E. Groedel
1988 Earl W. Veazey
1989 Thomas Bezigian
1990 John V. Benham
1991 David J. Bentley, Jr.
1992 Ronald B. Schultz
1993 Rhonda R. Nichols
1994 David A. Markgraf
1995 Russell H. Scamm
1996 Gary D. jerdee
1997 Richard W. Halle
1998 Thomas I Butler
1999 Ashok M. Adur
2000 Scott E. Marks

Previous Technical Award winners were as follows:

1967 V. T. Stannett
1968 Kenneth W. Britt
1969 Horace A. Spener
1970 Edwin C. Jahn
1971 Charles S. Maxwell
1972 T. A. Howells
1973 James J. Forsythe
1975 Robert T. Van Ness
1976 Alex Trofimow
1978 C. L. Hazelton
1979 Peter A. Yurcick
1981 J. Robert Wagner
1984 Morton Levine
1985 D. J. Smith
1986 Daniel Siegel
1987 Ken T. Thompson
1988 Alan A. Whillock
1989 Richard T. E. Sylvester
1990 Dragan Djordjevic
1991 Ray Edwards
1992 Robert E. Gregory
1993 Earl W. Veazey
1994 Alister M. Soutar
1995 Fred M. Singer
1996 Thomas I. Butler
1997 Bruce W. Foster
1998 George E. Ealer
1999 George Schroeder
2001 Peter F. Cloeren, Jr.

Growth Opportunities For The Division

by Jim Cooper

At the end of August 2000, I will become the Chairperson for the Polymers, Laminations and Coatings Division of TAPPI. I have the unenviable task of following a host of very dedicated and talented individuals such as John Perdikoulias, Gary Jerdee, Jeff Siegel, and John Benham. As John Perdikoulias mentioned in an article in “the PLACE” in December 2000, TAPPI is undergoing significant changes. Our division is also going to embark on momentous changes. At the division meeting in August, the group will undoubtedly change its name to feature PLACE an acronym for Polymers, Laminations, Adhesives, Coatings, and Extrusion. The division's new publication in Paper, Film and Foil CONVERTER is “the PLACE.” Changing the division name to parallel the publication will give the group a very easily understood and recognized brand.

Many members of the Polymers, Laminations and Coatings Division and especially the Marketing Committee of the division are trying to determine who comes to our conferences and short courses, how many of these people are newcomers, how many newcomers return to subsequent events, and the job function for each attendee. If the division can understand what draws people to division activities, it can concentrate on attractions to increase attendance and draw additional converters and end users. The format for our conference continues to change to address the preferences of the attendees. In this regard, I especially want to recognize the outstanding job that Harry Cordatos has done as Technical Program Chairman. The conference he has assembled for 2001 will be outstanding. Some features include a keynote address, “Fick's Second Law Or Diffusion for Dummies,” by Dr. Edward L. Cussler, University of Minnesota; Converter Panel Discussion; New Technology Showcase; and Flexible Packaging Case Studies An Interactive Workshop.

Another activity that received excellent response from attendees at the Polymers, Laminations and Coatings Conference in 2000 was the Gala Event. Gary Jerdee, Bruce Foster, and Jean Foster were instrumental in the plans for that event and are coordinating the function again in 2001. Using our new acronym, this event will also be the PLACE-Pool Lua At Conference End. Plan to attend the conference in San Diego and network with your peers in the industry at the Luau!

The Polymers, Laminations and Coatings Division has been publishing “the PLACE” in Paper, Film and Foil CONVERTER for one year. During that period, we have communicated division news and activities to suppliers, converters, and end users in the flexible packaging and converting industries. The publication has also given readers expanded summaries of technical papers presented at division sponsored events. We know that “the PLACE” has spread the word about our division and its activities to readers globally. Increases in attendance at division events will definitely rise consequently.

In closing, I want to acknowledge the TAPPI staff for their continued support and dedication to our division. Bill Stafford, Karen Van Duren, and Shirley Barton have done an excellent job to support our activities. If you have any questions about the Polymers, Laminations and Coatings Division and its conference or activities, please telephone me at 979-238-1123 or send me an e-mail at jlcooper@dow.com. I look forward to hearing from you or meeting you at a division function.

Fundamentals Of Roll Coating For Hot Melt Application

by Bob Dages
Kroenert Corp.
email:
bdages@kroenert.com

Application: Roll coating of hot melt products provides flexibility for products with a wide range of viscosities. The technique allows a balance of viscosity with coating weight control, speed, width, and other operating parameters.

Two general categories characterize the use of roll coaters for hot melts. The first involves the low viscosity, low melting point waxes used for wet bonding of materials or sealing of porous substrates. Application of these materials usually uses a dip and meter or kiss coating method. Today, such applications are few because the market has shifted toward film technologies for barrier applications.

The second general family of hot melts for roll application includes the materials commonly used for pressure sensitive adhesive applications, insulating foams, asphalt, and other materials that typically have a viscosity of a few thousand centipoises or higher. Purchasers of hot melt coating processes often ask why someone would choose a roll coater rather than a die application method. The impetus for roll coating lies in a desire for flexibility. A roll coater can provide faster changeover in deckling and chemistry. In addition, coating weight changes and stripe coating are easier with roll coating. For coating weights above 15 g/m2 and for applications that can sustain occasional small pinholes or structuring in the coating, roll coating will provide an optimum solution if the user needs flexibility.

Figure 1 (on page 66) shows a typical roll coating line. The system involves a face stock unwind at the top, right hand unwind, a liner unwind at the far left of the drawing, and a laminate winder at the bottom right of the drawing. The liner material unwind is side shifting to provide consistent alignment with the coating station deckling devices. This prevents over coating at the edge of the material. Critical elements are the tension isolating pull rolls that set the web tension in the coating nip. Beyond the coating nip is an ultraviolet (UV) curing station followed by a cooling roll or laminator. At this point, the face stock combines to the adhesive coated liner and proceeds to the winder.

Note that the systems are compatible for use with cooling or with UV curing. A crosslinking system requires orienting the web with the UV source above the coated web. In this way, tension losses do not cause the coating to foul the UV sources. When coating a thermal setting material, only the cooling roll is necessary. Switching the liner and face stock unwind positions and moving the cooling roll to a position below and to the left of the coating station changes the web path. The liner web travel is then in the opposite direction through the coating station.

Behind the coating line is the melting equipment. Recently developed acrylics often use melting and transfer through an extrusion system. For low volume requirements, drum or grid melters have use. The ideal arrangement will provide a smooth flow rate and a minimal history at elevated temperature. The roll coater has a reservoir of coating above the application point. It can tolerate some variation in the supply rate since the application rate to the web is independent of the pumping rate. A reservoir also has use as a support frame to support deckling wipes. The reservoir is above a fixed metering roll and an applicator roll.

Direct Roll Coating

A hot melt roll coating system can use various coating methods. In these methods, each roll of the system has a specific function. The most common system is the direct roll coating method. In this method, the coating transfers directly from the applicator roll to the web. The direction of rotation of the transfer roll is the same direction as the web travel. The coating is in a pond between and above the nip formed by the metering roll and the applicator roll. Edge dams on the side contain it and determine the width of the wetted surface. Two factors determine coating weight:

  • The gap between the metering roll and the applicator roll
  • The speed of the web (backing roll speed) relative to the applicator roll speed.

The first element, gap dimension, can vary to the limit the coating will bridge in the meter to applicator roll gap. Final determination depends on the desired coating weight and the ability of the coating to withstand the stretching that will occur when using a speed differential between the applicator roll and the web.

For example, assume the target coating weight is 100 g/m2 and 1 micron of coating thickness yields 1 g/m2. Starting with a gap of 400 microns means stretching the film to 0.25 its original thickness. This gives a 4 to 1 speed differential. Coating weight is therefore equal to the gap times the applicator roll speed divided by the web speed.

The gap has a limitation on the narrow end by the required coating weight variation. Coating weight variation is a function of the sum of roll runout (variation of the gap dimension) divided by gap dimension. Maximizing the gap and minimizing the roll runout therefore minimizes the coating weight variation. Practical limits do exist regarding the degree that roll runout can be minimized. On a 10-in. diameter roll for example, one-half of one-ten-thousandth of one inch (0.00005 in.) is possible on a grinder but may not be possible in a production environment. A practical limitation is 0.0001 in. Other schemes can achieve less coating weight variation. These include roll skewing and tandem bearing sets.

Roll skewing can improve precision when variation is symmetrical about the cross machine center line. The roll coater uses a device that varies the cross machine gap relationship between the applicator and metering rolls. Skewing occurs by tilting the metering roll from a level position relative to the applicator roll. This method cannot be zone controlled or coupled with a gauge and can give only an averaged improvement over the width of the material. Tandem bearing sets can minimize runout due to bearings. This requires the critical rolls to have two sets of bearings. Each bearing runout is measured and marked. The bearings are paired for installation with the runouts at 180 degree opposition. This method assures the runouts are mutually offsetting for minimum gap variation.

Other sources of variation include deflection of the backing roll in the nip between the applicator roll and the web and roll diameter variation due to temperature variation in the applicator roll and web nip. Supplying a support roll beneath the backing roll can manage both conditions. This roll supplies the structural integrity required to withstand the high forces at the nip. Cooling this roll carries away heat that may cause localized temperature increases on the surface of the rolls. Metering and applicator rolls have heating capability systems that maintain very small temperature differentials of ± 1°F across the surface of the rolls.

Management of speed differential and the gap give an operator the ability to achieve coating weights with low variations. Like any coating scenario, this is true for certain combinations of coating speed, rheology, and coating weight. Cases may exist when higher speeds or lower coat weights may render the operator incapable of achieving a desired coating finish with the two roll direct system. When transfer coating in the forward and direct method, forward film splitting may leave ridges in the coating profile in the machine direction. The alternatives are use of a three-roll indirect system or a reverse system.

Reverse Roll Coating

In this case, the applicator roll rotates in the direction opposing the web travel. Coating weight control depends on the gap setting between the applicator and metering rolls. The speed differential employed between the applicator roll and the web is very small approximately 1%. The applicator roll rotates at a speed greater than the web speed. This arrangement provides the optimum finish on the coating but has a limitation for higher coat weights only due to the lack of ability to offset the speeds

Three-Roll Coating

The next possibility is the three-roll system. This is a compromise of the previous two methods. It incorporates an intermediate roll allowing for a second film stretch. This therefore enhances the ability of the coating to stretch without detriment to the finished product. Achieving a 10 to 1 film stretch with this arrangement is possible. The technique has use where the lowest coat weights are necessary.

Stripe coating is also possible with this arrangement. In this case, roll coating can achieve a machine direction stripe pattern by an indirect roll transfer capability. This method uses deckling wipes positioned and sized according to the desired stripe. The coating wipes from the intermediate transfer roller and transfers to the applicator in a direct reflection of the desired stripe pattern. The applicator roll then transfers the hot melt to the web. Unused hot melt returns to the reservoir pond above the nip. The stripe scrapers typically use a high temperature polymer that is often the same material as the edge deckling wipes. The edge wipes and the reservoir end dams are the same devices. Their location is on a frame mounted over the reservoir box.

Operating Parameters

All the previously mentioned configurations are possible on a single machine frame. They can be adapted in a brief time depending upon application needs. In addition, an operator can also configure for a die applicator. The machine configurations described have had successful use for adhesives, foams, epoxies, asphalts, carbon loaded binders, and several other materials. Table I notes the application limits of the processes.

Note that each parameter described in the table complements the other parameters. The combinations create an operating window for a process. For example, a system coating 15 lb/ream of 10,000-cps material at 1,300 ft/min. may sacrifice some speed for additional coating weight. The direct method of roll coating with an intermediate roll can coat as low as 8 g/m2 up to 100 g/m2. The reverse roll method can apply higher coating weights, but it suffers at the low end of the coating weight range. It can apply from 25 to 500 g/m2. The roll coater can deliver hot melts and resins from 2,000 cps up to 250,000 cps. Higher viscosity coatings have used reduced speeds. One application of a 500,000-cps material had a speed of 20 ft/min. Roll coating techniques have operated successfully at speeds of 1,300 ft/min.

As previously discussed, the coating weight tolerance is variable and depends on such factors as speed, width, and weight. Considering the original equipment manufacturer's perspective, a safe tolerance is ± 5% on 20 g/m2 at 300 m/min. for a 2-m machine. A specialized machine can achieve 0.5% running at 100 m/min. while applying 30 g/m2 on a 1-m wide platform.

Some aspects of the machine such as cleaning time, changeover time, and maximum speed depend on localized capabilities. Nevertheless, the units are flexible and easy to operate and maintain.

A limiting factor is often the ability of an operation to melt and supply the hot melt practically at high application rates involving some combination of width, speed, and coating weight. A match of the hot melt application capacity with downstream processes often leads an operation to purchase a process that is run at less than the maximum operating speed. For example, a 48-in. wide hot melt pressure sensitive adhesive coater and laminator can supply several narrow width printers.

TABLE I - ROLL COATING OPERATION PARAMETERS
Substrates Paper, foil, and nonextensible films
Coating weight 17 to 100 g/m2 is ideal but 8 to 500 g/m2 is possible
Viscosity 2,000 to 250,000 cps
Width Up to 2.1 m
Gap Variable up to 0.5 mm
Coating finish Can provide a textured surface
Short runs Easy to clean and change width
Coating tolerance ± 5% on 20 g/m2
Stripe coating Yes
Speed 400 m/min.

Conclusion

Roll coating is an excellent technique for application of hot melt products in applications involving pressure sensitive adhesives, insulating foams, and other materials. Such hot melts can have viscosities ranging from a few thousand centipoises to considerably higher. Roll coaters can handle this entire range and provide additional advantages in flexibility to include rapid changeover, stripe coating, etc.

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 dbentley@unm.edu.

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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