Coextrusion: making the equipment fit the need

Published: July 01, 1996, By Boyle, Edward

Suppliers of coextrusion equipment keep moving forward to meet the needs of converters who are facing their own tough customers.

As with their counterparts in virtually every other segment of the converting industry, suppliers of coextruded film are facing ever-greater customer demands for product quality, price, and delivery times. And, they're turning to their equipment suppliers to help meet those demands.

The challenge, says William Hellmuth, senior product manager/blown film systems for Battenfeld Gloucester Engineering, is that priorities among converters of coextruded films vary. Some emphasize line speed; some consider film clarity a priority. But all want "a better film."

"It really all goes back to the individual customer," explains Hellmuth. "We do an awful lot of custom machines. Some customers push some heavy film output rates, others are pushing optical properties, like clarity. Of course, there's always a push for lighter films and source reduction. You always end up uncovering the bottleneck at some point."

Test Lines Mimic the Real Thing

Wayne Machine & Die Co. specializes in producing small coextrusion systems (up to 24 in. wide) that are used for test runs of various film types. Operations manager Dr. Joseph Scuralli says that customers are demanding as much from manufacturers of lab-type equipment as they are from makers of larger coextrusion equipment.

"Years ago when somebody said they wanted a lab test film line, it was a simple thing," he explains. "Now they want that line to be exactly like the larger ones, with air knifes, scrap winders, edge-trimming systems - everything that's used to make precision film. That's because a lot of people are facing greater demands as far as performance. They're being asked to bring together a lot of different plastics to satisfy their customers, and it's getting more and more difficult for these people."

In response to customer demand, Wayne Machine recently introduced its first coextrusion cast film system, the Yellow Jacket Turnkey system for the production of multilayer cast film from 8 to 24 in. wide. The versatile system is able to produce cast films from a single layer up to seven layers in all types of layer structures utilizing a wide range of thermoplastics and barrier materials.

The Yellow Jacket lines are supplied complete, including extruders, reconfigurable feedblock combining adaptor, flexible lip flat die, cast film takeoff with chill roll, air/vacuum knife, edge pinning, edge trim, torque winder, and dual-reel scrap take-up. The systems can be supplied with one control panel, with optional microprocessor programmable logic control, or with separate controls.

Wayne Machine, which has produced coextruded sheet film lines for much of its 38-year history, reports that its customers have recently seen a need for smaller, test-run-sized equipment for cast films as well. Now, says Scuralli, those companies can develop new products "with small amounts of material in small amounts of time."

Metallocenes Make Their Mark

Andrew Wheeler, sales manager of extrusion systems for Windmoeller & Hoelscher Corp., says that one of the biggest developments in the extrusion process involves not equipment but raw material called "metallocenes" that he says are "probably the biggest development since LLDPE [linear low-density polyethylene]."

"The strength and clarity properties of metallocenes will enable manufacturers to make products thinner, stronger, and with better optical properties than was ever thought possible," says Wheeler. They are also more efficient to extrude than more standard polyolefins, he adds.

However, warns Wheeler, not all extrusion equipment can run metallocenes trouble-free. In fact, he says, "a lot of people are not able to run them." Variables such as screw design, temperature, and shear can all adversely affect the finished film. If metallocenes are overheated, for example, the material becomes more viscous, and output drops dramatically.

According to Wheeler, Windmoeller & Hoelscher equipment can convert the revolutionary raw material without change. In fact, says Wheeler, W&H was the only exhibitor at the K'95 converting show [held in October 1995] to run the material.

"Metallocenes are allowing people to use materials they might not have been able to use before, with increased strength and clarity," notes Wheeler. "They are making a fairly big impact on the industry."

Windmoeller & Hoelscher offers equipment ranging from the most basic line for monolayer film to high-tech systems for six-layer coextruded barrier films in widths of 32 to 130 in.

The company's most recent innovation is the fully automated Varex[R] blown film extrusion line for the production of up to six-layer barrier film for grocery packaging applications. The heart of the Varex system is the newly developed five-layer die head, type B 400/500/5-ZIK-P-2, featuring the patented Optifil[R] P-2 automatic die.

Based on the company's extensive experience with three-layer systems, the new die was developed to meet the specific requirements of five-layer blown film extrusion, which is achieved using a variety of features, including computer-circulated spiral mandrel distributors, which keep pressure losses to a minimum even in small-volume production; a predistributor system with thermal separation of individual melt flows and separate heating; and a central cooling air supply for internal air exchange.

The Optifil P-2 automatic film gauge control ensures minimum film tolerances by precisely controlling melt temperatures before the film exits the die.

Unique Approach is Developed

Extrusion Dies Inc. (EDI) recently developed the Multiflow V manifold design for the advancement of flat coating, film, and sheet coextrusion applications. Don Garton, EDI's director of engineering, notes that the design of the new system is so unique that it was recently granted a patent.

Among the unique features of the system, says Garton, is a straight body back line in place of the angular configuration utilized in most coathanger manifold designs. This approach promotes uniform die body deflection, which minimizes polymer flow distribution changes in applications where polymer flow rate changes are required.

The EDI Multiflow V manifold design incorporates an elongated manifold cross section, with an increasing aspect ratio, which reduces the shear level in the back of the manifold, reducing the amount of interface distortion that is promoted by the manifold design.

In addition, Garton notes that the EDI unit design utilizes a cubic or nonliner preland/manifold interface that will produce a more uniform polymer flow distribution pattern.

To complement the Multiflow V manifold design, EDI also has developed the Ultraflow 1S coextrusion feedblock design that can be utilized in one, two, or three extruders to produce coextruded structures of one, two, or three layers. The design is unique, says Garton, because all of the flow channels are always in use, no matter how many polymer layers are being produced or what the structure configuration is.

"This characteristic," says Garton, "ensures that there is never a stagnant flow channel where carbon deposits may grow and later 'flush' into the system when the configuration is changed."

Bob Moeller, product manager of extrusion systems at Black Clawson, says his company includes EDI feedblock dies in its extrusion systems because of their efficient, clean-running nature, especially when using internally deckled dies.

"We're finding more of a need for a streamlined flow path to the die, and the feedblock can be a major point of hangups in some cases," says Moeller. "We have to eliminate any dead hang-up areas resulting from crust that develops on the edge trim during extrusion. With the developments and advances in the internal die and running trimless film on the edges, streamlined flow paths are a major advance. This block that EDI offers has that advantage. There are also some flow inserts from Claremont that help reduce some of the slow-flow problem."

Dies with Advanced Design

Filmaster Inc. has developed multilayered blown film coextrusion dies with an advanced design for streamlined flow of polymers. The company recently patented a low-pressure spiral die that can be changed to a spider pin without spirals. This allows the die to process heat-sensitive polymers, such as nylon, HDPE, LLDPE, ethylene vinyl alcohol (EVOH), polypropylene (PP), and PETG (a form of polyester), that require minimal residence time. The die also protects sensitive polymers with flow splitters (foil spacers) that eliminate stagnation and flow bushings that reduce back pressure and die shear.

Free ports on the Filmaster coextrusion dies are constructed at a flow angle that minimizes pressure drop, resistance, and die shear, resulting in a streamlined flow of extrudate. Newly patented design features also can be incorporated for the successful processing of ultra-sensitive polymers that reportedly may be destroyed in traditional die constructions.

In addition, Filmaster has introduced the 2+2 Dual Lip Northeaster air ring that is said to deliver ultimate bubble stability and higher outputs. The equipment allows precise and independent air control from both the lower and upper lips.

Winding at High Speeds

Battenfeld Gloucester recently introduced the Model 1002DS winder, said to be the world's fastest in-line slitter/winder for extrusion lines. It features an overlapping turret design with cantilevered swing-out shafts; a servo-driven turret index for rapid, precise, and repeatable positioning; AC flux vector spindle drives that provide better speed regulation and reduced maintenance compared with DC drives; a lay-on roll of composite material construction for reduced mass; and electrostatic transfer, eliminating adhesives and lowering operating costs. By utilizing narrower shaft widths, the Model 1002DS attains higher speeds due to a significant increase in the critical frequency of the shaft in comparison to a five-up, 20-in. line, reports the company.

These and other innovations, suppliers say, will continue to result in overall increases in production speed, product quality - or whatever priorities the film converter may emphasize.

"Everybody is a little bit different," says Battenfeld's Hellmuth. "In order to get a competitive edge, each one of our customers wants to have a different angle. That's what makes the industry and the job interesting."

Supplier Information:

Battenfeld Gloucester Engineering Co. Inc., Gloucester, MA; ph: 508/281-1800; fax: 508/283-9206. Circle 269.

Wayne Machine & Die Co., Totawa, NJ; ph: 201/256-7374; fax: 201/256-1778. Circle 270.

Windmoeller & Hoelscher Corp., Lincoln, RI; ph: 401/333-2770; fax: 401/333-6491. Extrusion Dies Inc., Chippewa Falls, WI; ph: 715/726-1201; fax: 715/726-2205. Circle 272.

Black Clawson Converting Machinery Corp., Fulton, NY; ph: 315/598-7121; fax: 315/593-0396. Circle 273.

Claremont Polymer Shapes Inc., Claremont Ont., Canada; ph: 416/649-2777; fax: 416/649-3795. Circle 274.

Filmaster Inc., Parsippany, NJ; ph: 201/263-4848; fax: 201/263-4888. Circle 275.