A completely new layer multiplier enables producers of cast film and sheet to obtain the substantial property enhancements of microlayer structures yet is easier to deploy, more compact, more accurate, and far more versatile than any other layer multiplier system, including one previously offered by EDI, the company announced today. The advanced layer multiplier was developed by EDI engineers and is available to purchasers without licensing or royalties. Tooling based on the new design can be supplied for applications over a large range of widths and has been used successfully for a 171 inches (4.3 m) product, according to Gary D. Oliver, vice president of technology. The system can be engineered to multiply materials from 3, 5, 7, 9 or more melt streams. As an example of the compactness and productivity of the system, Oliver cited the case of a layer multiplier for a product with a total of 84 microlayers. The tool consists of a series of four components: a 5 layer coextrusion feedblock, two multiplier modules, and another five-layer feedblock. The length of the tool is only 24 in. (609 mm), representing the total distance from the inlet of the polymer streams into the tool to the exit of the multiplied structure. The tool is being used at a typical line speed of 1,000 lb. (454 kg). “This compactness of EDI’s new layer multiplier is absolutely critical for maintaining streamlined flow, developing layer uniformity, and adapting to normal variations in material viscosity or extrusion rate,” said Oliver. “Some competing layer multipliers involve massive tools with long flow paths that compromise layer uniformity, limit adaptability, and multiply materials from a limited number of melt streams.” One factor in the compactness of the new EDI system is the development of a new version of the company’s Ultraflow® IV feedblock. A five-layer feedblock of this type is now only 6 in. (152 mm) long, one-third the size of the earlier version. The new layer-multiplier tooling can be installed in an existing extrusion line with only minor modifications, Oliver noted. The downtime required for cleaning out the system can be as little as four hours, as compared with a much longer period—as much as a week—with other systems.
As in standard coextrusion, multiple streams of molten polymer enter the layer multiplier system by going through a feedblock, which produces a conventionally sized (4 by ¾ in., or 102 by 19 mm) “sandwich” of three, five, or seven layers. The materials in this structure are subsequently multiplied in EDI’s proprietary layer multiplier modules. Finally, the resulting microlayer product enters a second feedblock, which produces another conventionally sized sandwich that passes into the manifold of a flat die, where the structure is expanded to the target product width. The finished product has a standard thickness, yet its internal structure can consist of many—even hundreds—of microlayers. EDI’s system can be used to multiply selected melt streams or all of the streams entering the system.
While layer-multiplied film and sheet are no thicker than their conventional counterparts, the multiplicity of microlayers in their internal structure generates synergistic effects that result in improved mechanical and barrier properties.
EDI has more experience with layer multiplier technology than any flat die builder, noted Oliver, beginning with work carried out under a U.S. Defense Department contract for developing long-shelf-life containers for military food supplies. Subsequently EDI continued its own development work on layer multiplication, drawing on the resources of its process laboratories at Chippewa Falls, WI, and on cooperative projects with extrusion processors in packaging and other markets. “We have done more research and product development in the field of layer multiplication than any other company in the world,” Oliver said.