PFFC - November 2007 - (Page 54) E X E C U T I V E S U M M A RY New Metering Pump Technology For Laminating Adhesives uses linear motion as opposed to rotary motion to move fluid. A LDP by Bruce Menk APPLICATION: A linear displacement pump can process one, two, and three component solvent borne, aqueous, and solventless adhesives. A new metering pump technology will handle one, two, and three component adhesives that are available in solvent or water or solventless. The technology uses a linear displacement pump (LDP). This is a double-acting, positive displacement, continuous flow, rod displacement pump driven by PLC controlled DC servo motors. The systems have wide ranging dispensing parameters. This paper discusses the comparative advantages of an LDP design, control features, dispensing parameters, and economic efficiencies of operation versus batch processing. Typical plural component dispensing systems in use today incorporate fluid metering devices such as piston pumps, gear pumps, flow meters, or progressive cavity pumps. The metering accuracy of these pumps can be affected by wear, viscosity variations, and phasing issues. A “clean slate” approach to fluid metering with a new pump design and control system overcomes limitations of other fluid metering pumps. A linear displacement pump is a positive displacement pump that implementation features a volumetrically accurate double-acting continuous flow rod pump. This has two sets of fluid cylinders where a center carriage plate reciprocates between the top and bottom plates driven by a ball screw. One set of cylinders is mounted on the top of the carriage plate, and one set of pump rods is mounted on the bottom of the carriage plate. As the carriage traverses down, the bottom set of cylinders are dispensing while the top set of cylinders are filling. When the pump reciprocates to traverse in the up direction, the top set of cylinders are dispensing while the bottom set of cylinders are filling. A linear transducer provides pump position feedback allowing an automation control device to reverse the pump at the end of each stroke. Integral to the operation of this LDP is a crossover valve or 4-way switching valve. A crossover valve directs fluid to and from the cylinder sets. In this LDP implementation, each set of cylinders is filled and dispensed from a single port. This design eliminates the use of check valves generally found in pumps featuring separate fill and dispense ports. When the LDP changes direction, the pneumatically actuated crossover valve switches the fill/dispense function of each cylinder set. E X E C U T I V E S U M M A RY Polyethylene Co-extruded Blown Film: Layer Arrangements For Optimum Optics And Stiffness by Lou Mele and Wen Lin, NOVA Chemicals APPLICATION: Layer arrangements influence the optical and tensile properties of three- layer polyethylene film structures. The blown film coextrusion process provides the opportunity to create film structures with optical and physical properties that typically could not be achieved in monolayer structures alone. A study evaluated the effect of layer arrangements on the optical and tensile properties of three-layer polyethylene film structures. Raman spectroscopy and atomic force microscopy (AFM) were used in an attempt to evaluate the hypotheses generated in a previous study and to establish a better understanding of the mechanism that contributed to the combination of good optical and stiffness properties. Good correlation between surface roughness and surface haze was observed, and the mechanism of the improvement on the optical properties was confirmed. An optimal layer arrangement was found and applied in the co-extruded blown films with LLDPE, LDPE, and HDPE blends. A recommendation was presented on materials selection and structure design that would give optimum optics and stiffness for the multilayer co-extruded films. Receive technical information delivered to your computer every other Monday from TAPPI’s PLACE Division. Subscribe on-line at www. tappi.org by selecting “Newsletters” under the Publications/Bookstore heading. ePLACE Electronic Newsletter The exceptional growth in the flexible packaging industry is fueled by form as much as function. Considerations regarding package appearance and texture are as important as product protection in garnering consumer attention today. In addition to high quality print and graphics, packages are also required to sparkle, shine, and stand up. The versatility of polyethylene is well suited to today’s complex packaging structures. It performs especially well in co-extrusions where available grades can provide the necessary toughness, heat-seal, stiffness, and optical properties. Previous studies have shown that the layer arrangement has a significant effect on the optical properties of co-extruded film, and the mechanism was speculated upon two hypotheses. Special crystalline structures (i.e. transcrystalline structure) are formed on the interfaces between each layer within the co-extruded film which have an impact on the overall optical properties. The roughness of the outside surface layer is solely responsible for the optical properties. The velocity profile at the die exit of the outside layer varies as layer distribution changes and consequently changes the surface roughness of the co-extruded film. In the first part of this paper, experiments were undertaken on a microstructure level aimied at better understanding the mechanisms and verifying the hypotheses. Based on the results, a variety of three-layer co-extruded films were made using linear low density polyethylene (LLDPE), high density polyethylene (HDPE), and low density polyethylene (LDPE) in an attempt to obtain optimal performance with respect to both optical and mechanical properties. This study of the impact of layer arrangement on the optical properties of polyethylene three-layer film has confirmed that the roughness of the outside surface layer is primarily responsible for the optical properties of co-extruded multilayer films. To obtain the complete version of these papers, go to www.tappi.org, and select “the PLACE” under the Publications/Bookstore heading. 54 | NOVEMBER 2007 Submit manuscripts for publication to dbentley@tappi.org. 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