Processing, thermoplastics film thickness

The paper gives an overview of effects occurring or acoustic treatment of dissolved and molten polymers. Emphasis is made on acoustic cavitation discovered recently not only in low-viscous fluids but also in molten polymers. Major guidelines have been specified for practical utilization of acoustic treatment of flowable polymers in molding intensification of extrusion processes, reduction in thickness of produced films, directed mechanical destruction, chemical activation of melts, etc. Efficiency of overlapping high-frequency vibrations in molding of molten thermoplastics is discussed in terms of power consumption. 

The GMP s process eliminates the use of sheet metal for the skin of the refrigerator door. In this application, the thermoplastic film forms a durable, protective outer skin with a wide choice of color options that are applied directly to the film. In addition more innovations exist apart from the film and thermoplastic interior liner, the doors consist entirely of polyurethane. GMP backs the thermoplastic film with an approximately 4 mm thick layer of the Baydur 110 structural foam polyurethane RIM system from Bayer AG that creates a rigid, dimensionally stable outer shell with no need for sheet metal. Then, GMP fills the space between this shell and the inner liner with insulating polyurethane foam, a rigid, low-density foam. The result is a self-supporting door that satisfies all stability, thermal insulation, and surface finish requirements. 

Film blowing (blown-film extrusion). The process of forming thermoplastic film wherein an extruded plastic tube is continuously inflated by internal air pressure, cooled, collapsed by rolls, and subsequently wound into rolls on thick cardboard cores. The tube is usually extruded vertically upward, and air is admitted through a passage in the center of the die as the molten tube emerges from the die. An air... 

Blowing and casting are the main processes used industrially for making films from thermoplastic polymers. Blown films are mostly used for food and rubbish bags. A blown film is extruded as a tube and the tube is filled with air to expand it to the desired size [88]. The film is then cooled, flattened and extruded again over an isolated bubble of air. Typical film thicknesses are 0.007-0.125 mm. High melt viscosity resin is required for processing a blown film so that the melt can be pulled upward from the die [88]. 

Liquid crystalline polymers [326,329-336] have found application as high modulus fibers and films with unique properties due to the formation of ordered lyotropic solutions or thermotropic melts which transform easily into highly oriented, extended chain structures in the soUd state. Thermotropic polymers are melt process-able and thick extrudates and molded parts are formed with high strength characteristics as in fiber reinforced thermoplastics. 

The volume of thermosetting powders sold exceeds that of thermoplastics by a wide margin. Thermoplastic resins are almost synonymous with fluidized-bed appHed thick-film functional coatings whereas thermosetting powders are used almost exclusively in electrostatic spray processes and appHed as thin-film decorative coatings. 

Polymer thick films also perform conductor, resistor, and dielectric functions, but here the polymeric resins remain an integral part after curing. Owing to the relatively low (120—165°C) processing temperatures, both plastic and ceramic substrates can be used, leading to overall low costs in materials and fabrication. A common conductive composition for flexible membrane switches in touch keyboards uses fine silver particles in a thermoplastic or thermoset polymeric binder. 

MOLDING/METALLIZATION. Molded thermoplastic circuit board substrates may be rendered selectively conductive by several additive process techniques including conductive polymeric thick film inks (PTF), and semi and fully additive electroless/electrolytic platings. Of the various chemical process methods developed to produce circuitry on a molded plastic substrate, one method practiced by Pathtek, A Kodak Company, combines both "catalytic" and "non-catalytic" resins in a highly automated commercialized two-shot molding/selective metallization process. 

Miscellaneous Extrusion-Applied Polymers. As mentioned earlier, there is a tendency to develop solventless magnet wire enamel formulations, and extrudable polymer systems would fulfill that requirement. There have been reports about extrusion of thin coatings of polyesters over copper wire. At this point, the state of the art allows extrusion of thin insulating films only with thermoplastic materials. The reliable extrusion of uniform and concentric insulating films of approximately 0.001-0.002 in. wall thickness is already an improvement over the more traditional extrusions of polyethylene, poly(vinyl chloride), and several fluoropolymers in much greater wall thicknesses. Because cross-linked insulation is ultimately required for most magnet wire applications, further materials development needs to be done to provide polymer compositions that are both extrudable as thin films and can be cross-linked in an economical process suitable for large-scale industrial application. 

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