Fluoropolymer Film Extrusion

Monoaxially and biaxially oriented films of fluoropolymer are made by melt extrusion of the resin into flat webs or tubes. The main function of orientation is to enhance the mechanical properties of the film such as tensile break strength and tear resistance. The decision to orient is usually made according to the requirements of the end use for mechanical properties. All process surfaces that contact molten fluoropolymers must be corrosion resistant because of the formation of corrosive compounds such as HF and HCl from the high-temperature degradation of these plastics. 

The die is designed such that the channels restrict the melt flow in a way that all the melt experiences the same amount of shear. The distance of travel is equalized by the restraints designed in the flow channels. The net effect is equal flow rates at the 

Films and sheets of various fluoropol5miers can be produced by different film formation techniques. Processing methods are described for some of these films. 

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Uses Melt-processable fluoropolymer for extrusion (wire coating, tubing, film), inj. molding, blow molding, compr. molding, rotomolding, electrostatic coating, industrial... 

Fluoropolymer-based additives are very useful, offering low temperature processability, chemical resistance, weatherability, self-extinguishing, and flexibility. Available as powders, pellets, dispersions or master batch concentrate (at additions of 250-1000 ppm), they are designed for use in PO film extrusion to eliminate melt fracture or problems arising from die build-up when running PO polymer with fillers and pigments [17, 59]. 

Almost every fluoropolymer is converted into high performance films by melt extrusion. The films have unique combinations of properties that include high temperature resistance, high strength, good chemical resistance, and a variety of specialized properties. Examples and properties of available commercial fluoropolymer films, which include release, one-side adherable, and two-side adherable products, are described in this section. FEP film, used for both lamination and release applications, is specified by ASTM Method D3368, as shown in Table 6.23. Tables 6.24 and 6.25 provide information about FEP film dimensions and properties. Tables 6.26 and 6.27 show the properties of PFA and ETFE films. 

Fiber and filament accounts for a relatively small share of all fluoropolymers extrusion. The principal end products are wire insulation, tubing, film, and sheet. Fluoropolymer films are widely used in release, surface protection, and packaging. Sheet and profile extrusions account for a small share of fluoropolymers consumption. 

The serendipitous discovery of polytetrafluoroethylene (PTFE) in 1938 by Roy J. Plunkett [82] and his co-workers at DuPont research laboratories has spurred the development of a variety of fluorine containing polymers, which include fluorosilicones, fluorinated polyurethanes, fluorinated thermoplastic elastomers, etc.. Many of the commercial fluoropolymers are suitable for melt processing via conventional injection molding, screw extrusion and blown film extrusion techniques. 

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. 

Fluoropolymers Polymers prepared Irom unsaturated fluorine-containing hydrocarbons. Has good chemical resistance, weatherability, thermal stability, antiadhesive properties, low friction, and flammability, but low creep resistance, strength, and difficulty processing. The properties vary with the fluorine content. Processed by extrusion and molding. Used as liners in chemical apparatus, in bearings, films, coatings, and containers. Also called Fluoroplastics. 

For practical purposes there are eight types of fluoropolymers, as summarized in Table F.7. Included in this family of plastics are polytetrafluoroethylene (FIFE), polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride (PVF), fluorinated ethylene propylene (FEP), and others. Depending on which of the fluoropolymers are used, they can be produced as molding materials, extrusion materials, dispersion, film, or tape. Processing of fluoropolymers requires adequate ventilation for the toxic gases (HF) that may be produced. 

Fluoropolymers Forming a non-stick film in extrusion die. to reduce die build-up. avoid sharkskin melt fracture, improve output, less equipment down-time... 

New additives based on fluoropolymers have been introduced by DuPont and by Dyneon, to promote free flowing in polyolefins for extrusion and blown film production. They appear to act by coating the interior surface of the extrusion die with a microscopically thin non-stick film, which reduces friction at the resin/die interface and allows the extrusion compound to flow freely and more rapidly through the die opening. The non-stick properties also prevent accumulation of resin particles at the exit of the die, so eliminating the major cause of die build-up. The coating is continuously renewed by the additive through the extrusion process. 

It is noticeable that the above mechanism is based on studies of fatty acid amides while other slip agents are also used for various purposes related with reduction of coefficient of fnction. Fluoropolymer additives, for example, are used to improve film extmsion in which they act in a similar manner during process as amides act in the final film. Fluoropolymer additive is also not compatible with polymer matrix. During extrusion it migrates to the surface of metal and forms film which has pronounced effect on production parameters. It reduces melt fraction, viscosity, shear rate, and gate pressure. This makes production faster and eneigy use lower. Some of these additives are developed in such a manner that they migrate only in a molten state but are immobilized within material after material solidifies. This makes them essentially absent from the film surface which in some post process operation is an important requirement. ... 

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