Coextrusion wire-coating

Calculated streamlines in a coextrusion wiring-coating die. (a) viscosity ratio of 0.2 (b) viscosity ratio of 2.0 (c) thickness ratio of 0.3333... 

The flat film and sheet coextrusion analyses mentioned earlier can be easily extended to the treatments of the wire coating and film blowing coextrusion processes. 

Coextrusion permits multiple-layer extrusion of film, sheet, pipes, tubing, profiles, wire coating, and extrusion coating. It is used mostly in packaging applications to obtain desired barrier properties. The process eliminates the need for a laminator for plastic-plastic surfaces, is less expensive, and provides property enhancement. 

Coextrusion is the simultaneous extrusion of two or more polymers through a single die where the polymers are joined together such that they form distinct, well-bonded layers forming a single extruded product. Coextrusion has been applied in film, sheet, tubing, blown film, wire coating, and profile extrusion. 

The common methods of processing LDPE are blown and cast film extrusion and coextrusion, extrusion coating, blow molding, injection molding, rotomolding, and wire extrusion. Explanations for these processes can he found in other articles in the Encyclopedia. 

Coextrusion. Coextrusion technology has been developed in conjunction with new polymers, providing continuously formed layered polymer structures such as the film structures required for flexible packaging. Coextrusion is perhaps the most economical method of combining polymers into functional multilayer products such as films, sheets, profiles, bottles, pipes, and wire coatings. 

Figure 4.36 Flow pattern of two Newtonian fluids in wire-coating coextrusion. Depending on the viscosity ratio, a big vortex can be produced in this die design [88].

Heng, F.L. and Mitsoulis, E. (1989) Numerical simulation of wire-coating coextrusion. Int. Polym. Proc., 4, 44—56. 

Coextrusion is an important technique for producing a well-bonded, multilayer product as sheet, film, tubing, wire coating, and most of the other forms made by conventional extrusion Such structures can be made to combine the properties of the resin used in each layer (e.g, gas barrier capability, moisture resistance, lower cost, chemical resistance, etc.). Because melt flow downstream of the extruder screw is invariably laminar, if two or more polymer streams can be combined as layers in a suitable die system, it is possible for them to emerge from the die in the same... 

MAJOR APPLICATIONS Major applications include blown and cast films for bags, shrink-wrap, packaging, and injection molding. Such films exhibit exceptional toughness, dart impact, and puncture resistance when compared to blown films of LDPE. Other applications include blow molding, pipe and conduit, lamination, coextrusion, rotomolding, and wire and cable coatings. There is considerable use of blends of LLDPE with LDPE in a wide variety of applications. 

Uses Extrusion grade engineering thermoplastic for tubes, industrial hoses, monofilaments, coatings for cable and wire, and for coextrusion with other materials for use as a barrier layer in containment appiics. Features General-purpose Carmine FG [MLG Enterprises]... 

Extrusion and forging are other routes for processing material in particulate form, whilst coextrusion and drawing can be used for coated fiber (wire). In extrusion, a powdered metal and chopped fiber are dispersed, placed in cans and then hot extruded to give a solid bar with aligned fibers. 

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