Basic Production Techniques of Polymer Films

The procedures for obtaining films from melts, including extrusion, calendering, molding, casting of polymer solutions and latexes, planing and rolling of 

Extrusion is widely applicable in production of films from thermoplastics. The polymers used in this process should be resistant to thermal-oxidative failure on transition to the viscous-flow state. The heads of the extruders are equipped with either annular or planar slits. 

Hose extrusion includes forcing of the polymer melt through the annular slit of the extrusion head, pneumatic blowing of the hose, folding and removal in vertical or horizontal direction. This method produces biaxial films with perfect physical-mechanical characteristics, it is rather simple and economical, and is suitable for the production of laminated film materials by co-extrusion. 

During plane-slit extrusion the melt leaving the head outlet is rapidly cooled down on cold rollers or in a water bath. Predominantly crystalline polymers are processed by plane-slit extrusion to obtain highly transparent and even thickness films, laminated or combined film materials. Special-purpose devices are needed to attain a uniaxial or biaxial film tension. 

Calendering takes place at a transient temperature between the polymer viscoelastic and viscous-flow states. Thermoplastic materials displaying a wide range of the flow temperatures and sufficient melt viscosity (e.g. PVC) 

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