Transmission Efficiency of plastic Films Part 1

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Film casting (slit-die extrusion): TRANSMISSION EFFICIENCY OF PLASTIC FILMS Slit-dies for flat film are wide in comparison with the diameter of the extruder head and this means that the flow path to the extreme edges of the die is longer than to the centre. Flow compensation is usually obtained by a manifold die a cross-section of which is shown in Figure. Cross-section of manifold-type dies for film 14
2.5 CALENDARING: TRANSMISSION EFFICIENCY OF PLASTIC FILMS In this process continuous sheet or film is made by passing heat, softened material between two or more rolls. Calendars were originally developed for processing rubber but they are now widely used for producing thermoplastics (mainly flexible PVC) sheet and film. In essence calendaring consists in feeding a plastics mass into the nip between two rolls where it is squeezed into a film that then passes round the remaining rolls. It then emerges as a continuous film the thickness of which is determined by the gap between the last pair of rolls. The surface of the film is determined by that of the last roll and can be glossy matt or embossed. After leaving the calendar the sheet is cooled by passing it over cooling rolls and is then fed through a beta-ray thickness gauge before it is reeled up. The plastics mix fed to the calendar may be a simple hot melt as in the case of polyethylene but with PVC a great deal of effort is put into the pre calendaring processes such as blending, mixing, gelling and straining. In addition to the polymer there may be inert mineral fillers (added to reduce the cost and modify the physical properties), pigments, lubricants (to assist in processing), stabilizers and plasticizers. The dry components (with the exception of the pigment) are loaded into a ribbon blender and agitated sufficiently to produce an even dispersion. If plasticizers are to be added they are sprayed into the powder mix during the initial period of blending. Beta-ray gauge 15
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Page 6 and 7: The strategy for the project, TRANS
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TRANSMISSION EFFICIENCY OF PLASTIC
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4. ANTI-STATIC ADDITIVES TRANSMISSI
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TRANSMISSION EFFICIENCY OF PLASTIC
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Butyl, GRS, polyurethane, neoprene
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Transmission Efficiency of plastic Films Part 1

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