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Stretch Film

Manufacturing of Blown Film - All blown films, whether Mono (Single Layer) or Co-Extruded (two or more layers) have the granular resin and any additives fed by a heated screw barrel, forcing the molten resin into a circular die. The molten resin is then blown vertically upwards and outwards (commonly called a bubble). The Bubble is gradually cooled by air as it ascends the tower. At the top of the tower the film is nipped together and drawn down to the slitting and winding stations via guide rollers. Blown Film is the preferred manufacturing method to achieve higher Mechanical Properties. The manufacturing costs are higher because the bubble is cooled by air. This reduces the output per man-hour.

Manufacturing of Cast Film -Cast Film also starts by having granular resin fed into a heated screw barrel. The molten resin is then fed through a narrow slot die. The dimension of the die helps determine the finished width and thickness of the film. The molten resin is then fed over a chilled roller which rapidly cools and solidifies the film .The film is then drawn through tension rollers to the slitting and winding stations.The philosophy behind manufacturing stretch film via the cast process has increased because it is the cheapest possible method of production (more output per man hour).

Application Differences -This is where the difference in mechanical properties between the two processes becomes very apparent. Blown film will feel very tough and resilient, whereas the Cast Film feels very soft and easy to stretch. The lower mechanical properties of the Cast Film are due to the single orientation of the molecular structure and fast cooling of the film. The Blown Film is cooled slowly and has a composite orientation of the molecular structure, thus increasing the mechanical properties of the film