GB810474A - Improvements in or relating to the manufacture of polyethylene plastic films - Google Patents

Abstract

One or both surfaces of smooth films of polyethylene plastic are coated with from 0.00125 to 0.125 per cent, based on the weight of the plastic, of a polyorganosiloxane as defined below. Alternatively, prior to its formation into a film, from 0.025 to 2.5, preferably 0.125, per cent of a polyorganosiloxane, as defined below, based on the weight of the polyethylene plastic, is incorporated in the latter. The polyorganosiloxane has the formula <FORM:0810474/IV (a)/1> wherein R and R1 each represent an alkyl, aryl or hydroxyl group and may be the same or different, R11 and R111 each represent an alkyl or aryl group and may be the same or different, and n is a whole number. The polyorganosiloxane may have an average molecular weight of 5000 to 30,000 and may be a liquid at ordinary temperatures. The siloxane may be applied to the film surfaces in the form of a solution in a volatile organic solvent such as a volatile chlorinated hydrocarbon, e.g. carbon tetrachloride, the film being then heated to evaporate the solvent. In an example, a continuous length of smooth polyethylene film 0.002 inch thick is passed over a felt wick dipping into a trough containing a 0.05 per cent solution of Silicone Fluid F115 in carbon tetrachloride, and the solvent is removed by evaporation in warm air, leaving a silicone coating, applied to one side only of the film, amounting to 0.01 per cent by weight, based on the weight of the film. Silicone Fluid F115 has an average molecular weight of 11,000 and all the hydrocarbon radicals in its molecule are methyl. In another example, 388 grams of polyethylene of average molecular weight 28,000 are fluxed on a 2-roll laboratory plastics mill at a roll temperature of 120 DEG C. with 12 grams of Silicone Fluid F115, and the mix is sheeted off, cooled and granulated. Then 167 grams of the granules are mixed with 4 kgs. of polythene in granular form by tumbling in a rotating drum, and the mixed granules are fed to a plastics extruder from which the polythene-silicone mixture is extruded at 140 DEG C. through an annular extrusion die 3 inches in diameter to form a film in the form of a tube 0.002 inch thick and containing 0.125 per cent of silicone, which is solidified by cooling in air at 20 DEG C. The film, after storate for three days following extrusion to give time for migration of the siloxane to the surface, has a slip value superior to that of plain polyethylene film. The films may be laminated to other flexible sheet material, such as woven and unwoven fabrics and fibrous paper (see Group VIII). Specifications 676,559 and 723,631 are referred to.