GB1117354A - Oriented heat-sealable polyethylene terephthalate plastic films - Google Patents

Abstract

1,117,354. Heat sealable polyethylene terephthalate films; laminates. IMPERIAL CHEMICAL INDUSTRIES Ltd. 15 April, 1966 [4 May, 1965], No. 18729/65. Headings B5B and B5N. A drawn and heat set polyethylene terephthalate film is caused to pass or travel over a cooled rotating roller so that one surface of the film is maintained in contact with the roller and a localized area of the opposite surface of the film is simultaneously subjected to an intensely hot flame (e.g. a flame at a temperature over 1500‹ C.), the rate of travel of the film being such that the period of residence of every point in the heated area of the film is sufficient to melt the surface of the film at that point but insufficient to cause distortion of the film. The flame may be produced by an oxyacetylene burner or a propane or butane burner. The surface of the film may be heated to a temperature which is at least 260‹ C. but below that at which decomposition of the film will occur. The roller may be hollow and cooled by applying a cooling liquid to its inner surface or the liquid may be applied externally to the peripheral surface of the roller so that it forms a continuous liquid film between the roller and the polyethylene terephthalate film. The chilled liquid may be water and by adjustment of the temperature of the chilled liquid and its rate of flow on the rollers the chilled liquid film may be maintained at 20‹ to 70‹ C. The thickness of the polymer film may be 0À00025 to 0À01 inch, preferably 0À002 to 0À01 inch. The film may be fed over the cooled roller at a speed of at least 10 feet/min. The effect of the local heating of the film is to render a surface layer of the film on which the flame has been directed amorphous and disoriented. The thickness of this layer is 5 to 50% of the total thickness of the film, its density is less than 1À35 and its birefringence is less than 0À130. A laminate may be produced by heating the treated polyethylene terephthalate film in contact with another film so that the amorphous layer of the P.T. film is sealed to the other film, which may also be a P.T. film which has been treated according to the invention. The laminate may be produced from two P.T. films both of which are oriented to a greater degree in the machine direction or in the transverse direction than in the other direction, the laminate being constructed in such a way that the direction of greater orientation of one film is at right angles to the 'direction of greater orientation of the other film which comprises the laminate. The sealing together of the films comprising the laminate may be effected by pressing them together at a temperature between 70‹ C. and the melting point of P.T., preferably at a temperature of 120‹ to 180‹ C. The sealing may be effected by means of heated rollers, an impulse heat sealer or a radio frequency heat sealing apparatus.