Patent GB-851053-A (GB)
Title: Treatment of flexible, thermoplastic, organic polymeric sheets and films
IPC: B32B27/00
Filed: 1957-01-01
Abstract: <PICT:0851053/IV(a)/1> A flexible sheet of chemically homogeneous crystalline thermo-plastic organic polymeric material has, on at least one surface thereof, localized heat-sealable areas forming an integral part of the sheet, said areas having a lower softening temperature and being amorphous or less crystalline than the remainder of the surface.  The softening temperature of the areas is preferably at least 10 DEG C. lower than that of the remainder of the surface.  The areas may be minute and only minutely separated one from another. They may include perforations through the sheet and may be surrounded by a grommet-like bead.  They may be confined to the borders and to spaced transverse areas of the sheet.  The polymeric material may be a polyester, a number of which are specified, a polyvinyl compound, a number of which are also specified, isotactic polystyrene, isotactic poly-alphabutylene, isotactic polypropylene, a chloro-trifluoroethylene polymer, or a polyamide.  The sheet may be made by melting it, e.g. by means of a stream of hot fluid, at the selected localized areas only, while maintaining the remainder of the sheet unmelted and immediately cooling the melted material, so that it resolidifies to form the amorphous or less crystalline areas of lower softening temperature.  In an example a polyethylene terephthalate film 52 is fed from a reel 51 over a rotating metal cylinder 53, the peripheral surface of which is perforated with about 237 uniformly space holes, each 33 mils. in diameter, per square inch, to a take-up roll 54.  Spaced about 1/4 inch from the drum is the outlet 57 of a jet which is supplied with air at 30 p.s.i.g. pressure from a pipe 58.  The jet is heated by a gas burner 56 so that the temperature of the air issuing from the jet is about 370 DEG C.  The diameter of the jet orifice is 25 mils.  The surface of the cylinder 53 is maintained at 55-70 DEG C. by means of a cooling jet of air 60 directed against the back surface of the cylinder. A film or sheet may be provided with a pigment coating or a thin metallic layer of aluminium or other metal, which may be painted on one or both sides thereof or coated thereon by a vacuum deposition process, and may then be treated in the apparatus shown under conditions normally producing beaded perforations so that the metal or pigment coating is ruptured in areas overlying the perforations of the metal cylinder 53.  Either surface of the thus perforated sheet or film may then be heat-sealed to other sheets or films to form a laminate having an intervening metallized or pigmented coating.  Polyethylene terephthalate film treated according to the invention may be heat-sealed to itself, or to untreated polyethylene terephthalate film, or to paper, woven fabrics, metal foils or glass.  If the treated areas of the film are confined to the borders and certain spaced transverse areas of a length of film, the intervening areas being imperforate, packages may be formed by feeding two lengths of such films to conventional packaging machines, which insert material to be packaged between the two films, during or after which the two films are heat-sealed to each other around the borders to enclose the packaged material.  The same procedure may be used with two films perforated throughout their entire areas so that the finished package is perforated throughout and hence may be used for infusion purposes. Specification 851,473 is referred to.