초록 ▼

Apparatus for heat-sealing polymer films which shrink when heated include provision for moving the zone of application of heat and pressure during the heat sealing process. This allows for shrinking of the polymer film in a region adjacent to the heat seal so that the film thickens and is more resis

Apparatus for heat-sealing polymer films which shrink when heated include provision for moving the zone of application of heat and pressure during the heat sealing process. This allows for shrinking of the polymer film in a region adjacent to the heat seal so that the film thickens and is more resistant to failure in use through peeling. The apparatus includes a pair of sealing bars (4, 5) one of which (4) is wedge-shaped and the other of which (5) is flat. Both bars are heated and one of them can be moved in direction (12) to apply pressure to film located between the bars. At the beginning of the heat sealing step pressure is applied over an initial zone along the apex of the wedge. Subsequently the bare (4) is rolled around an axis located near to the apex of the wedge, in the direction shown by the right hand end of arrow (13), to apply heat and pressure over a wider zone located adjacent to the initial zone.

대표청구항 ▼

1. A method of heat sealing together at least two films of heat shrinkable polymer material, the heat seal being linear and destined for high-shock-peel-strength from one predetermined side, in which the two films are subjected to heat, whereby the material in each film contracts in the plane of the

1. A method of heat sealing together at least two films of heat shrinkable polymer material, the heat seal being linear and destined for high-shock-peel-strength from one predetermined side, in which the two films are subjected to heat, whereby the material in each film contracts in the plane of the film and swells in thickness, and to simultaneous pressure in a squeezed zone so as to produce a heat seal comprising a bonded zone and, on at least the predetermined side, a non-bonded zone in which the film is swollen, in which in an initial stage heat and pressure are applied over an initial pressure zone constituted by a portion of the squeezed zone including the boundary of the squeezed zone located on said predetermined side, and in a second stage heat and pressure are applied over a second pressure zone which overlaps the initial pressure zone and extends from the boundary of said initial pressure zone opposite the boundary of the squeezed zone located on said predetermined side and includes at least a portion of the rest of the squeezed zone adjacent to the said initial pressure zone and pressure in at least a portion of the initial pressure zone located adjacent said squeezed zone boundary is reduced characterised in that heat and pressure are maintained in said overlap zone from the beginning of the initial stage to the end of the second stage.