| 摘要 |
Apparatus and method for heat sealing a selected segment of a web of at least two layers of biaxially oriented plastic film. The web layers are pressed together and a selected segment of the pressed web is heated above the bonding temperature of the plastic while adjacent web segments are maintained below that temperature. The surfaces pressing thus the heated web segment has a relatively lower surface friction than the surfaces pressing the adjacent web segment, whereby the layers of the heated segment of the web are physically unrestrained against shrinking during heating and are allowed to shrink back to their pre-oriented molecular configuration while the adjacent segment is restrained against movement. A hermetic bead seal is thus formed between the web layers. A product heat sealed according to the novel method is also disclosed. |
