| 摘要 |
A selectively openable seal line (34), especially for a container, comprises a seal (36) between first and second sheets (38, 40) each of which has an inner surface (44, 48) of a thermoplastic material, the seal line being formed between the inner surfaces. The seal is formed by a focused energy source, such as radio-frequency energy source, which melts the inner surface at the seal. The seal, as viewed in cross-section, has a bead area (54) of increased thickness at a break end (56) of the seal coextensive with the inner surfaces along less than all of the surface of the bead area, and a break line (58) inwardly of the break end (56), at the second sheet (40), substantially adjacent the bead area (54), and an arcuate depression (60) having a concave downward surface (62) extending from adjacent the break point to a minimum seal thickness point (64). |
