| 摘要 |
1,025,963. Seaming non-metallic sheet material. PIRELLI PLAST S.p.A. Feb. 12, 1963, No. 5603/63. Heading B5K. Extruded sheets of thermoplastic resin are heat sealed together along overlapped edges parallel to the direction in which extrusion is taking place, by imparting molecular orientation to the sheets by stretching the sheets both in said direction and in a direction normal thereto, and forming by heat sealing a sealing line having a continuous, non-rectilinear path. A tarpaulin 1 is formed by sealing together sheets 2, 3 overlapping at edges 4, 5. The sealing line 6 is in the form of a zig-zag line having rectilinear segments 7, 8 inclined at 45 degrees to the edges 4, 5 and connected at 9 by an arc of a circle having a very small radius. Weakened zones 10, 10<SP>1</SP> are formed on both sides of the line 6. Alternatively, a sinusoidal sealing line may be formed. A number of sealing lines may be provided either identical with or different from one another and disposed near one another. The sheets 2, 3 may be sealed by being continuously conveyed to an electrically-heated metal sealing wheel provided with a shaped projection to form the line 6. Alternatively, the sheets 2, 3 may be conveyed intermittently to a heated reciprocating plate having a suitably-shaped sealing projection. The sheets 2, 3 may be polyvinyl chloride, polystyrene, polyethylene or polypropylene. |
