| 摘要 |
PURPOSE:A polypropylene band for wrapping, having a high tensile strength, a low elongation rate, excellent rigidity, and excellent wear resistane and consisting of a low-stretched surface layer and a high-stretched inner layer, each having a specific expansion ratio. CONSTITUTION:A polypropylene strip 3 extruded from a die is stretched to 4-9 times in the volumetric ratio in the longitudinal direction. The surface of the stretched polypropylene strip 3 is heated to form non-oriented surface layer 21, and the whole of the strip 3 is stretched to 1.2-3 times to obtain an objective band 3c having a low-stretched surface layer 23 of an expansion ratio of 1.2-3 times and the inner layer 20 with a high-stretched portion 22 of an expansion ratio of 10-18 times. EFFECT:Since vertical cracking is hard to occur and tensile strength is increased without application of enbossing process to the surface of the band even thin bands can be applied to be used as the usual wrappers. |
