| 摘要 |
PURPOSE:To obtain a porous film improve in crosswise tensile strength and crosswise tearing strength, by forming a stripe pattern of specified irregularities on the surface of a film comprising a polyolefin and an inorganic filler and stretching this film. CONSTITUTION:A stripe pattern of such irregularities that the stripes are nearly parallel with the machine direction, the protrusing to recess depth ratio of this stripe is 0.2-0.9, and the pitch between adjacent protrusions is at least 50mu is formed by embossing on the surface of a film obtained from a mixture essentially consisting of 100pts.wt. polyolefin and 500pts.wt. or below inorganic filler. This film is stretched in at least the direction crossing the machine direction to obtain a gas-permeable film. When said pitch is below 50mu, no improving effect can be realized because the film cannot be embossed easily and unevenness of stretching is liable to occur. When it is above 2mm, it is impossible to improve mechanical properties, weightiness and stickiness because the film has an excessive flat area. |
