Mitsubishi Rayon Company, Limited

Hiroyuki Shimoyama

Hiroshi Sato

Munetsugu Nakatani

Naoki Mochida

Shuichi Sugimori

Hideto Kakita

Hiroshi Nakatsui

A translucent polypropylene film containing no .beta.-type crystallization nucleating agent which has, on at least one side, a surface layer composed of a two- or three-dimensional network structure, in which at least 1,000 network elements constituting the said network structure are present per cm.sup.2 of the film surface. The said film is obtained in such a manner that an unstretched polypropylene film having, on at least one side, a surface layer having a K value, which represents the amount of .beta.-type crystals present at a portion from the surface to a thickness of 10% in the thick-wall direction, of at least 0.1 is biaxially stretched under such conditions that the stretching temperature at the stretch initiation point is in the range of 145.degree. to 176.degree. C. and the stretch ratio in one direction is less than 8 times. The above-mentioned film is excellent in mechanical properties, quite dense in inner structure and high in airtightness, and the surface thereof has a fine uneven structure or fibril-like network structure, and has a favorable haze. Accordingly, the said film is used as a film for packing medicines, hygienic materials and foods, and as an insulating oil-impregnated dielectric film for condensers.

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Ohtake, Japan

Hiroyuki Shimoyama