To prevent oil absorption swelling by an insulating oil by using a film made of isotactic polypropylene having specific values of molecular weight polydispersity and isotacticity in a plastic film laminated sheet used as an insulating sheet of an oil-immersed cable.
The plastic film laminated sheet obtained by laminating a plastic film and kraft sheet adopts a film of isotactic polypropylene having molecular weight polydispersity of 4 or less as a plastic film and isotacticity of 98% or more of mmmm pentad fraction. As the kraft sheet, a sheet having airtightness of 20-5000 Gurley sec is preferable. Further, kraft sheet of a multilayer structure having a high airtightness layer having a high airtightness of 5000 Gurley sec or more, and a density of 0.7 g/cm3 or more, and a low density layer having an airtightness of 100 Gurlay or less and density of less than 0.7 g/cm3 is used, and the layer having low airtightness and low density is laminated preferably on the film.
ONO AKINOBU
TAKAHASHI SUSUMU
MIYATA HIROYUKI
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