MICROPOROUS FILM FORMED FROM RESIN COMPOSITION CONTAINING 4-METHYL-1-PENTENE-BASED POLYMER, SEPARATOR FOR BATTERY, AND LITHIUM ION BATTERY

To provide a microporous film which has a high rate of hole area and, moreover, low polluting property without impairing characteristics of a 4-methyl-1-pentene-based polymer such as high heat resistance and the like.SOLUTION: The present invention relates to a microporous film which is formed from a resin composition containing a 4-methyl-1-pentene-based polymer (X), in which a content of a structural unit derived from 4-methyl-1-pentene is 90 to 100 mol%, a content of a structural unit derived from at least one olefin selected from ethylene and α-olefins other than 4-methyl-1-pentene having 3 to 20 carbon atoms, is 0 to 10 mol%, and an amount of a decane-soluble part at 23°C is 5.0 mass% or less, and which satisfies the following requirement (I): (I) a Z-average molecular weight, Mz, of the microporous film is in the range of 1 million to 2 million as measured by gel permeation chromatography (GPC).SELECTED DRAWING: None 【課題】４−メチル−１−ペンテン系重合体の高い耐熱性等の特性を損なうことなく、開孔率が高く、しかも低汚染性を有する微多孔フィルムを提供することにある。【解決手段】本発明は、４−メチル−１−ペンテン由来の構成単位の含有量が９０〜１００モル％であり、エチレンおよび炭素原子数３〜２０の４−メチル−１−ペンテン以外のα−オレフィンから選ばれる少なくとも１種のオレフィン由来の構成単位の含有量が０〜１０モル％であり、２３℃デカン可溶部量が５．０質量％以下である、４−メチル−１−ペンテン系重合体（Ｘ）を含む樹脂組成物から形成され、下記要件（Ｉ）を満たす、微多孔フィルムに係る。（Ｉ）ゲルパーミエーションクロマトグラフィー（ＧＰＣ）で測定した、Ｚ平均分子量Ｍｚが１００万〜２００万の範囲にある。【選択図】なし