POLYVINYL ALCOHOL-BASED FILM, POLARIZING FILM AND POLARIZING PLATE AND METHOD FOR PRODUCING POLYVINYL ALCOHOL-BASED FILM

To provide: a polyvinyl alcohol-based film which is capable of obtaining a polarizing film which has excellent balance between swellability and extensibility during producing a polarizing film, causes no breakage during producing a thin polarizing film, exhibits high polarizing performance and has less color unevenness; a polarizing film and a polarizing plate using the polyvinyl alcohol-based film; and a method for producing the polyvinyl alcohol-based film.SOLUTION: There is provided a polyvinyl alcohol-based film in which when a rectangular first sample of 40 mm in the width direction (TD)×270 mm in the length direction (MD) cut from the central part in the width direction is immersed in water at 30°C for 30 seconds, the elongation amount WMD30 in the length direction at a portion of 250 mm in the length direction before immersion is 30 mm or more and 50 mm or less and when a rectangular second sample of 270 mm in the width direction (TD)×40 mm in the length direction (MD) cut from the central part in the width direction is immersed in water at 30°C for 300 seconds, the elongation amount WTD300 in the width direction at a portion of 250 mm in the width direction before immersion is 15 mm or more and 60 mm or less.SELECTED DRAWING: None 【課題】偏光膜製造時の膨潤性と延伸性とのバランスによく優れ、薄型偏光膜の製造時にも破断が生じず、高い偏光性能を示しかつ色ムラの少ない偏光膜を得ることができるポリビニルアルコール系フィルム、そのポリビニルアルコール系フィルムを用いた偏光膜および偏光板、ならびに上記ポリビニルアルコール系フィルムの製造方法を提供する。【解決手段】本発明のポリビニルアルコール系フィルムは、幅方向中央部から切り出す幅方向（ＴＤ）４０ｍｍ×長さ方向（ＭＤ）２７０ｍｍの長方形の第１サンプルを３０℃の水に３０秒間浸漬したときの、浸漬前の長さ方向２５０ｍｍの部分における長さ方向の伸び量ＷMD30が３０ｍｍ以上５０ｍｍ以下であり、かつ、幅方向中央部から切り出す幅方向（ＴＤ）２７０ｍｍ×長さ方向（ＭＤ）４０ｍｍの長方形の第２サンプルを３０℃の水に３００秒間浸漬したときの、浸漬前の幅方向２５０ｍｍの部分における幅方向の伸び量ＷTD300が１５ｍｍ以上６０ｍｍ以下である。【選択図】なし