METHOD FOR MANUFACTURING CELLULOSE ACYLATE FILM, LAMINATE CELLULOSE ACYLATE FILM, POLARIZING PLATE, AND LIQUID CRYSTAL DISPLAY DEVICE

PROBLEM TO BE SOLVED: To provide a method for manufacturing a cellulose acylate film that is excellent in formability of a long film and gives a polarizing plate with excellent durability and contrast property.SOLUTION: The method for manufacturing a cellulose acylate film aims manufacturing a laminate cellulose acylate film 20 having a three-layer structure composed of a cellulose acylate layer A21 having an acyl group substitution degree of 2.7 or less, and cellulose acylate layers B22, B23 adjoining on either side of the layer A21 and having an acyl group substitution degree larger than that of the layer A21. The method includes: a step (1) of preparing a solution 118 of a cellulose acetate resin (a) having an acyl group substitution degree of 2.7 or less; a step (2) of preparing a mixture solution of a cellulose acetate resin (b) having an acyl group substitution degree of larger than 2.8 and a cellulose acetate resin (d) having an acyl group substitution degree of 2.7 or less; and a step (3) of manufacturing the laminate cellulose acylate film 20 by co-flow casting of the above solution and the mixture solution. The laminate acylate film 20 has a surface roughness Ra of 2.0 or more. 【課題】長尺製膜性に優れ、かつ耐久性、コントラスト性に優れる偏光板を与えるセルロースアシレートフィルムの製造方法を提供する。【解決手段】アシル基置換度が２．７以下のセルロースアシレート層Ａ２１と、層Ａ２１の両側に隣接し層Ａ２１のアシル基置換度よりも大なセルロースアシレート層Ｂ２２，２３とからなる3層構成の積層体２０を有し、アシル基置換度が２．７以下のセルロースアセテート樹脂ａ溶液１１８を調製する工程（１）、アシル基置換度が２．８より大なセルロースアセテート樹脂ｂと、アシル基置換度が２．７以下のセルロースアセテート樹脂ｄの混合溶液を調製する工程（２）、及び該溶液と該溶液とを用いて共流延し、該積層セルロースアシレートフィルム２０を製造する工程（３）、を有し、かつ該積層アシレートフィルム２０の表面の粗さＲａ値が、２．０以上であるフィルムの製造方法。【選択図】図１