Laminated film for a prism sheet, a method of manufacturing a prism sheet laminated film, a prism sheet, and a display device

A prism sheet is composed of a base layer made from polyester, an adhesion layer formed on one of the surfaces of the base layer, a back layer formed on the other surface of the base layer, and a prism layer formed on the adhesion layer. A main constituent of the back layer is water-insoluble polymer with glass transition temperature (Tg) of at least 90° C. Average reflectivity of the back layer is at most 3.5% at wavelength in a range from 380 nm to 780 nm. By containing water-insoluble polymer with Tg of at least 90° C. as the main constituent, the back layer becomes free from contact damage caused by contact with the prism peaks of the adjacent prism sheet. Setting the average reflectivity of the back layer to at most 3.5% imparts brightness enhancement properties to the prism sheet.