Recently, development has been made regarding decrease in thickness and weight of a note board type personal computer. In parallel with this development, a polarizing plate used in a device such a liquid crystal display or an organic EL display has been eagerly sought to be increasingly thinner. Particularly, decrease in thickness of a protective film of a polarizing plate has been strongly required. However, it has been proved that a simple decrease in thickness of the polarizing plate protective film produces various problems. One of the problems regards moisture vapor permeation (moisture vapor transmittance). For example, as the thickness of a polarizing plate protective film decreases, the moisture vapor transmittance of the film becomes higher, resulting in lowering of durability of the polarizing plate. There have been proposed several methods in which moisture vapor transmittance is optimized. A film with a lower moisture vapor transmittance improves durability of a polarizing plate employing the film, however, too low moisture vapor transmittance has a defect in that an adhesive is difficult to be dried which is used to adhere a polarizing plate protective film to a polarizing film.
Therefore, a polarizing plate protective film with moisture vapor permeation property satisfying both the durability and the drying property is required. A cellulose ester film is used in most of polarizing plate protective films, and moisture vapor transmittance of the polarizing plate protective film employing the cellulose ester film is markedly deteriorated due to decrease in thickness. It is known that the high content of a plasticizer in the polarizing plate protective film improves a moisture vapor transmittance, however, a too high content of the plasticizer in the film causes problem of lowering dimensional stability of the film. A polarizing plate protective film having an excellent moisture vapor permeation property and an excellent film performance is required.