In general, a polarizer plate has a structure that contains a polarizer film having a structure in which polyvinyl alcohol (PVA) molecular chains are aligned in a predetermined direction and an iodine compound or a dichromatic polarizing substance is contained, or a structure that has a polyene structure formed by dehydration reaction of the polyvinyl alcohol film or the dehydrochlorination reaction of the polyvinyl chloride (PVC) film; and a triacetyl cellulose film (hereinafter, referred to as TAC film) acting as the protective film that is layered on the polarizer film using an aqueous adhesive made of a polyvinyl alcohol aqueous solution.
Both the polyvinyl alcohol film used as the polarizer and the TAC film used as the protective film for polarizers have poor heat resistance and humidity resistance. Therefore, if the polarizer plate that is made of the films is used at a high temperature or a high humidity atmosphere for a long period of time, the degree of polarization is reduced, the polarizer and the protective film are separated from each other, or optical properties are reduced. Thus, in terms of the purposes, there are various limits. As described above, the polarizer plate that has been commercialized until now has undesirable heat and moisture resistance. In addition, in the case of the TAC film, a change in in-plane retardation (Rin) and thickness retardation (Rth) is significant according to a change in the ambient temperature/humidity atmosphere. In particular, a change in retardation in respects to incident light at an inclined direction is significant. If the polarizer plate that includes the TAC film having the above-mentioned characteristics as the protective film is applied to a liquid crystal display, the viewing angle characteristics are changed according to the change in the ambient temperature/humidity atmosphere, thus reducing the image quality. In addition, in the case of the TAC film, a change in dimension is significant according to the change in the ambient temperature/humidity atmosphere and the photoelastic coefficient is relatively high, thus, after evaluation in respects to durability in a high heat and/or humidity atmosphere, a change in retardation occurs and light is leaked locally, thereby easily reducing the image quality.
As a material to avoid the disadvantages of the TAC film, a (meth)acrylic resin is well known. However, it is known that the (meth)acrylic resin is easily broken or splitted to cause problems in terms of transportability during the production of the polarizer plate and the productivity is poor.
In order to solve this problem, a method of blending an acryl resin with another resin or a toughnening agent (Japanese Unexamined Patent Application Publication Nos. 2006-284881 and 2006-284882) or a method of coextruding other resins to perform the layering (Japanese Unexamined Patent Application Publication Nos 2006-243681, 2006-215463, 2006-215465, and 2007-017555) has been suggested. However, theses methods have problems in that high intrinsic heat resistance and high transparency of the acryl resin are not sufficiently realized or there is a complicated layered structure.