1. Field of the Invention
The present invention relates to a polymer film exhibiting high retardation along thickness direction (Rth); a phase difference film, a polarizing plate, and a liquid crystal display device using the polymer film; and an Rth inducing agent.
2. Description of the Related Art
There have been known techniques of adding various additives to a polymer film, aiming at imparting thereto various functions.
An exemplary proposal has been made on a polymer film improved in ultraviolet absorption, by means of addition of a merocyanine-based compound, as a ultraviolet absorber, to the polymer film (i.e., JP-A-H08-239509). JP-A-2009-67973 discloses a polymer material containing a merocyanine-based compound as an ultraviolet absorber, a mold product manufactured by using the polymer material, and also a coated ultraviolet absorber layer. Other proposals have been made on use of a merocyanine-based compound as a wavelength dispersion modifier for polymer film (i.e., JP-A-2009-64006 and JP-A-2009-64007). JP-A-2009-270062, JP-A-2009-79213 and JP-A-2009-67983 have proposed techniques of using a merocyanine-based ultraviolet absorber combined with other types of ultraviolet absorber, aiming at improving the light stability.
Polymer film typically used as an optically compensatory film of liquid crystal display device is sometimes required to show high Rth. Increase in the amount of addition of the additive, aimed at elevating Rth, have however occasionally degraded the stability of manufacturing, due to deposition of the additive onto the surface of the film in the process of film making. In the field of manufacturing of polymer film typically adoptable to optical films, it is therefore very beneficial to provide an additive capable of ensuring high Rth even with a less amount of addition, while ensuring a desired level of wavelength dispersion.