Polymer Film, Optically-Compensatory Film, Process for Producing the Same, Polarizing Plate and Liquid-Crystal Display Device

Abstract

A polymer film that has: a ratio R (VT / VM) of a sound velocity in a transverse direction VT to a sound velocity in a machine direction VM of from 1.05 to 1.50; and an in-plane retardation Re(λ) and a thickness-direction retardation Rth(λ) satisfying formula (I): (I) 0≦Re(630)≦10, and |Rth(630)|≦25, wherein Re(λ) represents an in-plane retardation at a wavelength of λ (nm); and Rth(λ) represents a thickness-direction retardation at a wavelength of λ (nm).

Description

TECHNICAL FIELD[0001]This invention relates to polymer film useful in liquid crystal display devices, an optically compensatory film using a polymer film, a process for producing the same, optical materials such as a polarizing plate and a liquid-crystal display device.BACKGROUND ART[0002]Because of being excellent in toughness and flame retardancy, cellulose acylate films have been employed in photographic supports and various optical materials. In recent years, in particular, cellulose acylate films are frequently employed as optically transparent films for liquid crystal display devices. Owing to the high optical transparency and high optical isotropy, cellulose acylate films are favorable as optical materials for devices with the use of polarization such as liquid crystal display devices. Therefore, cellulose acylate films have been employed as optically compensatory film supports whereby display in looking from an angle can be compensated (viewing angle compensation).[0003]A po...

AI Technical Summary

Benefits of technology

The patent text describes a problem in the production of optical films and display devices that require low optical anisotropy, meaning they should have low values for in-plane retardation and thickness-direction retardation. Additionally, they should have controlled bonding properties and low wavelength dispersion, meaning they should have uniform optical properties regardless of the wavelength. The patent proposes a solution by providing a polymer film with low optical anisotropy, specifically a ratio of the sound velocity in the transverse direction to the sound velocity in the machine direction of not more than 10, and a tensile modulus in the transverse direction of not more than 600 kgf / mm2 and a ratio of the former to the latter of not more than 1.5. The polymer film should also have low wavelength dispersion, meaning it should have uniform optical properties regardless of the wavelength.

Problems solved by technology

In the case of using as a polarization film-protecting film, however, these optically transparent films suffer from a problem in the bonding properties to PVA.

Moreover, there still remains another problem that the optical characteristics in the entire film face are uneven.

However, these known compounds can only insufficiently lower the optical anisotropy of a cellulose-acylate film.

However, supporting materials proposed hitherto have large retardation after the stretching or shrinking treatment or polarizing plates constructed by using the thus obtained optically compensatory films as protecting films suffer from some problems in the bonding properties or durability.

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