The market for flat panel displays including liquid crystal panels and an organic electroluminescence panels has rapidly been expanding in recent years. In particular, the markets for small and medium-sized mobile devices, such as so-called smart phones and tablets, are growing sharply. Such small and medium-sized mobile devices need reductions in thickness and in weight along with enhancements in contrast of displayed images. Thinning of components constituting the devices, therefore, has been studied.
For example, a technique for producing a thin polarizing plate of a mobile device is disclosed (e.g., refer to PTL 1), which technique involves stretching of a laminate of a base material layer and a hydrophilic polymer layer.
According to the technique disclosed in PTL 1, the stretched hydrophilic polymer layer can be dyed with a dichroic substance and can function as a polarizer having a thickness of 10 μm or less, which is less than the thickness of conventional polarizers, that is, 20 μm or more.
Preparation of the polarizing plate requires, however, a transparent protective layer for protecting a surface of the polarizer. Since the protective layers used for the polarizing plates typically have a thickness of 60 to 100 μm, mere thinning of the polarizer as described above has no significant effect on reductions in thickness of the entire polarizing plates.
A technique for forming a protective layer by applying a curable resin directly on a polarizer to thin a polarizing plate is also disclosed (e.g., refer to PTL 2).
The technique disclosed in PTL 2 can provide a protective layer which is thinner than a protective film laminated to a polarizer with an adhesive, resulting in thinning of the polarizing plate. This technology provides a hard protective layer having a pencil hardness of 4H to prevent scratches on the surface of the polarizing plate.
Although a protective layer with high hardness formed on a polarizer with a thickness of 20 μm or more by curable resin coating does not cause problems such as insufficient polarization, a protective layer formed on a polarizer with a thickness of, for example, 10 μm or less would cause cracks or large distortion at the interface between the polarizer and the protective layer due to stress generated at the interface, resulting in a low polarization. Furthermore, a combination of a protective layer with a thin polarizer sometimes causes generation of color unevenness in the polarizing plate after preservation in a rolled form in the producing process.
Thus, a protective layer formed on a thin polarizer by curable resin coating cannot function as a polarizing plate having a small thickness and excellent polarization.
USPTO Backgrounds
USPTO Backgrounds