Polarizer and liquid crystal display element

Details Polarizer and liquid crystal display element Polarizer and liquid crystal display element

1999-10-06

2004-07-27

Pyon, Harold (Department: 1772)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

With viewing layer of specified composition

C428S001100, C534S577000, C349S096000, C349S097000, C349S106000

Reexamination Certificate

active

06767594

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to optics, and in particular to light polarizers and a liquid-crystal indicating elements based thereon.
A light polarizer, that transforms the natural light into the polarized light, and a liquid-crystal display (LCD) element based thereon are of the necessary elements of the up-to-date devices for displaying information on liquid crystals (LC), monitoring systems and light blocking.
DESCRIPTION OF THE PRIOR ART
The polarizers presently used are polymer films oriented by the uniaxial stretching, and dyed in mass by organic dyes, or iodine compounds. As a polymer, polyvinyl alcohol (PVA) is mainly used. see, e.g. U.S. Pat. No. 5,007,942 (1991).
Polarizers based on PVA dyed with iodine have high polarization characteristics and are widely used in production of liquid-crystal indicators for screens, watches, calculators, personal computers, etc.
However, an high cost and a low thermostability of the polarizers based on PVA do not allow to use them in the mass-production consumer goods, in particular in manufacture of multi-layer glass and films for automotive industry, construction, architecture. This circumstance, in its turn, calls forth development of new type of polarizers.
Known is a polarizer being a substrate whereon applied is molecularly oriented layer of dichroic dye capable of forming the nematic phase. see U.S. Pat. No. 2,544,659 (1951) and Patent of Japan 1-183602(A)(1989).
Said polarizer has an higher thermostability as compared with the polarizer based on PVA, because the polarizer's molecularly-oriented films of the dye has an high thermostability and can be formed on such stable materials as, e.g., glass.
Among drawbacks of the polarizer according to U.S. Pat. No. 2,544,659 and Patent of Japan 1-183602 (A) should be mentioned, first of all, an insufficient polarizing capability and a low contrast.
It is known a polarizer with higher polarizing characteristics (see Application PCT WO 94/28073(1994) which comprises a substrate whereon there is applied a thin film 0.1-1.5 mcm thick of the molecularly oriented layer of water-soluble dyes being sulfo-acids or their inorganic salts of azo- and polycyclic compounds, or their mixtures of the general formula (1):
{Chromogen}(SO
3
M)
n
, where: Chromogen is a chromophore system of a dye; M—H
+
, Li
+
, Na
+
K
+
, Cs
+
, NH
4
+
which are capable of forming a stable lyotropic liquid-crystal phase, allowing to produce the stable lyotropic liquid crystals (LLC) and compositions based thereon.
To produce a polarizer according to application PCT WO 94/28073: on the substrate surface applied are LLC of a dye, and simultaneously the mechanical orientation with subsequent evaporation of a solvent takes place. Thereby on the substrate surface formed a thin film of the molecularly-ordered dye layer is—a polarizing coating (PC) capable of efficiently polarizing the light. But said polarizer has the polarization characteristics which are still insufficient for use in the high-resolution LC-devices.
Also known are polarizers “operating” owing to other physical phenomena, for example, owing to different reflectances of light having different polarizations. Polarizers of this type are referred to as the reflecting ones, therein used are phenomena of the light polarization both in incidence and reflection of light beams from surface of any dielectric materials at inclined angles close to Brewster angle, and at the normal (perpendicular to the surface) incidence and light reflection from the surface of birefringent materials. In that case an improvement of the polarizing properties is achieved through use of multi-layer design of reflecting polarizers.
Also known is a polarizer (see Application PCT WO 95/17691 (1995) comprising at least one birefringent layer having such thickness that therein realized is the interference extremum at output of an optical polarizer at least for one linearly-polarized light component. Such polarizer includes interleaved layers of two transparent (non-absorbing in the operating wavelength range) polymer materials, among which at least one of them is the birefringent one. Birefringence in said polymer material is formed when a film manufactured by uniaxial stretching of such material in the same direction 2-10 times. The other layer of polymer material, interleaved in layers with the birefringent layer, is the optically isotropic one. The ordinary refraction index of the birefringent layer is equal to the refraction index of the optically isotropic layer.
Principle of operation of the known polarizer is as follows. One linearly-polarized component of the non-polarized light, to which component corresponds the extraordinary (greater) refraction index of the birefringent layer, is essentially reflected from a multi-layer optical polarizer owing to a difference of refraction indices at boundaries of the birefringent layer and optically isotropic layer. When thickness of the layers is of the wavelength order, the light beams reflected from boundaries of the layers interfere with one another. When thickness of the layers and their refraction indices are appropriately selected, the optical travel difference between the waves reflected from boundaries of the layers is equal to an integer of wavelengthes, i.e the reflected waves' interference result will be the interference maximum resulting in their mutual intensification. In this case reflection of the linearly-polarized component of the non-polarized light, to which component corresponds the extraordinary (greater) refraction index of the birefringent layer, is intensified significantly.
The ordinary (small) refraction index of the birefringent layer is selected to be essentially equal to the refraction index of the optically isotropic polymer layer, i.e. there is no difference (abrupt changes) of the refraction indices at boundaries of the birefringent and optically isotropic polymer layers. Therefore, the other linearly-polarized component of the incident non-polarized light, to which component the ordinary (small) refraction index of the birefringent layer corresponds, passes through the multi-layer optical polarizer completely without any reflections.
Thus, when the non-polarized light is incident on a known polarizer, one linearly-polarized component is reflected, and the other linearly-polarized component passes through the polarizer, i.e. the light polarization takes place both for the passing and the reflected lights.
The polarizer known from application PCT WO 95/17691 is a combined one and further comprises a dichroic polarizer having a weak absorption and dichroism, being the optically positioned with a reflecting optical polarizer. The role played by the additional dichroic polarizer, the transmission axis of which is parallel to the transmission axis of the reflecting optical polarizer, is reduced to elimination of the external light reflections when the combined polarizer is operated for the “translucency”.
One of the disadvantages of the known polarizer is a comparatively strong spectral dependence of its optical characteristics, i.e. dependence of the polarizing capacity and the reflection (and transmittance) index on the polarizable light wavelength. This disadvantage is caused by the circumstance that refraction indices in the used materials decrease as the polarized light wavelength increases.
The other disadvantage of the known polarizer according to Application PCT WO 95/17691 is the necessity to use a great number of the interleaving layers, which necessity is caused by the circumstance that the birefringence maximum value (difference between the ordinary and extraordinary refraction indices of a birefringent material) in transparent polymer materials is low and generally does not exceed 0.1-0.2. For this reason the reflection index from the layer boundaries is small, and for the purpose to obtain an high reflection as the whole from an optical polarizer, it is necessary to use a great number (100-600) of layers, application of which layers is an

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