Liquid crystal cells – elements and systems – Liquid crystal optical element
Patent
1997-07-09
2000-04-04
Berman, Susan W.
Liquid crystal cells, elements and systems
Liquid crystal optical element
349183, 349184, 349185, 349186, 349188, 349191, 349 92, 430 20, 428 11, G02F 113, C09K 1902
Patent
active
060467916
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a polymer dispersed liquid crystal electro-optical device, in which a liquid crystal and a polymer are compatibly dispersed, and a method for manufacturing the same.
DESCRIPTION OF RELATED ART
Conventionally, various types of display devices using a liquid crystal display have been popularized, and a majority of the devices employ a liquid crystal display according to a so-called TN (Twisted Nematic) type or a STN (Super Twisted Nematic) type. However, since these liquid crystal displays must use two polarizing plates, as is widely known, efficiency of light availability decreases, thereby disadvantageously causing a dark display.
Therefore, polymer dispersed liquid crystal display devices have been recently developed that do not need polarizing plates by utilizing a difference between a liquid crystal and a polymer. These polymer dispersed liquid crystal electro-optical devices are prepared such that a liquid crystal and a polymer are compatibly dispersed and phase-separated to form a liquid crystal polymer complex layer. These devices are in a transparent state in which light can be transmitted when the refractive indexes of the liquid crystal and the polymer have the same value due to application or removal of an electric field to or from the above-mentioned complex layer. These devices are in a cloudy state (translucent state) in which light is scattered if the refractive indexes are different from each other.
In these devices, a liquid crystal is dispersed in a polymer and the liquid crystal and the polymer are phase-separated to form a liquid crystal polymer complex layer under a condition in which liquid crystal molecules having positive dielectric anisotropy are aligned at random between two transparent substrates, as is described in U.S. Pat. No. 3,600,060 in detail. When no electric field is applied (without applied electric field), the refractive indexes of the randomly aligned liquid crystal and the polymer also aligned at random differ from each other, giving a light-scattering state in the liquid crystal polymer complex layer. Moreover, when an electric field is applied, the liquid crystal is aligned in the direction of the electric field by the electric field, and thus, the difference between the liquid crystal and the polymer disappear so that the liquid crystal polymer complex layer is rendered in a transparent state.
According to such polymer dispersed liquid crystal display devices, micro-particles of a liquid crystal are dispersed in a polymer, and further, the polymer is aligned at random. Thus, sufficient light transmittance cannot be obtained even when the liquid crystal and the polymer have the same refractive index, resulting in an incomplete transparent state. In addition, since the liquid crystal has an uneven particle diameter, the display quality is not uniform, leading to reduced reliability. Moreover, the response of each liquid crystal molecule to an electric field is nonuniform because the liquid crystal is also aligned at random when no electric field is applied. Thus, a problem occurs in that the threshold characteristics of transmittance of the device as a whole is not rapid.
Therefore, as is described in Japanese Patent Laid-Open No. 5-119302 and the like, a polymer dispersed liquid crystal display device has been proposed according to a system in which a sufficient light-transmitting state is achieved when no electric field is applied because a liquid crystal and a polymer are aligned in the same direction so that they have almost the same refractive index. A light-scattering state is achieved when an electric field is applied because only the liquid crystal is aligned in the direction along the electric field so that the refractive indexes of the liquid crystal and the polymer differ from each other. According to the above system, a transparent state superior to conventional ones can be obtained. In particular, a superior light-scattering state can also be obtained when applying an electric field by forming a
REFERENCES:
patent: 3600060 (1971-08-01), Churchill et al.
patent: 5225104 (1993-07-01), Van Steenkiste et al.
patent: 5494604 (1996-02-01), Chung
Kobayashi Hidekazu
Yamada Shuhei
Berman Susan W.
Seiko Epson Corporation
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