Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-09-22
2002-09-17
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S093000
Reexamination Certificate
active
06452650
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a polymer dispersion type liquid crystal display element of light-scattering mode, a producing method therefor and an apparatus for use in the producing method. More particularly, the invention relates to a polymer dispersion type liquid display element for use in liquid crystal televisions, computer terminals, liquid crystal projectors, and others, a producing method therefor and an apparatus for use in the producing method.
(2) Description of the Prior Art
Liquid crystal display element are widely used in various kinds of articles, including displays of wristwatches, and electronic calculators, navigation systems, notebook PCs, liquid crystal monitors, data projectors and projection liquid crystal TVs, taking advantage of their characteristics of low-profile, compact size, low voltage drive, and low power consumption. Among display modes of the liquid crystal display element, the TN (Twisted Nematic) mode is widely used, in which a liquid crystal display element having a structure of liquid crystal molecules being twisted at 90° below and above between two opposing, upper and lower substrates is held by two polarizers. The STN (Super Twisted Nematic) mode of liquid crystal display element designed to improve a time-division drive characteristic of the TN mode is also wisely used in, for instance, word processors for Japanese characters. Recently, information equipment is in actual use using ferro-electric liquid crystals, in which liquid crystal molecules are changed in alignment by means of spontaneous polarization of the liquid crystal molecules and the resultant electro-optical effects are used for displays.
These liquid crystal display element, however, require at least one polarizer, so that they involve the problems of darkness, necessity of alignment phase treatment and difficulties in controlling cell gap.
On the other hand, a different mode of liquid crystal display element has been proposed according to which the polarizer is no longer required for the liquid crystal display element, and the liquid crystal molecular alignments are controlled by electric field to produce an opaque state or a transparent state. In this mode of liquid crystal display element, a complex of liquid crystals and transparent polymers is held between two substrates and an ordinary ray refractive index of the liquid crystal molecules with anisotropy in positive dielectric constant is adapted to match with a refractive index of the transparent polymers. When a voltage is applied to allow the major axes of the liquid crystal molecules to be aligned in parallel with the electric field, to match the refractive index of the liquid crystal molecules with refractive index of the transparent polymers, the scattering of light does not occur at the phase boundary to thereby produce the transparent state. On the other hand, while no voltage is applied thereto, the liquid crystal molecules are being oriented in different directions and their refractive index does not match with that of the transparent polymer at the phase boundary between the liquid crystal and the transparent polymer, so that the light scattering occurs to produce the opaque state. With the aid of this phenomenon, the opaque state or the transparent state is produced.
A representative example of this mode is what is called NCAP (Nematic Curvilinear Aligned Phase) in which nematic liquid crystals are micro-encapsulated with polyvinyl alcohol or equivalent (Fine Particles and Industry, Vol. 22, No. 8 (1990)).
Further, there is another mode called PDLC (Polymer Dispersed Liquid Crystals) in which liquid crystal fine droplets are dispersed in polymer matrix (Flat Panel Display '91, on page 219, published by NIKKEI BP).
Also, there is a still another mode called PNLC (Polymer Network Liquid Crystals) having a structure of resins spreading in a continuous phase of liquid crystals in the form of a three dimensional network (Engineering Laboratory Report from Electric Information Institute, EID89-89, on page 1).
The complex of the liquid crystals and the transparent polymers are generally called as polymer dispersion type liquid crystals.
Typically, the method of producing the complex of the liquid crystals and the polymers includes the steps of: injecting a mixed composition, into which uncured resin monomers, such as ultraviolet curing acrylic or epoxy resins, and liquid crystal materials are dissolved, in between two substrates; and irradiating the mixed composition with ultraviolet to polymerize the resin monomers to produce a phase separation of the liquid crystals and the resins. This yields the structure of the liquid crystals being dispersed in the polymers or the structure of the polymer spreading in the liquid crystals in the form of network (Flat Panel Display '91, on page 219, published by NIKKEI BP, and Engineering Laboratory Report By Electric Information Institute, EID89-89, on page 1, for example).
Some examples of this polymer dispersion type liquid crystal are disclosed by Japanese Laid-Open Patent Publications No. Hei 5(1993)-80302 and No. Hei 7(1995)-181454, in which in order to improve scattering effects of the complex of the liquid crystals and polymers with respect to light, the liquid crystal droplets are deformed or compressed to have a flat plate-like shape in section (i.e., the length vertical to the substrates is smaller than the length parallel with the substrates). Specifically, the Japanese Laid-Open Patent Publication No. Hei 5(1993)-80302 discloses that flat plate-like liquid crystal droplets are formed by being pressed under conditions of heating and that it is preferable that the flat liquid crystal droplets have a compression rate (deformation ratio) of 1.2 to 5.0 (which equates to 20 to 80 on a deformation rate basis, as mentioned later). The Japanese Laid-Open Patent Publication No. Hei 7(1995)-181454 discloses that flat plate-like liquid crystal droplets are formed by being pressed while being irradiated with ultraviolet and that it is preferable that the liquid crystal droplets are deformed to have a thickness of ½ of a length in section; in practice, the liquid crystal droplets are deformed at the rate of about ½ to ¼ (which equates to 50 to 75 on a deformation rate basis, as mentioned later).
It is said that forming the liquid crystal droplets into flat plate-like shape provides advantages of increasing steepness and decreasing hysteresis.
Our study has proved, however, that when the liquid crystal droplets are deformed at the compression rate of 1.2 or more (which equates to 20 on a deformation rate basis, as mentioned later), as in the conventional examples mentioned above, deterioration in display characteristics such as reduction of contrast occurs, rather than improvement.
Further, according to Japanese Laid-Open Patent Publication No. Hei 5(1993)-80302, after the compressing process of the liquid crystals, the mixture is not subjected to any polymerization process. Due to this, the liquid crystal display element after compressed remain in the state in which polymerization reaction of the resin monomers immediately before compression is not yet completed and thus are incompletely cured. Hence, the compressing effects are relaxed with the passage of time, to cause the problem that the compressed liquid crystal droplets gradually return to their original before-compressed state. On the other hand, an attempt to prevent the relaxation of the compression effects after compression in the case where the mixture is not subjected to any polymerization process after the compressing process of the liquid crystals requires that the liquid crystal droplets are compressed in a state in which the polymerization of the resin monomers is completely concluded or is almost completely concluded. However, this disadvantageously needs much time for compression.
In this respect, according to Japanese Laid-Open Patent Publication No. Hei 7(1995)-181454, the mixture is polymerized after the compression
Inoue Kazuo
Kosako Shinya
Kubota Hirofumi
Nakao Kenji
Nishiyama Seiji
Duong Tai V.
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P
Sikes William L.
LandOfFree
Polymer dispersion type liquid crystal display element,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polymer dispersion type liquid crystal display element,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer dispersion type liquid crystal display element,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2855607