JP2002082325A - Cholesteric liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cholesteric liquid crystal display device in which irregularities in display due to uneven distribution of temperature are decreased. SOLUTION: The cholesteric liquid crystal display device is manufactured by holding a cholesteric liquid crystal 30 held between two substrates 11, 12 having transparent electrodes 21, 22, respectively, and forming a black light- absorbing layer 41 on the face opposite to the observation side. Then a heat linear layer 45 is formed on the light-absorbing layer 41.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cholesteric liquid crystal display device used as a display panel of an electronic device or an image recording / display medium.

[0002]

2. Description of the Related Art A cholesteric liquid crystal display element is capable of displaying a bright image by using the reflection of external light, has a memory property capable of maintaining the display contents even when the voltage is cut off, and has a simple matrix drive utilizing the memory property. In recent years, as a display element for electronic paper such as electronic newspapers and electronic books, it has features such as being able to display large-capacity, and being able to use a flexible substrate such as a resin because it does not require an active matrix for driving. Expectations are gathering.

The principle of operation of a cholesteric liquid crystal display device will be described below. Cholesteric liquid crystals are composed of rod-shaped molecules oriented in a spiral, and exhibit a selective reflection phenomenon of reflecting light having a wavelength corresponding to the spiral pitch. A cholesteric liquid crystal display device utilizing this phenomenon has a sectional structure as shown in FIG. That is, the cholesteric liquid crystal display element is composed of a cell in which a cholesteric liquid crystal 30 is sandwiched between two substrates 11 and 12 provided with transparent electrodes 21 and 22, respectively. The layer 41 is provided.

As shown in FIGS. 3 (a) to 3 (c), there are three types of orientation of the cholesteric liquid crystal in the cell: planar, focal conic, and homeotropic. In the planar orientation, the helical axis is oriented substantially perpendicular to the substrate surface, and color light in the selective reflection wavelength band is observed.
The focal conic orientation is a state in which the helical axis is oriented substantially parallel to the substrate surface, and is itself colorless, so that the above-described light absorption layer 41 is observed and a black appearance is obtained. Homeotropic alignment is a state in which the helical axis is loosened and molecules are aligned perpendicular to the substrate surface. Since this state itself is also colorless, the above-described light absorbing layer 41 is observed, and a black appearance is obtained.

The switching between the alignment states can be performed electrically. When a voltage is applied between the electrodes 21 and 22,
The planar orientation first changes to focal conic orientation,
When the voltage is further increased, the state changes to homeotropic alignment. On the other hand, when the voltage is slowly lowered from the homeotropic alignment, the state becomes focal conic alignment, and when the voltage is rapidly lowered, the state becomes the planar alignment. When no voltage is applied, since two orientation states, focal conic orientation and planar orientation, are stably present, memory properties can be displayed by utilizing these properties.

A multicolor cholesteric liquid crystal display device is shown in FIG.
As shown in FIG. 3, three cholesteric liquid crystals 30B, 30G, and 30R that reflect blue, green, and red color light, respectively.
Are obtained by laminating the liquid crystal display cells 51B, 51G, 51R having The cells are adhered with adhesive layers 71 and 72, and a light absorbing layer 41 is provided on the surface of the cell 51R opposite to the observation side. Here, blue, green, and red are 400 to 5, respectively.
It means color light belonging to the wavelength bands of 00 nm, 500 to 600 nm, and 600 to 700 nm. Specifically, by displaying one of the blue, green, and red display layers in a reflective state and the other two in a colorless state, blue, green, and red displays can be obtained. In addition, two of the blue, green, and red display layers
By setting one to a reflection state and the other to a colorless state, cyan, magenta, and yellow displays can be obtained. Also,
A white display can be obtained by making all of the blue, green, and red display layers reflective, and a black display can be obtained by making all of them blue.

[0007]

The switching of the cholesteric liquid crystal display element is performed by applying a pulse voltage. The pulse voltage required at this time is selected so that the change in the orientation of the liquid crystal is completed within the pulse application time. Since the response speed of the liquid crystal depends on the mobility of the liquid crystal molecules, that is, the viscosity, it is necessary to set a higher pulse voltage or a longer pulse application time at a low temperature. For this reason, temperature unevenness may occur in the surface of the display panel due to holding the display panel by hand or the influence of heat conduction from a drive circuit or a control circuit. In such a case, there is a problem that unevenness in viscosity occurs in the liquid crystal, thereby causing uneven display.

Accordingly, an object of the present invention is to provide a cholesteric liquid crystal display device in which display unevenness caused by temperature unevenness is reduced.

[0009]

The object of the present invention is to fill a cholesteric liquid crystal between substrates each having a transparent electrode,
This is achieved by a cholesteric liquid crystal display device provided with a light absorbing layer on the surface opposite to the observation surface, wherein a cholesteric liquid crystal display device provided with a soaking layer via the light absorbing layer.

A cholesteric liquid crystal display device according to the present invention comprises a plurality of cells each having cholesteric liquid crystal sealed between substrates each having a transparent electrode, and has a light absorbing layer on a surface opposite to an observation surface. Cholesteric liquid crystal display device, comprising a soaking layer provided with the light absorbing layer interposed therebetween.

Here, a metal foil such as aluminum or copper is preferably used as the soaking layer. In the present invention, since the heat equalizing layer diffuses heat and improves heat dissipation, temperature unevenness can be reduced. This allows
It is possible to reduce display unevenness due to temperature unevenness and obtain a cholesteric liquid crystal display element with improved display uniformity.

[0012]

<First Embodiment> FIG. 1 is a view showing one embodiment of a cholesteric liquid crystal display device according to the present invention. The cholesteric liquid crystal display element has a transparent electrode 2
The cholesteric liquid crystal 30 is sandwiched between two substrates 11 and 12 each having a substrate 1 and 22 and a black light absorbing layer 41 is provided on the surface opposite to the observation side. The heat equalizing layer 45 is provided via the light absorbing layer 41.

As a material of the heat equalizing layer 45, a material having high thermal conductivity is preferable, and metals such as aluminum and copper, semiconductors such as silicon and germanium, carbon graphite, alumina, and aluminum nitride can be used. These are used alone or as a dispersion in which powder is kneaded in a resin.

As the substrates 11 and 12, a transparent dielectric such as glass or a resin such as polycarbonate, polyethylene terephthalate, or polyethersulfone can be used. Flexible resin is used for the substrate 1
When used as 1 and 12, a metal foil such as aluminum or copper is preferably used as the heat equalizing layer 45 because it does not impair flexibility and can impart gas barrier properties.

As the transparent electrodes 21 and 22, ITO (I
ndium Tin Oxide), SnO ₂ , Zn
O: A light-transmitting conductive member such as a conductive oxide such as Al or a conductive resin such as polypyrrole or polyaniline is used. These are vapor deposition, sputtering, ion plating, sol-gel, coating, printing,
The film can be formed by an electrodeposition method or the like. After the film formation, it may be processed into a desired shape by using a lithography method or the like.

The cholesteric liquid crystal 30 includes nematic liquid crystal compositions such as cyanobiphenyl, phenylcyclohexyl, phenylbenzoate, cyclohexylbenzoate, azomethine, azobenzene, pyrimidine, dioxane, cyclohexylcyclohexane, and trans. What added the chiral agent which consists of a compound which has an optically active group like a cholesterol derivative or a 2-methylbutyl group can be used. The cholesteric liquid crystal 30 may be dispersed in a polymer matrix, polymerized into a gel, or encapsulated. Further, any of a high-molecular liquid crystal, a medium-molecular liquid crystal, and a low-molecular liquid crystal may be used, or a mixture thereof. The selective reflection wavelength of the cholesteric liquid crystal 30 is 400
It is assumed to be in the visible wavelength range between ８００800 nm.

The cholesteric liquid crystal layer 30 and each transparent electrode 2
A resin such as polyimide, an inorganic vapor-deposited film such as SiO, or a silane-based or ammonia-based surface modifier may be provided between the first and second layers as an alignment film. As the light absorbing layer 41, one that absorbs the selective reflection wavelength band is used, and its color tone can be appropriately selected in consideration of the display effect. It is preferable to use a material having high thermal conductivity. As the material, a paint containing a dye or a pigment, or a vapor-deposited film such as a metal or metal oxide film can be used.

<Embodiment 2> FIG. 2 is a view showing another embodiment of the cholesteric liquid crystal display device according to the present invention. The present embodiment relates to a multicolor cholesteric liquid crystal display device, and as shown in FIG. 10, cholesteric liquid crystals 30B, 30G, and 30R that selectively reflect blue, green, and red.
, The liquid crystal display cells 50B, 50G, 50
R is laminated via adhesive layers 71 and 72.
The light absorption layer 41 is provided on the surface of the liquid crystal cell 50R opposite to the observation side. In this embodiment, a heat equalizing layer 45 is provided with the light absorbing layer 41 interposed therebetween. Cells 50B, 50G, 50
The stacking order of R is not limited to this embodiment, and may be any order.

The adhesive layers 71 and 72 are translucent, and
12 is made of an adhesive or a pressure-sensitive adhesive having a refractive index close to that of the adhesive. Higher thermal conductivity is preferred. As the material, a resin such as acrylic, epoxy, urethane, or polyester is used. As the curing mode of the adhesive, an ultraviolet curing type, a thermosetting type, a hot melt type or the like can be used. In order to increase the thermal conductivity, a powder of a light-transmitting material having a high thermal conductivity, such as alumina or aluminum nitride, may be dispersed.

[0020]

According to the present invention, it is possible to obtain a cholesteric liquid crystal display device in which display unevenness caused by temperature unevenness is reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a cholesteric liquid crystal display device according to the present invention.

FIG. 2 is a diagram showing another embodiment of the cholesteric liquid crystal display device according to the present invention.

FIGS. 3A to 3C are diagrams illustrating three alignment states of a cholesteric liquid crystal.

FIG. 4 is a cross-sectional view of a conventional cholesteric liquid crystal display device.

FIG. 5 is a cross-sectional view of a conventional multicolor cholesteric liquid crystal display device.

[Explanation of symbols]

 11, 12 Substrate 21, 22 Transparent electrode 30, 30B, 30G, 30R Cholesteric liquid crystal 41 Light absorbing layer 45 Soaking layer 50B, 50G, 50R Liquid crystal display cell 71, 72 Adhesive layer

Continued on the front page (72) Inventor Taketo Hikiji 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. (Reference) 2H088 EA02 EA68 GA03 GA17 MA04 2H089 HA21 TA13 5G435 AA12 BB12 CC09 CC12 FF14 GG44 HH12

Claims (3)

[Claims] 1. A cholesteric liquid crystal display device having a cholesteric liquid crystal sealed between substrates each having a transparent electrode, and having a light absorbing layer on a surface opposite to an observation surface, wherein the cholesteric liquid crystal is uniformly arranged via the light absorbing layer. A cholesteric liquid crystal display device comprising a heat layer. 2. A cholesteric liquid crystal display device comprising: a plurality of cells each having cholesteric liquid crystal sealed between substrates each having a transparent electrode; and a light absorbing layer provided on a surface opposite to an observation surface. A cholesteric liquid crystal display device comprising a soaking layer provided through a light absorbing layer. 3. The cholesteric liquid crystal display device according to claim 1, wherein said soaking layer is made of a metal foil.