JP2001004995A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device which is bright and has high visibility and which can be produced at a low cost by forming a cholesteric liquid crystal film in which specified cholesteric alignment is fixed. SOLUTION: The reflection type liquid crystal display device is equipped with at least a liquid crystal cell reflection layer having a liquid crystal layer formed between two electrode substrates facing each other, and a cholesteric liquid crystal film in which such cholesteric alignment is fixed that the axial direction of helix in the cholesteric liquid crystal phase is not homogeneously parallel to the film thickness direction. Namely, the cholesteric liquid crystal film used forms such cholesteric alignment that the axial direction of helix in the cholesteric liquid crystal phase is not homogeneously parallel to the film thickness direction. As for an example of the cholesteric alignment, the cholesteric alignment is produced into such a state that the helical structure of normal cholesteric alignment regarded as a pseudo-layer structure is regularly or irregularly bent of folded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bright and highly visible reflective liquid crystal display device provided with a cholesteric liquid crystal film having a unique cholesteric alignment fixed.

[0002]

2. Description of the Related Art The use of liquid crystal display devices has expanded from calculators to word processor and personal computer displays due to the remarkable improvement in display performance. Furthermore, expectations for market expansion as displays for portable information terminal equipment, which can make full use of the thin and lightweight features of liquid crystal display devices, are increasing. For portable applications, since it is usually driven by a battery, it is important to reduce power consumption. For this reason, a liquid crystal display device for portable use requires a reflective type liquid crystal display device that does not require a backlight that consumes a large amount of power, and in particular, a type having a reflective plate with high contrast and high display quality has low power consumption. It can be made thinner, thinner and lighter, and is attracting attention.

In a reflection type liquid crystal display device, display is performed by light from a viewer side (indoor light or external light such as sunlight) without using a backlight. Therefore, improvement in brightness is strongly demanded. In recent years, in order to solve these problems, a single polarizing plate, which was conventionally required two, suppresses light loss. A fine structure is provided on the surface of the reflecting plate to collect incident light. And a diffusion film, and using a reflection hologram having a light condensing function.

However, of the above techniques, the method of reducing the number of polarizing plates or the combination of a specular reflection plate and a diffusion film can improve brightness, but the effect is not sufficient, and the surface of the reflection plate is not sufficiently effective. The method of providing a fine structure and the method of using a reflection hologram have a problem of an increase in cost and a decrease in productivity as compared with the case of using a conventional reflector.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and comprises a cholesteric liquid crystal film having a specific cholesteric orientation fixed thereon.
The present invention has led to the invention of a reflective liquid crystal display element which is bright, has high visibility, and can be easily manufactured at low cost.

[0006]

That is, the first aspect of the present invention is as follows.
Is a liquid crystal cell having a liquid crystal layer formed between two opposing electrode substrates, a cholesteric liquid crystal film having a cholesteric liquid crystal film in which the helical axis orientation in the reflective layer and the cholesteric liquid crystal phase is not uniformly parallel to the film thickness direction. The present invention relates to a reflection type liquid crystal display element provided at least.

A second aspect of the present invention relates to the reflective liquid crystal display device further comprising one or more polarizing layers.

A third aspect of the present invention relates to the reflective liquid crystal display device further comprising one or more optical compensation layers.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. The reflective liquid crystal display device of the present invention includes a liquid crystal cell having a liquid crystal layer formed between two opposing electrode substrates, a reflective layer, and a cholesteric liquid crystal film having a specific cholesteric alignment fixed.

The electrode substrate is not particularly limited, and a known electrode substrate for controlling a material exhibiting liquid crystallinity as a liquid crystal layer at the time of screen display can be used, and the object of the present invention can be achieved. If it is, there is no particular limitation.

The liquid crystal layer can be formed by filling the material exhibiting liquid crystal properties between the electrode substrates and disposing the material. The material exhibiting liquid crystallinity is not particularly limited, and examples thereof include ordinary low-molecular liquid crystals, high-molecular liquid crystals, and mixtures thereof that can form various liquid crystal cells. Dyes, chiral agents, and the like can be added to these as long as the liquid crystallinity is not impaired.

The liquid crystal cell may include, in addition to the electrode substrate and the material exhibiting liquid crystallinity, various components necessary for forming various types of liquid crystal cells described below. The type of the liquid crystal cell is not particularly limited, and is, for example, a GH (Guest Host) type, a TN (Twisted Nemati) type.
c) method, STN (Super Twisted Nematic) method, EC
B (Electrically Controlled Birefringence) method,
IPS (In-Plane Switching) method, VA (Vertical A)
lignment) method, OCB (Optically Compensated Biref)
Various systems such as a ring system, a HAN (Hybrid Aligned Nematic) system, a halftone gray scale system, a domain division system, and a display system using a ferroelectric liquid crystal or an anti-ferroelectric liquid crystal are exemplified.

There is no particular limitation on the driving method of the liquid crystal cell. A simple matrix method used for STN-LCDs and the like, a TFT (Thin Film Transistor) electrode, an MIM
(Metal Insulator Metal) electrode and TFD (Thin
Any driving method such as an active matrix method using an active electrode such as a film diode (electrode) or a plasma addressing method may be used.

The reflective layer provided in the reflective liquid crystal display element of the present invention is not particularly limited as long as it has a sufficiently high reflectance.
Examples thereof include metals such as gold, chromium and platinum, oxides such as magnesium oxide, dielectric multilayer films, liquid crystal films exhibiting selective reflection, and combinations thereof. These reflective layers may be flat or curved. Further, it may also serve as an electrode on the electrode substrate on the side opposite to the viewing side. The reflective layer may be not only a layer that does not transmit light but only reflects light but also a semi-transmissive layer that partially transmits light.

The position of the reflection layer in the reflection type liquid crystal display device of the present invention is not particularly limited as long as it is usually provided at a position opposite to the viewing side of the liquid crystal layer.
Next, the cholesteric liquid crystal film forms a cholesteric orientation in which the helical axis orientation in the cholesteric liquid crystal phase is not uniformly parallel to the film thickness direction. As an example of such a cholesteric orientation, when a spiral structure in a normal cholesteric orientation is regarded as a pseudo-layer structure,
One in which the layer structure is cholesterically oriented so as to be regularly or irregularly curved or bent. Such a state is generally called a fingerprint-like structure. When a fingerprint-like structure is formed, oily streaks are observed on the surface of the cholesteric liquid crystal layer. One embodiment of the cholesteric liquid crystal film of the present invention includes one having the above-mentioned fingerprint-like structure and forming an oily streak, but is not limited thereto.

In the cholesteric liquid crystal film of the present invention, the region where the helical axis orientation is not uniformly parallel to the film thickness direction is formed in any region of the entire film, the film surface, or the inside of the film. For example, it may be provided on a part of the film surface (film surface region) or on a part of the inside of the film (film inner region). Further, the region having the cholesteric orientation may be provided in a plurality of regions of the single-layer film, for example, a film front and back surface region and a plurality of film inner regions. Further, the region is not necessarily required to be formed as a layer having a uniform thickness on the film surface or inside, for example, as long as the region is formed on at least a part of the film surface or inside the film. Good. Further, the area may have a shape of a desired figure, pictogram, numeral, symbol, or the like. The cholesteric orientation as described above formed by the cholesteric liquid crystal film of the present invention can be easily confirmed by observing the surface shape and cross-sectional shape of the liquid crystal layer with an atomic force microscope, a transmission electron microscope, or the like.

The cholesteric liquid crystal film as described above has a fingerprint-like structure and a cholesteric orientation so as to form an oily streak by using, for example, a polymer liquid crystal, a low molecular liquid crystal or a mixture thereof as a film material. Thereafter, the orientation is fixed by a method according to the film material such as cooling or crosslinking, whereby a cholesteric liquid crystal film having a desired diffusion rate can be obtained. The conditions under which the cholesteric alignment having a desired diffusion rate can be formed are inconsistent because they vary depending on the type, composition, physical properties, etc. of the polymer liquid crystal or low molecular liquid crystal used as the film material. The cholesteric liquid crystal film of the present invention can be obtained by appropriately adjusting the heat treatment temperature, the heat treatment time, and the film thickness during the formation. The heat treatment temperature for forming the cholesteric orientation is usually 30 to 250 ° C, preferably 40 to 200 ° C, and particularly preferably 50 to 170 ° C.
Range. The heat treatment time is usually 5 seconds to 2 hours,
Preferably 10 seconds to 1 hour, particularly preferably 20 seconds to 3
The range is 0 minutes. Further, the film thickness of the cholesteric liquid crystal film is usually 0.3 to 30 μm, preferably 0.5 to 20 μm, particularly preferably 0.7 to 10 μm.
It is in the range of μm. By appropriately adjusting the heat treatment temperature, the heat treatment time, and the film thickness, a cholesteric liquid crystal film having various optical parameters optimal for the present invention described later can be obtained. Further, as a method of fixing the cholesteric alignment, when a polymer liquid crystal is used as a main component as a film material, for example, after a desired cholesteric liquid crystal phase is developed, the cholesteric alignment is fixed by quenching from the state. A method or the like can be adopted. When low-molecular liquid crystal is the main component,
A method in which a desired cholesteric liquid crystal phase is developed and cross-linked by light, heat, an electron beam, or the like while the state is maintained to fix the cholesteric alignment can be appropriately employed.

The polymer liquid crystal used as the film material of the cholesteric liquid crystal film is not particularly limited as long as the cholesteric orientation can be fixed, and any of a main chain type and a side chain type polymer liquid crystal can be used. . Specifically, polyester, polyamide, polycarbonate,
A main-chain type liquid crystal polymer such as polyesterimide, or a side-chain type liquid crystal polymer such as polyacrylate, polymethacrylate, polymalonate, and polysiloxane is exemplified. Among them, a liquid crystalline polyester which has good orientation in forming cholesteric orientation and is relatively easy to synthesize is desirable. Preferable examples of the structural unit of the liquid crystalline polyester include an aromatic or aliphatic diol unit, an aromatic or aliphatic dicarboxylic acid unit, and an aromatic or aliphatic hydroxycarboxylic acid unit.

The low-molecular liquid crystal used as a film material of the cholesteric liquid crystal film is, for example, a liquid crystal having a basic skeleton of a biphenyl derivative, a phenylbenzoate derivative, a stilbene derivative or the like into which a functional group such as an acryloyl group, a vinyl group or an epoxy group is introduced. Is mentioned. As the low-molecular liquid crystal, both lyotropic properties and thermotropic properties can be used, but those exhibiting thermotropic properties are more preferable from the viewpoint of workability, process and the like.

In order to improve the heat resistance of the finally obtained cholesteric liquid crystal film, in addition to a polymer liquid crystal or a low molecular weight liquid crystal in the film material, for example, a bis azide compound or A cross-linking agent such as glycidyl methacrylate can be added, and by adding these cross-linking agents, cross-linking can be performed with a cholesteric liquid crystal phase developed. Further, various additives such as a dichroic dye, a dye, a pigment, an antioxidant, an ultraviolet absorber, and a hard coat agent can be appropriately added to the film material as long as the effects of the present invention are not impaired.

The various optical parameters of the cholesteric liquid crystal film thus obtained cannot be determined unconditionally because they vary depending on the type of film material, heat treatment conditions, and the like. However, the wavelength band of cholesteric selective reflection is as follows.
Usually, it is preferably 30 to 150 nm, and the center wavelength of the cholesteric selective reflection is usually 380 to 780 n.
m, preferably in the visible range from 420 to 700 nm, or 8
The number of spiral turns in the near infrared region of from 00 to 2000 nm, preferably from 850 to 1100, and the number of spiral turns in the cholesteric orientation is usually 2 or more, preferably 2.2 or more, particularly preferably 2.5 or more, and more preferably cholesteric. The liquid crystal film has a diffusivity of 15% or more, preferably 20% or more and 90% or less, particularly preferably 30% or more and 85% or less. Here, the wavelength bandwidth of the cholesteric selective reflection referred to in the present invention means that when circularly polarized light in the same direction as the twisting direction of the liquid crystal molecules forming the cholesteric alignment is incident, the reflectance by the selective reflection is 70%.
% Means a wavelength range of not less than%. In addition, the diffusivity of the cholesteric liquid crystal film in the present invention is a diffusivity defined by a ratio ((SCE / SCI) × 100) of the regular reflection removal reflectance (SCE) and the regular reflection-containing reflectance (SCI). . The regular reflection-inclusive reflectance (SCI) refers to the total reflectance when an object to be measured is uniformly illuminated by diffuse illumination.
In addition, the specular reflection removal reflectance (SCE) is obtained by removing a specularly reflected light component from the total reflectance when an object to be measured is uniformly illuminated by diffuse illumination (consisting of a component of light diffused on the surface of the object to be measured).
It refers to diffuse reflectance (total reflectance = specular reflectance + diffuse reflectance). These specular reflection removal reflectance and specular reflection included reflectance can be determined by measuring in accordance with JIS-Z-8722 "Color measurement method-reflection and transmission object". As a specific measurement method, the measurement can be performed using a measuring instrument having a d / 8 (diffuse illumination 8 ゜ light receiving) illumination / light receiving optical system, for example, a spectrophotometer CM-3500d manufactured by Minolta.

The reflection type liquid crystal display device of the present invention usually comprises
At least one cholesteric liquid crystal film as described above is provided. In addition, a configuration in which a plurality of cholesteric liquid crystal films are laminated according to the application and required optical characteristics,
Further, a cholesteric liquid crystal film having one or more layers and a cholesteric alignment film in which a cholesteric orientation in which the helical axis orientation is uniformly parallel to the film thickness direction is fixed to one or more layers may be laminated. Good. When two or more cholesteric liquid crystal films and cholesteric alignment films having no diffractive area are laminated, two or more cholesteric liquid crystal films and cholesteric alignment films may be alternately laminated.

The position of the cholesteric liquid crystal film in the reflection type liquid crystal display device of the present invention is not particularly limited, but, for example, between the reflection layer and the liquid crystal layer and / or
Alternatively, it can be arranged at any position on the viewing side of the reflective layer, such as the viewing side of the liquid crystal layer. Specifically, when the reflective liquid crystal display element of the present invention does not have a polarizing layer, it is desirable to provide one or more layers on the viewing side of the liquid crystal layer and / or between the liquid crystal layer and the reflective layer. On the other hand, when the reflective liquid crystal display element of the present invention has a polarizing layer, it is desirable to provide one or more layers outside the polarizing layer and / or between the liquid crystal layer and the polarizing layer on the viewing side of the reflective layer.

The reflection type liquid crystal display device of the present invention comprises a liquid crystal cell, a reflection layer and a cholesteric liquid crystal film,
One or more polarizing layers, one or more optical compensation layers, a protective layer, an antireflection film, a prism sheet, a diffusion sheet, a light guide plate, or other components such as an adhesive layer or an adhesive layer for bonding these. Can also be included.

The polarizing layer is not particularly limited as long as the object of the present invention can be achieved, and a normal layer used for a liquid crystal display can be used. The arrangement position when the polarizing layer is provided in the reflective liquid crystal display element of the present invention,
It may be disposed directly in contact with the outer surface of the liquid crystal cell, or may be disposed separately from the surface of the electrode substrate via a cholesteric liquid crystal film or another layer.

As the optical compensation layer, known materials such as a stretched polymer film, one using a nematic liquid crystal substance, and one using a discotic liquid crystal substance can be used. By providing the reflection type liquid crystal display element of the present invention with the optical compensation layer, a more remarkable effect of improving visibility can be obtained by combination with a cholesteric liquid crystal film whose helical axis direction is not uniformly parallel to the film thickness direction.

The protective layer is not particularly limited, and various plastic films and the like can be used. By providing a protective layer, effects such as surface protection, increase in strength, and improvement in environmental reliability can be obtained.

The prism sheet, the diffusion sheet, and the light guide plate are not particularly limited, and known ones can be provided in the reflection type liquid crystal display device of the present invention. The method for producing the reflective liquid crystal display element of the present invention is not particularly limited, and a reflective layer, a cholesteric liquid crystal film and other layers provided as necessary may be provided outside the liquid crystal cell assembled by a known method. A method of forming the structure in the order in which the structure is obtained can be given. The method for obtaining each of the layers is not particularly limited, and can be obtained by appropriately employing a known method.

In order to obtain a stretched polymer film as an optical compensation layer, a polymer material is stretched, formed, rolled, drawn, solid extruded, blow-molded, vapor-deposited, or the like, and subjected to a known molding process. Can be. As a compensation layer using a liquid crystal material, a liquid crystal material including a nematic liquid crystal material or a discotic liquid crystal material was oriented in a desired state such as nematic alignment, twisted nematic alignment, cholesteric alignment, hybrid alignment, or twisted hybrid alignment. Thereafter, it can be obtained by a method of fixing by the same method as the fixing of the alignment in the cholesteric liquid crystal film described above, or the like.

[0030]

EXAMPLES Examples will be described below, but the present invention is not limited to these examples.

Reference Example 1 R having a glass transition temperature of 80 ° C.
A liquid crystalline polyester containing an optically active compound was formed on a triacetyl cellulose film having a rubbing polyimide layer by a spin coating method, and heat-treated at 135 ° C. for 5 minutes. When the film thickness of the film obtained was measured by a stylus film thickness meter, it was about 3.2 μm.

When the obtained film was observed by a polarizing microscope and a TEM observation of the cross section of the film, the cholesteric orientation in which the helical axis orientation in the cholesteric phase was not uniformly parallel to the film thickness direction was fixed, and the fingerprint-like structure and It was observed that oily streaks were formed. Further, the transmission spectrum of the film was measured with an ultraviolet-visible / near-infrared spectrophotometer V-570 manufactured by JASCO Corporation. A cholesteric liquid crystal exhibiting selective reflection with a center wavelength λs of about 800 nm and a selective reflection wavelength bandwidth Δλ of about 130 nm. It was confirmed that the film was formed on a triacetyl cellulose film having a rubbing polyimide layer.

(Example 1) The cholesteric liquid crystal film surface obtained in Reference Example 1 was bonded to a commercially available reflective liquid crystal display device such that the cholesteric liquid crystal film side was in contact with the display surface of the device.

When the brightness of the display was measured using a color luminance meter BM-5A manufactured by Topcon under general illumination on a reflective liquid crystal display device in which the film was bonded to the display surface, the cholesteric liquid crystal film was bonded. It was confirmed that the brightness was improved by about 40% as compared with the reflection type liquid crystal display device having no display.

Example 2 A liquid crystal material S-42 manufactured by Mitsui Toatsu Co., Ltd. was used as a liquid crystal material in ZLI-1840 manufactured by Merck.
8 was dissolved at 2% by weight to obtain a liquid crystal composition. The liquid crystal composition was injected between two electrode substrates each having an ITO transparent electrode and having a cell gap of 10 μm to form a liquid crystal layer, thereby producing a liquid crystal cell. An aluminum vapor-deposited reflection plate is attached to the surface opposite to the viewing side of the liquid crystal cell, and the cholesteric liquid crystal film obtained in Reference Example 1 is attached to the viewing side of the liquid crystal cell to produce a GH type liquid crystal display device. did.

When the brightness of the obtained GH type liquid crystal display device was measured in the same manner as in Example 1, it was confirmed that the brightness was significantly improved as compared with the device having no cholesteric liquid crystal film. Was.

Example 3 A liquid crystal composition was obtained by adding 2.7% by weight of Merck C-15 as a chiral agent to ZLI-2293 manufactured by Merck as a liquid crystal material. The liquid crystal composition was injected between two electrode substrates each having an ITO transparent electrode and having a cell gap of 6.2 μm, and a liquid crystal layer was formed to manufacture a liquid crystal cell. A polarizing plate is stuck on both sides of the liquid crystal cell, a reflecting plate is stuck on a polarizing plate opposite to the viewing side, and a cholesteric liquid crystal film obtained in Reference Example 1 is stuck on a viewing side, and
A reflective STN liquid crystal display device having a twist angle of 240 ° was manufactured.

When the brightness of the obtained reflective STN liquid crystal display device was measured in the same manner as in Example 1, it was confirmed that the brightness was greatly improved as compared with the device having no cholesteric liquid crystal film. Was done.

Example 4 A liquid crystal composition was obtained by adding 1.3% by weight of Merck C-15 as a chiral agent to ZLI-4792 manufactured by Merck as a liquid crystal material. The liquid crystal composition was injected between two electrode substrates each having an ITO transparent electrode and having a cell gap of 4.8 μm, and a liquid crystal layer was formed to produce a liquid crystal cell. A polarizing plate is stuck on both sides of the liquid crystal cell, a reflecting plate is stuck on a polarizing plate opposite to the viewing side, and a cholesteric liquid crystal film obtained in Reference Example 1 is stuck on a viewing side, and
A reflective TN liquid crystal display device having a twist angle of 90 ° was manufactured.

When the brightness of the obtained reflective TN liquid crystal display device was measured in the same manner as in Example 1, it was confirmed that the brightness was greatly improved as compared with the device having no cholesteric liquid crystal film. Was done.

Example 5 A liquid crystal composition was obtained by adding 2.0% by weight of Merck C-15 as a chiral agent to ZLI-4792 manufactured by Merck as a liquid crystal material. An electrode substrate provided with an ITO transparent electrode and an electrode substrate provided with an aluminum reflective electrode were placed at a cell gap of 2.2 μm.
m, the liquid crystal composition was injected between two electrode substrates to form a liquid crystal layer, whereby a liquid crystal cell was manufactured. Two optical compensation layers were stuck on the viewing side of this liquid crystal cell, that is, on the surface on the side of the ITO transparent electrode substrate, and a polarizing plate was stuck thereon. Further, the cholesteric liquid crystal film obtained in Reference Example 1 was pasted on a polarizing plate to produce a reflective TN liquid crystal display device having a twist angle of 63 °.

When the brightness of the obtained reflective TN liquid crystal display device was measured in the same manner as in Example 1, it was confirmed that the brightness was significantly improved as compared with the device having no cholesteric liquid crystal film. Was done.

[0043]

The reflection type liquid crystal display device of the present invention is provided with a cholesteric liquid crystal film having a cholesteric orientation in which the helical axis is not uniformly parallel to the film thickness direction. Thus, it is possible to obtain a reflection type liquid crystal display element which can be easily manufactured.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryo Nishimura 8 Chidori-cho, Naka-ku, Yokohama-shi, Kanagawa Pref. FA14Y FA15Y FB02 FB08 FD06 GA06 GA11 GA13 HA07 HA08 HA10 JA01 LA11 LA12 LA13 LA16 5C094 AA02 AA10 AA43 AA44 BA43 DA13 EA05 EA06 EB04 ED20 FA02 FB01 FB20 GB10

Claims (3)

[Claims] A cholesteric liquid crystal cell having a liquid crystal layer formed between two opposing electrode substrates, a cholesteric liquid crystal phase, a cholesteric liquid crystal phase, and a cholesteric liquid crystal phase in which a cholesteric orientation is not uniformly parallel to a film thickness direction. A reflective liquid crystal display device comprising at least a liquid crystal film. 2. The reflective liquid crystal display device according to claim 1, further comprising one or more polarizing layers. 3. The reflective liquid crystal display device according to claim 1, further comprising at least one optical compensation layer.