JPH0798452A - Reflection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the reflection type liquid crystal display device capable of making image display with a wide visual field angle without coloration regardless of the position of an external light source. CONSTITUTION:This reflection type liquid crystal display device is constituted by providing an observer's side electrode plate 2 arranged to face a rear surface electrode plate 1 with a light scattering layer 21 consisting essentially of a transparent resin and particulates dispersed into this transparent resin. The particulates having a small refractive index, optical average dispersion of <=0.09 and double rafraction of <=0.02 are applied by the transparent resin. Since the refractive index of the particulates is smaller than the refractive index of the transparent resin, a light scattering effect is high and since the optical average dispersion and double refractions are small, the coloration does not arise. The bright screen display free from the coloration is, therefore, made possible regardless of the position of the external light source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device, and more particularly to a wide viewing angle regardless of the position of an external light source.
Moreover, the present invention relates to an improvement in a reflective liquid crystal display device that enables a bright screen display without coloring.

[0002]

2. Description of the Related Art A liquid crystal display device of this type is generally shown in FIG.
A polarizing film (not shown) and transparent electrodes a4 and b4 as shown in FIG.
A pair of electrode plates a and b each provided with a liquid crystal substance c enclosed between these electrode plates a and b, the main part of which is formed. The film is made into linearly polarized light, and a voltage is applied to the liquid crystal substance c for each pixel to change its alignment state, and the polarization plane of the linearly polarized light that passes through that portion is rotated according to that alignment state to rotate it. The screen is displayed by blocking or transmitting the linearly polarized light by the polarizing film on the exit side according to the angle.
In a color liquid crystal display device that displays a color screen, a color filter layer for coloring polarized light is provided on one of the electrode plates a and b.

As a liquid crystal display device of this type,
A bright backlight for a display screen in which a light source (lamp) is arranged on the back surface or side surface of an electrode plate (hereinafter referred to as a back electrode plate) a located on the back side of a liquid crystal display device, and light rays are incident from the back electrode plate a side. Type or light guide type transmissive liquid crystal display device with a built-in lamp is widely used.

However, in this transmissive liquid crystal display device with a built-in lamp, the power consumed by the lamp is large.
Since it consumes substantially the same amount of power as other types of displays such as RTs and plasma displays, it has the drawbacks that the original low power consumption characteristics of liquid crystal display devices are impaired and that it becomes difficult to use it for a long time on the portable device. Was.

On the other hand, without incorporating such a lamp, outside light such as room light or natural light is made incident from an electrode plate (referred to as an observer side electrode plate) b located on the observer side of the apparatus,
There is also known a reflection type liquid crystal display device which reflects on a metal reflection film provided on the back electrode plate a and displays a screen by this reflected light. Since this device does not use a lamp, it consumes less power, and therefore has the advantage that it can withstand the long-term driving of a portable device.

In such a reflective liquid crystal display device, as the back electrode plate a, for example, as shown in FIG. 5, a base material a1 and a metal reflective film uniformly formed on the base material a1. a2 and a voltage application transparent electrode a4 provided on the metal reflection film a2 via color filter layers a3R, a3G, and a3B, or a main part thereof, or as shown in FIG. A back electrode plate or the like in which the metal reflection film a2 is uniformly provided on the surface of the substrate a1 opposite to the transparent electrode a4 is applied.

By the way, in this type of reflective liquid crystal display device, the metal reflection film a2 specularly reflects the incident light beam, so that the viewing angle is limited by the position of the light source of the external light. .

Therefore, in Japanese Patent Laid-Open No. 63-228887 or Photofabrication Symposium '92 sponsored by The Japan Printing Society, a metal thin film having uneven surface is applied as the metal reflection film a2 to obtain the metal reflection film a2.
A liquid crystal display device has been introduced in which the viewing angle of the display screen is widened by preventing the regular reflection of. That is, FIG. 7 is an explanatory view showing this liquid crystal display device. The back electrode plate a of this liquid crystal display device includes a base material a1 and a TFT element a6 provided on the base material a1 via an insulating layer a5. , This TFT element a6
The insulating resin layer a7 having an uneven surface provided thereon and the pixel-shaped metal thin-film metal reflection film a2 provided along the uneven surface of the insulating resin layer a7 constitute a main part. In this liquid crystal display device, since the metal reflection film a2 has an uneven surface reflecting the surface shape of the insulating resin layer a7, light can be diffusely reflected to widen the viewing angle of the display screen. It will be possible. In this liquid crystal display device, the TFT element a6 is the semiconductor portion a6.
2 and a semiconductor electrode a62 and a source electrode a61 and a drain electrode a63 which are provided on both sides of the semiconductor portion a62. The drain electrode a63 and the metal reflection film a2 are provided in the insulating layer a7 as a through hole. (Contact hole)
This metal reflective film a2 is used as a drive electrode for the liquid crystal substance. Further, in FIG. 7, b represents an electrode plate on the observer side, b1 is a base material thereof, and b2 is a transparent electrode uniformly provided on the base material b1. Further, c is a liquid crystal substance enclosed between the back electrode plate a and the observer-side electrode plate b, and d is a sealing material provided on the outer periphery of the liquid crystal display device.

As described above, the liquid crystal display device shown in FIG. 7 has an advantage that the viewing angle of the display screen can be widened, but on the other hand, the insulating resin layer a7 is formed at the time of manufacturing the device. A step and a step of providing unevenness on the surface are required, and a step of dry etching the insulating resin layer a7 to form a contact hole in order to electrically connect the drain electrode a63 and the metal-metal reflective film a2 is required. Therefore, there is a drawback that the productivity and the yield are extremely low. Further, in this liquid crystal display device, it is necessary to directly provide the metal reflection film a2 on the insulating resin layer a7 having the uneven surface by a method such as vacuum deposition or sputtering. At this formation stage, the metal reflection film a2 is oxidized. Alternatively, since it is easily hydroxylated, there is a problem that the original reflection performance of the metal reflection film a2 is impaired.

Under such a technical background, the applicant of the present invention has already proposed a liquid crystal display device in which a light scattering layer is provided on either the back electrode plate or the viewer side electrode plate (Japanese Patent Application No. 2000-242242). See Japanese Patent Application No. 5-102124 and Japanese Patent Application No. 5-170280).

According to this liquid crystal display device, display light is generated by the action of the light scattering layer whose main part is composed of a transparent resin and fine particles dispersed in the transparent resin and having a refractive index different from that of the transparent resin. Since it is scattered, the viewing angle of the display screen can be expanded regardless of the position of the external light source, and the manufacturing process of the device can be simplified, which has the advantage of improving production efficiency and yield. .

[0012]

However, in the above liquid crystal display device, since the fine particles having a refractive index different from that of the transparent resin are dispersed in the transparent resin, the refractive index of the transparent resin and the refractive index of the fine particles are different from each other. However, there is a problem that the display light is easily colored due to the difference between the two, or the birefringence or optical dispersion of the fine particles.

The present invention has been made by paying attention to such a problem, and its problem is that the viewing angle can be changed regardless of the position of the external light source while maintaining the advantages of the reflective liquid crystal display device. It is an object of the present invention to provide a reflective liquid crystal display device which enables a wide and bright screen display without coloring.

[0014]

That is, the invention according to claim 1 provides a back electrode plate provided with a metal reflection layer, and an observer provided facing the back electrode plate and provided with a transparent electrode. Assuming a reflective liquid crystal display device that includes a side electrode plate and a liquid crystal substance enclosed between these electrode plates and applies a voltage to each liquid crystal substance for each pixel to display a screen, the above-mentioned rear electrode plate Or on at least one of the observer-side electrode plates,
A light-scattering layer containing a transparent resin and fine particles dispersed in the transparent resin as a main component is provided, and the fine particles have a smaller refractive index than the transparent resin, and the optical average dispersion thereof is 0.09.
It is characterized in that it has a birefringence of 0.02 or less.

In such a technical means, since the material having the refractive index smaller than that of the transparent resin is applied as the fine particles forming a part of the light scattering layer, the viewing angle of the display screen becomes extremely wide. Therefore, a bright screen can be displayed regardless of the position of the external light source.

When the refractive index of the fine particles is larger than that of the transparent resin (for example, Ti having a refractive index of 2.5 to 2.9).
When O ₂ is dispersed as fine particles), the light scattering effect becomes insufficient and the viewing angle of the display screen is not sufficiently expanded. Figure 3
Is a graph showing this. That is, in a photosensitive phenol novolac epoxy resin having a refractive index of 1.57 after hardening, CaF ₂ (refractive index 1.43), PTFE
(Polytetrafluoroethylene, refractive index 1.35) and TiO ₂ (refractive index 2.49) fine particles were dispersed in 20% by weight respectively, and a coating solution was obtained using cellosolve acetate as a solvent. After coating and hardening this coating liquid on an aluminum thin film having a thickness of 0.2 μm provided on a glass substrate, a tungsten lamp is used for each coating hard film to form a visual angle (angle with the normal) 0 The brightness of each coated hard film was measured in the range of 60 degrees, and the results are shown in FIG. And
From FIG. 3, when CaF ₂ or PTFE having a refractive index smaller than that of the phenol novolac epoxy resin is applied as fine particles, Ti having a refractive index larger than that of the resin is applied.
The viewing angle is 10 to 6 compared with the case where O ₂ is applied as fine particles.
It can be confirmed that the brightness is high and the viewing angle is wide in the range of 0 degree.

Further, in this technical means, the above-mentioned optical average dispersion means a refractive index n _F for an F line having a wavelength of 0.486 μm and a refractive index n for a C line having a wavelength of 0.656 μm.
The difference with _C (n _F −n _C ). In the invention according to claim 1, the optical average dispersion of the fine particles is 0.0
Since it is 9 or less, when the light rays are refracted at the interface between the transparent resin and the fine particles, all visible rays are refracted in substantially the same direction without the refraction direction depending on the wavelength of the light rays.
Therefore, it is possible to prevent the display screen from being colored due to the optical average dispersion.

Next, when the fine particles have optical anisotropy, the refractive index of the fine particles varies depending on the plane of polarization of the light rays traveling in the fine particles. For example, in a uniaxial anisotropic crystal such as a tetragonal crystal, a hexagonal crystal, and a rhombic lattice crystal, the refractive index for a light beam having a polarization plane perpendicular to the axis of these crystals and the axis of the crystal There are two types of index of refraction, the index of refraction for light rays having parallel planes of polarization. Further, in biaxial anisotropic crystals such as orthorhombic crystals, monoclinic crystals, and triclinic crystals, there are three types of refractive indexes that differ depending on the plane of polarization of light rays (of these refractive indices, The difference between the maximum and the minimum is called birefringence). Then, the light rays incident on these anisotropic crystals are separated into respective polarized lights whose polarization planes are orthogonal to each other in the crystal, and the separated polarized lights have a speed (proportional to the reciprocal of the refractive index) corresponding to each refractive index. As it progresses, coloring of the emitted light beam occurs. On the other hand, when the birefringence of the fine particles is 0.02 or less, the birefringence is extremely small,
It is possible to prevent the display screen from being colored due to birefringence.

Examples of the fine particles satisfying the above-mentioned requirements include fine particles made of an inorganic substance and fine particles made of an organic polymer. And as the fine particles composed of an inorganic substance,
Fine particles having a cubic crystal structure called an equiaxed crystal, fine particles having a tetragonal crystal structure having a small birefringence similar to the equiaxed crystal, or amorphous fine particles can be applied. For example, CaF ₂ ,
Fluorine compounds such as MgF ₂ , SrF ₂ , LiF and NaF can be applied. Further, as the fine particles made of an organic substance,
PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy resin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PV
Fluorine-containing polymers such as DF (polyfluorovinylidene), ETFE (ethylene-tetrafluoroethylene copolymer), PVF (polyfluorovinyl), etc. can be exemplified, and fluorine atoms and fluorinated alkyl groups can be introduced into other polymers. It may be

Further, it is also possible to apply those obtained by subjecting the surface of the fluorine compound or the fluorine-containing polymer to an appropriate surface treatment as the fine particles. Examples of such surface treatment include, for example, SiO ₂ , ZrO ₂ , Al ₂ O
₃ , a treatment of coating and coating with ZnO, a transparent resin, a coupling agent, a surfactant, or the like. In addition to this, a treatment of causing a surface reaction with alcohol, amine, organic acid or the like can be exemplified.

On the other hand, the particle size of the above-mentioned fine particles is 0.05 to near the wavelength of visible light in order to improve the light scattering effect.
1.0 μm is desirable. When fine particles having a particle diameter of this level and a birefringence of 0.02 or less are applied, coloring of the display screen due to the birefringence does not substantially occur. It should be noted that some particles smaller than 0.05 μm or larger than 1.0 μm may be mixed in the fine particles, but they are smaller than the distance between the electrode plates in which the liquid crystal is sealed and do not disturb the normal alignment state of the liquid crystal. A particle size is desirable. The shape of these fine particles may be any shape such as a sphere, a disc, a gostone, a polygon, a rhombus, and a square plate.

Next, as the resin in which the above-mentioned fine particles are dispersed, a resin having a high visible light transmittance and having sufficient resistance to heat treatment and chemical treatment during the manufacturing process of the liquid crystal display device is desirable. For example, acrylic resin. , Epoxy resin, polyester resin, urethane resin, silicone resin, polyimide resin, etc. can be applied. When the light scattering layer is provided in a pattern, it is necessary to assemble the liquid crystal display device (for example, when wiring for electrical connection is provided). Therefore, an acrylic resin or epoxy having photosensitivity and developability is used. A system resin may be used. It is also possible to use a thermosetting resin or an ultraviolet curable resin.

The light-scattering layer can be formed by mixing and dispersing fine particles in a transparent resin, coating the transparent substrate with the fine particles, and drying. As the coating method, a flexographic printing method, a screen printing method, an offset printing method, a roll coating method or the like can be applied.

The light-scattering layer may be provided on either the observer-side electrode plate or the back electrode plate that constitutes the liquid crystal display device, but it is necessary to provide it on the optical path of the display light that constitutes the display screen.

Next, as the metal reflective layer provided on the back electrode plate in this technical means, silver, aluminum,
Aluminum alloy, magnesium, nickel, titanium,
A thin film of a metal such as chromium having a high visible light reflectance or a multi-layered metal thin film formed by laminating a large number of these thin films can be applied. The metal reflection film may be patterned into a stripe shape or a pixel shape to be used as a liquid crystal driving electrode. Further, a transparent thin film may be further laminated on this metal reflection film. As such a transparent thin film, an ITO thin film composed of indium oxide mixed with tin oxide as a dopant, an indium oxide thin film, a silicon oxide thin film, an aluminum oxide thin film, a zirconium oxide thin film, a magnesium oxide thin film and the like can be used. . Further, the metal reflection film is formed on the entire surface of the display screen or in a pattern such as a pixel shape,
A transparent electrode for driving a liquid crystal can be provided on the metal reflection film via a transparent insulating layer. As such a transparent electrode, in addition to the ITO thin film, a thin film obtained by adding titanium oxide, lead oxide, antimony oxide, bismuth oxide, hafnium oxide or yttrium oxide to indium oxide,
A thin film formed by adding aluminum oxide to zinc oxide, or a multilayer film formed by laminating a large number of these thin films can be used.

On the other hand, as the transparent electrode provided on the observer side electrode plate, a thin film obtained by adding titanium oxide, lead oxide, antimony oxide, bismuth oxide, hafnium oxide or yttrium oxide to the ITO thin film, indium oxide, A thin film formed by adding aluminum oxide to zinc oxide, or a multilayer film formed by laminating a large number of these thin films can be used.

In the reflective liquid crystal display device according to the first aspect of the present invention, since display light is not colored and white light can be displayed, the display light is colored in the optical path of the display light. A color screen can be displayed by providing a color filter layer. As this color filter layer, a well-known one can be used. For example, a color filter layer formed by printing a printing ink containing a colorant by a printing method, a photosensitive resin is applied, and a pattern is exposed by a photolithography method. A color filter layer obtained by dyeing the photosensitive resin remaining after development, a pigment obtained by applying a photosensitive resin in which a colorant is dispersed and exposing and developing it in a pattern according to the photolithography method. A color filter layer or the like prepared by a dispersion method can be used. In addition to this, it is also possible to use a color filter layer by an electrodeposition method which is manufactured by electrodepositing an electrodeposition resin containing a coloring material for each pixel.

As the substrate of the back electrode plate, it is possible to use a transparent substrate such as a glass plate, a plastic plate, or a plastic film, or an opaque substrate colored in black or the like.

[0029]

According to the invention of claim 1, a light scattering layer containing a transparent resin and fine particles dispersed in the transparent resin as a main component is provided on at least one of the back electrode plate and the observer-side electrode plate. In addition, since fine particles having a smaller refractive index than the transparent resin are used, the viewing angle of the display screen can be increased.

The optical average dispersion of the fine particles is 0.
Since it is 09 or less and its birefringence is 0.02 or less, it is possible to prevent coloration of the display screen based on optical average dispersion and birefringence.

[0031]

Embodiments of the present invention will now be described in detail with reference to the drawings.

[Embodiment 1] As shown in FIG. 1, a reflective liquid crystal display device according to this embodiment includes a back electrode plate 1 and an observer-side electrode plate 2 provided opposite to the back electrode plate 1. When,
The liquid crystal substance 3 enclosed between the electrode plates 1 and 2 and a polarizing plate and a retardation plate (not shown) form a main part. The back electrode plate 1 has a transparent substrate 10 and a pitch of 300 μm in a screen display region on the transparent substrate 10.
A metal reflection film 11 made of aluminum having a width of 290 μm and a thickness of 0.2 μm provided in a total of 480 stripe patterns.
And an ITO thin film 1 having a thickness of 0.07 μm formed on the metal reflection film 11 in the same pattern as the metal reflection film 11.
The main part is composed of 2 and. On the other hand, the viewer-side electrode plate 2 has a transparent substrate 20, a light-scattering layer 21 uniformly provided on the entire surface of the display region, and a total of 640 stripes having a pitch of 300 μm and a width of 290 μm on the light-scattering layer 21. ITO thin film 22 provided in a pattern and having a thickness of about 1.0 μm
(Area resistivity of about 7Ω / □) constitutes the main part. Further, the metal reflection film 11 and the ITO thin film 22 are provided in a stripe pattern in directions orthogonal to each other,
By applying a voltage between the metal reflective film 11 as a scanning line and the ITO thin film 22 as a signal line, the liquid crystal substance at the intersection is driven so that a screen display can be achieved.

The light-scattering layer 21 has CaF ₂ (refractive index: 1.43, optical average dispersion :) in a photosensitive phenol novolac epoxy resin having a refractive index of 1.57 when hardened.
22% by weight of 0.005, birefringence: 0).

The metal reflection film 11 and the ITO thin film 1 are also provided.
2 means that the metal thin film and the ITO thin film are continuously formed on the transparent substrate 20, and the IT is performed according to the photolithography method.
This is formed by patterning the O thin film and then etching the metal thin film using the remaining ITO thin film as an etching resist.

When a screen was displayed by applying a voltage between the metal reflection film 11 and the ITO thin film 22, the screen was white without coloring and had a wide viewing angle of 60 degrees with respect to the normal to the screen. The display screen could be recognized well even from an angle.

[Embodiment 2] In the reflection type liquid crystal display device according to this embodiment, as shown in FIG. 2, a back electrode plate 4 and an observer side electrode plate 5 provided facing the back electrode plate 4. When,
The liquid crystal substance 6 enclosed between the electrode plates 4 and 5 and a polarizing plate and a retardation plate (not shown) form a main part. The back electrode plate 4 has a transparent substrate 40 and a pitch of 300 μm in a screen display area on the transparent substrate 40.
A metal reflection film 4 made of aluminum having a width of 290 μm and a thickness of 0.15 μm provided in a total of 480 stripe patterns.
1 and an ITO thin film 42 having a thickness of 0.06 μm, which is provided on the metal reflection film 41 in the same pattern as the metal reflection film 41, constitutes its main part. On the other hand, the observer-side electrode plate 5 has a pitch of 100 μm between the transparent substrate 50 and a portion between pixels in the screen display area of the transparent substrate 50.
With a total of 1921 black stripes 53,
Three colors (red, green, blue) with a total of 1920 stripes in the pixel area between these black stripes
Color filter layers 54R, 54G, and 54B, and these black stripes 51 and color filter layers 54
A light-scattering layer 51 having a thickness of about 1 μm, which is uniformly provided on the entire surface of the screen display region by covering R, 54G, and 54B, and a pitch of 100 μm and a width of 90 at the pixel portion of the light-scattering layer 51.
The ITO thin film 52 (area resistivity of about 8 Ω / □), which is provided in 1920 stripes in total, constitutes the main part. Further, the metal reflection film 41 and the ITO thin film 52 are provided in a stripe pattern in a direction orthogonal to each other, and the metal reflection film 41 is used as a scanning line and the ITO thin film 52 is used as a signal line to apply a voltage between them to intersect each other. The liquid crystal material at the position is driven so that a screen display can be achieved.

The light-scattering layer 51 is made of a photosensitive phenol novolac epoxy resin having a refractive index of 1.57 when hardened with MaF ₂ (refractive index: 1.38, optical average dispersion:
0.006 and birefringence: 0.012) are dispersed in about 18% by weight.

Further, the color filter layers 54R, 5R
4G and 54B are formed by intaglio offset printing using an epoxy resin as a resin component and an organic pigment as a colorant component.

On the other hand, the metal reflection film 41 and the ITO thin film 4
2 means that a metal thin film and an ITO thin film are continuously formed on the transparent substrate 40, and I is formed according to the photolithography method.
This is formed by patterning the TO thin film and then etching the metal thin film using the remaining ITO thin film as an etching resist.

When a screen was displayed by applying a voltage between the metal reflection film 41 and the ITO thin film 52, the screen was vivid with high color purity, and the viewing angle was wide and the screen normal angle was 60. The display screen could be recognized well even when viewed from the angle of degrees.

[0041]

According to the invention of claim 1, the viewing angle of the display screen can be increased, and the display screen can be prevented from being colored due to optical average dispersion or birefringence. It has the effect of enabling a bright screen display without coloring regardless of the color.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display device according to a first embodiment.

FIG. 2 is a cross-sectional view of a liquid crystal display device according to a second embodiment.

FIG. 3 is a graph showing the relationship between the viewing angle and the brightness according to the refractive index of fine particles.

FIG. 4 is a cross-sectional view of a liquid crystal display device according to a conventional example.

FIG. 5 is a cross-sectional view of a back electrode plate according to a conventional example.

FIG. 6 is a cross-sectional view of a back electrode plate according to a conventional example.

FIG. 7 is a cross-sectional view of a reflective liquid crystal display device according to a conventional example.

[Explanation of symbols]

 1 Rear Electrode Plate 2 Observer Side Electrode Plate 3 Liquid Crystal Substance 4 Rear Electrode Plate 5 Observer Side Electrode Plate 6 Liquid Crystal Substance 10 Transparent Substrate 11 Metal Reflective Film 12 ITO Thin Film 20 Transparent Substrate 21 Light Scattering Layer 22 ITO Thin Film 40 Transparent Substrate 41 Metal reflective film 42 ITO thin film 50 Transparent substrate 51 Light scattering layer 52 ITO thin film 53 Black stripe 54R Color filter layer 54G Color filter layer 54B Color filter layer

Claims (1)

[Claims] 1. A back electrode plate provided with a metal reflective layer, an observer-side electrode plate provided facing the back electrode plate and provided with transparent electrodes, and enclosed between these electrode plates. A liquid crystal substance, wherein a liquid crystal substance is applied to each pixel to display a screen by applying a voltage to the liquid crystal substance, a transparent resin and the transparent resin are provided on at least one of the back electrode plate and the observer side electrode plate. A light-scattering layer containing, as a main component, fine particles dispersed in a resin is provided, and the fine particles have a smaller refractive index than the transparent resin, and the optical average dispersion thereof is 0.
A reflective liquid crystal display device having a birefringence of not more than 09 and not more than 0.02.