JPH11316373A - Reflection type liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high quality display by enabling a transparent state of an optical modulation layer to display arbitrary colors such as red, blue, green, etc., in an excellent contrast caused by composite action of a Bragg reflection layer and a scattering layer, and also to reproduce a color of a very high degree of brightness and purity when a voltage is applied. SOLUTION: A reflection type liquid crystal display, provided with an optical modulation layer 13 between a pair of electrode planes one of which is at least a transparent electrode, has such a structure that the optical modulation layer 13 varying a light scattering state by applying a voltage across the electrode planes and at least one or more kinds of Bragg reflection layer 20 behind the optical modulation layer 13 are arranged, and a scattering layer 30 is arranged behind the Bragg reflection layer 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device using a light scattering type liquid crystal display element.

[0002]

2. Description of the Related Art A liquid crystal display device has many excellent features, such as thinness and low power consumption, and is therefore frequently used as a display panel of equipment for various uses. As a display method of the liquid crystal display device, a TN (twisted nematic) mode or an STN (super twisted nematic) mode is used.
A method utilizing one or two polarizing plates typified by a mode and utilizing birefringence or optical rotation by a liquid crystal is widely and practically used as the most general method. TN mode or S
The light use efficiency of the TN mode is theoretically 50% or less due to light absorption loss by the polarizing plate, and the display becomes dark.

On the other hand, phase transition mode and polymer dispersion mode
There is a method using light scattering by liquid crystal without using a polarizing plate as represented by a liquid crystal. Since these light scattering methods do not require a polarizing plate, light absorption is not caused by the polarizing plate, and light can be used effectively, so that a bright display can be achieved. In recent years, among polymer light-scattering modes, polymer-dispersed liquid crystal panels, in particular, have attracted attention because they can be operated at low voltage and low hysteresis.

In a polymer-dispersed liquid crystal panel, a polymer layer is disposed between a pair of electrode substrates provided with at least one transparent electrode, and a positive dielectric anisotropy is formed in the polymer layer. Has a structure in which the nematic liquid crystal is dispersed as droplets or a fine continuous phase (hereinafter referred to as a polymer-dispersed liquid crystal layer). Generally, since a polarizing plate or an alignment film is unnecessary, light It has the characteristic that the utilization efficiency of the device can be increased to 80% or more.

In a polymer dispersed type liquid crystal panel, when no voltage is applied (OFF state), the display becomes a milky white state due to the light scattering action, and when the voltage is applied (ON state), the light scattering action is lost and the display is transparent. State. As a light scattering type liquid crystal display device utilizing a change in the light scattering state, there is, for example, a phase transition type liquid crystal display device in addition to the polymer dispersion type liquid crystal described above.

When these light-scattering type liquid crystal display devices are used as a reflection mode direct-view type display device, a color background plate is arranged behind the liquid crystal display device, and a color display is performed when the display device is in a transparent state. Is generally known.
FIG. 4 is a sectional view showing an example of a conventional reflection type liquid crystal display device. In FIG. 4, the liquid crystal panel 10 includes a transparent electrode 1.
A pair of transparent substrates 11A, 11B provided with 2A, 12B
And a polymer-dispersed liquid crystal layer 13A sandwiched between the transparent substrates 11A and 11B, and a colored background plate 50 on the back side (the lower side in the figure) of the liquid crystal panel 10.
Are arranged. The display principle will be described below with reference to FIGS.

FIG. 5 is an explanatory view showing a state in which no voltage is applied. The liquid crystal molecules in the polymer-dispersed liquid crystal layer 13A are oriented in various directions when no voltage is applied. Light incident on the molecule-dispersed liquid crystal layer 13A is scattered by light scattering at the interface between the liquid crystal and the polymer. That is, as shown in FIG. 5, when no voltage is applied, light L1 incident from the outside is scattered by the polymer dispersion layer 13A. Then, a part of the backscattering component L2 of the incident light L1 advances in the viewing direction, enters the eyes S0 of the observer, and is visually recognized as a white display.

Here, in the light scattering state of the light modulation layer such as the polymer-dispersed liquid crystal layer 13A, the ratio of the forward scattering component is generally considerably large. According to the measurement results of the polymer dispersion type liquid crystal device manufactured by the inventors, in the light scattering state, the ratio of back scattered light is 15% to 25% and the ratio of forward scattered light is 75% to 85%. Therefore, a considerable proportion of the incident light becomes forward scattered light L3, and this forward scattered light L3 enters the colored background plate 50. Note that the colored background plate 50 generally uses a pigment or a dye as a pigment, and thus has a large light absorption loss. For this reason, the forward scattered light L3 incident on the colored background plate 50 is absorbed by the colored background plate 50 at a considerable rate, and a part of the light in the specific wavelength range corresponding to the color becomes the diffuse reflection light L9. The diffuse reflected light L9 again enters the polymer dispersed liquid crystal layer 13A, is scattered by the polymer dispersed liquid crystal layer 13A, and reaches the observer's eyes S0 as forward scattered light L10 having a relatively strong light intensity. .

Therefore, the observer S0 recognizes the backscattering component L2 having a relatively small white luminance and the colored forward scattered light L10.
The mixture is visually recognized as a colored white display. Accordingly, when no voltage is applied, the luminance of whiteness is obtained only by the light component of the backscattering. Therefore, the luminance of whiteness is insufficient and at the same time, the diffused reflected light L9 from the colored background plate 50 Under the influence, the cloudy state is considerably colored.

FIG. 6 is an explanatory view of a voltage application state. When a voltage equal to or higher than the saturation voltage of the liquid crystal is applied between the transparent electrodes 12A and 12B, the liquid crystal molecules are arranged almost perpendicular to the surfaces of the substrates 11A and 11B. I do. In this state, the light scattering effect at the interface between the liquid crystal and the polymer is lost, and the polymer dispersed liquid crystal layer 1
3A is in a transparent state. Therefore, as shown in FIG. 6, the incident light L1 passes through the polymer dispersed liquid crystal layer 13A almost as it is, and reaches the colored background plate 50. In the colored background plate 50, a part of the light in the specific wavelength range corresponding to the color becomes the diffuse reflection light L9. The diffuse reflected light L9 again passes through the polymer dispersed liquid crystal layer 13A and reaches the observer's eyes S0.

Therefore, the observer S0 receives the diffuse reflected light L9.
Thereby, the colored background plate 50 can be visually recognized without deteriorating the color purity. As described above, the conventional reflection type liquid crystal display device performs colored display on a colored white background with low purity.

[0012]

As described above, the conventional reflection type liquid crystal display device performs a colored display on a colored white background with low purity. For this reason, the background color and the display color have the same color system, and the visibility of the conventional display system is extremely low. As a solution to this, in order to increase the backscattering component of the polymer dispersed liquid crystal layer that determines the white luminance,
There is a method of increasing the cell gap. However, the increase in the cell gap leads to an increase in the driving voltage, which impairs the low power consumption which is a feature of the reflection type liquid crystal display device. Further, there is a correlation between the thickness of the light modulating layer and the degree of white turbidity, but when the thickness of the light modulating layer exceeds a certain level, the degree of white turbidity reaches a plateau and becomes saturated. Therefore, it is meaningless to make the light modulation layer thicker.

Conventionally, in order to obtain sufficient whiteness in a cloudy state without increasing the thickness of the liquid crystal layer, a mirror surface made of a metal film such as aluminum (Al) or silver (Ag) is provided on the back surface of the liquid crystal panel. Further, there is known a system in which external light blocking means (hood) provided with a black absorber is provided on the upper surface of a liquid crystal element so that specular reflected light of external light is not directly viewed.

In this case, when the pixel is in the scattering state,
A white display is obtained by visually observing the scattered light of the incident angle light from a direction other than the specular reflection direction. When the pixels are in a transparent state, the light does not reach the observer's eyes, so a black display is performed. Is obtained. However, in this method, it is difficult to produce an arbitrary color such as blue, red, and green, and extra parts such as external light blocking means (hood) are added, and the outer shape of the liquid crystal display device is required. There is a problem that the system becomes more complicated and larger.

[0015] Due to these problems, it is conventionally very difficult for a reflection type liquid crystal display device of a light scattering mode using a polymer dispersion type liquid crystal panel or the like to simultaneously realize high brightness white and good display contrast. However, there is a problem that high-quality display quality cannot be obtained.

[0016]

As described above, in a reflection type liquid crystal display device of a light scattering mode using a conventional polymer dispersed type liquid crystal panel or the like, since the backscattered light intensity is generally small,
Insufficient luminance results in dark, colored white background, poor display contrast, and satisfactory color reproduction cannot be realized. Therefore, there is a problem that high-quality display quality cannot be obtained.

The reflection type liquid crystal display device of the present invention is intended to solve such a problem, and is a reflection type liquid crystal display device in a light scattering mode such as a polymer dispersion type liquid crystal having a low backscattering light intensity. However, when the voltage is not applied, the brightness of whiteness in a cloudy state is greatly improved, and at the same time, when a color system such as red, green, or blue is displayed, there is no problem that a white background is colored, and light scattering is performed. By improving the contrast ratio between the state and the transparent state, high-quality display quality with excellent color purity and high contrast of any color such as red, green, and blue with high brightness white such as paper white It is another object of the present invention to provide a reflection type liquid crystal display device having a low driving voltage, a high response speed, and a uniform display over a large area.

Further, for the purpose of enhancing not only the visibility but also the fashionability, the visibility of the display on the colored background is enhanced. In order to achieve the above-described object, a reflective liquid crystal display device according to the present invention includes a light modulation layer that changes a light scattering state by applying a voltage between electrode surfaces, and a Bragg disposed behind the light modulation layer. A reflective layer,
And a scattering layer disposed behind the Bragg reflection layer.

Here, a volume hologram was used as the Bragg reflection layer. Further, the angle of the interference fringes of the volume hologram was set to 30 degrees or less with respect to the electrode surface. Furthermore, the scattering wavelength region of the scattering layer and the reflection wavelength region of the Bragg reflection layer were set to have complementary colors. As a function of the provision of the above means, the reflection type liquid crystal display device of the present invention can be applied to a reflection type liquid crystal display device of a light scattering mode such as a polymer dispersion type liquid crystal having a low backscattered light intensity. When light is in a light scattering state, the brightness of whiteness can be greatly improved, and at the same time, when displaying a color system such as red, green and blue, the white background is not colored and the light scattering state is achieved. Vivid color display can be achieved by improving the contrast ratio with the transparent state. As a result, it is possible to realize high-quality display quality with excellent color purity and good contrast between white such as paper white and any color such as red, green and blue.

Further, since it is not necessary to perform a process of increasing the thickness of the light modulation layer in order to improve the brightness of whiteness, the driving voltage can be reduced, high-speed response can be obtained, and uniform display can be achieved over a large area. Is possible. Further, the display color and the background have a complementary color relationship with each other for the purpose of enhancing not only the visibility but also the fashionability. Therefore, a colorful and highly visible display can be realized.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of operation of a reflection type liquid crystal display device according to the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of a reflective liquid crystal display device according to a first embodiment of the present invention. In FIG. 1, a liquid crystal panel 10 includes a pair of transparent substrates 11A having transparent electrodes 12A and 12B,
11B, and a light modulating layer 13 sandwiched between the transparent substrates 11A and 11B (in the description of the operation principle of the present invention, a polymer-dispersed liquid crystal will be described as an example). The structure is such that the Bragg reflection layer 20 and the scattering layer 30 are arranged on the back side (lower side in the figure) of the panel 10. Hereinafter, description will be made with reference to FIGS. 2 and 3.

The display principle when no voltage is applied will be described with reference to FIG. The liquid crystal molecules in the light modulation layer 13 composed of the polymer-dispersed liquid crystal layer are oriented in various directions when no voltage is applied. The light is scattered by the light scattering action at the molecular interface. That is, when no voltage is applied, the incident light L1 from the outside is scattered by the light modulation layer 13. Then, a part of the back scattered light L2 of the incident light L1 advances in the viewing direction and reaches the observer's eye S0. Here, in the light scattering state of the light modulation layer 13, generally, the ratio of the forward scattering component is considerably large.
For this reason, a considerable proportion of the incident light becomes forward scattered light L3, and this forward scattered light L3
Incident on.

The Bragg reflection layer 20 has a very small light absorption loss and a very good light diffraction / transmission characteristic. Here, the Bragg reflection of the forward scattered light L3 is shown in FIG.
5 will be described. The Bragg reflection layer 9 in FIG. 15 has a layered structure including the interference fringes 20A with a pitch P. The forward scattered light L3, which is the incident light of the Bragg reflection layer, is reflected in a direction satisfying the relationship of λ = 2P sin φ (λ: wavelength, angle of φ incident light and interference fringes) according to Bragg's law, and diffracted light L4 is emitted. I do.

The Bragg reflection layer 20 can diffract light in a specific wavelength range of a visible light region satisfying the Bragg condition and transmit other visible light. Therefore, the forward scattered light L3 incident on the Bragg reflection layer 20 is:
In the Bragg reflection layer 20, light in a specific wavelength range is diffracted with high efficiency to become diffracted light L4 having an angle α. The diffracted light L4 enters the light modulation layer 13 again, is scattered by the light modulation layer 13, and
The observer's eyes S as forward scattered light L5 having a relatively strong light intensity
0 will be reached.

The transmitted light L 6 having a wavelength outside the specific wavelength range transmitted through the Bragg reflection layer 20 is incident on the scattering layer 30.
The scattering layer 30 scatters the transmitted light L6 to become scattered light L7. The scattered light L7 again passes through the Bragg reflection layer 20, enters the light modulation layer 13, is scattered by the light modulation layer 13, and reaches the observer's eyes S0 as forward scattered light L8 having a relatively strong light intensity. Will do.

Therefore, the incident light L1 becomes back scattered light L2, forward scattered light L5, L8, etc. scattered by the light modulation layer.
Since these scattered lights have very little absorption loss, the scattered light L2
The light synthesized by + L5 + L8 and the like is whitened again and is observed by the observer S0 as light without coloring. In this way, most of the incident light can be effectively utilized with very little light absorption loss from the external incident light, so that very bright and highly pure white can be realized.

The display principle of the voltage application state will be described with reference to FIG. When a voltage higher than the saturation voltage of the liquid crystal is applied between the transparent electrodes 12A and 12B, the liquid crystal molecules
They are arranged almost perpendicularly to the planes A and 11B. In this state, the light scattering function at the interface between the liquid crystal and the polymer disappears, and the light modulation layer 13 becomes transparent. Therefore, the incident light L1 passes through the light modulation layer 13 almost as it is, and the Bragg reflection layer 20
Incident on.

The Bragg reflection layer 20 can diffract light in a specific wavelength range in the visible light region and transmit other visible light. Accordingly, the incident light L1 is converted into light having a specific wavelength range with high efficiency and becomes diffracted light L4 and transmitted light L6 at an angle α with the Bragg reflection layer 20. The eye reaches S0. On the other hand, the transmitted light L6 is incident on the scattering layer 30. The scattering layer 30 scatters the incident light L6 to become scattered light L7. The scattered light L7 passes through the Bragg reflection layer 20 again, enters a voltage-applied region, that is, the light modulation layer 13 is transparent, and passes through the light modulation layer 13 almost as it is. The diffracted light L4 enters the field of view of the observer S0 at an angle α, and the scattered light L7 also
Enter the field of vision.

Here, as an example, regarding the visibility of the observer when the Bragg reflection layer 20 is a volume hologram,
The wavelength sensitivity characteristics of the diffracted light L4 shown in FIG. 16, the reproduced light incident angle sensitivity curve of the diffracted light L4 shown in FIG. 17, the reproduced light incident angle sensitivity curve of the scattered light L7 shown in FIG. 18, and the scattered light L7 shown in FIG. The description will be made using a composite curve of the sensitivity of the reproduction light incident angle. FIG. 16 shows a wavelength sensitivity curve of the diffracted light L4, showing the relationship between the reproduction light wavelength and the relative diffraction intensity, where λ0 is the recording light wavelength. For example, assuming that the relative diffraction intensity L0 is a light intensity that can be visually recognized by an observer, this means that the observer can visually recognize the diffracted light in a reproduction light wavelength range of λ11 to λ21. FIG.
The reproduction light is forward scattered light L3, and in FIG.
It is one.

FIG. 17 is a sensitivity curve of the incident angle of the reproduction light of the diffracted light L4, showing the relationship between the incident angle of the reproduction light and the relative diffraction intensity, where θ0 is the incident angle of the recording reference light. For example, assuming that the relative diffraction intensity L0 is a light intensity that can be visually recognized by the observer, it means that the observer can visually recognize the diffracted light within the range of the incident angle of the reproduction light θ11 to θ21. In other words, if the incident angle of the reproduction light is constant, it means that the observer's visual recognition range is from θ11 to θ21 around θ0.

That is, in the case of the embodiment of the present invention, at an angle of ± (θ11 + θ21) / 2 around the diffracted light L4,
The observer S0 can visually recognize the color. FIG. 18 is a diagram showing the sensitivity characteristic of the reproduction light incident angle of the scattered light L7. It can be seen that the relative light intensity is a constant value of L10 and does not depend on the reproduction light incident angle. FIG. 19 is a composite curve of the reproduction light incident angle sensitivity and FIG. 17 is a composite diagram of the reproduction light incident angle sensitivity characteristic diagram of the diffracted light L4 and the reproduction light incident angle sensitivity characteristic diagram of the scattered light L7, and the visibility of the observer S0. Is shown.

Here, the visibility of the observer S0 will be described with reference to the reproduction light incident angle sensitivity composite curve of FIG. Observer S
0 visually recognizes a combined light of the diffracted light L4 and the scattered light L7. Therefore, the observer S0 can visually recognize the relative diffracted light intensity equal to or higher than L01 (recognizable relative light intensity) shown by the reproduction light incident angle sensitivity composite curve in FIG. 19 in the range of θ12 to θ22. Further, the observer S0 visually recognizes only the scattered light L7 in the ranges of θ13 to θ12 and θ22 to θ23. However,
The light intensity of the scattered light L7 is considerably weaker than the diffracted light L4, and has little effect on the observer S0.

Therefore, the observer S0 visually recognizes only the light in the specific wavelength range diffracted substantially at the angle α, and sees the color corresponding to the light in the specific wavelength range as a bright color with high color purity. be able to. As described above, according to the configuration of the reflective liquid crystal device of this embodiment in which the Bragg reflection layer 20 is disposed behind the light modulation layer 13 and the scattering layer 30 is disposed behind the Bragg reflection layer 20, the forward scattering is achieved. Since the light can be utilized very efficiently, the white turbid state of the light modulation layer 13 composed of the polymer dispersed liquid crystal layer when no voltage is applied can be realized as white as paper white. Became. When the light modulating layer 13 is transparent when a voltage is applied, the combination of the Bragg reflection layer 20 and the scattering layer 30 allows any color such as red, blue, and green to be very vivid with good contrast. Can be realized, and high-quality display quality can be realized.

[0034]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional structural view of a reflection type liquid crystal display device of Embodiment 1. As shown in FIG.
0 denotes a pair of transparent substrates 11A and 11B provided with patterned transparent electrodes 12A and 12B,
The light modulation layer 13 is sandwiched between A and 11B. The liquid crystal panel 10 was prepared so that the cell gap was 10 μm.

A Bragg reflection layer 20 was disposed behind the liquid crystal panel 10 (the lower side in FIG. 1), and a scattering layer 30 was disposed behind the Bragg reflection layer 20. In the first embodiment, a smooth and transparent glass plate was used as the transparent substrates 11A and 11B. In addition, a transparent polymer film may be used for the transparent substrates 11A and 11B in addition to a smooth and transparent glass plate.

In the first embodiment, the transparent electrodes 12A and 12B are formed by sputtering or vacuum evaporation.
A transparent conductive film composed of an n2O3-SnO2 film (hereinafter referred to as an ITO film) patterned by photolithography was used. The transparent electrodes 12A and 12B have
A SnO2 film may be used in addition to the ITO film. In Example 1, a polymer dispersed liquid crystal layer was used as the light modulation layer 13. The polymer-dispersed liquid crystal layer is a mixed solution in which a polymer resin such as an acrylate monomer that undergoes a cross-linking reaction and polymerization by ultraviolet (UV), a nematic liquid crystal having positive dielectric anisotropy, and an ultraviolet curing initiator are uniformly mixed and dissolved. Is injected into an empty liquid crystal panel 10, only the polymer resin is cured by exposure to ultraviolet light, and a nematic liquid crystal having positive dielectric anisotropy is phase-separated. At this time, when the proportion of the polymer resin is larger in the mixed solution of the polymer resin and the nematic liquid crystal, independent liquid crystal droplets are formed. On the other hand, when the proportion of the polymer resin is small, the polymer resin forms a network (network) structure, and the liquid crystal exists as a continuous phase in the network structure of the polymer resin. . It is desirable that the liquid crystal droplet diameter and the pore diameter of the polymer network are as uniform as possible and the average particle diameter is in the range of 0.5 μm to 3.5 μm.
If the average particle diameter is out of this range, the light scattering state deteriorates and the contrast cannot be improved. More preferably, the average particle size is in the range of 0.8 μm to 1.8 μm.
The mixing ratio of the polymer resin and the nematic liquid crystal is 8:
2-1: 9. It should be noted that the liquid crystal continuous phase structure of the polymer network is easier to achieve lower voltage and lower hysteresis than the independent liquid crystal droplet particle structure. Therefore, preferably, the range of 4: 6 to 1: 9 is desirable.

As a scattering layer 30, a polyester film "Lumirror E60L" (188 μm in thickness) manufactured by Toray Industries, Inc. is used as a white diffuse reflecting layer having excellent diffuse reflectance characteristics in order to realize bright colors with high color purity. It was used. still,
As the scattering layer 30, a scattering layer made of another polymer film having a uniform diffuse reflectance over the entire wavelength in the visible light region and having high characteristics or a scattering layer made of an inorganic material such as barium sulfate powder is used. No problem.

In the first embodiment, the volume hologram polaroid (HB-GS) was used as the Bragg reflection layer 20. FIG. 8 is a graph showing wavelength-reflectance characteristics of the Bragg reflection layer 20 that diffracts green light of the volume hologram used in Example 1 measured by a spectral reflectometer. The measurement of the spectral reflectance is a result obtained by using a measuring instrument (Hitachi, Model 330, self-recording spectrophotometer) and measuring the system under the condition III of JIS28722.

In this way, a reflection type liquid crystal display device of a light scattering mode for green display was manufactured using each of the Bragg reflection layers 20 composed of the volume hologram 20A diffracting green light. When the reflection type liquid crystal display device in the light scattering mode for green display was observed under a fluorescent lamp of 60 W indoors, a bright green display was obtained on a white paper white background.

The Bragg reflection layer 20 composed of a volume hologram has a red display (HB-RS) and a blue display (HB-RS).
By using (B-BS), it is needless to say that a bright red or blue display can be similarly obtained on a white paper white background. In the first embodiment, a volume hologram is used for the Bragg reflection layer 20, but the same effect can be obtained by using a reflector using selective reflection of cholesteric liquid crystal.

In the first embodiment, the order in which the Bragg reflection layer 20 is externally arranged behind the liquid crystal panel 10 and the scattering layer 30 is arranged behind the Bragg reflection layer 20 is shown. 9, 10, 11, and 12, the effect of the present invention, that is, a vivid color purity on a white background such as paper white. The effect of reproducing a high color display is maintained as it is. Therefore, the first embodiment
1 and FIGS. 9 to 12, etc., may be selected as the optimal arrangement position and arrangement order of the components of the reflection type liquid crystal display device according to the application to be actually used. .

FIG. 9 shows that the Bragg reflection layer 20 is
It is configured to be arranged between 2B and the transparent substrate 11B. Therefore, the Bragg reflection layer 20 is disposed on the inner surface of the liquid crystal panel 10, and the scattering layer 30 is disposed externally. FIG.
Has a structure in which the Bragg reflection layer 20 is disposed on the transparent electrode 12B. Therefore, the Bragg reflection layer 20 is disposed on the inner surface of the liquid crystal panel 10, and the scattering layer 30 is disposed externally.

FIG. 11 shows that the Bragg reflection layer 20 is disposed below the transparent electrode 12B and the scattering layer 30 is disposed below the transparent electrode 12B.
Are arranged, and a transparent substrate 11B is arranged below the scattering layer 30. Therefore, the Bragg reflection layer 20 and the scattering layer 30 are disposed on the inner surface of the liquid crystal panel 10. FIG.
The structure is such that the Bragg reflection layer 20 is arranged on the transparent electrode 12B, the scattering layer 30 is arranged below the transparent electrode 12B, and the transparent substrate 11B is arranged below the scattering layer 30. Therefore, the Bragg reflection layer 20 and the scattering layer 30 are disposed on the inner surface of the liquid crystal panel 10.

Here, the Bragg reflection layer 20 of the volume hologram may be formed so that a volume hologram having the same spectral characteristics covers the entire display area of the liquid crystal panel, or different spectral characteristics may be provided for each pixel electrode. May be formed. This specific example is shown in FIGS.
Shown in In FIG. 13, a Bragg reflection layer 21 made of a volume hologram whose diffraction efficiency corresponding to the RGB wavelength band is increased on the electrodes 14R, 14G, and 14B.
R, 21G and 21B are formed.

In FIG. 14, the transparent substrate 11B and the transparent electrode 1
Between 4R, 14G, and 14B, Bragg reflection layers 20R, 20G, and 20B are formed by volume holograms whose diffraction efficiencies corresponding to the RGB wavelength bands are increased. With such a configuration, spatial color mixing becomes possible, and the number of displayable color reproductions can be greatly increased. Of course, instead of three primary colors such as RGB, R, G, B,
A Bragg reflection layer of a volume hologram having two arbitrary color configurations from colors such as Y, M, and C may be used.

The liquid crystal display panel 10 can be used in combination with an active element such as an MIM or a TFT. (Embodiment 2) Embodiment 2 will be described with reference to the sectional structural view of the reflection type liquid crystal display device of FIG. FIG. 7 is an explanatory diagram of a voltage application state. For simplification of description, transmitted light other than the diffracted light L4 reaching the observer S0 is the same as that in the first embodiment, and a description thereof will be omitted. When a voltage higher than the saturation voltage of the liquid crystal is applied between the transparent electrodes 12A and 12B, the liquid crystal molecules are
They are arranged almost perpendicularly to the planes A and 11B. In this state, the light scattering function at the interface between the liquid crystal and the polymer is lost, and the polymer dispersed liquid crystal layer 13A is in a transparent state. Therefore, the incident light L1 passes through the polymer-dispersed liquid crystal layer 13A almost as it is and enters the Bragg reflection layer 20. Therefore, the incident light L
1 is a diffracted light L4 obtained by diffracting light in a specific wavelength range with high efficiency by the Bragg reflection layer 20, and the diffracted light L4 passes through the polymer-dispersed liquid crystal layer 13A as it is, and the observer's eyes S
Reach 0.

In the second embodiment, the Bragg reflection layer 20
A volume hologram 20B having layered interference fringes 20A at an angle β with respect to the plane direction of the transparent substrate 11B was used. Here, as shown in FIG. 7, the angle at which the observer can visually recognize the diffracted light L4 changes depending on the angle β of the layered interference fringes 20A. That is, the observer S0 moves the substrate 11A by 2
The diffracted light L4 is visually recognized at an angle of β. In the experiment, visibility was significantly reduced at θ> 30 °.

In the state where no voltage is applied, as in Embodiment 1, most of the incident light can be effectively used as brightness of whiteness with very little light absorption loss of external incident light. , Very bright white with high purity can be realized.
In the experiment, in the range of β> 30 °, a reflective liquid crystal display device with low contrast and high visibility could not be obtained. On the other hand, in the range of β <30 °, a reflective liquid crystal display device having good contrast and high visibility was obtained. (Embodiment 3) Embodiment 3 will be described with reference to the sectional structural views of the reflection type liquid crystal display device shown in FIGS. FIG. 20 and FIG.
1 is substantially the same as FIG. 1 of the first embodiment to avoid repetition of the description, and therefore the details are omitted. The difference between FIG. 20 and FIG. 21 and FIG. 1 is that the scattering layer 30 of FIG.
FIG. 21 uses a colored scattering layer 31.

Here, a display principle using a colored background (a background color having a complementary color to the display color) instead of the paper white background of the first embodiment will be described with reference to FIGS. FIG. 20 is a diagram illustrating a state where no voltage is applied. The molecules of the liquid crystal in the light modulation layer 13 composed of the polymer dispersed liquid crystal layer are oriented in various directions when no voltage is applied. The light incident on the light modulation layer 13 is scattered by light scattering at the interface between the liquid crystal and the polymer. That is,
When no voltage is applied, the incident light L1 from the outside is
3 scattered. Then, a part of the backscattered light L22 of the incident light L1 advances in the viewing direction and reaches the observer's eyes S0. Here, in the light scattering state of the light modulation layer 13, generally, the ratio of the forward scattering component is considerably large. For this reason, a considerable proportion of the incident light becomes forward scattered light L23,
This forward scattered light L23 enters the Bragg reflection layer 20.

The Bragg reflection layer 20 can diffract light in a specific wavelength range of a visible light region satisfying the Bragg condition and transmit other visible light. Therefore, the forward scattered light L23 incident on the Bragg reflection layer 20
In the Bragg reflection layer 20, light in a specific wavelength range is diffracted with high efficiency and becomes diffracted light L24 having an angle α. Diffracted light L2
4 enters the light modulation layer 13 again, is scattered by the light modulation layer 13, and reaches the observer's eyes S0 as forward scattered light L25 having a relatively strong light intensity.

The transmitted light L 26 having a wavelength outside the specified wavelength range transmitted through the Bragg reflection layer 20 is incident on the colored scattering layer 31. The colored light scattering layer 31 scatters the transmitted light L26 to become scattered light L27. The scattered light L27 again passes through the Bragg reflection layer 20, enters the light modulation layer 13, is scattered by the light modulation layer 13, and has a relatively strong forward scattered light L2.
As 8, the image reaches the observer's eye S0.

In this embodiment, the Bragg reflection layer 20 is a Bragg reflection layer having very small light absorption loss and very excellent light diffraction and transmission characteristics. Further, as the colored scattering layer used in this example, FIG.
The colored scattering layer 31 having the spectral reflectance characteristic of FIG. 21 showing the relationship between the spectral reflectance characteristic of the Bragg reflection layer and the complementary color was used.

When a white light source is used for the incident light L1, the back scattered light L22 scattered by the light modulation layer and the forward scattered light L23
Is white light. Further, as the scattering characteristics of the light modulation layer 13 increase, the back scattered light L22 increases, and conversely, the forward scattered light L23, which is incident light of Bragg reflection, decreases. Further, since the forward scattered light L23 becomes smaller, the diffracted light L24 and the transmitted light L
26 also becomes smaller.

Further, as the scattering characteristic of the light modulating layer 13 increases, as described above, the forward scattered light L23 corresponding to the incident light of Bragg reflection decreases, and the forward scattered light other than the forward scattered light L23 that does not satisfy the Bragg condition is used. It becomes light and is transmitted without being diffracted by the Bragg reflection layer, and as a result, the scattered light L27 that does not depend on the incident angle is increased. Therefore, the forward scattered light L28 increases. In the case of the third embodiment, the diffracted light L24 is green, and the scattered light L27 and the forward scattered light L28 are pink.

Therefore, as the scattering characteristic of the light modulating layer 13 increases, the diffracted light L24 decreases and the forward scattered light L28 increases, so that the observer S0 can visually recognize the color of the colored scattering layer 31, that is, pink. I will be. FIG.
Is an explanatory diagram of a voltage applied state, and shows transparent electrodes 12A and 12A.
When a voltage equal to or higher than the saturation voltage of the liquid crystal is applied during B, the liquid crystal molecules are arranged almost perpendicular to the surfaces of the substrates 11A and 11B. In this state, the light scattering function at the interface between the liquid crystal and the polymer disappears, and the light modulation layer 13 becomes transparent. Therefore, the incident light L1 passes through the light modulation layer 13 as it is,
The light enters the Bragg reflection layer 20.

The Bragg reflection layer 20 can diffract light in a specific wavelength range in the visible light region and transmit other visible light. Therefore, the incident light L1 is converted into light of a specific wavelength range with high efficiency by the Bragg reflection layer 20 at an angle α.
The diffracted light L24 passes through the light modulation layer 13 as it is and reaches the observer's eye S0.

On the other hand, the transmitted light L 6 enters the colored scattering layer 31. In the colored scattering layer 31, the incident light L26 is scattered to become scattered light L27. The scattered light L27 passes through the Bragg reflection layer 20 again, enters the voltage-applied region, that is, the light modulation layer 13 is transparent, and the light modulation layer 1
3 is transmitted. The diffracted light L24 enters the visual field of the observer S0 at an angle α, and the scattered light L27 also enters the visual field of the observer S0. Here, as described in the first embodiment, the light intensity of the scattered light L27 is considerably weaker than that of the diffracted light L24, and the influence on the observer S0 is small. In the case of the third embodiment, the diffracted light L24 is green, and the scattered light L27 is pink.

Therefore, the observer S0 sees only the light in the specific wavelength range (green in the third embodiment) diffracted substantially at the angle α, and changes the color corresponding to the light in the specific wavelength range into a vivid color purity. As a high color, the observer S0 can see. As described above, the Bragg reflection layer 20 is arranged behind the light modulation layer 13 and the colored scattering layer 31 having a complementary color relationship with the diffracted light L24 is arranged behind the Bragg reflection layer 20 in this embodiment. With the configuration of the reflective liquid crystal device, high visibility can be realized even when performing color display on a colored background with high fashionability.

In the case of the third embodiment, a bright green display is realized on a colorful pink background. Since the pink color and the green color have a complementary color relationship with each other, high visibility was exhibited despite the colored display on the colored background. Further, in the case of the present embodiment, the relationship between complementary colors of green and pink is used, but if there is a complementary color relationship with each other, colorful and highly visible display can be realized similarly to the present embodiment.

[0060]

As described above, according to the present invention, the light modulating layer for changing the light scattering state by applying a voltage between the electrode surfaces and at least one kind of light modulating layer disposed behind the light modulating layer are provided. According to the reflection type liquid crystal display device having the Bragg reflection layer and the scattering layer provided behind the Bragg reflection layer, the reflection type liquid crystal in a light scattering mode such as a polymer dispersion type liquid crystal having a low backscattered light intensity. Even in a display device, when no voltage is applied,
The light scattering state of the light modulation layer can realize whiteness such as paper white. Also, when a voltage is applied, the transparent state of the light modulation layer can display an arbitrary color such as red, blue, or green with a good contrast display due to the combined action of the Bragg reflection layer and the scattering layer, and at the same time, be very vivid. High color purity and high quality display quality.

Further, since it is not necessary to increase the thickness of the light modulation layer in order to improve the brightness of whiteness, the driving voltage can be reduced, high-speed response can be obtained, and uniform display can be performed over a large area. Became possible.

[Brief description of the drawings]

FIG. 1 is a sectional view of a reflective liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a reflection type liquid crystal display device of Example 1 of the present invention in a state where no voltage is applied.

FIG. 3 is an explanatory diagram of a voltage application state of the reflective liquid crystal display device according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a conventional reflection type liquid crystal display device.

FIG. 5 is an explanatory diagram of a conventional reflection type liquid crystal display device in a state where no voltage is applied.

FIG. 6 is an explanatory diagram of a voltage application state of a conventional reflective liquid crystal display device.

FIG. 7 is a schematic cross-sectional view illustrating a configuration of a reflective liquid crystal display device according to a second embodiment of the present invention.

FIG. 8 is a table showing the spectral reflectance of a green volume hologram.

FIG. 9 is another configuration diagram of the reflective liquid crystal display device according to the first embodiment of the present invention.

FIG. 10 is another configuration diagram of the reflective liquid crystal display device according to the first embodiment of the present invention.

FIG. 11 is another configuration diagram of the reflective liquid crystal display device according to the first embodiment of the present invention.

FIG. 12 is another configuration diagram of the reflective liquid crystal display device according to the first embodiment of the present invention.

FIG. 13 is a cross-sectional structural view in which an RGB Bragg reflection layer is formed for each pixel electrode according to the first embodiment of the present invention (a Bragg reflection layer is arranged on the upper surface of a back electrode).

FIG. 14 is a cross-sectional structural view in which an RGB Bragg reflection layer is formed for each pixel electrode according to the first embodiment of the present invention (a Bragg reflection layer is arranged on the lower surface of the back electrode).

FIG. 15 is an explanatory diagram of Bragg reflection according to the first embodiment of the present invention.

FIG. 16 is a chart showing a wavelength sensitivity curve.

FIG. 17 is a table showing a reproduction light incident angle sensitivity curve.

FIG. 18 is a table showing a reproduction light incident angle sensitivity characteristic.

FIG. 19 is a table showing a reproduction light incident angle sensitivity composite curve.

FIG. 20 is an explanatory diagram of a reflection type liquid crystal display device according to a third embodiment of the present invention in a state where no voltage is applied.

FIG. 21 is an explanatory diagram of a voltage application state of the reflective liquid crystal display device according to the third embodiment of the present invention.

FIG. 22 is a table showing the spectral reflectance characteristics of the colored scattering layer of the third embodiment.

[Explanation of symbols]

11A, 11B Transparent substrate 12A, 12B, 14R, 14G, 14B Transparent electrode 13 Light modulation layer 13A Polymer dispersed liquid crystal layer 20, 21R, 21G, 21B Bragg reflection layer 20A Interference fringe 20B Volume hologram 30 Scattering layer 50 Colored background plate L0 , L01 Relative diffracted light intensity L1 Incident light L2, L22 Backscattered light L3, L5, L8, L10, Forward scattered light L23, L25, L28, Forward scattered light L4, L24 Diffracted light L6, L26 Transmitted light L7, L27 Reflected light S0 Observer θ0, θ11, θ12, θ13 Reconstructed light incident angle θ22, θ13, θ23 Reproduced light incident angle λ0, λ11, λ12 Reproduced light wavelength φ angle P pitch

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kaoru Takano 1-8-1, Nakase, Mihama-ku, Chiba-shi Inside Seiko Instruments Inc. (72) Inventor Hiroshi Sakuma 1-8-8, Nakase, Mihama-ku, Chiba-shi, Chiba Inside Iko Instruments Co., Ltd. (72) Inventor Takakazu Fukuchi 1-8-1, Nakase, Mihama-ku, Chiba City, Chiba Prefecture Inside Inko Instruments Co., Ltd. (72) Osamu Yamazaki 1-8-1, Nakase, Nakase, Mihama-ku, Chiba Prefecture Instruments Inc. (72) Naoto Shino Inventor 1-8-8 Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. (72) Masafumi Hoshino 1-8-1, Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. In-company (72) Inventor Yamamoto Flat Chiba, Chiba Prefecture Nakase, Mihama-ku 1-chome address 8 Co., Ltd. SII Earl di Center in

Claims (4)

[Claims] A light modulation layer provided between a pair of electrode surfaces, at least one of which is a transparent electrode, wherein the light modulation layer changes a light scattering state by applying a voltage between the electrode surfaces; 1. A reflective liquid crystal display device comprising: a Bragg reflection layer provided behind the Bragg reflection layer; and a scattering layer provided behind the Bragg reflection layer. 2. The reflection type liquid crystal display device according to claim 1, wherein the Bragg reflection layer is a volume hologram. 3. The reflection type liquid crystal display device according to claim 2, wherein an angle of the interference fringes of the volume hologram is 30 degrees or less with respect to an electrode surface. 4. The reflection type liquid crystal display device according to claim 1, wherein the scattering wavelength region of the scattering layer and the reflection wavelength region of the Bragg reflection layer have a complementary color relationship.