JPH09318969A - Reflection type liquid crystal display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change reflection characteristic in accordance with input data and optical environment on the periphery and to obtain bright and high-contrast display by arranging a 1st liquid crystal layer, a 2nd liquid crystal layer and a reflection film in order from a display surface side. SOLUTION: This device has transparent base plates 1 to 4 arranged at specified intervals and is provided with the 1st liquid crystal layer 5 containing a dichroic coloring matter and modulating the intensity of light in a specified wavelength region between the base plates 1 and 2. The 2nd liquid crystal layer 6 being a scattering type is interposed between the base plates 3 and 4. Then, the device is provided with transference electrodes 7a and 7b and oriented films 8a and 8b so as to interpose the liquid crystal layer 5 in between. It is also provided with a transference electrode 7c and a reflection electrode 9 functioning both as the reflection film and the electrode so as to interpose the liquid crystal layer 6 in between. By optimally driving the 1st and the 2nd liquid crystal layer 5 and 6 in accordance with display data, the high-contrast and bright display is realized.

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 a driving method thereof.

[0002]

2. Description of the Related Art Conventionally, a display element in a liquid crystal display device has a low power consumption because it is a non-light emitting element that modulates external light, and it is thin and lightweight, so that it can be applied to a flat panel display. Demonstrate, clocks, calculators, computer terminals, notebook computers and word processors, even television receivers,
It is currently used in a wide range of fields.

In order to construct a reflective liquid crystal display that does not use a backlight, only ambient light is used,
In order to obtain a bright display, a display using a guest-host liquid crystal without a polarizing plate and a micro color filter has been reported (Proceedings of SID, Vol.29 / 2,15).
7,1988). A reflective panel using this guest-host liquid crystal is constructed as shown in FIG. That is, the color filter layer 30 is provided on the surface of the one transparent substrate 21,
A transparent electrode (not shown) is formed on the color filter layer 30. A reflective film 29 is formed on the other transparent substrate 22 which faces, and the reflective film 29 also serves as a display electrode. A guest-host liquid crystal is sandwiched between these two substrates 21 and 22 to form a liquid crystal layer 25. Further, in order to obtain a bright display, a bright directional reflector having a concavo-convex shape of the reflecting film 29 is applied. By controlling the average inclination angle of the concavities and convexities, these obtain a reflector having directivity in reflection characteristics.

A two-layer liquid crystal display device in which a scattering liquid crystal and an absorptive liquid crystal are combined is disclosed in JP-A-5-40276 and JP-A-5-273576.
In all of these, a scattering type liquid crystal is arranged on the incident side of ambient light of a liquid crystal display device, and a scattering bear of the liquid crystal is applied to white display.

[0005]

However, in the above-mentioned conventional reflection type liquid crystal display device, the Proceedings of SI
In the reflector as disclosed in D, Vol.29 / 2,157,1988,
To obtain a bright display, narrow the viewing angle to some extent,
The range in which a bright display can be obtained was limited. Furthermore, the reflection characteristics of the reflector do not change even when the liquid crystal display is bright or dark, and even a dark bear reflects brightly, so it becomes brighter by applying a directional reflector, but the contrast changes. There was no In addition, there is a problem that the thickness of the liquid crystal layer cannot be controlled uniformly due to the unevenness of the steps, and the alignment failure of the liquid crystal material is likely to occur.

Further, in the two-layer type liquid crystal display device disclosed in Japanese Patent Laid-Open No. 5-40276 and Japanese Patent Laid-Open No. 5-273576, the scattering type liquid crystal layer is arranged on the display surface side, The white state uses the scattering state of the scattering type liquid crystal layer, that is, the scattering characteristic of the scattering type liquid crystal is merely used, and the reflection characteristic of the scattering type liquid crystal layer is not described, but even described. Not not.

As described above, the conventional reflection type liquid crystal display device cannot be said to fully exhibit the excellent features of the liquid crystal display element, such as thin weighing and low power consumption, and display of a portable information terminal. At present, there is a demand for a reflection type color display device which is insufficient as a device and which is bright and has excellent visibility.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to change the display of the reflection characteristics according to the input data of the liquid crystal display and the surrounding light environment. An object of the present invention is to provide a reflective liquid crystal display device with contrast.

[0009]

In order to solve the above-mentioned problems, in the present invention, a first liquid crystal layer whose light absorption state and transparent state can be controlled according to a first externally applied electric field, and a second liquid crystal layer In a reflective liquid crystal display device including a second liquid crystal layer capable of controlling a light scattering state and a transparent state according to an externally applied electric field and a reflective film, the first liquid crystal layer, the The second liquid crystal layer and the reflective film are arranged in this order.

Further, according to the present invention, in the above reflective liquid crystal display device, an absorption type color filter layer is provided.

Further, according to the present invention, in the above reflective liquid crystal display device, the first liquid crystal layer is composed of a layer in which a dichroic dye is dispersed in a liquid crystal material.

Further, according to the present invention, in the above reflective liquid crystal display device, the second liquid crystal layer is composed of a layer in which a liquid crystal material is dispersed in a photocurable compound.

Further, according to the present invention, in the above reflective liquid crystal display device, the liquid crystal molecules in the second liquid crystal layer are oriented.

Further, according to the present invention, in the above reflection type liquid crystal display device, the photocurable compound in the second liquid crystal layer is phase-separated from the liquid crystal molecules.

Further, according to the present invention, in the above-mentioned reflection type liquid crystal display device, the reflection film is composed of an inorganic dielectric mirror which selectively reflects a wavelength.

Further, according to the present invention, in the above-mentioned reflection type liquid crystal display device, the reflection film is composed of a holographic mirror.

Further, according to the present invention, in the above-mentioned reflection type liquid crystal display device, the reflection film is made of any one of a cholesteric liquid crystal, a composite of a cholesteric liquid crystal and a polymer material, or a cholesteric liquid crystal polymer.

Further, in the present invention, as a method of driving the above-mentioned reflection type liquid crystal display device, the reflection characteristic is controlled by changing the scattering state of the second liquid crystal layer by an electric field.

Further, according to the present invention, as a method of driving the above-mentioned reflection type liquid crystal display device, the first method is to display a dark state.
The second liquid crystal layer is controlled so that the second liquid crystal layer is set to the light absorbing state and the second liquid crystal layer is set to the transparent state. When displaying the bright state, the first liquid crystal layer is set to the light transparent state and the second liquid crystal layer is set. Is controlled so as to be in a light scattering state.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of essential parts showing a structure in which one picture element portion of a reflective liquid crystal display device according to a first embodiment of the present invention is enlarged. As shown in FIG. 1, this reflective liquid crystal display device has transparent substrates 1, 2, 3 and a substrate 4 which are arranged at a predetermined interval, and dichroism is provided between the transparent substrate 1 and the transparent substrate 2. A first liquid crystal layer 5 that modulates the light intensity of a specific wavelength region containing a dye, that is, a light absorption state and a transparent state can be controlled, is provided between the transparent substrate 3 and the substrate 4. The liquid crystal layer 6 is sandwiched. Then, the transparent electrodes 7a and 7b and the alignment films 8a and 8b are provided so as to sandwich the liquid crystal layer 5. Further, a transparent electrode 7c and a reflective electrode 9 which also functions as a reflective film and an electrode are provided so as to sandwich the liquid crystal layer 6 therebetween. The substrate 4 need not be transparent.

For the first liquid crystal layer 5, a liquid crystal layer capable of modulating the light intensity in the visible light region, that is, controlling the light absorption state and the transparent state is selected. In this embodiment, a guest-host liquid crystal mixed with a black dichroic dye is used. For the second liquid crystal layer, a scattering type liquid crystal layer, so-called polymer dispersion type liquid crystal is selected.

Further, in this embodiment, the transparent substrate 1,
As the transparent electrodes 7a, 7b and 7c arranged on the second and third surfaces, ITO films were formed by the sputtering method, respectively. In this embodiment, the film thickness of the ITO is 1000 Å
Set to. Further, on the substrate 4, as a reflection film mirror,
Aluminum was formed by a sputtering method to form the reflective electrode 9. The reflective electrode 9 can function not only as a reflective film but also as an electrode.

Between transparent substrates 1-transparent substrate 2, transparent substrate 3
-If the distance between the substrates 4 is too small, in addition to manufacturing problems,
The absorption and the scattering of light are insufficient, and if they are too large, the drive voltage required becomes large and the response speed becomes slow. Therefore, it is suitable that the distance between the transparent substrate 1 and the transparent substrate 2 and the distance between the transparent substrate 3 and the substrate 4 are in the range of 3 μm to 15 μm, and preferably 4 μm to 10 μm. Fiberglass (manufactured by Nippon Electric Glass Co., Ltd.) is used as a spacer to form a transparent substrate 1, a transparent substrate 2, a transparent substrate 3, and a substrate 4.
All the intervals were set to 8 μm.

As the liquid crystal alignment films 7a and 7b of the liquid crystal layer 5,
N, N-dimethyl-N-octadecyl-3-aminopropyltrimethoxysilyl chloride (N, N-dimethyl-N) having the property of vertically aligning liquid crystal molecules on the substrate surface
-octadecyl-3-aminopropyltrimethoxysilil chloride)
It was used.

The guest-host liquid crystal as the liquid crystal layer 5 is ZL.
I-4792 (manufactured by Merck) was used, and the chiral pitch was adjusted by the addition amount of S-811 (manufactured by Merck). One example is shown below. The ratio d / p between the thickness d of the liquid crystal layer and the chiral pitch p has a constraint that the contrast ratio is lowered if it is too small, and the driving voltage is increased if it is too large. Therefore, the value of d / p is appropriately in the range of 1 to 5. More preferably, l. 2 to 3 and is set to 2 in this embodiment.

Here, the reason why the ratio d / p between the cell thickness and the chiral pitch is set to 2 in this embodiment will be described below with reference to FIG. FIG. 2 shows the characteristics of the black guest-host liquid crystal applied to the liquid crystal layer 5 (the applied voltage dependence of the transmittance when d / p is changed). When the ratio d / p between the cell thickness and the chiral pitch is changed, the threshold voltage of the liquid crystal changes as shown in FIG. Generally, a reflective liquid crystal display device has a contrast ratio of 5
In addition to the above, the voltage that can be applied to the active element is required to be 10 volts or less. From FIG.
It can be seen that the optimum value of d / p that satisfies these requirements is 2. That is, when d / p = 2, the applied voltage 10
When the applied voltage is 0 V or less, the transmittance can be about 60% of the maximum value, and the contrast is about 8% when the applied voltage is 0 V.
%, The contrast ratio is about 7.5. On the other hand, when d / p = 3, the transmittance does not reach the maximum value when the applied voltage is 10 V or less, and when d / p = 1.5, the transmittance can reach the maximum value even when the applied voltage is 7 V or less. The contrast ratio is about 4.6.

Further, the dye concentration of the dichroic dye has a restriction that light is not sufficiently absorbed if it is too small, and if it is too large, it is emitted during low temperature storage. So 2
A suitable dye concentration of the chromatic dye is 1 to 10 wt%, and in this embodiment, it is set to 4 wt%. The contrast ratio in reflection of the first liquid crystal layer 5 of this embodiment was about 7.5.

In the present embodiment, an example using the white Taylor type guest-host mode in which the substrate surface is vertically aligned is described, but the present invention is not limited to this. For example, a white-tailor mode in which the substrate surface is subjected to parallel alignment treatment may be used, or another Heilmeier type guest-host mode may be used. Also, so-called NCAP (Nematic Curvilinear Aligned Phase) reported in SID92DIGEST, p.762, in which guest-host liquid crystal is microencapsulated with polymer material
May be used.

As one example of the method for producing the liquid crystal microcapsules, the following method can be mentioned. That is, first, the liquid crystal and the gum arabic solution are emulsified and mixed at room temperature or higher, and a gelatin solution having an equal concentration is added thereto. Next, when distilled water is added to adjust the pH (hydrogen ion concentration), gelatin and gum arabic react to produce a thick liquid polymer. Then, when the temperature is lowered, coacervation starts, and the gelatin / arabic gum film adheres to the periphery of the liquid crystal particles to form a capsule film. Further, a curing agent such as aldehyde is added to age the capsule film. A liquid crystal layer can be formed by printing an ink, which is obtained by adding a binder to this, on a transparent substrate.

Next, the second liquid crystal layer 6 will be described. In the present embodiment, the scattering type liquid crystal used as the second liquid crystal layer 6 is a polymer network type liquid crystal PNM-.
106 (manufactured by Dainippon Ink and Chemicals, Inc.). After injecting this composition into a liquid crystal cell, ultraviolet rays of 360 nm were irradiated for 60 seconds to produce a scattering type liquid crystal. The second liquid crystal layer 6 can control the cloudy-transparent state by the voltage imprinting force. FIG.
Shows the transmittance characteristic and the reflection characteristic with respect to the applied voltage. Since the backscattering performance of the scattering type liquid crystal used as the second liquid crystal layer 6 is low, a mirror is arranged on the back surface of the liquid crystal layer 6 to reflect all the incident light when the reflection characteristics are measured. .

FIG. 4 shows the reflection type liquid crystal display device of this embodiment (FIG. 1) and an optical system used for evaluating the reflection characteristics of the second liquid crystal layer 6 constituting the reflection type liquid crystal display device. This optical system is JISZ
In accordance with the diffused illumination / vertical light receiving method of 8722, a regular reflection removal type illumination light receiving type is adopted. A spectrophotometer CM-1000 manufactured by Minolta Co., Ltd. was used as a measuring device. The 100% reflectance is the standard diffuser plate.

As shown in FIG. 3, the reflectance of the second liquid crystal layer 6 shows a peak value when the applied voltage is 4 V due to the change of the scattering state of the liquid crystal layer, and is optimum for the scattering characteristic and the reflection characteristic of the liquid crystal. It turns out that a value exists.

The reflective liquid crystal display device of the first embodiment is
The first liquid crystal layer 5 and the second liquid crystal layer 6 described above are combined, that is, the transparent substrate 2 and the transparent substrate 3 are arranged in an overlapping manner.

Next, a method of driving the reflective liquid crystal display device of this embodiment will be described. First, in order to display a bright state, as shown in FIG. 1A, an external electric field is applied between the transparent electrodes 7a and 7b so that the first liquid crystal layer 5 is in a transparent state, and then, An external electric field is applied between the transparent electrode 7c and the reflective electrode 9 so that the second liquid crystal layer 6 is in a scattering state. In the present embodiment, as described above with reference to FIG. 3, when the applied voltage of the second liquid crystal layer 6 is 4 V, the brightest state is obtained.
The voltage applied to the liquid crystal layer 6 was 4V.

On the other hand, in order to display the dark state,
As shown in (B), an external electric field is applied between the transparent electrodes 7a and 7b so that the first liquid crystal layer 5 is in an absorption state (black display), and the second liquid crystal layer 6 is in a transparent state. An external electric field is applied between the transparent electrode 7c and the reflective electrode 9 so that In this state, since the reflected light is only the specular reflection component, the reflected light does not enter the observer. Therefore, in this embodiment, the voltage applied to the second liquid crystal layer 6 is set to 9 in order to display the dark state.
In the present embodiment, the degree of the scattering state of the second liquid crystal layer 6 can be controlled by the voltage applied to the second liquid crystal layer 6, as described above with reference to FIG. The brightness of the display can be changed accordingly.

As described above, in the present embodiment, these first
By optimally driving the liquid crystal layer 5 and the second liquid crystal layer 6 according to the display data, a bright display with high contrast can be achieved.

As a first comparative example, a liquid crystal layer is formed by using the same guest host as the first liquid crystal layer 5 of the first embodiment, and a directional reflector is arranged immediately behind the liquid crystal layer. A reflective liquid crystal display device having the structure shown in FIG. 5 was produced. As a result of measuring the characteristics, it was confirmed that both the contrast and brightness were improved in the first embodiment (see Table 1 below).

As a second comparative example, Japanese Patent Laid-Open No. 5-4
5672, from the display surface side, a scattering type liquid crystal layer,
An absorption type liquid crystal layer and a reflection film are arranged in sequence,
A reflective liquid crystal display device as shown in FIG. 6 was produced. In this second comparative example, the same polymer dispersed liquid crystal as the second liquid crystal layer 6 of the first embodiment is used for the scattering liquid crystal layer, and the first liquid crystal layer is used for the absorption liquid crystal layer. The same guest-host liquid crystal as the first liquid crystal layer of the embodiment was used.

For each of the first embodiment, the first comparative example, and the second comparative example, the results of measuring the reflectance in the bright state, the reflectance in the dark state, and the contrast ratio are
The results are shown in Table 1 below.

[0040]

[Table 1]

Table 2 below shows the values of the applied voltages to the liquid crystal layers of the first embodiment, the first comparative example, and the second comparative example in the measurement of Table 1 above.

[0042]

[Table 2]

According to Table 1, when the first embodiment is compared with the first comparative example, the first embodiment has a reflectance of 18.49% in the bright state. Is 17.8
0%, the reflectance in the dark state is 1.27% in the first embodiment, and 3.98% in the first comparative example. Therefore, the contrast ratio is the same as that in the first embodiment, which is 14.6%. In Comparative Example 1 of 4.48, the improvement of the reflectance in the dark state largely contributes to the improvement of the contrast ratio by 3 times or more. Further, when the first embodiment is compared with the second comparative example, the second embodiment has a second reflectance of 18.49% in the bright state reflectance.
The comparative example is 18.00%, and the reflectance in the dark state is 1.27% in the first embodiment, while the first comparative example is 2.05%,
Therefore, the contrast ratio is 14.6 in the first embodiment and 8.76 in the first comparative example. In this case as well, the improvement of the reflectance in the dark state greatly contributes to the contrast ratio of about 1.7.
It has improved twice. Thus, in the first embodiment,
It can be seen that both the contrast and the brightness (brightness reflectance) are improved as compared with the first comparative example and the second comparative example.

As described above, the reason why the contrast of the first embodiment is particularly higher than that of the second comparative example is that the lower reflectance in the dark state has a great influence. There is something. The cause of the decrease in the reflectance in the dark state in the first embodiment is considered as follows. Even if the scattering liquid crystal is in a transparent state, it does not transmit 100% as shown in FIG. 3, and small scattering and absorption exist. On the other hand, the absorption of the absorbing liquid crystal was not completely absorbed as shown in FIG. 2, and the transmittance was about 30%. In the dark state of the first embodiment, external light enters from the incident side thereof to the guest host liquid crystal absorption state → scattering liquid crystal transparent state → reflection film (reflection electrode) → scattering liquid crystal transparent state → guest host liquid crystal absorbing state. And proceed. On the other hand, in the second comparative example, external light enters from the incident side thereof in a transparent state of the scattering liquid crystal → absorption state of the guest-host liquid crystal → reflection film (reflection electrode) → absorption state of the guest-host liquid crystal → scattering liquid crystal. It progresses to a transparent state. Comparing the progress of these external lights, it is considered that the reflectance of the dark state could be lowered because the light absorption rate was higher in the first embodiment.

Next, as a second embodiment, a reflection type color liquid crystal display device having a color filter to which the present invention is applied will be described with reference to FIG. FIG. 7 is a cross-sectional view of essential parts showing a structure in which one picture element portion of a reflective liquid crystal display device according to a second embodiment of the present invention is enlarged.
The difference between the second embodiment and the first embodiment is that
As shown in FIG. 7, the color filter 10 and the flattening film 11 are only provided between the transparent substrate 1 and the transparent electrode 7, and the other structures are the same as those in the first embodiment. is there. In FIG. 5, members having the same functions as those in the first embodiment (FIG. 1) are designated by the same reference numerals.

In this embodiment, a pigment-dispersed color filter is used as the color filter 10, and its production is as follows. A photosensitive resist in which a red pigment was uniformly dispersed in a transparent photosensitive resin was applied on the transparent substrate 1. Specifically, using CR2000 manufactured by Fuji Hunt Electronics Technology Co., Ltd., a film having a thickness of 2.0 μm was formed by spin coating at 650 rpm. After that, pre-baking is performed at 80 ° C., exposure and development are performed using a predetermined mask, and finally, at 220 ° C., 30
Bake for a minute to form a red pattern. Furthermore, CG manufactured by Fuji Hunt Electronics Technology Co., Ltd.
2000, CB2000, and CK2000 were formed in the same process to form green, blue, and black patterns, respectively. Then, a flattening pus 11 for reducing the step was formed on this. The subsequent manufacturing of the device is similar to that of the first embodiment.

The operating principle of the color display device of the second embodiment is the same as that of the first embodiment, and the color display according to the present embodiment is also bright as in the first embodiment. It was confirmed that high contrast color display could be realized.

Next, as the third embodiment, the first
A reflection type color liquid crystal display device using an interference filter instead of the reflection film of the embodiment will be described with reference to FIG. FIG. 8 is a cross-sectional view of essential parts showing a structure in which one pixel portion of a reflective liquid crystal display device according to a third embodiment of the present invention is enlarged. In a third embodiment,
The difference from the first embodiment is that, as shown in FIG.
The interference filter 12 and the transparent electrode 7b are provided on the substrate 4, and the light absorption film 13 is further provided on the back side of the substrate 4 (the side opposite to the display surface). Other structures are the same as those of the first embodiment. Is similar to. In FIG. 8, members having the same functions as those in the first embodiment (FIG. 1) are
The same reference numbers are added.

In this embodiment, as the reflection film, the interference filter 12 in which two kinds of transparent inorganic dielectric thin films having different refractive indexes are alternately laminated is used. In practice, silicon dioxide is used as a substance having a low refractive index. (N = 1.46), and titanium dioxide (n = 2.4) was used as a substance having a high refractive index. The detailed manufacturing conditions of the interference filter are shown below.

The interference filter 12 is made of silicon dioxide (Si
O ₂ ) and titanium dioxide (TiO ₂ ) targets are used,
Thin films are alternately laminated by sputtering to form a multilayer film. In the regions 12a, 12b, and 12c in FIG. 8, the number of layers and the thickness are optimized so as to reflect red, green, and blue light, respectively. As the number of layers of the above-mentioned transparent dielectric thin film is increased, the spectral characteristics become steeper, and an interference filter excellent in color separation can be obtained. For example, the total thickness is set to 1.052 μm for blue, 0.821 μm for red, and 1.725 μm for green. After that, the photo processes of photoresist application, exposure, and development are repeated three times to form the red, green, and blue reflective color filters 12. FIG. 9 shows the characteristics of the interference filter used in this embodiment. From FIG. 9, it can be seen that an interference filter having excellent color separation is obtained.

After that, a reflective liquid crystal display device was manufactured in the same manner as in the first embodiment. However, in the present embodiment, an interference filter made of a dielectric thin film multilayer film is used in place of the reflective electrode 9 of the first embodiment, so that the transparent electrode 7a of the first embodiment is used as the transparent electrode 7d. , 7b and 7c, an ITO film was formed with a film thickness of 1000Å by a sputtering method. Further, in this embodiment, since the transparent substrate is used as the substrate 4, the substrate 4
Although the black or gray light absorbing film 13 is provided on the surface opposite to the transparent electrode 9 of the above, the light absorbing film may not be necessary, for example, when the substrate 4 is made of a light absorbing material.

The operating principle of the color display device of the third embodiment is the same as that of the first embodiment, and the color display according to the present embodiment is also bright as in the first embodiment. It was confirmed that high contrast color display could be realized.

Next, as a fourth embodiment, the third
An application of the present invention to a reflective color liquid crystal display device using a holographic color filter instead of the interference filter 12 of the embodiment will be described. 4th
In this embodiment, a holographic color filter is arranged at this position instead of the interference filter 12 of the third embodiment shown in FIG. 8, and the other structures are the same as those of the third embodiment. It is similar.

Next, a method of manufacturing the holographic color filter will be described. First, a photosensitive layer for hologram and a mirror are brought into close contact with each other, a predetermined mask is arranged, and laser light of red wavelength is vertically incident. The irradiated laser light interferes with the reflected light from the mirror, and interference fringes are recorded in the exposed portion of the photosensitive layer parallel to the surface direction. Such exposure is sequentially performed by shifting the mask, and interference fringes are recorded for green and blue in the same manner. Detailed production conditions are shown in Table 3 below.

[0055]

[Table 3]

The holographic color filter manufactured in this way is simply arranged at the position 12 in FIG. 8, and the other manufacturing method is the same as in the third embodiment, and the description thereof is omitted.

The operating principle of the color display device of the fourth embodiment is the same as that of the first embodiment, and the color display according to the present embodiment is also bright as in the first embodiment. It was confirmed that high contrast color display could be realized. Next, as a fifth embodiment, a reflection type liquid crystal display device provided with an alignment film for aligning liquid crystal molecules in a second liquid crystal layer formed by dispersing a liquid crystal material in a photocurable compound is shown in FIGS. This will be described with reference to 12.

FIG. 10 is a cross-sectional view of essential parts showing a structure in which one picture element portion of a reflective liquid crystal display device according to a fifth embodiment of the present invention is enlarged. The fifth embodiment is different from the first embodiment in that, as shown in FIG. 10, in a second liquid crystal layer 6'made of a so-called polymer dispersion type liquid crystal in which a liquid crystal material is dispersed in a photocurable compound. The alignment films 8c and 8d for aligning the liquid crystal molecules are provided and the second liquid crystal layer is aligned, and the other structures are the same as those in the first embodiment. In FIG. 10, members having the same functions as those in the first embodiment (FIG. 1) are designated by the same reference numerals.

As the first liquid crystal layer 5, a liquid crystal layer capable of modulating the light intensity in the visible light region, that is, controlling the light absorption state and the transparent state is selected as in the first embodiment. . Also in this embodiment, the guest-host liquid crystal mixed with the black dichroic dye is used. And, as for the second liquid crystal layer 6 ',
Similar to the first embodiment, a scattering type liquid crystal layer, so-called polymer dispersion type liquid crystal is selected.

In addition, the transparent electrode 7 disposed on the surfaces of the transparent substrates 1, 2, and 3 is the same as the first embodiment.
As a, 7b, and 7c, an ITO film is formed by a sputtering method, and the film thickness of the ITO is 1000Å
Set to. Further, on the substrate 4, as a reflection film mirror,
Aluminum was formed by a sputtering method to form the reflective electrode 9. The reflective electrode 9 can function not only as a reflective film but also as an electrode.

For the first liquid crystal layer 5, as in the first embodiment, the white Taylor type guest-host mode in which the surface of the substrate is vertically aligned is used.

Next, the second liquid crystal layer 6'and the alignment films 8c and 8d sandwiching it will be described. In this embodiment, the second liquid crystal layer 6'uses an oriented scattering type liquid crystal, and this orientation is due to the orientation films 8c and 8d. In this embodiment, Optomer AL4552 (manufactured by Nippon Synthetic Rubber Co., Ltd.) is used as the alignment films 8c and 8d.
This alignment film has the property of aligning liquid crystal molecules substantially parallel to the surface of the alignment film by rubbing the alignment film material. The alignment films 8c and 8d were formed by a printing method so that the film thickness was 700 Å after the rubbing treatment. In addition, the rubbing direction during the rubbing treatment was set to a so-called anti-parallel direction in which the upper and lower substrates are parallel to each other and opposite in direction.

As the second liquid crystal layer 6 ', polymer network type liquid crystal PNM-106 (manufactured by Dainippon Ink and Chemicals, Inc.) was used. After injecting this composition into a liquid crystal cell, 3
Ultraviolet light of 60 nm was irradiated for 60 seconds to cause the liquid crystal and the photocurable compound to undergo phase separation, and thus a scattering type liquid crystal was produced. This second liquid crystal layer 6'can control the cloudy-transparent state by the voltage imprinting force. Further, in the second liquid crystal layer 6 ′, since the liquid crystal molecules and the photocurable compound are phase-separated, only the liquid crystal molecules are aligned by the alignment films 8c and 8d.

The alignment film 8c manufactured as described above,
The liquid crystal molecules in the second liquid crystal layer 6 ′ provided with 8d are
Between −4, it was confirmed that the orientation was parallel to the rubbing direction as described above. Since the second liquid crystal layer 6'has a low backscattering performance, the reflective electrode 9 which is a mirror is arranged on the back surface of the alignment film 8d so as to reflect most of the incident light.

The distribution of the reflected light in the combination of the second liquid crystal layer 6'which is the scattering type liquid crystal and the reflective electrode 9 which is the reflective film is evaluated by using an optical system as shown in FIG. did. Note that this is for evaluating the in-plane reflection distribution, and the substrate and the alignment film are omitted in the figure.

As shown in FIG. 11, the scattering type liquid crystal layer (second
Of the liquid crystal layer) 6'and the reflection film (reflection electrode) 9 is incident on the sample from the direction of 30 degrees from the vertical direction, and the intensity of the light reflected in the vertical direction is measured in the plane direction of the sample. The measurement was performed while rotating in the direction of the arrow and changing φ. Note that the incident direction of light when φ = 0 ° and 180 ° is substantially parallel to the rubbing direction during the alignment treatment and the surface direction of the sample.

The results are shown in FIG. For comparison, the same measurement was performed on a sample composed of a scattering type liquid crystal layer corresponding to the second liquid crystal layer 6 of the first embodiment without alignment treatment. In FIG. 12, “a” indicates the measurement result by the standard white plate, “b” indicates the measurement result by the sample including the second liquid crystal layer 6 ′ of the present embodiment, and “c” indicates the above-mentioned measurement result. 3 is a measurement result of a sample including the second liquid crystal layer 6 according to the first embodiment.

From these measurement results, c of the sample without orientation is isotropically scattered in the plane, like a of the standard substrate. on the other hand. The sample b subjected to the orientation treatment in the present embodiment scatters anisotropically in the plane. That is, the reflectance (φ = 0 at an angle substantially parallel to the rubbing direction
And 180 °) is different from the reflectance (φ = 90 °, 270 °) at an angle substantially perpendicular to the rubbing direction. From this, according to the second liquid crystal layer 6 ′ that has been subjected to the alignment treatment of the present embodiment, it is possible to realize a brighter display by setting the direction of high reflectance as the viewing angle direction of the observer. Becomes

The driving conditions of the reflection type liquid crystal display device as shown in FIG. 10 constructed by using such a second liquid crystal layer 6'are the same as those in the first embodiment. That is, when the first liquid crystal layer 5 exhibits a black display in the absorption state,
The second liquid crystal layer 6 ′ is made transparent, and in this state, the reflected light is only the specular reflection component, so the reflected light does not enter the observer (dark state (B) in FIG. 10). Then, when the first liquid crystal layer 5 is in the transparent state, the second liquid crystal layer 6 ′ is brought into the scattering state (the bright state (A) in FIG. 10). Here, the degree of the scattering state can be changed according to the brightness of the surrounding environment. As described above, according to this embodiment, as in the above embodiments, a display with high contrast and bright display can be achieved, and the direction in which the reflectance of the second liquid crystal layer 6 ′ is high is set as the viewing angle direction of the observer. This makes it possible to realize a brighter display.

Although only the basic structure has been described in the first to fifth embodiments, the transparent substrates 1, 3 are used to form a liquid crystal display panel for actually displaying an image.
It is preferable to provide a thin film transistor or a two-terminal element (MIM element, varistor, or the like) on the top. Further, if a fiber plate having a thickness of 1 mm is used as the transparent substrates 2 and 3 provided between the two liquid crystal layers, parallax can be completely eliminated. Moreover, parallax can be completely eliminated by using a Selfocs lens, a microlens, or the like, instead of using a fiber plate for the transparent substrate.

The first liquid crystal layer can be applied to the present invention as long as it is a liquid crystal whose light absorption state and transparent state can be controlled by applying a voltage. For example, a twisted nematic liquid crystal that uses a polarizing plate, a super twisted nematic liquid crystal, a Heilmeier type guest-host liquid crystal, and the like can be given. Further, the second liquid crystal layer is applicable to the present invention as long as the light scattering state and the transparent state can be controlled by applying a voltage, for example,
Examples thereof include polymer dispersion type liquid crystal in which fine particles are dispersed, DSM method using nematic liquid crystal, and focal conic scattering by cholesteric liquid crystal.

In the third and fourth embodiments, an interference filter or a holographic color filter is used as the reflective color filter, but other reflective color filters may be used as a cholesteric liquid crystal or a composite of a cholesteric liquid crystal and a polymer material. It has been confirmed that the same effect is observed when the body or cholesteric liquid crystal polymer is used.

[0073]

As described above, according to the reflection type liquid crystal display device of the present invention, bright and high-contrast display can be obtained.

Further, according to the reflection type liquid crystal display device of the present invention having the transmission color filter or the reflection color filter, it is possible to realize a reflection type color liquid crystal display device capable of brightening multicolor display as compared with the conventional case.

Further, according to the present invention, since the reflection characteristic can be controlled by changing the scattering state of the second liquid crystal layer by the electric field in accordance with the brightness of the display, the contrast can be adjusted according to the input data. It is possible to obtain a high display of.

Further, according to the present invention, the reflection characteristic can be controlled by changing the scattering state of the second liquid crystal layer by the electric field according to the brightness of the environment in which the device is used. It is possible to realize a good display according to the surrounding light environment, such as having a strong scattering property and weakening the directivity, or weakening the scattering property in a dark place and increasing the directivity.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing the structure of a reflective liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a graph showing the applied voltage dependence of the transmittance of the first liquid crystal layer made of guest-host liquid crystal used in the first to fourth embodiments.

FIG. 3 is a graph showing applied voltage dependence of transmittance and reflectance of a second liquid crystal layer made of scattering type liquid crystal used in the first to fourth embodiments.

FIG. 4 is a diagram showing an evaluation optical system of a second liquid crystal layer made of scattering type liquid crystal used in the first to fourth embodiments.

FIG. 5 is a cross-sectional view of essential parts showing the structure of a reflective liquid crystal display device of a first comparative example.

FIG. 6 is a cross-sectional view of essential parts showing the structure of a reflective liquid crystal display device of a second comparative example.

FIG. 7 is a cross-sectional view of essential parts showing the structure of a reflective liquid crystal display device according to a second embodiment of the present invention.

FIG. 8 is a cross-sectional view of essential parts showing the structure of a reflective liquid crystal display device according to a third embodiment of the present invention.

FIG. 9 is a graph showing the wavelength dependence of the reflectance of the reflective color film (interference filter) used in the third embodiment.

FIG. 10 is a sectional view of a key portion showing the structure of a reflective liquid crystal display device according to a fifth embodiment of the present invention.

FIG. 11 is a schematic view showing an optical system for measuring the reflection distribution of a sample composed of the second liquid crystal layer 6 ′ of the fifth embodiment.

FIG. 12 shows the results of measurement of the reflection distributions of the sample composed of the second liquid crystal layer 6 ′ of the fifth embodiment and the sample composed of the first liquid crystal layer 6 of the first embodiment. It is a figure.

FIG. 13 is a cross-sectional view of essential parts showing the structure of a conventional reflective liquid crystal display device.

[Explanation of symbols]

 1,2,3 Transparent substrate 4 Substrate 5 First liquid crystal layer 6,6 'Second liquid crystal layer 7a, 7b, 7c, 7d Transparent electrode 8a, 8b, 8c, 8d Alignment film 9 Reflective film 10 Color filter 11 Flat Chemical film 12 Interference filter 13 Light absorbing film

Claims (11)

[Claims] 1. A first liquid crystal layer capable of controlling a light absorption state and a transparent state according to a first externally applied electric field, and a light scattering state and a transparent state according to a second externally applied electric field. In a reflective liquid crystal display device including a possible second liquid crystal layer and a reflective film, the first liquid crystal layer, the second liquid crystal layer,
A reflective liquid crystal display device characterized in that a reflective film is arranged in this order. 2. The reflection type liquid crystal display device according to claim 1, further comprising an absorption type color filter layer. 3. The reflective liquid crystal display device according to claim 1, wherein the first liquid crystal layer is a layer in which a dichroic dye is dispersed in a liquid crystal material. 4. The second liquid crystal layer comprises a layer in which a liquid crystal material is dispersed in a photocurable compound.
The reflective liquid crystal display device according to item 1. 5. The reflective liquid crystal display device according to claim 4, wherein liquid crystal molecules in the second liquid crystal layer are aligned. 6. The photocurable compound in the second liquid crystal layer is phase-separated from liquid crystal molecules.
The reflective liquid crystal display device according to item 5. 7. The reflective liquid crystal display device according to claim 1, wherein the reflective film is formed of an inorganic dielectric mirror that selectively reflects wavelength. 8. The reflective liquid crystal display device according to claim 1, wherein the reflective film is a holographic mirror. 9. The reflective liquid crystal display device according to claim 1, wherein the reflective film is made of any one of a cholesteric liquid crystal, a composite of a cholesteric liquid crystal and a polymer material, or a cholesteric liquid crystal polymer. . 10. The method for driving a reflective liquid crystal display device according to claim 1, wherein the reflection characteristic is controlled by changing a scattering state of the second liquid crystal layer by an electric field. A method for driving a reflective liquid crystal display device, comprising: 11. The method for driving a reflective liquid crystal display device according to claim 1, wherein the first liquid crystal layer is brought into a light absorbing state when displaying in a dark state. At the same time, the second liquid crystal layer is controlled so as to be in a transparent state, and when displaying in a bright state, the first liquid crystal layer is brought into a light transparent state and the second liquid crystal layer is brought into a light scattering state. A method for driving a reflective liquid crystal display device, which is characterized in that: