JPH07261156A - Light scattering type liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a light scattering type liquid crystal display device which permits low- voltage driving and has good display quality. CONSTITUTION:A liquid crystal layer 11 is sandwiched from above and below by transparent substrate 2, 3 of glass, etc., laminated with transparent electrodes 4, 5 and driving voltage is applied to these transparent electrodes by a driver to control the orientation of the liquid crystal molecules of the liquid crystal layer to control the display. In the liquid crystal layer 11, with second liquid crystal regions 9 and third liquid crystal regions 10 are dispersedly arranged in the first liquid crystal region 8 in an independent state. The liquid crystal molecule of the respective liquid crystal regions are in a random state and the light transmitted through the liquid crystal layer 11 scatters in the respective liquid crystal regions in a state of not impressing electric fields to these regions. In addition, the liquid crystals varying in average refractive index are used for the respective liquid crystal regions adjacent to each other and, therefore, the light is scattered at the boundaries of the liquid crystal regions. The ordinary light refractive indices (no) of the respective liquid crystal regions 8, 9, 10 are coincident with each other when the electric fields are impressed thereto. Since the arranging directions of the liquid crystal molecules of the respective liquid crystal regions 8, 9, 10 are unified and arranged in the electric field direction, the good light transmission state is obtd. and the low-voltage driving is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light scattering type liquid crystal display device having a liquid crystal layer in which a plurality of independent liquid crystal regions are dispersed.

[0002]

2. Description of the Related Art In recent years, research on application to display devices and dimming devices utilizing the light scattering effect in a composite of a polymer material and liquid crystal has become active. The polymer-dispersed liquid crystal material consisting of this polymer-liquid crystal composite has a structure in which liquid crystal droplets (microdroplets) having a diameter of several μm or less are dispersed in the polymer, or a liquid crystal is filled in a network polymer. By adopting a structure as described above and applying a voltage to the liquid crystal, the alignment direction of the liquid crystal molecules is aligned with the direction of the electric field, and the light transmission / scattering effect due to the matching of the refractive indexes of the polymer and the liquid crystal is utilized.

For example, when no electric field is applied, the optical axes of liquid crystal droplets are random, the effective refractive index of the liquid crystal does not match the refractive index of the polymer, and the liquid crystal is opaque due to the light scattering effect. It is in a white state.

When an electric field above the threshold value is applied, the optical axis of the liquid crystal is aligned in the electric field direction, for example, and the apparent refractive index (no) of the liquid crystal droplet corresponds to the ordinary ray of the liquid crystal. Since the refractive index (np) of the polymer is almost the same, the light scattering effect is weakened and the liquid crystal cell becomes transparent.

As described above, the conventional light-scattering liquid crystal display device using a polymer does not require a polarizing plate and controls the display by creating a light-scattering state and a light-transmitting state. It can be a device. In particular, polymer-dispersed liquid crystals include PDLC (Polymer Dispersed Liquid Crystal), due to differences in structure and manufacturing method.
PNLC (Polymer Network Liquid Crystal), NCA
P (Nematic Curvilinear Aligned), etc. are being developed for practical use.

[0006]

However, in such a conventional light-scattering type liquid crystal display device, since a liquid crystal layer in which a liquid crystal and a polymer are combined is used, a voltage drop occurs in the polymer layer. Is likely to occur, and the voltage actually applied to the liquid crystal is about a fraction of the applied voltage. Therefore, the polymer-dispersed liquid crystal display device has a problem that the driving voltage becomes high.

Therefore, in order to suppress the driving voltage of the liquid crystal to be low, it is possible to increase the mixing ratio of the liquid crystal, but there is a limit to the ratio of the liquid crystal mixed with the polymer resin, and if the ratio of the liquid crystal is raised too much, the light Therefore, there is a problem in that the display quality is deteriorated because the scattering property of is reduced.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a light scattering type liquid crystal display device which can be driven at a low voltage and has a good display quality.

[0009]

According to another aspect of the present invention, there is provided a light-scattering type liquid crystal display device, which comprises a pair of transparent substrates, which are arranged to face each other with a predetermined gap therebetween, and transparent electrodes are formed on respective surfaces of the transparent substrates. A liquid crystal layer formed between the pair of transparent substrates, the liquid crystal layer comprising only a plurality of independent liquid crystal regions each having an average refractive index different from each other; and applying a voltage to the liquid crystal layer and controlling an applied voltage value to the liquid crystal region. The above object is achieved by having display control means for changing the orientation state of each liquid crystal molecule between a state of transmitting light and a state of scattering light to perform display control.

A light-scattering type liquid crystal display device according to claim 2 is
The liquid crystal region of the liquid crystal layer according to the first aspect achieves the above object by the fact that the ordinary refractive index of the liquid crystal is substantially the same.

A light-scattering type liquid crystal display device according to claim 3 is
The above object is achieved by the liquid crystal regions of the liquid crystal layer according to the first aspect being composed of liquid crystals having substantially the same dielectric constant.

A light-scattering liquid crystal display device according to claim 4 is
At least one of the plurality of liquid crystal regions dispersed in the liquid crystal layer according to claim 1, 2 or 3 is a region of the liquid crystal enclosed by an encapsulant, thereby achieving the above object.

[0013]

In the light-scattering type liquid crystal display device according to claim 1, the liquid crystal layer in which a plurality of independent liquid crystal regions enclosed between transparent substrates are dispersedly arranged is composed of only a plurality of liquid crystal regions having different average refractive indexes. Since it is configured, it is possible to obtain good display quality by low voltage driving.

In the light-scattering type liquid crystal display device according to the second aspect, since the ordinary refractive index of each liquid crystal region of the liquid crystal layer is substantially the same, the liquid crystal molecules in each liquid crystal region are highly aligned and a good light is obtained. A transparent state can be obtained and display quality can be improved.

In the light-scattering type liquid crystal display device according to the third aspect, since each liquid crystal region of the liquid crystal layer is composed of liquid crystal having substantially the same dielectric constant, the entire liquid crystal layer can be driven at a low voltage.

In the light-scattering type liquid crystal display device according to claim 4, since at least one of the plurality of liquid crystal regions dispersed in the liquid crystal layer is encapsulated by an encapsulating material, independent liquid crystal regions are surely separated. Can be dispersed in another liquid crystal region, can be easily manufactured, and display quality can be improved.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 4 are views for explaining the light-scattering type liquid crystal display device of the present invention.

First, the structure will be described.

FIG. 1 is a cross-sectional configuration diagram of a light scattering type liquid crystal display device 1 of this embodiment.

As shown in FIG. 1, the light-scattering type liquid crystal display device 1 has two transparent substrates 2 and 3 made of glass plates, which are arranged in parallel with each other at a predetermined interval. On the opposing surface, for example, indium tin oxide (ITO) is formed into a film having a predetermined thickness by using a sputtering method or a vapor deposition method, and this is patterned to laminate the transparent electrodes 4 and 5 in a desired shape. And, in the peripheral portion between the two transparent substrates,
The sealing materials 6 and 7 are applied and the two transparent substrates 2 and 3 are bonded to each other to form a liquid crystal cell in which liquid crystal is sealed. The following liquid crystal material is enclosed in the liquid crystal cell to form the liquid crystal layer 11.

The characteristic structure of the light-scattering type liquid crystal display device of the present invention is the liquid crystal layer 11 enclosed in the liquid crystal cell.
Is composed of two or more independent liquid crystal regions, and liquid crystal molecules in each liquid crystal region are randomly aligned.

Then, in this embodiment, as shown in FIG. 1, for example, the first liquid crystal region 8, the second liquid crystal region 9, and the third liquid crystal region 9 are formed.
The three liquid crystal regions of the liquid crystal region 10 are made of liquid crystal materials having different average refractive indexes. Therefore, when no electric field is applied, the liquid crystal molecules are in a random state in each liquid crystal region, which causes a light scattering effect, and there is a difference in average refractive index between adjacent liquid crystal regions. The light scattering effect is added, and a high light scattering state can be obtained as the entire liquid crystal layer 11.

That is, since the light-scattering liquid crystal display device of this embodiment obtains the light-scattering effect by utilizing the difference in average refractive index between independent liquid crystal regions, the conventional polymer-dispersed liquid crystal is used. It is possible to prevent the transmission of light in the polymer portion, which is a problem, and improve the degree of scattering in a state where no electric field is applied.

Further, the liquid crystal of each liquid crystal region of the present embodiment is preferably such that the refractive index anisotropy (Δn = ne-no) obtained by subtracting the ordinary light refractive index (no) from the extraordinary light refractive index (ne) is as large as possible. Desirably, in this case, the degree of light scattering is increased, and a preferable light scattering effect is obtained.

Further, the liquid crystals in the adjacent liquid crystal regions of this embodiment are liquid crystal materials having different average refractive indexes as described above, and liquid crystal materials having substantially the same ordinary refractive index (no) are used. As shown in FIG. 2, when a predetermined voltage of the power source 21 is applied between the transparent electrodes 4 and 5 by turning on the switch section 22, liquid crystal molecules are arranged along the direction of the electric field.
At this time, since each of the liquid crystal regions 8 to 10 in the liquid crystal layer 11 is composed of liquid crystal having the same ordinary light refractive index (no), a state in which light is not scattered can be obtained. A good light transmission state is obtained in which the incident light passes through the liquid crystal layer 11 and is directly transmitted in the direction of arrow B.

Further, by varying the applied voltage applied to the liquid crystal layer 11, the amount of transmitted light can be adjusted and a halftone can be displayed.

By the way, as described above, the conventional polymer-dispersed liquid crystal is a liquid crystal layer composed of a polymer / liquid crystal composite in which spherical droplets (microdroplets) of liquid crystal having a diameter of several μm or less are dispersed in a polymer. However, since a polymer that is a dielectric material causes a voltage drop, the driving voltage of the liquid crystal must be high. In this respect, the liquid crystal layer 11 of the present embodiment is filled with not only the dispersed liquid crystal regions 9 and 10 but also the liquid crystal regions 8 having predetermined characteristics between the liquid crystal regions. The voltage drop does not occur and the applied voltage for driving the liquid crystal can be lowered. Specific effects will be described with reference to FIG.

FIG. 3 is a chart showing the results of comparison between the drive voltage and the contrast ratio of the present invention and the conventional example.

As shown in FIG. 3, conventionally, 50-100
Although a driving voltage of about 10 to 100 V was required to obtain the contrast ratio of 1., the light scattering type liquid crystal display device of the present invention has a contrast ratio of about 20 to 100 at about 1 to 3 V. Thus, the driving voltage can be lowered to about 1/10 to 1/30. That is,
According to the light-scattering type liquid crystal display device of the present invention, it is possible to drive with a drive voltage equivalent to that of a liquid crystal display element of a normal single material.

In the present invention, unlike the conventional polymer-dispersed liquid crystal, in which a polymer that easily transmits light is interposed between dispersed liquid crystal regions, liquid crystal molecules are randomly aligned. This is because the voltage drop due to the polymer disappears because the liquid crystal region is interposed.

As described above, in the light-scattering type liquid crystal display device of this embodiment, the liquid crystal layer 11 is formed only by a plurality of liquid crystal regions having the ordinary refractive indexes (no) substantially equal to each other and having different average refractive indexes. Therefore, by adjusting the voltage applied to the liquid crystal, it is possible to obtain a light scattering state with a large scattering degree to a good light transmitting state, and it is possible to obtain a clear image display with high contrast at a low driving voltage.

The liquid crystal material used in each liquid crystal region of this embodiment may be any liquid crystal having the above-mentioned various characteristics. For example, a cholesteric liquid crystal material, a nematic liquid crystal material, or the like adjusted to have a predetermined ordinary light refractive index or average refractive index can be used.

Further, as the liquid crystal material of the present embodiment, liquid crystal having a property that the dielectric constants of the respective liquid crystal regions are substantially equal to each other in addition to the above characteristics is used. As a result, uniform display quality can be obtained over the entire liquid crystal layer by low voltage driving.

Next, the operation will be described.

First, as shown in FIG. 1, transparent substrates 2 and 3 such as glass on which transparent electrodes 4 and 5 made of ITO are laminated.
The liquid crystal layer 11 is sandwiched from above and below, and a drive voltage is applied to the transparent electrode by using a driver (not shown) to control the alignment of liquid crystal molecules in the liquid crystal layer, thereby performing display control.

The liquid crystal layer 11 has a second liquid crystal layer in the first liquid crystal region 8.
The liquid crystal region 9 and the third liquid crystal region 10 are dispersed and arranged in an independent state. And in the state where no electric field is applied,
Since the liquid crystal molecules in each liquid crystal region are in a random state, the light transmitted through the liquid crystal layer 11 is scattered in each liquid crystal region. Further, since liquid crystals having different average refractive indexes are used in the adjacent liquid crystal regions, light scattering also occurs at the boundary surface between the liquid crystal regions. As described above, in the light-scattering liquid crystal display device of this embodiment, when no electric field is applied, light is scattered in each liquid crystal region and also scattered at the interface between the liquid crystal regions, so that the light is sufficiently transmitted. Can be disturbed.

Next, as shown in FIG. 2, the switch 22 is closed and a driving voltage above the threshold is applied from the power source 21 to the liquid crystal layer 1.
When it is applied to 1, the liquid crystal molecules of the liquid crystal regions 8, 9, 10 are arranged along the direction of the electric field. Here, in this example, since the ordinary refractive index (no) and the dielectric constant of the liquid crystal regions 8, 9 and 10 are set to be substantially the same, even if each liquid crystal region is independent, the alignment direction of the liquid crystal molecules is Since they coincide with each other, it is possible to obtain a good light transmission state in which the light is not scattered and the light incident from the arrow A passes directly to the arrow B.

As shown in FIG. 2, when the drive voltage is applied, the first liquid crystal region 8, the second liquid crystal region 9 and the third liquid crystal region 10 are each made of a liquid crystal material. Unlike the molecular dispersion type liquid crystal, no voltage drop occurs in the polymer part, and it is possible to drive at a low voltage.

Therefore, the light-scattering type liquid crystal display device of this embodiment has a contrast ratio of about 1/10 to 1/1 which is substantially equal to that of the conventional polymer dispersion type liquid crystal as shown in the chart of FIG.
It can be obtained with a low driving voltage of about 30.

Next, FIG. 4 is a cross-sectional configuration diagram of a light scattering type liquid crystal display device 31 according to another embodiment of the present invention.

In FIG. 4, the same reference numerals as those in FIG. 1 indicate the same or corresponding parts, and the description thereof will be omitted. Further, the fourth liquid crystal region 32, the fifth liquid crystal region 33, the sixth liquid crystal region 34, and the seventh liquid crystal region 35, which form the liquid crystal layer 36, respectively, have the same ordinary refractive index as in the above-described embodiment, and each have an ordinary light refractive index. The average refractive index of the liquid crystals is different from each other, and the liquid crystals are made of liquid crystals having substantially the same dielectric constant. Here, the liquid crystal regions 33, 34, and 35 are each encapsulated in an encapsulant 37, separated so that the liquid crystal materials are not mixed with each other, and then dispersed in the fourth liquid crystal region 32. .

There are various sizes of fine-diameter capsules in which the liquid crystal material is enclosed, and the smaller the capsules, the higher the electric field condition for controlling the orientation of the liquid crystal molecules in the capsules. This is because the amount of encapsulant per unit volume is large, so that the voltage drop due to this encapsulant is included.

On the contrary, if the size of the capsule is increased,
Although the electric field for controlling the alignment of liquid crystal molecules is small,
Response time is long.

Therefore, it is desirable that the size of the capsule is such that any of the above problems does not occur, and that the size is uniform. This is because if the capsule size is not uniform, the alignment of liquid crystal molecules when an electric field is applied may become non-uniform depending on the size of the capsule. In this embodiment, capsules having a predetermined particle size within the range of several μm to several tens of μm are formed and dispersed in the fourth liquid crystal region 32 shown in FIG.

The above-mentioned capsule material can be formed by using various resins and polymers. In this embodiment, polyvinyl alcohol (P
VA) is preferably used. This PVA has a relatively large dielectric constant and has a refractive index close to that of a preferable liquid crystal material, and thus is excellent as an encapsulating material. In addition, capsule materials other than PVA include gelatin, Carbopole, and Gantrez (Ga
ntrez) and can be used alone or in combination with other polymers.

Next, in order to manufacture the encapsulated liquid crystal of the present embodiment, a solution in which the above-mentioned encapsulating material, the desired liquid crystal material, and possibly a carrier medium such as water are combined is prepared and mixed. For example, the amount of PVA in this solution is between 5% and
About 20%, preferably about 7%, PV
The preferred ratio changes depending on the molecular weight of A. For example, P
If the molecular weight of VA is too large, it will look like glass and PV
When A is too small, it becomes a capsule material with low viscosity,
The liquid crystal inside will flow out and you will not be able to make a liquid crystal in a capsule.

In mixing these materials, a mixer such as a blender or a colloid mill is used to form an emulsion. The particle size of the capsule can be adjusted by the degree of mixing of the mixer.

Then, in the step of drying the emulsified liquid thus formed, it is possible to cure the capsule medium such as PVA to a satisfactory hardness by possibly eliminating the carrier medium such as water. The liquid crystal material-encapsulated capsule encapsulated in the above process has a substantially spherical shape.

As shown in FIG. 4, the various encapsulated liquid crystals 33, 34, 35 are covered with an encapsulant material 37 such as PVA to form independent liquid crystal regions.
Dispersed and arranged in the liquid crystal region 32. When a driving voltage is applied between the transparent electrodes 4 and 5 using the liquid crystal layer 36, the liquid crystal molecules in the liquid crystal regions 32, 33, 34 and 35 are arranged along the electric field direction. Here, each liquid crystal region 32, 3
Since the ordinary light refractive indices (no) of 3, 34, and 35 are set to be almost the same, the alignment directions of the liquid crystal molecules are aligned, light scattering is eliminated, and a good light transmission state can be obtained.

Further, the fourth liquid crystal region 32, the fifth liquid crystal region 33, the sixth liquid crystal region 34 and the seventh liquid crystal region 35 which compose the liquid crystal layer 36 are all made of a liquid crystal material and are used for each liquid crystal region. It is adjusted so that the dielectric constants of the known liquid crystals are equal. Therefore, the light-scattering type liquid crystal display device of the embodiment of FIG. 4 has almost no voltage drop due to the polymer unlike the conventional polymer dispersed liquid crystal, and it is possible to directly apply the voltage to the liquid crystal layer 11. It can be driven at a low voltage.

Further, when no electric field is applied, the liquid crystal molecules in each of the liquid crystal regions 33 to 35 are in a random state, so that the light transmitted through the liquid crystal layer 11 is scattered in each liquid crystal region and is adjacent to each other. Since liquid crystals with different average refractive indices are used between the liquid crystal regions, light is scattered even at the boundary surface of the liquid crystal regions, and light transmission (reflection of light in the case of a reflective liquid crystal device) can be sufficiently prevented. .

Therefore, in the embodiment of FIG. 4, liquid crystal having a predetermined characteristic is encapsulated in the encapsulant 37 to surely separate each liquid crystal region and disperse it in the fourth liquid crystal region 32.
To provide a light-scattering liquid crystal display device that can disperse liquid crystals having different characteristics without mixing, can be driven at a low voltage, can obtain a high contrast ratio, and has good image quality. You can

[0054]

According to the light-scattering type liquid crystal display device of the first aspect, the liquid crystal layer formed by dispersing and disposing a plurality of independent liquid crystal regions sealed between the transparent substrates is composed of only the liquid crystal regions. Therefore, a large light scattering state can be obtained, and good display quality can be obtained by low voltage driving.

According to the light-scattering type liquid crystal display device of the second aspect, since the ordinary refractive indexes of the liquid crystal regions of the liquid crystal layer are substantially equal to each other, a good light transmission state is obtained and the display quality is improved. Can be made.

According to the light-scattering type liquid crystal display device of the third aspect, since the liquid crystal regions of the liquid crystal layer are composed of liquid crystals having substantially the same dielectric constant, the entire liquid crystal layer can be driven uniformly at a low voltage. You can

According to the light-scattering type liquid crystal display device of the fourth aspect, since at least one of the plurality of liquid crystal regions dispersed in the liquid crystal layer is enclosed in the encapsulating material, the plurality of independent liquid crystal regions are surely separated. In this state, it can be dispersed in another liquid crystal region, and the display quality can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a liquid crystal panel of a light-scattering type liquid crystal display device of this embodiment.

FIG. 2 is a cross-sectional view of a liquid crystal panel showing an alignment state of liquid crystals when an electric field is applied to the liquid crystal layer.

FIG. 3 is a chart showing a comparison result of a driving voltage and a contrast ratio of the present invention and a conventional example.

FIG. 4 is a cross-sectional configuration diagram of a liquid crystal panel of a light scattering type liquid crystal display device according to another embodiment of the present invention.

[Explanation of symbols]

 1 light scattering type liquid crystal display device 2,3 transparent substrate 4,5 transparent electrode 6,7 sealing material 8 first liquid crystal region 9 second liquid crystal region 10 third liquid crystal region 11 liquid crystal layer 21 power supply 22 switch 31 light scattering liquid crystal display Device 32 Fourth liquid crystal region 33 Fifth liquid crystal region 34 Sixth liquid crystal region 35 Seventh liquid crystal region 36 Liquid crystal layer 37 Encapsulation material

Claims (4)

[Claims] 1. A pair of transparent substrates, which are arranged so as to face each other with a predetermined gap therebetween and have transparent electrodes formed on the respective surfaces facing each other, and an average refractive index formed between the pair of transparent substrates. A liquid crystal layer composed of only a plurality of different independent liquid crystal regions, a voltage is applied to the liquid crystal layer, the applied voltage value is controlled, and the alignment state of each liquid crystal molecule in the liquid crystal region is transmitted and light is transmitted. A light-scattering liquid crystal display device, comprising: a display control unit that performs display control by changing between a scattering state and a scattering state. 2. The light-scattering liquid crystal display device according to claim 1, wherein the liquid crystal regions of the liquid crystal layer have substantially the same ordinary light refractive index. 3. The light-scattering liquid crystal display device according to claim 2, wherein each liquid crystal region of the liquid crystal layer is composed of liquid crystal having substantially the same dielectric constant. 4. The light-scattering liquid crystal according to claim 1, wherein at least one of the plurality of liquid crystal regions dispersed in the liquid crystal layer is a liquid crystal region encapsulated by an encapsulant. Display device.