JP2806689B2 - Light scattering type liquid crystal display - Google Patents

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, and more particularly to a light scattering type liquid crystal display device in which a liquid crystal material is held in a polymer compound having a network structure.

[0002]

2. Description of the Related Art A conventional light scattering type liquid crystal display device is shown in FIG.
As shown in FIG. 12 and FIG.
Polymer-dispersed liquid crystal layer 13 composed of liquid crystal 120 and polymer compound 122 between glass substrates 111 and 112 provided with
0 is sandwiched. That is, as shown in FIG. 11, two glass substrates (to be liquid crystal panels) 111 and 112 on which transparent electrode lines 113 and 114 are formed are prepared, and these glass substrates 111 and 112 are connected to the transparent electrode lines 113 and 114.
Attach them with an appropriate gap of about 10 μm so that 114 intersect. Next, a mixture of a UV-polymerizable high molecular compound precursor and a liquid crystal material is filled and sealed in the gap, and subsequently, the panel is irradiated with UV light. As a result, as shown in FIG. 12, the polymer compound precursor is polymerized into the polymer compound 122, and phase separation occurs with the liquid crystal 120 (the polymer dispersed liquid crystal layer 130 is formed). That is, the liquid crystal molecules 121 are
Dispersed in 22 network structures. At this time, the liquid crystal molecules 12
Of 1, the liquid crystal molecules 121 in the vicinity of the interface with the polymer compound (carrier) 122 are oriented along the interface, and thus the orientation direction of the liquid crystal molecules 121 in the panel is random as a whole.

In this state (in a state where no voltage is applied), when light is incident on the panel, the incident light is scattered (scattered state). This is because the orientation of the liquid crystal molecules 121 is random, so that the birefringence of the light incident on the liquid crystal 120 is not uniform, and the refractive index of the liquid crystal 120 at the interface between the liquid crystal 120 and the polymer compound 122 is high. It is said that refraction occurs when the refractive index is an average of the extraordinary refractive index and the ordinary light refractive index. Next, the transparent electrode lines 113, 1
When a voltage is applied to the liquid crystal layer 14 to apply an electric field to the polymer dispersed liquid crystal layer 130, as shown in FIG.
Are oriented in the direction of the electric field, the light scattering effect described above is reduced, and the liquid crystal layer 130 becomes transparent (transmission state). In the light scattering type liquid crystal display device, image display is performed by controlling the scattering state and the transmission state depending on whether or not a voltage is applied to the electrode layers 113 and 114.

Actually, as shown in FIG. 14, the transmission intensity of the light transmitted through the liquid crystal panel is such that a voltage is applied to the liquid crystal panel when the incident angle (the angle with respect to the optical axis of the light incident on the liquid crystal panel) is around 0 °. The transmission intensity when a voltage is applied to the liquid crystal panel (curve b) is higher than the transmission intensity when no voltage is applied (curve a). Therefore, an image can be displayed using the difference in the transmission intensity.

[0005]

By the way, the greater the difference in light transmission intensity between the scattering state and the transmission state, the greater the contrast ratio and the better the display characteristics. However, in the above-mentioned conventional light scattering type liquid crystal display device, in the transmission intensity (curve a) in the scattering state shown in FIG. this is,
This indicates that, of the light incident on the panel, a component that travels straight in the panel is large (in the case where the light is completely scattered, the incident light becomes の of the maximum value of the transmission intensity corresponding to an incident angle of 0 °). It becomes a gentle curve with an angle of 60 °.) For this reason, the conventional light scattering type liquid crystal display device has a problem that contrast is not good.

Here, in order to improve the contrast property which enhances the scattering property, means for increasing the thickness of the polymer-dispersed liquid crystal layer 130 can be considered. However, as the thickness of the liquid crystal layer 130 increases, the driving voltage must be increased in order to obtain a sufficient transmittance, and the response time of the liquid crystal 120 also increases. Therefore, there is a limit to increasing the thickness of the liquid crystal layer 130. Rather, the thickness of the liquid crystal layer 130 must be reduced in order to reduce the drive voltage and increase the response speed.

An object of the present invention is to provide a light scattering type liquid crystal display device which can improve the contrast between the scattering state and the transmission state without increasing the driving voltage or increasing the response time. .

[0008]

According to a first aspect of the present invention, there is provided a light-scattering type liquid crystal display device, wherein electrode layers are provided on inner surfaces of two opposing substrates, respectively. When a polymer-dispersed liquid crystal layer formed by dispersing a liquid crystal in a gap between network-like polymer compounds is sandwiched, and no voltage is applied to the electrode layer, the polymer-dispersed liquid crystal layer is oriented in the orientation direction of liquid crystal molecules. Is random and scatters incident light, while when a voltage is applied to the electrode layer, the polymer-dispersed liquid crystal layer is aligned in a liquid crystal molecule alignment direction so that incident light is transmitted. In the liquid crystal display device, between the electrode layer and the polymer-dispersed liquid crystal layer, the liquid crystal has a refractive index substantially equal to the ordinary light refractive index of the liquid crystal, and has an uneven surface on the polymer-dispersed liquid crystal layer side. Comprising an intermediate layer formed with
The two electrode layers each form a stripe pattern, intersect each other to form a pixel at each intersection, and on the surface of the intermediate layer on the polymer dispersed liquid crystal layer side, each pixel for each pixel. It is characterized in that one concave portion of a corresponding size is provided.

According to a second aspect of the present invention, there is provided a light scattering type liquid crystal display device according to the first aspect.
The intermediate layer is made of the same material as the polymer compound.

According to a third aspect of the present invention, there is provided the light scattering type liquid crystal display device according to the first or second aspect, wherein one of the two substrates is provided with each of the pixels. A thin film transistor.

[0011]

In the light scattering type liquid crystal display device according to the first aspect, when no voltage is applied, the orientation of the liquid crystal molecules is random, so that the refractive index of the liquid crystal is larger than the ordinary ray refractive index. That is, the refractive index of the liquid crystal is larger than the refractive index of the intermediate layer (substantially equal to the ordinary light refractive index of the liquid crystal). Therefore,
Incident light is refracted at the interface between the liquid crystal and the intermediate layer. At this time, since the interface between the liquid crystal and the intermediate layer has irregularities, the incident light is largely scattered, and the straight component of the light is reduced as compared with the related art. On the other hand, when a voltage is applied, the liquid crystal molecules are aligned in the direction of the electric field, so that the refractive index of the liquid crystal is equal to the ordinary light refractive index. That is, the refractive index of the liquid crystal is substantially equal to the refractive index of the intermediate layer. Therefore, no refraction or scattering occurs at the interface between the liquid crystal and the intermediate layer, and the incident light travels straight as it is in the prior art. As a result, the difference in the light transmission intensity between the voltage non-applied state (scattering state) and the voltage applied state (transmission state) is larger than in the related art, and the contrast is improved. The drive voltage increases by the amount of the voltage applied to the liquid crystal due to the voltage drop in the intermediate layer, but falls within the allowable range. Note that the response time does not increase because the thickness of the liquid crystal layer (polymer-dispersed liquid crystal layer) is not increased.

In addition, the two electrode layers form a stripe pattern, and intersect each other to form a pixel at each intersection, and the intermediate layer has a surface on the polymer dispersion type liquid crystal layer side facing the pixel. Since each pixel has one concave portion of a corresponding size, the difference in light transmission intensity between the scattering state and the transmission state in each pixel increases. As a result, the contrast is improved.

In the light scattering type liquid crystal display device according to the second aspect, the intermediate layer is made of the same material as the polymer compound.
The intermediate layer and the polymer-dispersed liquid crystal layer adhere well and there is no occurrence of peeling.

In the light scattering type liquid crystal display device according to the third aspect, since a thin film transistor is provided for each pixel on one of the two substrates, active matrix driving can be performed with a good contrast.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the light scattering type liquid crystal display device of the present invention will be described in detail with reference to embodiments.

FIG. 1 shows a cross section of a light scattering type liquid crystal display device on which the present invention is based. This light-scattering type liquid crystal display device has two glass substrates 11, 12,
12, transparent electrode wires (electrode layers) 13 and 14 provided on the inner surface
And a polymer-dispersed liquid crystal layer 30 held between the transparent electrode lines 13 and 14. Further, between the one substrate 11 and the polymer dispersed liquid crystal layer 30, a refractive index substantially equal to the ordinary light refractive index of the liquid crystal 20 in the polymer dispersed liquid crystal layer 30, and the polymer dispersed liquid crystal An intermediate layer 15 having irregularities formed on a surface 15a on the layer 30 side is provided.

The light scattering type liquid crystal display device is manufactured as follows.

First, an indium tin oxide (ITO) film is formed on each of the two glass substrates 11 and 12 by a sputtering method, and is striped using a photolithographic method in the same manner as that shown in FIG. The transparent electrode lines 13 and 14 are formed by patterning.

Next, as shown in FIG.
Acrylic resin dissolved in a solvent (refractive index: 1.5)
Is applied using a spin coater and heated to form a film, thereby forming the intermediate layer 15. At this time, the thickness of the intermediate layer 15 is 2 μm.
And Then, on top of this, a resist for patterning
(Not shown), mask exposure, development, intermediate layer surface 1
Perform etching and resist stripping for 5a,
A large number of recesses (resulting in unevenness) 16 are formed on the intermediate layer surface 15a. At this time, when the intermediate layer surface 15a is viewed from above, the pattern layout is as shown in FIG. 2 (FIG. 3 corresponds to a section taken along the line II-III 'in FIG. 2. In FIG. Recess 1 for simplicity
6, ... indicate only one part. ). In this example, four to five sets of concavities and convexities were formed within one width (and thus one pixel) of the stripe-shaped transparent electrode line 13.

Next, as shown in FIG.
The electrodes 1 and 12 are arranged with a gap of about 10 microns (about the same as the conventional one) so that the transparent electrodes 13 and 14 are inside and cross each other. Between these two substrates 11 and 12,
After spraying a large number of plastic beads having a diameter of 15 μm, the substrates 11 and 12 are bonded with a sealing resin. Subsequently, the photopolymerizable acrylic polymer compound 22 was injected from the injection port.
A mixture of a monomer or oligomer (refractive index: 1.5) and the liquid crystal material 20 (ordinary refractive index: 1.5) is injected. After that, the injected mixture is irradiated with ultraviolet rays to polymerize the monomer or oligomer, and the polymer compound phase 22 and the liquid crystal phase 20 are structurally phase-separated. As a result, the polymer compound 22 has a network structure, and the liquid crystal 20 is dispersed between the networks of the polymer compound 22 (production completed).

In this light scattering type liquid crystal display device, as shown by a curve a in FIG. 4, when no voltage is applied (scattering state),
The intensity of the straight component of the transmitted light (in the vicinity of the incident angle of 0 °) was reduced as compared with the conventional case. Thereby, the contrast between the scattering state and the transmission state could be improved.

The reason is considered as follows. As shown in FIG. 5, when no voltage is applied,
The light L incident with 0 is refracted when passing through the interface 15a between the polymer-dispersed liquid crystal 20 and the intermediate layer 15 in addition to being scattered in the liquid crystal 20. This means that when no voltage is applied,
This is because the refractive index of the liquid crystal 20 and the refractive index of the intermediate layer 15 are different. That is, when no voltage is applied, the orientation direction of the liquid crystal molecules 21 is random, so that the refractive index of the liquid crystal 20 becomes larger than the ordinary light refractive index (equal to the refractive index of the intermediate layer 15). Therefore, the incident light L that has reached the interface 15a between the liquid crystal 20 and the intermediate layer 15 does not go straight but is refracted. At this time, since the unevenness is formed at the interface 15a between the liquid crystal 20 and the intermediate layer 15, the incident light is scattered more than in the conventional case, and the straight component of the transmitted light is reduced. on the other hand,
In the voltage applied state (transmission state), as shown in FIG. 6, the liquid crystal molecules 21 are oriented in the direction of the electric field, so that the refractive index of the liquid crystal 20 becomes the ordinary light refractive index and becomes equal to the refractive index of the intermediate layer 15. Therefore, the interface 15a between the liquid crystal 20 and the intermediate layer 15
In this case, refraction and scattering do not occur, and the intensity of the transmitted light is at the same level as in the related art, as shown by the curve b in FIG. In this way, the difference in light transmission intensity between the scattering state and the transmission state is enlarged, and the contrast is improved. The drive voltage increases by the amount of the voltage applied to the liquid crystal due to the voltage drop in the intermediate layer, but falls within the allowable range.
Since the thickness of the polymer-dispersed liquid crystal layer 30 was not increased, the response time did not increase.

FIGS. 7 and 8 show a cross section of a main part of the light scattering type liquid crystal display device according to one embodiment of the present invention (a portion where an intermediate layer 85 is provided on a substrate 81 on one side). 7 shows a plane, and FIG. 8 shows a cross section taken along line VIII-VIII 'in FIG.

This light scattering type liquid crystal display device has an intermediate layer 85.
A concave portion 8 having a dimension corresponding to one width of the stripe-shaped transparent electrode line 83 (accordingly, one pixel) is formed on the surface 85a of the
6 are provided. That is, similar to the examples of FIGS.
A transparent electrode wire (ITO electrode) 83 is formed on a glass substrate 81, and an acrylic resin to be an intermediate layer 85 is formed thereon.
(Film thickness: 2 μm). Subsequently, a recess 86 is formed in the surface 85a of the intermediate layer 85 by performing photography and etching. At this time, by making the phenomenon of the resist longer than the appropriate time, the thickness of the resist around the pattern of each concave portion 86 is reduced. When the intermediate layer 85 is etched in this state, the periphery of the pattern is also slightly etched, and a concave pattern as shown in FIG. 8 is obtained. Thereafter, as in the examples of FIGS. 1 to 6, the glass substrate is bonded to another glass substrate with an ITO electrode, and a polymer dispersed liquid crystal layer is formed in the gap.

In this embodiment, the contrast between the scattering state and the transmission state can be further improved, and good characteristics can be obtained.

FIG. 10 shows a cross section of a light scattering type liquid crystal display device of another embodiment.

This light scattering type liquid crystal display device has a thin film transistor as a switching element for each pixel. First, on one surface of a glass substrate 101, a thin film transistor 109 and a pixel electrode (ITO electrode) 106 are formed in an array by a known method, and an acrylic resin film is patterned thereon, similarly to the above embodiment, to form an intermediate layer. 108 is formed. At this time, as shown in FIG. 9, one recess 91 having a size corresponding to each pixel is provided on the surface 108a of the intermediate layer 108 for each pixel 106 (FIG. 10 shows IX-IX in FIG. 9). 'Line section is shown.) 94 is a gate electrode line. Thereafter, as shown in FIG. 10, the substrate is bonded to a counter substrate 102 provided on an ITO electrode 103, and a polymer dispersion comprising a polymer compound 104 and a liquid crystal 105 is provided in the gap between the substrates 101 and 102, as in the above embodiment. Type liquid crystal layer 90
To form Reference numeral 107 denotes a passivation film made of silicon nitride.

This liquid crystal panel was arranged in a normal projection optical system. At this time, light was incident from the substrate side where the intermediate layer 108 was not formed, that is, from the counter substrate 102 side. In this case, the projected image on the screen is bright,
As a result, good characteristics with high contrast were obtained as compared with the case where a conventional liquid crystal panel was used.

Incidentally, the intermediate layer 108 may be formed on the counter substrate 102 side. In this case, light is incident on the thin film transistor substrate 101 side.

In each of the above examples, the intermediate layers 15, 85, and 108 are all formed of an acrylic resin, but the present invention is not limited to this. The material for the intermediate layer may be any material as long as it is substantially equal to the ordinary light refractive index of the liquid crystal to be used. For example, polyimide may be used.

[0031]

As is apparent from the above description, the light scattering type liquid crystal display device according to the first aspect has a refractive index substantially equal to the ordinary ray refractive index of the liquid crystal between the electrode layer and the polymer dispersed type liquid crystal layer. Holding
In addition, since an intermediate layer having irregularities formed on the surface on the polymer dispersed liquid crystal layer side is provided, no voltage is applied (scattering state).
In this case, the refractive index of the liquid crystal becomes larger than the refractive index of the intermediate layer, and the incident light can be scattered at the uneven interface between the polymer-dispersed liquid crystal layer and the intermediate layer as compared with the conventional case. Thus, the straight component of light can be reduced. On the other hand, in the voltage applied state (transmission state), the refractive index of the liquid crystal becomes equal to the refractive index of the intermediate layer, and no refraction or scattering occurs at the interface,
As in the conventional case, the incident light can travel straight. Therefore, the difference in light transmission intensity between the scattering state and the transmission state can be increased as compared with the related art, and the contrast can be improved. As for the driving voltage, the voltage applied to the liquid crystal decreases due to the voltage drop in the intermediate layer.
Enter the acceptable range. In addition, since the thickness of the liquid crystal layer is not increased, it is possible to prevent the response time from being lengthened.

In addition, the two electrode layers form a stripe pattern, and cross each other to form a pixel at each crossing point. Each pixel has one recess of the corresponding size.
As a result, the difference in light transmission intensity between the scattering state and the transmission state in each pixel increases. As a result,
The contrast can be improved.

In the light scattering type liquid crystal display device according to the second aspect, the intermediate layer is made of the same material as the polymer compound.
The intermediate layer and the polymer-dispersed liquid crystal layer are in good contact with each other, and the occurrence of peeling can be avoided.

In the light scattering type liquid crystal display device according to the third aspect, since the thin film transistor is provided for each of the pixels on one of the two substrates, active matrix driving can be performed with a good contrast.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a light scattering type liquid crystal display device on which the present invention is based.

FIG. 2 is a diagram showing a surface of an intermediate layer provided on one substrate of the light scattering type liquid crystal display device.

FIG. 3 is a view showing a cross section taken along line III-III ′ in FIG. 2;

FIG. 4 is a diagram showing a light transmission intensity in a scattering state and a transmission state of the light scattering type liquid crystal display device.

FIG. 5 is a diagram illustrating an operation of the light scattering type liquid crystal display device in a scattering state.

FIG. 6 is a diagram illustrating an operation of the light scattering type liquid crystal display device in a transmission state.

FIG. 7 is a diagram showing a surface of an intermediate layer provided on one substrate of the light scattering type liquid crystal display device according to one embodiment of the present invention.

FIG. 8 is a view showing a cross section taken along line VIII-VIII ′ in FIG. 7;

FIG. 9 is a diagram showing a surface of an intermediate layer provided on one substrate of a light scattering type liquid crystal display device according to another embodiment of the present invention.

FIG. 10 is a diagram showing a cross-sectional structure of the light scattering type liquid crystal display device.

FIG. 11 shows a configuration 2 of the conventional light scattering type liquid crystal display device.
FIG. 3 is a diagram illustrating a single substrate.

FIG. 12 is a diagram showing a cross section (scattering state) of a conventional light scattering type liquid crystal display device.

FIG. 13 is a diagram showing a cross section (transmission state) of a conventional light scattering type liquid crystal display device.

FIG. 14 shows a scattering state of a conventional light scattering type liquid crystal display device,
FIG. 3 is a diagram illustrating transmission intensity of light in a transmission state.

[Explanation of symbols]

 11, 12, 81, 101, 102 Glass substrate 13, 14 Transparent electrode wire 15, 85, 108 Intermediate layer 15a, 85a, 108a Intermediate layer surface 16, 86, 91 Concave 20, 105 Liquid crystal 21 Liquid crystal molecule 22, 104 Polymer Compound 30,90 Polymer dispersed liquid crystal layer 103,106 ITO electrode 107 Passivation film 109 Thin film transistor

Claims (3)

(57) [Claims] 1. An electrode layer is provided on each of inner surfaces of two opposing substrates, and a polymer-dispersed liquid crystal layer formed by dispersing liquid crystal in a gap between mesh-like polymer compounds is sandwiched between the electrode layers. When a voltage is not applied to the electrode layer, the polymer-dispersed liquid crystal layer scatters incident light while the orientation direction of liquid crystal molecules is random, and when a voltage is applied to the electrode layer, the polymer is dispersed. In a light-scattering type liquid crystal display device in which the dispersion type liquid crystal layer is arranged such that the orientation direction of liquid crystal molecules is aligned and the incident light is transmitted, an ordinary ray of the liquid crystal is provided between the electrode layer and the polymer dispersion type liquid crystal layer. It has an index of refraction substantially equal to the index of refraction, and comprises an intermediate layer in which irregularities are formed on the surface on the side of the polymer-dispersed liquid crystal layer. The two electrode layers each form a stripe pattern and intersect each other. Pixels are formed at each intersection, and A light-scattering type liquid crystal display device, characterized in that one concave portion having a size corresponding to each pixel is provided for each of the pixels on a surface of the intermediate layer on the side of the polymer-dispersed liquid crystal layer. 2. The light-scattering type liquid crystal display device according to claim 1, wherein the intermediate layer is made of the same material as the polymer compound. 3. The light-scattering type liquid crystal display device according to claim 1, wherein a thin film transistor is provided for each of the pixels on one of the two substrates.