JPH10319404A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bright and excellent whiteness degree and display contrast without increasing a driving voltage by arranging a plurality of vertically oriented areas and horizontally oriented areas at least on one of substrate surfaces and also composing a display layer of a mixture of a nematic liquid crystal material, and a polymer resin. SOLUTION: Oriented films 7a, 8a formed on an upper substrate 1 and a lower substrates 2 are horizontally oriented films, and an oriented film 9b is a vertically oriented film partially formed on the oriented film 8a. Therefore, a surface of the substrate 2 is a multi-oriented area where many areas orienting the liquid crystal molecules 41 vertically and horizontally exit together. Moreover, a liquid crystal layer 40 filled between the upper and lower substrates 1, 2 is composed of a mixture of the liquid crystal molecules 41 and polymer resin 42. And in a voltage impression area 11, the liquid crystal molecules 41 are uniformly oriented approximately in the vertical direction, and incident light 15a is absorbed and display appearance becomes black. On the other hand, in a non-voltage impression area, incident light 16a is scattered and a bright white display appearance is obtainable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display and, more particularly, to a light scattering type reflection type liquid crystal display.

[0002]

2. Description of the Related Art Heretofore, a reflection type liquid crystal display device has been greatly developed and spread as an information transmission medium for a watch, a calculator, a cellular phone, a small portable device, various home electric appliances and the like as a display device operated with a small power. Was. Display mode is also T
Numerous types such as N type (twisted nematic), STN type (super twisted nematic), and ferroelectric type have been invented. However, all of them use a polarizing plate, and in reality, about 60% of the light incident on the liquid crystal display device is absorbed by the polarizing plate, resulting in a dark screen. The display is far from easy to see, for example, a black display on a white background. In particular, in a reflection type color liquid crystal display device, at most one of the light incident on the display device is absorbed by light absorption of both the polarizing plate and the color filter.
Since the display reflects 0% or less of light, the display is very dark, far from bright and vivid color display such as printed matter display.

In order to solve the above-mentioned drawbacks, as a method of realizing a bright display without using a polarizing plate, a conventional example 1 (Japanese Patent Publication No. 3-52843) and a conventional example 2 (Japanese Unexamined Patent Publication No. Sho 63-271) are known.
233) has been proposed and expected. Each of the above-mentioned conventional examples is called a polymer dispersion type (PDLC type) liquid crystal display, and each uses a mixture of a nematic liquid crystal material and a polymer resin as a display layer sandwiched between a pair of substrates. The two refractive indices (n1, n2, (n1>) of a nematic liquid crystal exhibiting
n2)) (herein, n2) and the refractive index (np) of the polymer resin are made to substantially match (n2 ≒ np). When no voltage is applied, the refractive index (approximately n1) of the liquid crystal and the refractive index np of the polymer resin viewed from the display observer direction are made different from each other,
Reflects and refracts incident light at the interface between the liquid crystal and the polymer resin,
As a result, the incident light is scattered. The display appearance in this state looks white (cloudy) to the observer. On the other hand, when a voltage is applied, the direction of the molecular axis of the liquid crystal molecules is changed by the voltage, and the refractive index of the liquid crystal as viewed from a display observer becomes substantially n2, and substantially matches the refractive index np of the polymer resin (n2ｎnp) To do
Most of the incident light is reflected at the interface between the liquid crystal and the polymer resin,
It is transmitted as it is without refraction. Therefore, the appearance of the liquid crystal display at that time becomes transparent. However, if a black body is previously arranged on the lower surface of the liquid crystal display, the display appearance becomes black. As described above, it is possible to switch between white and black for display depending on whether or not a voltage is applied.

[0004] Since the above-mentioned polymer dispersed (PDLC) liquid crystal display does not use a polarizing plate, it can be expected that a reflective display which is essentially brighter than a conventional TN liquid crystal display can be obtained. Further, there is a possibility that a bright reflection type color liquid crystal display device can be realized by arranging color filters of red, blue, and green corresponding to the display pixels.

[0005]

However, there are actually the following problems, and the above-mentioned reflective liquid crystal display device using a polymer dispersed liquid crystal display and a reflective color liquid crystal display device are put into practical use as products. Has not been reached.

The problem is that the backscattering degree is low. Therefore, a sufficient white background cannot be obtained, resulting in a dark display.

The degree of backscattering indicates the ratio of incident light which is scattered by the display layer in the light scattering state and how much of the scattered light returns to the display observer. Therefore, the higher the value, the brighter the reflection-type display image is obtained. It is generally said that the white background of newspaper has a backscattering degree of about 70%.
In a conventional polymer-dispersed light-scattering liquid crystal display, the degree of backscattering is about 20% even at a high level,
This makes the display darker than a TN type liquid crystal display using a polarizing plate. In order to increase the backscattering degree, the distance between the pair of substrates is increased, that is, the thickness of the display layer is increased, or the concentration of the polymer resin in the display layer is increased. As a result, a voltage of about 30 volts or more is required to obtain a bright white display, which leads to an increase in power consumption for display and a drive. Circuit ICs also have the disadvantage of being more expensive.

Further, increasing the concentration of the polymer resin or increasing the thickness of the display layer causes an increase in the light scattering degree of the transmission portion even when a voltage is applied, and therefore, the blackness is reduced. This causes a decrease in the display contrast ratio.

The magnitude of light scattering at the time of black display is as follows.
It can be easily understood that it is proportional to the thickness of the display layer and the concentration of the polymer resin.

The present invention is intended to solve the above-mentioned problems in the conventional polymer-dispersion type (PDLC type) liquid crystal display device, in order to obtain a high light-scattering property (bright white background), a thickness of a display layer,
It is necessary to increase the concentration of the polymer resin, so that a high driving voltage is required, power consumption is increased, and there is a problem as a display device of a portable device.

[0011] In addition, even during black display, the degree of scattering increases, so that the display contrast ratio decreases. Reflective black-and-white liquid crystal that is brighter and has good whiteness and display contrast ratio without increasing the thickness of the display layer or the concentration of the polymer resin, and thus without increasing the driving voltage. It is an object to provide a display device or a reflective color liquid crystal display device.

[0012]

According to the first aspect of the present invention, in a liquid crystal display device having a display layer sandwiched between a pair of substrates, at least one of the substrates has one of the substrates. A plurality of vertical alignment regions and a plurality of horizontal alignment regions are respectively arranged on the surface on the display layer side, and the display layer is made of at least a mixture of a nematic liquid crystal material and a polymer resin. A display device.

According to a second aspect of the present invention, there is provided the liquid crystal display device according to the first aspect, wherein a color filter layer is disposed on one of the pair of substrates. .

[0014]

Next, embodiments of the present invention will be described with reference to the accompanying drawings.

(First Embodiment) FIGS. 1A and 1B
1 is a cross-sectional view illustrating a basic structure and operation of a liquid crystal display device according to the present invention. Reference numerals 1 and 2 denote a pair of substrates each including an upper substrate and a lower substrate. Reference numerals 3 and 4 denote transparent electrodes provided on the upper and lower substrates 1 and 2, respectively, which are made of indium oxide or tin oxide or a mixture thereof. 7a and 8a are alignment films formed on the upper substrate 1 and the lower substrate 2, respectively.
A horizontal alignment film capable of aligning liquid crystal molecules in parallel to the surfaces of the substrates 1 and 2. Polyimide, polyvinyl alcohol and other various resins are used as the material. Polyimide resins having excellent heat resistance and chemical stability are used. preferable. Reference numeral 9b denotes an alignment film partially formed on the horizontal alignment film 8a, which is a vertical alignment film having an ability to align liquid crystal molecules perpendicularly to the surface of the substrate 2. Therefore, the surface of the substrate 2 is composed of a plurality of alignment regions in which a number of regions for vertically aligning liquid crystal molecules and a region for horizontally aligning liquid crystal molecules are mixed. Reference numeral 40 denotes a display layer inserted between the upper and lower substrates 1 and 2, and the liquid crystal molecules 4
1 and a polymer resin 42. The method of forming the display layer 40 may be considered to be the same as the method shown in the conventional example 2, in which a mixture of a low molecular weight photocurable resin and the above nematic liquid crystal material is inserted between the upper and lower substrates 1 and 2. After that, when light is irradiated with ultraviolet light or the like, the low-molecular-weight photocurable resin is polymerized, polymerized, separated and precipitated in a liquid crystal material.

As the liquid crystal molecules 41, a nematic liquid crystal material having a positive dielectric anisotropy is used. The nematic liquid crystal molecules 41 usually have an elongated rod-like molecular shape,
In the figure, the liquid crystal molecules are represented by elongated lines, and the length direction of this line indicates the major axis direction of the liquid crystal molecules. Liquid crystal molecules usually have birefringence. For example, in BDH-BL007, a liquid crystal material manufactured by Merck, the refractive index (n1) in one direction is 1.82, the refractive index (n2) in the other direction is 1.53, and the birefringence (△ n) becomes 0.29.

Here, similarly to the conventional example 2, the refractive index (np) of the separated and precipitated polymer resin 42 and the refractive index (n2) of one of the liquid crystal molecules 41 exhibiting birefringence are obtained. Are selected in advance so that (n2 略 np, (n1> n2)) substantially agrees with each other, the other refractive index (n1) of the liquid crystal molecules 41 and the refractive index of the polymer resin 42 ( np), the incident light 13a is refracted and reflected at the interface between the liquid crystal molecules 41 and the polymer resin 42, and is scattered as a result. The light is absorbed by the light absorber (here, a black body), but the rest is returned to the front surface of the display device as backscattered light 13c. Therefore, the display appearance at this time is white (cloudy), but the brightness is proportional to the magnitude of the backscattered light.

Further, in the present embodiment, FIG.
As shown in (a), the liquid crystal molecules 41 are vertically aligned on the vertical alignment region 9b, and are horizontally aligned on the horizontal alignment regions 7a and 8a. Therefore, as shown in FIG. 1A, a liquid crystal region in which the orientation direction is sharply changed exists in the intermediate region. Therefore, there are many regions in the liquid crystal portion having different directions of liquid crystal molecules, which means that there are many interfaces having different refractive indexes, and the incident light 14 as shown in FIG.
a is refracted and reflected, and is scattered as a result, and a part of the scattered light is forward scattered light 14b and reaches the lower light absorber (here, a black body) 5 and is absorbed there, but the rest is back scattered light. 14c is returned to the front of the liquid crystal display device. Therefore, the backscattered light can be increased without increasing the concentration of the polymer resin and without increasing the thickness of the display layer (1).
3c + 14c), and a brighter white display appearance can be obtained.

Here, in order to obtain a brighter display appearance, the smaller the area of each of the vertical alignment region 9b and the horizontal alignment region 8a, the smaller the density of the refractive index boundary surface existing in the display layer 40. Clearly, the backscattered light 14c increases and a bright white appearance is obtained, but in consideration of manufacturability, the diameter of each alignment region is 1 μm to 100 μm.
m is desirable.

Next, the display operation will be described with reference to FIG. The same reference numerals are used for the same reference numerals in the drawings, and the description of each member is omitted. Reference numeral 11 denotes a voltage application region (pixel) corresponding to one pixel. In this region 11, since the liquid crystal molecules 41 have a positive dielectric anisotropy as described above, the upper and lower substrates 1, 2 Are arranged almost uniformly in the vertical direction. Therefore, in the voltage application region 11, the refractive index of the liquid crystal portion becomes n2 when viewed from the front of the display, and the boundary surface having a different refractive index almost disappears in the liquid crystal portion. Further, since the refractive index of the liquid crystal portion is substantially equal to the refractive index (np) of the polymer resin 42 (n2pnp), the incident light 15a is transmitted through the display layer 40 without being scattered. It reaches the absorber 5 and is absorbed there. Therefore, the display appearance of the voltage application area 11 is black.

On the other hand, in the no-voltage application region (pixel) 12,
As described above, the incident light 16a is scattered at the refractive index boundary surface in the liquid crystal portion and at the boundary surface between the liquid crystal and the polymer resin 42, and a part thereof becomes the forward scattered light 16b and becomes a light absorber. 5, but the rest is backscattered light 16c and 1
Since it is 6d and returned to the display front, a white display appearance brighter than the conventional example can be obtained. .

As described above, in the present embodiment, it is necessary to increase the display driving voltage without increasing the concentration of the polymer resin 42 or the thickness of the display layer 40. Thus, a reflective liquid crystal display device having a brighter white appearance can be realized. Further, since the concentration of the polymer resin 42 and the thickness of the display layer are not increased, light scattering in the voltage application region (pixel) 11 is not increased, and a black appearance as in the related art is obtained. Can be improved. From another point of view, even if the concentration of the polymer resin 42 is reduced, a white appearance similar to that of the related art can be obtained, so that it is easily understood that a display with a higher contrast ratio can be realized.

As described above, according to the present embodiment, the display contrast ratio is high without increasing the display drive voltage,
A liquid crystal display device having a bright display appearance can be provided, and a low-power, easy-to-read portable electronic device using the liquid crystal display device can be realized.

Next, a multiple alignment processing method in which a large number of the vertical alignment regions 9b and the horizontal alignment regions 8a are mixed will be described with reference to FIG.
This will be described with reference to (a) and (b). 2 is a lower substrate and 4 is a transparent electrode. As described above, the same reference numerals are used for members common to those shown in FIG. First, FIG.
As shown in (a), the horizontal alignment material is roll-coated,
The lower substrate 2 / transparent electrode 4 is uniformly coated on the surface of the lower substrate 2 / transparent electrode 4 by a spin coating method, an offset printing method or the like, and a heat treatment is performed to obtain a uniform horizontal alignment film 8a. This step is common to the current liquid crystal display manufacturing steps. Next, as shown in FIG. 2B, the vertical alignment material is temporarily transferred from the plate patterned by the offset printing method onto the roller 50, and is further retransferred onto the surface on the lower substrate 2 side, and heat treatment is performed. If it is added, a patterned uniform vertical alignment film 9b is obtained. As the vertical alignment material, for example, JALS-204 manufactured by Nippon Synthetic Rubber Co., Ltd.
There is. The offset printing method described here is suitable as a method for printing a resin material in a high-definition pattern.
It can handle up to m diameter pattern printing. Photolithography is suitable for higher definition patterning.
Although this method is not shown, it is the same as described above until a uniform horizontal alignment film is formed. After that, a vertical alignment film is uniformly printed and baked thereon, and then a photoresist is further printed and dried thereon, and a photomask having a desired pattern is placed thereon and exposed and developed. By dissolving and removing the vertical alignment film in the portion where no
A multiple alignment film having a finer pattern can be formed.

Since a plurality of alignment films having a desired pattern can be formed by the above-described method, the light scattering type liquid crystal display device capable of freely controlling the light scattering degree can be realized.

In the above-described method, the horizontal alignment films 7a and 8a are formed in order to obtain the horizontal alignment more reliably. Usually, however, the glass surface has the property of aligning liquid crystal molecules horizontally. Therefore, when glass is used for the upper and lower substrates 1 and 2, the intended purpose can be achieved even if the horizontal alignment films 7a and 8a are omitted.

Further, in FIG. 1, a plurality of alignment processes in which a plurality of horizontal and vertical alignment regions are mixed are performed only on the lower substrate 2. However, if the processes are performed on both the upper, lower, and both substrates, This is preferable because the density of the boundary surface of the refractive index in the display layer 40 increases and the white display appearance becomes bright.

(Second Embodiment) FIG. 3 is a sectional view of a reflective type color liquid crystal display device according to a second embodiment of the present invention. In the present embodiment, the light scattering type liquid crystal display device shown in the above-described first embodiment is basically used, but here, the lowermost surface of the liquid crystal display device is used in the first embodiment. A specular reflector 19 is used in place of the light absorber described above. In addition, red 20a and green 2
The present invention provides a reflective color liquid crystal display device as a whole by adding each color filter layer of Ob and blue 20c. In FIG. 3, the same reference numerals are used for members common to those in the previous drawings, and a description thereof will not be repeated.

Numerals 7a and 7b denote a horizontal alignment film and a vertical alignment film, respectively. On the inner surface of the upper substrate 1, a plurality of horizontal alignment portions and vertical alignment portions are subjected to a plurality of alignment treatments as shown in FIG. ing. Although the horizontal alignment film 8a is formed on the lower substrate 2 side, the effect of the present invention can be achieved by using a vertical alignment film or a plurality of horizontal / vertical alignment films instead. The display layer 40 is also made of a mixture of a nematic liquid crystal 41 having high birefringence and a positive dielectric anisotropy, and a polymer resin 42, similarly to the first embodiment. Accordingly, the behavior of the display layer 40 in the voltage application region (pixel) 11 and the voltage non-application region (pixel) 12 is the same as described in the first embodiment, and the voltage non-application region (pixel) 1
Light 17a incident on the blue color filter layer 2
0c, the light becomes blue light and reaches the display layer 40. The light is scattered at the boundary between the refractive index inside the liquid crystal and the boundary between the liquid crystal 41 and the polymer resin 42. 19, the light is reflected there, passes through the display layer 40 again, further passes through the blue color filter layer 20c, becomes blue scattered reflected light 17b, and enters the display observer's eyes. Similarly, the backscattered light 17c generated at the boundary between the refractive index inside the liquid crystal and the boundary between the liquid crystal 41 and the polymer resin 42 again passes through the blue color filter layer 20c to become blue light, and becomes a blue light for the display observer. Get into my eyes. Therefore, in the present embodiment, as described above, the specular reflector 19 is used on the lowermost surface, and forward scattered light is also reflected and effectively returned to the display front side. Become. In particular, the color filter layer (20a,
20b, 20c), 60-70% of the incident light is absorbed by the color filter layer, so that it is possible to use the remaining incident light effectively to realize a bright reflective liquid crystal display device. However, as described above, in the present embodiment, the use of the specular reflector 19 makes it possible to effectively use forward scattered light as reflected light.
More preferred. In this way, even when no voltage is applied to other pixels, a display appearance can be obtained by bright scattered light of the color of the cutter filter corresponding to each pixel.

On the other hand, the light 18a incident on the voltage application region (pixel) 11 passes through the green color filter layer 20b to become green light and enters the display layer 40. Here, as described above, the inside of the liquid crystal and the Since there is almost no interface having a different refractive index at the interface between the liquid crystal and the polymer resin, the light reaches the specular reflector 19 as it is without being scattered by light, and is specularly reflected there and directly reaches the eyes of the display observer ( 18b).
At this time, the display observer sees an object in the incident direction of the incident light 18a. If the object is black, the display appearance of the voltage application region (pixel) 11 is black.
Thus, in the present embodiment, the light scattering property is high and the light reflection is high without increasing the thickness of the display layer 40, without increasing the concentration of the polymer resin 42, and without increasing the driving voltage. Type color liquid crystal display device can be realized.
Further, in the present embodiment, a brighter reflective color liquid crystal display device using the specular reflector 19 is provided. Further, even if the light absorbing plate 5 used in the first embodiment is used instead of the specular reflector 19 used in the present embodiment, the display contrast ratio is high and bright with low voltage and low power consumption, which are the effects of the present invention. Obviously, a reflection type color liquid crystal display device can be obtained. These all depend on the above-described liquid crystal display system in which the light scattering property is improved without increasing the voltage by the multiple alignment treatment according to the present invention.

In the first embodiment, if the specular reflector used in the second embodiment is used instead of the light absorber 5, a reflective liquid crystal display device having a brighter white background. Needless to say, However, in this case, care must be taken to make the color of the object reflected in the specular reflection direction of the specular reflector closer to black as viewed from the display observer.

[0032]

As described above, according to the present invention, the light scattering property can be improved without increasing the display driving voltage and power consumption as compared with the prior art polymer dispersion type (PDLC type) liquid crystal display device. A reflective liquid crystal display device that is bright and has a display appearance with a high display contrast ratio can be realized. Further, by combining with a color filter, a bright reflective color liquid crystal display device can be obtained, and a portable electronic device having a low-power and easy-to-read display can be realized using the same.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of a manufacturing process of a multiple orientation process used in the present invention.

FIG. 3 is a cross-sectional view of a liquid crystal display device according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Upper substrate 2 ... Lower substrate 3, 4 ... Transparent electrode 7a, 8a ... Horizontal alignment film 9b ... Vertical alignment film 5 ... Light absorption plate 40 ... Display layer 41 ... Nematic liquid crystal molecules 42 ... Polymer resin 13a, 14a, 15a, 16a ... Incident light

Claims (2)

[Claims] 1. A liquid crystal display device having a display layer sandwiched between a pair of substrates, wherein at least one of the substrates has a vertical alignment region and a horizontal alignment region on a surface on the display layer side. And a display layer is composed of at least a mixture of a nematic liquid crystal material and a polymer resin. 2. The liquid crystal display device according to claim 1, wherein a color filter layer is provided on one of the pair of substrates.