JPS6032167B2 - LCD color display device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a liquid crystal color display device.

Conventionally, as a color display method using nematic liquid crystal,
ECB (Electrically Contr.
(Or, D
AP(De rmationofvenjcaINig
A system called phases) is known.

In the case of a liquid crystal with positive dielectric anisotropy, the liquid crystal is sandwiched between two substrates that have been treated so that the long axis direction of the molecules of the liquid crystal is aligned horizontally to the substrate surface, and the dielectric anisotropy is negative. In the case of a liquid crystal, the liquid crystal is sandwiched between two substrates that have been treated so that the long axis direction of the liquid crystal molecules is aligned perpendicular to the substrate surface, and when a voltage of a certain strength or higher is applied, the liquid crystal molecules This is a method of displaying colors using two polarizers due to the phenomenon that the rear refractive index of the liquid crystal layer changes as the liquid crystal layer tilts toward the opposite direction. However, in this ECB (DAP) method, the voltage required to tilt the molecules with respect to the substrate surface from the initial alignment state (the threshold voltage) is high, and therefore the operating voltage is high.

Furthermore, the voltage range in which various colors such as red, blue, and green can be displayed is very narrow, and several colors change between the function voltage and about IV, making color selection very difficult. In other words, it is extremely difficult to control the hue with voltage, and for this reason, the stability and precision of the power supply are particularly required. Because of these shortcomings,
The ECB system has not been put to practical use as an effective liquid crystal color display device. The present invention has been made in view of the above points, and provides a liquid crystal color display device with a low operating voltage (skin s) and a wide voltage range in which hue can be modulated.

That is, a nematic liquid crystal layer with positive dielectric anisotropy is held in a container consisting of two substrates, at least one of which is transparent, on which electrodes are integrally or partially provided, and the optical path of the container holding this liquid crystal is For example, an applied voltage (dish s) of a liquid crystal color display device in which a polarizer is provided, liquid crystal molecules are horizontally aligned on the inner surface of one substrate of the container, and liquid crystal molecules are vertically aligned on the inner surface of the other substrate. The present invention provides a color display device provided with means for displaying multiple colors by changing the birefringence of the liquid crystal by changing the birefringence of the liquid crystal.

That is, in the present invention, liquid crystal molecules are horizontally aligned on the inner surface of one substrate of a container holding a positive nematic liquid crystal with anisotropy, and liquid crystal molecules are aligned vertically on the inner surface of the other substrate. The voltage (r) applied to the treated liquid crystal color display device
ms), a magnetic field, etc., to change the birefringence of the liquid crystal, thereby making it possible to display multiple colors such as red, blue, and intermediate colors.

By changing the birefringence of the liquid crystal based on such alignment means, the operating voltages corresponding to red, green, and blue are low and the intervals between these operating voltages are wide, and color separation is extremely good, and the same cell can be used one after another. The feature is that the desired color can be displayed simply by changing the voltage, magnetic field, etc. To explain in more detail, one transparent substrate is treated so that the long axes of liquid crystal molecules are aligned horizontally on the substrate surface, and the other substrate surface is treated so that the long axes of liquid crystal molecules are aligned perpendicularly to the substrate surface. A liquid crystal cell is created in which a nematic liquid crystal with positive dielectric anisotropy is sandwiched between two substrates having transparent electrodes treated with A liquid crystal display structure with polarizers installed on both sides of the liquid crystal layer, and means for displaying multiple colors by changing the voltage applied to the liquid crystal layer in a region where the birefringence of the liquid crystal changes. A liquid crystal color display device consisting of the following is obtained.

Examples of the present invention will be described below.

FIG. 1 is a schematic cross-sectional view for explaining a liquid crystal color display device according to the present invention.

Transparent substrates 1 and 2 are provided integrally or partially with two transparent electrodes 9, for example, on a glass substrate, and on the surface of the substrate 1 having the electrodes 9, the long edges of the liquid crystal molecules 3 are arranged parallel to the substrate 1. The two surfaces of the substrates having the electrodes 9 are treated so that the most axes of the liquid crystal molecules 3 are aligned perpendicular to the substrate 2, and the substrates 1 and 2 are arranged so that the treated surfaces face each other. and sandwich the LCD 3.

FIG. 1 is a cross-sectional view schematically showing the arrangement of liquid crystal molecules 3 in the liquid crystal layer at this time. As a result, the liquid crystal molecules are arranged continuously from the substrate 1 to the substrate 2 in a diagonal pattern of approximately 900 degrees. For example, polarizers 4 and 5 are placed on both sides of the light of this liquid crystal cell.
Set up. In this state, the incident light 6 becomes linearly polarized light by the polarizing plate 4, and due to the back refraction of this liquid crystal layer, it passes through the liquid crystal cell and forms elliptically polarized light. Furthermore, this elliptically polarized light that matches the polarization plane of the polarizer 5 is transmitted through the polarizer 5. Therefore, when the incident light 6 is white light, the light passing through the polarizer 5 exhibits a hue due to an interference phenomenon. This hue can be modulated by changing the thickness of the liquid crystal layer, and by changing the thickness of the liquid crystal layer with no voltage applied, any color such as red, blue, lines, intermediate colors, etc. can be displayed. In particular, a liquid crystal cell is created in which the liquid crystal molecules 3 are aligned in a certain direction parallel to the surface of the substrate 1 by polishing the surface of the substrate 1, that is, horizontally aligned, and the polarizers 4 and 5 are made orthogonal to each other. Furthermore, when the polishing direction and one polarizer are placed in the 450 direction, the transmission intensity is the highest and the hue is the brightest. Similarly,
Even when the polarizers 4 and 5 are placed parallel to each other in the liquid crystal cell, and one polarizer is placed in the 45o direction relative to the polishing direction, the liquid crystal cell exhibits a hue complementary to the hue. When the orientation of the polarizer and the polishing direction is other than 45o, the transmitted light intensity changes. Further, even if the polarizers 4 and 5 are set in a direction other than orthogonal or parallel, hue display is possible, and a different hue is exhibited than when the polarizers 4 and 5 are set orthogonal or parallel. In this way, by changing the position of the polarizer, light intensity modulation and hue modulation are possible. Next, lead terminals are taken out from the transparent electrodes 9 of the substrates 1 and 2 and connected to the switch 8 via the electrode 7.

By turning on the switch 8, the tilt angle of the liquid crystal molecules is
The birefringence of the liquid crystal layer changes continuously as the applied voltage increases from a state where no voltage is applied, and as a result, the birefringence of the liquid crystal layer changes according to the value of the voltage applied to the liquid crystal. Optically, when monochromatic light is incident on a liquid crystal layer, the transmitted light intensity changes. When the incident light 6 is white light, a change in the hue of the transmitted light is obtained due to a change in the birefringence of the liquid crystal as the applied voltage increases. In the region where the birefringence index does not change even when the voltage is increased, that is, in the saturated region of the birefringence index, the color becomes black or white, and the hue disappears or becomes very pale. The voltage in the saturation region of this birefringence is
Although it varies depending on the birefringence of the nematic liquid crystal layer and the thickness of the liquid crystal layer when no voltage is applied, it is usually 8V to 10V in practical use.
That's about it. In addition, unlike the BCB method, the liquid crystal molecules 3 already have a mirror oblique angle when no voltage is applied, so by applying a low pressure, the oblique angle of the liquid crystal molecules can be changed, which means that the threshold voltage can be changed. It is possible to optically change the hue with a very low voltage. Moreover, in the display device according to the present invention, the voltage difference between each hue such as red, blue, green, etc. is large compared to the ECB method, so the permissible fluctuation range of the voltage applied to the liquid crystal to display a certain hue is large. It can be taken. In the LCD color display according to the present invention, as a horizontal alignment treatment for controlling the arrangement of liquid crystal molecules on the surface of one of the two transparent substrates forming the container, on which the transparent electrode is applied. Examples of methods include polishing the substrate with a cotton polisher or various abrasives, diagonally depositing various inorganic substances on the substrate, coating the substrate with an organic silane compound and polishing it, and forming a certain kind of polymer film on the substrate. be. In addition, examples of vertical alignment treatments to control the arrangement of liquid crystal molecules on the surface of the other substrate on which the transparent electrode is applied include acid treatment of the substrate, substrate treatment with various surfactants, and organic silane-based treatment. Examples include coating a compound on a substrate.

Further, the liquid crystal used in the liquid crystal display device according to the present invention preferably has positive dielectric anisotropy.

For example, as a liquid crystal with positive dielectric anisotropy, compounds represented by the general chemical structural formula (X: alkyl group, alkoxy group, alkyloxy group, etc.) can be used alone or as a mixture.

An example of a compound represented by the above single-pronged chemical structural formula is 4'
-n-butoxybenzylidene-4-cya/aryne, 4'
-n-hexylbenzylidene-4-cyanoaniline, 4
'-n-benzene-4-cyanobiphenyl and the like.

The negative liquid crystal used for comparison is, for example, a compound represented by a general chemical formula (X, Y=alkyl group, alkoxy group, alkyloxy group, etc.), which is used alone or as a mixture.

An example of a compound represented by the above general chemical structural formula is:
Examples include 4'-methoxybenzylidene-41n-phthylaniline, 4-ethoxybenzylidene-41n-butylaniline, and 4'mutoxy41n-phthylazoxybenzene.

A liquid crystal with positive dielectric anisotropy indicates that the dielectric constant in the long axis direction of the liquid crystal molecules is larger than the permittivity in the direction perpendicular to the long axis of the liquid crystal molecules, and conversely, a liquid crystal with negative dielectric anisotropy has a dielectric constant in the long axis direction of the liquid crystal molecules. The dielectric constant in the direction perpendicular to is larger.

As described above, the liquid crystal color display device according to the present invention requires extremely low voltage for color display, and the voltage difference between displaying various hues is large, so the power supply stability and precision tolerance range is wide. It has features superior to conventional liquid crystal color display devices such as the ECB system. Further, in the liquid crystal color display device according to the present invention, even if the liquid crystal container does not have a transparent electrode, hue modulation is possible as long as a means for changing the slope of the liquid crystal molecules, such as applying a magnetic field, is provided.

Furthermore, compared to the conventional ECB method, the device of the present invention is less affected by the accuracy (variation in thickness) of the thickness of the liquid crystal cell, and is extremely advantageous in manufacturing the liquid crystal cell. Furthermore, although the principle of the liquid crystal color display device of the present invention has been explained only in the case of a transmissive type with reference to FIG. 1, in the configuration shown in FIG. display device,
Even a reflective display device in which one substrate of a liquid crystal container is a reflective plate having an electrode has excellent performance equivalent to that of a transmissive color display device. In particular, in the case of the latter reflective type, it is sufficient to place a polarizer on the side facing the reflector, so
Unlike the transmission type, only one polarizer is required. Hereinafter, in order to clarify the usefulness of the device of the present invention, a detailed explanation will be given by giving Examples and Comparative Examples.

Example 1 Among two glass substrates coated with transparent electrodes, the surface of one substrate having the electrodes is subjected to horizontal alignment treatment, for example, by polishing (mbbing) with a cotton cloth in a certain direction, and the other is The surface of each substrate on which the electrodes were applied was subjected to vertical alignment treatment, for example, by coating with organic silane.

Arrange these two substrates so that their processing surfaces face each other,
A liquid crystal container was formed. At this time, the distance between the electrodes was set to 8 distances using a spacer. This container has a liquid crystal display, for example 4'...
Methoxybenzylidene-4-n-butylaniline (hereinafter referred to as M former BA) and 4'-n-butoxybenzylidene-
A mixture of two types of nematic liquid crystals, 4-cyanoaniline (hereinafter referred to as BBCA), was injected to form a liquid crystal cell. The mixing ratio of this mixed liquid crystal was 4 parts of M old BA and 4 parts of BBCAI. This mixed liquid crystal has positive dielectric anisotropy and a nematic temperature range of 80 to 570°C. The transmitted light intensity was measured under a Nikon polarizing microscope using red (R) (maximum transmitted wavelength 632.7 nm).
Using three types of filters: , loosely G) (maximum transmission wavelength 554.m), and blue leg (maximum transmission wavelength 452.m), the results are as follows: This was done by detecting changes in the amount of transmitted light.

A sine wave AC voltage of 500 Hz was used for driving to change the birefringence index of the liquid crystal, and the voltage applied between the electrodes was changed from OV. The polarizer plates, which are the two polarizers of a polarizing microscope, are orthogonal, and the polishing direction of the liquid crystal cell and one polarizer are 45
It was installed to take the 0 direction. The results are shown in FIG. 2. In addition, changes in hue due to voltage application were observed with the naked eye under the above settings. In this example, the color is yellow-green when no flea field is applied. The relationship between hue and applied voltage is shown in Table 1. The hue modulation possible region shown in FIG. 2 is a voltage region in which it is possible to display the most vivid hues such as red, blue, and green when observing hue changes due to voltage application with the naked eye. oy
to 1.5V (nns). Also, from green to blue,
As shown in Table 1, the voltage width between each hue from blue to red is 0.3 V (plate s). Note that since the applied voltage for controlling the hue is an effective voltage (skin s), any means for changing the effective voltage may be used. For example, even if the pulse width of the applied voltage is changed, excellent color display can be achieved as well. As is clear, this makes it easy to control various hues at low voltages, and the liquid crystal display device according to the present invention exhibits unprecedented performance. Comparative Example 1 Two glass substrates coated with transparent electrodes were polished by polishing the surfaces of the glass substrates coated with the electrodes in a certain direction with a cotton cloth, aligning the polishing directions, and arranging the electrode surfaces so that they faced each other. A conventional ECB type liquid crystal container was formed.

At this time, the distance between the electrodes was set to 8 Buddhas using a subaser.
The mixed liquid crystal of Example 1 was poured into this liquid crystal container. Measurements were made in the same manner as in Example 1, and the relationship between hue and applied voltage as observed with the naked eye is shown in Table 1. This comparative example relates to a hue display device using the conventionally known ECB method, and is the first example.
As is clear from the table, each hue of green, blue, and red is displayed at around 2V, and the hue can be modulated by 0.4V from 1.8V to 2.2V.

Further, the voltage difference between each hue was 0.1V, which was extremely small. As described above, compared to Example 1, in this comparative example regarding the well-known EBC method, the applied voltage required to display each hue of green, blue, and red is doubled to tripled. Since the voltage difference between each hue is extremely small at one-third, hue control is extremely difficult. Table 1 Comparative Example 2 A liquid crystal, such as MBBA and 4'-ethoxybenzylidene-4-n-butylaniline (hereinafter referred to as E) was added to the liquid crystal container of Example 1.
A liquid crystal cell was prepared by injecting a mixture of two types of nematic liquid crystals (referred to as BBA).

At this time, the distance between the electrodes was set to 5 mm using a spacer.
In this case, the mixing ratio of liquid crystal was 3 parts of M old BA and 2 parts of EBBA. This mixed liquid crystal has negative dielectric anisotropy and a nematic temperature range of 60 to 530°C. The measurement of transmitted light intensity was the same as in Example 1.

The results are shown in Figure 3, and the relationship between hue and applied voltage is
Shown in the table. In this example, the hue was red when no voltage was applied. The hue modulation range shown in FIG. 3 is from OV to 4V (rms), and the voltage difference between each hue is approximately IV, indicating that a higher voltage than in the case of Example 1 is required. Comparative Example 3 The glass surfaces of two glass substrates coated with transparent electrodes were subjected to a vertical alignment treatment using organic silane, and the treated surfaces were arranged to face each other to form a liquid crystal container.

At this time, the distance between the electrodes was set to five peaks using a spacer. A liquid crystal cell was prepared by injecting the liquid crystal of Example 2 into this container, and measurements were carried out in the same manner as in Example 1. The measurement results of transmitted light intensity are shown in FIG. 4, and the relationship between hue and applied voltage is shown in Table 2. This comparative example based on the prior art relates to a hue display device using an ECB method, which is different from the first comparative example.
From FIG. 4 and Table 2, it can be seen that the hue modulation range is as high as 5.5V to 7.4V, and the voltage required to display each hue is much higher than in Example 1.
Table 2 Example 2 The liquid crystal cell of Example 1 was installed so that the two polarized lights of a polarizing microscope were made parallel and the polishing direction of the liquid crystal cell and the polarizer were in the 450 direction.

Measurements were carried out in the same manner as in Example 1, and the results are shown in FIG. Furthermore, Table 3 shows the relationship between hue and applied voltage. This example shows a hue change that is complementary to the hue change of Example 1. Therefore, as in Example 1, the hue modulation range was very low at 1.5 V (skin s) from OV, and the voltage difference between each hue was wide at 0.3 V, demonstrating excellent performance. As explained using the figures in Table 3 and above, in liquid crystals with positive dielectric anisotropy, the operating voltage that enables hue modulation is low, and the difference in applied voltage between hues is wide, so that voltage fluctuations can be easily controlled. It can be taken in large quantities.

As described above, according to the present invention, it is possible to obtain a low-voltage, low-power consumption type liquid crystal color display device that has a low operating voltage, wide applied voltage difference between hues, and has high practical value that can tolerate large voltage fluctuations. be able to.

In the above embodiment, a transmissive liquid crystal cell is provided as shown in FIG. 1, and polarizers are provided on both sides of the cell. It may also be configured as a reflective surface. In this case, the polarizer may be provided only on the incident optical path side, which is the optical path of the liquid crystal cell.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining an embodiment of the device of the present invention;
Figures 2 and 5 are curves of display characteristics of each color versus applied voltage to the liquid crystal cell in different embodiments of the device shown in Figure 1, and Figures 3 and 4 are liquid crystal cells according to the liquid crystal color display device used for comparison. FIG. 3 is a diagram of each color display characteristic curve with respect to applied voltage. 1, 2...Substrate, 3...Liquid crystal molecules, 4,5
...Polarizer, 9...Electrode, 6...
...Light, 7...Power, 8 """ switch.

Claims (1)

[Claims] 1 First and second substrates, at least one of which is transparent, provided with first and second electrodes, respectively, and a nematic liquid crystal with positive dielectric anisotropy provided between the first and second substrates. a means for horizontally aligning the liquid crystal molecules of the nematic liquid crystal provided on the first substrate; a means for vertically aligning the liquid crystal molecules provided on the second substrate; and a means provided on the optical path of the nematic liquid crystal. What is claimed is: 1. A liquid crystal color display device comprising: a polarizer having a nematic liquid crystal; and means for displaying multiple colors by changing the birefringence of the nematic liquid crystal.