JPH07134316A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To perform display of high time-division driving with good brightness and color contrast and to perform bright and clear display with decreased color slurring over the entire part of a visible light area by using optical means which convert linearly polarized light into approximately circularly polarized light in any of the wavelengths corresponding to the three primary colors in the visible light region. CONSTITUTION:A liquid crystal layer 21 is held by oriented films 23 and electrodes 24. The electrodes 24 consist of, for example, striped electrodes intersecting orthogonally with each other so as to constitute a matrix above and below and serve as means for impressing voltages to the liquid crystal layer 21. The optical means 2 convert the linearly polarized light to the approximately circularly polarized light in any of the wavelengths corresponding to the three primary color in the visible light region in an on state or off state. The cholesteric liquid crystal layers 1 laminated on a light absorption layer 3 consisting of a black thin metallic film are so arranged that the selective wavelengths vary alternately in a stripe shape so as to reflect the circularly polarized light beams of the prescribed wavelength respectively varying with red, blue and green.

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 device using a cholesteric liquid crystal having wavelength selectivity.

[0002]

2. Description of the Related Art Conventionally, a field effect type liquid crystal display has an advantage that a thin display can be constructed with low power consumption. The most typical display device of this kind is one in which a chiral nematic liquid crystal layer as shown in Japanese Patent Publication No. 51-13666 is sandwiched by crossed Nicols, but the display is narrow and the display can be performed by high time division driving. Absent. Therefore, a display mode in which liquid crystal molecules are twisted by more than 180 degrees as disclosed in JP-A-60-107020 has been proposed and put into practical use. However, since the display mode uses the birefringence of the liquid crystal as described above, high-order interference light is easily mixed in, and practical contrast is difficult to obtain unless it is a transmissive type. This is a drawback mainly caused by the light loss due to the two polarizing plates and the viewing angle dependence of the polarization axis.
It exceeds 0%. Further, in color display, light loss is further increased by the filter. In the transmissive display, an illuminating means is required on the back side, which not only makes the display thicker but also consumes more power, which reduces the original advantage of the liquid crystal display that is thin and consumes less power. .

On the other hand, there is a so-called guest-host type or white-tailor type liquid crystal display in which a dye is added to a nematic liquid crystal in order to perform color display. In this method, a dye is mixed in the liquid crystal, and the color of the dye is changed to an achromatic color as the liquid crystal changes the array direction depending on the presence or absence of an electric field. Similarly, for direct color display, there is also a proposal of a short-pitch cholesteric liquid crystal display that utilizes a coloring phenomenon due to the temperature dependence of liquid crystal for display.
However, liquid crystals that respond to an electric field and stabilize color control, and dyes that have vivid colors and are compatible with liquid crystal molecules have not been put to practical use.
Also, they have poor color purity as a result of higher order interference.

[0004]

As described above, in any of the liquid crystals, the light utilization efficiency is extremely low, and there are many problems to be solved in terms of materials or other reasons, and therefore the light utilization efficiency that can be practically used is high. The reality is that there is no liquid crystal display. Therefore, we previously proposed that the cholesteric liquid crystal and the optical means are laminated, and the light of a specific wavelength reflected by the cholesteric liquid crystal with high efficiency is selected by the optical means for display. However, such a display means has a drawback that a display unit must be formed for each color in order to perform full-color display in order to utilize the wavelength dependence of the cholesteric liquid crystal.

[0005]

In view of the above-mentioned problems, the present invention provides full-color display with a simple structure in utilizing a polarization mode of a specific wavelength with high efficiency and has circular polarization selectivity. A cholesteric liquid crystal layer and an optical means having a birefringent property laminated on the cholesteric liquid crystal layer, the optical means including a liquid crystal layer having at least a voltage applying means, and at least three primary colors in a visible light region. It is configured to convert linearly polarized light into substantially circularly polarized light at any of the corresponding wavelengths.

The present invention is also directed to a light absorbing layer, a plurality of cholesteric liquid crystal layers laminated on the light absorbing layer for reflecting circularly polarized light having different predetermined wavelengths, and a phase plate laminated on the cholesteric liquid crystal layer. And an optical means comprising a liquid crystal layer having an electric field applying means and a polarizer, wherein the liquid crystal layer has a birefringence property for producing substantially circularly polarized light for each of the specific wavelengths of the cholesteric liquid crystal layer. I have.

[0007]

By this, for example, each light of red, blue and green is
Circularly polarized light is reflected by the cholesteric liquid crystal layer with almost no absorption, and transmission / shading can be efficiently controlled at any wavelength when passing through the liquid crystal layer.

[0008]

FIG. 1 is a sectional view of a liquid crystal display according to an embodiment of the present invention, in which reference numeral 1 denotes a cholesteric liquid crystal layer having circularly polarized light selectivity, which allows a right (or left) circularly polarized light of a specific wavelength to be rotated. It reflects and transmits other wavelengths as well as light of reverse circularly polarized light. Denoted at 2 is an optical means having a birefringent property, which is laminated on the cholesteric liquid crystal layer 1, and comprises a liquid crystal layer 21 and a polarizer 22.
Have. The liquid crystal layer 21 is sandwiched between an alignment film 23 and an electrode 24. The electrode 24 is composed of, for example, stripe electrodes that are orthogonal to each other so as to form a matrix above and below, and serves as a voltage applying means to the liquid crystal layer 21. The optical means 2 is
In the ON state or the OFF state, linearly polarized light is converted into substantially circularly polarized light at any of the wavelengths corresponding to the three primary colors in the visible light range.

In such a display, a light absorption layer 3 made of a black metal thin film is laminated on the back surface of the cholesteric liquid crystal layer 1 on a base 10 made of plate glass or the like, and laminated on the light absorption layer 3. The cholesteric liquid crystal layer 1 is red,
The selected wavelengths are alternately arranged in stripes so as to reflect circularly polarized light having different predetermined wavelengths of blue and green, and the liquid crystal layer 21 is provided in the optical means 2 as necessary. A laminated thin film phase plate 26 is provided,
The liquid crystal layer 21 has birefringence so as to generate substantially circularly polarized light for each specific wavelength of the cholesteric liquid crystal layer 1. Such a circularly polarized light is configured to be selectively transmitted or blocked by the polarizer 22, and for this purpose, the liquid crystal layer 21 includes, for example, twisted nematic liquid crystal in which liquid crystal molecules are twisted by approximately 90 degrees, or liquid crystal molecules having 180 to It is a super twist nematic liquid crystal twisted by 360 degrees and has a predetermined retardation value.

In such a structure, for example, in the case of red display, if light in the vicinity of a wavelength of 610 nm is reflected by the cholesteric liquid crystal layer 1 with left-handed circularly polarized light, light with right-handed circularly polarized light or other color wavelengths is reflected. Light passes through the cholesteric liquid crystal layer 1 and does not contribute to display. The red left-handed circularly polarized light reflected by the cholesteric liquid crystal layer 1 is transmitted and blocked by the optical means 2. Specifically, when the electric field is not applied, the phase is advanced by π by the retardation-adjusted optical means 2 to become left polarized light. Then, when the electric field is applied, the retardation is destroyed, so that the light is transmitted through the optical means 2 without changing the right polarization. Then, in the polarizer 22, these lights are reflected in the direction opposite to the selected wavelength range when there is no electric field, and are reflected, so that the display color is achromatic (black), and when the electric field is transmitted, the display becomes red and the display becomes red. The light absorption at this time is extremely small. By selecting the optical axis of the polarizer 22, it is possible to have red when no electric field is applied and black when an electric field is applied.

According to such a display principle, it is preferable that the light transmitted through the cholesteric liquid crystal layer 1 be absorbed and that the elliptically polarized light component is reduced by the optical means.
The light absorption layer 3 and the phase plate 26 described above play this role. The phase plate 26 may be a thin film layer of polymer resin rather than a plate, and functions as a quarter-wave plate, and the liquid crystal layer 21 has a birefringent property such that the optical means produces low-order circularly polarized light in the visible light region. It is preferable to have the role of a half-wave plate. The light reflected by the cholesteric liquid crystal layer 1 is substantially linearly polarized by the phase plate 26, and the polarization axis is rotated by the liquid crystal layer 27. Therefore, the polarizer 22 may be a linear polarizing plate, and the utilization efficiency in transmitting light is high. It gets even higher.

In the above example, the cholesteric liquid crystal layer 1 can be made of a polymer liquid crystal material having a cholesteric phase as disclosed in JP-A-57-165480 and JP-A-61-137133. For example, it is possible to use a siloxane ring in which an acrylic group and a cholesteric liquid crystal, which bond to another ring, are alternately bonded to the periphery. The cholesteric liquid crystal layer 1 has wavelength selectivity depending on the cholesteric pitch. Such a cholesteric liquid crystal layer 1 is preferable because one layer is fixed at different pitches depending on the location because the flatness of the entire display surface is good, and the stability is increased by covering with a protective layer 11.

On the other hand, the optical means 2 is a cholesteric liquid crystal layer 1.
Since the high reflectance for circularly polarized light due to is utilized, it is preferable to control the polarization for each selected wavelength of the cholesteric liquid crystal layer. That is, it is preferable in terms of sharpness of the display color to change the optical characteristics of the optical means 2 for each selected wavelength corresponding to the cholesteric liquid crystal layers of a plurality of colors. However, since the selected wavelength of the cholesteric liquid crystal layer 1 differs depending on the location, the optical means 2 also has different optical characteristics depending on the location, and if the characteristics must be accurately laminated according to the arrangement of the cholesteric liquid crystal layer, a dot matrix display is required. Considering that the pixel pitch of (graphic display, etc.) is around 100 μm, it becomes an extremely complicated work. Therefore, in order to substantially simplify the structure without color shift, it was examined that the optical means 2 has the same structure even if the selection wavelength of the cholesteric liquid crystal layer 1 changes. Specifically, when the so-called red, green, and blue wavelengths are selected as the cholesteric liquid crystal layer 1, the optical means 2 is configured to be substantially circularly polarized light in the entire wavelength range including these three wavelengths.

More specifically, when a layer having a birefringent property is used as the optical means 2, if the birefringent layer is sandwiched by crossed Nicols, the intensity of light transmitted through the laminate is I = I _0. sin ² (2θ) sin ² {(π / λ) Δnd} Where I ₀ is the intensity of incident light, θ is the angle between the polarization axis and the birefringence axis, λ is the wavelength of the referenced light, and Δn is the birefringence of the birefringent layer. , D are the thickness of the birefringent layer. As is clear from this equation, the light passing through the laminate has wavelength dependence, so that the optical means 2 or the liquid crystal layers 21 and 27 therein should be circularly polarized for a specific wavelength of the cholesteric liquid crystal layer 1. However, it does not become circularly polarized light for other wavelengths.

Therefore, in such a display, if left-handed circularly polarized light is made to rotate in the green of 545 nm, for example, as shown in the curve A of FIG.
In red and blue of 450 nm, it becomes elliptically polarized light. Therefore, in order to approximate circularly polarized light even in these wavelength ranges, the optical means is configured such that the liquid crystal layer has a predetermined birefringence index over substantially the entire visible light range. As a result, more vivid colors can be displayed. In order to make such a configuration, it is preferable to make the magnitude of the voltage different for each color and to make the retardation of the local region at the selected wavelength different.

As a method of making such retardations different, there is a method of controlling the tilt angle. That is, taking an optical means for performing primary circularly polarized light as an example, it is 590
When circularly polarized in the vicinity of nm (green), the retardation of the optical means is large in the vicinity of 450 nm (blue), and the retardation is small in the vicinity of 620 nm (red). On the other hand, when the angle formed by the liquid crystal molecules with the surface of the substrate (tilt angle) increases, the retardation decreases. The tilt angle can be increased by increasing the magnitude of the applied voltage. Therefore, the tilt angle is reduced to 3 degrees in the red color selection layer and is increased in the blue color selection layer. The applied voltage may be set as follows. Curve B in FIG. 2 exemplifies a case where an applied voltage is applied to each color zone in this way, and elliptically polarized light that largely deviates from circularly polarized light is not generated even in blue.

When controlling the tilt angle in this way, if the liquid crystal layer 21 is driven by a simple matrix type, a so-called OFF
Since the non-selection voltage is applied in this state, if the bias value of the non-selection voltage is made different for each color, it becomes possible to adjust with an extremely simple configuration. Therefore, a large circularly polarized light component can be used for display in any of the three primary colors.

Instead of controlling the tilt angle, the optical characteristics of the phase plate 26 may be adjusted. In this case, assuming that the phase plate 26 is formed by uniaxially stretching a thin film, the optical means 2 may be in the 1/4 wavelength and 3/4 wavelength states when the phase plate 26 is ON and when it is OFF. The retardation may be adjusted accordingly. Since the retardation depends on the stretched amount, it can be adjusted by rubbing. Therefore, mask rubbing may be performed according to the stripe of the cholesteric liquid crystal layer 1 according to the wavelength, and the rubbing frequency or rubbing strength may be changed according to the color. When a retardation phase plate 26 having a previously adjusted retardation is used instead of rubbing after forming a thin film, the uniaxial stretching axis may be arranged parallel or perpendicular to one molecular axis of the liquid crystal layer 21 made of a nematic liquid crystal. In the method of adjusting the optical means 2 so as to make the linearly polarized light circularly polarized for each color by devising the phase plate 26 in this way, for any of the three primary colors, care should be taken to make the optical characteristics uniform. However, it is possible to obtain the optical means 2 which alternately has three types of characteristics of substantially completely circularly polarized light.

[0019]

As described above, in the present invention, attention is paid to light in a specific wavelength range, light in that wavelength range is effectively used, and an electric field is not applied to a liquid crystal utilizing wavelength selectivity. As for electrical response, the high level technology can be used as it is by the laminated liquid crystal layer, high time division drive display with bright color contrast can be performed, and low order circular polarization characteristics as an optical means including the drive liquid crystal layer. Since the linearly polarized light is converted into circularly polarized light with respect to at least three primary colors in the visible light region and the phase plate is used, the optical means has circularly polarized light characteristics with respect to the three primary colors. We were able to provide a liquid crystal display with a simple structure that allows clear display with little color shift over the entire area.

[Brief description of drawings]

FIG. 1 is a sectional view of a liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram of optical means used in the present invention.

[Explanation of symbols]

 1 Cholesteric Liquid Crystal Layer 2 Optical Means 21 Liquid Crystal Layer 22 Polarizer 26 Phase Plate 3 Light Absorbing Layer

Front page continuation (72) Inventor Tsuyoshi Susaki 3-201 Minamiyoshikata, Tottori-shi, Tottori Sanyo Electric Co., Ltd. (72) Yoshio Suzuki 3-201 Minamiyoshikata, Tottori-shi, Tottori Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. A liquid crystal layer having a cholesteric liquid crystal layer having circularly polarized light selectivity and optical means having birefringence laminated on the cholesteric liquid crystal layer, the optical means having at least a voltage applying means. And a liquid crystal display that converts linearly polarized light into substantially circularly polarized light at any of wavelengths corresponding to at least three primary colors in the visible light range. 2. A light absorbing layer, a plurality of cholesteric liquid crystal layers which are laminated on the light absorbing layer and reflect circularly polarized light of different predetermined wavelengths, a phase plate and an electric field which are laminated on the cholesteric liquid crystal layer. And a liquid crystal layer having an application unit and an optical unit composed of a polarizer, wherein the liquid crystal layer has a birefringence property for producing substantially circularly polarized light for each of specific wavelengths of the cholesteric liquid crystal layer. A liquid crystal display characterized in that