JPH0784279A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which is simple in constitution, has high utilization efficiency of light and is capable of making bright display. CONSTITUTION:A short pitch colesteric liquid crystal layer reflects light in a prescribed rotating direction of a specific wavelength and allows the transmission of the light of a reverse direction. An optical means having double refractiveness is laminated on the colesteric liquid crystal layer having circularly polarized light selectivity by utilizing this nature. This optical means 2 has the liquid crystal layer 21 having a voltage impressing means and a polarizer 22 and is constituted to generate the circularly polarized light of low order within a visible light area in an on-state or off-state. The optical means is otherwise is composed of a phase plate, the liquid crystal layer and the polarizer and the liquid crystal is provided with such double refractiveness that the optical means generate the circularly polarized light of the low order within the visible light region. A light absorptive layer is arranged on the rear surface of the cholesteric liquid crystal.

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 which holds a chiral nematic liquid crystal layer with orthogonal Nicols as shown in Japanese Patent Laid-Open No. 51-13666. I can't do it. 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.

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.

[0004]

However, since the display mode in which such a nematic liquid crystal molecule is held by the twisted polarizing plate utilizes the birefringence of the liquid crystal, high-order interference light which is difficult to use for display is easily mixed, If it is not a transmission type, it is difficult to obtain practical contrast. This is a drawback mainly caused by the light loss due to the polarizing plate and the viewing angle dependence of the polarization axis, and the light loss generally exceeds 50%. Further, in color display, the 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. .

In addition, as a liquid crystal display using a guest-host type or a cholesteric liquid crystal, a liquid crystal which responds to an electric field and stabilizes color control has not been developed yet. Furthermore, the former requires dyes that have vivid colors and are compatible with liquid crystal molecules because the dyes limit the electro-optical properties inherent in liquid crystals, but such dyes and liquid crystals having electrically superior properties are practically used. Has not reached. The latter also has poor color purity as a result of higher order interference.

As described above, in any of the liquid crystals, there is a liquid crystal display having a high light utilization efficiency that can be practically used because the light utilization efficiency is extremely low and there are many problems to be solved in terms of materials or other matters. The reality is not.

[0007]

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. It has a cholesteric liquid crystal layer and optical means having birefringence laminated on the cholesteric liquid crystal layer, and the optical means includes a liquid crystal layer having at least a voltage applying means, and is in the visible light range in an ON state or an OFF state. It is configured to generate low-order circularly polarized light.

Further, the present invention comprises a light absorbing layer, a cholesteric liquid crystal layer laminated on the light absorbing layer for reflecting circularly polarized light of a specific wavelength, a phase plate laminated on the cholesteric liquid crystal layer, and an electric field applying means. The liquid crystal layer has an optical means including a liquid crystal layer and a polarizer, and the liquid crystal layer has a birefringence property such that the optical means generates low-order circularly polarized light in the visible light region.

[0009]

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 at any wavelength when passing through the liquid crystal layer, high-order interference components are allowed to pass through without increasing mischief and transmitted or blocked by optical means. It

[0010]

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 by an alignment film 23 and an electrode 24, which are provided by laminating a protective film or the like on the inner surface of each substrate, and the electrodes 24 are orthogonal to each other so as to form, for example, a matrix above and below. It is composed of stripe electrodes and serves as a voltage applying means for the liquid crystal layer 21. Further, the optical means 2 is configured to generate low-order circularly polarized light in the visible light region in the ON state or the OFF state, and selectively transmit or block this by the polarizer 22, for which the liquid crystal layer 21 is formed. For example, twisted nematic liquid crystal in which liquid crystal molecules are twisted by approximately 90 degrees, or liquid crystal molecules in 180 to 3
It is a super twist nematic liquid crystal twisted by 60 degrees and has a predetermined retardation value.

In such a structure, it is assumed that the cholesteric liquid crystal layer 1 is arranged such that layers having selectivity for red, green and blue wavelengths are aligned. For example, in the case of red display, if light having a wavelength near 610 nm, which is a red wavelength, is reflected by the cholesteric liquid crystal layer 1 by left circularly polarized light, right circularly polarized light and light of other color wavelengths are generated. It transmits 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 shielded by the optical layer 2. Specifically, when no electric field is applied, the retardation-adjusted liquid crystal layer 21 advances the phase by π, resulting in left polarized light. Then, when the electric field is applied, the retardation is destroyed, so that the light is transmitted through the liquid crystal layer 21 with the right polarization as it is. Then, since these lights are lights in the opposite direction of the selected wavelength range when there is no electric field in the polarizer 22, the display color is achromatic (black), and when the electric field is applied, it is transmitted and the display becomes red, Light absorption at this time is extremely small.

From 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 in the optical layer be small. In this case, as shown in FIG. 2, a liquid crystal display is provided on the light absorption layer 3, the cholesteric liquid crystal layer 1 laminated on the light absorption layer 3 and reflecting circularly polarized light of a specific wavelength, and the cholesteric liquid crystal layer 1. The optical means 2 may be composed of a laminated phase plate 26, a liquid crystal layer 27 having an electric field applying means, and a polarizer 22. Further, the phase plate 26 may be a thin film layer of polymer resin rather than a plate, functions as a quarter-wave plate, and serves as a liquid crystal layer 2.
It is preferable that 7 has a birefringence so that the optical means produces a low-order circularly polarized light in the visible light region and has a role of a ½ wavelength 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 is more efficient in light transmission.

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, for example, 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. In this case, since the spiral direction of the cholesteric phase must be along the optical axis even if no electric field is applied to this cholesteric liquid crystal during display,
For the purpose of improving the adhesion of the cholesteric liquid crystal layer 1 to the supporting substrate 11, an -OH group is added to the acrylic group,
In the initial stage of cholesteric, when the orientation is performed by an electric field or a magnetic field, the dielectric anisotropy of the cholesteric bonded to the siloxane ring is specified, and for example, the dielectric anisotropy is made negative and a high electric field is applied in the thickness direction. It is preferable to consider such as enclosing molecular liquid crystals. The cholesteric liquid crystal layer 1 has wavelength selectivity depending on the pitch of cholesteric. In such a cholesteric liquid crystal layer, since the extraordinary refractive index n _e (T) is proportional to the temperature dependence of the liquid crystal order parameter S (T), the extraordinary refractive indices n _o (T), n _e
(T), temperature dependence can be reduced by properly designing the temperature-dependent spiral pitch P (T), or additivity holds, so blending cholesteric liquid crystals with different pitches so that a predetermined color can be selected. Good.

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 varies 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 so-called red, green, and blue wavelengths are selected as the cholesteric liquid crystal layer 1, perfect circularly polarized light is obtained with respect to a predetermined wavelength, but the total wavelength range including these three wavelengths is substantially The optical means 2 is such that it becomes elliptically polarized light.

More specifically, when a layer having birefringence is used as the optical means 2, when the birefringence 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. Figure 3 shows 560 nm in the on state
It shows the characteristics of a birefringent body that circularly polarizes in the vicinity, and the retardation Δn · d (retention) is 14
The case of 0 nm is illustrated, and the case of primary circularly polarized light is illustrated. High-order circularly polarized light has a characteristic that multiple sine curve waves with the horizontal axis on the short wavelength side compressed appear in the visible light region, so right circularly polarized light at one wavelength, left circularly polarized light at another wavelength, For other wavelengths, the polarization mode differs for each wavelength, such as elliptically polarized light having different rotation directions, and uniform display control cannot be performed. Therefore, in order to adjust the birefringence in the ON state, retardation adjustment of the liquid crystal layer or the like should be performed so as to make circular polarization of lower order, more preferably first order, with respect to a specific wavelength in the visible light region. is there.

Similarly, a curve A in FIG. 4 shows the characteristic of a birefringent body that circularly polarizes in the vicinity of 560 nm in the OFF state, that is, in the state where a non-selection voltage is applied in the simple matrix driving, and the retardation. Δn · d is 4
The case of 20 nm is illustrated. It can be said that it is secondary circularly polarized in the visible light region. In the case of high-order circularly polarized light, a characteristic curve that increases to the right or to the left in the visible light region and does not monotonically increase is not obtained, and a predetermined circularly polarized light component does not exist for each selected wavelength of the cholesteric liquid crystal layer. Therefore, as long as the optical means 2 produces low-order circularly polarized light in the visible light region when the liquid crystal layer is in the ON state or the OFF state, the optical means 2 does not substantially need to have different characteristics depending on the location and can perform color display. .

Such an optical means 2 includes a chiral having a Δn · d of 0.07 to 0.115 containing 60 to 80% by weight of difluorophenyl ester cyclohexane, cyanofluorophenyl ester, cyclohexane cyclohexene, cyclohexanecarboxylic sun phenyl ester and the like. A single liquid crystal layer made of nematic or a layered body of a liquid crystal layer such as polycarbonate, polyvinyl alcohol, polyester, polypropylene, cellulose acetate, polyvinyl butyrol and the like is stacked to obtain the characteristics illustrated in FIGS. The optical means 2 included therein can be configured, and vivid colors can be displayed. The characteristic curve B in FIG. 4 shows the transmission characteristic during color display in such an optical means.

[0018]

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 it has a liquid crystal display, it is possible to provide a liquid crystal display having a simple structure capable of producing clear display with little color shift over the entire visible light range.

[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 sectional view of a liquid crystal display according to another embodiment of the present invention.

FIG. 3 is a characteristic diagram of optical means used in the present invention.

FIG. 4 is a characteristic diagram of the optical means and the liquid crystal display of the present invention.

[Explanation of symbols]

 1 Cholesteric Liquid Crystal Layer 2 Optical Means 21 Liquid Crystal Layer 22 Polarizer 26 Phase Plate 27 Liquid Crystal Layer 3 Light Absorbing Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuyoshi Susaki 3-201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd. (72) Inventor Yoshio Suzuki 3-201 Minamiyoshikata, Tottori City Tottori Prefecture Sanyo Denki Within the corporation

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 low-order circularly polarized light in the visible light range in the ON state or the OFF state. 2. A light absorption layer, a cholesteric liquid crystal layer laminated on the light absorption layer for reflecting circularly polarized light of a specific wavelength, a phase plate laminated on the cholesteric liquid crystal layer, and an electric field applying means. A liquid crystal layer and a polarizer, wherein the liquid crystal layer has a birefringence so that the optical means produces a low-order circularly polarized light in the visible light region. display.