JPH02197816A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To form background and display parts which are colorless and to allow black and white and color displays as well as to improve a high contrast ratio and the dependency of a display characteristic on a visual angle by approximately equaling the dependency on wavelengths of the phase difference between a liquid crystal element and a double refractive film. CONSTITUTION:A twisted nematic liquid crystal having a twisted structure is disposed between an upper substrate 5 and lower substrate 8 consisting of light transparent glass plates. Polarizing plates 1, 10 are disposed on the outside surfaces of the upper substrate 5 and the lower substrate 8 and the double refractive film 3 is disposed between the upper substrate 5 and the upper polarizing plate 1. Further, an external light source 12 is disposed on the outside surface of the lower polarizing plate 10, by which the liquid crystal display element is constituted. Phase correction is executed in the entire wavelength region by using the double refractive film 3 which has the dependency on wavelengths approximately equal to the dependency of liquid crystal molecules on wavelengths and realizes the black and white display. Since the phase correction is executed in the entire wavelength region, the colors of the background and display parts are made colorless and, therefore, the black and white and color displays are enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal display device, and particularly relates to a field-effect liquid crystal display device that has excellent time-division driving characteristics and is capable of black-and-white and color display. .

[Conventional technology]

Conventionally, in liquid crystal display devices having time-division driving characteristics, at least one of the background and the display is colored, and black and white display cannot be performed.

However, in recent years, demands for improving the image quality and increasing the amount of display information of liquid crystal display devices have become stricter, and the required specifications are shifting from black-and-white display to color display. For this reason, as in the device structure shown in Fig. 2, the liquid crystal device has a two-layer structure, and the product Δn-d of the thickness d (μm) of the liquid crystal layer and the anisotropy Δn of the refractive index of the liquid crystal is calculated between the two devices. The twist angles representing the twist of the liquid crystal molecules were made equal, and the twist directions were reversed. As a result, the polarization state of the liquid crystal element is shown in FIG. 9 as shown in FIG. Linearly polarized light incident on a liquid crystal element produces a one phase difference and becomes elliptically polarized light, but by arranging a liquid crystal element with an opposite twist, the phase is corrected and becomes linearly polarized light again, making black and white display possible (colophon, Nagata ,Wada:
Television Society Technical Report, 11. p79.1987).

On the other hand, a method has also been proposed that uses a birefringent film to perform phase correction and achieve black-and-white display (Nagae, Hirata, and Komura: Technical Report of the Television Society of Japan).

12, p29-34.1988).

[Problem to be solved by the invention]

The above conventional technology requires the use of two liquid crystal elements as a liquid crystal display device, and has low mass productivity.

Furthermore, when the liquid crystal element is viewed from an oblique direction, the contrast ratio, which is the ratio of the brightness of the background part to the display part, changes greatly, resulting in poor viewing angle characteristics. FIG. 4 shows the viewing angle characteristics of the horizontal contrast ratio of the liquid crystal element, and FIG. 5 shows the viewing angle characteristics in the vertical direction. As the viewing angle increases, the contrast ratio decreases, and when the viewing angle is 40 degrees or more, the contrast ratio decreases.

The contrast ratio becomes 1 or less, and black and white reversal development occurs.

In addition, when a birefringent plastic film is used, the wavelength dependence of the retardation is not taken into account, and the sixth
As shown in the figure, which shows the wavelength dependence of transmitted light, there was a problem in that the five-phase correction was not completed completely and the contrast ratio was low.

An object of the present invention is to make the background and the display part achromatic to enable black-and-white and color display, and to improve the high contrast ratio and viewing angle dependence of one display characteristic.

[Means to solve the problem]

A first feature of the present invention to achieve the above object is to make the wavelength dependence of the retardation of the liquid crystal element and the birefringent film approximately equal.

Furthermore, a second feature of the present invention for further improving viewing angle characteristics is the use of an optically biaxial crystal.

[Effect]

Twisted nematic type liquid crystal elements, which have excellent time-division driving characteristics, have a color on at least one of the background or the display area.In contrast, reverse-twisted liquid crystal elements are stacked to create a two-layer liquid crystal element. By doing so, it is possible to perform black and white display by performing phase correction, but when the liquid crystal element is viewed from an oblique direction, the contrast ratio changes greatly and there is a problem in the viewing angle dependence of the display characteristics. Furthermore, when a birefringent film was used, the contrast ratio was low because the wavelength dependence of the retardation was not taken into consideration.

By making the wavelength dependencies of the liquid crystal element and the birefringent film approximately equal, the contrast ratio and viewing angle characteristics were improved.

In order to further improve the viewing angle characteristics, an optically biaxial crystal may be used as the birefringent film. This is because the change in phase difference due to viewing angle is small.

〔Example〕

Hereinafter, a liquid crystal display element suitable for carrying out the present invention will be described in detail using the drawings.

(Example 1) FIG. 1 is a perspective view of the element structure of a liquid crystal display element according to the present invention.

In the figure, a twisted nematic liquid crystal having a twisted structure is arranged between an upper substrate 5 and a lower substrate 8 made of transparent glass plates. Also, the upper substrate 5. Polarizing plates 1 and 10 are arranged on the outer surface of the lower substrate 8, and a birefringent film 3 is arranged between the upper substrate 5 and the upper polarizing plate 1. Further, an external light source 12 is disposed on the outer surface of the lower polarizing plate 10, and a liquid crystal display element is configured.

The liquid crystal is a nematic liquid crystal whose main components are biphenyl liquid crystal and ester cyclohexane liquid crystal, with 0.5% by weight of an optically active substance (Merck & Co., Ltd. 3811) added, and Δn=0.118° of the liquid crystal layer. Thickness d is 6.5μm
It was set so that Δn−d=0.77 μm.

The twist direction and twist angle α of the liquid crystal molecules 7 are determined by the rubbing direction 6 of the upper electrode substrate 5 and the rubbing direction 9 of the lower electrode substrate 8.
, and the added optically active substance, and in this example, it was set to 240 degrees.

A polycarbonate film was used as the birefringent film 3, and Δn-d was set to 0.56 μm.

Further, the angle formed between the stretching axis 4 of the polycarbonate film and the upper rubbing axis 6 is 90 degrees.

Polarizing plates 1 and 10 are Nitto Denko G1 with a polarization rate of 99.9%.
229DV, the angle between the absorption axis (or polarization axis) 11 of the lower polarizing plate 10 and the lower rubbing axis 9 is 45 degrees, and the absorption axis (or polarization axis) 2 of the upper polarizing plate 1 and the stretching of the polycarbonate film. The angle formed by the axis 4 was 75 degrees.

Further, although a cold cathode tube is used as the light source 12, a hot cathode tube, an electroluminescent tube, or an external light utilizing type using a reflector without using a light source may be used.

Figure 7 shows the CIE color of the background and display area in this example.
Shown in chromaticity coordinates. As shown in the figure, both the background color and the display color are close to those of the C light source, achieving a roughly black and white display.

Further, the contrast ratio at this time is 15:1.

The relational expression for the phase difference between the liquid crystal element and the birefringent film can be derived using a Jones matrix, and the twist angle of the liquid crystal element is set to 01. The optical path difference is (Δn-d)1, and the optical path difference of the birefringent film is π+θL")-2rrzcλ
It is expressed by the following relational expression: 2(θ-d)x”/

When the above equation is satisfied in the range of λ=450 nm to 650 nm, phase correction is completed and a complete white or black display is obtained.

General 1 The wavelength dependence of the refractive index of liquid crystal molecules is Δn(λ)
It is expressed by the force relational expression =A+B/(λ2-λ02),
In this example, A=0.0764. B=4443.8 (
μm”), λo=263.5 (nm), the eighth
The figure shows the wavelength dependence of Δn-d of liquid crystal molecules and the wavelength dependence of Δn-d of a birefringent film that realizes black-and-white display derived from the above formula, which is roughly similar to the wavelength dependence shown in Figure 8. By using the film, phase correction is achieved over the entire wavelength range. However, the phase difference changes depending on the value of the integer m in the above equation.

FIG. 17 shows the wavelength dependence of the retardation between the liquid crystal element and the birefringent film. When m = 1, the wavelength dependence of the phase difference between the film and the liquid crystal element is approximately the same, phase correction is more complete, and black and white display is achieved, and the contrast ratio is 30:1, which is equivalent to the two-layer liquid crystal system. can get.

In order to obtain a birefringent film with wavelength dependence of m=1 in Figure 8, it is sufficient to use a material with so-called anomalous dispersion, in which the refractive index increases on the long wavelength side. This is described in detail in, for example, "Optics", written by Kozo Ishiguro, (Kyoritsu Zensho), p.260.

In Figure 18, when an absorption peak occurs at a given wavelength, a divergence phenomenon occurs in the refractive index dispersion curve, and when the absorption peak is in the near infrared, the refractive index becomes larger on the longer wavelength side in the visible light region. .

For example, it is possible to have the above-mentioned anomalous dispersion by using the polystyrene film shown in FIG. 19, or by adding to the film a dye such as naphthalocyanine or tsuksin that has an absorption peak in the near-infrared region.

Furthermore, as another means of obtaining the wavelength dependence shown in FIG.
This is also possible by laminating films with different wavelength dependencies.

Figure 9 shows the viewing angle characteristics of the contrast ratio in the left and right directions.
The range where the contrast ratio is 2:1 or more is 40 degrees,
In the case of the conventional two-layer liquid crystal system, the angle is wider than 30 degrees. Further, FIG. 10 shows the viewing angle characteristics of the contrast ratio in the vertical direction, and the black and white reversal phenomenon in which the contrast ratio becomes less than 1 does not occur, and the viewing angle characteristics are superior to those of the two-layer liquid crystal system.

The liquid crystal molecules were observed under crossed Nicols using a polarizing microscope shown in FIG. 11 using a condenser lens. The polycarbonate film is an optically biaxial crystal as shown in the conoscopic image, whereas the polycarbonate film is an optically biaxial crystal as shown in the conoscopic image shown in FIG. Figure 13 shows the viewing angle dependence of the transmittance when the polarizing plates are crossed nicols and a parallel alignment liquid crystal element and a single polycarbonate film are inserted.When the transmittance in the vertical direction is 1, it is 45 degrees. In the direction, the liquid crystal is 0.4, while the polycarbonate film is 0.6, i.e. the optically biaxial crystal is
There is little change in phase difference due to viewing angle, and viewing angle characteristics of display characteristics such as contrast ratio are excellent.

[Example 2] In FIG. 1, as the optically biaxial crystal 3, Δn-d
= Using two 0.3 μm polycarbonate films,
The sheets are stacked with their stretching axes shifted.

The angle formed was set to 10 degrees based on the contrast ratio relationship shown in FIG. The angle between the stretching axis of the upper film and the absorption axis (or polarization axis) 2 of the upper polarizing plate was 40 degrees, and the other element configurations were the same as in Example 1.

Figure 15 shows the background color and display color in this example.
Shown in E chromaticity coordinates.

When compared with Figure 7, the CIE chromaticity coordinates indicate that the background color is (0
, 35, 0, 35) to (0, 33, 0, 33), and the display color changes from (0, 29, 0, 36) to (Q, 33° 0.3
4), both are close to the C light source (0, 31, 0, 31), achieving a roughly black and white display.

Further, the contrast ratio at this time is 20:1.

[Example 3] In the device configuration of Example 1, the optically biaxial crystal 3 shown in FIG. Color display is possible by combining dye-type and dye-type color filters.

FIG. 16 shows display colors in CIE chromaticity coordinates.

In addition, the area indicated by the dotted line in the same figure is a thin film transistor (T
PT) shows the range of color reproducibility of a color liquid crystal television. As can be seen from the figure, the range of color reproducibility of this example is equivalent to that of a TPT color liquid crystal television.

〔Effect of the invention〕

According to the present invention, since phase correction is performed in the entire wavelength range,
The background and display color can be made achromatic, so
This has the effect of allowing black and white and color display.

Furthermore, the use of optically biaxial crystals has the effect of improving viewing angle characteristics compared to conventional two-layer structure liquid crystal elements.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a liquid crystal element of the present invention, Figure 2 is a perspective view of a liquid crystal element in the prior art, Figure 3 is a diagram showing the polarization state of the liquid crystal element in the prior art, and Figure 4 is a liquid crystal element in the prior art. FIG. 5 is a diagram showing the viewing angle characteristics of the contrast ratio in the horizontal direction of the device. FIG. 5 is a diagram showing the viewing angle characteristics of the contrast ratio in the vertical direction of a liquid crystal device in the prior art. FIG. 6 is a diagram showing the wavelength dependence of transmitted light in the prior art. 7 is a diagram showing the display color and background color of the liquid crystal element in the present invention and CIE chromaticity coordinates, and FIG. Diagram showing wavelength dependence, No. 9
FIG. 10 is a diagram showing the viewing angle characteristics of the contrast ratio in the horizontal direction of the liquid crystal element in the present invention, FIG. 10 is a diagram showing the viewing angle characteristics of the contrast ratio in the vertical direction of the liquid crystal element in the present invention,
Figure 11 shows a conoscopic image of liquid crystal molecules; Figure 12 shows a conoscopic image of liquid crystal molecules;
The figure shows a conoscope image of a polycarbonate film, FIG. 13 shows the viewing angle dependence of the transmittance of a parallel alignment liquid crystal element and a polycarbonate film, and FIG. 14 shows a phase plate in the second embodiment of the present invention. The relationship between the angle formed by the stretching axis of the film and the contrast ratio, FIG. 15 is a diagram showing the display color and background color in the second embodiment of the present invention in CIE chromaticity coordinates, and FIG. 16 is a diagram showing the third embodiment of the present invention. Figure 17 is a diagram showing the wavelength dependence of phase difference, Figure 18 is a diagram showing the phenomenon of anomalous dispersion, and Figure 19 is a diagram showing the range of one display color in the example of CIE chromaticity coordinates. FIG. 3 is a diagram showing an absorption spectrum of polystyrene. 1.19...Upper polarizing plate, 2,13...Absorption axis of upper polarizing plate, 3...Optical biaxial crystal, 4...Stretching axis, 5゜22...Liquid crystal for driving upper electrode substrate of the element, 6;
14°16...Rubbing direction of upper substrate, 7,15,
17...Liquid crystal molecules, 8,25...Lower electrode substrate of driving liquid crystal element, 9,16.24...Rubbing direction of lower substrate, 10.26...Lower polarizing plate, 11 .18...
- Polarization axis of lower polarizing plate, ]-2, 27... Light source. Figure 1 Figure 2 Figure 3 Liquid crystal element for driving incident light polarizing plate Liquid crystal element for correction Polarizing plate Outgoing light 1... Upper polarizing plate 2... Absorption axis 3...・Optical biaxial crystal 4...Stretching axis 5...Upper electrode substrate 6...Upper rubbing direction 7...Liquid crystal molecules 8... ...Lower electrode substrate 9 ...Lower rubbing axis 10 ...Lower polarizing plate 11 ...Absorption axis 12 ...Light source linearly polarized light elliptical polarized light straight line Polarization diagram Diagram Diagram λ (nm) Diagram Left-right viewing angle Diagram Wavelength (nm) Diagram 1 O Diagram 11 Factors Diagram 12 Diagram Diagram Angle formed by stretching axis Diagram Diagram 15 Diagram Figure Wavelength (μ) Wave number (crn-')

Claims (1)

[Claims] 1. A nematic liquid crystal having positive dielectric anisotropy and added with an optically active substance is sandwiched between a pair of upper and lower electrode substrates arranged oppositely, and the thickness between the electrode substrates is A spiral structure is formed that is twisted in the horizontal direction, and the polarization axes or absorption axes of a pair of polarizing plates provided on both sides of the spiral structure are arranged at a predetermined angle with respect to the alignment direction of liquid crystal molecules of an adjacent electrode substrate. In the liquid crystal display device, one or more birefringent films are disposed on at least one of the polarizing plate and the electrode substrate, and the thickness d (μm) and the anisotropy of the refractive index of the birefringent film are determined. The product of the difference Δn, the wavelength dependence of the phase difference caused by Δn・d, and the wavelength dependence of the phase difference caused by Δn・d of the liquid crystal display element and the twist angle θ are approximately equal. A liquid crystal display device characterized by: 2. In the liquid crystal display device according to claim 1, the twist angle of the liquid crystal element is θ_1, and Δn·d is (Δn·
d)_1, Δn・d of the birefringent film (Δn・d)
_2, the wavelength of light is λ, and m is any integer, (
Δn・d)_2={(Δn・d)_1^2+λ^2(m
π^2+θ_1^2)-2mπλ^2(θ_1^2+(
Δn・d)_1^2/λ^2)^1^/^2^1^/
A liquid crystal display device characterized by approximately satisfying the relational expression ^2. 3. In the liquid crystal display device according to claim 1, two or more birefringent films having different wavelength dependencies of retardation are laminated, and the wavelength dependence of the retardation of the laminated birefringent films and the liquid crystal A liquid crystal display device characterized in that the wavelength dependence of the phase difference of the elements is approximately equal. 4. The liquid crystal display device according to claim 1, wherein the birefringent film is an optically biaxial crystal. 5. In the liquid crystal display device according to claim 4, when the polarizing plate is placed in a crossed nicol state, and a birefringent film is inserted therebetween so that its stretching axis is at 45 degrees with the absorption axis of the polarizing plate. . A liquid crystal display device, characterized in that the transmittance of the interference light is 0.6 or more in a 45 degree direction, when the direction perpendicular to the film is 1. 6. The liquid crystal display device according to claim 1, which is capable of displaying color by combining with a color filter.