JPH05289052A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which can obtain a stable black-and-white display having a modulation and a stable contrast. CONSTITUTION:In the liquid crystal display device 1 constituted by laminating a first polarizing plate 2, a first phase difference plate 3, a second phase difference plate 4, a liquid crystal display element 5 in which a supertwisted nematic liquid crystal 14 is interposed between a pair of transparency substrates 8, 9, a second polarizing plate 6, and a reflecting plate 7 for reflecting an incident light from the liquid crystal display element 5, in this order, retardation values of a first and a second phase difference plates 3, 4 are both set to 400nm-470nm, an intersection angle of a lagging axis of a first phase difference plate 3 and a lagging axis of a second phase difference plate 4 is set to 35 degrees - 55 degrees, and the producted. DELTAn of liquid crystal layer thickness (d) of the liquid crystal display element 5 and refractive index anisotropy DELTAn is set to 0.80-0.94.

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 of super twisted nematic type (hereinafter referred to as STN type) having a retardation plate as an optical compensating plate.

[0002]

2. Description of the Related Art In a reflection type STN type liquid crystal display device provided with a retardation plate as an optical compensation plate, a phase difference of one layer having a retardation value of about 560 nm is provided on the front surface (display surface) side of a liquid crystal display element. Only one retardation plate composed of layers is arranged, and d · Δn of the liquid crystal display element is 0.75 to 0.85.
Is. d is the thickness of the liquid crystal layer between the liquid crystal display element substrates, and Δn is the refractive index anisotropy of the liquid crystal display element.

[0003]

However, in the liquid crystal display device having the above-mentioned configuration and arrangement conditions, complete color correction is not performed, and the white color which is the background color when no voltage is applied is colored, resulting in a clear black-and-white display. , A large change in color tone due to temperature changes in the operating environment, stable contrast cannot be obtained with respect to temperature changes, and a large change in color tone due to variations in the liquid crystal display element thickness and retardation value of the retardation plate. I have a problem.

An object of the present invention is to solve the above problems and to provide a liquid crystal display device capable of obtaining a stable and stable monochrome display and a stable contrast.

[0005]

The present invention provides a first polarizing plate,
A first retardation plate, a second retardation plate, a liquid crystal display device in which a super twisted nematic liquid crystal is interposed between a pair of translucent substrates, a second polarizing plate, and a reflection plate for reflecting incident light from the liquid crystal display device. In the liquid crystal display device configured by stacking in this order, the retardation values of the first and second retardation plates are both 400 nm to 470 nm, and the slow axis of the first retardation plate and the second phase difference are The intersection angle with the slow axis of the plate is set to 35 to 55 degrees, and the product d · Δ of the liquid crystal layer thickness d of the liquid crystal display element and the refractive index anisotropy Δn.
The liquid crystal display device is characterized in that n is set to 0.80 to 0.94.

[0006]

According to the present invention, the retardation values of the first and second retardation films, the crossing angles of the slow axes of the first and second retardation films, and d · Δn of the liquid crystal display element are optimized. In the super twisted nematic liquid crystal display device, the background color tone when no voltage is applied is brighter and closer to an achromatic color, stable black and white display can be realized, and stable contrast against temperature change is also achieved. Can be obtained. Generally, in a liquid crystal display device, the retardation value of the retardation plate, the crossing angle of the slow axes of the retardation plate, and d · Δn of the liquid crystal display element act in association with each other. If the value is out of the defined range, stable black and white display cannot be obtained, and the background color is colored and the display color does not become black. The present invention provides optimum arrangement conditions for solving these problems.

[0007]

1 is a sectional view showing the structure of a liquid crystal display device 1 according to an embodiment of the present invention. The liquid crystal display device 1 is configured by laminating a first polarizing plate 2, a first retardation plate 3, a second retardation plate 4, a liquid crystal display element 5, a second polarizing plate 6, and a reflection plate 7 in this order. It The first and second polarizing plates 2 and 6 are
A neutral gray type polarizing plate having a single transmittance of 44.5% and a polarization degree of 97.8% is used. For example, F-1205DuN (trade name) manufactured by Nitto Denko Corporation is used.
The first and second retardation plates 3 and 4 are each made of a single layer of uniaxially stretched polymer film such as polycarbonate,
The thickness is about 50 μm and the retardation value is 400.
nm to 470 nm is used. The crossing angle of the slow axis of each retardation plate is set to 35 degrees to 55 degrees.

The liquid crystal display element 5 is composed of electrodes 10 and 11 made of ITO (indium tin oxide) or the like and polyimide or the like on opposite surfaces of a pair of translucent substrates 8 and 9 made of glass or plastic. The alignment films 12 and 13 are formed, and the liquid crystal 14 to which the levorotatory chiral substance is added is sealed between the translucent substrates 8 and 9. The twist angle of the liquid crystal molecule is 240 degrees, and d · Δn
(D is the thickness of the liquid crystal layer 14 and Δn is the refractive index anisotropy of the liquid crystal 14) = 0.80 to 0.94. The electrode formation pattern is segment type, simple matrix type,
Any of active matrix type may be used.

The reflection plate 7 is an omnidirectional reflection plate and is formed by forming a reflection film 16 made of aluminum or the like on the surface of the substrate 15 made of synthetic resin on the liquid crystal display element 5 side.

FIG. 2 is a view showing the arrangement conditions of the respective constituent members of the liquid crystal display device 1. In FIG. 2, an arrow P1 indicates the alignment axis of liquid crystal molecules of the transparent substrate 8 that constitutes the liquid crystal display element 5, and an arrow P2 indicates a transparent substrate 9 that constitutes the liquid crystal display element 5.
, The arrow P3 is the absorption axis of the first polarizing plate, the arrow P4 is the absorption axis of the second polarizing plate 6, the arrow P5 is the slow axis of the first retardation plate 3, and the arrow P6 is The slow axis of the second retardation plate 4 is shown respectively.

The angle α is the angle between the liquid crystal molecule alignment axis P1 of the transparent substrate 8 and the absorption axis P3 of the first polarizing plate 2.
The angle β is an angle formed by the liquid crystal molecule alignment axis P2 of the transparent substrate 9 and the absorption axis P4 of the second polarizing plate 6, and the angle γ is the liquid crystal molecule alignment axis P1 of the transparent substrate 8 and the first retardation plate. 3 slow axis P5
And the angle θ is the angle between the liquid crystal molecule alignment axis P1 of the transparent substrate 8 and the slow axis P6 of the second retardation plate 4,
The angle φ represents the twist angle of the liquid crystal molecules.

In this embodiment, α = 45 degrees, β = 50 degrees,
γ = 115 degrees, θ = 70 degrees, and φ = 240 degrees. Therefore, the angle formed by the slow axis P5 and the slow axis P6 is 45 degrees.

3 and 4 are graphs showing the measurement results of the viewing angle characteristics of the liquid crystal display device 1. FIG. 3 shows the viewing angle characteristics of the liquid crystal display device in the 12: 00-6: 00 direction.
Shows the viewing angle characteristics of the liquid crystal display device in the 9: 00-3: 00 direction. The viewing angle characteristic is a change in contrast with a change in viewing angle. The visual angle is the inclination angle of the visual line from the normal direction of the display surface of the display device. In FIG. 3, the solid line L1 indicates the viewing angle characteristics of the liquid crystal display device 1, and the broken line L2 indicates the viewing angle characteristics of the conventional liquid crystal display device. In FIG. 4, the solid line L3
Indicates the viewing angle characteristics of the liquid crystal display device 1, and the broken line L4 indicates the viewing angle characteristics of the conventional liquid crystal display device. The liquid crystal display device has a 1/200 duty, 1
It was driven with a / 13 bias.

As can be seen from FIGS. 3 and 4, the liquid crystal display device 1 of the present embodiment has a very good contrast and a good viewing angle characteristic as compared with the conventional liquid crystal display device.

Table 1 below shows the comparison result of the brightness of the background color of each liquid crystal display device of this embodiment and the prior art.

[0016]

[Table 1]

Here, the brightness (L *) of the background color is CI
E1976L * a * b * display system (JIS Z8729-
(1980)) is a uniform perceptual color space and is defined by the following equation.

[0018]

[Equation 1] L * = 116 (Y / Yo) ¹ / 3-16

[0019]

[Expression 2] a * = 500 [(X / Xo) ¹ / 3- (Y / Yo) ^1/3 ]

[0020]

## EQU3 ## b * = 200 [(Y / Yo) ¹ / 3- (Z / Zo) ^1/3 ] where Xo, Yo, and Zo are tristimulus values of standard light used for illumination. , X, Y, and Z are tristimulus values of the target object, and L * is a quantity representing lightness.

As described above, the liquid crystal display device 1 of this embodiment
It can be seen that has a higher brightness and a brighter background color than the conventional liquid crystal display device. That is, a clear black and white display can be obtained.

In this embodiment, two retardation plates each composed of one retardation layer are laminated, but one retardation plate composed of two retardation layers may be used.

[0023]

As described above, according to the present invention, in the reflection type super twisted nematic type liquid crystal display device, the color tone of white, which is the background color when no voltage is applied, is made an achromatic color. It is possible to provide a liquid crystal display device that realizes a certain monochrome display and high contrast.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a liquid crystal display device 1 which is an embodiment of the present invention.

FIG. 2 is a diagram showing an arrangement condition of each component of the liquid crystal display device 1.

FIG. 3 is a graph showing measurement results of viewing angle characteristics of the liquid crystal display device 1.

FIG. 4 is a graph showing measurement results of viewing angle characteristics of the liquid crystal display device 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 1st polarizing plate 3 1st retardation plate 4 2nd retardation plate 5 Liquid crystal display element 6 2nd polarizing plate 7 Reflector plate 8 and 9 Translucent substrate 10 and 11 Electrode 12 and 13 Alignment film 14 Liquid crystal P1 Liquid crystal molecule alignment axis of transparent substrate 8 P2 Liquid crystal molecule alignment axis of transparent substrate 9 P3 Absorption axis of first polarizing plate P4 Absorption axis of second polarizing plate P5 Slow axis of first retardation plate P6 Slow axis of second retardation plate α Angle formed by liquid crystal molecule alignment axis P1 and absorption axis P3 β Angle formed by liquid crystal molecule alignment axis P2 and absorption axis P4 γ Liquid crystal molecule alignment axis P1 and first retardation plate 4 Slow axis P5
Angle θ between the liquid crystal molecule alignment axis P1 and the slow axis P6 of the second retardation plate 4.
Angle formed by φ and twist angle of liquid crystal molecule

Claims (1)

[Claims] 1. A first polarizing plate, a first retardation plate, a second retardation plate, a liquid crystal display element in which a super twisted nematic liquid crystal is interposed between a pair of transparent substrates, a second polarizing plate, and the liquid crystal display. In a liquid crystal display device configured by laminating a reflection plate that reflects incident light from an element in this order, the retardation values of the first and second retardation plates are both 400 nm to 470 nm, and the first retardation plate is Of the liquid crystal layer thickness d of the liquid crystal display element and the refractive index anisotropy Δn are set to 35 ° to 55 °, and the product of the liquid crystal layer thickness d and the refractive index anisotropy Δn is set to 35 ° to 55 °. A liquid crystal display device, wherein Δn is set to 0.80 to 0.94.