JPH04308814A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a high-contrast display at the time of multiplex driving by matching the light emission wavelength of an illuminating means with the wavelength to minimize the threshold value characteristic of the voltage-to- transmittance characteristic of a liquid crystal. CONSTITUTION:Oriented films are applied on transparent electrode patterns and are subjected to an orientation treatment. Light transparent base materials 1a and 1b are stuck to each other by using a sealing material 2 to form a cell and a liquid crystal is injected therein. Further, polarizing plates 3a and 3b are stuck respectively to the surfaces of the light transmissive base materials 1a and 1b on the side opposite from the surfaces formed with the transparent electrode patterns. The illuminating means 4 is provided on the outer side of the one polarizing plate. The light transparent base material 1b positioned on at least the illuminating means 4 side is formed of a transparent plastic film. The illuminating means having the light emission wavelength coinciding with the wavelength to minimize the sharpness of the liquid crystal panel 5 is selected by taking the dependency of the sharpness on the light source in consideration and is used for the illuminating means 4.

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, and more particularly to a liquid crystal display device capable of providing high contrast.

0002

[Prior Art] Conventionally, liquid crystal is sealed in a space formed by a substrate and a peripheral seal to form a liquid crystal cell, transparent electrodes and alignment films are formed on the inner surface of the substrate, and illumination means is provided on the outside of a polarizing plate. A transmissive liquid crystal display device is known.

[0003] JP-A-2-135315 discloses that the liquid crystal display device uses illumination means having emission wavelengths around 450 nm and 560 nm, where the change in transmittance is maximum when voltage is applied to the liquid crystal cell. are doing.

0004

[Problems to be Solved by the Invention] In the conventional liquid crystal display device, when the device is statically driven, it is possible to apply a voltage to the liquid crystal with a sufficiently large on/off potential difference, and the lighting Since the emission wavelength of the means is set to the wavelength at which the change in transmittance is maximum when a voltage is applied to the liquid crystal cell, the obtained contrast is large.

However, when a liquid crystal display device is multiplex driven, it is not possible to arbitrarily set the driving voltage, so even if the conventional device is used, a high contrast cannot necessarily be obtained.

The present invention is intended to solve the above-mentioned problems, and its purpose is to provide a liquid crystal display device that can provide high contrast even when driven in multiplex mode.

[0007]

[Means for Solving the Problems] The liquid crystal display device of the present invention comprises a liquid crystal cell in which a liquid crystal is sandwiched between transparent substrates having transparent electrode patterns formed on opposing surfaces; In a liquid crystal display device in which polarizing plates are disposed on both outer sides, an illumination means is provided on one outside of the polarizing plate, and the emission wavelength band of the illumination means is such that the light emission wavelength range corresponds to the transmission when a voltage is applied to the liquid crystal cell. It is characterized by matching the wavelength band in which the sharpness of the rate change is minimum.

The present invention will be explained below using the drawings. FIG. 2 shows a voltage versus transmittance curve obtained by static driving using a conventional liquid crystal display device. Here, VON and VOFF represent the voltages applied to the liquid crystal, TON and TOFF represent the transmittance at VON and VOFF, respectively, and the contrast obtained is TOFF/TON. Further, the emission wavelength of the illumination means is set to a wavelength at which a change in transmittance when a voltage is applied to the liquid crystal cell becomes maximum.

In the characteristic curve, the voltage when the transmittance changes by 10% is V10, and the voltage when the transmittance changes by 90% is V90.
Then, the threshold characteristic (sharpness: γ) is V90
/V10. However, since this value varies greatly depending on the liquid crystal material used, it is an important parameter for selecting a liquid crystal material. The smaller the value, the better the multiplexability. In other words, high duty ratio display is possible.

By the way, it has been found that the sharpness value changes depending on the wavelength of the light source. As shown in Table 1,
Depending on the three types of light sources used, the sharpness values obtained from the measurement results of the voltage versus transmittance curve of the test liquid crystal cell differ. Measurements are performed by applying a 128 Hz square wave.

[0011]

[Table 1]

[0012] The measuring device is configured to be able to measure voltage versus transmittance characteristics using a diopter-corrected light receiving element. The dependence of the obtained sharpness on the light source wavelength is considered to be due to the applied voltage of the spectral distribution characteristics of the liquid crystal.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of the structure of a liquid crystal display device according to the present invention. 1a and 1b are translucent base materials on which transparent electrode patterns (not shown) are formed on mutually opposing surfaces. An alignment film (not shown) is coated on the transparent electrode pattern for alignment treatment. The translucent base materials 1a and 1b are bonded together using the sealing material 2 to form a cell, and a liquid crystal (not shown) is attached.
is injected into the cell. Polarizing plates 3a are provided on opposite surfaces of the transparent electrode pattern forming surfaces of the transparent substrates 1a and 1b, respectively.
, and 3b are attached, and furthermore, an illumination means 4 is provided on the outside of one of the polarizing plates. At this time, it is preferable to use a transparent plastic film as at least the light-transmitting base material 1b located on the illumination means 4 side in order to improve display quality. The illumination means 4 is selected so that its emission wavelength matches the wavelength at which the sharpness of the liquid crystal panel 5 is minimized by considering the dependence of sharpness on the light source shown in Table 1 above.

When the liquid crystal display device is driven in a multiplex manner, the voltage versus transmittance curves obtained are shown separately into two curves, one for selection and one for non-selection, as shown in FIG. Here, for example, the contrast at the driving voltage Vop is obtained from the transmittance TNS and TS as TNS/TS. As described above, in the case of multiplex driving, even if an illumination means having a wavelength at which the change in transmittance is maximum is used, as seen in the conventional liquid crystal display device, the contrast does not necessarily increase.

However, if the liquid crystal display device of the present invention is used, the TNS
/TS can be increased, and high contrast can be obtained.

[0016]

[Effects of the Invention] (1) The liquid crystal display device of the present invention matches the emission wavelength of its illumination means with the wavelength that minimizes the threshold characteristic (sharpness) of the voltage versus transmittance characteristic of the liquid crystal. , a high-contrast display can be obtained, especially during multiplex driving.

(2) Furthermore, by using a transparent plastic film as at least one of the light-transmitting substrates, display quality with excellent visual characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a configuration example of a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing a voltage versus transmittance curve obtained when a conventional liquid crystal display device is statically driven.

FIG. 3 is a diagram showing a voltage versus transmittance curve obtained when the liquid crystal display device of the present invention is multiplex driven.

[Explanation of symbols]

1a, 1b Translucent base material 2 Seal material 3a, 3b Polarizing plate 4. Illumination means 5. LCD panel

Claims (3)

[Claims] 1. A liquid crystal display comprising a liquid crystal cell in which a liquid crystal is sandwiched between transparent substrates having transparent electrode patterns formed on opposing surfaces, and polarizing plates arranged on both outsides of the liquid crystal cell. In the device, an illumination means is provided outside one of the polarizing plates, and the emission wavelength of the illumination means coincides with a wavelength band in which the sharpness of a change in transmittance when a voltage is applied to the liquid crystal cell is minimized. A liquid crystal display device characterized by: 2. The liquid crystal display device according to claim 1, wherein at least one of the light-transmitting substrates is a plastic film. 3. The liquid crystal display device according to claim 1, wherein the device is multiplex driven.