JP2000221486A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display device having ligitness and high color purity in the case of any of transmission and reflection type ones by disposing a 2nd color filter between a semi-transmissive reflecting layer or a semi-transmissive reflecting plate and a light source. SOLUTION: A 2nd color filter 61 is disposed between a semi-transmissive reflecting plate 40 and a backlight 70 besides a conventional color filter 13. When the resulting device is used as a reflection type one, the color filters function as filters having good spectral characteristics because outside light passes the 1st color filter 13 two times. In the case of use as a transmission type one, filter performance is exhibited as the product of a spectral characteristic of the 2nd color filter 61 and a spectral characteristic of the 1st color filter 13. If the same color filter as the 1st color filter 13 is used as the 2nd color filter 61, the two filters function as a filter having the same spectral characteristics as a reflection type one and high color purity is attained even in transmission.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called transflective liquid crystal display element which can be used in both a reflection type and a transmission type.

[0002]

2. Description of the Related Art Transflective monochrome liquid crystal panels are widely used in portable small information devices such as mobile phones. on the other hand,
The development of reflective color panels for low power consumption is also active. The application of the reflective color panel is mainly considered to be a small personal information device. It has been considered to use a transflective color panel for the reflective type, but it is difficult to obtain high display quality for both applications because the optical design of the color filter differs greatly between the reflective type and the transmissive type. there were.

That is, in a reflection type color panel, brightness is given the highest priority, and accordingly, the average transmittance of a color filter is set to be higher. Furthermore, in the reflection type, since the incident external light passes through the color filter twice, it is necessary to set the average transmittance of the color filter to be high to secure the brightness. On the other hand, in the transmission type, light passes through the color filter only once, so that the average transmittance of the filter is set to be low in order to obtain a sufficient filtering effect. Therefore, when a color filter optimized for reflection is used in transmission, sufficient color purity cannot be obtained. Conversely, there is a problem that the color filter optimized for transmission does not have sufficient brightness at the time of reflection.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems encountered in the conventional transflective color liquid crystal display device, and is bright in both the transmissive and reflective types and has high color purity. It is an object to provide a liquid crystal display element.

[0005]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal cell, a transflective plate behind the liquid crystal cell, a light source for illuminating the liquid crystal cell from behind (hereinafter also referred to as a backlight), and the liquid crystal. In a liquid crystal display device including at least a color filter (hereinafter, referred to as a first color filter) in a cell, a second color filter is provided between the transflective layer or the transflector and a light source. The above problem was solved by providing a liquid crystal display element characterized by being provided.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view of a conventional transflective liquid crystal display device. Liquid crystal layer 1 sandwiched between glass substrates 11 and 12
5 are formed. 21 and 22 are transparent electrodes for applying a voltage to the liquid crystal layer, 31 and 32 are polarizing plates provided as needed, 50 is an optical element such as a retardation plate provided as needed, 13 is a color filter, 40 is a transflective plate, and 80 is a backlight unit. The transflective plate 40 reflects a part of the incident light and transmits the other, and is known as a thin metal film or a hologram sheet having polarization selectivity in reflection characteristics.

When external light enters such an element from the polarizing plate 32 side, the light reflected by the reflecting plate passes through the color filter twice. On the other hand, when the backlight unit 80 is turned on and used in the transmission mode, light passes through the filter only once. In the reflection mode, it is necessary to use a color filter having a higher transmittance than that used in the transmission type in consideration of transmitting through the color filter twice and minimizing light loss due to the filter. FIGS. 2 and 3 show examples of the spectrum of light transmitted through such a reflection mode color filter. FIG. 2 shows a case where light passes through only once, and FIG. 3 shows a case where light is transmitted twice.
From these figures, it can be seen that a color filter designed for reflection can obtain only extremely low color purity during transmission.

FIG. 4 is a schematic sectional view of an example of the liquid crystal display device of the present invention. In the present invention, the conventional color filter 1
In addition to 3, a second color filter 61 is provided between the transflective plate 40 and the backlight 70. In this configuration, when the element is used as a reflection type, external light transmits twice through the first color filter 13 so that the color filter functions as a filter having spectral characteristics as shown in FIG. When used as a transmission type, the performance of the filter is expressed as the product of the spectral characteristics of the second color filter and the spectral characteristics of the first color filter. For example, when the same color filter as the first color filter is used as the second color filter, the two filters function as a filter having the spectral characteristics shown in FIG. 3, and high color purity can be obtained even when transmitted. it can.

In FIG. 4, the second color filter 61 is
First color filter 13 and substrate 11, polarizing plate 31,
It is arranged via the reflection slope 40. In such an arrangement, when the light from the light source is diffused light, color mixing may occur. Reference numeral 80 in FIG. 4 denotes an optical unit provided to prevent such color mixing and for concentrating the optical path of the illumination light in a specific direction. The optical means 80 functions to specify the light of the illumination light in the direction of the observer, and to reduce the light transmitted through filters of different colors among the light emitted from the light source. As such an element, a triangular fine prism is formed.
Preferred examples include a brand name BEF, a microlouver, and a microlens group manufactured by Company M.

[0010] A forward scattering layer 90 can also be provided. The forward scattering layer 90 has a function of diffusing the light transmitted through the liquid crystal cell, and thus a wide viewing angle can be obtained even with the above-mentioned collected illumination light, which is preferable. As the forward scattering layer 90, a composite of a resin and fine particles, an embossed resin film, or the like can be used. Although the forward scattering layer is provided on the uppermost layer in this drawing, it may be provided below the polarizing plate or the phase difference plate 50.

Reference numeral 62 denotes a black mask provided between pixels, which is provided to obtain higher color purity during transmission. In general, when a black mask is used in a reflection type, the black mask lowers the reflectance, so that the black mask is generally not used with priority given to brightness. However, with such a configuration, the color purity is reduced even during transmission. FIG.
In the example, the black mask is formed only on the second color filter. Therefore, the black mask hardly functions at the time of reflection, and a bright display is obtained. At the time of transmission, the black mask functions as a black mask to obtain high color purity.

The material of the black mask is Cr, A
For example, a resin layer containing a metal such as l, a black pigment or a dye can be exemplified. Although the position of the black mask is provided in the same plane as the second color filter on the back surface of the transflective plate in this example, it may be any position between the transflective plate and the liquid crystal layer.

FIG. 5 shows another configuration example of the liquid crystal display device of the present invention. In this embodiment, the first color filter 13 and the second color filter 61 are formed between the substrates 11 and 12, and the transflective layer 4 is disposed between the two filters.
0 is formed. In this example, since the second color filter is disposed close to the first color filter, it is preferable that color mixing of light from the light source does not occur. Further, an optical unit for focusing the optical path of the illumination light in a specific direction as shown by 80 in FIG. 4 can be provided. Further, a forward scattering layer similar to that shown by 90 in FIG. 4 can be provided. In particular, in the present configuration, since providing a diffuser performance to the reflector increases the number of steps, a configuration in which the reflector is a mirror surface and a forward scattering layer is provided is particularly preferably used. Further, similarly to the first example, the black mask 61 can be provided on the back side of the transflective plate.

The display method that can be used in the liquid crystal display element of the present invention is not particularly specified, and in the first example, all conventionally known display methods can be used. Also,
In the second example, a display method in which one or more polarizing plates are not used is preferably used. In addition, an optical element such as a phase difference plate can be used as necessary.

The color filter which can be used in the liquid crystal display device of the present invention is not particularly limited, and a color filter formed by a conventionally known method such as a dyeing method, a pigment dispersion resist method, a printing method, an electrodeposition method, and a transfer method. A filter can be used. The color filter may be a single color or a plurality of colors.

The average transmittance (simple average in the visible wavelength region) of the first color filter is preferably from 40% to 80%, more preferably from 50% to 70%. If the transmittance is low, the display becomes dark during reflection display, and if it is too high, the color purity becomes insufficient. The average transmittance of the second color filter is preferably from 30% to 80%, more preferably from 40% to 70%. If the transmittance is low, it is necessary to increase the luminance of the backlight in order to obtain sufficient luminance, which leads to an increase in power consumption, which is not preferable. If it is too high, the color purity will be insufficient.
An auxiliary layer such as an overcoat may be formed on the color filter as needed. Further, the spectral transmittance and the average transmittance of the color filter may be different between the first filter and the second filter. For example, the spectral transmittance can be varied depending on the spectral characteristics of the liquid crystal layer and the polarizing plate backlight.

As a substrate that can be used, a light-transmitting glass, a resin plate, or a resin film can be used. In particular, in the configuration example 1, the first color filter and the second color filter are preferably arranged close to each other, and a resin plate or a resin film, which can be easily thinned, particularly a resin film may be used as the lower substrate. preferable.

[0018]

Embodiments of the present invention will be described below.

Example 1 A display element shown in FIG. 4 was manufactured using a glass substrate having a thickness of 0.4 mm. As the color filters 13 and 61, color filters having transmission characteristics shown in FIG. 2 were used. Pixel electrodes are 0.3mm pitch, gap between electrodes is 30
It was formed on the pixel electrode 13 in a stripe shape of μm. The display method was STN, and color compensation was performed by the phase plate 32. For the reflector 40 and the lower polarizer 31, a transflector WTM1 with a polarizer manufactured by Sanritz was used, and for the upper polarizer, LLC29818 of the company was used. A hot-cathode tube is used for the backlight.
MEF BEF was placed. This display element had good contrast and color purity both at the time of reflection and at the time of transmission.

Comparative Example 1 An element was produced in Example 1 without providing a second filter. In this device, good contrast was obtained when used in a reflection type, but the color purity was extremely reduced in a transmission type display with a backlight lit.

Example 2 A display element shown in FIG. 4 was prepared using a resin film mainly composed of polycarbonate having a thickness of 0.1 mm. As the color filters 13 and 61, color filters having transmission characteristics shown in FIG. 2 were used. The pixel electrode is 0.1
It was formed on the pixel electrode 13 in a stripe shape with an mm pitch and a gap between electrodes of 10 μm. The display method was STN and color compensation was performed by the phase plate 32. Other configurations were the same as in the first embodiment. In this display element, good contrast and color purity were obtained both in reflection and in transmission even though the pitch was finer than in Example 1.

Example 3 In Example 2, a light-shielding layer (black mask) made of a photoresist in which a black pigment was dispersed was formed between the filters of the second filter. This device had the same display as that of Example 2 at the time of reflection, but the color purity at the time of transmission was improved.

Example 4 In Example 3, the light-shielding layer was formed of Al. This device had excellent display similar to that of Example 3 in transmission, and further improved brightness in reflection.

Example 5 A display element shown in FIG. 5 was manufactured using a glass substrate having a thickness of 0.4 mm. As the color filters 13 and 61, color filters having transmission characteristics shown in FIG. 2 were used. Pixel electrodes are 0.1mm pitch, gap between electrodes is 10
It was formed on the pixel electrode 13 in a stripe shape of μm. The display method was STN, and color compensation was performed by the phase plate 32. A semi-transmissive film was formed on the reflector 40 by Al evaporation. LLC29818 manufactured by Sanritz was used as the upper polarizing plate. A hot cathode tube was used for the backlight. The black mask 62 was formed by patterning an Al film. On the uppermost surface of the device, a forward scattering plate in which titanium oxide was dispersed in a resin was provided. This display element provided good contrast and color purity both in reflection and transmission, and had a wider viewing angle.

[0025]

[Effect] 1. (1) A liquid crystal display element capable of performing bright display in reflective display and high color purity in transmissive display can be provided. 2. Claim 2 It is possible to provide a liquid crystal display element capable of performing display with higher color purity without lowering of color purity due to light leakage. 3. According to the third aspect of the present invention, it is possible to provide a liquid crystal display element capable of obtaining a brighter display at the time of reflective display. 4. (4) A liquid crystal display element capable of displaying a color purity with little color mixture even when the first color filter and the second color filter are separated from each other can be provided. 5. Claim 5 It is possible to provide a liquid crystal display element capable of performing high-color-purity display with little color mixing and a wide viewing angle even when the first color filter and the second color filter are separated. 6. A sixth aspect of the present invention provides a liquid crystal display device having a wide viewing angle and high color purity without color mixing by two filters even in transmissive display.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a conventional transflective liquid crystal display device.

FIG. 2 is a diagram illustrating a spectrum of light when light passes through a color filter for a reflection mode only once.

FIG. 3 is a diagram illustrating a spectrum of light when transmitted twice through a color filter for a reflection mode.

FIG. 4 is a schematic sectional view of an example of the liquid crystal display device of the present invention.

FIG. 5 is a schematic sectional view of another example of the liquid crystal display device of the present invention.

[Explanation of symbols]

7 First Color Filter 11 Glass Substrate 12 Glass Substrate 13 First Color Filter 15 Liquid Crystal Layer 21 Transparent Electrode for Applying Voltage to Liquid Crystal Layer 22 Transparent Electrode for Applying Voltage to Liquid Crystal Layer 31 Polarizer 32 Polarization Plate 50 Optical element such as retardation plate 40 Transflective plate 61 Second color filter 62 Black mask provided between pixels 80 Optical means 90 provided to prevent color mixing, which concentrates the optical path of illumination light in a specific direction 90 Forward scattering layer

Claims (6)

[Claims] 1. A liquid crystal cell, a transflective plate behind the liquid crystal cell, a light source (hereinafter, also referred to as a backlight) for illuminating the liquid crystal cell from behind, and a color filter (hereinafter, referred to as a backlight) inside the liquid crystal cell. A liquid crystal display device comprising at least a first color filter) and a second color filter provided between the transflective layer or the transflector and the light source. 2. The liquid crystal display device according to claim 1, further comprising a light-shielding layer for preventing light from leaking from a gap of the second color filter. 3. The liquid crystal display device according to claim 2, wherein the light shielding layer is provided between the transflective plate and the liquid crystal layer. 4. The liquid crystal display device according to claim 1, further comprising an optical unit for focusing an optical path of illumination light of the backlight in a specific direction. 5. The liquid crystal display device according to claim 4, further comprising a forward scattering layer. 6. The liquid crystal display device according to claim 1, wherein the first color filter and the second color filter are provided in a liquid crystal cell.