JPH10339871A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display device capable of reproducing a bright and vivid red color and realizing natural full color display. SOLUTION: In this reflection type liquid crystal display device; a reflection electrode is formed on either of a pair of base plates opposed by putting a liquid crystal layer in between, and a light transmissive counter electrode and a color filter are formed on the other. On the condition of a light source being D65 and visual field being 2 deg., the color filter has a red color filter transmitting light whose chromaticity coordinates (x, y) in an XYZ color coordinate system chromaticity diagram satisfies expressions 0.37<=x<=0.43 and 0.28<=y<=0.32. Thus, a hue is prevented from being changed and the bright red color with good visibility is reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device having a small size and low power consumption, and more particularly to a color type reflection type liquid crystal display device which reproduces red light which is bright and has good visibility.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device has been used as a display of information terminal equipment. This liquid crystal display device includes a transmission type in which a backlight system as a light source is mounted and enables bright display, and a reflection type in which display is performed by reflecting ambient light.

[0003] The above-mentioned transmission type liquid crystal display device has a problem that it can display brightly, but has a large weight and a large power consumption because it has a backlight. On the other hand, the reflection-type liquid crystal display device has the advantage of light weight and low power consumption because it is not necessary to use a backlight. Therefore, the reflection type liquid crystal display device is widely used especially for a display of a portable information terminal device.

By the way, as a reflection type liquid crystal display device,
Many monochrome display devices such as TN and STN modes have been put to practical use. Also, to realize colorization,
A reflective liquid crystal display device in which each pixel is provided with an RGB micro color filter is also under development.

In general, in a reflection type liquid crystal display device, since ambient light passes through a color filter twice, if a color filter used in a transmission type liquid crystal display device is applied as it is, the light transmittance is reduced. Is extremely reduced, and the display becomes dark. for that reason,
Color filters used in conventional reflective liquid crystal display devices are:
Those having high light transmittance were used.

As a specific example, the wavelength-transmittance characteristics of a red color filter used in transmission type and reflection type liquid crystal display devices will be described. In FIG. 10, reference numeral 61 denotes a color filter used in a transmission type liquid crystal display device,
Reference numeral 2 corresponds to a color filter used in a reflection type liquid crystal display device.

As can be seen from FIG. 10, a red color filter used in a transmission type liquid crystal display device efficiently absorbs light in a wavelength region of 580 nm or less, whereas a red color filter used in a reflection type liquid crystal display device. Has a higher transmittance of light in a wavelength region of 580 nm or less than a red color filter used in a transmission type liquid crystal display device.

[0008]

In such a color filter used in a conventional reflection type liquid crystal display device, the transmittance of light in a wavelength region of 580 nm or less is simply improved in order to secure brightness. Therefore, there is a problem that the hue is slightly changed. Such a change in hue occurs in any of the red, green, and blue color filters, and red changes in the orange direction, green changes in the yellow-green direction, and blue changes in the cyan direction. In addition, the white color displayed by the additive color mixture also becomes a display with a yellowish or bluish tint. In particular, the reddish-tinged orange has caused a marked decrease in visibility.

Further, when performing full-color display,
Since the color balance is destroyed due to the change in the hue of red, green, and blue, a desired display color cannot be reproduced, resulting in a decrease in display quality.

The reason why such a change in hue occurs will be described with reference to a red color filter as an example.

In a red color filter as shown in FIG. 10B, in order to improve transmittance, a green wavelength region (around 540 nm) and a blue wavelength region (450 nm) are used.
m), the hue is slightly shifted in the green and blue directions.
The shift in the blue direction is hardly considered, but the shift in the green direction is recognized as red with a yellow tint, and as a result, the hue changes in the orange direction and is recognized.

The above-described change in hue was particularly noticeable in red and white.

The present invention has been made in view of the above problems, and has as its object to provide a reflection type liquid crystal display device capable of suppressing a change in hue and performing color display with good visibility. Is what you do.

[0014]

According to a first aspect of the present invention, there is provided a reflective liquid crystal display device in which a reflective electrode is formed on one of a pair of substrates opposed to each other with a liquid crystal layer interposed therebetween, and a light-transmitting opposing substrate is formed on the other. In a reflective liquid crystal display device in which electrodes and three color filters of red, green, and blue are formed, a D ₆₅ light source and 2
The light whose chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram satisfy the respective expressions of 0.37 ≦ x ≦ 0.43 and 0.28 ≦ y ≦ 0.32 under the condition of the visual field. And a red color filter that transmits light.

Since the transmittance of the light satisfying the above-mentioned equations is suppressed to a low value in the green wavelength region, it is possible to prevent a change in hue and to prevent the light in the blue wavelength region from being transmitted. Since the ratio is large, it is possible to reproduce red with good visibility without deteriorating brightness.

In the above-mentioned reflection type liquid crystal display device,
The chromaticity coordinates (x, y) in the white XYZ color system chromaticity diagram obtained by the additive color mixture of the color filter are:
0.28 ≦ x ≦ 0.31, and 0.29 ≦ y ≦ 0.33
If the green and blue color filters are set so as to satisfy the following equations, white without color can be reproduced.

Furthermore, 0.29 ≦ x ≦ 0.33 and 0.
A green color filter that transmits light satisfying each of the following expressions: 37 ≦ y ≦ 0.43; 0.17 ≦ x ≦ 0.22; and x
+ 0.04 ≦ y ≦ x + 0.08, by having a blue color filter that transmits light satisfying the respective expressions, it is possible to prevent a change in hue for green and blue, and to provide good visibility. It becomes possible to reproduce green and blue.

In particular, when performing full-color display,
The color balance does not collapse due to the change in the hue of red, green, and blue, and a desired color can be reproduced.

[0019]

Embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 6 is a sectional view of a reflection type liquid crystal display device 30 according to an embodiment of the present invention. The TFT 40 is formed on one substrate 31 using a known technique. Further, here, the uneven organic insulating films 42a, 4a
2b is formed, and the TFT 4 is formed through the contact hole 43.
The reflection electrode 38 was formed so as to be electrically connected to 0. Further, an alignment film 44 is formed thereon.

The structure of the opposite substrate, which is the other substrate, is as follows. A color filter 46 is provided on the substrate 45.
Are formed. The color filter 46 is provided on the substrate 31.
Any of red, green and blue color filters 46a is formed in a region corresponding to the reflective electrode 38, and a black filter 46b is formed in a region not corresponding to the reflective electrode 38. A protective film (not shown) is formed on the entire surface of the color filter 46, a transparent electrode 47 made of ITO or the like is formed thereon with a thickness of 150 nm, and an alignment film 48 is further formed thereon.

The substrate 45 having the above-described configuration and the substrate 31
Is bonded so that the position of one of the red, green, and blue filters and the reflective electrode 38 coincide with each other.

As the liquid crystal layer 49, for example, a guest-host liquid crystal mixed with a black dye (trade name: ZLI-
2327), an optically active substance (manufactured by Merck, trade name S8)
11) is used in which 4.5% is mixed. In the present embodiment, the liquid crystal layer 49 is formed using a liquid crystal having electro-optical characteristics as shown in FIG.

Ideally, the liquid crystal layer should have optical characteristics such that the reflectance in the dark state is lower and the reflectance in the bright state is higher. In particular, when the reflectance in the dark state is 15% or less, a color display with high contrast and high saturation can be realized. If the reflectance in the bright state is 40% or more, three color filters can be applied.

In this embodiment, the guest-host liquid crystal is used for the liquid crystal layer. However, if the reflectance in the dark state and the light state is at the above-mentioned level, another liquid crystal requiring a polarizing plate such as TN or STN may be used. You may use it.

Next, the structure of the color filter 46 will be described. As described above, the color filter 46 includes red, green, and blue color filters 46a that form color pixels.
And a black filter 46b forming a light shielding portion.

FIG. 1 shows a spectral transmittance characteristic 11 of a red color filter used in the present embodiment and a spectral transmittance characteristic 12 of a red color filter used in a conventional reflection type liquid crystal display device. is there. As can be seen from this figure, the transmittance of light in the green wavelength region is suppressed and the transmittance of light in the blue wavelength region is higher than that of the conventional red color filter. 1 in FIG.
When the spectral transmittance characteristic indicated by 2 is represented by chromaticity coordinates (x, y), it is (0.392, 0.301). The measurement of spectral transmittance of the color filter using the micro color analyzer (manufactured by Otsuka Electronics Co., Ltd.), measurement conditions 2 illuminant D ₆₅
° Measured by the transmittance of the visual field. The transmittance was 7059.
The light transmittance of glass (manufactured by Corning) was determined as 100%.

Here, the D ₆₅ light source and the 2 ° visual field will be described. The _D65 light source is the same as the light illuminated by daylight and is used for measuring the object color.
Has a wavelength component as shown in FIG. Note that this D
_{The 65} light sources are CIE and ISO reference lights. In addition, the 2 ° visual field means that the human eye is 1 ° to 1 ° as shown in FIG.
It is the feeling when recognizing things at a viewing angle of 4 °. As shown in FIG. 9B, the sensation when recognizing an object at a viewing angle greater than 4 ° is called a 10 ° viewing angle. These sensations are all provided to standardize human color sensation.

Next, a voltage was applied to the reflective electrode corresponding to the red color filter, and the brightness of the display screen and the red visibility were examined. The red color filter used in the reflection type liquid crystal display device of the present embodiment has a reduced transmittance of light in a green wavelength region and a reduced light transmittance in a blue wavelength region as shown in FIG. Since the transmittance was large, the hue could be prevented from changing to orange, and red with good visibility could be reproduced. Also,
Since the transmittance of light in the blue wavelength region is large,
By suppressing the transmittance of the light in the green wavelength region, the overall transmittance was reduced, and it was possible to prevent the brightness from being impaired, thereby achieving a bright display.

As described above, in order to obtain a bright and highly visible red color, a color filter that transmits light in the hatched area of FIG. 2 in the XYZ color system chromaticity diagram may be used. That is, 0.37 ≦ x ≦ 0.43 and 0.28 ≦
Any color filter that transmits light that satisfies each of the expressions y ≦ 0.32 may be used.

If x is smaller than this area, the display color becomes pale and blurred. Also, when x becomes large, a bright red color can be displayed, but the display becomes dark, which is not suitable for a reflective liquid crystal display device.

If the value of y deviates from the above-mentioned area, the color tone balance will be lost, and it will not be suitable for full-color display. In particular, when the value of y increases, the hue changes to orange, which is noticeably recognized, and the visibility decreases.

The red color filter is XY.
Of the tristimulus values in the Z color system, the value of Y at the time of reflection is 4
If it is 0 or more and 65 or less, sufficient brightness can be obtained.

(Embodiment 2) In a reflection type liquid crystal display device having the same configuration as that of Embodiment 1, the spectral characteristics of the green and blue color filters are changed by using the red color filter used in Embodiment 1. The white color obtained by these additive color mixing is represented by chromaticity coordinates (x,
y) is within the shaded area shown in FIG. 5, that is, 0.28 ≦ x ≦
0.31 and 0.29 ≦ y ≦ 0.33. Furthermore, if the value of Y is 50 or more and 70 or less among the tristimulus values in the XYZ color system, sufficient brightness can be obtained.

The color filter used in the liquid crystal display device needs to be formed by laminating a transparent conductive thin film such as ITO, a protective film, and the like.
In particular, it is known that the hue of white changes. Therefore, the theoretical white point in the XYZ color system is (0.31
3, 0.329), but by subtracting the change in hue in advance and setting white in the shaded area in FIG. 5, good white without coloration is reproduced when used as a color filter. can do.

In the present embodiment, the chromaticity coordinates (x, y) in the XYZ color system are represented by a green color filter in FIG.
, That is, light that satisfies the expressions of 0.29 ≦ x ≦ 0.33 and 0.37 ≦ y ≦ 0.43, and the blue color filter is XY.
The chromaticity coordinates (x, y) in the Z color system are the light in the shaded area shown in FIG. 4, that is, 0.17 ≦ x ≦ 0.22 and x
+ 0.04 ≦ y ≦ x + 0.08 A color filter that transmits light satisfying the expressions: Thereby, when white display was performed by lighting the entire surface, it was possible to reproduce good white without coloring. Further, green and blue, which were bright and had good visibility, could be reproduced.

With respect to the green color filter, the hue changes to cyan when x becomes smaller than the shaded area shown in FIG. 3, and the hue changes to yellow-green when x becomes larger. Also, when y becomes small,
If the display color becomes pale and blurred, and y becomes large, a bright green color can be displayed, but the display becomes dark, which is not suitable for a reflective liquid crystal display device.

With respect to the blue color filter, if x is smaller than the shaded area shown in FIG. 4, a vivid blue color can be displayed, but the display becomes dark. Will be gone. x
Becomes large, the hue changes to cyan, and the display color also becomes pale and blurred. Also, when y decreases, the hue changes to magenta, and when y increases, the hue changes to cyan.

The green color filter is XY
Of the tristimulus values in the Z color system, the value of Y at the time of reflection is 7
If the value is 5 or more and 90 or less, sufficient brightness can be obtained. If the value of Y at the time of reflection is 35 or more and 60 or less among the tristimulus values in the XYZ color system, the blue color filter has sufficient brightness. Is obtained.

[0040]

As described above, in the reflection type liquid crystal display device of the present invention, a reflection electrode is formed on one of a pair of substrates opposed to each other with a liquid crystal layer interposed therebetween, and a translucent counter electrode and a red electrode are formed on the other. , green, in the reflection type liquid crystal display device having a color filter formed consisting of three colors of blue, in the condition of illuminant D ₆₅ and 2 ° field of view, the chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram , 0.37 ≦ x ≦ 0.43, and 0.28
Since it has a red color filter that transmits light that satisfies each expression of ≦ y ≦ 0.32, it is possible to prevent a change in hue from occurring and to reproduce bright red with good visibility. It has the effect of being able to.

Further, in the reflection type liquid crystal display device,
The chromaticity coordinates (x, y) in the white XYZ color system chromaticity diagram obtained by the additive color mixture of the color filter are:
0.28 ≦ x ≦ 0.31, and 0.29 ≦ y ≦ 0.33
By setting the green and blue color filters so as to satisfy each of the following expressions, it is possible to reproduce white without color.

Further, 0.29 ≦ x ≦ 0.33 and 0.
A green color filter that transmits light satisfying each of the following expressions: 37 ≦ y ≦ 0.43; 0.17 ≦ x ≦ 0.22; and x
+ 0.04 ≦ y ≦ x + 0.08, by having a blue color filter that transmits light satisfying the respective expressions, it is possible to prevent a change in hue for green and blue, and to provide good visibility. This produces an effect that green and blue can be reproduced. In particular, when performing full-color display, the color balance is not lost due to the change in the hue of red, green, and blue, and an effect that a desired color can be reproduced can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a spectral transmittance characteristic of a red color filter according to the present invention.

FIG. 2 is a diagram showing chromaticity coordinates of a red color filter according to the present invention.

FIG. 3 is a diagram illustrating chromaticity coordinates of a green color filter according to the present invention.

FIG. 4 is a diagram showing chromaticity coordinates of a blue color filter according to the present invention.

FIG. 5 is a diagram showing chromaticity coordinates of white obtained by additive color mixture using a single color filter according to the present invention.

FIG. 6 is a cross-sectional configuration diagram of a reflective liquid crystal display device of the present invention.

FIG. 7 is a diagram showing electro-optical characteristics of a liquid crystal layer used in the reflection type liquid crystal display device of the present invention.

8 is a spectral distribution diagram of illuminant D _65.

FIG. 9 is a diagram illustrating a 2 ° visual field and a 10 ° visual field.

FIG. 10 is a diagram showing spectral transmittance characteristics of a red color filter used in a conventional liquid crystal display device.

[Explanation of symbols]

11 Red color filter used in the reflection type liquid crystal display device of the present invention 12 Red color filter used in the conventional reflection type liquid crystal display device 30 Reflection type liquid crystal display device 31 Substrate 38 Reflection electrode 40 TFT 42 Organic insulating film 43 Contact hole 44 Alignment film 45 Substrate 46 Color filter 49 Liquid crystal layer

Claims (3)

[Claims] 1. A reflection panel in which a reflective electrode is formed on one of a pair of substrates opposed to each other with a liquid crystal layer interposed therebetween, and a transmissive counter electrode and a color filter of three colors of red, green and blue are formed on the other. in type liquid crystal display device, in the condition of the illuminant D ₆₅ and 2 ° field of view, the chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram, 0.37 ≦ x ≦
A reflective liquid crystal display device comprising a red color filter that transmits light satisfying each of 0.43 and 0.28 ≦ y ≦ 0.32. 2. Under the condition of D ₆₅ light source and 2 ° field of view,
The chromaticity coordinates (x, y) in the white XYZ color system chromaticity diagram obtained by the additive color mixture of the color filter are:
0.28 ≦ x ≦ 0.31, and 0.29 ≦ y ≦ 0.33
2. The reflective liquid crystal display device according to claim 1, wherein the following formulas are satisfied. 3. Under the condition of D ₆₅ light source and 2 ° field of view,
The chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram are
0.29 ≦ x ≦ 0.33 and 0.37 ≦ y ≦ 0.43
And a green color filter that transmits light satisfying the following expressions: 0.17 ≦ x ≦ 0.22, and x + 0.04 ≦ y ≦
3. A blue color filter that transmits light satisfying each of x + 0.08.
The reflective liquid crystal display device as described in the above.