JP2002350830A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device with little color variation resulting from variation in a viewing angle and with high display quality. SOLUTION: The liquid crystal display device comprises a pixel consisting of three sub-pixels 4r, 4g, 4b respectively displaying red, green and blue. Areas of the three sub-pixels 4r, 4g, 4b are different from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have the characteristics of being thin, light, and low in power consumption, and are therefore being used in the field of small and medium-sized video display devices such as movies and car navigation systems, personal computers, word processors and PCs.
It is widely used for flat displays such as still image display fields such as monitors, and the market is rapidly expanding. More recently, commercial products using a TFT liquid crystal display device capable of displaying moving images as a TV display have begun to be commercialized. In the TV field, a liquid crystal display device with higher brightness and higher display quality has been developed with the goal of a CRT. In particular, research for improving or overcoming the viewing angle dependence inherent in liquid crystal displays has been actively conducted.

[0003] As a description of a conventional liquid crystal display device, a TFT
A liquid crystal display device will be described as an example. FIG. 5 is a side sectional view of a liquid crystal cell of the TFT type liquid crystal display device. 1 is TF
It is a T substrate. Reference numeral 2 denotes a color filter substrate having a black matrix 3, a colored layer 4, and a transparent electrode 5. TFT substrate 1 and color filter substrate 2
Are respectively formed with an alignment film 6a and an alignment film 6b,
Rubbing treatment has been performed on the alignment films 6a and 6b.

[0006] The TFT substrate 1 and the color filter substrate 2 are arranged so as to form a predetermined gap, and spacers 7 are dispersed in the gap. Spacer 7 is 4 μm
Resin beads, which are dispersed at a density of 140 beads / mm ² . TFT substrate 1 and color filter substrate 2
Then, a liquid crystal is filled in the gap to form a twisted nematic liquid crystal cell S. At this time, the thickness of the liquid crystal layer formed in the gap is 5.0 μm.

[0005] On both sides of the liquid crystal cell S, retardation plates 8a and 8b and polarizing plates 9a and 9b made of an optical medium having negative refractive index anisotropy in which the main axes are hybridly arranged are attached in a predetermined attachment direction. It is attached. FIG. 6 shows the relationship between the rubbing direction and the directions of attaching the polarizing plate and the retardation plate. Numeral 11 denotes a rubbing direction of the TFT substrate 1. 12
Is the rubbing direction of the color filter substrate 2. The rubbing process is performed so that the respective rubbing directions 11 and 12 become 90 °.

[0006] As shown in FIG. 6, a liquid crystal cell S includes a TFT.
It is sandwiched between the phase difference plate 8a on the substrate 1 side and the phase difference plate 8b on the color filter substrate 2 side. Phase difference plates 8a, 8b
Represents optical compensation of the black display state of the liquid crystal cell S. The phase difference plates 8a and 8b can improve the viewing angle-contrast characteristics of the liquid crystal display device and expand the high contrast range. 19a is the polarization axis of the polarizing plate 9a on the TFT substrate 1 side, and 19b is the polarization axis of the polarizing plate 9b on the color filter substrate 2 side. The liquid crystal cell S includes a polarizing plate 9a,
9b. The polarization axis 19a of the polarizing plate 9a is arranged in the same direction as the rubbing direction 12 of the color filter substrate 2, and the polarization axis 19b of the polarizing plate 9b is arranged in the same direction as the rubbing direction 11 of the TFT substrate 1.

FIG. 7 is a schematic plan view of a pixel of a conventional liquid crystal display device. The pixel includes sub-pixels 4 r, 4 g, and 4 b forming a colored layer 4 and a black matrix 3. One pixel includes three sub-pixels 4r, 4g, and 4b, and performs red display, green display, and blue display, respectively.
As shown in FIG. 7, the sub-pixels 4r, 4g, and 4b are arranged via the black matrix 3 and have the same area. Sub-pixels 4r, 4g, 4
b have the same length in the vertical direction, and each sub-pixel 4r, 4g, 4b
Have the same length Lr, Lg, Lb.

[0008]

In the above-mentioned conventional liquid crystal display device, in the halftone display region, mismatch of optical compensation between the liquid crystal cell and the phase difference plates 8a and 8b may occur. In particular, a phenomenon occurs in which the display is colored yellow when the viewing angle θ is changed in the left-right direction. This is a very serious problem that significantly lowers the display quality of the liquid crystal display device. FIG. 8 shows the wavelength-transmittance characteristics of the liquid crystal cell when the coloring layer 4 is not provided. As shown in FIG. 8, it can be seen that as the viewing angle θ increases, the transmittance on the short wavelength side (blue) decreases. In other words, when the viewing angle θ increases, the blue component becomes difficult to transmit through the liquid crystal cell,
As a result, the blue component in the display decreases. Therefore, the display is biased toward red and green components, and the display is colored yellow.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid crystal display device having a small color change when a viewing angle is changed and having high display quality.

[0010]

A liquid crystal display device according to the present invention is a liquid crystal display device in which one pixel is composed of three sub-pixels for displaying red, green and blue.
Since the areas of the two sub-pixels are different, it is possible to compensate for a decrease in the blue component due to a change in the viewing angle.

In the liquid crystal display device according to the present invention, the sub-pixel for displaying blue has a larger area than the sub-pixel for displaying red or green. The reduction can be compensated.

Further, in the liquid crystal display device of the present invention, the three sub-pixels for displaying red, green and blue are each rectangular, and the length of each of the three sub-pixels in the vertical direction is equal to each other. By changing the ratio of the lengths of the sub-pixels in the horizontal direction, the area ratios are changed, so that the area ratios of the sub-pixels can be easily adjusted.

Further, in the liquid crystal display device of the present invention, when the lateral lengths of the three sub-pixels for displaying red, green and blue are Lr, Lg and Lb, respectively, Lb> L.
r and Lb ≧ Lg, or Lb ≧ Lr and Lb> L
Since the relationship is g, it is possible to compensate for a decrease in the blue component due to a change in the viewing angle.

The liquid crystal display device of the present invention is provided with a retardation plate made of an optical medium having a negative refractive index anisotropy in which the main axes are hybridly arranged and a liquid crystal layer of a twisted nematic system. it can.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic structure of a liquid crystal cell of a liquid crystal display according to an embodiment of the present invention is the same as that of the TFT type liquid crystal display described with reference to FIG. . The difference is that the area of each sub-pixel is different as in the schematic plan view of the pixel of the liquid crystal display device according to the embodiment shown in FIG. Hereinafter, a liquid crystal display device according to an embodiment will be described with reference to the drawings.

As shown in FIG. 1, one pixel of the liquid crystal display device according to the embodiment is composed of three sub-pixels 4r, 4g, 4b for displaying red, green and blue, and a black matrix 3. The areas of the sub-pixels 4r, 4g, and 4b are different. The sub-pixels 4r, 4g, and 4b are substantially rectangular, and their horizontal lengths are Lr, Lg, and Lb, respectively. Since the vertical lengths of the sub-pixels 4r, 4g, and 4b are all equal, the area ratio of the sub-pixels 4r, 4g, and 4b is equal to the ratio of the horizontal lengths Lr, Lg, and Lb.

First, the effective area of the sub-pixel at the viewing angle θ will be described. FIG. 2 is a side sectional view of the liquid crystal cell for explaining the effective area of the sub-pixel at the viewing angle θ. As shown in FIG. 2A, assuming that the horizontal length of one sub-pixel is L and the thickness of the liquid crystal layer is d, the effective horizontal length of the sub-pixel at the viewing angle θ is L _θ = (L-d × ta
nθ). On the other hand, as shown in FIG. 2B, when the horizontal length of the sub-pixel becomes a times L (0 <a ≦ 1), the effective horizontal length of the sub-pixel at the viewing angle θ is obtained. It's L '
_θ = (a × L−d × tan θ). Here, since the vertical lengths of the sub-pixels are equal, the horizontal lengths _Lθ and L ′
The ratio of _θ is the area ratio of the sub-pixel.

Here, the effective area ratio of the sub-pixel is calculated by (effective area of the sub-pixel having a horizontal length of a × L) / (effective area of the sub-pixel having a horizontal length of L). Area). FIG. 3 shows the relationship between the effective area ratio of the sub-pixels and the viewing angle θ. The values at this time are L = 80 μm, d = 5 μm, a =
0.8. In FIG. 1, for example, Lr: Lg: Lb =
Assuming that 0.8: 0.8: 1, the area ratio at the front (viewing angle θ = 0 °) is 0.8: 0.8: 1.
The area ratio at 80 ° is 0.7: 0.7: 1 from FIG. That is, the area ratio of the sub-pixel 4b that performs blue display is increasing. That is, as the viewing angle θ increases, the apparent blue component in the display increases.

According to the wavelength-transmittance characteristic of the liquid crystal cell in the halftone display without the coloring layer 4 shown in FIG. 8, the transmittance on the short wavelength side (blue) decreases as the viewing angle θ increases. ,
By making the areas of the sub-pixels 4r, 4g, and 4b different from each other as described above, the decrease in the blue component can be compensated. That is, by setting the horizontal length of the sub-pixels 4r, 4g, and 4b to Lb> Lg or Lb> Lr, the transmittance at the short wavelength (blue) is increased, and the transmittance at the long wavelength (red) is increased. Can be lowered. Actually, Lb> Lr
And Lb ≧ Lg, or Lb ≧ Lr and Lb> Lg
The sub-pixels 4r, 4g, and 4b may be created so as to satisfy the following relationship.

Next, the change of the chromaticity coordinates with respect to the change of the viewing angle θ will be described. FIG. 4 is a diagram showing a change in chromaticity coordinates with respect to a change in the viewing angle θ. This is because birefringence Δn = 0.0
This is a change in chromaticity of the liquid crystal cell when the viewing angle θ is changed in the left-right direction using the liquid crystal No. 84 and the thickness of the liquid crystal layer = 4.7 μm. When the ratio of Lr, Lg, Lb is 1: 1: 1, 0.9:
The results of changing the viewing angle θ for three types of 0.9: 1 and 0.8: 0.8: 1 are shown. This u'v '
In the chromaticity coordinates, near v ′, the color becomes closer to yellow as v ′ increases. FIG. 4 shows that v ′ becomes smaller when the ratio is 0.8: 0.8: 1. That is, it is possible to improve the coloring of yellow in the case of this ratio.

The ratio of Lr, Lg, Lb is not limited to the above-mentioned value of 0.8: 0.8: 1.

As described above, according to the liquid crystal display device according to the embodiment, the horizontal length of the three sub-pixels 4r, 4g, and 4b for displaying red, green, and blue which constitute one pixel is described. Lr, Lg, and Lb are different from each other so that the area of the sub-pixel 4b is larger than the area of each of the sub-pixels 4r and 4g. Even if the area ratio increases, and the transmittance of the blue component decreases, the phenomenon that the display is colored yellow can be improved.

Although the liquid crystal display device according to the embodiment is a liquid crystal layer of a twisted nematic type, the present invention is not limited to this type, and similar effects can be obtained with liquid crystal layers of other types. Can be For example, IPS (In-Plane
Switching), VA (Vertically Aligned),
A liquid crystal layer of an OCB (Optically Compensated Birefringence) system or the like may be used. Using these liquid crystal layers,
3 for displaying red, green, and blue as in the embodiment.
By making the area ratios of the two sub-pixels different, it is possible to improve the coloring phenomenon when the viewing angle is changed, and to realize a liquid crystal display device with high display quality.

[0024]

As described above, according to the present invention, in a liquid crystal display device in which one pixel includes three sub-pixels for displaying red, green, and blue, the area ratio of the three sub-pixels When the viewing angle is changed, the phenomenon that the display is colored yellow especially when the viewing angle is changed in the left-right direction can be improved, and a liquid crystal display device with high display quality can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing a pixel of a liquid crystal display device according to an embodiment.

FIG. 2 is a side cross-sectional view of a liquid crystal cell for explaining an effective area of a sub-pixel. FIG.
FIG. 6B is an explanatory diagram when the width of the sub-pixel is a × L.

FIG. 3 is a diagram showing a relationship between an effective area ratio of a sub-pixel and a viewing angle θ;

FIG. 4 is a diagram showing a change in chromaticity coordinates with respect to a change in a viewing angle θ.

FIG. 5 is a side sectional view of a liquid crystal cell of a TFT type liquid crystal display device.

FIG. 6 is a diagram showing a relationship between a rubbing direction and a direction in which a polarizing plate and a phase difference plate are attached.

FIG. 7 is a plan view schematically showing a pixel of a conventional liquid crystal display device.

FIG. 8 is a graph showing wavelength-transmittance characteristics of a liquid crystal cell.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 TFT substrate 2 color filter substrate 3 black matrix 4 coloring layer 4r red display sub-pixel 4g green display sub-pixel 4b blue display sub-pixel 5 transparent electrode 6a alignment film 6b alignment film 7 spacer 8a retardation plate 8b Phase difference plate 9a Polarizing plate 9b Polarizing plate 11 Rubbing direction of TFT substrate 12 Rubbing direction of color filter substrate 19a Polarizing axis of polarizing plate 19b Polarizing axis of polarizing plate S Liquid crystal cell d Thickness of liquid crystal layer L Length of subpixel in horizontal direction next to the sub-pixels for displaying horizontal length Lg green sub pixel for displaying the L _theta of effective lateral subpixel length L _'theta effective horizontal length Lr red subpixel Length Lb Horizontal length of sub-pixel displaying blue θ Viewing angle

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/30 390 G09F 9/30 390C F term (Reference) 2H048 BB01 BB02 BB07 BB42 2H090 KA05 LA01 LA04 LA06 LA09 LA15 MA03 2H091 FA02Y FA08X FA08Z FA11X FA35Y GA02 GA06 GA13 HA07 LA15 LA19 LA20 2H092 GA14 GA15 HA04 JA24 JB52 NA01 PA02 PA08 PA10 PA11 5C094 AA08 BA03 BA12 BA43 CA19 CA24 EA04 ED14

Claims (5)

[Claims] 1. A liquid crystal display device in which one pixel includes three sub-pixels for displaying red, green, and blue, wherein the three sub-pixels have different areas. apparatus. 2. The liquid crystal display device according to claim 1, wherein the sub-pixel for displaying blue has a larger area than the sub-pixel for displaying red or green. 3. The three sub-pixels for displaying red, green, and blue are each rectangular, and the length of each of the three sub-pixels in the vertical direction is equal to the length of each of the three sub-pixels. 3. The liquid crystal display device according to claim 1, wherein an area ratio is changed by changing a ratio of the height. 4. The horizontal lengths of the three sub-pixels for displaying red, green, and blue are represented by Lr, Lg, and Lb, respectively.
Lb> Lr and Lb ≧ Lg, or L
4. The liquid crystal display device according to claim 3, wherein the relationship b ≧ Lr and Lb> Lg is satisfied. 5. The liquid crystal display device according to claim 1, further comprising a retardation plate made of an optical medium having a negative refractive index anisotropy and having a main axis hybridly arranged, and a twisted nematic liquid crystal layer. A liquid crystal display device according to any one of the above.