JP2002014333A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve display quality by suppressing coloring by interferential colors. SOLUTION: In the liquid crystal display element manufactured by interposing an optical retardation plate and a liquid crystal cell 1 in which a liquid crystal 10 is sealed as homogeneously aligned between two polarizing plates, a blue filter B in a color filter part 20 of the liquid crystal cell 1 is formed thinnest, a red filter R is formed thicker than the blue filter, and a green filter G is formed thickest. Consequently, the layer thickness DB of the liquid crystal in the region corresponding to the blue filter B is determined to give the highest transmittance, the layer thickness DR in the region corresponding to the red filter R is formed to give lower transmittance than in the region of the blue filter B, and the layer thickness DG in the region corresponding to the green filter G is formed to give the lowest transmittance. Thus, the wavelength dependency of the liquid crystal layer and the optical retardation plate corresponding to the filters R, G, B can be controlled to almost equal, and coloring by interferential colors can be suppressed to improve the chromaticity and to improve the display quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal display device, since the liquid crystal has birefringence, coloring due to interference colors is inevitable. In order to eliminate the coloring, a liquid crystal layer is formed by using a retardation plate. There is a method in which the phase difference generated in the above is corrected to compensate for the coloring due to the interference color accompanying the wavelength dependence of the liquid crystal layer.
3 to 5 are diagrams showing one example. In this liquid crystal display element, as shown in FIG. 3, a retardation plate 2 is disposed on one surface side (upper surface side in FIG. 3) of a liquid crystal cell 1, and the liquid crystal cell 1 and the retardation plate 2 are combined with two polarizing plates. The structure is sandwiched between the plates 3 and 4.

The liquid crystal cell 1 includes a pair of transparent substrates 5 and 6, as shown in FIG. These pair of substrates 5,
Numerals 6 are arranged so as to face each other up and down. Transparent electrodes 7 and 8 made of a transparent conductive material such as ITO are provided on the opposing surfaces of the pair of substrates 5 and 6, respectively. In addition, of the pair of substrates 5 and 6, the color filter portion 9 is provided on the transparent electrode 8 of the lower substrate 6 shown in FIG.
Is provided. Then, the transparent electrode 7 on the upper substrate 5
The liquid crystal 10 is homogeneously aligned and sealed between the substrate and the color filter section 9 of the lower substrate 6. In this case, as shown in FIG. 4, rubbing treatment is performed on each surface of the transparent electrode 7 of the upper substrate 5 and the color filter portion 9 of the lower substrate 6 so that the rubbing directions 10a are parallel to each other. I have.

The color filter section 9 comprises a red filter R, a green filter G and a blue filter B, as shown in FIG. 5, and these filters R, G and B are all formed with the same film thickness. . Thus, the liquid crystal layer thicknesses D at the locations corresponding to the filters R, G, and B are all set to the same thickness (about 3.4 μm). Note that a black matrix (not shown) for preventing light leakage is provided on the lower substrate 6 at a location corresponding to each of the filters R, G, and B.
Is provided. The upper and lower two polarizing plates 3 and 4
As shown in FIG. 4, the respective polarization axes 3a, 4a are orthogonal to each other, and the rubbing directions 10 of the substrates 5, 6 of the liquid crystal cell 1 are different.
intersects at approximately 45 °. Further, the retardation plate 2 is disposed between the upper substrate 5 and the upper polarizing plate 3, and the slow axis 2 a of the retardation plate 2 is set in the rubbing direction 10 of the upper substrate 5.
intersects at approximately 90 °.

[0005]

However, in such a liquid crystal display device, since the filters R, G, and B of the color filter section 9 are all formed with the same film thickness, each of the filters R, G, and B is formed. , The thickness D of each liquid crystal layer at the position corresponding to is also the same, so that the refractive index anisotropy Δ
wavelength dependence by the product Δnd of n and the cell gap d;
The wavelength dependence of the phase difference plate 2 differs for each liquid crystal layer at a location corresponding to each of the filters R, G, and B, and when a voltage is applied, halftone display and black display are colored, thereby deteriorating the display quality. There's a problem. In particular, in such a homogeneously aligned liquid crystal display device, the chromaticity and transmittance greatly depend on the liquid crystal layer thickness D, and the larger the liquid crystal layer thickness D, the stronger the yellowish display in white display. is there.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the chromaticity by suppressing coloring due to the interference color due to the wavelength dependence of a portion corresponding to each filter, thereby improving display quality.

[0007]

According to the present invention, a color filter section including a red filter, a green filter, and a blue filter is provided on one of opposing surfaces of a pair of substrates, and a liquid crystal is homogeneously aligned between the pair of substrates. A liquid crystal cell sealed and sealed, a retardation plate for compensating for a phase difference caused by a liquid crystal layer in the liquid crystal cell, and two polarized lights which are disposed so as to sandwich the liquid crystal cell and the retardation plate and whose polarization axes are orthogonal to each other. A liquid crystal display element comprising: a color filter portion, wherein the thickness of the blue filter is formed to be the thinnest, and the thickness of the red filter is formed to be thicker than the blue filter; It is characterized by having the largest thickness.

According to the present invention, in the color filter portion, the thickness of the blue filter is formed to be the thinnest, the thickness of the red filter is formed to be thicker than this, and the thickness of the green filter is formed to be the thickest. Thereby, the liquid crystal layer thickness at the portion corresponding to the blue filter is made the thickest, and the transmittance at this portion is made highest, and the liquid crystal layer thickness at the portion corresponding to the red filter is made thinner than the portion corresponding to the blue filter, In addition, the transmittance at this location can be made lower than that at the location corresponding to the blue filter, the liquid crystal layer thickness at the location corresponding to the green filter can be made the thinnest, and the transmittance at this location can be made the lowest. The wavelength dependence of each liquid crystal layer at the location corresponding to the filter and the wavelength dependence of the retardation plate can be made close to the same level. Suppressing the coloration due to interference colors due to the presence of it is possible to improve the chromaticity, thereby improving the display quality.

In this case, as described in claim 2, each polarization axis of the two polarizing plates intersects at approximately 45 ° with the rubbing direction of the pair of substrates, and the slow axis of the retardation plate. Is approximately 9 with respect to one rubbing direction of the pair of substrates.
T = sin ² (Δnd / λ) where T is the transmissivity of the portion corresponding to each of the filters, Δn is the refractive index anisotropy, d is the cell gap, and λ is the wavelength of the incident light. ) The transmittance T of the portion corresponding to the blue filter represented by
However, by setting the cell gap d to be the maximum when λ = 550 nm, it is possible to improve the chromaticity by suppressing yellowish coloring in halftone display and black display particularly in homogeneous alignment. it can.

According to a third aspect of the present invention, by disposing a retardation plate for compensating chromaticity between the two polarizing plates, the coloring due to interference colors is further suppressed and the chromaticity is improved. The display quality can be further improved. Furthermore, as described in claim 4, a reflection type or semi-transmission type having high chromaticity display performance is provided by providing a reflection plate or a semi-transmission reflection plate outside one of the two polarization plates. Type liquid crystal display element can be obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a liquid crystal display device according to the present invention will be described below with reference to FIGS. The same parts as those of the conventional example shown in FIGS. This liquid crystal display element has a structure of a color filter section 20 different from that of the conventional example, and the other structure is almost the same as that of the conventional example. In the color filter section 20, the red filter R, the green filter G, and the blue filter B have different thicknesses, respectively.
Is formed to be the thinnest, the red filter R is formed to be thicker than the blue filter B, and the green filter G is formed to be the thickest.

In this case, the transmittances T of the portions corresponding to the filters R, G, and B are as follows: T = sin ² , where Δn is the refractive index anisotropy, d is the cell gap, and λ is the wavelength of the incident light. (Δnd / λ). In this equation, when λ = 550 nm,
The cell gap d is set such that the transmittance TB at the location corresponding to the blue filter B is maximized. For example, the liquid crystal layer has a refractive index anisotropy Δn of 0.09, the retardation plate 2 is made of polycarbonate, and its retardation is 50 n.
m, the liquid crystal layer thickness DB at the portion corresponding to the blue filter B has the highest transmittance, for example, 3.4 μm.
Is set to

The liquid crystal layer thickness DR at the portion corresponding to the red filter R is set to a thickness at which the transmittance is lower than that at the portion of the blue filter B, for example, 3.1 μm. The liquid crystal layer thickness DG is set to a thickness with the lowest transmittance, for example, 3.0 μm. Also in this embodiment, the two upper and lower polarizing plates 3 and 4 have the respective polarizing axes 3a and 4a orthogonal to each other and are approximately 45 ° with respect to the rubbing direction 10a of the substrates 5 and 6 of the liquid crystal cell 1. Intersect at The retardation plate 2 is disposed between the upper substrate 5 and the upper polarizing plate 3, and the slow axis 2 a thereof intersects the rubbing direction 10 a of the upper substrate 5 at substantially 90 °. .

In such a liquid crystal display element, the thickness of the blue filter B is formed to be the thinnest, the thickness of the red filter R is formed to be thicker than this, and the thickness of the green filter G is formed to be the thickest. The liquid crystal layer thickness DB at the portion corresponding to the blue filter B is made the thickest, the transmittance at this portion is made the highest, and the liquid crystal layer thickness DR at the portion corresponding to the red filter R is made larger than the portion corresponding to the blue filter B. And the transmittance at this location is made higher than the location corresponding to the blue filter B, the liquid crystal layer thickness DG at the location corresponding to the green filter G is made thinnest, and the transmittance at this location is made the lowest. be able to. For this reason, the wavelength dependence of each liquid crystal layer and the wavelength dependence of the retardation plate 2 at locations corresponding to each of the filters R, G, and B can be made close to the same level, whereby each of the filters R, G, and B can be obtained. Can be suppressed from being caused by the interference color due to the wavelength dependence of the portion corresponding to the above.

That is, in the conventional liquid crystal display element, since the wavelength dependence of each liquid crystal layer and the wavelength dependence of the phase difference plate 2 at the portions corresponding to the filters R, G, and B are different, a voltage is applied. Then, as shown by the curve indicated by the cross mark in FIG.
Initially, the color shifts to the blue direction, then moves in the direction of yellowing, and becomes yellowish as the display changes from halftone display to black display. In the liquid crystal display device of this embodiment, the filters correspond to the filters R, G, and B, respectively. Since the wavelength dependence of each liquid crystal layer at the location and the wavelength dependence of the phase difference plate 2 are almost the same, when a voltage is applied, the halftone display is performed as shown by the curve indicated by a triangle in FIG. In addition, the rate of movement in the yellowing direction in black display becomes smaller than that in the conventional liquid crystal display device. For this reason, it is possible to suppress the coloring due to the interference color due to the wavelength dependence of the portion corresponding to each of the filters R, G, and B, thereby improving the chromaticity, thereby improving the display quality.

In the above embodiment, the upper polarizing plate 3
Although the case where the phase difference plate 2 is disposed between the liquid crystal cell 1 and the liquid crystal cell 1 has been described, the present invention is not limited thereto, and the phase difference plate 2 may be disposed between the liquid crystal cell 1 and the lower polarizing plate 4. Alternatively, the retardation plate 2 may be divided into two portions and provided between the upper polarizing plate 3 and the liquid crystal cell 1 and between the liquid crystal cell 1 and the lower polarizing plate 4, respectively.

In the above embodiment, the liquid crystal cell 1 and the retardation plate 2 are sandwiched between the upper and lower two polarizing plates 3 and 4. However, the present invention is not limited to this. The structure which added the phase difference plate may be sufficient. In this case, a chromaticity compensating retarder is provided between the upper polarizer 3 and the retarder 2 or between the liquid crystal cell 1 and the lower polarizer 4 or both. When the retardation plate 2 is divided into two and arranged above and below the liquid crystal cell 1, the upper polarizing plate 3
A chromaticity compensating retardation plate may be provided between the upper and lower retardation plates, or between the lower polarizing plate 4 and the lower retardation plate, or both. In this case, the chromaticity can be further improved by the chromaticity compensating retardation plate.

Furthermore, in each of the above-described embodiments and the modifications thereof, the transmissive type is described in any case. However, the present invention is not limited to this, and one of the upper and lower polarizing plates 3, 4 may be used, for example, the lower one. A reflector or a transflector may be provided on the lower surface of the polarizing plate 4 on the side. In this way, a reflective or transflective liquid crystal display device having high chromaticity display performance can be obtained.

[0019]

As described above, according to the present invention, a liquid crystal cell in which liquid crystals are homogeneously aligned and sealed, a retardation plate for compensating for a phase difference caused by a liquid crystal layer in the liquid crystal cell, In a liquid crystal display device comprising a cell and two polarizing plates arranged with a phase difference plate interposed therebetween,
Of the color filter portions provided on one of the opposing surfaces of the pair of substrates of the liquid crystal cell, the thickness of the blue filter is formed to be the thinnest, the thickness of the red filter is formed to be thicker than this, and the thickness of the green filter is formed. The thickness of the liquid crystal layer at the portion corresponding to the blue filter is set to the highest transmittance, and the thickness of the liquid crystal layer at the portion corresponding to the red filter is set to a thickness at which the transmittance is lower than that of the blue filter. The thickness of the liquid crystal layer at the portion corresponding to the green filter can be set to the thickness with the lowest transmittance, thereby the wavelength dependence of each liquid crystal layer at the portion corresponding to each filter and the wavelength dependence of the retardation plate. And the similarity can be brought close to the same level. Therefore, it is possible to suppress the coloring due to the interference color due to the wavelength dependence of the portion corresponding to each filter, to improve the chromaticity, and to improve the display quality. .

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part of a liquid crystal cell in one embodiment of a liquid crystal display device of the present invention.

FIG. 2 is a front chromaticity diagram of the liquid crystal display element of FIG. 1 and a conventional liquid crystal display element when a voltage is applied.

FIG. 3 is a cross-sectional view of a conventional liquid crystal display element.

FIG. 4 is a view showing optical axes of respective members of the liquid crystal display element of FIG. 3;

5 is an enlarged sectional view of a main part of a liquid crystal cell in the liquid crystal display device of FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal cell 2 phase difference plate 3, 4 polarizing plate 5, 6 substrate 10 liquid crystal 20 color filter part R red filter G green filter B blue filter

Claims (4)

[Claims] A liquid crystal cell in which a color filter portion including a red filter, a green filter, and a blue filter is provided on one of opposing surfaces of a pair of substrates, and a liquid crystal is homogeneously aligned and sealed between the pair of substrates; A liquid crystal display device comprising: a phase difference plate for compensating for a phase difference caused by a liquid crystal layer in the liquid crystal cell; and two polarizing plates disposed so as to sandwich the liquid crystal cell and the phase difference plate and having polarization axes orthogonal to each other. In the color filter portion, the thickness of the blue filter is formed to be the thinnest, the thickness of the red filter is formed to be thicker than the blue filter, and the thickness of the green filter is formed to be the thickest. Characteristic liquid crystal display element. 2. A polarization axis of each of the two polarizing plates intersects at approximately 45 ° with a rubbing direction of the pair of substrates, and a slow axis of the retardation plate is a rubbing direction of one of the pair of substrates. The direction intersects at about 90 ° with respect to the direction, T is the transmittance of the portion corresponding to each filter, Δn is the refractive index anisotropy, d is the cell gap, and λ is the wavelength of the incident light. sin ² (Δnd / λ), transmittance T at a location corresponding to the blue filter
2. The liquid crystal display device according to claim 1, wherein the cell gap d is set to be maximum when λ = 550 nm. 3. The liquid crystal display device according to claim 1, wherein a retardation plate for compensating chromaticity is disposed between the two polarizing plates. 4. A liquid crystal display device according to claim 1, wherein a reflection plate or a transflective plate is provided outside one of the two polarizing plates. .