JP3048872B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a super-twisted nematic (hereinafter referred to as ST) for performing color compensation using a phase difference plate.
N) liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, this STN type liquid crystal display device has been disclosed in, for example, the International Display Society Report (SID93DIGEST 61-6).
It has high-speed response as shown in 4). This S
In the TN type liquid crystal display device, the liquid crystal layer thickness d is small,
The liquid crystal material is characterized in that the refractive index anisotropy Δn thereof is large. Regarding the response characteristics of this STN-type liquid crystal display device, the larger the refractive index anisotropy Δn of the liquid crystal material, the higher the viscosity of the liquid crystal material and adversely affect the response time. It is well known that the liquid crystal layer thickness d more affects the response time than the liquid crystal layer thickness d, and the liquid crystal layer thickness d is more effective than the response time.
Therefore, to improve the response characteristics, the liquid crystal layer thickness d
Need to be thinner. Therefore, in order to keep the product d · Δn of the liquid crystal layer thickness d and the refractive index anisotropy Δn of the STN type liquid crystal material at a constant value in order to make the brightness equal, the liquid crystal layer pressure d was reduced. It is necessary to select an STN-type liquid crystal material having a large refractive index anisotropy Δn.

[0003] For example, specifically, in the International Display Society Report Collection (SID94DIGEST61-64), about 2
The STN type liquid crystal display element having a response time of 00 ms to 300 ms has a cell gap between a pair of upper and lower electrode substrates, that is, a liquid crystal layer thickness d of about 6 μm, and a refractive index anisotropy Δ of a liquid crystal material.
n is set to 0.14, and the product d · Δn is set to 0.1.
It is set to 84 μm. The wavelength dependence of the refractive index anisotropy Δn of such a liquid crystal material is determined by the conventional retardation film polycarbonate (P) which has a relatively small wavelength dependence.
It matches the wavelength dependence of C), and optical compensation can be performed in all wavelength ranges, and a high-quality display can be obtained.

On the other hand, in an STN type liquid crystal display device having a high response speed of 100 ms, which has a response time shorter than 200 ms to 300 ms of the above STN type liquid crystal display device, a cell gap between a pair of upper and lower electrode substrates, that is, a liquid crystal layer. If the thickness d is set to about 4 μm and the product d · Δn is set to 0.84 μm as in the case described above, it is necessary to set the refractive index anisotropy Δn of the liquid crystal material to 0.21. That is, since the refractive index anisotropy Δn = 0.21 of this liquid crystal material is larger than the above-described wavelength dependence of the refractive index anisotropy Δn = 0.14, mismatching occurs in the wavelength dependence of polycarbonate (PC). As a result, optical compensation cannot be performed in all wavelength ranges.

As a method for avoiding such a mismatch, it has been proposed to use polysulfone or polyethersulfone for the retardation film. That is, it has been disclosed that a phase difference plate having a large wavelength dispersion is used in a liquid crystal display element having a high-speed response. In addition,
Japanese Patent Laid-Open No. 50249 discloses that polysulfone or polyether sulfone is used as a material of a retardation plate.

[0006]

In the above-mentioned conventional high-speed response STN-type liquid crystal display device, high-speed response and high contrast are achieved by using a retardation plate having high wavelength dispersion. There was a problem that the viewing angle was narrow.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an STN type liquid crystal display device which can obtain a wide viewing angle with a high speed response without deteriorating high contrast.

[0008]

According to the present invention, there is provided a liquid crystal display device in which a liquid crystal display element having a super twisted nematic liquid crystal is interposed between a pair of polarizing plates. It has high wavelength dispersion between the back electrode substrate and one of the polarizing plates, and has a two-dimensional refractive index of n
x, ny, and when the refractive index in the thickness direction is nz, a lower retardation plate having a refractive index of nx> ny ≧ nz is provided, and a lower retardation plate is provided between the front-side electrode substrate of the liquid crystal display element and the other polarizing plate. And an upper retardation plate having a wavelength dispersion of not more than a high wavelength dispersion value of the lower retardation plate and having a refractive index of nx>nz> ny, thereby achieving the above object. Is done.

Preferably, the product d of the liquid crystal layer thickness d of the liquid crystal and the refractive index anisotropy Δn in the liquid crystal display device of the present invention.
Δn is 0.7 μm or more.

Preferably, the liquid crystal layer thickness d of the liquid crystal in the liquid crystal display device of the present invention is 2 μm <d <5 μm.

Further, preferably, the wavelength dispersion value α (Δn450n) of the lower retardation plate in the liquid crystal display device of the present invention.
m / Δn550 nm) is 1.15 ≦ α ≦ 1.20, and the wavelength dispersion value α (Δn450 nm) of the upper retardation plate is
/ Δn550 nm) is 1.05 ≦ α <1.15.

Preferably, the angle between the slow axis of the phase difference plate and the rubbing axis of the electrode substrate closest to the slow axis in the liquid crystal display device of the present invention is 70 ° to 85 °.
Is set within the range.

[0013]

In the present invention, the lower retardation plate has a high wavelength dispersion, a three-dimensional refractive index satisfying the relationship of nx> ny ≧ nz, and the upper retardation plate has a lower retardation plate. Having a wavelength dispersibility equal to or less than the high wavelength dispersion value of the plate, and nx
>Nz> ny, the three-dimensional refractive index can be set to 100 msec according to the experimental result of the embodiment described later.
When trying to obtain the above high-speed response, high contrast is not impaired, and the viewing angle is wide.

If the product d · Δn of the liquid crystal layer thickness d and the refractive index anisotropy Δn is 0.7 μm or more, the brightness (brightness)
Does not become small and slightly dark, and the positional relationship between the components such as the polarizing plate and the retardation plate in the present invention can be easily adapted.

Further, when the liquid crystal layer thickness d is 2 μm or less,
In order to obtain a predetermined brightness, the wavelength dependence of the liquid crystal material becomes considerably large, and a phase difference plate having a wavelength dispersion value α matching this to 1.20 or more is required. Such a retardation plate does not exist at the present time, and is a mismatch. When the thickness d of the liquid crystal layer is 5 μm or more, the response time becomes slow, and the high-speed response of about 100 msec of the present invention cannot be achieved. When the thickness d of the liquid crystal layer is 5 μm or more, in order to obtain a predetermined brightness, the wavelength dependence of the liquid crystal material is considerably reduced, and the wavelength dispersion α at this time is 1.15 ≦ α ≦ 1. .20 even mismatch.

Further, the lower phase plate has a wavelength dispersion value α.
(Δn450 nm / Δn550 nm) is 1.15 ≦ α ≦
A high-wavelength dispersion of 1.20 is used by using a retardation plate, and a chromatic dispersion value α (Δn450 nm / Δn550n) is provided on the upper retardation plate.
If m) uses a high wavelength dispersion property of 1.05 ≦ α <1.15, a high-speed response and high contrast are not impaired, and a wider viewing angle can be obtained.

Further, the positional relationship between the polarizing plate and the phase difference plate is set so that the contrast and the viewing angle characteristics are optimized, and the slow axis of the phase difference plate and the electrode substrate closest to the slow axis are set. Is set within a range of 70 ° to 85 °.

[0018]

Embodiments of the present invention will be described below.

Embodiment 1 FIG. 1 is a sectional view showing the structure of a liquid crystal display device according to Embodiment 1 of the present invention.

In FIG. 1, the liquid crystal display device 1 is provided with polarizing plates 3 and 4 on the upper and lower sides of a liquid crystal display element 2, respectively, and an upper phase difference plate 5 is provided between the liquid crystal display element 2 and the polarizing plate 3. In addition, a lower retardation plate 6 is provided between the liquid crystal display element 2 and the polarizing plate 4.

The structure of the front-side electrode substrate 7 showing the display side of the liquid crystal display element 2 is such that the stripe-shaped transparent electrodes 9 are provided on a translucent substrate 8 and an alignment film 10 is provided thereon. I have.

The back electrode substrate 11 of the liquid crystal display element 2
In this configuration, a color filter 13 is provided at a position corresponding to a pixel on the translucent substrate 12, and a lattice-like light-shielding film 14 is provided between the pixels. These color filters 1
3 and a thermosetting resin overcoat 1 on the light shielding film 14
5 are provided. Further, a stripe-shaped transparent electrode 16 is provided thereon, and an alignment film 17 is provided on the transparent electrode 16.

The pair of electrode substrates 7 and 11 are adhered to each other with an adhesive 18 so that the stripe-shaped transparent electrodes 9 and 16 are orthogonally opposed to each other, and a liquid crystal 19 is sealed between the substrates. Is configured.

At this time, the twist angle of the STN liquid crystal molecules in the liquid crystal 19 was set to 260 °, and the cell gap between the pair of upper and lower electrode substrates 7 and 11, ie, the liquid crystal layer thickness was set to 3.5 μm. The refractive index anisotropy Δ of the liquid crystal 19
The value of n is 0.215, and the product d · Δn is 0.7
The thickness was 5 μm.

In the first embodiment, the wavelength dispersion value α (Δn450) of the lower retardation plate 6 having high wavelength dispersion
nm / Δn550 nm) was set to 1.15. Examples of the material of the retardation plate 6 include polysulfone (PSF) and polyether sulfone (PESF). In the first embodiment, polysulfone (PSF) is used. FIG. 2 shows the wavelength dispersion characteristics of the polymer film in the case of the polysulfone (PSF) and the polyether sulfone (PESF). Further, the retardation plate 6 sets the refractive indexes in the three-dimensional direction to nx and nx, respectively.
When ny and nz, nx> ny ≧ nz. The wavelength dispersion value of the upper retardation plate 5 having a wavelength dispersion value of 1.15 or less is set to α = 1.
08 was set. As a material of the retardation plate 5, for example, polycarbonate (PC) or polyarylate (PA)
R), polystyrene, polyethylene phthalate, polymethyl methacrylate, and the like. Polycarbonate (PC) is used in the first embodiment. FIG. 2 shows the wavelength dispersion characteristics of the polymer film in the case of polycarbonate (PC) and polyarylate (PAR). Further, the phase difference plate 5
Means that the refractive indices in the three-dimensional direction are nx, ny, and nz, respectively.
Has a refractive index of nx>nz> ny, and Nz =
The Nz value represented by (nx-nz) / (nx-ny) is 0
<Nz ≦ 0.5 is selected, but in the first embodiment, Nz = 0.3.

As described above, the refractive index anisotropy Δn of the liquid crystal 19 used in the first embodiment is 0.215, and the curve A in FIG. And the wavelength dependence of the lower retardation plate 6 having the above-mentioned condition, and optical compensation can be performed in all wavelength ranges. The wavelength dependence curve B of the refractive index in FIG.
The case where n is 0.134 is shown.

FIG. 4 is a diagram showing the positional relationship of each component in the liquid crystal display device of FIG.

In FIG. 4, the rubbing axis of the alignment film 10 of the upper electrode substrate 7 located on the upper side is denoted by R1, and the rubbing axis of the alignment film 17 of the lower electrode substrate 11 located on the lower side is denoted by R2. These rubbing axes R1,
The intersection angle a of R2 is 260 °. Further, an angle b between the rubbing axis R1 closest to the slow axis R3 of the upper phase difference plate 5 and the rubbing axis R1 is set to 75 °, and the angle b between the slow axis R4 of the lower phase difference plate 6 and the The angle c between the rubbing axis R2 and the approaching rubbing axis R2 was set to 80 °. Further, an angle d between the absorption axis R5 of the upper polarizing plate 3 and the rubbing axis R1 is set to 45 °,
The angle e between the absorption axis R6 of the lower polarizing plate 4 and the rubbing axis R2 was set to 35 °. The positional relationship between these constituent materials is set so that contrast and visual characteristics are optimized.

In the following, the angle b between the slow axis R3 of the upper retardation plate 5 and the rubbing axis R1 and the angle c between the slow axis R4 of the lower retardation plate 6 and the rubbing axis R2 are changed. Are shown.

[0030]

[Table 1]

As can be seen from (Table 1), the first embodiment
The angle b between the slow axis R3 of the phase difference plate 5 and the rubbing axis R1 is set to 75 °, and the angle formed between the slow axis R4 and the rubbing axis R2 of the phase difference plate 6 shown in the first embodiment. c = 8
In the case of 0 °, it is understood that the contrast Co is optimal when it is 40.

The following Table 2 shows the contrast Co, the response time, and the visual direction (vertical direction) of the liquid crystal display device 1 used in Example 1 and Comparative Examples 1 and 2 from 12:00 to 6:00. 9:00 to 3:00 shows the range of contrast Co ≧ 4 in the visual direction (left-right direction).

[0033]

[Table 2]

In Comparative Example 1 of Table 2 above, two retardation plates were respectively arranged between the liquid crystal display element 2 of Example 1 and a pair of polarizing plates, and the two The lower retardation plate 6 of the first embodiment in which both retardation plates have high wavelength dispersion.
This is the case where the same retardation plate is used. In this case, the two retardation plates use polysulfone (PSF).
Further, both of the two retardation plates have the property of nx> ny ≧ nz. These two retardation plates are referred to as P
It is called SF. Also, in Comparative Example 1,
The positional relationship between the constituent materials was set so that the contrast and the viewing angle characteristics were optimized. Taking FIG. 4 as an example, the angle b between the slow axis R3 of the upper phase difference plate and the rubbing axis R1 is 80.
角, the angle c between the slow axis R4 of the lower retardation plate and the rubbing axis R2 is 80 °, the angle d between the absorption axis R5 of the upper polarizer and the rubbing axis R1 is 55 °, and the angle of the lower polarizer is 55 °. The angle between the absorption axis R6 and the rubbing axis R2 was set to 45 °.

In Comparative Example 2 of Table 2, two retardation plates were respectively arranged between the liquid crystal display element 2 of Example 1 and a pair of polarizing plates. Are the same retardation plates as the upper retardation plate 5 of the first embodiment having the wavelength dispersion value α = 1.08, and these two retardation plates are both nx>nz> ny. (PC) having a three-dimensional refractive index of These two retardation plates are hereinafter referred to as PCZ. Further, in Comparative Example 2, the positional relationship between the constituent materials is set so that the contrast and the viewing angle characteristics are optimized, and the configuration is the same as that in Comparative Example 1.

From this (Table 2), Comparative Example 1 can be regarded as the above-mentioned prior art. In Comparative Example 1, the contrast Co was 40, and the response time was 100 m.
s, which means that high-speed response can be achieved with high contrast, but on the other hand, it can be seen that the vertical viewing angle is much narrower than in the first embodiment. In Comparative Example 2, the contrast Co was 20, the response time was 100 ms, and higher contrast was not achieved. The vertical viewing angle was wider than that of Comparative Example 1. It can be seen that the viewing angle of Example 2 is narrower than that of Example 1. Therefore, the vertical viewing angle is 1 in the first embodiment.
In both the 2:00 and 6:00 directions, the viewing angle is increased by about 10 ° compared to Comparative Examples 1 and 2. Further, it can be seen that the viewing angle in the left-right direction in Example 1 is larger than that in Comparative Examples 1 and 2 even at 3:00.

Here, the viewing angle characteristics in each direction will be described in more detail.

FIGS. 5, 6, and 7 are graphs showing the omnidirectional contrast viewing angle characteristics of Example 1, Comparative Example 1, and Comparative Example 2, respectively, that is, isocontrast.

In FIGS. 5 to 7, numerals 0 to 345 represent angles in the visual angle direction, and the symbol is φ. That is, φ = 0 ° is 6:00, φ = 90 ° is 3:00, φ =
180 ° corresponds to 12:00, and φ = 270 ° corresponds to 9:00. Also, the numbers 0 to 50 in the columns inside the graph are:
The angle from the vertical direction to the horizontal direction with respect to the substrate is represented by θ. That is, it can be understood that FIGS. 5 to 7 are views in which the liquid crystal display device is viewed from directly above.

The contrast was Co = 1.
0, Co = 4, and Co = 1 or more. In particular, the contrast Co = 1 indicates a region where the display is not inverted, and is a region having a contrast that can be seen as a minimum display, and it can be determined that the viewing angle is wide because this is wide.

First, it can be understood from the viewing angle characteristic curve of equal contrast of FIG. 7 showing Comparative Example 2 that the range of contrast Co = 10 and Co = 4 is narrow, while the range of contrast Co = 1 is narrow. It turns out that it is quite wide in the left-right direction. This is because both the retarders used are nx>nz> n
This is because it has a three-dimensional refractive index of y, and it can be said that contrast change with respect to vision is good. The reason why the maximum contrast of Comparative Example 2 is low is that there is a mismatch between the retardation plate having a small wavelength dependence and the liquid crystal material having a large wavelength dependence, and color compensation (optical compensation) can be completely performed. It is not.

Next, it can be understood from the equicontrast viewing angle characteristic curve of FIG. 6 showing Comparative Example 1 that the range of contrast Co = 10 and Co = 4 is wide and the range of contrast Co = 1 is wide. It can be seen that the width is smaller than that of Comparative Example 2.

On the other hand, it can be understood from the equicontrast viewing angle characteristic curve of FIG. 5 showing the first embodiment that the contrast Co = 1 can be obtained without narrowing the range of the contrast Co = 10 and Co = 4. It can be seen that the range is expanded compared to Comparative Example 1. That is, while achieving high contrast, the range of contrast Co = 1 is expanded as compared with Comparative Example 1. Also, it can be seen that the range of the contrast Co = 1 is equal to or larger than the range of Comparative Example 2 having a wide range.

Further, the ON of the embodiment 1 and the comparative examples 1 and 2
The color tone and lightness at the time and at the time of OFF are shown in the following (Table 3).

[0045]

[Table 3]

In this (Table 3), L * represents lightness, and u * and v * each represent chromaticity. These L
*, U * and v * are defined in the CIE color system.

It is understood from Table 3 that the lightness L * when OFF in Comparative Example 2 is 0.51, which is higher than the lightness L * in Example 1 and Comparative Example 1. I understand. Normally, in the transmissive type, when OFF, a black display is exhibited. Therefore, the closer the value of L * is to 0, the greater the shielding power. That is, in Comparative Example 2, it is understood that a large value of L * does not have a shielding power and complete optical compensation cannot be performed. From this, it is clear that the contrast of Comparative Example 2 is low.

The chromaticities u * and v * of the above (Table 3) are shown in FIG.

FIG. 8 shows that Example 1 had no difference in chromaticity from Comparative Example 1 as the prior art, and achieved excellent optical compensation. That is, according to the first embodiment, a high-contrast, high-quality liquid crystal display device can be obtained.

(Embodiment 2) In this embodiment 2, d · △ n = 0.75 μm (d = 0.35, で
n = 0.215), but d · △ n =
It was set to 0.84 μm (d = 0.4, Δn = 0.21), and it was confirmed by simulation that the same effect as in the first embodiment can be obtained with d · Δn = 0.84 μm.

In the second embodiment, the twist angle of the STN liquid crystal molecules of the liquid crystal injected into the cell is set to 260 °.
The cell gap between the pair of upper and lower electrode substrates, that is, the liquid crystal layer thickness d was set to 4 μm. Further, the value of the refractive index anisotropy Δn of this liquid crystal is set to 0.21, and the product d · Δn is set to 0.81.
4 μm. The type of the phase difference plate used and the positional relationship between the constituent members are the same as in the first embodiment. Further, Example 2 (PCZ + PSF), Comparative Example 3 (PSF + PSF),
As Comparative Example 4 (PCZ + PCZ), the same comparison as in Example 1 was performed. The results of this simulation are shown in FIGS.

First, in the viewing angle characteristic curve of equal contrast of FIG. 10 showing Comparative Example 3 (PSF + PSF),
The result was wide in the horizontal direction but narrow in the vertical direction. Also,
In the viewing angle characteristic curve of equal contrast of FIG. 11 showing Comparative Example 4 (PCZ + PCZ), the upward direction (12: 0)
0) was considerably wide, and the horizontal direction was narrow.

Next, in the viewing angle characteristics of the contrast in FIG. 9 showing the second embodiment (PCZ + PSF), it can be seen that the horizontal direction is wide and the vertical direction is also wide. Therefore, even when d · Δn = 0.84 μm in the second embodiment, the effect of the present invention is remarkably exhibited, and the viewing angle can be widened.

Here, the reason why the cell gap, that is, the liquid crystal layer thickness d is 2 μm <d <5 μm, will be described.

According to the present invention, when the liquid crystal layer thickness d = 2 μm, the product d of the liquid crystal layer thickness d and the refractive index anisotropy Δn of the liquid crystal material is obtained.
If an attempt is made to maintain Δn at a constant value (for example, d · Δn = 0.75 μm) in order to obtain a predetermined brightness, Δn
= 0.375, and the wavelength dependence of the liquid crystal material is considerably increased. Therefore, it is necessary to use a retardation film having a wavelength dispersion value α of 1.20 or more to match this, and such a retardation film is not present but a mismatch. If a retardation film having a wavelength dispersion value α of 1.20 or more is present, the thickness d of the liquid crystal layer may be 2 μm or less, matching the wavelength dependence of the liquid crystal material.

When the liquid crystal layer thickness d = 5 μm, the product d · Δn of the liquid crystal layer thickness d and the refractive index anisotropy Δn of the liquid crystal material is maintained at a constant value in order to obtain a predetermined brightness. If this is attempted, the refractive index anisotropy Δn = 0.150, and the wavelength dependence of the liquid crystal material is considerably reduced. Therefore, even if the chromatic dispersion value α at this time is 1.15 ≦ α ≦ 1.20, it means a mismatch. Further, d = 5 μm
With the above, the response time becomes slow, and 100 msec of the present invention is used.
A high-speed response of a degree cannot be achieved.

Therefore, the cell gap, that is, the liquid crystal layer thickness d needs to be d <5 μm, and preferably 2 μm <d <5 μm. Further, considering the high-speed response, 2 μm <d <4 μm
m is optimal.

The reason why it is optimal that d · Δn is 0.7 μm or more will be described. That is, when d · Δn is smaller than 0.7 μm, the brightness (brightness) becomes small and becomes slightly dark visually, making it difficult to see as a liquid crystal display device, and the polarizing plate and the phase difference plate of the present invention. This makes it impossible to properly adapt the positional relationship between the components.
Therefore, in Examples 1 and 2, an upper retardation plate, a liquid crystal display element having STN liquid crystal therein, and a lower retardation plate are interposed in this order between a pair of polarizing plates, and the thickness d of the liquid crystal layer is 2 μm. <D <5 μm, and the lower retardation plate has a wavelength dispersion value α (Δn450 nm / Δn550 nm) of 1.
In a retardation plate satisfying 15 ≦ α ≦ 1.20, nx> ny ≧ n
z has a refractive index of 1.05 ≦ α <1.15 which is equal to or less than the wavelength dispersion value of the lower retardation plate, and
Further, it has a refractive index of nx>nz> ny.

In the present invention, the angle between the rubbing axis of the substrate closest to the slow axis of the phase difference plate and the rubbing axis of the substrate is 70 ° to 8 °.
By setting the angle in the range of 5 °, it is possible to obtain high-contrast, high-speed display capable of high-speed response without using a retardation plate having high wavelength dispersion in both of the liquid crystal display elements with high-speed response. In addition, the conventional problem that the viewing angle is narrow is less likely to occur, and a wider viewing angle can be achieved.

As described above, according to the first and second embodiments,
STN-LC with high-speed response of about 100msec
In order to compose D, it corresponds to the cell gap required, that is, the liquid crystal layer thickness d, and the liquid crystal material has a large refractive index anisotropy Δn and a high contrast and wide contrast which are problems when the wavelength dispersion is large. The compatibility between the viewing angle and the wavelength dispersion of the retardation plate and nx,
This can be realized by optimizing the combination of the three-dimensional refractive indices of ny and nx, and a liquid crystal display device with a high response speed and a wide viewing angle can be obtained without deteriorating high contrast.

[0061]

As described above, according to the present invention, a retardation plate having high wavelength dispersion is arranged below a liquid crystal display element,
Since a retardation plate having a wavelength dispersion property equal to or less than the high wavelength dispersion value of the lower retardation plate is disposed above the liquid crystal display element,
In configuring a liquid crystal display device having a high-speed response of about 00 msec, it is possible to achieve both high contrast and a wide viewing angle.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a liquid crystal display device 1 according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the wavelength dependence of the retarders 5 and 6 of FIG. 1 and other retarders.

FIG. 3 shows an embodiment of the present invention (Δn = 0.215) 1 and Δn.
It is a figure which shows the wavelength dependence of the refractive index in the liquid crystal material of = 0.134.

FIG. 4 is a diagram showing a positional relationship between components in the liquid crystal display device 1 of FIG.

FIG. 5 is a view showing a viewing angle characteristic curve of equal contrast according to the first embodiment of the present invention.

6 is a view showing a viewing angle characteristic curve of equal contrast of Comparative Example 1. FIG.

FIG. 7 is a view showing a viewing angle characteristic curve of equal contrast of Comparative Example 2.

FIG. 8 is a CIE chromaticity diagram showing the chromaticity of Example 1, Comparative Example 1, and Comparative Example 2 when ON and OFF.

FIG. 9 is a view showing a viewing angle characteristic curve of equal contrast according to the second embodiment of the present invention.

FIG. 10 is a view showing a viewing angle characteristic curve of equal contrast of Comparative Example 3.

11 is a view showing a viewing angle characteristic curve of equal contrast of Comparative Example 4. FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal display device 2 liquid crystal display element 3, 4 polarizing plate 5 upper retardation plate 6 lower retardation plate 7 front electrode substrate 8, 12 translucent substrate 9, 16 transparent electrode 10, 17 alignment film 11 back electrode substrate 19 liquid crystal

Continuation of the front page (56) References JP-A-4-194820 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/13363

Claims (5)

(57) [Claims] 1. A liquid crystal display device in which a liquid crystal display element in which a super twisted nematic liquid crystal is sandwiched between a front-side electrode substrate and a back-side electrode substrate is interposed between a pair of polarizing plates. And a lower retardation plate having high wavelength dispersion and a three-dimensional refractive index in a relationship of nx> ny ≧ nz is provided between the one polarizing plate and the other polarizing plate. A liquid crystal display device provided with an upper retardation plate having a wavelength dispersion equal to or less than a high wavelength dispersion value of the lower retardation plate and having a three-dimensional refractive index in a relationship of nx>nz> ny. 2. The liquid crystal display device according to claim 1, wherein the product d · Δn of the liquid crystal layer thickness d and the refractive index anisotropy Δn is 0.7 μm or more. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display element has a liquid crystal layer thickness d of 2 μm <d <5 μm. 4. The wavelength dispersion value α (Δn) of the lower retardation plate
450 nm / Δn550 nm) 1.15 ≦ α ≦ 1.2
0, the wavelength dispersion value α (Δn45) of the upper retardation plate.
2. The liquid crystal display device according to claim 1, wherein (0 nm / Δn550 nm) satisfies 1.05 ≦ α <1.15. 5. An angle between a slow axis of the phase difference plate and a rubbing axis of an electrode substrate closest to the slow axis is 70 ° to 5 °.
The liquid crystal display device according to claim 1, wherein the angle is set within a range of 85 °.