JPH03230120A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a tin lightweight liq. crystal device enabling clear black-and- white display and ensuring a wide angle of vision by using uniaxially stretched polycarbonate films as phase plates and specifying the direction of laminating of the films. CONSTITUTION:An upper laminated phase plate 2 and a lower phase plate 4 are set above and below an STN liq. crystal cell 3 and uniaxially stretched polycarbonate films are used as the plates 2, 4. the upper plate 2 is obtd. by laminating two phase plates and these plates are laminated at >=20 deg. angle of crossing of the lagging axis of the 1st plate and that of the 2nd plate so that the direction of the lagging axis of the 2nd plate is made parallel to a direction in which the dependency of the retardation value of the 1st plate on elevation is minimized. The angle of crossing of the delay phase axis of the phase plate adjacent to the cell 3 and the axis of rubbing of the substrate adjacent to the plate is regulated to 70-90 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a super twist type liquid crystal display device using a retardation plate as an optical compensator.

<Prior Art> Generally, a super twist type liquid crystal display device is colored yellow-green or blue, but by using an optical compensator, color correction can be performed and a bright and clear white/black display can be obtained. Therefore, the display quality is improved and it can be used as a display for A-A devices such as word processors and computers.

As a super twist type liquid crystal display device with color compensation, there is a two-layer type super twist type liquid crystal display device.
The coloration generated in the first layer (driving cell) is corrected in the second layer (optical compensation cell) to make it achromatic. This structure requires two liquid crystal cells compared to a single-layer super-twist type liquid crystal display device, and therefore has the problem that the display device becomes thicker and weighs more.

In order to solve this problem, by using a retardation plate made of a uniaxially stretched polymer film as an optical compensator,
A thin and lightweight super twist type liquid crystal display device has been developed. However, since the retardation plate is made by stretching a polymer film, the optical properties are different in the direction in which the film is stretched and in the direction perpendicular to this direction, making it difficult to compare with a two-layer super twist type liquid crystal display device. The super twist type liquid crystal display device using a retardation plate has a problem in that the color change is large depending on the viewing angle or the elevation angle, that is, the viewing angle is narrow.

<Problems to be Solved by the Invention> - A retardation plate made of an axially stretched polymer film is used as an optical compensator for optical anisotropy. However, the refractive index (birefringence) is different between the direction in which the polymer film is stretched and the direction perpendicular thereto. Retardation (Δn-d), which is the product of the refractive index Δn and the film thickness d, is a physical quantity that gives the phase of light, but it differs between the direction in which the polymer film is stretched and the direction perpendicular to this, for example. - In a retardation plate corresponding to an axial positive crystal, retardation tends to decrease in the stretching direction and increase in the direction orthogonal to this. When combined with a liquid crystal display cell, the difference between the retardation of the retardation plate and the retardation ratio of the liquid crystal display cell becomes large, especially in the stretching direction of the retardation plate, so the transmitted light produces a phase difference. , to color. In other words, color compensation is no longer performed, the contrast of the display decreases, and the viewing angle becomes narrower.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and aims to provide a liquid crystal display device that is thin, lightweight, provides clear white/black display, and has a wide viewing angle.

Means for Solving the Problems> The present invention provides a super twist type liquid crystal display device using a retardation plate made of a uniaxially stretched polymer film as an optical compensator, in which a retardation plate 7 is provided on at least one side of a liquid crystal display cell. It has two laminated retardation plates in which the phase retardation plate is added, and the intersection angle between the slow axis of the first layer retardation plate and the slow axis of the second layer retardation plate is 20 degrees or more. , and the slow axis direction of the second layer is parallel to the direction in which the elevation angle dependence of the retardation value of the first layer is the minimum, and the liquid crystal display cell is The intersection angle between the slow axis of the adjacent retardation plate and the rubbing axis of the adjacent substrate of the liquid crystal display cell is 70
degree to 90 degrees, and each retardation plate is made of a uniaxially stretched polymer film of polycarbonate.

The laminated retardation plate may be disposed on only one side of the liquid crystal display cell or on the front and back sides of the liquid crystal display cell.

In addition, in the case of a combination of laminated and single layer, one side of the liquid crystal display cell is the laminated retardation plate, and the other side is the slow axis of the retardation plate adjacent to the liquid crystal display cell and the adjacent substrate of the liquid crystal display cell. A single-layer retardation plate having an intersecting angle of 70 degrees to 90 degrees with the rubbing axis is arranged, and the single-layer retardation plate is made of a uniaxially stretched polymer film of polycarbonate.

<Function> Uniaxially stretched polymer film is used as a retardation plate because of its optical anisotropy. That is, the relative phase difference between the light (ordinary rays and extraordinary rays) that has passed through the liquid crystal panel is canceled out by transmitting it through a retardation plate, or the phases are aligned.
It is achromatic.

This color compensation utilizes the property that the refractive index of the polymer film in the stretching direction is different from the refractive index in the direction orthogonal thereto. On the other hand, regarding the viewing angle characteristics of the retardation plate, three-dimensional refractive index must be considered. Now, the refractive index in the three-dimensional direction of the retardation plate is n
, o (stretching direction), nTD (direction orthogonal to the stretching direction)
, n ZD (thickness direction), the refractive index and letter day/gin when viewed from the stretching direction and the direction orthogonal thereto are expressed by the following formula, where φ is the elevation angle from the normal direction of the retardation plate. Given.

(1) When viewed from the stretching direction, the refractive index is nMn・Inxn'n zo'/ (nxo'sin'l+nz
o'cos'φ)l l/! -nT.

Retardation RMD"△MD' d / Cosφ (2) Refractive index △nTI when viewed from the direction orthogonal to the stretching direction) nMo (nto'nzo'/ (nTn'1
iin'φ+nzn"cO8"φ)l"'Phase difference RTD
=ΔnTo + d/cosφ By measuring the refractive index in each three-dimensional direction and substituting it into the above equation, FIG. 3 is obtained.

FIG. 3 shows the relationship between the change in retardation angle and the elevation angle of the retardation plate, which was determined from a theoretical formula. From this result, it can be seen that in the stretching direction of the retardation plate, the retardation ratio decreases, and in the direction perpendicular to the stretching direction, the retardation ratio tends to increase (in the case of -axiality positive sign).

By the way, -axially stretched polymer films of polycarbonate (PC) and polyvinyl alcohol (PVA) are known as retardation plates, and the results of measuring the retardation/g of the retardation plate with respect to the elevation angle using Senarmont's method are as follows. are shown in FIG. 4(A) (polycarbonate) and FIG. 4(B) (polyvinyl alcohol). However, the retardation/yellow value when viewed from directly above must be 1. It is normalized as 0. In addition, the orientation is set with the stretching direction O'' and the direction orthogonal to the stretching direction 90°, and measurements are taken every 15° between them. This result is consistent with the tendency obtained from the above-mentioned theoretical formula. The change rate of retardation with respect to the elevation angle is determined from Fig. 4 (A) and (B), and Fig. S (A) and (
B) is obtained.

On the other hand, FIG. 6 shows the results of determining the rate of change in retardation with respect to the elevation angle of the liquid crystal display cell. When such a retardation plate and a liquid crystal display cell are combined, there is a large difference between the retardation of the liquid crystal display cell and the retardation of the retardation plate in the stretching direction of the retardation plate. (light rays, extraordinary rays) produce a phase difference and are colored. As a result, the contrast of the display decreases, and the viewing angle becomes narrower. Therefore, in order to widen the viewing angle, an optical compensator with a small rate of change in retardation can be obtained by laminating retardation plates.

Figures 5(A) and 5(B)--representing changes in azimuth and elevation angle retardation with respect to the respective stretching directions for polycarbonate and polyvinyl alcohol retardation plates. According to m-, polycarbonate retardation plates (Fig. 5(A)) shows that at elevation angles of 15° and 30°, the change in retardation due to azimuth is slight. But 45°, 600
At this point, changes in retardation depending on orientation can be clearly seen. In particular, at an elevation angle of 600, the rate of change is about twice that in the stretching direction and in the direction perpendicular to the stretching direction.

On the other hand, a polyvinyl alcohol retardation plate (Fig. 5 (
B)) At an elevation angle of 15°, there is not much change in the retardation of 7:1 depending on the azimuth, but at an elevation angle of 45° and 60°, the change is more drastic than that of the polycarbonate retardation plate.
At 90°, the rate of change is as much as 8 times between the stretching axis and the 90° direction.

Therefore, as the elevation angle increases, the rate of change in the retardation of the polycarbonate retardation plate is smaller than that of the polyvinyl alcohol retardation plate, so in order to keep the retardation change with respect to the viewing angle (elevation angle) low, the former polycarbonate retardation plate is Appropriate.

At this time, it is necessary to consider the vibration planes of the ordinary rays and extraordinary rays passing through the retardation plate and the vibration planes of the ordinary rays and extraordinary rays passing through the liquid crystal display cell. The vibration plane of the ordinary ray is called the fast axis, and the vibration plane of the extraordinary ray is called the slow axis. When two retardation plates are stacked, the stacking method in which their fast axes (or slow axes) are parallel to each other is referred to as the slow axis. The way in which the fast axes (additional and slow axes) are orthogonal to each other is called phase subtraction.

As a result of numerous studies, we have found that the retardation change is smaller when the retardation plates are stacked additively, resulting in a wider viewing angle. Furthermore, when two layers of retardation plates are stacked additively, the viewing angle cannot be effectively widened unless the intersection angle of the slow axes of the first and second layer retardation plates is 20 degrees or more. I realized that.

In particular, when laminating two retardation plates, as shown in Fig. 5 (A)
It is effective to use the direction that minimizes the elevation dependence shown by . At this time, with respect to the direction in which the retardation/yon change with respect to the elevation angle of the first layer retardation plate is minimized,
It has been found that stacking the second layer of retardation plates so that their slow axes are parallel to each other reduces the change in retardation and enlarges the viewing angle when combined with a liquid crystal display cell.

Laying the slow axes of the second layer retardation plates parallel to each other in the direction in which the retardation change of the first layer retardation plate is minimized means that each retardation plate (7) l/tad. −/yon change is mutually aligned in the direction that minimizes the change,
As a result, in the laminated retardation plate, the decrease in the retardation value in the stretching direction is suppressed, and the change in retardation value is made uniform, so when combined with a liquid crystal display cell, the retardation plate in the stretching direction is suppressed. The letter day/yon difference will be smaller and the viewing angle will be wider.

The most appropriate angle of intersection of the slow axes of the first and second layer retardation plates was in the range of 200 to 400.

In addition, when laminating layers, the retardation plate adjacent to the liquid crystal display cell must be arranged reciprocally with respect to the liquid crystal cell for color compensation to occur, so the slow axis of the retardation plate adjacent to the liquid crystal display cell is It has been found that optimal color compensation is obtained at an angle of 70 to 90 degrees with respect to the rubbing axis of the adjacent substrate of the display cell.

The laminated arrangement conditions described so far apply even when retardation plates are placed on the front and back sides of the liquid crystal display cell, or when a laminated retardation plate is used on one side and a single layer retardation plate is used on the other side.
A similar effect can be obtained. Note that when the retardation plates disposed on the front and back surfaces are arranged symmetrically with respect to the liquid crystal display cell, a liquid crystal display device with a wide viewing angle can be obtained.

<Example> Embodiments of the present invention will be described based on FIGS. 1 and 2.

FIG. 1 is an explanatory diagram showing the structure of an embodiment of the present invention described below, in which 1 is an upper polarizing plate, 2 is an upper laminated retardation plate,
3 is an STN liquid crystal cell, 4 is a lower retardation plate, and 5 is a lower polarizing plate. The upper polarizing plate 1 is a neutral gray type polarizing plate with a single transmittance of 42% and a polarization degree of 9999%.
The upper laminated retardation plate 2 is made of a polycarbonate uniaxially stretched polymer film with a thickness of 50 μm and has a retardation value of 380 to 580 nm when laminated.
C material is enclosed, twist angle is 240 degrees, d△n (d is the liquid crystal layer thickness, △n is the value of refractive index anisotropy) = 0.83 to 0.9
A panel set at 2 μm was used. Further, the lower retardation plate 4 may not be provided at all, may be a single layer retardation plate, or may be similarly provided with two retardation plates. When a laminated or single-layer retardation plate is provided, the retardation plate is made of a uniaxially stretched polymer film of polycarbonate and has the same retardation value as the upper retardation plate 2. As for the lower polarizing plate 5, the same one as the upper polarizing plate 1 was used.

In this case, the arrangement positional relationship when stacking the respective constituent members will be explained using FIG. 2.

Among the arrows shown in FIG. 2, Pl is the liquid crystal molecule orientation axis of the upper substrate constituting the STN liquid crystal cell 3, P2 is the liquid crystal molecule orientation axis of the lower substrate, P3 is the absorption axis of the upper polarizing plate 1, and P4 is The absorption axis of the lower polarizing plate 5, P5 is the ST of the upper laminated retardation plate 2.
N slow axis (stretching direction) of the retardation plate adjacent to the liquid crystal cell,
P6 is the slow axis (stretching direction) of the retardation plate adjacent to the STN liquid crystal cell of the lower retardation plate 4, and θ1 is the liquid crystal molecule orientation axis P1 of the upper substrate and adjacent to the STN liquid crystal cell of the upper laminated retardation plate P5. The angle between the slow axis of the retardation plate and the slow axis of the retardation plate, θ, is the angle between the liquid crystal molecule orientation axis P2 of the lower substrate and the slow axis of the retardation plate adjacent to the STN liquid crystal cell of the lower retardation plate P6, α represents the angle between the liquid crystal molecule orientation axis P2 of the lower substrate and the absorption axis P4 of the lower polarizing plate 5, and β represents the angle between the liquid crystal molecule orientation axis P1 of the upper substrate and the absorption axis P3 of the upper polarizing plate 1. ing.

In order to stack retardation plates, color compensation must be ensured when stacking. Therefore, we first considered optimizing the arrangement of the retardation plates without stacking them.

The upper retardation plate 2 has a retardation value of 580 nm, and the liquid crystal cell 3 has a dΔn of 0.83 μm and a twist angle of 240 degrees.

e, -50°, 60°, 700.80°, 90', 1
00' and 110', and color compensation was examined. At this time, α and β were arbitrarily moved and adjusted to obtain a white/black display. As a result, it was found that color compensation can be obtained when θ1-700 to 90'.

Next, the upper and lower retardation plates 2 and 4 have a retardation value of 400 nm, and the liquid crystal cell 3 has a dΔn of 0.
92 μm1 with a twist angle of 240 degrees. θ
1-50°, 60', 70°, 80°90°, 100°
, 110°, θ2-1300, 120°, 11O°, 1
00', 90°, 80°, and 70°, and checked the color compensation. The result was also θ1-70~900 (θ, = 110'~
It was found that color compensation can be obtained when the angle is 90°).

It has been found that the more color compensation is obtained, the wider the viewing angle becomes. Therefore, when stacking retardation plates, the retardation plate adjacent to the liquid crystal cell should be 70'≦01≦90° (90°
≦θ, ≦110').

Example 1 Lamination of retardation plates is performed such that the retardation plate adjacent to the liquid crystal cell is first stacked.
The second layer will be laminated below. Each retardation plate is made of polycarbonate-axially stretched polymer film, and two sheets are laminated together.

The retardation of the first and second layer retardation plates is 40.
0nm, and d△n of liquid crystal cell 3 is 0°92μ.
m1 Use one with a twist angle of 240 degrees.

Note that the first embodiment is a case where the lower retardation plate 4 is not provided.

Here, θ is set to 70°, and the intersection angles of the slow axes (stretching direction) of the first and second layer retardation plates are 010° and 20°.
As a result of adjusting the viewing angle and color compensation by setting the angle to 20°, 30', 40°, and 500, good results were obtained when the intersection angle was between 20° and 40', and the best result was especially when the intersection angle was 25°. Met. At this time, the values were α-40' and β-50'. At this time, 29° in the viewing angle direction and 14° in the anti-viewing angle direction were obtained, and the viewing angle was about 7° wider in the viewing angle direction than when no lamination was performed.

Example 2 The number of laminated layers of the upper laminated retardation plate 2 was set to two, and the retardation of the first and second layer retardation plates was 200 nm, and dΔn of the liquid crystal cell 3 was as follows. 0.90μm1
Use one with a twist angle of 240 degrees. The lower retardation plate 4 is not laminated, but is made of a single sheet, and has a retardation of 400.
nm is used. Each of the laminated and single layer retardation plates is composed of a uniaxially stretched polymeric film of polycarbonate.

Set θl-90°, θ, = 90', and
The intersection angle of the slow axes (stretching direction) of the retardation plate in each layer is O',
As a result of examining the viewing angle and color compensation by setting the intersection angle to 10', 20°, 30°, 40°, and 50°, good results were obtained when the intersection angle was between 20° and 40', especially when the intersection angle was 30°. It was optimal when At this time, α-1300 and β=200. At this time, the viewing angle was widened by about 5° in the viewing angle direction and about 3° in the opposite viewing angle direction, compared to when no lamination was performed.

Example 3 The number of laminated layers of the upper laminated retardation plate 2 is two, and the first layer is
The second layer retardation plate has a retardation of 200 nm, and the number of stacked layers of the lower retardation plate 4 is two.
The retardation plate for the second layer is 200n in retardation.
Use m. Each of the upper and lower laminated retardation plates is made of a uniaxially stretched polymer film of polycarbonate. d△n of liquid crystal cell 3 is 0.90μ
m1 Use one with a twist angle of 240 degrees. θ1=9
0°θ, = 90', and both the upper laminated retardation plate 2 and the lower laminated retardation plate 4 are aligned with the slow axes of the first and second layers (
(Stretching direction) crossing angle 0°, 10', 20°, 30°, 40
As a result of examining the viewing angle and color compensation, good results were obtained when the crossing angle was between 20° and 40°, and in particular, the crossing angle of 30' was optimal. α at this time =
80°, β=5°. At this time, the viewing angle was widened by about 2° in the viewing angle direction and about 7° in the opposite viewing angle direction compared to when no lamination was performed.

Comparative Example 1 In Example 1, the material of each retardation plate of the upper laminated retardation plate 2 was changed from polycarbonate to polyvinyl alcohol. The other configuration 1 conditions and the like are completely the same as those described in the first embodiment. As a result of viewing angle measurement when the intersecting angle was set to 25°, Comparative Example 1 had an angle of 20° in the viewing angle direction and 120 in the anti-viewing angle direction, which was 9° in the viewing angle direction than when using the polycarbonate retardation plate in Example 1. The viewing angle was inferior by 2° in the direction opposite to the viewing angle.

Comparative Example 2 In Example 2, similarly, the material of each of the 21 upper laminated retardation plates and the lower retardation plate 4 was changed from polycarbonate to polyvinyl Alfur. The other configuration 1 conditions and the like are completely the same as those described in the first embodiment. However, since polyvinyl alcohol does not have a retardation plate having a wavelength of 200 nm, polycarbonate was used as the material for each retardation plate of the upper laminated retardation plate. The intersection angle was set to 30°, and the viewing angle was measured. In Comparative Example 2, it was 35° in the viewing angle direction and 14° in the opposite viewing angle direction. The viewing angle was 9° inferior to that in Example 2 when the polycarbonate retardation plate was used in the opposite viewing angle direction.

As is clear from the results of Comparative Examples 1 and 2, a liquid crystal display device using a polycarbonate retardation plate has a wider viewing angle than a liquid crystal display device using a polyvinyl alcohol retardation plate. As shown in Fig. 5(A) and Fig. 5(B), the polycarbonate retardation plate has an elevation angle of 15° and a 3.
At 00, no change in retardation due to orientation is observed,
This is because the retardation change rate at elevation angles of 45° and 60° is also 1/4 of the change rate of the polyvinyl alcohol retardation plate.

A comparison table between Example 1.2 and Comparative Examples 1 and 2 is shown below.

FIG. 7 shows the results of measuring the viewing angle characteristics for the optimal combination example of Example 1 among the above examples. FIG. 8 shows the results of measuring the viewing angle characteristics for the optimal combination of Examples 2 and 3.

<Effects of the Invention> According to the present invention, since the retardation change with respect to the viewing angle (elevation angle) of the retardation plate can be reduced, the display contrast can be improved in a thin, lightweight, and super twist type liquid crystal display device using the retardation plate. A high-quality liquid crystal display device with less viewing angle dependence can be obtained by taking advantage of the favorable characteristics.

[Brief explanation of drawings]

Fig. 1 is a structural explanatory drawing of a liquid crystal display device to provide a detailed explanation of the present invention, Fig. 2 is a plan view showing the positional relationship of the same embodiment, and Fig. 3 is a diagram showing the elevation angle of the retardation plate obtained from the theoretical formula. A diagram showing the relationship between retardation changes, Figure 4 (A),
(B) is a diagram showing the relationship between the change in retardation angle and the actually measured elevation angle of polycarbonate and polyvinyl alcohol retardation plates, respectively. 6 is a diagram showing the relationship between the retardation change rate in all directions of the liquid crystal panel, and FIG. 7 is a diagram showing the viewing angle characteristics for the optimal combination example in Example 1. FIG. 8 is a diagram showing the results of actual measurement of the viewing angle characteristics for the optimal combination example of the second and third embodiments. 1: Upper polarizing plate, 2: Upper laminated retardation plate, 3: STN liquid crystal cell, 4. lower laminated retardation plate, 5. Lower polarizer.

Claims (1)

[Claims] 1. In a super twist type liquid crystal display device using a retardation plate made of a uniaxially stretched polymer film as an optical compensator, two sheets having retardation added to at least one side of the liquid crystal display cell The intersecting angle between the slow axis of the first layer retardation plate and the slow axis of the second layer retardation plate is 20 degrees or more, and With respect to the direction where the elevation angle dependence of the retardation value of the retardation plate is minimum,
The second layer is laminated so that its slow axis direction is parallel, and the intersection angle between the slow axis of the retardation plate adjacent to the liquid crystal display cell and the rubbing axis of the substrate adjacent to the liquid crystal display cell is 70 degrees. 90 degrees, and each retardation plate is made of a uniaxially stretched polymer film of polycarbonate. 2. A liquid crystal display device according to claim 1, characterized in that a laminated retardation plate is disposed on the front and back sides of a liquid crystal display cell. 3. In the liquid crystal display device according to claim 1, a laminated retardation plate is arranged on one side of the liquid crystal display cell,
On the other side, the intersection angle between the slow axis of the retardation plate adjacent to the liquid crystal display cell and the rubbing axis of the substrate adjacent to the liquid crystal display cell is 7.
1. A liquid crystal display device comprising a single-layer retardation plate having an angle of 0 to 90 degrees, the single-layer retardation plate being made of a uniaxially stretched polymer film of polycarbonate.