JP2659810B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a super twist type liquid crystal display device using a retardation plate.

<Prior Art> In general, a super twist type liquid crystal display device is colored yellow green or blue, but by using an optical compensator, color correction is performed and a bright and clear white / black display is obtained. Therefore, the display quality is improved, and the display can be used as a display of OA equipment such as a word processor and a computer.

As a super twist type liquid crystal display device which has been subjected to color compensation, there is a two-layer type super twist type liquid crystal display device, and coloring generated in the first layer (driving cell) is performed in the second layer (optical compensation cell). The color is corrected and achromatic. This structure requires two liquid crystal cells as compared with a single-layer super twist type liquid crystal display device, and thus has a problem that the thickness of the display device is increased and the weight is increased.

In order to solve this problem, a thin and lightweight super twist type liquid crystal display device has been developed by using a retardation plate made of a uniaxially stretched polymer film as an optical compensator. However, since the retardation film is made by stretching a polymer film, the optical properties are different between the stretching direction of the film and the direction perpendicular to the stretching direction, and the retardation plate is different from the two-layer type super twist type liquid crystal display device. The phase difference plate type super twist type liquid crystal display device has a problem that a color change due to a viewing angle or an elevation angle is large, that is, a viewing angle is narrow.

<Problems to be Solved by the Invention> A retardation plate composed of a uniaxially stretched polymer film uses optical anisotropy as an optical compensator. However, the refractive index (birefringence) differs between the stretching direction of the polymer film and the direction perpendicular thereto. The retardation (Δn · d), which is given by the product of the refractive index Δn and the thickness d of the film, is a physical quantity that gives the phase of light, and differs between the stretching direction of the polymer film and the direction perpendicular thereto. For example, in a retardation plate corresponding to a uniaxial normal crystal, retardation tends to decrease in a stretching direction and increase in a direction perpendicular to the retardation. When combined with a liquid crystal display cell,
In particular, in the stretching direction of the retardation plate, the difference between the retardation of the retardation plate and the retardation of the liquid crystal display cell increases, so that the transmitted light causes a phase difference and is colored. That is, color compensation is not performed, and the display contrast is reduced, so that the viewing angle is narrowed.

The present invention solves such a problem,
It is an object of the present invention to provide a liquid crystal display device which is thin, lightweight, can provide clear white / black display, and has a wide viewing angle.

<Means for Solving the Problems> According to the present invention, a plurality of retardation plates disposed on both main surfaces of a liquid crystal layer and disposed on one of the main surfaces are arranged so that retardation is added. The intersection angle between the slow axis of the first-layer phase difference plate and the slow axis of the n-th phase difference plate is set to 20 degrees or more and 40 degrees or less, and the liquid crystal display cell The intersection angle between the slow axis of the phase difference plate adjacent to the rubbing axis of the substrate adjacent to the liquid crystal display cell and the rubbing axis of the liquid crystal display cell is set from 70 degrees to 90 degrees. Also,
Further, the present invention is characterized in that the retardation plates to be disposed are disposed on the front and rear surfaces of the liquid crystal display cell, and are disposed symmetrically with respect to the liquid crystal display cell.

<Operation> This is because of the optical anisotropy of a uniaxially stretched polymer film used as a retardation plate. That is, the relative phase difference between the light (the ordinary ray and the extraordinary ray) that has passed through the liquid crystal panel is canceled out by passing through the phase difference plate, or the phases are made equal to each other to make the color achromatic.

This color compensation utilizes the property that the refractive index in the stretching direction of the polymer film and the refractive index in the direction perpendicular thereto are different. On the other hand, the viewing angle characteristics of the retardation plate must consider a three-dimensional refractive index. Now, the refractive index in the three-dimensional direction of the retarder is
n _MD (drawing direction), n _TD (direction orthogonal to drawing direction), n
_{Assuming that ZD} (thickness direction), the refractive index and the retardation as viewed from the stretching direction and the direction orthogonal thereto are given by the following formula, where 仰 is the elevation angle from the normal direction of the retardation plate.

(1) When viewed from the stretching direction Phase difference R _MD = { _MD d / cos} (2) When viewed from the direction perpendicular to the stretching direction Phase difference R _TD = {n _TD · d / cos} When the refractive indices in the three-dimensional directions are measured and substituted into the above equation, FIG. 3 is obtained. FIG. 3 shows the relationship between the elevation angle of the retardation plate and the change in retardation obtained from the theoretical formula. From this result, it is found that the retardation tends to decrease in the stretching direction of the retardation plate, and to increase in the direction perpendicular to the stretching direction (in the case of a uniaxial positive sign).

FIG. 4 shows the result of measuring the retardation of the retardation plate with respect to the elevation angle by the method of Senarmont. However, the retardation value when viewed from directly above is 1.0
It has been standardized as The orientation is measured every 15 ° with the stretching direction being 0 ° and the direction perpendicular to the stretching direction being 90 °. This result is consistent with the tendency obtained from the above theoretical formula. When the rate of change of the retardation with respect to the elevation angle is obtained from FIG. 4, FIG. 5 is obtained. On the other hand, FIG. 6 shows the result of determining the rate of change of the 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, the difference between the retardation of the liquid crystal display cell and the retardation of the retardation plate is large in the stretching direction of the retardation plate, and the transmitted light (usually Rays,
The extraordinary ray) causes a phase difference and is colored. As a result, the display angle is reduced because the display contrast is reduced. Therefore, in order to widen the viewing angle, an optical compensator having a small retardation change rate may be obtained by laminating retardation plates.

However, at this time, it is necessary to consider the vibration plane of the ordinary ray and the extraordinary ray passing through the phase difference plate and the oscillation plane of the ordinary ray and the extraordinary ray passing through the liquid crystal display cell. The vibrating plane of the ordinary ray is called the fast axis, and the vibrating plane of the extraordinary ray is called the slow axis. When two phase difference bodies are superimposed, the superposition method of making the fast axes (or slow axes) parallel to each other is called phase. In addition, a superposition method in which the fast axes (slow axes) are orthogonal to each other is called subtraction. As a result of many studies, we have found that when the retardation plates are additively laminated, the change in retardation is reduced, and as a result, the viewing angle is increased. Further, when the retardation plate is additionally laminated with n layers, the first layer and the nth layer
It was found that the viewing angle would not be effectively widened unless the crossing angle of the slow axis of the phase difference plate of the layer was 20 degrees or more. When stacking, color compensation must be considered. At this time, it is better to arrange the retardation plates from the second layer to the (n-1) th layer at the intersection angle of the slow axis of the first layer and the nth layer. The color difference is not compensated unless the retardation plate adjacent to is compensated for the liquid crystal cell.
It has been found that optimal color compensation can be obtained when the slow axis of the phase difference plate adjacent to the liquid crystal display cell is 70 to 90 degrees with respect to the rubbing axis of the substrate adjacent to the liquid crystal display cell.

The same effect can be obtained even when the retardation plates are arranged on the front and back surfaces of the liquid crystal display cell under the above-described lamination condition. At this time, when the retardation plates provided on the front and rear surfaces are disposed in a symmetric relationship with respect to the liquid crystal display cell, a liquid crystal display device having a wide viewing angle can be obtained.

<Example> An example of the present invention will be described with reference to FIGS.

FIG. 1 is a diagram showing a structure of an embodiment of the present invention described below, wherein 1 is an upper polarizing plate, 2 is an upper laminated retardation plate,
Denotes an STN liquid crystal cell, 4 denotes a lower laminated retardation plate, and 5 denotes a lower polarizing plate. The upper polarizer 1 has a single transmittance of 42% and a degree of polarization of 9
A 9.99% neutral gray type polarizing plate is used. The upper laminated retardation film 2 is made of a uniaxially stretched polymer film (polycarbonate) and has a thickness of 50 μm and a retardation value of 380 to 580 nm when laminated. Is filled with an LC material to which a levorotatory chiral dopant is added, and the twist angle is set to 240 degrees and d △ n (d is the thickness of the liquid crystal layer, Δn is the value of the refractive index anisotropy) = 0.83 to 0.92 μm. Panel was used. Also, the lower laminated retardation plate 4 is
The same number and the same retardation value as in the above were used, and the lower polarizing plate 5 was the same as the upper polarizing plate 1.

With reference to FIG. 2, a description will be given of an arrangement positional relationship in stacking the respective constituent members in this case.

2, P1 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 polarizer 1, and P4 is the arrow. The absorption axis of the lower polarizing plate 5, P5 is the slow axis (stretching direction) of the retardation plate adjacent to the STN liquid crystal cell of the upper laminated retardation plate 2, and P6 is the STN liquid crystal cell of the lower laminated retardation plate 4. The slow axis (stretching direction) of the adjacent retardation plate, θ ₁ is the angle between the liquid crystal molecule alignment axis P1 of the upper substrate and the slow axis of the retardation plate adjacent to the STN liquid crystal cell of the upper laminated retardation plate P5. , the angle between the slow axis of the retardation plate theta ₂ adjacent to the STN liquid crystal cell of the liquid crystal molecular orientation axis P2 and the lower laminated retardation plate P6 of the lower substrate, alpha crystal molecular orientation axis of the lower substrate P2
Represents an angle between the liquid crystal molecule orientation axis P1 of the upper substrate and the absorption axis P3 of the upper polarizing plate.

Claim 2 of the present invention satisfies the condition of θ ₁ + θ ₂ = 180 ° (constant) since the upper laminated phase difference plate and the lower laminated phase difference plate are symmetrically arranged. In order to stack the retardation plates, color compensation at the time of stacking must be ensured. Therefore, first, optimization of the arrangement of the phase difference plates was examined without stacking the phase difference plates.

A liquid crystal cell 3 having a d △ n of 0.83 μm and a twist angle of 240 ° is used as the upper retardation plate. θ ₁ = 50 ゜, 60 ゜, 70 ゜, 80
゜, 90 ゜, 100 ゜, 110 ゜ were set, and the color compensation was examined. still,
At this time, α and β were arbitrarily moved and adjusted so as to obtain white / black display. As a result, it was found that color compensation was obtained when θ ₁ = 70 ° to 90 °.

Next, the upper and lower retarders having a retardation value of 400 nm were used, and d 、 n of the liquid crystal cell 3 was 0.92 μm.
m, having a twist angle of 240 degrees. θ ₁ = 50 ゜, 60
゜, 70 ゜, 80 ゜, 90 ゜, 100 ゜, 110 ゜, θ ₂ = 130 ゜, 120 ゜, 1
As a result of setting color at 10 °, 100 °, 90 °, 80 °, and 70 °, and examining color compensation, color compensation was also obtained when θ ₁ = 70 ° to 90 ° (θ ₂ = 110 ° to 90 °). I found out.

At this time, it has been found that the viewing angle becomes wider as the color compensation is obtained. Therefore, when a phase difference plate is laminated, the phase difference plate adjacent to the liquid crystal cell is 70 ° ≦ θ ₁ ≦ 90 ° (90 ° ≦ θ
₂ ≦ 110 °).

Example 1 A phase difference plate is laminated with a phase difference plate adjacent to a liquid crystal cell as a first layer, and then with a second layer, a third layer, and so on. The number of layers of the upper laminated phase difference plate 2 is set to two, and the retardation of the first layer
The liquid crystal cell 3 has a d △ n of 0.92 μm.
m, having a twist angle of 240 degrees. θ1 = 70 °, and the crossing angles of the slow axes (stretching directions) of the first and second retarders are 0 °, 10 °, 20 °, 30 °, 40 °, 50 °. As a result of examining the viewing angle and the color compensation, good results were obtained when the crossing angle was in the range of 20 ° to 40 °, and the optimum was particularly obtained when the crossing angle was 25 °. At this time, α = 40 ° and β = 50 °. At this time, the viewing angle was increased by about 7 ° in the viewing angle direction as compared with the case where the layers were not stacked.

Example 2 The number of layers of the laminated retardation plate 2 was set to two, the first and second retardation plates used had a retardation of 200 nm, and d △ n of the liquid crystal cell 3 was , 0.90 μm, and a twist angle of 240 ° are used. The lower laminated retardation plate 4 is not laminated and is made into one sheet, and one having a retardation of 400 nm is used. θ ₁ = 90 ° θ ₂ = 90 °, and the crossing angles of the slow axes (stretching directions) of the retardation plates of the first layer and the second layer are 0 °, 10 °, 20 °, 30 °. As a result of examining the viewing angle and the color compensation at a setting of 40 ° and 50 °, good results were obtained when the crossing angle was in the range of 20 ° to 40 °, and the optimum was particularly obtained when the crossing angle was 30 °. At this time, α = 130 ° and β = 20 °. At this time, the viewing angle was increased by about 5 ° in the viewing angle direction and by about 3 ° in the anti-viewing angle direction as compared with the case where the layers were not stacked.

Example 3 The number of laminations of the laminated retardation plate 2 was two, and the retardation plates of the first layer and the second layer had a retardation of 200 nm. And the retardation plate of the first layer and the second layer has retardation.
Use a 200nm one. D △ n of the liquid crystal cell 3 is 0.90
Use a micrometer with a twist angle of 240 degrees. θ ₁ = 90
Θ, θ ₂ = 90 °, and the upper laminated retarder 2 and the lower laminated retarder 4 both have an intersection angle of 0 ° between the slow axis (stretching direction) of the first layer and the second layer. , 10 ゜, 20 ゜, 30 ゜, 40 ゜, 50 ゜, and as a result of checking the viewing angle and color compensation, the intersection angle was 20 ゜ -40
Good results were obtained when the angle was ゜, and the optimum was especially obtained when the crossing angle was 30 °. At this time, α = 180 ° and β = 5 °. At this time, the viewing angle was increased by about 2 ° in the viewing angle direction and by about 7 ° in the anti-viewing angle direction as compared with the case where the layers were not stacked.

FIG. 7 shows the results of measuring the viewing angle characteristics of the optimal combination example in the first embodiment among the above-described embodiments. FIG. 8 shows the results of measuring the viewing angle characteristics of the optimal combination examples in the second and third embodiments.

<Effects of the Invention> According to the present invention, a change in retardation with respect to the viewing angle (elevation angle) of a retardation plate can be reduced.
A high-quality liquid crystal display device that is lightweight and has good display contrast and that is less dependent on viewing angle can be obtained.

[Brief description of the drawings]

FIG. 1 is a drawing for explaining the structure of a liquid crystal display device for explaining an embodiment of the present invention, FIG. 2 is a plan view showing the positional relationship of the embodiment, and FIG. FIG. 4 shows the relationship between the retardation change and the actually measured elevation angle of the retardation plate, and FIG. 5 shows the relationship between the retardation change rates in all directions of the retardation plate. , FIG. 6 is a diagram showing the relationship of the retardation change rate in all directions of the liquid crystal panel, and FIG. FIG. 8 is a view showing the results of actually measuring the viewing angle characteristics of the optimum combination examples in the second and third embodiments. 1: Upper polarizer, 2: Upper laminated retarder, 3: STN liquid crystal cell, 4: Lower laminated retarder, 5: Lower polarizer.

Continuation of front page (72) Inventor Yumi Yoshimura 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-2-33130 (JP, A)

Claims (2)

(57) [Claims] 1. A liquid crystal display device comprising a pair of polarizers and a liquid crystal layer super-twisted nematic aligned and a laminate of retarders comprising a plurality of uniaxially stretched polymer films interposed therebetween. Are disposed on both main surfaces of the liquid crystal layer, and n (n is an integer of 2 or more) of the retardation films laminated on one main surface of the liquid crystal layer are arranged so that retardation thereof is added. The intersection angle between the slow axis of the first layer located closer to the liquid crystal layer and the slow axis of the n-th layer located farther from the liquid crystal layer is 20 degrees or more and 40 degrees or less. A liquid crystal display device wherein the slow axis of the first layer intersects the alignment axis of the closest liquid crystal molecule of the liquid crystal layer at an angle of 70 degrees or more and 90 degrees or less. 2. The liquid crystal layer according to claim 1, wherein the slow axis of the first phase difference plate disposed on one main surface side of the liquid crystal layer forms an angle between the slow axis of the liquid crystal layer and the alignment axis of the closest liquid crystal molecules of the liquid crystal layer. The sum of the slow axis of the retardation plate of the first layer disposed on the other main surface side of the layer and the angle formed with the alignment axis of the closest liquid crystal molecules of the liquid crystal layer is set to approximately 180 degrees. The liquid crystal display device according to claim 1, wherein