JPH02125224A - Electrooptic element - Google Patents

Abstract

PURPOSE:To increase a visual field angle with simple constitution by providing a couple of polarizing plates arranged on the top and reverse sides across a liquid crystal cell and a couple of phase films arranged between the polarizing plates, and making the drawing axes of the couple of phase films cross each other at right angles. CONSTITUTION:The electrooptic element consists of the nematic liquid crystal cell 5 which is twisted and oriented between opposite electrodes and the couple of polarizing plates 2 and 7 arranged across the liquid crystal cell 5, the couple of phase films 8 and 9 are provided between the couple of polarizing plates 2 and 7, and the drawing axes 10 and 11 of the phase films 8 and 9 are made to cross each other at right angles. Namely, the couple of polarizing films 8 and 9 are inserted and visual angle characteristics are improved in the arrangement relation between the liquid crystal cell 5 and polarizing plates 2 and 7 without causing variation in display performance which is viewed from the front. Consequently, the visual angle dependency of the contrast and hue is reduced to increase the visual field angle.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electro-optical element, particularly an electro-optical element using twisted oriented nematic liquid crystal, which has excellent viewing angle characteristics.

Conventional Electro-optical elements that have a field-effect liquid crystal panel sandwiched between a pair of polarizing plates include twisted nematic mode (1°N mode) using nematic liquid crystal twisted at approximately 90°, and 90° twisted nematic mode. There is an electro-optical element of vertical twisted nematic mode (STN mode) that is oriented at a twist angle of .degree. or more and less than 360.degree. In particular, when using these electro-optical elements as direct-view display devices, the viewing angle characteristics of contrast and color tone are
It is generally inferior to the widely used CRT, and is one of the drawbacks of liquid crystal display devices.

Figures 3(a) and 3(b) show the contrast of an electro-optical element in a conventional TN mode with a normally black display format in which the polarizing plate is arranged in a parallel Nicol state and the light is blocked when the light is not turned on. Regarding the viewing angle dependence, FIG. 4 shows the relationship between the orientation direction of the liquid crystal panel of this electro-optical element and the direction of the transmission axis of the polarizing plate. The light Ω 2 emitted from the light source 21 passes through a polarizing plate 24 having a transmission axis 23 at an angle of 7 from the vertical direction 22 of one display surface, and enters the TN cell 25 as linearly polarized light in this direction. The inner surface of the lower substrate 26 of the T N cell is aligned by rubbing in the direction 27 shown by the arrow pointing toward the mouth, and the inner surface of the upper substrate 28 is aligned in the direction 29 that intersects with this direction. There is. The incident linearly polarized light exits as linearly polarized light at a position where the plane of polarization has been rotated by an angle Ω as it passes through the TN center. When the TN hill is not lit, the illumination light is blocked by a polarizing plate 31 whose transmission axis 30 is disposed orthogonal to the emitted linearly polarized light. By applying a voltage to the TN cell and aligning the liquid crystal perpendicularly to the substrate surface, the rotation of the upper leg of linearly polarized light is canceled and the illumination light is transmitted in the viewing direction. Figure 3 (aL (b) is Ω-90°, the product of the refractive index anisotropy of nematic liquid crystal 11Δ[1 and the rail thickness d of the TN cell, Δn-d = 470 nm] The left and right sides of the TN cell with the above configuration The visual angle dependence of directional contrast and the vertical visual angle dependence are shown.

Problems to be Solved by the Invention Conventional TN mode or STN mode liquid crystal electro-optical elements have viewing angle dependence in contrast and color tone, which is a major drawback as a direct-view display device. The present invention provides an electro-optical element that has a relatively simple configuration and can expand the viewing angle.

Means for Solving the Problems The electro-optical element of the present invention comprises a twisted oriented nematic liquid crystal cell between opposing electrodes, and a pair of polarizing plates disposed on the front and back sides with the liquid crystal cell in between. At least one pair of phase films is provided between the pair of polarizing plates, and the stretching axes of the pair of phase films are substantially perpendicular to each other.

TN mode or S mode configured by sandwiching two polarizing plates
Several models explain why viewing angle dependence of contrast and color tone occurs in liquid crystal optical elements such as TN mode. When linearly polarized light is incident on a TN mode or STN mode liquid crystal panel, the output light generally becomes elliptically polarized light. (If you specify the temporary transmission axis of the 1,1 light and the alignment direction of the liquid crystal cell, the output light may become linearly polarized in a certain direction. By arranging the position, it is possible to control the transmission and blocking of light. However, this is a function seen from the front of the liquid crystal cell, and the elliptically polarized component of the emitted light remains in the viewing angle direction that is deviated from the front, and the light Even in the blocked state, light leaks when viewed from an angle, and this phenomenon includes wavelength dispersion, resulting in color change and color tone changing with the viewing angle.Such contrast and color tone characteristics in arbitrary three-dimensional directions are due to the liquid crystal inside the KI product cell. By modeling the molecular orientation three-dimensionally, B e r r
Prediction calculations are performed using numerical analysis such as ETSA's 4×4 matrix method, and the optical design of the liquid crystal panel is based on this. In this way, it is generally believed that the viewing angle dependence is mainly related to the optical characteristics inside the liquid crystal cell. In contrast, the present invention focuses on the fact that the optical properties of the polarizing plate itself have a large viewing angle dependence, and has found that this can be improved by using a phase film as described below.

Of course, in an STN mode liquid crystal cell, there is no solution in which incident linearly polarized light becomes linearly polarized light upon exit (also, wavelength dispersion is large, and there is a problem that the background color changes from blue to yellow. Attempts have been made to improve these display characteristics by inserting anisotropic bodies between polarizing plates.On the other hand, the phase films used in the present invention are used in pairs, and they are arranged approximately orthogonally. If the product Δn-d of the refractive index anisotropy Δn and the film thickness d of the pair of phase films is equal, the light that passes perpendicularly through the pair of phase films will be After being birefringent and undergoing a phase change in the eye, the second layer undergoes an opposite phase change and returns to its original state, with no apparent change.In this way, the pair of phase films of the present invention can be inserted into This prevents or minimizes changes in display performance when viewed from the front, and improves viewing angle characteristics in the arrangement relationship between the liquid crystal cell and the polarizing plate.

As shown in FIG. 5(a), the transmission axes 32 and 33 of the polarizing plate
θ9o direction and θ45 when arranged in orthogonal Nicols
The viewing angle dependence of the degree of polarization in the direction is shown in Figures 5(b) and (c).
). Here, the degree of polarization is determined by arranging the transmission axis of the polarizing plate in parallel Nicols, and the transmittance seen from the vertical direction is T//,
Arranged in the above-mentioned orthogonal nicols, the transmittance when viewed from any direction is defined as θ.

It is defined as In this way, the polarization axis direction θ45°0−
The degree of polarization seen from θ0.45 has little dependence on the viewing angle and has excellent light-shielding properties in the crossed Nicols state, while in the θ0. The viewing angle dependence of the degree of polarization when viewed from θ9° is large, and large light leakage is observed from oblique directions.

On the other hand, as shown in FIG. As shown by curve (2) in FIG. 6(C), the viewing angle dependence of the degree of polarization in the viewing angle θSG direction is improved.

Here, Nonobu I shows viewing angle dependence when no phase film is inserted.

In addition, as shown in FIG. 6(b), a pair of phase films whose stretching axes 35 and 36 are orthogonal to each other is placed between two polarizing plates, and the phase film is aligned with the transmission axes 32 and 33 of the adjacent polarizing plate. Similarly, when the films were arranged so that their stretching axes were perpendicular to each other, an improvement in the viewing angle dependence of the degree of polarization in the viewing angle θ9o direction was observed, as shown by curve ① in FIG. 6(c).

Although the viewing angle dependence of the degree of polarization when the polarizing plates are arranged in crossed nicols can be greatly improved by using a phase film, it is difficult to apply this to an electro-optical device in which a nematic liquid crystal panel is sandwiched between a pair of polarizing plates. In this case, when the alignment direction of this nematic liquid crystal and the stretching axis of the adjacent phase film are arranged almost parallel to each other, the same effect as above can be obtained.Elements that have a common surface are given the same number to make the explanation easier to understand. did.

Example 1 FIG. 1 is a perspective view showing a first example of the electro-optical element of the present invention. In this method, the transmission axes 3 and 4 of the two polarizing plates 1 and 2 are arranged parallel to each other in Nicols, and the 90°
``This is an electro-optical element with a normally black display format that has a TN cell 5 sandwiched between them. The direction of the transmission axis 3 of the polarizing plate 1 and the orientation direction of the upper surface of the TN cell are in this case parallel, and the phase film 8 with the pair of stretching axes 10 and 11 orthogonal therebetween is parallel to the direction of the transmission axis 3 of the polarizing plate 1. and 9 were inserted, and the orientation direction and the stretching axis 11 of the adjacent phase film 9 were arranged in parallel.Furthermore, the transmission axis 3 of the upper polarizing plate 1 and the stretching axis 10 of the adjacent phase film 8 are arranged orthogonally. That is, the configuration of this embodiment satisfies the second, third, and fourth claims.

Figures 2 (a) and (b) show the product of the refractive index anisotropy Δr] of the conventional liquid crystal panel shown in Figure 4 as a TN cell, that is, the nematic liquid crystal with a twist angle of 90°, and the cell thickness d. A liquid crystal panel with Δn-d=4700 m is used, and the product of refractive index anisotropy Δn and film thickness d is Δn-d=300n.
2 shows the viewing angle dependence of the contrast in the horizontal direction and the vertical direction when two phase films of m are used and arranged in the above configuration.

Here θ0. The definition of θ90 is the same as in FIG.

It can be seen that the viewing angle is significantly expanded in both the horizontal and vertical directions compared to the conventional example shown in FIG. Furthermore, when examining the spectral transmittance in the front direction of the electro-optical element of this example in a light-blocking state, no change was observed in the wavelength at which the transmittance is minimum and the transmittance at that wavelength. The transmittance was slightly lower. As a result, the color tone characteristics from the front direction hardly change depending on the presence or absence of a pair of phase films, and the front contrast decreases in transmittance in the dark state more than the decrease in transmittance in the bright state due to the insertion of the phase film. Contrast has improved.

In addition, the change in color tone in diagonal directions has been significantly reduced compared to the conventional example.

Note that in the configuration shown in Figure 1, illumination light is incident from polarizing plate 2 and viewed from polarizing plate l, and conversely, illumination light is incident from polarizing plate 1 and viewed from polarizing plate 2. When viewing, they are almost equivalent in terms of viewing angle dependence, and a configuration in which the top and bottom of FIG. 1 are reversed is also effective.

The intersection angle of the stretching axes of the pair of phase films is 90″ - 10′
A range of is appropriate. At angles greater than this, uniaxial optical anisotropy combined in the pair of phase films appears, changing the display characteristics of the electro-optical element when viewed from the front, resulting in a significant decrease in contrast.

Embodiment 2 FIG. 7 is a perspective view showing a second embodiment of the electro-optical element of the present invention, and the embodiment shown in FIG. The difference is that the stretching axes 10 of the phase films 8 are not perpendicular to each other but are arranged in parallel. That is,
The configuration of this embodiment corresponds to claims 2 and 4. TNt!, which has a normally black display format with such a configuration. This model also had all the features shown in the first embodiment described above. However, the change in color tone when viewed from an oblique direction is slightly larger than in the first embodiment. In other words, the fact that the transmission axis of the polarizing plate and the stretching axis of the adjacent phase film are almost perpendicular to each other has the effect of minimizing changes in the spectral characteristics of leaked light when viewed from an oblique direction (and reducing coloration). It shows that there is.

Note that, similar to the first embodiment, a configuration in which FIG. 7 is turned upside down is also effective in this embodiment.

Example-3 FIG. 8 is a perspective view showing a third example of the present invention,
A pair of orthogonal phase films 8 and 9 are
This is the case when they are placed separately on both sides. The upper orientation direction 7 of the TN cell 5 and the stretching axis 10 of the adjacent phase film 8- are arranged in parallel. Similarly, the orientation direction 6 of the working q of the TN cell 5 and the stretching axis 11 of the phase film 9 adjacent thereto are arranged parallel to each other. This configuration satisfies claim 2. The normally black display format TN cell having such a configuration also has all the features shown in the first embodiment. However, the change in color tone when viewed from an oblique direction is slightly larger than in the first embodiment.

It should be noted that, similar to the first embodiment, a configuration obtained by inverting the configuration shown in FIG. 8 is also effective in this embodiment.

Example-4 FIG. 9 is a perspective view showing a fourth example of the present invention,
Unlike the first to third embodiments, this embodiment uses a normally white display format TN cell in which two polarizing plates are arranged in crossed Nicols. The only difference from FIG. 1 is the transmission axis direction 4 of the polarizing plate 2. In this case as well, almost the same characteristics as in Figure 1 were observed. In particular, in this display mode with the conventional configuration, the viewing angle range in the vertical direction was narrow, which had the disadvantage of causing image inversion, but the viewing angle range of contrast and color tone in this direction has been greatly expanded, and image inversion has been reduced. It was done.

The normally white display type TN cell configuration corresponding to the second and third embodiments had the same effect as described above.

In realizing the configuration of the present invention, a composite film in which a polarizing plate and a phase film are combined can be used. That is, an electro-optical element having the structure of the present invention can be formed by combining a composite film in which the transmission axis of the polarizing layer and the stretching axis of the phase film are substantially orthogonal or substantially parallel. Furthermore, the present invention uses a composite film in which a polarizing layer and a phase sheet [. It is possible to form an electro-optical element having the following configuration. The use of these composite films simplifies the manufacture of electro-optical elements.

Furthermore, it is also possible to form an electro-optical element using these composite films as a substrate of a liquid crystal panel. By making it into a film, it can be made thinner and lighter, making it particularly convenient to carry when used as a display device.

The pair of nearly orthogonal phase films of the present invention cancels the optical action as a phase plate when viewed from the front by making the product Δ[1・d of the refractive index anisotropy Δn and the film thickness d almost equal. I can do it.

Optimization of the front display performance of the electro-optical element becomes easy.

Furthermore, the present invention can be widely applied to 1) cases where an optically anisotropic body is provided between a pair of polarizing plates in addition to a pair of phase films. By inserting a phase film as an optically anisotropic material, the color tone characteristics of the electro-optical element can be improved. In addition, as an optically anisotropic material, a nematic liquid crystal with an opposite twist that is almost equal to that of the liquid crystal cell is used, and the product Δn-d of its refractive index anisotropy Δn and the cell thickness d is approximately equal to that of the liquid crystal cell. The effects of this patent have been recognized in electro-optical elements with a layered structure. Electro-optical elements with this type of configuration are used to improve the color tone characteristics in the front direction, that is, to make the background color black and white to improve visibility, but generally the viewing angle dependence of contrast and color tone is sacrificed. It has become. In contrast, the present invention was able to improve the viewing angle characteristics, which were the drawbacks mentioned above, without impairing the display characteristics from the front direction.

Although the electro-optical element for color display was not specifically mentioned in the above explanation, this patent describes an electro-optical element for full-color image display that has a built-in switching element, consists of a large number of pixels, and is combined with an RGB color filter. Particularly effective. It significantly improves viewing angle characteristics, which are inferior to conventional color CRTs, and achieves display performance comparable to CRTs.

Effects of the Invention As described above, according to the present invention, TN mode, STN
The present invention can reduce the viewing angle dependence of contrast and color tone of liquid crystal electro-optical elements such as mode, two-layer TN mode, and two-layer STN mode, and can greatly expand the viewing angle, and is of great industrial value.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the structure of a first embodiment of the electro-optical element of the present invention, and FIGS. 2(a) and 2(b) are horizontal and vertical directions of the electro-optical element of the first embodiment. Characteristic diagram showing the viewing angle dependence of the contrast of Fig. 3(a), (
b) is a characteristic diagram showing viewing angle dependence of an electro-optical element according to the prior art, FIG. 4 is a perspective view showing a conventional electro-optical element, and FIG. FIGS. 5(b) and (C) are perspective views of the polarizing plates arranged in FIG. (b) is a perspective view when a phase film is combined with FIG. 8, and 9 are respectively the second embodiment of the present invention. FIG. 7 is a perspective view of an electro-optical element showing third and fourth examples. 1.2...Polarizing plate, 3,4...Transmission axis of polarizing plate, 5...Liquid crystal cell, 6,7...
・Alignment direction of liquid crystal cell, 8, 9...Pair of phase films, 10.11...Stretching axis of phase film, 31.24...Polarizing plate, 23.30・・・・・・
...Transmission axis of polarizing plate, 25...Liquid crystal cell, 27
．． 29...Alignment direction of liquid crystal cell, 32.33.
...Polarizing plate, 34,35.36... Phase film. Name of agent: Patent attorney Shigetaka Awano 1 person δ9---
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Claims (11)

[Claims] (1) A twisted oriented nematic liquid crystal cell is provided between opposing electrodes, a pair of polarizing plates are placed on the front and back sides of the liquid crystal cell, and at least one pair of phase films is placed between the pair of polarizing plates. . An electro-optical element, wherein the stretching axes of the pair of phase films are substantially perpendicular to each other. (2) The electro-optical element according to claim 1, wherein the orientation direction of the nematic liquid crystal and the stretching axis of the phase film adjacent thereto are arranged substantially parallel to each other. (3) Claim 2, wherein the transmission axis of the polarizing plate and the stretching axis of the phase film adjacent thereto are substantially perpendicular to each other.
The electro-optical element described. (4) The electro-optical element according to claim 2 or 3, wherein a pair of phase films is arranged between one polarizing plate and a liquid crystal cell. (5) Refractive index anisotropy Δ of each phase film of the pair
2. The electro-optical element according to claim 1, wherein the product Δn·d of n and the thickness d of the phase film is approximately equal. (6) The electro-optical element according to claim 1, wherein the polarizing plate and the phase film are a composite film in which the transmission axis of the polarizing plate and the stretching axis of the phase film are substantially orthogonal or substantially parallel. (7) In claim 1, the composite is composed of a pair of phase films whose stretching axes are substantially orthogonal to each other and arranged on one side of a polarizing layer, and a transmission axis of the polarizing layer is substantially orthogonal to either of the stretching axes. An electro-optical element characterized by being a film. (8) Claim 1, characterized in that the composite film according to claim 6 or 7 is used as a substrate of a liquid crystal cell.
The electro-optical element described. (9) The electro-optical element according to claim 1, further comprising at least one layer of optically anisotropic material between the pair of polarizing plates, in addition to the pair of phase films. (10) The electro-optical element according to claim 9, wherein the optically anisotropic body is a phase film. (11) The optically anisotropic body is a nematic liquid crystal whose twist angle is almost equal to and opposite to that of the liquid crystal cell, and whose refractive index anisotropy is Δ
10. The electro-optical element according to claim 9, wherein a product Δn·d of n and cell thickness d is approximately equal to that of a liquid crystal cell.