JPH02111918A - Liquid crystal electrooptic element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal electrooptic element of a wide visual angle by forming an optically anisotropic substance in such a manner that, of the three main refractive indices possessed by this substance, certain one refractive index N is smaller than the other two refractive indices and the axis corresponding to this refractive index is in a direction nearly horizontal with the substrate surface of a liquid crystal cell. CONSTITUTION:The refractive index N3e of the extraordinary light of the optically anisotropic substance is smaller than the refractive indices N1o, N2o of ordinary light. The value of DELTAN (identicalNo-Ne) of the optically anisotropic substance decreases as Ne increases when the incident light from the direction inclined by a certain angle in the X-axis direction from, for example, the Z-axis direction of such refractive index ellipsoid 82 is considered. The difference in retardation between the liquid crystal cell and the optically anisotropic substance generated in the direction inclined from the Z-axis direction is minimized if the refractive index ellipsoid 82 of the optically anisotropic substance is made into a disk shape in such a manner. The similar compensation relation is the same with the incident light from all the other directions. The compensation in a wide visual field region is enabled in this way and the wider visual angle is obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a liquid crystal electro-optical device.

[Conventional technology] Conventional New Twisted Nematic Mode (hereinafter referred to as NT)
(referred to as N mode) eliminates the display coloration characteristic of the conventional super twisted nematic mode.
As proposed in Japanese Patent Application No. 121701/1982,
A liquid crystal cell (hereinafter referred to as a display cell) that performs display and an optical anisotropic body are provided between a pair of polarizing plates.

FIG. 7 shows a cross-sectional view of a conventional liquid crystal electro-optical element. In the figure, 1 is an upper polarizing plate, 2 is a liquid crystal cell (display cell), 5 is an optically anisotropic body, and 4 is a lower polarizing plate. In the display cell,
A liquid crystal SS-4008 (Δn=0.15) manufactured by Chisso Corporation was used, and a cell with a cell gap d of 6.0 μm was twisted and oriented. At this time, the retardation Δnd is 0.90μ
It becomes m. On the other hand, for the optically anisotropic material, a twistedly oriented liquid crystal cell (compensation cell) is used, and Δnd is also set to 0°90μ.
It was set to m.

FIG. 8 shows a relationship diagram of each axis of a conventional liquid crystal electro-optical element. The angle 40 that the polarization axis (absorption axis) direction 20 of the upper polarizing plate makes with the rubbing direction 21 of the upper substrate of the display cell is 4 to the left.
5° The twist angle 41 of the display cell is 210° to the left. The angle 42 formed by the rubbing direction 22 of the lower substrate of the display cell and the rubbing direction 23 of the upper substrate of the compensation cell is 90°. The twist angle 43 of the compensation cell is 210° to the right. The angle 44 between the polarization axis (absorption axis) direction 25 of the side polarizing plate and the rubbing direction 24 of the lower substrate of the compensation cell was set to 45° to the left.

A conventional liquid crystal electro-optical element manufactured under the above conditions exhibits electro-optical characteristics with extremely little coloring, as shown in FIG. 3, when measured in a direction perpendicular to the panel surface.

[Problems to be Solved by the Invention] However, the conventional liquid crystal electro-optical device using the NTN mode has a problem that the viewing angle range (hereinafter simply referred to as viewing angle) in which the display can be clearly recognized is narrow.

FIG. 9 shows viewing angle characteristics of a conventional liquid crystal electro-optical element.

The center of the figure is perpendicular to the panel surface, and the outer circles are each at an angle of inclination of 10° from the vertical direction, starting from the inside.
20' 30° 40° 50° 60° directions are shown. Further, the four directions of top, bottom, left and right in the figure correspond to the four directions shown in FIG. Here 70.71.72.
73 are equal contrast lines with contrast ratios of 1.5, 10.20, respectively. Also, the shaded area is
This is an area where the contrast ratio becomes 1 or less and the display is inverted.

As described above, the conventional liquid crystal electro-optical device using the NTN mode has a particularly narrow viewing angle in the upward direction. This is because the amount of light when not selected changes greatly depending on the viewing angle direction, causing the display to be reversed. This inversion of the display is a major factor in psychologically making the viewing angle seem narrower.

The present invention is intended to solve these problems, and its purpose is to provide a liquid crystal electro-optical element with a wide viewing angle.

[Means for Solving the Problems] The liquid crystal electro-optical device of the present invention includes a liquid crystal cell comprising a twistedly oriented liquid crystal sandwiched between two opposing electrode substrates, and at least one optically different layer in addition to the liquid crystal. In a liquid crystal electro-optical element comprising a parallelepiped and a pair of polarizing plates disposed on both sides of the parallelepiped, the optically anisotropic body has three main refractive indices N1o, N2o, N3e,
One refractive index N32 is the other two refractive index N1o,
It is characterized in that an axis smaller than N2o and corresponding to its refractive index N3e is in a direction substantially horizontal to the substrate surface of the liquid crystal cell.

Further, the optically anisotropic body is characterized in that at least two polymer stretched films are laminated.

Further, the optically anisotropic body is a liquid crystal cell formed by sandwiching a twistedly oriented liquid crystal having optically negative uniaxiality between two substrates.

[Effect] For color compensation in conventional liquid crystal electro-optical elements.

The optically anisotropic body was designed with a focus on compensation in the direction perpendicular to the panel surface, and compensation in other directions was not considered.

The optical compensation mechanism of a conventional liquid crystal electro-optical element will be explained with reference to FIG. Here, for simplicity, we will consider the case where the twist angle of the liquid crystal cell is 0''.The refractive index ellipsoid 81 of the liquid crystal cell for display and the refractive index ellipsoid 83 of the optically anisotropic body for color compensation are as follows. Both are confectionery-shaped spheroids.The refractive index ellipsoid 81 of the liquid crystal cell has three main refractive indices n1o
, n2o, and n3e, of which n3e is the refractive index in the long axis direction of the liquid crystal molecule, n2o is the refractive index in the direction perpendicular to this within the panel surface, and nlo is the refractive index in the direction perpendicular to the panel surface. be. One optically anisotropic refractive index ellipsoid 83 is also
Three major refractions 1Nio, N2o, N5ef! :Have. In the case where the optically anisotropic material is a uniaxially stretched film, N3e is the refractive index in the stretching direction of the uniaxially stretched film, N2
o is the refractive index in the direction perpendicular to the film plane, Nlo
is the refractive index in the thickness direction of the film. In addition, when the optically anisotropic body is a liquid crystal cell, N3e is the refractive index in the long axis direction of the liquid crystal molecules, N2o is the refractive index in the direction perpendicular to this within the panel surface, and N10 is the refractive index in the direction perpendicular to the panel surface. It is the refractive index.

The two index ellipsoids 81 and 83 are stacked so that their optical axes are perpendicular to each other, so light incident from the direction perpendicular to the panel surface (Z-axis direction in the figure) is Ordinary light and extraordinary light are exchanged between the liquid crystal cell and the optically anisotropic body, and are emitted as they are. Therefore, for example, under crossed Nicol conditions, the display becomes pitch black, and all colors of light are completely compensated.

However, the compensation of the optical anisotropic body is not sufficient for light incident from directions other than the Z-axis direction.

For example, consider light incident from a direction inclined at a certain angle from the Z-axis direction to the long axis direction of the liquid crystal of the liquid crystal cell (X-axis direction in the figure). From this direction, the refractive index ne of the extraordinary light of the liquid crystal cell becomes apparently small, so the value of the refractive index anisotropy Δn of the liquid crystal cell becomes small. However, since the refractive index N01NeO value of the ordinary light and extraordinary light of one optically anisotropic body is constant regardless of the incident angle, there is a difference in retardation between the liquid crystal cell and the optically anisotropic body, and a sufficient Compensation will not be possible.

In the present invention, by making the refractive index ellipsoid, which is an optically anisotropic object for color compensation, into a disk shape, it is possible to perform compensation over a wider viewing angle. FIG. 6 is a diagram showing the optical compensation mechanism of the liquid crystal electro-optical element of the present invention. Here, unlike the conventional case, the refractive index N3e of the extraordinary light of the optically anisotropic body is smaller than the refractive index N1o and N2° of the ordinary light. Although such a refractive index ellipsoid 82 is completely equivalent to the conventional one as far as it is viewed from the Z-axis direction, it has different properties in other directions. For example, consider a case where light is incident from a direction tilted by a certain angle from the Z-axis direction to the X-axis direction. From this direction, as described above, since ne of the liquid crystal cell appears to be smaller, the value of Δn (=ne−no) becomes smaller. In contrast, ΔN (=N
The value of o−Ne) similarly decreases because Ne increases. By making the refractive index ellipsoid of the optically anisotropic body into a disk shape in this way, it is possible to minimize the difference between the liquid crystal cell and the optically anisotropic body's turbulence, which occurs in a direction tilted from the Z-axis direction. can. A similar compensation relationship holds not only for the direction inclined to the X-axis direction but also for light incident from all other directions. Therefore, according to the present invention, compensation can be performed in a wider viewing area than in the past, and a wider viewing angle can be obtained.

Even when the liquid crystal cell has a twist angle, the compensation principle is exactly the same. In that case, as shown in FIGS. 7 and 5, the side of the optically anisotropic body also has a twist angle in the opposite direction to that of the liquid crystal cell. The two layers (correspondence indicated by arrow 17 in the figure) that are symmetrical to the plane of contact between the liquid crystal cell and the optically anisotropic body have the above-mentioned compensatory relationship. Therefore, even when there is a twist angle, the viewing angle is wider when the refractive index ellipsoid of the optically anisotropic body has a disk shape.

[Example] Hereinafter, the details of the present invention will be shown by examples.

(Example 1) FIG. 1 shows a cross-sectional view of a liquid crystal electro-optical element in Example 1 of the present invention. In the figure, 1 is an upper polarizing plate, 2 is a liquid crystal cell (display cell), 3 is an optically anisotropic body, and 4 is a lower polarizing plate. The display cell is a liquid crystal 5S-4008 manufactured by Chisso Corporation (
Δn=0.15), cell gap d is 6.0 μm
The cells were twisted and oriented. At this time, the retardation Δnd becomes 0.90 μm.

On the other hand, polymethyl methacrylate (P
A stack of 10 uniaxially stretched films obtained by stretching MMA) in silicone oil at 1000C was used. Normal polymer films have the property that their refractive index increases in the stretching direction when stretched, but PMMA, poly-α-methyl fluoroacrylate (PMFA), etc. have the property that their refractive index decreases in the stretching direction. have. The refractive index of this -axially stretched film is N1o=1. 516, N2o=1.
518, N5e=1.509. - The layer thickness per layer is 10 μm, the retardation is 0.09 μm.

FIG. 2 shows a diagram of the relationship between each axis. The angle 40 that the polarization axis (absorption axis) direction 20 of the upper polarizing plate makes with the rubbing direction 21 of the upper substrate of the display cell is 45 degrees to the left.The twist angle of the display cell is 4.
1 to the left 210° Angle 45 that the stretching direction 30 of the first layer of uniaxially stretched film of the optically anisotropic body makes with the rubbing direction 22 of the lower substrate of the display cell is 10.5° to the right n+1 of the optically anisotropic body The angle between the stretching direction of the uniaxially stretched film of the layer 1 and the stretching direction of the uniaxially stretched film of the nth layer is 21° to the right. ) The angle 46 formed by the direction 25 was 90° (that is, crossed Nicols).

As shown in FIG. 3, the liquid crystal electro-optical element of the present invention exhibits almost the same characteristics as the conventional liquid crystal electro-optical element, as long as it is viewed from the direction perpendicular to the panel surface.

FIG. 4 shows the viewing angle characteristics of the liquid crystal electro-optical element in Example 1. Here, 70, 71, 72, and 73 indicate equal contrast lines with a contrast ratio of 1.5, 10.20, respectively. In the present invention, since there is less change in the amount of light during non-selection than in the conventional case, the viewing angle in the upward direction is particularly wider compared to the conventional one shown in FIG.

(Example 2) In Example 1, a stretched polymer film was used as the optically anisotropic body, but a liquid crystal cell may also be used. In order to make an optically anisotropic body have a disc-shaped refractive index ellipsoid as shown in FIG.
A liquid crystal (e<No) may be used. Examples of liquid crystals having optically negative uniaxiality include discotic liquid crystals and cholesteric liquid crystals, but the use of discotic liquid crystals is advantageous in terms of ease of alignment. Therefore, we installed a discotic liquid crystal at 15 in Figure 5.
As shown in , the optical axis is oriented horizontally to the substrate,
And it was oriented by a rubbing method so that it had a twist in the direction perpendicular to the substrate.

FIG. 5 and FIG. 8 respectively show a cross-sectional view and an axial relationship diagram of a liquid crystal electro-optical element in Example 2 of the present invention. The optical characteristics and viewing angle characteristics obtained in Example 2 are the same as those in Example 1 shown in FIGS. 3 and 4. The characteristics of Example 2 are that, compared to the case of using a uniaxially stretched film as in Example 1, it is easier to make the layer thickness of the optically anisotropic body uniform, and the process of laminating multiple films is not required. be.

[Effects of the Invention] As described above, according to the present invention, the viewing angle can be widened by using a stretched polymer film or a liquid crystal cell having optically negative uniaxiality as the optically anisotropic body. It has the effect of

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal electro-optical element in Example 1 of the present invention. FIG. 2 is a diagram showing the relationship between the respective axes of the liquid crystal electro-optical element in Example 1 of the present invention. FIG. 3 is a diagram showing electro-optical characteristics of the present invention and a conventional liquid crystal electro-optical element. FIG. 4 is a diagram showing viewing angle characteristics of the liquid crystal electro-optical element of the present invention. FIG. 5 is a cross-sectional view of a liquid crystal electro-optical element in Example 2 of the present invention. FIG. 6 is a diagram showing the optical compensation mechanism of the liquid crystal electro-optical element of the present invention. FIG. 7 is a cross-sectional view of a conventional liquid crystal electro-optical element. FIG. 8 is a diagram showing the relationship between the axes of Example 2 of the present invention and a conventional liquid crystal electro-optical element. FIG. 9 is a diagram showing viewing angle characteristics of a conventional liquid crystal electro-optical element. FIG. 10 is a diagram showing the optical compensation mechanism of a conventional liquid crystal electro-optical element. 1. Upper polarizing plate 2. Liquid crystal cell (display cell) 3. Optical anisotropic body (N 3e < N 2o ~N lo
) 4゜5゜6゜7゜8゜9゜10゜11゜12゜13゜14゜15゜Liquid crystal 16゜17゜20゜21゜22゜23゜24゜Lower polarizer optically anisotropic (N 3e> N 2o ~ N lo) Upper substrate of display cell Lower substrate of display cell Upper substrate of compensation cell Lower substrate of compensation cell Transparent electrode Counterclockwise twisted oriented nematic liquid crystal 1st layer uniaxially stretched film 2Nth The 10th layer of the uniaxially stretched film is a uniaxially stretched film with clockwise twisted orientation.Nematic liquid crystal with clockwise twisted orientation. Rubbing direction 25 of the lower substrate 9 of the rubbing direction compensation cell of the upper substrate 8 of the rubbing direction compensation cell of the upper substrate 8 of the rubbing direction display cell of the upper substrate 6, and the polarization axis of the lower polarizing plate 4 (absorption axis) direction 30, I
Stretching direction of JiJ-th uniaxially stretched film 12 31.27
! Stretching direction 32 to 38.3 of the uniaxially stretched film 13
~Stretching direction 39 of the 9th layer uniaxially stretched film, lOJ! The stretching direction 40 of the J-th uniaxially stretched film 14, the angle 41 between the direction 20 of the polarization axis of the upper polarizing plate and the rubbing direction 21 of the upper substrate of the display cell, the twist angle 42 of the display cell, and the angle 41 of the direction of the polarization axis of the upper polarizing plate with the rubbing direction 21 of the upper substrate of the display cell, The angle 43 between the rubbing direction 22 and the rubbing direction 23 of the upper substrate of the compensation cell, the twist angle 44 of the compensation cell, and the direction 25 of the polarization axis of the lower polarizing plate are complementary to the rubbing direction 24 of the lower substrate of the cell. Angle 45.1 Angle 46 that the stretching direction 30 of the thin uniaxially stretched film makes with the rubbing direction 22 of the lower substrate of the display cell, A direction 20 of the polarization axis of the upper polarizing plate and a direction 25 of the polarization axis of the lower polarizing plate. The angle 50.The stretching direction 31 of the second layer uniaxially stretched film is I
The angle formed with the stretching direction 30 of the Nth uniaxially stretched film is 51 to 58. An angle 60 between the stretching direction of the n+1th layer uniaxially stretched film and the stretching direction of the nJiJth uniaxially stretched film, a voltage transmittance curve 61 for light with a wavelength of 450 nm (blue light), and a voltage transmittance curve 61 for light with a wavelength of 550 nm (green light). Voltage transmittance curve 62, voltage transmittance curve 70 for light with a wavelength of 650 nm (red light), isocontrast line 71 with contrast ratio 1, isocontrast line 72 with contrast ratio 5, isocontrast line 73 with contrast ratio 10, contrast ratio 20 isocontrast line 81, refractive index ellipsoid 82 of the liquid crystal cell, refractive index ellipsoid 83 of the optically anisotropic body of the present invention, refractive index ellipsoid number of the conventional optically anisotropic body. Figure 2.0 2, S To ν Naro @ F Self (\)'n No. 30 Figure 5 4 Dokun 8 Figure 7 Lower Figure 9

Claims (2)

[Claims] (1) A liquid crystal cell consisting of a twistedly oriented liquid crystal sandwiched between two opposing electrode substrates, at least one layer of optically anisotropic material other than the liquid crystal, and a pair of liquid crystal cells disposed on both sides with the liquid crystal interposed therebetween. In a liquid crystal electro-optical element equipped with a polarizing plate,
Three main refractive indices N1_o that the optically anisotropic body has
, N2_o, N3_e, one refractive index N3_e
is smaller than the other two refractive indices N1_o and N2_o,
A liquid crystal electro-optical element, wherein the axis corresponding to the refractive index N3_e is in a direction substantially horizontal to the substrate surface of the liquid crystal cell. (2) The liquid crystal electro-optical element according to claim 1, wherein the optically anisotropic body is a laminate of at least two stretched polymer films.