JPH0369915A - liquid crystal electro-optical element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

[Prior Art] The conventional twisted nematic mode (hereinafter referred to as TN mode) is a liquid crystal display mode in which polarizing plates are placed between liquid crystal cells with a twist angle of approximately 90 degrees.The TN mode has a negative display mode. There are two display modes: a normally black mode with a positive display, and a normally white mode with a positive display, but since both modes are capable of black and white display with little color change, they are used as the liquid crystal display mode of a full color display using a color filter. It was optimal.

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

FIG. 6 shows an example of the viewing angle characteristics of a conventional liquid crystal electro-optical element with a cell thickness of 5. 0 μm (Δn d == O.

The center of Figure 0, which shows the viewing angle characteristics of a normally white mode T Ns liquid crystal electro-optical element (40 μm), indicates the direction perpendicular to the panel surface, and the outer circles indicate the tilt angle from the vertical direction, starting from the inside. 10゜20° 30＠40
” 50 @ 60' (7) The four directions (up, down, left and right) in Figure 0 that indicate the direction are the directions in which the liquid crystal panel is observed, and this time the rubbing direction of the upper electrode substrate of the liquid crystal electro-optical element is 45 degrees to the lower right. The rubbing direction of the lower electrode substrate was set to be 45'' on the lower left. 601, 602, and 603 are equal contrast lines with a contrast ratio of 10, 30, and 100, respectively. Furthermore, a shaded area 604 is an area where the order of gradation is reversed when gradation is displayed.

In this way, conventional liquid crystal electro-optical elements using the TN mode have a wide viewing angle where a particularly high contrast ratio can be obtained;
The viewing angle at which accurate gradation can be displayed is extremely narrow, and if accurate gradation cannot be displayed, there is a possibility that the displayed content may be misunderstood. It is dangerous and inappropriate for use in critical locations. 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] A liquid crystal electro-optical element of the present invention includes a liquid crystal cell formed by sandwiching a nematic liquid crystal between two electrode substrates facing each other, and at least one liquid crystal cell disposed on both sides with the liquid crystal cell sandwiched therebetween. It is equipped with a two-layer optically anisotropic material and a pair of polarizing plates placed on both sides with the optically anisotropic material in between, and has one of the three main refractive indices N1o, N2o, and N3e of the optically anisotropic material. , one refractive index N3e is the other two refractions $ N 1o, N2o
The axis that is smaller than and corresponds to its refractive index N3e is
It is characterized in that it is located in a direction substantially horizontal to the substrate surface of the liquid crystal cell and coincides with the alignment direction of liquid crystal molecules on the adjacent electrode substrate. Further, the optically anisotropic body is a stretched polymer film.

[Operation] Optical compensation of the refractive index ellipsoid of liquid crystal molecules near the upper and lower electrode substrates in the conventional TN mode will be explained with reference to FIG. 501 is the upper polarizing plate, 502 is the refractive index ellipsoid of the liquid crystal molecules near the upper substrate, 503 is the refractive index ellipsoid of the bulk of the liquid crystal layer, 504 is the refractive index ellipsoid of the liquid crystal molecules near the lower substrate, and 505 is the lower refractive index ellipsoid. When no voltage is applied to the liquid crystal cell, the liquid crystal molecules representing the side polarizers are tilted from the electrode substrate surface by a certain pretilt angle with their long axes being approximately parallel to the electrode substrate surface. It is twisted and oriented between. When a voltage is applied, the liquid crystal molecules are aligned with their long axes perpendicular to the electrode substrates. However, since the liquid crystal molecules on the upper and lower electrode substrates are restrained by the alignment regulating force from the alignment film, the liquid crystal molecules near the upper and lower electrode substrates do not behave like the liquid crystal molecules in the bulk of the liquid crystal layer. There is almost no movement even when a voltage is applied.For this reason, in a TN mode panel, the refractive index ellipsoid 503 of the liquid crystal layer, which changes when a voltage is applied, is placed near the electrode substrate, where the refractive index ellipsoid 503 does not change even when a voltage is applied. refractive index ellipsoids 502 and 5
04 is sandwiching it from above and below.

The refractive ellipsoids 502 and 504 near the upper and lower electrode substrates have three main refractions 1nto, n2o, and n3e, of which n3e is the refractive index in the long axis direction of the liquid crystal molecule, n2
o is a refractive index in a direction perpendicular to the panel surface, and nlo is a refractive index in a direction perpendicular to the panel surface. The refractive index ellipsoid 503 of the liquid crystal layer also has three main refractive indices n1o, n2o, n
It has 3e. Among these, 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 nlo is the refractive index in the direction perpendicular to the panel surface. 50
The index ellipsoids of No. 2 and No. 504 have their optically extraordinary axes perpendicular to each other, so that the index ellipsoids of No. 2 and No.
Since the refractive index ellipsoids 502 and 504 of the liquid crystal molecules near the electrode substrate are completely compensated for each other, light incident from the Z-axis direction in the figure is affected only by the refractive index ellipsoid 503 of the liquid crystal layer. become. In conventional TN mode liquid crystal electro-optical elements, such optical compensation is naturally performed. However, for light incident from directions other than the Z-axis,
Compensation for the refractive index ellipsoid of liquid crystal molecules near the upper and lower electrode substrates is not sufficient.

For example, let's consider light incident from a direction inclined by a certain angle from the X-axis direction to the long axis direction of the liquid crystal molecules on the upper electrode substrate (X-axis direction in the figure). Since the refractive index ne of the extraordinary light of the refractive index ellipsoid becomes smaller apparently, the value of the refractive index anisotropy Δn of the liquid crystal molecules near the upper electrode substrate becomes smaller. However, the refractive index of the ordinary light and extraordinary light of the refractive index ellipsoid near the lower electrode substrate is
, ne is constant regardless of the angle of incidence, so
A difference occurs in the beam turbulence between the refractive index anisotropic bodies near the upper and lower electrode substrates, and sufficient compensation cannot be achieved.

In the present invention, by arranging optical compensation plates on both sides of the liquid crystal cell to compensate for the refractive index ellipsoids near the upper and lower electrode substrates, the refractive index ellipsoids in the vicinity of the upper and lower electrode substrates can be compensated for even when the viewing angle is changed. -Improved viewing angle characteristics by eliminating differences in the angle of view. FIG. 4 is a diagram showing the optical compensation mechanism of the liquid crystal electro-optical element of the present invention. The optically anisotropic body 402 whose refractive index N3e of extraordinary light is smaller than the refractive indices N1o and N2o of ordinary light is arranged so that the axis corresponding to the refractive index N3e is the refractive index n3e of the extraordinary light of the refractive index ellipsoid 403 near the electrode substrate. For example, let's consider light incident from a direction tilted by a certain angle from the X-axis direction to the X-axis direction. As ne of the refractive index ellipsoid near the upper electrode substrate apparently becomes smaller, the value of Δn (min-ne-no) becomes smaller. On the other hand, the value of ΔN (MiNo−Ne) of the optically anisotropic body similarly becomes smaller because Ne becomes larger. In this way, the refractive index ellipsoid 402 near the upper electrode substrate and the refractive index ellipsoid of the optical compensator 403 can minimize the difference in retardation that occurs in a direction tilted from the X-axis direction. On the other hand, the refractive ellipsoid 40 near the lower electrode substrate
Even if the ΔN of the optically anisotropic body 406 adjacent to the ΔN of the optically anisotropic body 406 is tilted from the X-axis direction to the X-axis direction, its value remains constant regardless of the incident angle, and compensation is always performed. 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, the refractive index ellipsoid near the upper and lower electrode substrates is always compensated even when the viewing angle is changed, so that a wider viewing angle can be obtained.

[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 device manufactured as an example of the present invention, in which 101 is an upper polarizing plate;
2 is an upper optically anisotropic body, 103 is a liquid crystal cell, 104 is a lower optically anisotropic body, and 105 is a lower polarizing plate. The liquid crystal cell has 320x220x3 TPTs on the lower electrode substrate 131.
Red, blue,
It has a green color filter. The liquid crystal 132 used was ZLI-3279 manufactured by Merck & Co. (7) (Δn=0.084), and the cell gear d was set to 4.8 μm so that Δnd was 0.40 μm. Optical anisotropic bodies 2 and 5 were made using uniaxially stretched films obtained by stretching polymethyl methacrylate (PMMA) in silicone oil at 100°C.
Ordinary polymer films have the property that their refractive index increases in the stretching direction when they are stretched, but PMMA, poly-α-methyl fluoroacrylate (PMFA), etc. have the property that their refractive index decreases in the stretching direction. ing. The refractive index of this -axis stretched film is N1o=1.514, N2o=1.5
16, N5e=1. 511, retardation is 0
．． 05 μm.

FIG. 2 shows a diagram of the relationship between each axis. The polarization axis (absorption axis) direction 201 of the upper polarizing plate, the stretching direction 202 of the upper optically anisotropic body, and the rubbing direction 203 of the upper electrode substrate are arranged in parallel, and similarly, the rubbing direction 204 of the lower electrode substrate, the lower side The stretching direction 205 of the optically anisotropic body, the polarization axis of the lower polarizing plate (
The angle formed by the rubbing direction 203 of the upper electrode substrate and the rubbing direction 2° 4 of the lower electrode substrate, in which the absorption axis direction 206 is arranged in parallel, is 90 degrees.

FIG. 3 shows the viewing angle characteristics of the liquid crystal electro-optical element in Example 1, where 301 and 302.3O3 are equal contrast lines with contrast ratios of 10, 30, and 100, respectively. Furthermore, a shaded area 304 is an area where the order of gradations is reversed when displaying gradations.The liquid crystal electro-optical element of the present invention is located close to the upper and lower electrodes of the liquid crystal cell no matter what angle the light is incident on. The index ellipsoid of the liquid crystal molecules is always compensated for. For this reason, when FIG. 3 is compared with the conventional FIG. 6, inversion of gradation is particularly difficult to occur, and the area where accurate gradation can be displayed is widened.

Although the embodiments have been described above, the present invention can be widely applied not only to the above embodiments but also to widening the viewing angle of liquid crystal electro-optical elements.

[Effects of the Invention] As described above, the present invention has the effect of widening the viewing angle by arranging optical compensation plates above and below the liquid crystal cell.

[Brief explanation of drawings]

FIG. 1 is a diagram showing 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 viewing angle characteristics of the liquid crystal electro-optical element of the present invention. FIG. 4 is a diagram showing the optical compensation mechanism of the liquid crystal electro-optical element of the present invention. FIG. 5 is a diagram showing the optical compensation mechanism of a conventional liquid crystal electro-optical element. FIG. 6 is a diagram showing viewing angle characteristics of a conventional liquid crystal electro-optical element. 101... Upper polarizing plate 102... Upper optically anisotropic body 103... Liquid crystal cell 104... Lower optically anisotropic body 105... Lower polarizing plate 131... Upper electrode substrate 132 ...Liquid crystal 133...Lower electrode substrate 201...Polarization axis (absorption axis) direction 202 of upper polarizing plate
...Stretching direction of the upper optically anisotropic body 203...Rubbing direction of the upper electrode substrate 204...Rubbing direction of the lower electrode substrate 205...Stretching direction of the lower optically anisotropic body 20
B... Polarization axis (absorption axis) direction of the lower polarizing plate 301...
- Equal contrast line 302 with a contrast ratio of 10...
Isocontrast line 303 with a contrast ratio of 30...Isocontrast line 304 with a contrast ratio of 100...A region where gradation inversion occurs 401...Upper polarizing plate 402...Refractive index ellipse of the upper optically anisotropic body Body 403・
...Refractive index ellipsoid 404 of liquid crystal molecules near the upper electrode substrate...Refractive index ellipsoid 405 of the liquid crystal layer...Refractive index ellipsoid 406 of liquid crystal molecules near the lower electrode substrate...Lower optical Anisotropic refractive index ellipsoid 407・
...Lower polarizing plate 501...Upper polarizing plate 502...Refractive index ellipsoid 503 of liquid crystal molecules near the upper electrode substrate...Refractive index ellipsoid 504 of the liquid crystal layer...Near the lower electrode substrate Refractive index ellipsoid 505 of liquid crystal molecules...lower polarizing plate 601...isocontrast line 6 with contrast ratio 10
02...Equicontrast line 60 with contrast ratio 30
3...Isocontrast line 604 with a contrast ratio of 100...A region where gradation inversion occurs or more

Claims (2)

[Claims] (1) A liquid crystal cell consisting of a nematic liquid crystal sandwiched between two electrode substrates facing each other, at least two layers of optically anisotropic material placed on both sides of the liquid crystal cell, and both sides of the liquid crystal cell sandwiched therebetween. In a liquid crystal electro-optical device comprising a pair of polarizing plates arranged at The axis that is smaller than the two refractive indexes N1o and N2o and corresponds to the refractive index N3e is in a direction substantially horizontal to the substrate surface of the liquid crystal cell, and is in line with the alignment direction of liquid crystal molecules on the adjacent electrode substrate. A liquid crystal electro-optical element characterized by matching. (2) The liquid crystal electro-optical element according to claim 1, wherein the optically anisotropic body is a stretched polymer film.