JP2718078B2 - Liquid crystal electro-optical element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal electro-optical element.

[Prior Art] In the conventional homogeneous ECB mode, display is performed by controlling birefringence of liquid crystal, so that coloring of display is inevitable. For the purpose of eliminating this coloring, it has been conventionally proposed to provide an optically anisotropic body in addition to a liquid crystal cell for performing display.

FIG. 6 is a 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, 5 is an optically anisotropic body, and 4 is a lower polarizing plate.

The liquid crystal cell includes a liquid crystal SS-4008 (△ n = 0.
Using (15), homogeneous alignment was performed between two transparent electrode substrates. The retardation Δnd of the liquid crystal layer thickness d is
The thickness was set to 6.0 μm so as to be 0.90 μm. On the other hand, a uniaxially stretched film manufactured by Sumitomo Chemical Co., Ltd. was used as the optically anisotropic body. This uniaxially stretched film is a polymer film containing polycarbonate as a main component, and has a retardation of 0.90 μm.

FIG. 7 shows a relation diagram of each axis of the conventional liquid crystal electro-optical element. The angle 21 between the polarization axis (absorption axis) direction 11 of the upper polarizer and the rubbing direction 12 of the upper substrate of the liquid crystal cell is 45 ° to the left,
The angle 22 between the rubbing direction 13 of the lower substrate of the liquid crystal cell and the stretching direction 14 of the uniaxially stretched film is 90 °, and the angle 23 between the polarization axis (absorption axis) direction 15 of the lower polarizing plate and 14 is 45 ° on the left. did.

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

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

FIG. 8 shows viewing angle characteristics of a conventional liquid crystal electro-optical element. The center of the figure is the direction perpendicular to the panel surface, and the outer circles are the inclination angles 10 °, 20 °,
The directions of 30 ゜, 40 ゜, 50 ゜ and 60 ゜ are shown. The four directions of up, down, left, and right in the figure correspond to the four directions shown in FIG. Here, 41 is an iso-contrast line with a contrast ratio of 10.

As can be seen from FIG. 8, the viewing angle of the conventional liquid crystal electro-optical element is extremely narrow. The cause of such a narrow viewing angle is
This is mainly because the amount of light at the time of non-selection, that is, at the time of off-state changes significantly depending on the viewing direction.

The present invention solves such a problem, and an object of the present invention is to provide a liquid crystal electro-optical element having a wide viewing angle and little display coloration.

[Means for Solving the Problems] A liquid crystal electro-optical element according to the present invention includes a liquid crystal cell in which a liquid crystal is sandwiched between a pair of substrates, at least one optically anisotropic body, and a pair of polarizing plates. A liquid crystal electro-optical element in which the liquid crystal cell and the optically anisotropic body are arranged between the pair of polarizing plates, wherein the liquid crystal cell is provided with a liquid crystal that is homogeneously aligned without being twisted; Refractions N1o, N in three directions
2o, and N3e, the value of the refractive index N3e indicating a refractive index in a direction substantially horizontal to the substrate surface is another refractive index N1
It is characterized by having characteristics smaller than the values of o and N2o.

Further, the optically anisotropic material is formed of a stretched polymer film, wherein N3e is a refractive index in a stretching direction of the polymer film, and N1o is orthogonal to the stretching direction, and a film of the polymer film is formed. N2o is a refractive index in a direction orthogonal to the stretching direction and the film thickness direction.

Further, the optically anisotropic body is composed of a liquid crystal cell in which a liquid crystal having optically negative uniaxial property is sandwiched between a pair of substrates, wherein N1o is a refractive index in a cell thickness direction, and N3e is the substrate. And N2o is a refractive index in a direction orthogonal to N1o and N3e.

[Operation] The optically anisotropic body for color compensation in the conventional liquid crystal electro-optical element is designed mainly for compensation in a direction perpendicular to the panel surface, and compensation in other directions is considered. Not.

FIG. 9 is a diagram showing a mechanism of optical compensation of a conventional liquid crystal electro-optical element. The refractive index ellipsoid 51 of the liquid crystal cell and the refractive index ellipsoid 53 of an optically anisotropic body for coloring compensation are both cigar spheroids. Index ellipsoid of liquid crystal cell
51 has three main refractive indices n1o, n2o, n3e,
Among them, n3e is the refractive index in the major axis direction of the liquid crystal molecule, n2o is the refractive index in the direction perpendicular to the panel surface, and n1o is the refractive index in the direction perpendicular to the panel surface. The refractive index ellipsoid 53 of one optically anisotropic body also has three main refractive indices N1o, N2o, and N3e, of which N3e is the refractive index in the stretching direction of the uniaxially stretched film, and N2o is in the film plane. The refractive index perpendicular to this, N
1o is the refractive index in the thickness direction of the film.

Since the two index ellipsoids 51 and 53 are stacked such that their optical anomalous axes are perpendicular to each other,
Light incident from a direction perpendicular to the panel surface (the Z-axis direction in the figure) is switched between ordinary light and extraordinary light between the liquid crystal cell and the optically anisotropic body, and is emitted as it is. Thus, for example, under crossed Nicols, the display becomes black, and light of all colors is completely compensated.

However, for light incident from a direction other than the Z-axis direction, compensation of the optically anisotropic body is not sufficient. For example, Z
Consider light incident from a direction inclined by a certain angle from the axial direction to the major axis direction of the liquid crystal of the liquid crystal cell (the X-axis direction in the figure). From this direction, the refractive index of the extraordinary light of the liquid crystal cell
Since ne is apparently small, the value of the refractive index anisotropy Δn of the liquid crystal cell is also small. However, since the refractive index No and Ne of ordinary light and extraordinary light of one optical anisotropic substance are constant irrespective of the angle of incidence, there is a difference in retardation between the liquid crystal cell and the optical anisotropic substance. , Sufficient compensation cannot be achieved.

In the present invention, compensation is possible at a wider viewing angle by making the refractive index ellipsoid of the optically anisotropic body into a disk shape. FIG. 5 is a diagram showing a mechanism of optical compensation 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 indexes N1o and N2o of the ordinary light. Such an index ellipsoid 52,
As seen from the Z-axis direction, it is completely equivalent to the conventional one. However, for example, when considering light incident from a direction inclined at a certain angle in the X-axis direction from the Z-axis direction, ne of the liquid crystal cell decreases according to the incident angle, and Δn (≡ne−no) decreases. On the other hand, Ne of the optically anisotropic body increases to compensate for it, and ΔN (ΔNo−Ne) decreases. Such a compensation relationship is the same for light incident from all other directions. Therefore, according to the present invention, it is possible to perform compensation in a wider area than before, and a wider viewing angle can be obtained.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 FIG. 1 shows a sectional view of a liquid crystal electro-optical element according to Example 1 of the present invention. In the figure, 1 is an upper polarizing plate, 2 is a liquid crystal cell, 3 is an optically anisotropic body, and 4 is a lower polarizing plate. For the liquid crystal cell, a liquid crystal SS-4008 (Δn = 0.15) manufactured by Chisso was used, and a homogeneous alignment was performed between the two transparent electrode substrates. The retardation Δnd of the liquid crystal layer thickness d is 0.90 μm.
m was set to 6.0 μm. On the other hand, optically anisotropic materials include poly-α-methyl fluoroacrylate (PMFA)
Was used at 100 ° C. to obtain a uniaxially stretched film. Ordinary polymer films have the property of increasing the refractive index in the stretching direction when stretched, whereas PMFA and polymethyl methacrylate (PMMA) have the property of decreasing the refractive index in the stretching direction. I have. The refractive index of this uniaxially stretched film is N1o = 1.534, N2o = 1.538, and N3e = 1.502. Since the film thickness is 25 μm, the retardation is
0.90 μm.

FIG. 2 shows a relationship diagram of each axis. The angle 21 between the polarization axis (absorption axis) direction 11 of the upper polarizer and the rubbing direction 12 of the upper substrate of the liquid crystal cell is 45 ° to the left, and the rubbing direction 13 of the lower substrate of the liquid crystal cell and the stretching direction 14 of the uniaxially stretched film. Eggplant
22 was set to 0 °, and the angle 23 between the polarization axis (absorption axis) direction 15 of the lower polarizing plate and 14 was set to 45 ° to the right.

As shown in FIG. 3, the liquid crystal electro-optical element of the present invention exhibits the same characteristics as those of the conventional liquid crystal electro-optical element as seen 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, reference numeral 41 denotes an iso-contrast line having a contrast ratio of 10. Comparing FIG. 4 with FIG. 8, it can be seen that the viewing angle in the left-right direction is particularly large.

(Example 2) In Example 1, a polymer stretched film was used as the optically anisotropic body, but a liquid crystal cell can also be used. In order for the optically anisotropic body to have a disk-shaped refractive index ellipsoid as shown in FIG.
The liquid crystal may be oriented so that the optical axis is oriented in a direction parallel to the substrate. As the liquid crystal having optically negative uniaxiality, for example, a discotic liquid crystal or a cholesteric liquid crystal can be considered, but it is easier to use a discotic liquid crystal in terms of alignment.

1 and 2 show a sectional view and an axial relation diagram of a liquid crystal electro-optical element according to Example 2 of the present invention, respectively. Optical characteristics and viewing angle characteristics obtained in the second embodiment are the same as those in the first embodiment shown in FIGS. The feature of Example 2 is that the thickness of the optically anisotropic body is easily made uniform as compared with the case of using a uniaxially stretched film as in Example 1.

It should be noted that the liquid crystal electro-optical element of the present invention is not suitable for large-capacity display by a simple matrix method because the steepness of the voltage-transmittance characteristic is poor. However, if an active matrix method in which an active element is provided in each pixel is used, display with a wider viewing angle can be performed than in the case where a conventional TN mode is used.

[Effects of the Invention] As described above, the present invention has refractive indices N1o, N2o, and N3e in three directions, respectively, and indicates the value of the refractive index N3e indicating the refractive index in a direction substantially horizontal to the substrate surface. Is another refractive index N1
o, an optical anisotropic body having characteristics smaller than the value of N2o, that is, by arranging an optical anisotropic body having an optically negative characteristic, the coloring of the liquid crystal cell by the optical anisotropic body. Can compensate. Further, a liquid crystal electro-optical element having a wide viewing angle can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal electro-optical element according to the present invention. FIG. 2 is a diagram showing the relationship between each axis of the liquid crystal electro-optical element of the present invention. FIG. 3 is a view showing the electro-optical characteristics of the present invention and the conventional liquid crystal electro-optical element. FIG. 4 is a view showing viewing angle characteristics of the liquid crystal electro-optical element of the present invention. FIG. 5 is a diagram showing a mechanism of optical compensation of the liquid crystal electro-optical element of the present invention. FIG. 6 is a sectional view of a conventional liquid crystal electro-optical element. FIG. 7 is a diagram showing a relationship between axes of a conventional liquid crystal electro-optical element. FIG. 8 is a diagram showing viewing angle characteristics of a conventional liquid crystal electro-optical element. FIG. 9 is a diagram showing a mechanism of optical compensation of a conventional liquid crystal electro-optical element. DESCRIPTION OF SYMBOLS 1 ... Upper polarizing plate 2 ... Liquid crystal cell 3 ... Optical anisotropic body (N3e <N2o-N1o) 4 ... Lower polarizing plate 5 ... Optical anisotropic body (N3e> N2o-N1o) 6 ... … Upper substrate 7… Lower substrate 8… Transparent electrode 9… Homogeneously aligned liquid crystal 11… Direction of polarization axis (absorption axis) of upper polarizer 1 12… Rubbing direction of upper substrate 6 of liquid crystal cell 13… The rubbing direction of the lower substrate 7 of the liquid crystal cell 14 The stretching direction of the uniaxially stretched film (the optical axis direction of the discotic liquid crystal in Example 2) 15 The direction of the polarization axis (absorption axis) of the lower polarizing plate 4 21: Angle formed by the direction 11 of the polarization axis of the upper polarizer and the rubbing direction 12 of the upper substrate of the liquid crystal cell. 22 ... The angle between the rubbing direction 13 of the lower substrate of the liquid crystal cell and the stretching direction 14 of the uniaxially stretched film. 23 ... The angle between the direction 15 of the polarization axis of the lower polarizing plate and the stretching direction 14 of the uniaxially stretched film. 31: Voltage transmittance curve for light with a wavelength of 450 nm (blue light). 32: Voltage transmittance curve for light with a wavelength of 550 nm (green light). 33: Voltage transmittance curve for light with a wavelength of 650 nm (red light). 41: Isocontrast line with a contrast ratio of 10 51: Index ellipsoid of liquid crystal cell 52: Index ellipsoid of optically anisotropic body of the present invention 53: Index ellipse of conventional optically anisotropic body body

Claims (3)

(57) [Claims] 1. A liquid crystal cell having a liquid crystal sandwiched between a pair of substrates, at least one optically anisotropic body, and a pair of polarizing plates, wherein the liquid crystal cell and the polarizing plate are interposed between the pair of polarizing plates. In a liquid crystal electro-optical element having an optically anisotropic body disposed therein, a liquid crystal having a homogeneous orientation without twist is sandwiched in the liquid crystal cell, and the optically anisotropic body has a refractive index N1o in each of three directions. , N2
o, and N3e, the value of the refractive index N3e indicating a refractive index in a direction substantially horizontal to the substrate surface is another refractive index N1o,
A liquid crystal electro-optical element having characteristics smaller than the value of N2o. 2. The optically anisotropic material comprises a stretched polymer film, wherein N3e is a refractive index in a stretching direction of the polymer film, N1o is orthogonal to the stretching direction,
The refractive index in the thickness direction of the polymer film, the N2
2. The liquid crystal electro-optical element according to claim 1, wherein o is a refractive index in a direction orthogonal to the stretching direction and the film thickness direction. 3. The optically anisotropic body comprises a liquid crystal cell in which liquid crystal having optically negative uniaxial property is sandwiched between integral substrates, wherein N1o is a refractive index in a cell thickness direction, and N3e is a liquid crystal cell. The liquid crystal electro-optical device according to claim 1, wherein is a refractive index in a horizontal direction with respect to the substrate, and N2o is a refractive index in a direction orthogonal to the N1o and the N3e.