JP2779822B2 - Liquid crystal electro-optical element - Google Patents

Description

The present invention relates to a liquid crystal electric device.

[Prior Art] The conventional New Twisted Nematic mode eliminates the coloring of the display peculiar to the conventional Super Twisted Nematic mode, and has been proposed by the present applicant in Japanese Patent Application No. 62-121701, for example. As described above, a liquid crystal cell for performing display and an optically anisotropic body are separately provided between a pair of polarizing plates. A mode using a liquid crystal cell as the optically anisotropic body (hereinafter referred to as NTN mode) and a mode using a uniaxially stretched polymer film (hereinafter referred to as FTN mode)
However, the feature of the FTN mode is that it is lighter and cheaper than the NTN mode.

FIG. 7 is a cross-sectional view of a conventional liquid crystal electro-optical element utilizing the FTN mode. In the figure, 1 is an upper polarizing plate, 2 is a liquid crystal cell, 5 is a uniaxially stretched film, and 4 is a lower polarizing plate.
The liquid crystal 9 of the liquid crystal cell includes a liquid crystal SS-4008 (Δ
Using n = 0.15), the cells were twisted to have a cell gap d of 6.0 μm. At this time, the retardation Δnd is 0.
90 μm.

On the other hand, as the uniaxially stretched film, a polycarbonate polymer film Sumikalite manufactured by Sumitomo Chemical Co., Ltd. was used. The refractive indices are N1o = 1.518, N2o = 1.517, N3e = 1.5
22. The film thickness is 90 μm and the retardation is 0.
45 μm. Here, N3e is the refractive index in the stretching direction of the film, that is, in the optical axis direction. Thus, in the conventional uniaxially stretched film, the refraction Ne of extraordinary light is larger than the refractive index No of ordinary light. According to “Latest Technologies for Liquid Crystals”, 3rd edition, p. 21 issued by the Industrial Research Council, such properties of the optically anisotropic body are expressed as having optically positive uniaxiality.

FIG. 8 shows a relationship diagram of each axis of the conventional liquid crystal electro-optical element. The angle 20 between the polarization axis (absorption axis) direction 10 of the upper polarizer and the rubbing direction 11 of the upper substrate of the liquid crystal cell is set to the left 117.
゜, the twist angle 21 of the liquid crystal cell is 240 ° left, the angle 24 between the stretching direction 15 of the uniaxially stretched film and the rubbing direction 12 of the lower substrate of the liquid crystal cell is 65 ° left, and the polarization axis (absorption axis) of the lower polarizer )
The angle 25 between the direction 14 and 15 was set to 20 ° to the right.

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

[Problems to be Solved by the Invention] However, the conventional liquid crystal electro-optical element using the FTN mode has a viewing angle range (hereinafter simply referred to as a viewing angle) in which a display can be viewed better than the liquid optical element using the NTT mode. ) Is narrow.

FIG. 9 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 circles outside are the inclination angles 10 from the vertical direction in order from the inside.
The directions of ゜, 20 ゜, 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, 40, 41, and 42 are isocontrast lines having contrast ratios of 1, 5, and 10, respectively.
The shaded portion is a region where the contrast ratio becomes 1 or less and the display is inverted.

As described above, the conventional liquid crystal electro-optical element using the FTN mode has a narrow high-contrast region, and the display is easily inverted. This reversal of the display is a major factor that makes the viewing angle feel psychologically narrow.

The present invention solves such a problem, and provides a liquid crystal electro-optical element having a wide viewing angle by using a polymer stretched film having an optically negative uniaxial property as an optical anisotropic body. The purpose is.

[Means for Solving the Problems] In the liquid crystal electro-optical element of the present invention, a liquid crystal cell in which a twisted liquid crystal is sandwiched between a pair of substrates and at least one layer of an optically anisotropic material are disposed between a pair of polarizing plates. In the liquid crystal electro-optical element, the optically anisotropic body has refractive indices N1o and N2 in three directions, respectively.
o, and N3e, wherein the value of the refractive index N3e in a direction substantially horizontal to the substrate surface has a characteristic smaller than the values of the other refractive indexes N1o and N2o.

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

[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.

Reference numeral 51 in FIG. 10 denotes a refractive index ellipse of a conventional optically positive uniaxially stretched uniaxially stretched film. On the other hand, in FIG.
Numeral 50 denotes a refractive index ellipsoid of the optically negative uniaxially stretched film of the present invention. Both have exactly the same birefringence when observed from a direction perpendicular to the panel surface. However, since the value of the refractive index N1o corresponding to the direction perpendicular to the panel surface is different, when observed from an oblique direction, the birefringence differs from the conventional one. Therefore, by optimizing the value of N1o,
It is possible to increase the viewing angle without impairing the display characteristics in the front direction of the panel.

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 a uniaxially stretched film, and 4 is a lower polarizing plate. As the liquid crystal cell, a liquid crystal SS-4008 manufactured by Chisso was used, and the liquid crystal cell was twist-aligned to a cell having a cell gap d of 6.0 μm.

On the other hand, for the uniaxially stretched film, polymethyl methacrylate (PMMA) was stretched in silicone oil at 100 ° C. and used. Ordinary polymer films have the property of increasing the refractive index in the stretching direction when stretched and having optically positive uniaxiality. However, RMMA and poly-α-methyl methyl fluoroacrylate (PMFA)
Conversely, the refractive index in the stretching direction decreases and has a property of negative uniaxiality. The refractive index of this uniaxially stretched film is N1o
= 1.516, N2o = 1.518, N3e = 1.509. The film thickness is 50 μm and the retardation is 0.45 μm.

FIG. 2 shows a relationship diagram of each axis. The angle 20 between the polarization axis (absorption axis) direction 10 of the upper polarizer and the rubbing direction 11 of the upper substrate of the liquid crystal cell is 117 ° to the left, the twist angle 21 of the liquid crystal cell is 240 ° to the left, and the stretching direction 13 of the uniaxially stretched film is The angle 22 between the rubbing direction 12 of the lower substrate of the liquid crystal cell and the polarization axis (absorption axis) direction 14 of the lower polarizer and the angle 23 between the rubbing direction 12 and the lower polarizing plate 12 of the liquid crystal cell are set to 25 and 70, respectively.
゜

The liquid crystal electro-optical element of the present invention exhibits substantially the same characteristics as the conventional liquid crystal electro-optical element shown in FIG. 3 when viewed from a direction perpendicular to the panel surface.

FIG. 4 shows the viewing angle characteristics of the liquid crystal electro-optical element in Example 1. In the present invention, since the change in the amount of light at the time of non-selection is smaller than that in the related art, the inversion of the display is less likely to occur, and the region having a high contrast is widened.

(Example 2) In the uniaxially stretched film, there are many cell conditions for compensating for the retardation of the liquid crystal cell in addition to the conditions shown in Example 1. In the second embodiment, one condition other than the first embodiment will be introduced.

FIG. 1 is 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 a uniaxially stretched film, and 4 is a lower polarizing plate. The liquid crystal cell includes a liquid crystal ZLI-4151-100 (Δn =
Using 0.18), the cells were aligned in a twisted cell having a cell gap d of 5.0 μm. At this time, the retardation becomes 0.90 μm.

On the other hand, for uniaxially stretched film, PMFA was stretched in silicone oil at 100 ° C. and used. The uniaxially stretched film has a refractive index of N1o = 1.534, N2o = 1.538, and N3e = 1.502, and has optically negative uniaxiality. 15μ film thickness
m, the retardation is 0.54 μm.

FIG. 5 shows a relationship diagram of each axis. The angle 20 between the polarization axis (absorption axis) direction 10 of the upper polarizer and the rubbing direction 11 of the upper substrate of the liquid crystal cell is 45 ° left, and the twist angle 21 of the liquid crystal cell is left.
The angle 22 at which the stretching direction 13 of the uniaxially stretched film forms the rubbing direction 12 of the lower substrate of the liquid crystal cell is 0 °, and the angle 23 at which the polarizing axis (absorption axis) direction 14 of the lower polarizing plate forms 13 is 135 at the left.゜

Also in the present embodiment, the viewing angle is widened as compared with the case where a uniaxially stretched film having optically positive uniaxiality is conventionally used.

[Effects of the Invention] As described above, the optically anisotropic body has refractive indices N1o, N2o, and N3e in three directions, respectively, and the value of the refractive index N3e in a direction substantially horizontal to the substrate surface is different from that of the other. Since it has characteristics smaller than the values of the refractive indexes N1o and N2o, the viewing angle characteristics of the liquid crystal electro-optical element can be greatly improved, and 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 illustrating a relationship between axes of the liquid crystal electro-optical element according to the first embodiment of the present invention. FIG. 3 is a view showing the electro-optical characteristics of the liquid crystal electro-optical element of Example 1 and the conventional liquid crystal. FIG. 4 is a diagram illustrating viewing angle characteristics of the liquid crystal electro-optical element according to the first embodiment of the present invention. FIG. 5 is a diagram showing a relationship between axes of the liquid crystal electro-optical element according to the second embodiment of the present invention. FIG. 6 is a diagram showing a mechanism of optical compensation of the liquid crystal electro-optical element of the present invention. FIG. 7 is a sectional view of a conventional liquid crystal electro-optical element. FIG. 8 is a diagram showing a relationship between axes of 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 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 ... Uniaxially stretched film having optically negative uniaxial property (N3e <N2o to N1o) 4 ... Lower polarizing plate 5 ... Optically positive uniaxial property ... A liquid crystal cell upper substrate 7 a liquid crystal cell lower substrate 8 a transparent electrode 9 a twisted nematic liquid crystal 10. Direction of polarization axis (absorption axis) 11: Rubbing direction of upper substrate 6 of liquid crystal cell 12: Rubbing direction of lower substrate 7 of liquid crystal cell 13: Stretching direction of uniaxially stretched film 3 14: Lower polarizing plate 4 The direction of the polarization axis (absorption axis) of 15 ... The stretching direction of the uniaxially stretched film 5 20 ... The angle between the direction 10 of the polarization axis of the upper polarizing plate and the rubbing direction 11 of the upper substrate of the liquid crystal cell 21 ... The liquid crystal cell The torsion angle 22 of the uniaxially stretched film is the rubbing direction 12 of the lower substrate of the liquid crystal cell. The angle 23 between the direction 14 of the axis of polarization of the lower polarizing plate and the stretching direction 13 of the uniaxially stretched film 24 The direction 24 of the stretching of the uniaxially stretched film is the same as the rubbing direction 12 of the lower substrate of the liquid crystal cell. Angle 25: An angle between the direction 14 of the polarization axis of the lower polarizing plate and the stretching direction 15 of the uniaxially stretched film 30: A voltage transmittance curve for light having a wavelength of 450 nm (blue light) 31: Light having a wavelength of 550 nm Voltage transmittance curve for green light 32: Voltage transmittance curve for light of 650 nm wavelength (red light) 40 Isocontrast line with contrast ratio 1 41 Isocontrast line with contrast ratio 5 42 Contrast ratio 10 isocontrast lines 50... Refractive index ellipsoid of uniaxially stretched film 3 51.

Claims (2)

(57) [Claims] 1. A liquid crystal electro-optical element comprising: a liquid crystal cell having a twisted liquid crystal sandwiched between a pair of substrates; and at least one optically anisotropic body disposed between a pair of polarizing plates. The anisotropic body has three different refractive indices N1o, N2o,
And N3e, wherein the value of the refractive index N3e in a direction substantially horizontal to the surface of the substrate has a characteristic smaller than the values of the other refractive indexes N1o and N2o. 2. The polymer film wherein the optically anisotropic material is stretched, wherein N3e is a refractive index in a stretching direction of the polymer film, and N1o is orthogonal to the stretching direction and the polymer film is Is the refractive index in the thickness direction of the N2o
2. The liquid crystal electro-optical device according to claim 1, wherein は is a refractive index in a direction orthogonal to the stretching direction.