JPH02306217A - Liquid crystal electrooptical element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal electrooptical element in which a visual angle is wide and, simultaneously, a coloring is a little by making a certain refractive index: among three main refractive indices provided to an optical anisotropic body smaller than the other two refractive indices and, simultaneously, making an axis corresponding to the refractive index approximately parallel to the substrate surface of a liquid crystal cell. CONSTITUTION:Between an upper side polarizing plate 1 and a lower side polarizing plate 4, a liquid crystal cell 2 to sandwich a liquid crystal 9 to be approximately homogeneous-oriented between electrode substrates and an optical anisotropic body 3 with one layer are arranged. A certain refractive index N3e among three main refractive indices N1o, N2o and N3e provided to the optical anisotropic body 3 is made smaller than the other two refractive indices N1o and N2o, and simultaneously, the axis corresponding to the refractive index N3e is in a direction approximately parallel to the substrate surface of the liquid crystal cell 2. The pretilt directions of the liquid crystal molecules of two opposed substrate surfaces of the liquid crystal cell 2 are mutually surface-symmetrical to the center surface of a liquid crystal layer. By such an execution, the liquid crystal electrooptical element, in which the visual angle is wide and, simultaneously, the coloring of a display is a little, can be realized.

Description

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

[Prior Art] A conventional liquid crystal electro-optical element called a π cell uses a liquid crystal cell in which the pretilt direction of liquid crystal molecules on the surface of a pair of substrates is plane symmetric with respect to the center plane of the liquid crystal layer.
Achieves high-speed response.

However, since this element performs display by controlling the birefringence of the liquid crystal, there is a unique coloring in the display. In order to eliminate this coloring, it has been proposed in the past to provide an optically anisotropic body in addition to the π cell, such as in Japanese Patent Application No. 62-58706.

FIG. 3 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, 5 is an optical anisotropic body,
4 is a lower polarizing plate.

The liquid crystal cell is Chisso's liquid crystal 5S-5003 (Δn
=0.08) to achieve substantially homogeneous alignment between two transparent electrode substrates. Further, the liquid crystal layer thickness d was set to 5.0 μm so that the retardation Δnd was 0.40 μm. On the other hand, a uniaxially stretched polymeric film containing polycarbonate as a main component was used as the optically anisotropic body. Its retardation is 0.35 μm.

FIG. 4 shows a relationship diagram of each axis of a conventional liquid crystal electro-optical element. Since the rubbing directions of the upper and lower substrates of the liquid crystal cell are the same, the pretilt direction of the liquid crystal molecules on the substrate surface is
As shown in FIG. 3, it has plane symmetry with respect to the center plane of the liquid crystal layer. The other axis relationship is that the polarization axis (absorption axis) direction 11 of the upper polarizing plate is the rubbing direction 12 of the upper substrate of the liquid crystal cell.
The angle 21 formed by this is 45'' to the left, the angle 22 formed by 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 polarization axis (absorption axis) direction 15 of the lower polarizing plate is 14 The angle 23 made with this is set to 456 to the left.

The conventional liquid crystal electro-optical device introduced above has a rise of 0.
．． It has an excellent response characteristic of 3 ms and a fall time of 2.1 ms, and coloring is suppressed to an extremely small level by compensation using an optical anisotropic body.

[Problems to be Solved by the Invention] However, conventional liquid crystal electro-optical elements have a problem in that the viewing angle range (hereinafter simply referred to as viewing angle) in which display can be clearly recognized is narrow. Conventional liquid crystal electro-optical elements have 1:
The viewing angle range having a contrast ratio of 10 or more was ±15° in the vertical direction and ±20' in the horizontal direction. The reason for such a narrow viewing angle is mainly that the light weight when not selected, that is, when it is off, changes significantly depending on the viewing direction.

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

[Means for Solving the Problems] The liquid crystal electro-optical device of the present invention includes a liquid crystal cell comprising a substantially homogeneously oriented liquid crystal sandwiched between two opposing electrode substrates, and at least one optical layer other than the liquid crystal. In a liquid crystal electro-optical element comprising an anisotropic body and a pair of polarizing plates disposed on both sides with the anisotropic body in between, among the three main refractive indices Nio, N2o, and N3e of the optical anisotropic body,
One refractive index N3e is the other two refractive index Nio, N
2o, and the axis corresponding to the refractive index N3e is located in a direction substantially horizontal to the substrate surface of the liquid crystal cell.

Further, the pretilt directions of the liquid crystal molecules on the surfaces of the two opposing substrates of the liquid crystal cell are plane symmetrical to each other with respect to the central plane of the liquid crystal layer.

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, 3 is an optical anisotropic body, and 4 is a lower polarizing plate. The liquid crystal cell used was Chisso's liquid crystal 5S-5003 (△n=0.0
8) to achieve substantially homogeneous alignment between two transparent electrode substrates. In addition, the liquid crystal layer thickness d is the retardation Δn
It was set to 5.0 μm so that d was 0.140 μm.

On the other hand, a uniaxially stretched film obtained by stretching polystyrene (PS) was used as the optically anisotropic body. Ordinary polymer films have the property that the refractive index in the stretching direction increases when stretched, but PS and polymethyl methacrylate (PMMA)
On the contrary, the refractive index in the stretching direction decreases. The refractive index of this −axially stretched film is N1o=1.5
36, N2o=1.538, N5e=1.524. Here, N3e is the refractive index in the stretching direction of the uniaxially stretched film, N2o is the refractive index in the direction perpendicular to this within the film plane,
Nl.

represents the refractive index in the thickness direction of the film.

Note that the film thickness is 25 μm, so the retardation is 0.
．． It becomes 35 μm.

FIG. 2 shows a diagram of the relationship between each axis. Since the rubbing directions of the upper and lower substrates of the liquid crystal cell are the same, the pretilt direction of the liquid crystal molecules on the substrate surface is plane symmetrical with respect to the center plane of the liquid crystal layer, as shown in FIG. The other axis relationships are as follows: The angle 21 between the polarization axis (absorption axis) direction 11 of the upper polarizing plate and the rubbing direction 12 of the upper substrate of the liquid crystal cell is 45° to the left.
, the angle 22 formed by the rubbing direction 13 of the lower substrate of the liquid crystal cell and the stretching direction 14 of the uniaxially stretched film is 0°, and the angle 23 formed by the polarization axis (absorption axis) direction 15 of the lower polarizing plate with 14 is 45° to the right. And so.

The liquid crystal electro-optical element of the present invention exhibits exactly the same electro-optic characteristics as a conventional liquid crystal electro-optical element, as long as it is viewed from the direction perpendicular to the panel surface. That is, it has excellent response characteristics and color characteristics as in the conventional case.

Furthermore, the viewing angle range with a contrast ratio of 1:10 or more has expanded significantly by ±25° in the vertical direction and ±60'' in the horizontal direction.The reasons for this wide viewing angle are:
This is mainly because the change in viewing angle of the amount of light during off-time is compensated by the uniaxially stretched film having a large refractive index in the film thickness direction.

[Effects of the Invention] As described above, according to the present invention, by using a stretched polymer film having optically negative uniaxiality as the optically anisotropic body, coloring of the display can be eliminated, and This has the effect of widening the viewing angle.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a liquid crystal electro-optical element of the present invention. FIG. 2 is a diagram showing the relationship between the respective axes of the liquid crystal electro-optical element of the present invention. FIG. 3 is a cross-sectional view of a conventional liquid crystal electro-optical element. FIG. 4 is a diagram showing the relationship between the axes of a conventional liquid crystal electro-optical element. 1, upper polarizing plate 2, liquid crystal cell 3, optically anisotropic body (N 3e < N 2o −N 1o
) 4, lower polarizing plate 5, optically anisotropic body (N 3e > N 2o ~ N 1o
) 6, upper substrate 7, lower substrate 8, transparent electrode 9, homogeneously aligned liquid crystal 11, direction 12 of the polarization axis (absorption axis) of the upper polarizing plate 1, rubbing direction 13 of the upper substrate 6 of the liquid crystal cell, The rubbing direction 14 of the lower substrate 7, the stretching direction 15 of the -axis stretched film, the direction 21 of the polarizing axis (absorption axis) of the lower polarizing plate 4, and the direction 11 of the polarizing axis of the upper polarizing plate are the same as those of the upper substrate of the liquid crystal cell. Angle formed with rubbing direction 12. 22. An 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. An angle between the direction 15 of the polarization axis of the lower polarizing plate and the stretching direction 14 of the uniaxially stretched film. Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Kizobe Suzuki (1 person) Figure 2 Figure 3

Claims (2)

[Claims] (1) A liquid crystal cell comprising a substantially homogeneously 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 disposed on both sides with the two electrode substrates sandwiched therebetween. In the liquid crystal electro-optical element comprising a polarizing plate, one of the three main refractive indices N1o, N2o, and N3e of the optically anisotropic body has a certain refractive index N3e.
is smaller than the other two refractive indexes Nio and N2o, and the axis corresponding to the refractive index N3e is in a direction substantially horizontal to the substrate surface of the liquid crystal cell. (2) The liquid crystal electro-optical device according to claim 1, wherein the pretilt directions of liquid crystal molecules on the surfaces of the two opposing substrates of the liquid crystal cell are plane symmetrical to each other with respect to the central plane of the liquid crystal layer.