JPH0350523A - Electrooptical device - Google Patents

Abstract

PURPOSE:To obtain a high-contrast, uncolored device with good visibility by setting the twist angle of liquid crystal molecules to >=100 deg. and forming a finely uneven surface as a surface which contacts the liquid crystal layer of at least one of a couple of electrode substrates. CONSTITUTION:The twist angle of the liquid crystal molecules of a liquid crystal cell 10 is set to >=100 deg. and the surface of at least one of both the electrode substrates 11 and 12, i.e. 12 on the side of the liquid crystal layer 13 is formed finely uneven by etching, etc. The unevenness extends to the border part of the liquid crystal layer 13 through an extremely thin transparent electrode 12a and an oriented film 12b, and consequently the thickness (d) of the liquid crystal layer 13 varies finely and continuously. Consequently, the high-contrast, uncolored device with the good visibility is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electro-optical device such as a liquid crystal display device or a liquid crystal shutter, and particularly to an electro-optical device that supports a liquid crystal layer in which liquid crystal molecules are twisted and oriented between a pair of opposing electrode substrates. This invention relates to a liquid crystal cell consisting of a liquid crystal cell and an electro-optical device equipped with a polarizing plate on the outside of the liquid crystal cell. [Prior art] For example, in a liquid crystal display device using a flat electrode substrate, if the thickness d of the liquid crystal layer is non-uniform, the so-called retardation tan Δn-d (Δn is refractive index anisotropy) changes. coloring occurs. Further, if the deviation between the molecular axis of the liquid crystal molecules and the polarization axis of the polarizing plate becomes large, there is a problem that coloration occurs due to the birefringence effect.

On the other hand, by providing fine irregularities on the liquid crystal layer side surface of at least one electrode substrate of the pair of electrode substrates and continuously changing the data density 4 minutely over the entire display surface, coloring can be achieved. (
For example, Japanese Patent Laid-Open No. 61137132) is known, but the conventional one is of the so-called twisted nematic type (hereinafter referred to as TN type) in which the twist angle of the liquid crystal molecules is about 90 degrees, so it has a contrast (quadrant). There were problems such as poor sex (sexuality). On the other hand, as a method for improving contrast, a so-called super twisted non-matic type (hereinafter referred to as STN type) type display device in which the torsion angle of the l&item molecule is set to 906 or more is known. Since the birefringence effect is used as the basic display principle,
Coloring was inevitable. Therefore, the present applicant previously proposed in JP-A No. 64-519 to provide an optically anisotropic body such as a liquid crystal cell for correcting the above-mentioned coloring in addition to the display liquid crystal cell. Because of the structure, there are problems such as an increase in the overall thickness. Furthermore, the thickness of the liquid crystal layer must be controlled to be extremely uniform, which is technically difficult.

[Problem to be solved by the invention]

The present invention was proposed in view of the above-mentioned problems, and an object of the present invention is to provide an electro-optical device that has high contrast without using a liquid crystal cell for color correction as described above, and is not colored. ．． [Means for Solving the Problems] In order to achieve the above object, the present invention has the following precepts. That is, in an electro-optical device comprising a liquid crystal cell that supports a liquid crystal layer in which liquid crystal molecules are twisted and oriented between a pair of opposing electrode substrates, and a polarizing plate on the outside of the liquid crystal cell, the twist angle of the liquid crystal molecules is is set to 100° or more, and
The present invention is characterized in that fine irregularities are provided on the surface of at least one of the pair of electrode substrates that is in contact with the liquid crystal layer.

[For production]

As shown above, the twist angle of the liquid crystal molecules in the liquid crystal cell is 100@
By setting the above, it is possible to increase the contrast, and by providing minute irregularities on the surface of at least one electrode substrate on the liquid crystal layer side, it is possible to provide an electro-optical device without coloration. becomes. [Embodiment] FIG. 1 is a longitudinal sectional view of a liquid crystal display device as an electro-optical device showing an embodiment of the present invention.

In the figure, l.2 is a pair of upper and lower polarizing plates, IO is a liquid crystal cell provided between both polarizing plates l.2, and a liquid crystal 113 is supported between electrode substrates l1 and l2 made of a pair of upper and lower glass plates. It is a precept. Liquid crystal layer 1 of each electrode substrate 11 and 12
On the 3 sides, transparent electrodes 1 1a-12 made of ITO, etc.
a and alignment films 1lb-12b are provided. 14
is a sealing member that also serves as a spacer for maintaining distance. In the illustrated example, fine irregularities are formed by etching or the like on the surface of the liquid crystal layer 13 of one of the electrode substrates l1 and 12, l2. The unevenness is formed on the liquid crystal N13 through an extremely thin transparent electrode 12a and an alignment film 12b.
This spreads to the boundary between the liquid crystal 7I13 and the thickness d of the liquid crystal 7I13 changes minutely and continuously. The above-mentioned irregularities may be provided on the other electrode substrate 11 or both temporary electrode bases 11-12. Furthermore, the above-mentioned unevenness only needs to be able to change at least the thickness of the liquid crystal layer, and the unevenness can be formed by any suitable means. For example, a thin film or the like is provided on the surface of the electrode substrate on the liquid crystal layer side to form unevenness on the surface. It is also possible. Furthermore, the height h of the above-mentioned irregularities is set to at least a height such that the upper and lower electrode substrates do not come into contact with each other. In addition, the distance l between the peaks and valleys of the unevenness is 10 to 500 μm.
, preferably about 60 to 150 μm. Further, the minimum thickness d of the liquid crystal layer {fidmin is preferably 5 μm5 and the maximum value dtaax is preferably about 10 am. FIG. 2 is an explanatory diagram showing the relationship between each axis in the liquid crystal display device shown in FIG.
・The direction of the polarization axis (absorption axis) of 2, Q is the direction of both polarizing plates 1・
2, Rll-R12 is the direction of the molecular axis (rubbing direction) of the liquid crystal molecules adjacent to each electrode substrate 11-12, and T is the angle formed by the polarization axis (absorption axis) of the liquid crystal molecules in Figure 1, from top to bottom. Represents the direction and angle of twist.

The above angle Q is set to approximately 90° for positive display and approximately 0@ for negative display. Further, the above-mentioned angle T, that is, the twist angle of the liquid crystal molecules is set to 100° or more, preferably 110° to 160 m. Also, the twist direction can be either left or right. Experimental example l In the above figures 1 and 2, the angle Q is 90° and the angle T is 1
50°, and the distance l between the peaks and valleys of the unevenness is 60°.
~150 μm, the height h of the unevenness is 0 to 5 μm, the minimum value d Ilin of the thickness d of the liquid crystal layer is 5 μm, and the maximum value d I
IIax is set to 9 μm, and the liquid crystal layer l3
When a liquid crystal display device having a Δn-d of 0.415 to 0.747 μm was prepared using a nematic liquid crystal having a refractive index anisotropy Δn of 0.083, the following characteristics were obtained.

That is, the appearance color when no voltage is applied is x = 0.31, ! in the CIE chromaticity diagram. = 0.31, and degree T was 1.15. The contrast ratio during time-division driving is shown in Table 1 below. Table 1 In the above table, Comparative Example 1 has an angle T of 90°, and the other configurations are the same as Experimental Example 1, with the contrast ratio of a TN type liquid crystal display device having horizontal unevenness. Comparative Example 2 has an angle T of 90°. This represents the contrast ratio of a TN type liquid crystal display device with a liquid crystal layer thickness of 5 μm and Δn=0.11, which is formed flat with no unevenness on the electrode substrate at 90°. As is clear from the table above, according to the present invention, a display with high contrast can be obtained. Furthermore, the viewing angle characteristics of Experimental Example 1 and Comparative Examples 1 and 2 are shown in Fig. 3. In the figure, A-B-C are the experimental examples l, respectively.
・Duty ratio 1716 in Comparative Example 1 and Comparative Example 2.
It represents the contrast ratio at a viewing angle of 10゛ when driven at a bias ratio of 1/4, and is based on the above experimental example 1 based on the present invention.
It can be seen that the viewing angle characteristics are excellent. Experimental Examples 2 to 7 Furthermore, a liquid crystal display device that differed only in the twist angle from Experimental Example 1 was created and its characteristics were investigated. The results are shown in Comparative Example I.
A comparison with 2 is summarized in Table 2 below. Table 2 The α value in the above table is the ratio of the voltage value Vαl that gives 50% transmittance at a viewing angle of 10” and the voltage value Vα2 that gives 50% transmittance at a viewing angle of 30°■ α1 /Vα2, which represents the voltage fluctuation when the viewing angle is changed.The γ value is the voltage value VTI at which 90% transmittance is obtained when the viewing angle is 10°.
and the voltage value Vy2 at which a transmittance of 10% is obtained Vrl
/Vγ2, which represents the steepness. Further, the contrast is the contrast ratio when driving at a duty ratio of 1/16 and a bias ratio of 1/4.

As can be seen from Table 2 above, according to the present invention, viewing angle characteristics and contrast ratio can be improved. [Effects of the Invention] As explained above, according to the present invention, it is possible to achieve high contrast and uncolored visibility without providing a liquid crystal cell for color correction separately from the liquid crystal cell for display as described above. A good electro-optical device is obtained.

Additionally, the viewing angle is wider than the conventional TN type, and coloring does not occur even at low viewing angles.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view of an electro-optical device showing an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the relationship between each axis, and Fig. 3 is a graph showing viewing angle characteristics according to an experimental example based on the present invention.

Claims (1)

[Claims] (1) In an electro-optical device comprising a liquid crystal cell in which a liquid crystal layer in which liquid crystal molecules are twisted and oriented is sandwiched between a pair of opposing electrode substrates, and a polarizing plate on the outside of the liquid crystal cell, the twisting of the liquid crystal molecules is In addition to setting the angle to 100° or more,
An electro-optical device characterized in that a surface of at least one of the pair of electrode substrates on the side in contact with a liquid crystal layer is provided with fine irregularities.