JPS5940623A - Twisted nematic type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a titled display device adapted to multiplex driving by increasing the twist angle of liquid crystal molecules and specifying the direction of the polarization axis of the polarization plates to be adhered to the top and bottom of a cell. CONSTITUTION:A nematic liquid crystal 4 is sealed between substrates 1A and 1B provided with transparent electrodes 2A, 2B to constitute a liquid crystal cell 5 (a symbol 3 is a sealant), and polarization plates 6A, 6B are disposed on both sides thereof (a symbol 7 is a reflection plate), whereby a twisted nematic type liquid crystal display device is formed. The twist angle of the liquid crystal molecules and the polarization axis direction of the polarization plates in the above-mentioned device are so determined that the relations (i) 46 deg.<=(phi1,phi2)<=60 deg., (ii) 180 deg.<=(phi1+phi2+theta1+theta2)<=210 deg. are satisfied (phi1, phi2 are respectively the angles of the orientation 9 of the liquid crystal molecules near the upper substrate 1A and the orientation 10 of the liquid crystal molecules near the lower substrate 1B when viewed from the observer's direction 8, theta1, theta2 are respectively the angles of the polarization axis 11 of the upper polarization plate 6A and the polarization axis 12 of the lower polarization plate 6B when viewed from the direction 8).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a twisted nematic liquid crystal display device suitable for multiplex driving.

Liquid crystal display devices have advantages such as low voltage IJJA operation and low power consumption, and are used in various fields mainly in twist mode. Even more now.

With the increase in display capacity, the demand for multiplex drives has increased from the conventional study drive, and they are now being used for program calculators, microcomputer terminal displays, etc.

It is expected that the capacity of liquid crystal display devices will continue to increase. However, as the display capacity increases, that is, as the multi-plexing property increases, the display contrast tends to decrease, and an important point is how to maintain this display contrast.

For this reason, the polarization axes of polarizing plates, which were conventionally set perpendicular or parallel, are slightly shifted. Alternatively, the display contrast has been improved by improving the margin in the viewer direction by, for example, making the alignment direction of the liquid crystal asymmetrical when viewed from the viewer direction.

However, these methods have a margin of 11 from the direction of the observer.
However, retardation is more likely to occur. As the viewing direction changes little by little, the display contrast suddenly decreases.
In some cases, there are drawbacks such as the tgo becoming completely invisible,
The degree of freedom in design was low.

The present invention provides (1) a twisted nematic liquid crystal display device in which various measures can be taken in order to prevent such drawbacks of the conventional art and to improve the margin; is 46°≦ψ1. ψ2≦
60°, and when the intersecting angle that is not the intersecting angle at which the inner optical plane propagates is θl + θ2, then 1
The present invention is a twisted nematic liquid crystal display device characterized in that 80°≦ψ, −+−tp, and +0102≦210°.

The liquid crystal display device of the present invention has an improved margin during multiplex driving, and has good sharpness and contrast.

The twisted nematic liquid crystal display device of the present invention improves the characteristics of a liquid crystal cell for multiplex driving by not relying only on the liquid crystal material, but by changing the initial alignment direction of liquid crystal molecules near the substrate, increasing the twist angle of the liquid crystal, and increasing the twist angle of the liquid crystal. By appropriately selecting the orientation of the polarizing plates, characteristics suitable for multiplex driving can be achieved.

This will be explained below according to the diagram. FIG. 1 is a sectional view of a twisted nematic liquid crystal display device of the present invention. The basic structure of the cell is exactly the same as a conventional reflective TN liquid crystal cell. That is, transparency is the pole (2A).

The substrates (IA) and (IB) provided with (2B) are facing each other and sealed with a cooling agent (3), and a nematic liquid crystal (4) is injected to form a liquid crystal cell (5), with polarized light on both sides. Board (6
A) and (6B) are provided, and a reflector plate (7) is further installed on one side thereof.

Conventionally, liquid crystal molecules near the substrates (IA) and (IE) are aligned so that they differ by 90 degrees, so the liquid crystal molecules form a helical structure with an angle of about 90 degrees between the substrates. However, in the present invention, the helical structure of the liquid crystal molecules is oriented at 92 degrees or more, cholesteric liquid crystal or nematic liquid crystal to which an optically active substance is added [7] is used, and the binding angle of the polarizing plate is adjusted. The aim was to change the characteristics and improve the characteristics.

Note that each constituent material of this liquid crystal display device can be a known material, and the substrate is a transparent substrate made of glass, plastic, etc. with a transparent electrode layered thereon.
．． Undercoat such as ax2o, BtOZ, Zr
O□5 Polyimide, silicone, etc. may be provided with an oat (- coat), and the electrode +!i may also be a two-layer electrode, a composite electrode of a transparent electrode and a metal wire, etc. Segment, dot matrix, multi-IL dot matrix, analog clock) (applicable to turns, bar graphs, and other glaze patterns).

In addition, sealing materials include various thermosetting resins such as epoxy resins, silicone resins, and fluorine resins, ultraviolet curing resins, inorganic adhesives with frit stops, and in the case of plastic substrates, high frequency and heat treatment.

It is also possible to seal by melting with ultrasonic waves, laser, etc., or it is sufficient to form a liquid crystal cell by injecting liquid crystal and sealing.

The nematic liquid crystal sealed in the liquid crystal cell in the present invention may be any liquid crystal having a twisted nematic structure, and cholesteric liquid crystal or an optically active substance is added to prevent reverse orientation. In particular, it is preferable to use a liquid crystal with a product Δn-d of the refractive index anisotropy Δn of the liquid crystal and the gap d (μm) of the liquid crystal cell between α5 and [17] because interference coloring that occurs near the voltage threshold due to polarization axis rotation is less likely to occur. stomach.

A levorotary cell will be explained below, but a dextrorotatory cell can be explained in exactly the same way if the symmetry 0 is taken into account.

FIG. 2 is a schematic diagram showing the positional relationship between liquid crystal molecules and the polarization axis of a polarizing plate in the vicinity of the substrate.

Here, (9) is the orientation direction of liquid crystal molecules in the vicinity of the upper substrate (initial orientation direction), (10) 11 is the orientation direction of liquid crystal molecules in the vicinity of the lower substrate, and the viewer direction (
8) respectively sII+1. Let it be P2.

Also, (11) is the polarization axis of the upper polarizing film, (12)
The polarization axis of the lower polarizing film is θ1. Let it be θ2.

In this case, the intersection angle θl+θ2 of these two polarizing plates is the intersection angle of the direction in which the polarization plane propagates (180°-01-02)
This is the intersection angle on the opposite side.

Here, at t, the polarization axis of the polarizing plate is positioned perpendicular to the long axis direction of the liquid crystal molecules near the substrate (top layer), but in addition to this, the polarization axis of the polarizer is positioned parallel to the long axis direction of the liquid crystal molecules (11 points). ) There is a way to position it. Regarding the method of attaching these two polarizing plates, if 5ense is used in this way, in the present invention, 46°≦ψ1. ψ2≦60°, 180°≦ψl
+ψ20θ1+θ2≦210°.

This is because ψl and ψ2 are set to be 46° or more because the multiplex property decreases if the change is less than 45°, and 60°
ψ1. ψ2 is 46°
≦ψl, ψ2≦60°.

Also, θ1. θ, is △θ−ψ1+ψ2−(180°−01
-θ2), the range 'J' from Δθ-Ω to 60°! Rotation in the direction of the opening number is not preferable because the multiplex characteristic deteriorates, and it is preferable to rotate it by 1 to 50 degrees, and the optimum value exists within this range.

In order to match the observer direction and the clear vision direction, θl−θ2
．． It is preferable that ψl=ψ2. In this way, θ1=
θ2. When ψl - ψ2, the viewer's direction coincides with the clear vision direction, and the display contrast is most easily seen when viewed from the viewer's side, and the display contrast does not suddenly decrease even if the viewer moves from side to side.

Examples will be shown based on the above definitions. Table 1 shows the results of examining changes in properties by changing the twist angle of liquid crystal molecules under overlaying conditions. The nematic liquid crystal in the example is composed of: 'Furthermore, when the intersection angle of the initial alignment direction of the liquid crystal molecules becomes large, the liquid crystal molecules are reversely oriented in the direction of the smaller V1 intersection angle by screwing, so to prevent this, cholesteric liquid crystal is added and the liquid crystal molecules are aligned in advance in the desired direction. Rotate it so that it is essentially the same angle as the 80° intersection angle.

In other words, the pitch meeting P due to the addition of cholesteric 7i'j crystals
(μlI]), the cell gap is d (μm), and the intersection angle of the initial orientation is ψ1+ψz (aeg), then (1/P
Cholesteric liquid crystal is added so that X 360"::-9's -+-t12-80, that is, P"knee □□ μm ψ1+ψ2-80/(.

Example 1 This is an example in which ψl-ψ2 = 55° and 1, △θ-0°.
This is an example of 5°0°.

Here, △θ is the difference between the twist angle of the liquid crystal molecules (ψ! + ψ2) and the angle at which the plane of polarization rotates (180° - θl - 02) when light propagates inside the liquid crystal cell. (ψ1+ψ2
)-(180°-θl-θ2).

2411 Table 1 M85G * M890 + Mqllll
is a parameter that serves as a guideline for matrix drive,
The second one shows the steepness of the rise characteristic, and the third one shows the viewing angle dependence.
θ-10°) M day 90- Vso (θ; 10°)/V
+o (θ=10°)'q1o −Vso (θ−40°
)/V2O(θ-10°). Also, 0 is the angle measured from the normal direction of the liquid crystal cell to the clear viewing direction, Vll
l) l vso + Vllll are the voltages at which the relative brightness is 90ch, 50%, and 10%, respectively.

If the angle of the screw of the liquid crystal molecule is larger than 92°, Mo5
(1, Msg. and Mqto t showed an almost increasing trend, and as a result, Ma5 (1.
qto also showed an increasing trend of it ti. As typical examples, Comparative Example (ψ1=ψ2-45°, Δθ-0°) and Example 1 (ψ1-ψ2-55°, Δθ=0°) are shown in Table 1, and the difference is obvious. There was 1, but ψl + ψ2 was 12
When the angle exceeded 0°, there was a tendency for the contrast to suddenly decrease.

In this Example 1, Mo2 (1°M2B
9. Both n of 5 and Mqto are large. As a result, M85(1・M(1+o and MBso ” M(1+o
was increased and showed excellent multiplexability.

Contrary to this Example 1, when ψ1+ψ2 was less than 90'', the multiplex characteristic t deteriorated.

Also, the twist angle ψ1+ψ2 of the liquid crystal molecules is 92-120°, and Δθ is ψ1+ψ1+θ1+θ2-180.
By changing the angle within a range of 30° from °fro', the multiplex characteristics were further improved. This is clear from the comparison between Example 2 and Example 1. In Example 2, the angle was ψ1-ψ2-55゛, and in the example with the θ plate -〇, -45°, the fillet was △θ-20°, and the polarization was M as the axis rotates
Ma2O-Mqto and Memo increased despite an increase in qro and a slight decrease in Mo56 and Msg6.
``Mqto Vi increased, and the multiplex property improved.However, [7°] This △θ usually has a point where the multiplex property is best within the range of 0 to 60°, so experiments using liquid crystal material, ψ, etc. It is sufficient to find the optimum value using C.

Rotation of this Δθ in the direction opposite to that of Example 2, that is, in the direction of Δθ<0°, deteriorated the multiplex property.

In addition, if the twist angle of the liquid crystal molecules is 1ψ2T&:11 other than 7' (also change △θ by 0 to 30°yc
Results similar to those in Example 2 were obtained.

As described above, in the present invention, as the twist angle of the liquid crystal molecules is increased and the rotation angle of the polarizing plate is increased, the multiplex property is improved, but if the screw angle fL of the liquid crystal molecules is increased too much, the contrast deteriorates. Furthermore, if the polarizing plate is rotated too much to increase △θ, the polarization axis and the long axis direction of the liquid crystal molecules will deviate from the right angle by a large amount, which will make back coloring due to retardation noticeable and the angle dependence will also decrease. . As a result of studying these, it was found that the twist angle of the liquid crystal molecules is 46°<tpl, ψ2<60°, and the rotation angle of the polarizing plate is uO<Δθ<60°.

In addition, the refractive index anisotropy Δn of the liquid crystal and the cell gap d (μm
) is a pan meter that has a large optical effect during multiplex drive, but in the present invention, a particularly excellent effect is obtained when Δn・d is 0.5 to 0.7 μm. I was taken out. That is, Δn−d is a hue that is acceptable also in terms of the background color of cell Fj in this range, and
It has the advantage that when the polarization axis is largely rotated, coloring due to interference that occurs near the voltage threshold in a cell where Δn-d is 1 μm or more is difficult to increase. Therefore, the effects of the present invention can be utilized to the fullest, and the lack of steepness in optical characteristics, which was a drawback in conventional cells of Δn-d;di (15 to 0.7 μm), can be easily improved.

As described above, the present invention is based on the twist angle of liquid crystal molecules in a TN type liquid crystal cell. Excellent multiplex characteristics can be obtained by making the comb wider than the conventional 90° angle and by rotating the polarizing axes of the polarizing plates attached above and below the liquid crystal cell in an appropriate direction.

[Brief explanation of the drawing]

FIG. 1: A cross-sectional view of a TN type liquid crystal display device. Figure 2: Schematic diagram showing the positional relationship between liquid crystal molecules and the polarization axis. IA, IB: Substrate 2A, 2B: Transparent electrode 6, 6B: Polarizing plate

Claims (1)

[Claims] In an istnemanac type liquid crystal display device, an initial alignment direction ψ1. ψ2 is 46°≦ψweight+t
When p2≦60°, the intersecting angle that is not the intersecting angle at which the inner optical surface of the intersecting angle of the polarization axes of the polarizing plate propagates is θl+02, then 180°≦91−■−ψλ+θl+θ2≦210°
A twisted nematic liquid crystal display device characterized by: (2) The product △n-d of the refractive index anisotropy △n of the Nemanak liquid crystal and the gap a (pm) of the liquid crystal cell is α5≦Δn
The twisted nematic liquid crystal display device according to claim 1, characterized in that -a≦α7 μm. (3) 181'≦ψ1+ψ2+θl+θ2≦210°
A twisted nematic liquid crystal display device according to item 1 of the claimed patent application, characterized in that: