JPH01270024A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a high contrast ratio even if the liquid crystal display element is observed from a diagonal direction in a wide range by setting the angle between the max. absorption axes of 1st and 2nd polarizing plates at nearly 90 deg. and setting the respective max. absorption axes at nearly 45 deg. angle with the stretching axis of a 1st quarter-wave phase difference plate. CONSTITUTION:A liquid crystal 7 is sandwiched between the opposed 1st faces of a 1st substrate 3 which has scanning electrodes on the 1st face and has the perpendicularly oriented layer having a slight pretilt angle of 0.02-5 deg. thereon and a 2nd substrate 4 which has signal electrodes and has a slight pretilt angle of 0.02-5 deg. with said electrodes. The 1st and 2nd quarter-wave phase difference plates 2, 5 are disposed between the 2nd faces of these two substrates 3, 4 and the 1st, 2nd polarizing plates 1, 6 on the outermost side in such a manner that the stretching axes 10 thereof are nearly 90 deg. with each other. The display device is so constituted that the max. absorption axes of the two polarizing plates 1, 6 are nearly 45 deg. with the stretching axis 10 of the phase difference plate 2 and the angle between the max. absorption axes 9 of the two polarizing plates 1, 6 is nearly 90 deg..

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a liquid crystal display element, and particularly relates to a so-called liquid crystal display element that is aligned almost vertically when no voltage is applied and displays by controlling birefringence by applying a voltage. The present invention relates to a birefringence controlled liquid crystal display element.

(Prior Art) Conventionally, a birefringence-controlled liquid crystal display element has a liquid crystal cell in which a liquid crystal with negative dielectric anisotropy is vertically aligned between substrates on which transparent electrodes are formed. It has a structure in which a polarizing plate is placed on each side.

When no electric field is applied to the electrode, there is no birefringence effect, so no light is transmitted and the electrode is in a black state. When an electric field is applied to the electrodes, the liquid crystal molecules tilt in the horizontal direction, and the birefringence effect allows light to pass through, resulting in a bright state. At this time, since the direction in which the molecules tilt is random,
If they are aligned in a certain direction, the uniformity of the screen is better and an easier-to-read display can be obtained.

Normally, when this configuration is used, a display with a high foot-last ratio can be obtained when viewed directly in front of the panel, but in a direction tilted from the front, the magnitude of birefringence changes compared to the front.
The display becomes colored, more light leaks, and the contrast ratio becomes lower.

Therefore, the contrast ratio when observed from an oblique direction is improved by using a polarizing means that compensates for birefringence, that is, polarized light close to circularly polarized light, as described in JP-A No. 60-256121. A method is proposed.

FIG. 3 shows the structure of this liquid crystal display element.

In the figure, 1 is the first polarizing plate, 2 is the first 1/4 wavelength retardation plate, 3 is the first substrate, 4 is the second substrate, and 5 is the second 1/4 wavelength retardation plate.
A four-wavelength retardation plate, 6 a second polarizing plate, 7 a liquid crystal, 8 a rubbing direction, 9 a maximum absorption axis, 10 a stretching axis, 11 a light source, and 12 a liquid crystal cell.

(Problem to be Solved by the Invention) However, even with the liquid crystal display device described in JP-A-60-256121, the viewing angle range in which a good contrast ratio can be obtained is limited to the oblique direction within a certain observation plane. In practice, it was difficult to obtain a good contrast ratio from oblique directions over a wide observation plane.

Further, the first and second quarter wavelength retardation plates 2 as described above may be used.
5' and the first and second polarizing plates 1.6, it is difficult to obtain a dark state and a considerable amount of light passes through, resulting in a difficult to see display.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a birefringence-controlled liquid crystal display element that can obtain a high contrast ratio even when viewed obliquely over a wide range.

[Structure of the Invention (Means for Solving the Problem) A first substrate having a scanning electrode on a first surface and a vertical alignment layer thereon having a slight pretilt angle of 0.02 to 5'';
On the first surface, a second substrate having a signal electrode and a vertical alignment layer thereon having a slight pretilt angle of 0.02 to 5@ is installed so that the first surfaces of the respective substrates are substantially opposed to each other. , a liquid crystal cell comprising a liquid crystal composition having negative dielectric anisotropy sandwiched between the first and second substrates;
a liquid crystal display element comprising first and second polarizing plates disposed outside the second surface of each of the first and second substrates, the second surface of each of the first and second substrates and the first polarizing plate; ,
The first and second quarter-wave retardation plates are arranged between the second polarizing plate and the first quarter-wave retardation plate so that the stretching axis direction of the first quarter-wave retardation plate tilts the liquid crystal molecules at the center of the liquid crystal cell. It forms an angle of approximately 45'' with respect to a straight line obtained by projecting the direction onto the first substrate, and the first and second quarter-wave retardation plates are arranged such that their stretching axes are approximately 90 degrees apart from each other. and the first
The maximum absorption axes of each of the polarizing plate and the second polarizing plate are arranged at an angle of approximately 45'' with respect to the stretching axis of the first 1/4 wavelength retardation plate, and the maximum absorption axis of the first polarizing plate The liquid crystal display element is characterized in that the angle between the axis and the maximum absorption axis of the second polarizing plate is approximately 90''.

When the viewing angle direction is set obliquely from the normal to the center of the panel surface of the liquid crystal cell, the center of the liquid crystal cell is The tilt direction of the liquid crystal molecules is shifted by about 45'' from a straight line obtained by projecting onto the substrate of the liquid crystal cell.

(Operation) According to this invention, since it is configured as described above,
A high contrast ratio can be obtained even when viewed from an oblique direction over a wide range. Moreover, it has a good contrast ratio in the direction of the viewing angle and in a wide range extending to the left and right of the viewing angle.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

The birefringence controlled liquid crystal display element according to the present invention is constructed as shown in FIGS. 1 and 2, and the same parts as in the conventional example (FIG. 3) are given the same reference numerals.

That is, the liquid crystal display element of the present invention includes a liquid crystal cell 12, and first and second liquid crystal cells disposed opposite to each other on the outside of the liquid crystal cell 12.
a polarizing plate 1.6, and first and second quarter-wave retardation plates 2.5 disposed between the first and second polarizing plates 1.6 and the liquid crystal cell 12. It has become.

The liquid crystal cell 12 has first and second cells disposed facing each other.
A liquid crystal 7 having negative dielectric constant anisotropy is filled between the first and second substrates 3.4. The first substrate 3 has a transparent scanning electrode on the first surface (the surface facing the liquid crystal 7) and a vertical alignment layer thereon having a minute pretilt angle of 0.02 to 5''. The substrate 4 of No. 2 has a transparent signal electrode on its first surface (the surface facing the liquid crystal 7) and a vertical alignment layer thereon having a minute pretilt angle of 0.02 to 5''. In this example, a -basic chromium complex was used as the vertical alignment agent.

Moreover, EN-18 (Chisso Corporation) was used for the liquid crystal.

Further, as described above, between the second surfaces of the first and second substrates 3.4 and the first and second polarizing plates 1.6, there is a first
, a second 1/4 wavelength retardation plate 2.5 is disposed.

In this case, the direction of the stretching axis of the first 1/4 wavelength retardation plate 2 is about 45 degrees with respect to the straight line obtained by projecting the tilt direction of the liquid crystal molecules at the center of the liquid crystal cell 12 onto the first substrate 3. ' is set to form an angle.

Further, the first and second quarter-wavelength retardation plates 2.5 are arranged so that their stretching axes are approximately 90 degrees apart from each other.

Furthermore, the first polarizing plate 1 and the second polarizing plate 6 are arranged such that their respective maximum absorption axes form an angle of approximately 45@ with respect to the stretching axis of the first 174-wavelength retardation plate 2, and The angle between the maximum absorption axis of the first polarizing plate 1 and the maximum absorption axis of the second polarizing plate 6 is set to approximately 90''.

In addition, when the viewing angle direction is set obliquely from the normal to the center of the panel surface of the liquid crystal cell 12, the liquid crystal The tilt direction of the liquid crystal molecules at the center of the cell 12 is shifted by about 45@ from a straight line obtained by projecting onto the first and second substrates 3.4.

During operation, when a voltage is applied to the liquid crystal cell 12 in which liquid crystal with negative dielectric anisotropy is vertically aligned between the scanning electrode and the signal electrode, the liquid crystal molecules are tilted in the horizontal direction. Here, if the liquid crystal molecules are positioned perpendicularly to the first and second substrates 3.4 when no voltage is applied, the liquid crystal molecules tilt in random directions from the vertical direction when a voltage is applied.

By the way, when the liquid crystal cell 12 is placed between the first and second polarizing plates 1.6 and observed, a bright state and a dark state exist in the same pixel. Furthermore, when the viewing angle is changed, the bright state and dark state are reversed, resulting in a display that is even more difficult to see. One way to improve this is to align and tilt the liquid crystal molecules in the same direction when voltage is applied. To do this, it is necessary to arrange the liquid crystal molecules in advance at an angle slightly tilted from the vertical (pretilt angle).

The pretilt angle is set to 0 in order not to deteriorate the display performance.
．． A value in the range of 02 to 5'' is good; if it exceeds 5@, the rise of the voltage-transmittance characteristic may be poor, or a small amount of light may be transmitted although it should be in a dark state.

In this invention, the first and second quarters are placed on both sides of the liquid crystal cell 12.
A so-called circularly polarizing plate, which is a combination of a wavelength retardation plate 2.5 and first and second polarizing plates 1.6, is arranged.

The angle between the maximum absorption axis of the polarizing plate and the stretching axis of the 1/4 wavelength retardation plate is normally 45", but in order to correct the slight phase shift of the retardation plate at around 174 wavelengths, the angle is slightly The angle may also be adjusted.

As described in the above-mentioned Japanese Patent Application Laid-Open No. 60-256121, by arranging the polarizing plate and the 174-wavelength retardation plate as shown in Figure 3, 1. A quarter-wavelength retardation plate compensates for the phase difference that occurs when the light passes through the cell, improving the contrast ratio when viewed from an oblique direction.

However, this effect is due to the fact that the angle between the maximum absorption axis of the first polarizing plate 1 and the maximum absorption axis of the second polarizing plate 6 is 90
The @ configuration is more noticeable.

Therefore, in the present invention, the distance is set to 90'' as described above.

In other words, the contrast ratio is improved only in a certain observation plane, for example, the x-z plane, when observed from an oblique angle φ, but by adopting the configuration shown in Figure 1, the contrast ratio is improved when observed obliquely over a wide range. A high contrast ratio can be obtained even in the case of high contrast. However, in this case, the area with excellent visibility where a good contrast ratio can be obtained even in areas where the angle φ in the oblique direction is large is when the oblique direction is viewed from the direction of the leading axis of the 1/4 wavelength retardation plate. Yes, visibility may be poor depending on the viewing angle.

Therefore, the above-mentioned best direction of visibility is adjusted to the direction that humans actually see. Therefore, as shown in Figure 2, 1/4
The stretching axis of the wavelength retardation plate is set in the viewing angle direction, and a straight line shifted by 45 inches from this straight line coincides with the straight line created by projecting the tilt direction of the liquid crystal molecules at the center of the liquid crystal cell 12 onto the first substrate 3. It is necessary to do so.

By adopting this configuration, it is possible to realize a liquid crystal display element having a good contrast ratio in the direction of the viewing angle and in a wide range extending from the left and right sides thereof.

[Effects of the Invention] As described above, according to the present invention, a high contrast ratio can be obtained even when observing from an oblique direction over a wide range.

That is, the liquid crystal display element of this invention is 1/2o.

When time-division driving was performed at different duty ratios, the equal contrast curves showed good curves in the viewing angle direction and on the left and right sides thereof, as shown in FIG. Moreover, the contrast ratio was also large enough for practical use.

Incidentally, the isocontrast curve of the conventional liquid crystal display element (Fig. 3) is shown in Fig. 5, which shows that the contrast ratio is low and the viewing angle varies widely depending on the direction.
The display was difficult to see.

[Brief explanation of the drawing]

1 and 2 are exploded perspective views of a liquid crystal display element according to an embodiment of the present invention, Figure 3 is an exploded perspective view of a conventional liquid crystal display element, and Figure 4 is an exploded perspective view of a liquid crystal display element according to an embodiment of the present invention. A characteristic curve diagram showing an equal contrast curve representing the viewing angle of a conventional liquid crystal display element (Fig. 2) when viewed from the surroundings, and Fig. 5 shows the viewing angle of a conventional liquid crystal display element when viewed from the surroundings. FIG. 3 is a characteristic curve diagram showing isocontrast curves representing the magnitude of . DESCRIPTION OF SYMBOLS 1... First polarizing plate, 2... First 1/4 wavelength retardation plate, 3... First substrate, 4... Second substrate, 5...
...Second 1/4 wavelength retardation plate, 6...Second polarizing plate, 7...Liquid crystal, 8...Rubbing direction, 9...Maximum absorption axis, 10...Stretching axis , 11... light source, 12...
-Liquid crystal cell, x, y, z... orthogonal coordinate axes, φ... viewing angle, α... tilt angle. Applicant's agent Patent attorney Takehiko Suzue "@)-vll Figure 1 Viewing angle 7 phrases p-11 Figure 2 Takashi viewing angle 700 stitches 11 Figure 3

Claims (1)

[Claims] a first substrate comprising a scanning electrode on a first surface and a vertical alignment layer thereon having a slight pretilt angle of 0.02 to 5°;
A second substrate having a signal electrode on the first surface and a vertical alignment layer thereon having a slight pretilt angle of 0.02 to 5° is installed so that the first surfaces of the respective substrates face each other. a liquid crystal cell comprising a liquid crystal composition having negative dielectric constant anisotropy sandwiched between first and second substrates; and a liquid crystal cell disposed outside the second surface of each of the first and second substrates. In the liquid crystal display element comprising first and second polarizing plates, the first and second polarizing plates
The first and second 1/4 wavelength retardation plates are disposed between the second surface of each of the substrates and the first and second polarizing plates.
The direction of the stretching axis of the four-wavelength retardation plate forms an angle of approximately 45° with respect to a straight line obtained by projecting the tilt direction of liquid crystal molecules at the center of the liquid crystal cell onto the first substrate; Two 1/4 wavelength retardation plates have their stretching axes approximately 90 degrees apart from each other.
The maximum absorption axes of the first polarizing plate and the second polarizing plate are at an angle of approximately 45° with respect to the stretching axis of the first quarter wavelength retardation plate. 1. A liquid crystal display element, characterized in that the angle between the maximum absorption axis of the first polarizing plate and the maximum absorption axis of the second polarizing plate is approximately 90°.