JP2908386B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having an achromatic background color.

[0002]

2. Description of the Related Art A liquid crystal display element has a TN mode depending on an operation mode.
Type, DS type, GH type, DAP type, thermal writing type, etc. Among them, TN type liquid crystal display elements are often used as display elements for calculators and measuring instruments.

In recent years, as demands for increasing the display capacity and increasing the display area of a word processor, a personal computer, and the like have increased, TN liquid crystal display elements have problems such as insufficient contrast and a narrow viewing angle range. Therefore, development of a liquid crystal display element using a new operation mode has been urgently required.

[0004] As a liquid crystal display device meeting such a demand, for example, the SB described in Japanese Patent Application Laid-Open No. 60-10702 is disclosed.
Attention has been paid to an E (super twisted via flange effect) type liquid crystal display device of a controlled birefringence type. The configuration of the SBE type liquid crystal display element includes:
Two transparent substrates each having a transparent electrode formed on at least one side are opposed to each other, and the periphery is sealed to form a cell, and a nematic liquid crystal is put in the cell. The distance between the opposing substrates is 3 to 12
The nematic liquid crystal is a cyclohexane-based, ester-based, biphenyl-based or pyrimidine-based liquid crystal. A chiral agent is added to the nematic liquid crystal, and the molecular axes of the liquid crystal molecules are twisted between a pair of substrates at an angle of 180 to 360 °. Also, the liquid crystal molecules are oriented at an angle of 5 ° with respect to the plane of the substrate due to the orientation film on the substrate.
It has a larger tilt angle θ. And the retardation R = △ nd · cos2θ of the liquid crystal cell is
It is 0.6 to 1.4 μm.

Further, in the SBE type liquid crystal display device in which the twist of the molecular axis is 270 °, a polarizing plate is preferably disposed on the front and back surfaces outside the substrate, and the transmission axis of the front polarizing plate is aligned with the molecular orientation of the front substrate. The best configuration is about 30 ° clockwise with respect to the direction, and the transmission axis of the rear polarizer is about 30 ° counterclockwise or about 60 ° clockwise with respect to the orientation direction of the rear substrate. . The former configuration provides a bright yellow display in the non-selected state and a black display in the selected state (yellow mode), and the latter configuration provides a deep blue display in the non-selected state and transparency in the selected state. (Blue mode).

In the SBE type liquid crystal display device having such a configuration, the change of transmitted light with respect to the voltage is steep, and the high contrast and the wide viewing angle are obtained even when the multiplex driving is performed for a plurality of digits.

On the other hand, as an example of a liquid crystal display device in which the breach angle is reduced by a rubbing technique, the twist angle of the liquid crystal is reduced.
So-called ST (super twist) with 100 to 200 °
A liquid crystal display device is known (SID86DIGET, p122).

As another example, Japanese Patent Application Laid-Open No. Sho 60-73525 discloses that the optical axes of the front and rear polarizing plates are almost the same as those of a cell having a retardation R of 0.5 to 0.8 μm and a twist angle of liquid crystal molecules of 270 °. The liquid crystal display element is set to 90 °, and the direction in which the optical axis of the polarizing plate bisects the director is considered good.

In any of such liquid crystal display devices, the background color is colored, not achromatic. For this reason,
A black display on a yellow background or a white display on a blue background. Visibility evaluation differs depending on the observer's visual perception, and the visibility (contrast etc.) is reduced by the background color for some people. Some evaluate it. Further, since both the ST type and SBE type liquid crystal display elements use birefringence, color unevenness is likely to occur due to a difference in the distance between the transparent substrates, and color change and temperature change from the viewing angle direction. The color change when doing was large.

In the TN type liquid crystal display element, colorization is easy by providing a color filter, whereas in the SBE type liquid crystal display element, colorization is impossible because the background color is colored. Was.

An OMI type liquid crystal display device is known as an example in which this point is improved (Appl. Phys. Lett. 50 (5) 1987).
p.236). That is, the liquid crystal has a twist angle of 180 °, a retardation Δn · d · cos 2θ of 0.5 to 0.6 μm, and one of the transmission axes of the polarizing plate is parallel to the rubbing axis.
The angle of the absorption axis of the polarizing plates is 90 °.

However, in this OMI type liquid crystal display device,
Since the twist angle of the liquid crystal is 180 °, the change of the transmitted light with respect to the voltage is not so steep. When the driving duty ratio is reduced, there are problems such as insufficient contrast, narrow viewing angle, and dark background. Was.

Japanese Patent Application Laid-Open No. Sho 57-46227 and Japanese Patent Application Laid-Open No. Sho 57-46227 disclose such background darkness and insufficient contrast.
JP-A-96315 and JP-A-57-125919 disclose a liquid crystal display device in which two liquid crystal cells are stacked and a polarizing plate is placed on both sides thereof to display a black and white display.
An example of application of the method is described in JJAP (26, NOV.11.L17787 (1987)).

These features are such that the twist directions of the two liquid crystal cells are made opposite to each other, and the retardations of the respective liquid crystal cells are made substantially equal.

That is, as shown in FIG. 6, the linearly polarized light 103 that has passed through the polarizing plate 3 becomes elliptically polarized light 101 ′ by passing through the first liquid crystal cell 5. The elliptically polarized light passes through the second liquid crystal cell 6, which has a twist angle almost opposite to that of the first liquid crystal cell 5 and has almost the same retardation, and becomes linearly polarized light 102 '. Pass through,
Perceived by human eyes.

What is important here is that the first liquid crystal cell 5 and the second liquid crystal cell 6 have optically complementary properties. Thus, the wavelength dependence of the elliptical shape after passing through the first liquid crystal cell 5 is complementary to the wavelength dependence of the elliptical shape of the second liquid crystal cell 6. As a result, the light transmitted through the first and second liquid crystal cells 5 and 6 has no wavelength dependency, and an achromatic display without coloring is obtained. This means
It also shows that all light in the visible region can be used for display, resulting in a bright display.

At this time, since the first liquid crystal cell 5 and the second liquid crystal cell 6 need to be optically complementary, the retardation of each liquid crystal cell is, for example, ±
It is necessary that they are almost the same within 0.05 μm.

Note that electrodes are formed on the substrates 1 and 1 'of the first liquid crystal cell 5 and driven in the same manner as a normal dot matrix type liquid crystal display device.
No electrode is formed on 2 ', and the liquid crystal is not driven, but is simply used for correcting an elliptical shape.

As described above, the ST-type liquid crystal display device of the two-layer cell type has the advantages of displaying black and white and increasing the number of digits, but has a narrower viewing angle than the SBE type or the OMI type. Including the yield of the two liquid crystal cells, the use of two liquid crystal cells becomes very expensive.

[0020]

As described above, the so-called ST type liquid crystal display device or SBE type liquid crystal display device having a twist angle of 180 ° or more has a colored background and an achromatic OMI having no background. In the case of the liquid crystal display device of the type, a liquid crystal display device having a high contrast and a bright background could not be obtained.

A liquid crystal display device using two ST type liquid crystal cells has a high contrast with a black and white display having no color on the background, but is expensive.

The present invention is directed to a liquid crystal display device which performs display based on a birefringence effect, and has a bright background, an achromatic color, a high contrast, and a wide viewing angle. An object is to provide an element at low cost.

[0023]

According to the liquid crystal display device of the present invention, a liquid crystal composition is held between a first substrate and a second substrate, which are disposed to face each other, and a first substrate and a second substrate. , A liquid crystal display device having a liquid crystal cell displaying by a birefringence effect based on a twist alignment, and first and second polarizing plates disposed on both sides of the liquid crystal cell, wherein a first polarizing plate and a second polarizing plate are provided. Is disposed so that the transmittance becomes maximum when a voltage is applied to the liquid crystal composition, and a first optical element is provided between the first substrate and the first polarizing plate on the first substrate side. first optical single lifting axis
Delay plate, the first light Chi lifting the second optical axis to the first polarizer side
Retardation value equal to the retardation value of the retarder
A second optical delay plate having the following formula: wherein, when an acute angle among angles formed by the first and second optical axes is a twist angle between the optical delay plates, the second optical delay plate moves from the second optical axis to the first optical axis. The liquid crystal display element is characterized in that the twist direction is set to the same direction as the direction of the twist alignment from the first substrate to the second substrate so as to eliminate the undesired birefringence effect.

The operation of the liquid crystal display device of the present invention will be described.
FIG. 5 is a diagram for explaining the display principle of, for example, an SBE type liquid crystal display element or an ST type liquid crystal display element which performs display by the birefringence effect of the related art. Polarizing plates 3 and 4 are arranged before and after a liquid crystal cell 5 (comprising substrates 1, 1 'and a liquid crystal composition sandwiched therebetween). The linearly polarized light 103 passing through the polarizing plate 3 passes through the liquid crystal cell 5 and generally becomes elliptically polarized light 101 ′. The elliptically polarized light passing through the liquid crystal cell 5 passes through the polarizing plate 4 placed at a predetermined angle, and is sensed by human eyes. The shape of the ellipse at this time is the twist angle あ る, which is the twist angle of the liquid crystal molecules in the liquid crystal cell 5, and the retardation R
= △ nd · cos 2θ and wavelength input.
Here, Δn is the birefringence of the liquid crystal composition in the liquid crystal cell 5,
d is the cell thickness (substrate spacing), and θ is the tilt angle.

In general, the transmittance changes depending on the wavelength, and the transmitted light is colored. By applying an electric field to the liquid crystal cell and changing the orientation of the liquid crystal molecules, the birefringence Δn is effectively changed, whereby the retardation R is changed and the transmittance is changed, and display is performed using this. .

The above-described two-layer system has a basic configuration in which two liquid crystal cells having optically complementary properties to each other are used.

The present invention has a structure in which two optical delay plates are arranged on one side of one liquid crystal cell, and its operation will be described with reference to FIG. Linearly polarized light 10 passing through polarizing plate 3
3 becomes elliptically polarized light 101 'by passing through the liquid crystal cell 5. The optical delay plates 10 and 11 are placed on the upper side of the liquid crystal cell, and the elliptically polarized light 101 ′ is changed into the linearly polarized light 102 ′. What is important at this time is to convert the elliptically polarized light 101 ′ that has passed through the liquid crystal cell 5 into linearly polarized light or polarized light 102 ′ that is close to linearly polarized light.

According to the study by the present inventors, a structure in which two optical delay plates are stacked is good. When only one optical retardation plate is used, the polarized light 102 'is not completely linearly polarized light but is somewhat elliptical, the black level is not completely black, is gray, and the contrast is slightly inferior.

When the number of layers is three or more, the polarization
Is close to linearly polarized light, the contrast is very high, and the visibility is good. However, the use of three or more optical delay plates makes the liquid crystal display element expensive.

In the case of a two-layered structure, the above-mentioned effects cannot be obtained only by arranging two optical delay plates arbitrarily, and the optical axes of the first and second optical delay plates are changed. When the acute angle is the torsion angle between the optical delay plates,
The twist direction from the optical axis of the second optical delay plate to the optical axis of the first optical delay plate is the same as the twist direction of the liquid crystal molecules from the first substrate to the second substrate. Was obtained, and a high-contrast black-and-white display was obtained. When the direction was reversed, coloring was recognized in the display color.

It is preferable that the twist angle be large so that the orientation angle of the liquid crystal molecules changes rapidly with the voltage.
Preferably between 0 ° and 270 °.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> Hereinafter, an embodiment of a liquid crystal display device according to the present invention will be described in detail with reference to FIG. 1 and FIG.

FIG. 3 is a sectional view of the liquid crystal display device of the present invention. Transparent electrodes 7, 7 'and an alignment film 8, made of polyimide,
The substrates 1 and 1 'on which 8' are formed are installed substantially parallel to each other. A liquid crystal composition 9 is sealed between the substrates 1 and 1 ', and the periphery thereof is sealed and fixed with a sealant 12 made of an epoxy adhesive. And a liquid crystal cell 5. This liquid crystal cell 5
, The liquid crystal molecules are twisted counterclockwise at a twist angle ψ = 240 ° according to the orientation direction r of the substrate 1 and the orientation direction r ′ of the substrate 1 ′, the tilt angle θ is 1.5 degrees, and the cell thickness (substrate thickness) The interval d is 6.6 μm.

The liquid crystal cell 5 contains ZLI371 as a liquid crystal composition.
1 S-811 as a counterclockwise chiral agent (manufactured by Merck)
(E. Merck) by d / pt (d: substrate spacing, pt:
(Pitch) was about 0.6. Since the birefringence Δn1 of the liquid crystal composition was 0.1045, the retardation R = Δndcos2θ was about 0.69 μm.

On the other hand, the first optical delay plate 10 made of stretched polyvinyl alcohol and having a thickness of about 0.5 μm is arranged so that the stretching direction is A1 = 48 degrees from the horizontal direction, and the second
Of the optical retardation plate 11 was arranged at A2 = 5 degrees from the horizontal direction. At this time, the retardation value R of the first optical delay plate 10 is 0.365 μm, the retardation R of the second optical delay plate 11 is 0.365 μm, and the angles of the polarizing plates are P1 = 68 degrees and P2 = −40. Degree. At this time, the direction of the acute angle twist formed by the optical axis from the second optical delay plate 11 to the first optical delay plate 10 was 43 degrees counterclockwise.

FIG. 4 shows the wavelength dependence of the transmittance when a voltage is applied to the liquid crystal cell 5 and the liquid crystal is turned on and off in this embodiment. As can be seen from the figure, the non-lighting and light-on transmittances were flat and achromatic, regardless of the waveform, and were black in non-lighting and white in light-on, a so-called normally black mode. . When the liquid crystal cell was multiplex-driven at a duty of 1/200, the contrast was as high as 14: 1, and the viewing angle was wide.

Example 2 In Example 1, first and second optical delay plates and first and second polarizing plates were arranged in a liquid crystal cell as described below.

The first optical delay plate 10 is arranged so that the stretching direction is A1 = 27 degrees from the horizontal direction, and the stretching direction of the second optical delay plate 11 is A2 = -22 degrees from the horizontal direction. Was placed. At this time, the retardation value R of the first optical delay plate 10 is 0.400 μm, the retardation value R of the second optical delay plate 11 is 0.400 μm, and the angles of the polarizing plates are P1 = 47 degrees and P2 = −. It was 64 degrees. At this time, the acute angle twist direction formed by the optical axis from the second optical delay plate 11 to the first optical delay plate 10 was 49 degrees counterclockwise.

The display is in the normally black mode, and when driven in the same manner as in the first embodiment, the contrast is about 1
A display having a high ratio of 2: 1 and a wide viewing angle was obtained.

Reference Example In the liquid crystal cell of Example 1, a first optical delay plate having a retardation value of 0.299 μm was set so that the stretching direction was A1 = 45 degrees from the horizontal direction, and the retardation value was placed thereon. A second optical delay plate of 0.394 μm was set at A2 = 5 ° from the horizontal direction, and the first and second polarizing plates were set at absorption axes P1 = 69 ° and P2 = -23 °. .

At this time, the direction of the acute angle formed by the optical axis from the second optical delay plate 11 to the first optical delay plate 10 was counterclockwise by 40 degrees.

At this time, the negative / positive is reversed from that of the embodiment-1, and the display is white when not lit and black when lit, which is a so-called normally white mode, and the contrast is about 11:
1. In addition, a display having a wide viewing angle was obtained.

<Comparative Example> In Example 1, the first optical delay plate 10 was disposed so that the stretching direction was A1 = 6 degrees from the horizontal direction, and the stretching direction of the second optical delay plate 11 was placed thereon. Were arranged at A2 = 48 degrees from the horizontal direction. At this time, the acute twist direction formed by the optical axes of the two optical delay plates was clockwise by 42 degrees.

As shown in FIG. 7, the wavelength dependence upon driving in the same manner as in Example 1 was confirmed to have a yellow background color.

[0045]

According to the present invention, it is possible to provide a liquid crystal display device having a bright background, an achromatic color, a high contrast, and a wide viewing angle at a low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the alignment direction, the direction of the absorption axis of a polarizing plate, and the direction of the optical axis of an optical delay plate in a liquid crystal display device according to one embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the liquid crystal display device of the present invention.

FIG. 3 is a sectional view of a liquid crystal display device according to one embodiment of the present invention.

FIG. 4 is a diagram showing the wavelength dependence of the transmittance of the liquid crystal display device of the present invention.

FIG. 5 is a diagram for explaining the operation of a conventional liquid crystal display element.

FIG. 6 is a view for explaining the operation of a conventional liquid crystal display element.

FIG. 7 is a diagram showing the wavelength dependence of the transmittance of a liquid crystal display element of a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1 '... Substrate 3 ... 1st polarizing plate 4 ... 2nd polarizing plate 5 ... Liquid crystal cell 10 ... 1st optical delay plate 11 ... 2nd optical delay plate

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Susumu Kondo 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Corporation Yokohama Office (72) Inventor Akio Murayama 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Corporation Inside the Yokohama Office (72) Inventor Shoichi Matsumoto 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Toshiba Corporation Inside the Yokohama Office (56) References JP-A-1-254917 (JP, A) JP-A-1-304422 ( JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G02F 1/1335 610

Claims (3)

(57) [Claims] 1. A first arranged opposite to each other, and a second substrate, the liquid crystal composition is held between the first substrate and the second substrate, and displays the birefringence effect based on twisted alignment In a liquid crystal display device having a liquid crystal cell and first and second polarizers disposed on both sides of the liquid crystal cell, the first polarizer and the second polarizer apply a voltage to a liquid crystal composition. The first substrate and the first polarizing plate are arranged so that the transmittance is maximized in a state where the voltage is applied.
First the first optical delay plate one lifting an optical axis, said first lifting Chi said first optical delay the second optical axis on the polarizing plate side to the substrate side of the
Has a retardation value equal to the retardation value of the board
A second optical delay plate is provided, and when an acute angle of an angle formed by the first and second optical axes is a twist angle between the optical delay plates, the angle from the second optical axis to the first optical axis is changed. A liquid crystal display element, wherein a twist direction is set in the same direction as the direction of the twist alignment from the first substrate to the second substrate so as to eliminate the undesired birefringence effect. 2. The distance between the first and second substrates is 3
2. The method according to claim 1, wherein the distance is set to about 12 .mu.m.
The liquid crystal display element as described in the above. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal composition is twist-aligned at an angle of 180 to 360 °.