JPH0219828A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain inexpensively a display element having noncolored and light background and wide view field angle by disposing a first and second optical delay plate between a second substrate and a second polarizing plate, and specifying a retardation of a liquid crystal cell and a retardation of each optical delay plate. CONSTITUTION:A first optical delay plate 10 and a second optical delay plate 11 are disposed successively from a second substrate 1' side to between the second substrate 1' and a second polarizing plate 4. In this stage, a retardation R0=DELTAn.d.cos<2>theta of a liquid crystal cell 5 is regulated to 0.4-1.3mum, a retardation of the first optical delay plate 10 is regulated to 0.25-0.35mum, and the retardation of the second optical delay plate 11 is regulated to 0.35-0.45mum, wherein d is a distance between the first substrate 1 and the second substrate 1', theta is a tilt angle of the liquid crystal compsn., and DELTAn is the birefringence factor of the liquid crystal compsn. Thus, a liquid crystal display element having noncolored and light background and wide view field angle is obtd. inexpensively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element in which the background color is achromatic.

(Prior art) Liquid crystal display elements are classified into TN type, DS type, and G type depending on the operation mode.
There are H type, DAP type, thermal writing type, etc., and among them, TN type liquid crystal display elements are often used as display elements for calculators, measuring instruments, etc.

By the way, in recent years, as the demand for increased display capacity and larger display area for word processors, personal computers, etc. has increased, TN type liquid crystal display elements have
Due to problems such as insufficient contrast and narrow viewing angle range, there has been an urgent need to develop liquid crystal display elements with new operating modes.

As a liquid crystal display element that meets such demands, for example, 5BE (
Birefringence control type liquid crystal display devices (super twisted pie frigidity effect) are attracting attention. The structure of this SBE type liquid crystal display element is such that two transparent substrates each having a transparent electrode formed on at least one side are placed facing each other, their peripheries are sealed to form a cell, and a nematic liquid crystal is placed in this cell. The distance between the opposing boards is 3 to 121
JJn, and cyclohexane-based, ester-based, biphenyl-based, and pyrimidine-based liquid crystals are used as nematic liquid crystals. A chiral agent is added to the nematic liquid crystal, and the molecular axis of the liquid crystal molecules is 180 to 360.
It is twisted between a pair of substrates at a degree angle. Further, the liquid crystal molecules have a tilt angle θ of more than 5° such that the molecular axes of the liquid crystal molecules are inclined with respect to the plane of the substrate due to the alignment film on the substrate. And the retardation R of the liquid crystal cell = △n-d-cos2
θ is 0.6 to 1.4 willow.

In addition, in an SBE type liquid crystal display element in which the molecular axis has a twist of 270°, polarizing plates are preferably arranged on the outer front and rear surfaces of the substrate, so that the transmission axis of the front polarizing plate is relative to the molecular orientation direction of the front substrate. The best configuration is when the transmission axis of the rear polarizing plate is approximately 30' counterclockwise or approximately 60' clockwise with respect to the alignment direction of the rear substrate.

Among these, the former configuration is displayed in bright yellow in the unselected state,
A black display is obtained in the selected state (yellow mode), and the latter configuration provides a deep blue display in the non-selected state, and becomes transparent in the selected state (blue mode).

In the SBE type liquid crystal display element having such a configuration, the transmitted light changes sharply with respect to the voltage, and even when multi-digit multiplex driving is performed, the display element has high contrast and a wide viewing angle.

On the other hand, as an example of a liquid crystal display element whose pretilt angle is reduced by rubbing technology, the twist angle of the liquid crystal is reduced by ioo to 20
So-called ST (super twist) type liquid crystal display elements with a
122).

As another example, JP-A-60-73525 discloses that for a cell with a retardation R of 0.5 to 0.8 IJIn and a twist angle of 270 degrees of liquid crystal molecules, the optical axes of the front and rear polarizing plates are approximately A liquid crystal display element is shown in which the direction is preferably 90° and the optical axis of the polarizing plate bisects the director.

Now, in all of these liquid crystal display elements, the background color is not achromatic but colored. For this reason, the display is black on a yellow background or white on a blue background, and the visibility evaluation varies depending on the visual sense of the observer, and for some people, visibility (contrast, etc.) may decrease depending on the background color. Some people say that it is. In addition, since both ST' type and USBE type liquid crystal display elements utilize birefringence,
Color unevenness is likely to occur due to differences in the spacing between transparent plates.
The color changes from the viewing angle direction and when the temperature changed were large.

In addition, in TN type liquid crystal display elements, it is easy to create colors by disposing color filters, whereas SBE
type liquid crystal display elements have a colored background, making it impossible to display them in color.

An OMI type liquid crystal display element is known as an example that improves this point (Appl, Phys, Lett, 50 (
5) 1987 p. 236). That is, the twist angle of the liquid crystal is 180', and the retardation R=△nd-cos
The value of 2θ is 0.5 to 0.64S@The transmission axis of one of the light plates is parallel to the rubbing axis, and the angle of the absorption axes of the two polarizing plates is 90'.

However, in this OMI type liquid crystal display element, since the twist angle of the liquid crystal is 180 degrees, the change in transmitted light with respect to voltage is not very steep, and when the drive duty ratio is reduced, contrast is insufficient.

There were problems such as a narrow viewing angle and a dark background.

To solve this problem of background darkness and lack of contrast, Japanese Unexamined Patent Publication Nos. 57-46227 and 1983-
No. 96315 and Japanese Unexamined Patent Publication No. 57-125919 propose a liquid crystal display element in which two liquid crystal cells are stacked and polarizing plates are placed on both sides to display a black and white display.
An example of applying this method to an LCD is JJAP (26, NOV,
11.117784 (1987)).

These characteristics are such that the twist directions of the two liquid crystal cells are opposite to each other, and the waviness of each liquid crystal cell is approximately equal.

That is, as shown in FIG. 6, the linearly polarized light 103 that has passed through the polarizing plate 3 becomes circularly polarized light 101' by passing through the first liquid crystal cell 5. The polarized light inside the foil becomes linearly polarized light 102' by passing through the second liquid crystal cell 6, which has an opposite twist angle and approximately the same twist angle as the first liquid crystal cell 5, and also has approximately the same wating angle, and becomes linearly polarized light 102'. pass through,
perceptible to the human eye.

What is important here is that the first liquid crystal opening 5 and the second liquid crystal cell 6 have optically complementary properties.

Thereby, the wavelength dependence of the shape inside the foil after passing through the first liquid crystal cell 5 becomes complementary to the wavelength dependence of the shape inside the foil due to the second liquid crystal cell 6. As a result, 1. The transmitted light of the second liquid crystal cell 5.6 has no wavelength dependence, and an achromatic color display with no coloration can be achieved by 1%. This also shows that all the light in the visible region can be used for display, resulting in a bright display.

At this time, it is necessary for the first liquid crystal cell 5 and the second liquid crystal cell 6 to be optically complementary, so that the water duration of each liquid crystal cell is approximately the same within ±0.05 dust, for example. It is necessary that

Note that electrodes are formed on the substrates 1, 1- of the first liquid crystal cell 5 and driven in the same way as a normal dot matrix type liquid crystal display element, and the substrates 2, 2- of the liquid crystal cell 6 of the second option are It is used simply for correcting the shape inside the foil without forming electrodes or driving the liquid crystal.

In this way, the two-layer cell type ST type liquid crystal display element has the advantage of being able to display black and white and increase the number of digits, but the viewing angle is narrower than that of the SBE type and OMI type, and the two Using two liquid crystal cells becomes very expensive if the yield of the liquid crystal cells is taken into account.

(Problems to be Solved by the Invention) As mentioned above, so-called ST type liquid crystal display elements and SBE type liquid crystal display elements with a twist angle of 180° or more have a colored background, and an achromatic OMI with no colored background. In the case of a type liquid crystal display element, it was not possible to obtain a liquid crystal display element with high contrast and a bright background.

In addition, a liquid crystal display element using two ST type liquid crystal cells has a black and white display with no colored background and has high contrast, but is expensive.

The present invention is intended to solve the above-mentioned conventional problems, and an object of the present invention is to provide a liquid crystal display element having an achromatic and bright background, high contrast, and a wide viewing angle at a low cost.

[Structure of the Invention] (Means for Solving the Problems) The liquid crystal display element of the present invention includes first and second substrates, each having electrodes formed on their opposing surfaces and placed opposite each other, and a first substrate and a second substrate. A liquid crystal cell made of a liquid crystal composition twisted and oriented between a second substrate and a first and second liquid crystal cell arranged on both sides of the liquid crystal cell.
In a liquid crystal display device having a polarizing plate, first and second optical retardation plates are disposed from the first substrate side between the first substrate and the first polarizing plate, and the first substrate and the If the distance between the second substrates is d, the tilt angle of the liquid crystal composition is θ, and the birefringence of the liquid crystal composition is Δn, then the water duration of the liquid crystal cell is the value of R0 (=Δn-d-cos2θ), which is O84. The first optical retardation plate has a retardation of 0.25 to 0.35 μm, and the second optical retardation plate has a retardation of 0.35 to 0.45 μm. This is a liquid crystal display element.

(for production) The operation of the liquid crystal display element of the present invention will be explained.

FIG. 5 shows a display using the conventional birefringence effect.
FIG. 2 is a diagram illustrating the display principle of, for example, an SBE type liquid crystal display element or an ST type liquid crystal display element. Polarizing plates 3.4 are disposed before and after the liquid crystal cell 5 (consisting of substrates 1, 1' and a liquid crystal composition sandwiched therebetween). The linearly polarized light 103 that has passed through the polarizing plate 3 generally becomes circularly polarized light 1Ol- by passing through the liquid crystal cell 5. The elliptically polarized light that has passed through the liquid crystal cell 5 passes through the polarizing plate 4 placed at a predetermined angle and is sensed by the human eye. The shape of the ellipse at this time is the liquid crystal cell 5
It is determined by the twist angle ψ which is the twist angle of the liquid crystal molecules at , the retardation R=Δnψd−cos2θ, and the wavelength. 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.

Generally, 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, which changes the retardation R and changes the transmittance, which is used to perform display.

The basic structure of the above-mentioned two-layer system is to use two such liquid crystal cells each having optically complementary properties.

Now, the present invention has a configuration in which two optical delay plates are arranged on one side of one liquid crystal cell, and its operation will be explained using FIG. 2. The linearly polarized light 103 that has passed through the polarizing plate 3 becomes elliptically polarized light 101' by passing through the liquid crystal cell 5. An optical retardation plate 10.11 is placed above the liquid crystal cell, and the elliptically polarized light 101- is converted into linearly polarized light 102', which is sensed by the human eye via the polarizing plate 4.

What is important at this time is that the elliptically polarized light 1 that has passed through the liquid crystal cell 5
01- into linearly polarized light, or into polarized light 102' which is close to linearly polarized light.

According to studies conducted by the present inventors, a structure in which two optical delay plates were laminated was favorable. Note that when only one optical delay plate is used, the polarized light 102' is not completely linearly polarized but somewhat elliptical, the black level is not completely black but gray, and the contrast is somewhat inferior.

In addition, when the number of laminated layers is three or more, the polarized light 102- becomes close to linearly polarized light, and the contrast 1-last is very high and the visibility is good. However, using three or more optical delay plates make it expensive.

Further, it is preferable that the optical axes of the two optical delay plates form an angle in the range of 35 degrees to 60 degrees. , Also, so that the orientation angle of liquid crystal molecules changes rapidly with respect to voltage,
The larger the twist angle, the better it is between 180″ and 270°, and the cell retardation is 0 for black and white display.
．． The thickness is preferably between 4 and 1.3 μm.

(Example) Hereinafter, an example of the liquid crystal display element according to the present invention will be described in detail using FIGS. 1 and 4.

FIG. 3 shows a cross-sectional view of the liquid crystal display element of the present invention.

Transparent electrodes 7, 7- and alignment film 8°8- made of polyimide
A liquid crystal composition 9 is sealed between the substrates 1 and 1- formed thereon, and the liquid crystal composition 9 is sealed and fixed around the substrate with a sealant 12 made of epoxy adhesive. , a liquid crystal cell 5. In this liquid crystal cell 5, the liquid crystal molecules are twisted counterclockwise by an angle of 11/, =
240", the tilt angle is 1.5 degrees, and the cell thickness and substrate spacing (d) is 6.61JII4.

In the liquid crystal cell 5, as a liquid crystal composition, ZLI3711 (manufactured by Merck & Co., Ltd.) and S-811 (E
, manufactured by Merck & Co.) to d/pt (d: substrate spacing, pt:
Pitch) was added to approximately 0.6.

Since the birefringence Δn of this liquid crystal composition was 0.1045, the retardation R=Δn−d−cos2θ was about 0.77 m.

On the other hand, it is made of stretched polyvinyl alcohol with a thickness of about 0.5
The stretching direction of the first optical delay plate 10 of the leg is 4 from the horizontal direction.
5 degrees, and the second optical delay plate 1 is placed above it.
The stretching direction of 1 is arranged at 6.5 degrees from the horizontal direction. Further, at this time, the retardation value R of the first optical retardation plate 10 is 0.299 μs, the retardation value R of the second optical retardation plate 11 is 0.394 μs, and the angle of polarization is Pt− from the horizontal direction. 69 degrees, P2 = -17 degrees (first
(see diagram).

In this example, 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 is expressed as
As shown in the figure. As can be seen from the figure, the transmittance when the light is off and when the light is on is flat and achromatic regardless of the waveform, and the display is black when the light is off and white when the light is on, which is rare in the so-called normally black mode. . Ta. In addition, this liquid crystal cell is
The contrast when driving multipretas at /200 duty was as high as 11:1, and the viewing angle was wide.

(Comparative Example) In the example, the second optical delay plate 11 was removed. FIG. 6 shows the wavelength dependence of the liquid crystal element during lighting and astigmatism. It is clear from the figure that the yellow color appears in the case of astigmatism.
Also, when lit, it was white or pale yellow.

[Effects of the Invention] According to the present invention, a liquid crystal display element with a bright, achromatic background, high contrast, and a wide viewing angle can be obtained at low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the alignment direction, the absorption axis direction of the polarizing plate, and the optical axis direction of the optical retardation plate in a liquid crystal display element according to an embodiment of the present invention, and FIG. FIG. 3 is a cross-sectional view of a liquid crystal display element according to an embodiment of the present invention, FIG. 4 is a diagram showing the wavelength dependence of transmittance of the liquid crystal display element of the present invention, and FIGS. FIG. 6 is a diagram illustrating the operation of a conventional liquid crystal display element, and FIG. 7 is a diagram showing the wavelength dependence of the transmittance of a comparative liquid crystal display element. Chika tea now spear■ Chicha 1 side

Claims (2)

[Claims] (1) A liquid crystal cell consisting of first and second substrates, each having electrodes formed on opposing surfaces and placed opposite each other, and a liquid crystal composition twisted and oriented between the first substrate and the second substrate. and,
In the liquid crystal display device having first and second polarizing plates arranged on both sides of the liquid crystal cell, between the first substrate and the first polarizing plate, the first and second polarizing plates are arranged from the first substrate side. an optical delay plate arranged, where d is the distance between the first substrate and the second substrate, θ is the tilt angle of the liquid crystal composition, and Δn is the birefringence of the liquid crystal composition, The retardation of the liquid crystal cell is R_0 (=Δ
n・d・cos^2θ) is in the range of 0.4 to 1.3 μm, the retardation of the first optical retardation plate is in the range of 0.25 to 0.35 μm, and the retardation of the second optical retardation plate is in the range of 0.25 to 0.35 μm. A liquid crystal display element characterized by having a retardation of 0.35 to 0.45 μm. (2) The liquid crystal display element according to claim 1, wherein the optical axes of the first and second optical delay plates form an angle in the range of 35 degrees to 60 degrees.