JPH0219835A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain inexpensively a liquid crystal display element having a noncolored light background and a wide view field angle by disposing a first and a second optical delay plate between a first substrate and a second polarizing plate and regulating both optical delay plates thereof to have an almost same retardation. CONSTITUTION:A first and a second substrates 1, 1' facing oppositely to each other and a first and a second polarizing plates 3, 4 disposed to both sides of a liquid crystal cell 5 are provided, and a first and a second optical delay plate 10, 11 counted from the second substrate 1' side are arranged between the second substrate 1, and the second polarizing plate 4. The first and the second optical delay plate 10, 11 are regulated to have an almost same retardation, which is within a range between 0.25 to 0.45mum. If the retardation of the optical delay plates 10, 11 are smaller than 0.25mum or larger than 0.45mum, an almost linearly polarized light is not obtd., and colored display is obtd. Thus, a liquid crystal display element having a noncolored light background and a wide view field angle is obtd. inexpensively.

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 to a liquid crystal display element whose 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, and the periphery is sealed to form a cell, and a nematic liquid crystal is placed in this cell. The distance between the opposing boards is 3 to 12N
1, 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 axes of the liquid crystal molecules are twisted at an angle of 180 to 3600 between a pair of substrates. In addition, liquid crystal molecules are
Due to the alignment film on the substrate, its molecular axis is oriented at 5° relative to the plane of the substrate.
It has a tilt angle θ of a slope greater than °. and,
The retardation R=Δnd-cos2θ of the liquid crystal cell is 0.6 to 1.4tJJr1.

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 degrees counterclockwise or approximately 60 inches clockwise with respect to the alignment 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), while the latter provides a deep blue display in the non-selected state and a transparent display in the selected state. Becomes (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 to 100-20.
So-called ST (super twist) type liquid crystal display elements with a
p122>.

As another example, Japanese Patent Application Laid-Open No. 60-73525 discloses that for a cell in which the retardation R is 0.5 to 0.8 legs and the twist angle of the liquid crystal molecules is 270°, the optical axes of the front and rear polarizing plates are approximately 90", and the optical axis of the polarizing plate is 2
A liquid crystal display element is shown in which the direction of separation is considered to be good.

Now, in such 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 SBE type liquid crystal display elements utilize birefringence, color unevenness is likely to occur due to differences in the spacing between transparent substrates, and color changes and temperature changes from the viewing angle direction. There was a big color change when I did it.

In addition, in TN type liquid crystal display elements, it is easy to create colors by disposing color filters, whereas SBE
With type liquid crystal display elements, colorization was impossible because the background color was colored.

An OMI type liquid crystal display element is known as an example that improves this point (ADDl, Phys, Lett, 50 (
5) 19879.236). That is, the twist angle of the liquid crystal is 180'', the retardation R=△n-d-cos2
The value of θ ranges from 0.5 to 0.6, the transmission axis of one of the polarizing 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, the twist angle of the liquid crystal is 180 degrees, so 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 (2B, NOV,
11.117784 (1987)).

These features are such that the twist directions of the two liquid crystal cells are opposite to each other, and the retardation 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 elliptically polarized light 101' by passing through the first liquid crystal cell 5. This circularly polarized light becomes linearly polarized light 102' by passing through the second liquid crystal cell 6, which has an opposite twist angle and is almost equal to that of the first liquid crystal cell 5, and also has a retardation that is almost equal to that of the first liquid crystal cell 5, and becomes linearly polarized light 102'. pass through,
perceptible to the human eye.

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

Thereby, the wavelength dependence of the elliptical shape after passing through the first liquid crystal cell 5 becomes complementary to the wavelength dependence of the elliptical shape 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 display without coloration can be obtained. 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 the retardation of each liquid crystal cell must be approximately the same, for example within ±0.05. It is necessary to go there.

Note that electrodes are formed on the substrates 1, 1- of the first liquid crystal cell 5, and driven in the same manner as a normal dot matrix type liquid crystal display element, and electrodes are formed on the substrates 2, 2' of the liquid crystal cell 6 of the power cylinder 2. is used simply for correcting the elliptical shape 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 arranged from the first substrate side between the first substrate and the first polarizing plate, and the first and second optical retardation plates are arranged from the first substrate side. The optical retardation plate is a liquid crystal display element characterized in that it has substantially the same retardation, and the retardation is in the range of 0.25 to 0.45 μm.

(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 and 4 are disposed in front of a liquid crystal cell 5 consisting of a substrate 1.1' and a liquid crystal composition sandwiched therebetween. The linearly polarized light 103 that has passed through the polarizing plate 3 generally becomes elliptically polarized light 101' by passing through the liquid crystal cell 5. The elliptically polarized light that passed through the liquid crystal cell 5 is
The light passes through a polarizing plate 4 placed at a predetermined angle and is detected by the human eye. The shape of the ellipse at this time is determined by the twist angle, which is the twist angle of the liquid crystal molecules in the liquid crystal cell 5, the retardation R=Δnd-cos2θ, and the wavelength. Here, 8n is the birefringence of the liquid crystal composition in the liquid crystal cell 5, d is the cell thickness (the thickness of the cell and the distance between the substrates), 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 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 is very high and visibility is good. However, using three or more optical delay plates makes the liquid crystal display element expensive. do.

In addition, a sword with a laminated structure of two sheets is particularly suitable for two layers as in the present invention.
It is preferable for mass production that the retardations of the two optical retardation plates be the same, and in this case, the retardation of the first and second optical retardation plates is in the range of 0.25 to 0.45. effect was obtained, and a high contrast black and white display was obtained.

The retardation of the optical delay plate is 0.25tI! If it is smaller than II or larger than 0.45 mu, it will not be possible to polarize the polarized light 102', which is close to linearly polarized light, by 1q, and the displayed color will be colored.

Note that it is better to have a larger twist angle, so that the orientation angle of liquid crystal molecules changes rapidly with respect to voltage.
A value between 70° is good.

Further, one optical delay plate can also serve as one substrate.

(Example) <Example 1> Hereinafter, an example of a 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 1.1' and 1.1' formed thereon, and a liquid crystal composition 9 is sealed and fixed around the substrate 1.1' 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 the orientation direction r of the substrate 1 and the orientation direction r' of the substrate 1' at a twist angle 'l/=24
The tilt angle θ is 1.5 degrees, and the cell thickness (substrate spacing) d is 6.6 degrees.

In the liquid crystal cell 5, as a liquid crystal composition, ZLI3711 (manufactured by Merck & Co., Ltd.) and 5-81'L as a counterclockwise chiral agent were added.
(E, manufactured by Merck & Co.) was added so that d/pt (pt: pitch) was about 0.6. Since the birefringence Δn G(to, 1045) of this liquid crystal composition, the retardation R=Δn−d−cos2θ was approximately 0.
69JJ! It was.

On the other hand, it is made of stretched polyvinyl alcohol with a thickness of about 0.5
IJ! The first optical retardation plate 10 of n is arranged so that the stretching direction is A+ = 48 degrees from the horizontal direction, and the second
The stretching direction of the optical delay plate 11 is arranged at an angle of A2-5 degrees from the horizontal direction. Further, at this time, the retardation value R of the first optical retardation plate 10 is 0.365 Yanagi, and the retardation value R of the second optical retardation plate 11 is 0.365 Yanagi.
The retardation value R of the
See figure.

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 measured in the fourth example.
As shown in the figure. As can be seen from the figure, the transmittance when not lit and when lit is flat and achromatic regardless of the waveform, and the display is black when not lit and white when lit, which is the so-called normally black mode. Ta. Ta. In addition, this liquid crystal cell is
The contrast was high at 14:1 when driving the multipretas at /200 duty, and the viewing angle was wide.

<Example 2> In Example 1, the first and second optical delay plates, the first,
The second polarizing plate was arranged as follows.

The stretching direction of the first optical retardation plate 10 is A1=
The second optical retardation plate 11 was placed thereon so that the extending direction of the second optical retardation plate 11 was A2=-22 degrees from the horizontal direction. Further, the retardation value R of the first optical retardation plate 10 at this time is 0.400/m, the retardation value R of the second optical retardation plate 11 is 0.400m, and the angle of the polarizing plate is p,=47 degrees, P2=-64 degrees.

The display is in normally black mode, and when driven in the same manner as in Example 1, the contrast is high at approximately 12:1.
In addition, a display with a wide viewing angle was obtained.

[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. Agent Patent Attorney Nori Chika Ken Yudo Takehana Kikuoγ r Koiteruko J Akira■

Claims (1)

[Claims] First electrodes are formed on opposing surfaces, and the first electrodes are arranged opposite to each other.
, a second substrate, a liquid crystal cell made of a liquid crystal composition twisted and oriented between the first substrate and the second substrate, and first and second polarized light disposed on both sides of the liquid crystal cell. In the liquid crystal display device having a plate, first and second optical retardation plates are arranged between the first substrate and the first polarizing plate from the first substrate side, and the first and second optical retardation plates are disposed from the first substrate side. A liquid crystal display device, wherein the optical retardation plates have substantially the same retardation, and the retardation is in the range of 0.25 to 0.45 μm.