JPH0237318A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To inexpensively obtain the liquid crystal display element which has the colorless and bright background and has high contrast and wide field angle by constituting the element in such a manner that the optical axis direction of the optical delay plate adjacent to the liquid crystal cell has 55-80 deg. angle with the major axis direction of the liquid crystal molecules in contact with a substrate adjacent to said optical delay plate. CONSTITUTION:This display element has the liquid crystal cell 5 consisting of 1st and 2nd substrates 1, 1' on the opposite surfaces of which electrodes are formed respectively and which are installed to face each other and a liquid crystal compsn. 9 twisted and oriented between the 1st substrate 1' and the 2nd substrate 1 and 1st and 2nd polarizing plates 4, 3 disposed on both sides of the cell 5. At least one sheet of the optical delay plate 10 is disposed between the 1st substrate 1' and the 1st polarizing plate 4. The element is so constituted that the optical axis direction of the plate 10 adjacent to the substrate 1' has the angle ranging 55-80 deg. with the major axis direction of the liquid crystal molecules in contact with the substrate 1'. The liquid crystal display element which has the colorless and bright background and has the high contrast and the wide field angle is inexpensively obtd. in this way.

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 pyrefrigence 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 opposing substrates is 3 to 12μ
m, 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 between a pair of substrates at an angle of 180 to 360°. 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 water duration R=Δn-d-cos''θ of the liquid crystal cell is 0.6 to 1.4 μm.

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 configuration of the composer has a bright yellow display in the unselected state and a black display in the selected state (yellow mode), and the latter configuration has a deep blue display in the unselected state and a transparent display 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 100 to 20.
So-called ST (super twist) type liquid crystal display elements with an angle of 0° are known (SID-86DIGE,
p122).

As another example, JP-A No. 60-73525@publication discloses that the optical axis of the polarizing plate in front of a cell in which the water dageion R is 0.5 to 0.8 μ... and the twist angle of the liquid crystal molecules is 270°. is approximately 90', and the optical axis of the polarizing plate is approximately 90' from the director.
A liquid crystal display element is shown in which the direction of separation is considered to be good.

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 depending on the person, 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 may occur due to differences in the spacing between transparent substrates.
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 (Apl, Phys, Lett, 50(5)).
) 1987 p. 236). In other words, the twist angle of the liquid crystal is 180°, and the rotation R = Δn-d-cos2θ
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, 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 decreased, the contrast l- is insufficient.

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

As a solution to the darkness of the background and the lack of contrast, Japanese Patent Laid-Open No. 57-46227 and Japanese Patent Laid-Open No. 57-57
In JP-A-96315 and JP-A-57-125919, a liquid crystal display element was proposed in which two liquid crystal cells were stacked and polarizing plates were placed on both sides to display a black and white display.
An example of application of the E method LCD is JJAP (26, NOV
, 11.117784 (1987)).

These characteristics are such that the twist directions of the liquid crystal molecules in the two liquid crystal cells are opposite to each other and the twist angle is the same, and the waviness of each liquid crystal cell is approximately equal, and the adjacent liquid crystals in the two liquid crystal cells The molecules are combined so that their optical axes are perpendicular.

Also, as shown in FIG. 10, 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 elliptically polarized light becomes linearly polarized light 102- by passing through the second liquid crystal cell 6, which has an opposite twist angle and substantially the same twist angle as the first liquid crystal cell 5, and also has substantially the same retardation. pass through and be detected by 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 cells 5 and 6 has no wavelength dependence, and an achromatic color display 19 without color change is achieved. 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 that the first liquid crystal cell 5 and the second liquid crystal cell 6 be optically complementary, so the retardation of each liquid crystal cell must be approximately the same, for example within ±0.05 μm. is necessary.

Note that electrodes are formed on the substrates 1 and 1' of the first liquid crystal cell 5 and driven in the same way as a normal dot matrix type liquid crystal display element, while on the other hand, the substrates 2 and 2- of the second liquid crystal cell 6 are formed with electrodes. It 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 0tVII 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 a high contrast ratio of 1 to last and a bright background.

In addition, a liquid crystal display element using two ST type liquid crystal cells provides a black and white display with no colored background and 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 an inexpensive liquid crystal display element with an achromatic and bright background, high contrast i~, and a wide viewing angle.

[Structure of the Invention] (Means for Solving the Problems) The liquid crystal display element of the present invention includes first and second single plates facing each other and having electrodes formed on their opposing surfaces, and a first substrate. In a liquid crystal display device having 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 polarizing plates arranged on both sides of the liquid crystal cell, the first substrate and At least one optical retardation plate is disposed between the first polarizing plate and the optical retardation plate adjacent to the first substrate. The liquid crystal display element is characterized by forming an angle in the range of 55 degrees to 80 degrees.

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

FIG. 9 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 before and after 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 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 determined by the twist angle ψ which is the twist angle of the liquid crystal molecules in the liquid crystal cell 5, the retardation R=Δnd-cos2θ, and the wavelength formula. Here, Δn is the birefringence of the liquid crystal composition in the liquid crystal cell 5, d is the cell thickness (cell thickness and 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 changes dynamically, 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 shown in FIG. 10 is to use two such liquid crystal cells each having optically complementary properties.

Now, in the liquid crystal display element of the present invention, at least one optical retardation plate is arranged on at least one side of the liquid crystal cell, and the optical axis direction of the optical retardation plate adjacent to the liquid crystal cell is the same as that of the optical retardation plate. It forms an angle in the range of 55 degrees to 80 degrees with the long axis direction of the liquid crystal molecules in contact with the adjacent substrate.

FIG. 6 is a diagram showing two optical delay plates arranged on one side of a liquid crystal cell. Linearly polarized light 1 passed through polarizing plate 3
03 becomes elliptically polarized light 101 by passing through the liquid crystal cell 5
− becomes. An optical delay plate 10 is placed above the liquid crystal cell 5,
The elliptically polarized light 101' is converted into elliptically polarized light 102-, which is close to linearly polarized light, and is sensed by the human eye via the second 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.

Further, the structure is not limited to the one shown in FIG. 3, but it is also possible to arrange optical retardation plates above and below the liquid crystal cell 5, respectively, or to use two or more optical delay plates stacked one on top of the other. In this case, it is preferable for mass production to use optical delay plates with the same characteristics. Note that when only one optical delay plate is used, the black level is not completely black, but is gray, and the contrast is somewhat inferior.

In addition, it is better for the twist angle of the liquid crystal composition to be large so that the orientation angle of the liquid crystal molecules changes rapidly with respect to the voltage.
Preferably, the angle is between 80° and 270°.

The optical retardation plate made of a stretched organic film can also serve as a substrate for a liquid crystal cell.

According to the studies of the present inventors, the above effect is achieved when the optical axis direction of the optical retardation plate and the long axis direction of the liquid crystal molecules are in the range of 55 degrees to 80 degrees, as shown in the following examples. If the angle is .

(Example) Examples of the liquid crystal display element according to the present invention will be described in detail below with reference to FIGS. 1 to 6.

<Example 1> FIG. 2 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 with a sealant 15 made of epoxy adhesive. , a liquid crystal cell 5. In this liquid crystal cell 5, the liquid crystal molecules are twisted counterclockwise at a twist angle of 14/=240° according to the orientation direction r of the substrate 1 and the orientation direction r' of the substrate 1', and the tilt angle θ is 1.5 degrees. , and the cell thickness (cell thickness and substrate spacing) d is 6.6 μIII (see FIG. 1). At this time, the long axis of the liquid crystal molecules at the interface between substrates 1 and 1' is r.

r', and at the interface with the closing plate 1-, the liquid crystal molecules have an optical axis at an angle of 130 degrees.

The liquid crystal cell 5 contains ZLI3711 (E
, manufactured by Merck & Co.) as a counterclockwise chiral agent.
(E, manufactured by Merck & Co.) was added so that d/pt (p: pitch) was about 0.6. Since the birefringence Δn of this liquid crystal composition was 01045, the retardation R-Δn-d·CO52θ was about 0.7 μm.

On the other hand, it is made of stretched polyvinyl alcohol with a thickness of about 0.5
The first optical retardation plate 10 with a diameter of μm is arranged so that its stretching direction (optical axis) is AI = 48 degrees from the horizontal direction, and above it, the stretching direction of the second optical retardation plate 11 is △2 degrees from the horizontal direction.
= placed at 5 degrees. At this time, the wading value R of the first optical retardation plate 10 was 0.365 μm, and the wading value R of the second optical retardation plate 11 was 0.365 μm. A first optical retardation plate is placed outside the liquid crystal cell and the second optical delay plate 11.
, and a second polarizing plate 3°4 were installed at polarizing plate angles of pi = -3.5° and P2 = 68° from the horizontal direction, respectively, as shown in FIG.

That is, the angle between the optical axis of the liquid crystal molecules and the optical retardation plate is 78 degrees.

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 using a third method.
As shown in the figure. As can be seen from the figure, both the astigmatism and the transmittance when the light is on are flat and achromatic regardless of the waveform, and the display is white when the light is off and black when the light is on, which is the so-called normally black mode. Ta. Also, this liquid crystal cell is 1/2
When multiplexed at 00 duty, the contrast was high at approximately 11:1, and the viewing angle was wide.

<Example 2> In Example 1, the first optical retardation plate 10 having a cotton dage R of 0.300 μm was arranged at A1=43°, and the second optical retardation plate 11 had a cotton dage Rt of 0.300 μm.
fiO14001tm was placed at A2-8°. Also, the angle of the absorption axes of the polarizing plates 3 and 4 is pl = 72°,
P2 = -19°. That is, the angle between the optical axis of the liquid crystal molecules and the optical retardation plate is 73 degrees.

This liquid crystal display element was in a so-called normally black mode, and when driven in the same manner as in Example 1, a display with a high contrast of approximately 8:1 and a wide viewing angle was obtained.

<Example 3> ZLi23 was added as a liquid crystal composition to the liquid crystal cell 5 of Example 1.
10 (E, manufactured by Merck & Co., Ltd.) was used. The birefringence Δn of this liquid crystal composition is 0.11. The water duration of the liquid crystal cell was approximately 0.73 μm. An optical retardation plate was laminated on this liquid crystal cell in the same manner as in Example 1.

The first optical delay plate 10 has a cotton dageion R of 0.2
A plate having a diameter R of 99 μm was placed at A1=45°, and a second optical retardation plate 11 having a water duration R of 0.394 μm was placed at A2=65°. Further, the angles of the absorption axes of the polarizing plate 3°4 were set to P1 = 69° and P2 = -17°.

That is, the angle between the optical axis of the liquid crystal molecules and the optical retardation plate is 75 degrees.

This liquid crystal display element is a so-called normally black seven-color display, and when driven in the same manner as in Example 1, the display had a high contrast of about 11:1 and a wide viewing angle.

<Example 4> ZL115 was added as a liquid crystal composition to the liquid crystal cell 5 of Example 1.
77 (E, manufactured by Merck & Co.) was used. The birefringence Δn of this liquid crystal composition is 0.115. The water duration of the liquid crystal cell was determined to be R=Δnd-cos2θ of approximately 0.76 μm. In the same manner as in Example 1, an optical retardation plate was laminated and arranged on this liquid crystal cell.

As the first optical delay plate 10, Watadasion R or 0.3
A 65 μm plate was placed at A1=90°, and a second optical retardation plate 11 with a water duration R of 0.630 μm was placed at A2=135°. Further, the angles of the absorption axes of the polarizing plate 3.4 were set to p1 = 85° and P2 = O'. That is, the angle between the optical axis of the liquid crystal molecules and the optical retardation plate is 60 degrees.

This liquid crystal display element is a so-called normally black liquid crystal display element, and when driven in the same manner as in Example 1, a display with a high contrast of about 9:1 and a wide viewing angle was obtained.

<Example 5> ZLI23 was added as a liquid crystal composition to the liquid crystal cell 5 of Example 1.
10 (E, manufactured by Merck & Co., Ltd.) was used. The birefringence Δn of this liquid crystal composition is 0.11. The water duration of the liquid crystal cell was approximately 0.73 μm (R=Δnd-cos2θ). In the same manner as in Example 1, an optical retardation plate was laminated and arranged on this liquid crystal cell.

The first optical delay plate 10 has a cotton dageion R of 0.4.
00 μm is placed at AI = 27°, and the water duration R is 0.400 μm as the second optical retardation plate 11.
was placed at A2 = -22°. In addition, polarizing plate 3.
The angle of the absorption axis of No. 4 was set to pl = 47° and P2 = -64. That is, the angle between the optical axis of the liquid crystal molecules and the optical delay plate is 57
degree.

This liquid crystal display element was in a so-called normally black mode, and when driven in the same manner as in Example 1, a display with a high contrast of about 10:1 and a wide viewing angle was obtained.

<Example 6> ZLI39 was added as a liquid crystal composition to the liquid crystal cell 5 of Example 1.
70 (E, manufactured by Merck & Co., Ltd.) was used. The birefringence n of this liquid crystal composition is 0.096. The R-Δn-d-cos2θ of the liquid crystal cell was about 0.63 μm. In this liquid crystal cell, as shown in FIG.
One sheet was placed at each °. Further, the angles of the absorption axes of the eccentric plates 3 and 4 were set to pl = 14° and P2 = 23°. That is, the angle between the optical axis of the liquid crystal molecules and the optical delay plate is 65 degrees.

This liquid crystal display element was in a so-called normally black mode, and when driven in the same manner as in Example 1, a display with a high contrast of approximately 7:1 and a wide viewing angle was obtained.

<Example 7> In Example 6, the optical retardation plate and polarizing plate were
=84°, Pi =93°, and P2 =115°.

That is, the angle between the optical axis of the liquid crystal molecules and the optical retardation plate is 66 degrees.

This liquid crystal display element was in a so-called normally black mode, and when driven in the same manner as in Example 1, a display with a high contrast of approximately 8:1 and a wide viewing angle was obtained.

<Example 8> Zshi136 was added as a liquid crystal composition to the liquid crystal cell 5 of Example 1.
95-000 (E, manufactured by Merck & Co.) was used. The birefringence Δn of this liquid crystal composition is 0.120.

As shown in FIG. 5, this liquid crystal cell has a first optical retardation plate 10 on the lower side of the liquid crystal cell 5 with a retardation R of 0.
A 400μm one is placed at A1=85°, and the liquid crystal cell 5
A retardation R is provided as a second optical delay plate 11 on the upper side of the
The one with 0.400 μIII was placed at A2=70'. Also, the angle of the absorption axes of polarizing plates 3 and 4 is PI = 80'
, P2 = 12°. That is, the angle between the optical axis of each optical retardation plate and the long axis direction of the liquid crystal molecules adjacent to each optical retardation plate is 80.85°. This indicates that the optical axis of the second optical retardation plate needs to be installed substantially perpendicular to the liquid crystal molecules, but the optical axis of the first optical retardation plate may be deviated from the perpendicularity.

In a case where optical retardation plates are arranged on both sides of a liquid crystal cell as in this example, the angle between the optical axis of the optical retardation plate on either side and the optical axis of the liquid crystal molecules is in the range of 55 degrees to 80 degrees. It's good to have.

This liquid crystal display element was in a so-called normally black mode, and when driven in the same manner as in Example 1, a display with a high contrast of about 20:1 and a wide viewing angle was obtained.

<Example 9> In Example 8, ZLI37'+ was used as the liquid crystal composition.
1 (E, manufactured by Merck & Co., Ltd.) was used. The birefringence of this liquid crystal composition is 0.1045. The first one is on the bottom of the liquid crystal cell.
The retardation R of the optical delay plate 10 is 0.365.
A μm one is placed at AI=90', and the second optical delay plate 11 is placed above the liquid crystal cell with a retardation R of 0.
The 300 μm one was placed at A2 = 60'. Also, the angles of the absorption axes of polarizing plates 3 and 4 are P1 = 48°, P2 =
It was set to 19°. The angle between the optical axis of each optical retardation plate and the long axis direction of the liquid crystal molecules adjacent to each optical retardation plate is 60" and 90°.

This liquid crystal display element was in a so-called normally black mode, and when driven in the same manner as in Example 1, a display with a high contrast of about 10:1 and a wide viewing angle was obtained.

(Comparative Example 1) In Example 6, the optical axes of the liquid crystal molecules and the optical retardation plate were set to 0.
It was set up so that it would be the same. That is, the optical axis of the optical delay plate was set at 130 degrees from the horizontal direction. FIG. 7 shows the wavelength dependence of the liquid crystal display element in this comparative example when it is lit and when it is not lit. As is clear from the figure, 1. It is white when lit, but has a yellow color when not lit.

(Comparative Example 2) In Example 1, the optical axis of the first optical retardation plate 10 was set at 90 degrees with the optical axis of the liquid crystal molecules at the substrate 1-interface, that is, A1
= 60 degrees. FIG. 8 shows the wavelength dependence of the liquid crystal display element in this comparative example when it is lit and when it is not lit. As is clear from the figure, 1. It is white or pale yellow when lit, and blue when not lit.

[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 orientation direction of a liquid crystal display element, the absorption axis direction of a polarizing plate, and the optical axis direction of an optical retardation plate according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of the present invention. FIG. 3 is a diagram showing the wavelength dependence of the transmittance of the liquid crystal display element of the present invention, and FIGS. 4 and 5 are diagrams each showing the configuration of other embodiments of the present invention. , FIG. 6 is a diagram explaining the present invention in detail, FIGS. 7 and 8 are diagrams showing the wavelength dependence of the transmittance of an example liquid crystal display element, and FIG.
10 and 10 are diagrams each illustrating the operation of a conventional liquid crystal display element. Agent Patent Attorney Nori Chika Ken Yudo Take Hana Kikuo Sanzu γ Masu ■ Similar υ zO ] 1 Chief, D Su^ko? 90 people

Claims (1)

[Claims] First electrodes are formed on opposing surfaces, and the first electrodes are arranged opposite to each other.
and 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. At least one optical retardation plate is disposed between the first substrate and the first polarizing plate, and the optical retardation plate adjacent to the first substrate is A liquid crystal display element, wherein the optical axis direction forms an angle in the range of 55 degrees to 80 degrees with the long axis direction of the liquid crystal molecules in contact with the first substrate.