JPH01100517A - Liquid crystal display panel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Summary] The present invention provides 5TN (Super Twister Ne) in which the twist angle of liquid crystal molecules is preferably 180 degrees or more.
matic) type liquid crystal cell (hereinafter referred to as the drive cell) and a liquid crystal cell in which the liquid crystal molecules are twisted in the opposite direction by the same angle □ degrees (hereinafter referred to as the compensation cell), an electric field is applied to the compensation cell. In order to improve the contrast ratio of a two-layer structure panel without adding any This is what I did.

[Industrial application field]

The present invention relates to a liquid crystal display panel that is particularly effective for use in large-sized displays such as word processors and personal computers.

As a liquid crystal display device capable of color display, there is a demand for a large-capacity liquid crystal display device capable of monochrome display using a simple matrix display and capable of multi-line display.

[Conventional technology]

Conventional liquid crystal display panels have transparent electrodes and alignment films laminated on a pair of transparent insulating substrates sandwiched between two polarizing plates when viewed from the direction of light incidence, and a liquid crystal is placed between these transparent insulating substrates. By enclosing the liquid crystal and subjecting the alignment film to alignment treatment, the liquid crystal molecules in the transparent substrate sandwiched between the upper polarizing plate and the lower polarizing plate are twisted.

In addition, the liquid crystal display panel has different characteristics due to the twist angle of the liquid crystal molecules.
Generally, the twist angle is roughly divided into TN (Twisted Nematic) method with a twist angle of 90 degrees or less and STN method with a twist angle of 90 degrees or more.

[Problem that the invention seeks to solve]

However, in the above-mentioned TN type liquid crystal display panel, the amount of transmitted light does not fluctuate sharply with respect to the voltage applied to the liquid crystal, so it is possible to display a large-capacity screen with a simple matrix structure and increase the number of black lines on a white background to about 400. It is difficult to do so.

Furthermore, the above-mentioned STN type liquid crystal display panel is capable of displaying a large capacity because the amount of transmitted light fluctuates sharply with respect to the voltage applied to the liquid crystal, but because it is a display method that utilizes the birefringence of light, it is The dispersion of light is large, and the display is colored like black on a yellow-green background (background color) or blue on a white background (background color), making it difficult to display black and white on a white background or white on a black background. Even with the use of color filters, it was difficult to display in color.

The present invention combines the advantages of the two types of liquid crystal display panels described above, so that the amount of transmitted light changes sharply with respect to the voltage applied to the liquid crystal, and the dispersion of light with respect to transmitted light is reduced. To provide a liquid crystal display panel capable of displaying a white multi-line display on a large screen on a black background.

[Means for solving problems]

The liquid crystal display panel of the present invention for achieving the above object includes:
A drive cell in which liquid crystal molecules are twisted at a predetermined angle, and a compensation cell in which the twist direction of the liquid crystal molecules is opposite to that of the liquid crystal cell and are twisted at approximately the same angle are stacked, and the refractive index anisotropy Δn of the liquid crystal molecules is stacked. and the cell thickness d, Δn−d
is different between the drive cell and the compensation cell.

[Effect]

By setting the relationship of Δn-d between the drive cell and the compensation cell as described above, for example, the optical characteristics of the compensation cell can be adjusted to compensate for the non-selection voltage applied in a two-layer structure panel in which the drive cell and the compensation cell are laminated. Since the optical properties are almost similar to those of the cell, there is no need to apply a voltage to the compensation cell.

In other words, in a two-layer structure panel consisting of a drive cell and a compensation cell in which the twist angle of the liquid crystal molecules is the same and the twist angle is opposite to each other, if Δn−d is also the same in both cells, one liquid crystal cell (compensation cell) FIG. 7 shows the relationship between the light transmittance of the panel and the applied voltage (transmittance-voltage curve) when no electric field is applied.

Except in exceptional cases, most liquid crystal display panels do not display in a state where no voltage is applied and a state where a voltage is completely applied (static drive) due to the limitations of their driving method, but instead use a non-selective voltage. VOFF and selection voltage V
. H is displayed (dynamic drive), and V OFF
The ratio α (α=VON/■.FF) between V(IH) and V(IH) is determined by the display capacity (number of display lines).

As shown in FIG. 7, when no voltage is applied to the compensation cell, the ratio selection voltage V. , F is applied, the transmittance does not become zero. ■ This is the ratio selection voltage to the driving cell. Even though FF is applied, no voltage is applied to the compensation cell, so the liquid crystal alignment states of both cells do not match, and the compensation cell cannot perform complete compensation. .

In order to prevent this sharp decrease in contrast ratio, for example, a solid electrode is provided on the compensation cell so that when the non-selection voltage is applied to the drive cell, the non-selection voltage is also applied to the compensation cell. If FF is applied, the 8th
Since the transmittance-voltage characteristics shown in the figure are obtained, it is possible to improve the contrast ratio.

However, in the above method, the structure and control become complicated, which causes problems in terms of design and manufacturing.

However, in the present invention, by selecting Δn-d between the drive cell and the compensation cell, it is no longer necessary to apply voltage to the compensation cell.
An inexpensive liquid crystal display panel with simple structure and control can be realized.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing the basic structure of the liquid crystal display panel of the present invention in an expanded state, and FIG. 2 is a perspective view showing the relationship between the liquid crystal twist direction of each cell and the polarization axis direction of the polarizing element in FIG.
3 is a plan view for explaining the liquid crystal twist state of each cell in FIG. 1, and FIG. 4 is a side view showing the specific structure of the liquid crystal display panel of the present invention. 5 is a diagram showing the relationship between the liquid crystal twist direction, polarization axis direction, and orientation direction of the panel shown in FIG. 4. FIG.
A characteristic diagram showing the relationship between the d ratio and the transmittance, and FIGS. 7 and 8 are characteristic diagrams showing the transmittance-voltage relationship related to the liquid crystal display panel of the present invention.

As shown in FIG. 1, the panel structure of the present invention includes a first polarizer 1 having a polarization axis when viewed from the incident direction of light A, and a 90
It has a liquid crystal that is twisted preferably 180 degrees or more,
Compensation using a drive cell 2, which is a liquid crystal panel having control electrodes forming a matrix, and a liquid crystal panel having a liquid crystal twisted in the opposite direction and at approximately the same angle as the liquid crystal sealed in the liquid crystal panel 2. Cell 3 and polarization axis E
It has a structure in which a second polarizer 4 having a polarizer and a second polarizer 4 are stacked.

The liquid crystals in the drive cell 2 and the compensation cell 3 have refractive index anisotropy (referred to as refractive index), which is the difference in refractive index between the long axis (ordinary ray) and the short axis (extraordinary ray) of liquid crystal molecules, as described later. In some cases)
Different types of liquid crystal molecules with different Δn are enclosed,
Further, the twist directions of the liquid crystal molecules sealed in each cell 2 and 3 are set to be opposite to each other and at substantially the same twist angle.

In addition, the liquid crystals in each cell 2.3 were selected to have the same parameters as possible for liquid crystal molecules such as elastic modulus, dielectric constant, viscosity, twist pitch length, phase transition temperature, etc. other than the refractive index anisotropy Δn. is preferable.

When the liquid crystal sealed in the drive cell 2 is twisted counterclockwise in the direction of arrow B with respect to the direction of light incidence shown by arrow A, the liquid crystal sealed in the compensation cell 3 is twisted with respect to the direction of light incidence shown by arrow A. It is twisted clockwise in the direction of arrow C.

As shown in FIG. 5, which is an explanatory diagram of the main part of FIG.
．． In the alignment direction shown in 2-5 and the alignment direction of liquid crystal molecules 3A and 3E of the compensation cell 3 in the alignment direction 3-1.3-5, the alignment direction 2-1 and 3-5, and the alignment direction 2- 5 and 3
-1 so that they are orthogonal.

Furthermore, the twist angles of the liquid crystals in the two cells 2.3 are made the same. Furthermore, the cell parameters of cell W- (liquid crystal layer thickness) and pretilt angle of the two cells 2.3 are made the same.

Then, as shown in FIG. 3, which is an explanatory diagram of the main part of FIG. 1, the liquid crystal molecules 2A, 2B, 2B, and
Compensation i o- Liquid crystal molecules 3B, 3D--3A of compensation cell 3, that is, liquid crystal molecules located at the same distance from the center of the two panels, viewed from the light incident side The long axis directions of the molecules, 2-1, 2-2--2-5 and 3-5, 3-4-...-3-1, are at right angles to each other. oriented in the direction.

Further, the relationship between the liquid crystal twist direction of each cell 2.3 and the polarization axis of the polarizer 1.4 is as shown in FIG. When the long axis direction 3-5 of the liquid crystal molecules 3E in the compensation cell 3 is oriented in the y-axis direction, the polarization axis of the first polarizer is 45 degrees clockwise from the X-axis, and the polarization axis of the second polarizer is 45 degrees clockwise from the X-axis. Axis E is oriented 45 degrees counterclockwise from the X axis.

Furthermore, the drive cell 2 is provided with a matrix-like control electrode that changes the twisted state of the liquid crystal molecules (untwists and makes each liquid crystal molecule stand perpendicular to the panel surface) as described above, but the compensation cell 3 There is no means for applying an electric field to liquid crystal molecules such as a matrix control electrode or a solid electrode.

In a liquid crystal display panel having such a configuration, the propagation operation of light incident on the panel will be explained with reference to FIGS. 1 and 3.

Light incident on the panel from the outside in the direction of arrow A is converted into linearly polarized light such as 101 and 102 by the first polarizer 1. Here, a non-selection voltage is applied to the pixel position where the matrix electrodes of the drive cell 2 intersect. In other words, consider the case where the voltage is turned off. At this time, drive cell 2
The liquid crystal molecules inside are twisted, and linearly polarized light 101 becomes elliptically polarized light 103.

This light then passes through the compensation cell 3.

If no voltage is applied to the drive cell 2 here, the third
As shown in the figure, liquid crystals 2E and 3A, liquid crystals 2D and 3B, liquid crystals 2C and 3C, liquid crystals 2B and 30. What are liquid crystals 2A and 3E?
Since the effects of rotating the optical axis of the light and changing the phase of the light are opposite to each other, the rotation of the light is canceled out by each combination of liquid crystals, and the light passing through the compensation cell 3 becomes linearly polarized light 104. Become. This linearly polarized light 104
is blocked by the second polarizer 4, resulting in a dark state.

Next, a selection voltage is applied to the pixels forming the matrix electrode of the drive cell 2. In other words, consider the case where a voltage is applied to the drive cell 2. At this time, the liquid crystal molecules in the drive cell 2 are standing, and the linearly polarized light 102 passes through the liquid crystal molecules and is emitted in the form of linearly polarized light 105. Product Δn of refractive index anisotropy Δn of liquid crystal molecules in drive cell 2 and compensation cell 3 and cell thickness d
When the value of −d is in the range from 0.5 μm to 1.68 μm, this light further passes through the compensation cell 3 and becomes elliptically polarized light 106, and this elliptically polarized light 106 further passes through the second polarizer 4 and becomes linearly polarized light. It becomes 107 and becomes a bright state.

By driving the drive cell 2 using the multiplex driving method in this manner, a negative monochrome display of white on a black background can be realized.

The specific structure of the liquid crystal display panel of the present invention having such a configuration will be explained using FIG. 4.5.

As shown in FIG. 4, a driving cell 2 is located between the first polarizer 1 and the second polarizer 4 along the direction of light incidence as shown by arrow A.
and compensation cell 3 are laminated. The drive cell 2 has stripe-shaped transparent electrodes 21 and 22 that are perpendicular to each other and constitute a matrix, on which alignment films 23 and 24 made of polyimide resin are formed, and are sealed in a predetermined manner with an epoxy sealant 25 mixed with a spacer. It is formed from a pair of transparent glass substrates 26 and 27 in which a liquid crystal sealed space is formed, and a liquid crystal 28 is sealed in the liquid crystal sealed space.

The back side of this glass substrate 27 and the epoxy sealant 29
A transparent glass substrate 31 with a predetermined liquid crystal enclosure space formed therein.
Alignment films 32 and 33 are formed thereon, and a liquid crystal 3 having a different refractive index anisotropy Δn from the liquid crystal 28 is formed in the liquid crystal enclosed space.
4 is enclosed to form a compensation cell 3.

Using FIG. 5, which is an explanatory diagram of the main part of FIG. 4, the orientation direction of the liquid crystal 28, 34 in FIG. Second polarizer 1.
The relationship between the polarization directions in No. 4 will be described.

In FIG. 5, the X axis is taken in the rubbing direction of the alignment film 23.

Liquid crystal molecules 2A and 3E in the liquid crystal 28 and liquid crystal 34, 2
B and 3C.

2C and 3B, 2E and 3A each have oblique shadows on the substrate surface at right angles, and the liquid crystal molecules in each liquid crystal panel are twisted 270 degrees, and the twist directions are opposite to each other. It has become. The twist angle of the liquid crystal molecules can be 90 degrees or more, but in this example, the twist angle is 270 degrees or more.
I take it as a degree.

In order to obtain such a twist direction, the rubbing direction of the alignment film 23 is 2-1, which is the same direction as the alignment direction of the liquid crystal molecules 2A.
The rubbing direction of the alignment film 24 is the direction of the liquid crystal molecules 2E.
The rubbing direction of the alignment film 32 indicates the 3-1 direction, which is the same direction as the twist direction of the liquid crystal molecules 3^, and the alignment direction of the alignment film 33 indicates the direction 2-5, which is the same direction as the alignment direction.
N! The 3-5 direction, which is the same direction as the orientation direction, is shown. That is, the rubbing direction of the alignment film 24 and the rubbing direction of the alignment film 33 are rubbed in opposite directions.

In addition, in the drive cell 2 and the compensation cell 3, 28.34 uses two types of liquid crystal molecules with different refractive index anisotropy Δn, but on the other hand, they are set to the same cell thickness and use the same alignment film. ing. Furthermore, the rubbing density was also the same.

Furthermore, the polarization axis of the first polarizer 1 is installed so as to be oriented 45 degrees clockwise from the X axis, and the polarization axis E of the second polarizer 4 is oriented at 45 degrees clockwise from the X axis.
is designed to have a polarization direction at 45 degrees counterclockwise with respect to the X axis.

Further, a voltage is applied between the transparent electrodes 21 and 22 in accordance with a desired display pattern using a multiplex driving method similar to when driving a TN type liquid crystal display device.

In this panel structure, it is possible to replace the transparent glass substrate 27 with two transparent glass substrates. Furthermore, in this panel structure, the positions of the drive cell 2 and the compensation cell 3 can be interchanged. Regarding the product Δn−d of the refractive index anisotropy Δn and the cell thickness d, in the above embodiment, the Δn value is
and compensation cell 3, the present invention can also be realized by using a method in which the Δn value is the same, that is, the same liquid crystal is used in drive cell 2 and compensation cell 3, and the cell thickness d of cell 2.3 is changed instead. be.

As described above, the liquid crystal display panel according to the present invention has two layers including a drive cell and a compensation cell in which the twist states of liquid crystal molecules are in opposite directions and the product Δn-d of refractive index anisotropy Δn and cell thickness d is different from each other. With this structure, it is possible to provide a large screen panel capable of displaying black and white (white on a black background) only by applying an electric field to the drive cell through voltage control without applying any electric field to the compensation cell.

Next, a specific experimental example according to the present invention will be described. The compensation cell 3 has a cell thickness d=7.2 μm and a liquid crystal refractive index anisotropy Δ
n = 0.141, twist angle 270° (clockwise),
Δn-d = 1.015, while the cell thickness of drive cell 2 is d = 7.2 μm, and the refractive index anisotropy of the liquid crystal is Δn = 0.15.
3, twist angle 270' (counterclockwise), Δn・d =
It was set to 1.102. In this case, Δn·d of the drive cell 2 is 1.09 times that of the compensation cell 3.

In this panel, the contrast ratio of 8.5 was improved to 15 when no voltage was applied to the compensation cell 3. Furthermore, since there is no need to apply a voltage to the compensation cell 3, the structure is simplified.

Also, the allowable range of the ratio of Δn-d is as shown in Figure 6.
■Non-select voltage to compensation cell. Comparing the light transmittance characteristics of the panel when FF is applied, if the Δn-d of the drive cell 2 is set to 1.07 to 1.12 times the Δn-d of the compensation cell 3, the same contrast (black background) will be obtained. The contrast ratio (contrast ratio of white display) for white display is obtained.

Further, in a range in which the ratio of Δn-d is 1.02 to 1.20 times, the contrast ratio is slightly inferior to that in the case where V o is applied, but it is sufficiently practical.

〔Effect of the invention〕

As described above, according to the present invention, a large-screen liquid crystal display panel capable of black-and-white display with good contrast can be provided at low cost.
Its practical effects are enormous.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the basic structure of the liquid crystal display panel of the present invention in an expanded state, and FIG. 2 is a perspective view showing the relationship between the liquid crystal twist direction of each cell and the polarization axis direction of the polarizing element in FIG. A plan view seen from the direction of light A in the figure, FIG. 3 is a plan view for explaining the liquid crystal twist state of each cell in FIG.
FIG. 4 is a side sectional view showing the specific structure of the liquid crystal display panel of the present invention, FIG. 5 is a diagram showing the relationship between the liquid crystal twist direction, polarization axis direction, and orientation direction of the panel in FIG. Δn of the drive cell and compensation cell in the liquid crystal display panel of the invention
7 and 8 are characteristic diagrams showing the relationship between the transmittance and the voltage related to the liquid crystal display panel of the present invention. [Explanation of symbols] 1 is the first polarizer, 2 is the drive cell, 2A, 2B, 2C, 2
D. 2E, 3A, 3B, 3C, 3D, 3E, 28.34 are liquid crystals, 3 is a compensation cell, 4 is a second polarizer, 21.22 is a transparent electrode, 23, 24, 32.33 is an alignment film, 25. 29 is a sealant, and 26, 27, and 31 are transparent glass substrates. 103 mef\n''' Goose 1 Komari sacrilege Δya 1F trigram (Jiriten Shichi Jl/Kugo 4m゛ Haru strike) 1 bow and ↓ Jealous Achi group b■~E red and white direction and 9 knightly hands 1h to Ujutsu 2 Zu Ryuen Shima + 8

Claims (8)

[Claims] (1) A drive cell in which liquid crystal molecules are twisted at a predetermined angle,
A compensation cell in which the twist direction of the liquid crystal molecules is opposite to the liquid crystal cell and twisted at almost the same angle is laminated, and the product Δn·d of the refractive index anisotropy Δn of the liquid crystal molecules and the cell thickness d is as described above. A liquid crystal display panel characterized in that the drive cell and the compensation cell are different. (2) The liquid crystal display panel according to claim 1, wherein the liquid crystal molecule twist angle of the drive cell is 180 degrees or more. (3) The liquid crystal display according to claim 1, wherein the drive cell is provided with a control electrode that changes the twist state of the liquid crystal molecules, and the compensation cell is not provided with a control electrode. panel. (4) The liquid crystal display panel according to claim 1, wherein the product Δn·d of the drive cell is larger than that of the compensation cell. (5) The product Δn·d of the drive cell is 1.02 to 1.20 times that of the compensation cell, preferably 1.07 to 1.
The liquid crystal display panel according to claim 3, which is 12 times larger. (6) The product Δn·d of the drive cell is 0.51 to 1.68
μm, the product Δn・d of the compensation cell is 0.5 to 1.4 μm
A liquid crystal display panel according to claim 5, characterized in that: (7) A patent claim characterized in that the product Δn·d of the drive cell is made larger than the product Δn·d of the compensation cell by making the refractive index anisotropy Δn larger than Δn of the compensation cell. 4. The liquid crystal display panel according to item 4. (8) The product Δn·d of the drive cell is determined by making the cell thickness d larger than d of the compensation cell, and the product Δn·d of the compensation cell.
The liquid crystal display panel according to claim 4, characterized in that the liquid crystal display panel is made larger.