JPH01147430A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To enable black display on a white background and white display on a black background by specifying the angle between the orientation direction of a liquid crystal and the transmission or absorption axis of polarizers and the angle between the respective layers and the orientation direction of the liquid crystal. CONSTITUTION:This display element is constituted of a 1st liquid crystal layer 16 which is held in place between a pair of substrates 11 and 21, is oriented approximately horizontally to the substrates and has the structure twisted by >=120 deg. and <=360 deg. in the thickness direction, the 2nd liquid crystal layer 26 which is partitioned from the 1st liquid crystal layer 16 by the light transparent substrate 21 and is held in place between substrates 21 and 31, and a pair of the polarizers 17, 27. The element is so constituted that at least one of the angles between the liquid crystal orientation direction on the substrates 11, 31 adjacent to the polarizers 17, 27 and the transmission or absorption axes of the polarizers 17, 28 is <=25 deg. and further the angle between the respective layers on the substrate 21 and the orientation direction is >=30 deg. and <=110 deg.. The large-capacity black and white display by simple matrix driving is thereby enabled.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a liquid crystal display element.

[Prior art]

The display mode of liquid crystals that has been mainly used in the past is called the twisted nematic (TN) type, in which the liquid crystal molecules are twisted approximately 90 degrees between a pair of upper and lower substrates, and the rotation of the plane of polarization by the liquid crystal is called the twisted nematic (TN) type. This method takes advantage of the fact that the effect disappears due to voltage. This display mode was sufficient for low time division driving of watches, calculators, etc., but when driving high time division 1 to increase the display capacity, it has the disadvantage that contrast decreases and the viewing angle becomes narrower. was there. This is because with high time-division driving, the ratio of voltages applied to selected points and non-selected points approaches 1, and in order to obtain a display element with high contrast and a wide viewing angle, the relative transmittance of the element must be 10%. Varying voltage V,. and the voltage v5° that changes by 50% (v
It is necessary to make the steepness γ expressed by 5o/v1o as small as possible.

In the case of twisted nematic type, this γ value is 1.13
That's about it. In order to reduce this γ value, a method has been proposed in which the twist angle of the liquid crystal molecules is increased and the polarization axis is shifted from the orientation direction, and this method is called SBE mode or STN mode. According to such a system, the γ value can be reduced to 1.1 or less, and high time-division driving of about 1/400 duty is possible. However, this method uses coloring due to birefringence and its change due to voltage, so
There are strict requirements for liquid crystal layer thickness accuracy, for example, ±0.1
Cells must be created within μm, resulting in
With SBE and STN types, product production is extremely difficult, resulting in a lower quality product rate and higher costs.Also, these types use coloring due to birefringence and its change due to voltage. However, the display is on a colored background, making it difficult to display in black and white. Furthermore, light leakage occurs depending on the wavelength, making it difficult to use as a light shutter for color display.

〔the purpose〕

The present invention overcomes the drawbacks seen in the prior art, has high time division drive characteristics, can display black on a white background or white on a black background, has less unevenness in one color, and can display colors. The purpose of the present invention is to provide a liquid crystal display element.

[Composition, action]

According to the present invention, the first liquid crystal layer is sandwiched between a pair of substrates, is oriented substantially horizontally with respect to the substrates, and has a twisted structure of 120° or more and 360° or less in the thickness direction; is composed of a second liquid crystal layer and a pair of polarizers, which are partitioned by one or more transparent substrates and sandwiched between the substrates, and at least one of the first liquid crystal layer and the second liquid crystal layer. , the angle between the liquid crystal orientation direction on the substrate adjacent to the polarizer and the transmission axis or absorption axis of the polarizer is 25° or less, and the second liquid crystal layer and the first liquid crystal layer are separated from each other. There is provided a liquid crystal display element characterized in that the angle between the alignment directions of liquid crystal in each layer on a substrate is 30° or more and 110° or less.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of the structure of a conventional STN type liquid crystal display element.

In this figure, a first substrate 11' having an alignment film 15' formed thereon and a transparent electrode 13' subjected to alignment treatment;
A similar second substrate 21' is arranged to be spaced apart and facing each other,
A liquid crystal 33' is sealed between them to form a liquid crystal cell. 23' is a transparent electrode, and 25' is an alignment film.

35' indicates a sealant. This liquid crystal cell is sandwiched between a first polarizer 17' and a second polarizer 27' to constitute a liquid crystal display element.

FIG. 2 is a sectional view showing an example of the structure of the liquid crystal display element of the present invention. The first liquid crystal R1J16 is formed between a first substrate 11 on which transparent electrodes 13 are formed and which has been subjected to an alignment process, and a second substrate 21 which has been subjected to a similar process. On the opposite side of the substrate 21 from the first liquid crystal layer.

A second liquid crystal layer 26 is formed between the third substrate 31 and the third substrate 31 . In the first liquid crystal layer, the liquid crystal is
The liquid crystal molecules are aligned substantially horizontally, and the liquid crystal molecules are preferentially aligned along the direction of the alignment process. In this case, "substantially horizontal" with respect to the orientation of liquid crystal molecules means that the tilt angle of the liquid crystal molecules with respect to the substrate is approximately in the range of 0 to 30 degrees.

As the substrate, transparent glass, plastic film, or the like can be used.

Figure 4 shows the preferential alignment direction of liquid crystal.

The preferred alignment direction D1 of liquid crystal molecules on the first substrate 11 and the second
The liquid crystal molecules are ω between the preferential alignment direction D2 on the substrate 21 and
It has a twisted structure. As described above, ω1 is the twist angle determined by the orientation treatment, and this orientation control can be performed by conventionally known oblique vapor deposition or by rubbing with cotton cloth after forming an inorganic or organic film. In addition.

In the present invention, the liquid crystal preferably used is a nematic liquid crystal having positive dielectric anisotropy to which cholesteric liquid crystal or chiral nematic liquid crystal is added and adjusted to an appropriate pitch. In this case, if ω1 is small, the steepness will worsen and the 1 time division drive characteristic will deteriorate, and if ω1 is too large, scattering structure will occur when an electric field is applied, which will deteriorate display quality, which is not preferable. From these things, ω1 is 12
It must be between 0@ and 360°.

In Fig. 2, the twist direction is configured to be counterclockwise from the first substrate to the second substrate, but it may be twisted clockwise depending on the orientation treatment direction or selection of cholesteric liquid crystal or chiral nematic liquid crystal. You can also do it.

In FIG. 2, on the opposite side of the first liquid crystal layer from the polarizer,
A second liquid crystal layer 26 is formed between substrate 21 and third substrate 31. The sides of both substrates that are in contact with the liquid crystal are subjected to an alignment treatment that preferentially orients the liquid crystal molecules substantially horizontally. For the alignment treatment, a method similar to that for aligning the first liquid crystal layer can be used, but it is not necessary to use the same method. As the liquid crystal, smectic liquid crystal, nematic liquid crystal, or nematic liquid crystal to which cholesteric liquid crystal or chiral nematic liquid crystal is added can be advantageously used. As shown in FIG. 4, the preferential alignment direction of liquid crystal molecules on the second substrate 21 and
The liquid crystal has a structure twisted by ω2 between the preferential orientation direction of 1 and 1.

In FIG. 2, transparent electrodes 33 and 43 are also shown provided on the surface of the substrate constituting the second liquid crystal layer, but these may be omitted. Further, the substrate separating both liquid crystal layers may be composed of two or more substrates as shown in FIG. 3.

In such a configuration, when passing through the first liquid crystal layer,
Light becomes elliptically polarized light with different ellipticity and elliptical azimuth depending on its wavelength. The principle of the present invention is to return this to linearly polarized light or elliptically polarized light close to linearly polarized light using the second liquid crystal layer, and to pass it through a polarizer placed parallel or at right angles to the linearly polarized light, thereby producing white or black light, respectively. This is to obtain the background color when no voltage is applied. In order to realize this principle and obtain a display element that is capable of black-and-white display, has excellent display quality, and has little color unevenness, it is necessary to determine the alignment direction of the liquid crystal on the substrate adjacent to the polarizer and the transmission axis or absorption axis of the polarizer. The angle between the axes (β for the first liquid crystal layer and the second liquid crystal layer, respectively)
β2), at least one of them is elliptical so that the angle is 25° or less, and the angle δ formed by the orientation direction of each layer on the substrate that partitions the first liquid crystal layer and the second liquid crystal layer is 30°.
It is necessary to set the value to be greater than or equal to '110' and less than or equal to 110.

In FIG. 4, the twist direction of the first liquid crystal layer is shown as positive, but the angle formed by the alignment direction of the liquid crystal is −150° or more −
70° or less is also included in the above range. Also.

The second liquid crystal layer may or may not be twisted in the same way as the first liquid crystal layer, and the direction of twist may be the same or opposite to that of the first liquid crystal layer. may be,
Regarding β, −25@ or more and +25” or less are also included in the above range.

In the present invention, at least one of β1 and β2 is set at 25° or less; in this case, the second liquid crystal layer is at 120° or less.
In the case of a torsion angle of ``'' or less, β is preferably 25° or less, and β2 is preferably 25° or more and 65° or less. If β2 is 25'' or less, the effects of the present invention will not be achieved. .

In the present invention, at least one of β□ and β2 is 25
However, if both are 25 degrees or less, either the contrast or the background color will be sacrificed. Therefore, β1 and β2
It is preferable that one of the angles is 25° or more and 65° or less.

The preferred condition for β is that one side is 25″ or less and the other side is 25″ or less.
@In the case of 65″ or more, the refractive index anisotropy of the liquid crystal layer where β is 25° or less is Δn, and the liquid crystal layer thickness is d (μm)
When β is 25° or more and 65° or less, the refractive index anisotropy of the liquid crystal layer is ΔN, and the liquid crystal layer thickness is D (μ + n), the liquid crystal display element of the present invention satisfies the following formula. preferable.

ΔND-0,1≦Δnd≦8ND+0.5 Under such conditions, the background color becomes white or black depending on the value of β, and becomes black and white, respectively, when a voltage is applied. When the background is white, if Δnd is less than the lower limit, the background becomes yellowish. Moreover, if it exceeds the upper limit, the color becomes purple, blue, or blue-green, and the background cannot be made white or black. In the arrangement of polarizing plates where the background is black, outside the above condition range and when the background is white, coloring of the complementary color of the illustrated color will occur. .5 μm or less, and ΔND is preferably 0.1 μm or more and 1.0 μm or less. Outside this range, it will not only be difficult to make the background color white or black, but also the contrast will decrease. do.

In the present invention, when both β is 25" or less, the difference in the product Δnd of the refractive index anisotropy and the liquid crystal layer thickness of the first liquid crystal layer and the second liquid crystal layer is -0.5 to +0.5 μm. This is preferable because it is a range or the background is white or black.

It is also possible to provide a transparent electrode in the second liquid crystal layer and drive it simultaneously with or separately from the first liquid crystal layer.

Thus, in the liquid crystal display element of the present invention, the background color of the cell can be set to white or black by satisfying the above conditions. Further, when a voltage is applied, the display becomes black or white, respectively, and black and white display is possible.

Note that the steepness of the voltage pass rate characteristic of the liquid crystal display element of the present invention is 1.05 or less, similar to the conventional STN type liquid crystal display element, and has excellent time-division drive characteristics.

〔effect〕

Since the liquid crystal display element of the present invention has little color change due to changes in cell thickness, color unevenness is less likely to occur. Furthermore, since it has excellent steepness, it can be used as a liquid crystal display element with a large display capacity. What's more, it is a simple matrix-driven system that was previously impossible.

The amount can be displayed in black and white. Furthermore, since there is little light leakage due to wavelength, it can be used as a light shutter for color displays.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Polyimide was coated and rubbed on a glass substrate having a transparent electrode, and the upper and lower substrates were bonded together so that the twist angle was 180@. The distance between the upper and lower boards is determined by spacers.
It was configured to have a thickness of 7 μm. Δn=0 between the upper and lower boards.
A first liquid crystal cell was prepared by filling a nematic liquid crystal No. 10 to which chiral nematic liquid crystal S-811, which induces counterclockwise twisting, was added. Δncl−0.7μ
m.

A second liquid crystal cell prepared in the same manner and having a twist angle of Oo (homogeneous alignment) and Δnd=0.3 μm was superimposed on the first liquid crystal cell. The first liquid crystal cell is located at the bottom of the first liquid crystal cell.
The polarizer was arranged so that the rubbing direction on the lower side of the cell and the transmission axis of the polarizer were parallel (01=0).

At the top of the second cell, the rubbing direction of the second cell and the transmission axis of the polarizer are rotated counterclockwise by 45° (θ2 = 45°).
The polarizer was placed so as to form an angle of .

When the second cell is rotated horizontally on top of the first cell while maintaining the above polarizing plate relationship, the rubbing direction on the first upper substrate side and the rubbing direction on the lower substrate side of the second cell are clockwise. When the angle of 60° (δ=60°) was formed, the background color was closest to white. When voltage was applied to the first cell, the application point became black. Also, rotate θ2 clockwise (θ, = +
45°), the cell turned black and turned white when voltage was applied. This element had a steepness of 1.04 and exhibited excellent time-division drive characteristics. Further, no color change was detected even when the liquid crystal layer thickness changed by about 0.5 μm.

Example 2 Same as Example 1, twist angle is 180', θ1
= 06, Δnd = 0.7 μm, and
Twist angle is Oo, θ, = 45”, Δnd = 0.6 p
m and a second liquid crystal cell were stacked so that δ=60°. This element was black when no voltage was applied, and turned white when voltage was applied. Black and white were reversed by setting θ = -45°.

Also, similar to Example 1, excellent steepness was exhibited.

Example 3 Same as Example 1, twist angle is 220°, θ1=
The first liquid crystal cell has Oa, Δnd=0.8 μm, twist angle is 1806, θ2=-45”, Δnd=0.5
A second liquid crystal cell having p w+ was superimposed so that δ=45°.

This element was white when no voltage was applied, and turned black when voltage was applied. When θ2=45°, black and white were reversed.

Also, similar to Example 1, excellent steepness was exhibited.

[Brief Description of the Drawings] Fig. 1 is a sectional view showing an example of the structure of a conventional liquid crystal display element, Fig. 2 is a sectional view showing an example of the structure of the liquid crystal display element of the present invention, and Fig. 3 is a modified example thereof. be. FIG. 4 is an explanatory diagram of the angular relationship of the liquid crystal display element of the present invention. 11', 21', 11, 21, 31.41...Substrate, 15', 25', 15.25°35.45
...Alignment film, 13', 23', 13, 23, 33
．． 43...electrode, 17', 27', 17.2
7...Polarizer. (1 idiot) Figure 3

Claims (1)

[Claims] (1) A first liquid crystal layer that is sandwiched between a pair of substrates, is oriented substantially horizontally to the substrates, and has a twisted structure of 120° or more and 360° or less in the thickness direction; It is composed of a second liquid crystal layer partitioned by one or more transparent substrates and sandwiched between the substrates, and a pair of polarizers, and in at least one of the first liquid crystal layer and the second liquid crystal layer, The angle between the liquid crystal orientation direction on the substrate adjacent to the polarizer and the transmission axis or absorption axis of the polarizer is 25° or less,
A liquid crystal display element, characterized in that the angle formed by the orientation direction of liquid crystal in each layer on the substrate separating the second liquid crystal layer and the first liquid crystal layer is 30° or more and 110° or less.