JPH0243515A - Optical compensating liquid crystal display element - Google Patents

Abstract

PURPOSE:To effectively preventing the generation of coloring on a display image and to obtain a wide visual angle by providing the title liquid crystal display element with specific 1st and 2nd liquid crystal cells, setting up the 1st cell side transparent substrate out of two translucent substrate of the 2nd liquid crystal cells to an optically isotropic state and setting up the other substrate to an optically anisotropic state. CONSTITUTION:The 2nd liquid crystal cell 10 is unitedly joined with the surface of the 1st liquid crystal cell 20, i.e. the surface of the substrate 21B, through a bonding agent 16. When it is defined that the liquid crystal double refractive index of the 1st liquid crystal layer 23 is DELTAn1, the layer thickness is d1, the liquid crystal double refractive index of the 2nd liquid crystal layer 13 is DELTAn2, and the layer thickness is d2, the shown formula I is satisfied. Out of the two transparent substrate 11A, 11B of the 2nd liquid crystal cell 10, the substrate 11A on the 1st cell side is set up to the optically isotropic state and the other substrate 11B is set up to the optically anisotropic state. Consequently, black- and-white display can be attained, display quality can be improved, coloring is not observed at the time of observing a display image from an oblique direction, and a visual field can be expanded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optically compensated liquid crystal display element.

[Prior Art] A twisted nematic type liquid crystal display element (hereinafter referred to as a TN type liquid crystal display element), which has been well known as a conventional liquid crystal display element, has a 90 degree spiral structure between two electrode substrates. It is composed of a liquid crystal cell provided with a liquid crystal layer and a pair of polarizing plates provided to sandwich the liquid crystal cell.

This TN type liquid crystal display element has been the mainstream of liquid crystal display elements, but in recent years, as dot matrix type liquid crystal display elements have become larger, the number of time divisions has increased, and the conventional TN type liquid crystal display element It is becoming difficult to cope with the time-division characteristics of 1,764 or more, and both contrast and viewing angle deteriorate especially in time-division driving with a duty of 1764 or more.

In contrast, super twisted nematic type (ST) liquid crystal molecules are twisted 200 to 270 degrees between substrates.
N type) and 5BE (Super Twisted Bir
efringene effect) type liquid crystal display elements have been proposed, and it has been reported that wide viewing angles and high contrast can be obtained (T, J, 5cheffer
at al, :SID Digest 120 (198
5)).

[Problems to be Solved by the Invention] However, these STN type and SBE type liquid crystal display elements utilize the birefringence of the liquid crystal, so there is a problem that the display is displayed on a five-colored background. In order to overcome this drawback, a method has been proposed in which two layers of liquid crystal cells are stacked to obtain a colorless background. Color change (coloring)
This will cause problems.

On the other hand, liquid crystal display elements using flexible films are attracting attention from the viewpoints of thinner and lighter liquid crystal display elements, as well as lower strength, workability, and cost.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a novel optically compensated liquid crystal display element that is lightweight, thin, wide viewing angle, and can be realized at low cost. With the goal.

[Means to solve the problem] The present invention will be explained below.

The optically compensated liquid crystal display element of the present invention includes a first liquid crystal cell;
It has a second liquid crystal cell and two polarizing plates.

The first liquid crystal cell has two substrates and a first liquid crystal layer. The two substrates are optically transparent and have display electrodes.

The first liquid crystal layer is sandwiched between the two substrates, is oriented substantially parallel to each substrate, and is oriented at an angle of 120 degrees or more in the thickness direction.
It has a twisted structure of 60 degrees or less and exhibits positive dielectric anisotropy.

The second liquid crystal cell includes two light-transmitting substrates and a second liquid crystal layer sandwiched between these light-transmitting substrates and oriented substantially parallel to each light-transmitting substrate. Regarding the first and second liquid crystal layers, "aligned approximately parallel to each substrate or each transparent substrate" means that the liquid crystal molecules are oriented substantially parallel to each substrate or each transparent substrate. This means that the tilt angle is in the range of approximately 0 to 30 degrees.

The second liquid crystal cell is stacked on one substrate of the first liquid crystal cell, and two polarizing plates sandwich the stack of the first and second liquid crystal cells.

Furthermore, what are the materials and structures of the first and second liquid crystal cells?

The liquid crystal birefringence in the first liquid crystal layer is Δn1, and the layer thickness is d.
l, ΔJ is the liquid crystal birefringence in the second liquid crystal layer.

The layer thickness is d! When ! It is set so that Δn1dl−Δnzdx l≦0.8 μm.

Also, of the two transparent substrates of the second liquid crystal cell, the first
A substantially optically isotropic substrate may be used as the transparent substrate on the side of the liquid crystal cell, and an optically anisotropic plastic film substrate may be used as the other transparent substrate.

[Example] A detailed description will be given below with reference to the drawings.

FIG. 1 shows one embodiment of the invention.

In FIG. 1, reference numeral 20 indicates a first liquid crystal cell, and reference numeral 10 indicates a second liquid crystal cell.

In the first liquid crystal cell 20, the first liquid crystal layer 23 has two
A sealing material 24 is used to seal between the two substrates 21A and 21B. In this embodiment, the substrates 21A and 21B are both glass plates, and the substrate 21A has a transparent electrode 2.
7A and an alignment film 22A are formed. Similarly, substrate 2
An electrode 27B and an alignment film 22B are formed on 1B.

The substrates 2XA and 21B are distributed with the surfaces on which the electrodes and alignment films are formed facing each other in parallel, and the liquid crystal layer z3 is sandwiched between them. electrode 27A,
27B constitutes a display electrode.

On this first liquid crystal cell 20, that is, on the substrate 21B, a second liquid crystal cell 10 is integrated with the first liquid crystal cell 20 using a bonding agent 16. a first with a bonding agent 16;
Although bonding of the second liquid crystal cell 20.10 is a desirable form, the use of a bonding agent is not necessary.

The second liquid crystal cell 10 is formed by sealing a liquid crystal layer 13 between translucent substrates 11A and IIB arranged parallel to each other and facing each other using a sealing material 4, and the translucent substrate 11A.

Alignment films 12A and 12B are formed on mutually opposing surfaces of 11B.

The stacked body of these first and second liquid crystal cells 20.10 is.

It is sandwiched between polarizing plates 15 and 25.

Image display is performed by driving the display electrode of the first liquid crystal cell 20 by applying a voltage and using light transmitted from the polarizing plate 25 side to the polarizing plate 15 side.

FIG. 2 shows the preferential alignment direction of liquid crystal.

In the first liquid crystal cell 20, between the preferential alignment direction D1 of liquid crystal molecules on the glass substrate 21A and the preferential alignment direction D2 of the glass substrate 21B, the liquid crystal molecules of the liquid crystal layer 23 are ω□
It has a nine-screw structure.

In this way, ω is the torsion angle determined by the orientation treatment, and this orientation control can be achieved by conventionally known oblique deposition, but it is particularly performed by the rubbing method, in which an inorganic or organic film is formed and then rubbed with cotton cloth or the like. be able to.

The liquid crystal of the liquid crystal layer 23 is preferably a nematic liquid crystal with positive dielectric anisotropy, added with cholesteric liquid crystal or chiral nematic liquid crystal, and adjusted to an appropriate pitch. In this case, if ω is small, the steepness is low. This deteriorates the time-sharing characteristics.

If ω is too large, a scattering structure will occur when an electric field is applied, causing a decline in the quality of the displayed image.

Therefore, ω needs to be greater than or equal to 120 degrees and less than or equal to 360 degrees.

In FIG. 2, the twist direction is configured to be counterclockwise from the substrate 21A to the substrate 21B, but it can also be twisted clockwise depending on the orientation treatment direction and selection of cholesteric liquid crystal or chiral nematic liquid crystal.

Similarly, as shown in FIG. 2, in the second liquid crystal cell 10, the preferential alignment direction D3 of the liquid crystal molecules of the liquid crystal fi 13 on the transparent substrate 11A, the preferential alignment direction D3 on the transparent substrate 11B, In between, the liquid crystal has a twisted structure by ω2.

The alignment treatment of the liquid crystal layer 13 of the second liquid crystal cell 10 is performed using the liquid crystal [
Although a method similar to the orientation treatment of No. 23 can be used,
The liquid crystal 13, which does not necessarily need to be aligned in the same manner as the liquid crystal layer 23, is preferably a smectic liquid crystal, a nematic liquid crystal, or a nematic liquid crystal to which cholesteric liquid crystal or chiral nematic liquid crystal is added.

In the second liquid crystal cell 10. Two transparent substrates 11A
The transparent substrate 11 on the liquid crystal cell 20 side of the JIB
A is optically isotropic, and the transparent substrate 11B is an optically anisotropic plastic film.

[Function] In such a configuration, when light that enters the first liquid crystal cell 20 from the polarizing plate 25 side passes through the liquid crystal layer 23, the light has an ellipticity and an azimuth that differ depending on its wavelength. It becomes elliptically polarized light.

This elliptically polarized light is returned to linearly polarized light or elliptically polarized light approximated by linearly polarized light by the liquid crystal layer 13.

By passing the linearly polarized light through a polarizing plate 15 arranged parallel to or perpendicular to the linearly polarized light, the background color of the display when no voltage is applied is set to white or black, respectively.

In order to obtain a display element that is capable of black-and-white display, has excellent display quality, and has little color unevenness using such a display principle, the liquid crystal birefringence of the liquid crystal layer 23 should be Δn1, the layer thickness should be d, and the liquid crystal layer 23 should have a birefringence of Δn1, a layer thickness of d, and When the liquid crystal birefringence at 1!113 is Δn7 and the layer thickness is d2.

1Δn, dl−Δn*dz l≦0.6p m, (Δnl a!−Δn2d2)
This is because when the distance is +0.6 μm or more, the displayed image is colored in the order of blue, green, and orange, and the same coloring occurs even when the distance exceeds −0.6 μm.

The relationship between the above values of 1Δn, d, -Δnxdx I and the background color of the display image of the liquid crystal display element is shown in the following table.

Table 1Δn1dl−Δn*dm! Cμm) Background color 1.2 Orange 1.0 Green 0.8 Blue-green 0.7 Blue 0.6 Navy 0.5 Black 0.4 Beige 0.3 Beige 0.2 White 0.1 White O, O White This The table shows that when the angle between the polarizing plate transmission axis and the liquid crystal alignment direction in the substrate 21A is β1, and the angle between the polarizing plate transmission axis and the liquid crystal alignment direction in the transparent substrate 11A is β2, these are β□=β, 245 degrees and the twist angles ω2 and ω are both 180 degrees, but one of the polarizing plates is 90 degrees.
When rotated by degrees, the colors become complementary tones.

In FIG. 2, δ is the angle between the preferential alignment direction D of the liquid crystal 23 on the substrate 21B side and the preferential alignment direction of the liquid crystal 13 on the transparent substrate 11A side. is liquid crystal [2
When the direction of twist in No. 3 is positive, it is preferably 60 degrees or more and 120 degrees or less, or -120 degrees or more and -60 degrees or less.

The liquid crystal layer 13 has been described as having a twist of ω in FIG. Orientation is fine, but liquid crystal layer 13
It is preferable that the twist direction is opposite to the twist direction of the liquid crystal layer 23, and the twist angle is 0 degrees or more and 72 degrees.
The twist angle is preferably 0 degrees or less, and more preferably 120 degrees or more and 360 degrees or less.

Further, it is preferable that Δn, d be in the range of 0.4 to 1.3 μm, because if this range is exceeded, the contrast will deteriorate.

By satisfying the above conditions, the background color of the display can be set to black or a color close to this, or white or a color close to this. Also, when the background color is black or a color close to black, the image part to which voltage is applied becomes white or a color close to this, and when the background color is white or a color close to this, it becomes black or a color close to this. , substantially black and white display is possible.

Further, the steepness of the voltage transmittance characteristic is 1.05 or less, similar to the conventional STN type liquid crystal display element, and has excellent time division characteristics.

Now, one feature of the present invention is that among the two transparent substrates 11A and IIB in the second liquid crystal cell 10, the transparent substrate 11A on the first liquid crystal cell 20 side is optically isotropic. The transparent substrate 11B is an optically anisotropic plastic film.

When the transparent substrate 11A is isotropic, the first liquid crystal cell 2
The elliptically polarized light due to 0 enters the liquid crystal layer 13 without being affected by the polarization state by the transparent substrate 11A, and the elliptically polarized light from the liquid crystal layer 1
3, linear polarization is achieved better.

However, if the transparent substrate 11A is optically anisotropic, the polarization state of the elliptically polarized light incident from the first liquid crystal cell 20 will be changed by the transparent substrate 11A.

The elliptical polarization characteristics of the light incident on the liquid crystal layer 13 are different from the elliptical polarization characteristics of the first liquid crystal cell 10. For this reason, the linear polarization function of the liquid crystal layer 13 is not fully exhibited, and the displayed color becomes a slightly pale black.

Further, the reason why an optically anisotropic substrate is used as the transparent substrate 11B is that it has been found that the viewing angle characteristics are widened due to the refractive index anisotropy of the transparent substrate 11B.

If an optically isotropic substrate is used as the transparent substrate 11B, the image or background will be colored when the displayed image is viewed from an oblique direction. However, if an optically anisotropic material is used for the transparent substrate 11B as in the present invention, the above-mentioned coloring will not occur even when the displayed image is viewed from an oblique direction, and the viewing angle will be substantially widened.

As the light-transmitting substrate 11A, glass, a non-stretched plastic film such as polyether sulfone, polycarbonate, acrylic resin, or polyarylate film can be used.

Further, as the transparent substrate 11B, a plastic film is used, and a typical example is a uniaxially stretched polyester film.

Furthermore, the polarizing plate 15 and the light-transmitting substrate 11B can be integrated using a polarizing plate-integrated plastic film in which a -axis stretched polyester film has a polarizing function.

[Effects of the Invention] As described above, according to the present invention, a novel optically compensated liquid crystal display element can be provided.

In this element, among the transparent substrates of the second liquid crystal cell, the one on the side of the first liquid crystal cell is optically isotropic.
Coloring of the displayed image can be effectively prevented, and since the other transparent substrate is optically anisotropic, a wide viewing angle can be achieved.

Furthermore, since the optically anisotropic light-transmitting substrate is a plastic film, the thickness of the element can be effectively controlled, and a high-quality display image can be obtained without the floating feeling of the displayed image.

Furthermore, by using plastic film, the device can be realized at low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing one embodiment of the present invention.
FIG. 2 is a diagram for explaining the twist angle of liquid crystal in a second liquid crystal cell.

Claims (1)

[Claims] It is sandwiched between two optically transparent substrates having display electrodes, is oriented substantially parallel to each of the substrates, and has a diameter of 120 mm in the thickness direction.
a first liquid crystal cell having a first liquid crystal layer having a twisted structure of not less than 360 degrees and exhibiting positive dielectric anisotropy, two transparent substrates, and these transparent substrates; a second liquid crystal cell having a second liquid crystal layer sandwiched between the substrates and oriented substantially parallel to each light-transmitting substrate; of liquid crystal cells are stacked, and these first
, a liquid crystal display element having a structure in which a stacked body of a second liquid crystal cell is sandwiched between two polarizing plates, the liquid crystal birefringence of the first liquid crystal layer being Δn_1, the layer thickness being d_1, The liquid crystal birefringence in the second liquid crystal layer is Δn
_2. When the layer thickness is d_2, it should be set so that |Δn_1d_1−Δn_2d_2|≦0.6 μm, and of the two transparent substrates of the second liquid crystal cell, the one on the side of the first liquid crystal cell An optically compensated liquid crystal display element, characterized in that a substantially optically isotropic substrate is used as a light-transmitting substrate, and a flexible film having optical anisotropy is used as the other light-transmitting substrate.