JPH07128659A - Liquid crystal display element formed by using optical anisotropic element - Google Patents

Abstract

PURPOSE:To improve a display contrast, gradation characteristic and visual characteristic of display colors without degrading the front surface contrast by allowing at least >=2 regions varying in orientation states of liquid crystal molecules to exist in a liquid crystal cell and using at least one sheet of optically anisotropic elements between two sheets of polarizing elements. CONSTITUTION:This liquid crystal display element consists of the liquid crystal cell formed by holding a liquid crystal between two sheets of electrode substrates and two sheets of the polarizing elements arranged on both sides thereof and is constituted by allowing the >=2 regions varying in the orientation state of the liquid crystal molecules to exist in the liquid crystal cell and using at least one sheet of the optically anisotropic elements between two sheets of the polarizing elements. The optical axes of the optically anisotropic elements are so determined as to exist in the normal direction of the film. The relation between the refractive indices nx, ny orthogonal with each other existing within the film plane of such optically anisotropic elements and the curving rate nz in the normal direction of the film is so set as to be nx=ny>nz.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using an optical anisotropic element capable of improving display contrast, gradation characteristics and viewing angle characteristics of display colors.

[0002]

2. Description of the Related Art CRTs, which are the mainstream of display devices for OA equipment such as Japanese word processors and desktop personal computers
Have been converted into liquid crystal display elements which have the great advantages of thinness, light weight, and low power consumption. Most of the liquid crystal display elements (hereinafter, referred to as LCDs) that are currently popular use twisted nematic liquid crystals. The display method using such a liquid crystal can be roughly classified into a birefringence mode and an optical rotation mode.

An LCD using a birefringence mode has a twisted angle of 90 ° or more in the alignment of liquid crystal molecules and has steep electro-optical characteristics. Therefore, a simple matrix without active elements (thin film transistor or diode). A large-capacity display can be obtained by time-division driving even with a striped electrode structure. However, the response speed is slow (hundreds of milliseconds), and it is difficult to display the gradation,
It has a drawback that the viewing angle characteristics are remarkably poor, and it does not exceed the display performance of liquid crystal display devices (TFT-LCD, MIM-LCD, etc.) using active elements.

For the TFT-LCD and MIM-LCD, a rotation mode display system (TN type liquid crystal display element) in which the alignment state of liquid crystal molecules is twisted by about 90 ° is used. This display method is the most effective method as compared with other LCDs because it has a high response speed (several + milliseconds), can easily obtain a black and white display, and has a high display contrast. However, since the twisted nematic liquid crystal is used, there is a problem in the viewing angle characteristics that the display color and the display contrast are changed depending on the viewing direction due to the principle of the display method.
The display performance of T is exceeded.

As seen in SID '92 Digest, page 798, etc., there has been proposed a method of compensating the viewing angle characteristic by dividing a pixel and inverting the tilt directions when a voltage is applied. According to this method, the viewing angle characteristics relating to the gradation inversion in the vertical direction are improved, but the viewing angle characteristics of the contrast are hardly improved.

Further, as seen in JP-A-4-229828 and JP-A-4-258923, a viewing angle is enlarged by disposing a retardation film between a pair of polarizing films and a TN liquid crystal cell. A method of trying is proposed.

The retardation film proposed in the above patent publication has a retardation of almost zero in the direction perpendicular to the surface of the liquid crystal cell, does not exert any optical action from the front and tilts. When the liquid crystal cell has a retardation, the retardation is manifested in the liquid crystal cell. However, even with these methods, the viewing angle of LCD is still insufficient, and further improvement is desired. In particular, when considered as a vehicle-mounted type or as a substitute for a CRT, the current viewing angle cannot cope with the situation.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a liquid crystal display element using an optical anisotropic element capable of improving display contrast, gradation characteristics and viewing angle characteristics of display color without lowering front contrast. It is provided.

[0009]

The above-mentioned objects have been achieved by the following means. (1) In a liquid crystal display element composed of a liquid crystal cell in which a liquid crystal is sandwiched between two electrode substrates and two polarizing elements arranged on both sides of the liquid crystal cell, the liquid crystal cells have different alignment states of liquid crystal molecules. A liquid crystal display device comprising two or more regions and using at least one optically anisotropic element between two polarizing elements. (2) The liquid crystal display element according to the above (1), wherein the optical axis of the optically anisotropic element is in the film normal direction. (3) The relation between the refractive indices nx and ny orthogonal to each other in the film plane of the optically anisotropic element and the refractive index nz in the film normal direction is nx = ny> nz. 2) The liquid crystal display element described. (4) The liquid crystal display element according to the above (3), wherein the optical anisotropic element has a retardation in light of 632.8 nm of 50 nm to 1000 nm.

The operation of the present invention will be described below with reference to the drawings, taking a TN type liquid crystal display device as an example. 1 and 2 show the polarization state of light propagating in the liquid crystal cell when a voltage higher than the threshold voltage is applied to the liquid crystal cell, and show a bright state when no voltage is applied. . FIG. 1 is a diagram showing a polarization state of light when light is vertically incident on a liquid crystal cell. When the natural light L0 is vertically incident on the polarizing film A having the polarization axis PA, the light transmitted through the polarizing film A is linearly polarized light L.
It becomes 1.

LC in the figure is a schematic representation of one liquid crystal molecule model showing the alignment state of liquid crystal molecules when a sufficient voltage is applied to the TN liquid crystal cell. When the molecular long axis of the liquid crystal molecule LC in the liquid crystal cell is parallel to the light path L1, there is no difference in the refractive index on the incident surface (in the plane perpendicular to the light path), and the light propagates in the liquid crystal cell. There is no phase difference between ordinary light and extraordinary light, and the linearly polarized light L1 propagates as it is when it passes through the liquid crystal cell. The polarization axis PB of the polarization film B is the polarization axis P of the polarization film A.
When set to be perpendicular to A, the light L2 that has passed through the liquid crystal cell cannot pass through the polarizing film and is in a dark state.

FIG. 2 is a diagram showing a polarization state of light when the light obliquely enters the liquid crystal cell. Natural light of incident light L
When 0 is obliquely incident, the polarized light L transmitted through the polarizing film A
1 becomes almost linearly polarized light. (In the actual case, it becomes elliptically polarized light due to the characteristics of the polarizing film). In this case, a difference in refractive index occurs on the incident surface of the liquid crystal cell due to the anisotropy of the refractive index of the liquid crystal,
The light L2 that passes through the liquid crystal cell becomes elliptically polarized light and the polarizing film B
Through. The transmission of light in such an oblique incidence undesirably lowers the contrast.

The present invention is intended to prevent such a decrease in contrast due to oblique incidence, improve viewing angle characteristics, and at the same time improve front contrast.

It is presumed as follows that the viewing angle characteristics of the liquid crystal display device were significantly improved by the present invention. Most TN-LCDs adopt a normal white mode. In this mode, the transmittance of light from the black display portion remarkably increases as the viewing angle is increased, resulting in a sharp decrease in contrast. The black display is the state when a voltage is applied, but at this time, the TN cell can be regarded as a positive uniaxial optical anisotropic body in which the optical axis is slightly tilted from the direction normal to the surface of the cell. This slight tilt of the optical axis not only causes birefringence even in front of the cell, but also causes significant asymmetry of the viewing angle in the vertical direction of the cell, that is, in the principal viewing angle direction, which significantly impairs the viewing angle in either one or both directions become. This is in agreement with the actual phenomenon.

In order to eliminate the asymmetry of the vertical viewing angle due to the inclination of the optical axis of the liquid crystal, one pixel is divided into two or more regions, and the optical axis of the liquid crystal is divided in the divided regions. A method in which the orientation state is changed so that the tilt directions are different so that the birefringence from the front disappears as a whole (hereinafter, orientation division method) is very effective. Since the asymmetry of the alignment state of the liquid crystal is improved, the vertical viewing angle becomes symmetric.

However, the viewing angle characteristic of contrast is hardly improved by this method alone. This is because although the birefringence from the front is eliminated by the orientation division method, the birefringence appears from an oblique view. In order to compensate for this birefringence from an oblique direction, it is suitable to use a negative uniaxial optical anisotropic body as shown in FIG. The direction of the optical axis of this negative uniaxial optically anisotropic body is the film normal direction.

As described above, by combining the orientation division method and the negative uniaxial optical anisotropic body, the viewing angle characteristics of the TN liquid crystal cell can be greatly improved.

In the present invention, the liquid crystal cell has two or more regions having different alignment states of liquid crystal molecules. It is preferable to divide one pixel into two or more regions and change the alignment state of liquid crystal molecules between the regions. In the present invention, the method of changing the alignment state of the liquid crystal molecules between the regions is not particularly limited, but the method of changing the rubbing direction substantially, the method of changing the voltage applied to each region, the applied electric field There is a method to change the direction.

The optically anisotropic element used in the present invention is preferably an optically negative uniaxial optically anisotropic element. The term “optically negative uniaxial” means that there is only one optical axis in which birefringence does not occur and the refractive index in the optical axis direction is smaller than the refractive index in the direction orthogonal to the optical axis. . The optical anisotropic element used in the present invention preferably has an optical axis substantially in the film normal direction.

The main refractive index perpendicular to each other in the film plane of the optical anisotropic element used in the present invention is nx and ny, the main refractive index in the film normal direction is nz, and the thickness of the optical anisotropic element is Where d is the retardation in the present invention, in the light of wavelength 632.8 nm, (nx
−nz) × d.

63 of the optical anisotropic element used in the present invention
Retardation in light of 2.8 nm is 50 nm to
It is preferably 1000 nm. Furthermore, 50 nm
It is preferably ˜600 nm.

The optical anisotropic element in the present invention is provided as a polymer film, a plate-like material, or a coating film on another support. The light transmittance of the optically anisotropic element is preferably 80% or more, more preferably 90% or more.

The polymer material used for the optical anisotropic element in the present invention is not particularly limited, but is preferably polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyvinyl. Alcohol, polyamide, polyimide,
Polyolefin, polyvinyl chloride, cellulosic polymer, polyacrylonitrile, polystyrene, polymethylmethacrylate, trade name Zeonex 280, which is a polyolefin material manufactured by Nippon Zeon, and a binary system,
Ternary polymers, various polymers, graft copolymers, blends and the like are preferably used. Further, a sheet in which a low molecular liquid crystal having positive or negative intrinsic birefringence is dispersed in a polymer matrix may be used.

A photoisomerizable substance may be used as the optically anisotropic substance in the present invention. What is a photoisomerizable substance?
It causes stereoisomerization or structural isomerization by light, and preferably causes reverse isomerization by light or heat of another wavelength. Examples of these compounds include azobenzene compounds, benzaldoxime compounds, azomethine compounds, stilbene compounds, spiropyran compounds, spirooxazine compounds, fulgide compounds, diaryl ethene compounds, cinnamic acid compounds, Examples thereof include retinal compounds and hemithioindigo compounds. These photoisomerizable substances may be monomers or polymers, and in the case of a polymer, the photoisomerizable group may be in the main chain or the side chain.

Further, as the optically anisotropic substance in the present invention, a liquid crystal compound or a compound capable of forming a liquid crystal may be used.

A detailed description will be given below with reference to embodiments.

【Example】

Comparative Example 1 A polyimide alignment film is coated on a glass substrate provided with a TFT array and a glass substrate facing the glass substrate, and each glass substrate is rubbed only once. These glass substrates are washed, printed with a sealant, sprayed with a gap agent to make a gap of 4.8 μm, and then two glass substrates are laminated so that the rubbing directions are orthogonal to each other and heated to give a sealant. Cure. Injecting liquid crystal under vacuum, 9
A TN type liquid crystal cell with 0 ° twist alignment is formed.

Polarizing films are attached to both surfaces of this TN type liquid crystal cell. The direction of the transmission axis of the polarizing film is set to be the same as the rubbing direction of the adjacent glass substrate, and the transmission axes of the two polarizing films are made orthogonal to each other to form a normally white mode TN type liquid crystal display element.

A rectangular wave voltage of 55 Hz was applied to this TN type liquid crystal display device, and the relationship between the transmittance from the front and the voltage was measured using LCD-5000 manufactured by Otsuka Electronics. The result is shown in FIG. Here, the light transmittance in the state where no voltage is applied is set to 100%. Using LCD-5000,
Measure the light transmittance when the voltage is 0V and 5V, and measure 0V / 5
The viewing angle characteristics of V contrast were evaluated. FIG. 5 shows iso-contrast lines connecting the points where the contrast is 10. The center of the drawing corresponds to the front direction, and the upper, lower, left and right sides of the drawing correspond to the upper, lower, left and right directions, respectively. The concentric circles from the center are tilt angles from the front in the order of 20 °, 40 °, 60 from the inside.
Corresponds to °.

Comparative Example 2 A polyimide alignment film is coated on a glass substrate provided with a TFT array and a glass substrate facing the glass substrate, and a rubbing process is performed in the process shown in FIG. First, a resist pattern is formed in a half area of one pixel on a substrate that has been subjected to a normal rubbing process in the rubbing 1 step. afterwards,
In the step of rubbing 2, rubbing treatment is performed in the direction opposite to that of rubbing 1. Finally, the resist is peeled off. In this way, one pixel is divided into two regions whose rubbing directions are opposite.

The glass substrate thus obtained is washed, a sealant is printed, a gap agent is dispersed, and the gap is set to 4.
After the thickness is set to 8 μm, the two glass substrates are laminated so that the rubbing direction is as shown in FIG. 7, and heated to cure the sealant. Liquid crystal is injected under vacuum, 90 in each area
A twisted alignment division type TN liquid crystal cell is formed.

Polarizing films are attached to both surfaces of this TN type liquid crystal cell. The direction of the transmission axis of the polarizing film is the same as the rubbing direction of the adjacent glass substrate, and the transmission axes of the two polarizing films are made orthogonal to each other to form a normally white mode alignment division type TN liquid crystal display element. .

The relationship between the transmittance and the voltage from the front of this TN type liquid crystal display element was the same as in FIG. This liquid crystal display element was evaluated for viewing angle characteristics in the same manner as in Comparative Example 1. The result is shown in FIG.

Example 1 Polycarbonate having a molecular weight of 120,000 obtained by condensation of phosgene and bisphenol A was dissolved in methylene dichloride to prepare an 18% solution. This was cast on a steel drum and continuously stripped and dried to obtain a film having a thickness of 60 μm. This film was measured for retardation from the front at a wavelength of 632.8 nm with an ellipsometer AEP-100 manufactured by Shimadzu Corporation to be 85 nm.
Met. This is probably due to the tension when the film was stripped from the steel drum.

When the film was heat relaxed in an atmosphere of 190 ° C. for 1 hour, the retardation from the front became almost zero. This film was longitudinally uniaxially stretched under a stretching condition of 180 ° C. Then, this film was stretched in a transverse direction by tenter under a stretching condition of 180 ° C. to obtain a biaxially stretched film.

N of the optically anisotropic element thus obtained
Evaluation of x, ny, and nz was performed using an ellipsometer AEP-100 manufactured by Shimadzu Corporation. As a result, nx = 1.
584, ny = 1.584, nz = 1.579,
It became nx = nz> ny. Retardation (nx-
nz) × d was 300 nm. Further, the retardation from the front was 0, and it was confirmed that the optical axis was in the normal direction to the film.

This optical anisotropic element was attached to the upper substrate of the split orientation type TN type liquid crystal cell prepared in Comparative Example 2, and polarizing films were attached to both sides of this TN type liquid crystal cell. The direction of the transmission axis of the polarizing film is the same as the rubbing direction of the adjacent glass substrate, and the transmission axes of the two polarizing films are orthogonal to each other.
A normally white mode alignment division type TN liquid crystal display device was formed.

The relationship between the transmittance and the voltage from the front of this TN type liquid crystal display element was the same as in FIG. This liquid crystal display element was evaluated for viewing angle characteristics in the same manner as in Comparative Example 1. The result is shown in FIG.

Example 2 In the same manner as in Example 1, a polycarbonate film having a thickness of 60 μm and a retardation from the front of 0 was obtained.
This film was stretched in the machine direction and the transverse direction under a stretching condition of 180 ° C. to obtain a biaxially stretched film.

N of the optically anisotropic element thus obtained
x, ny, and nz are nx = 1.583 and ny = 1.58.
3, nz = 1.580, and nx = nz> ny. Retardation (nx-nz) × d is 180 nm
Met. Further, the retardation from the front was 0, and it was confirmed that the optical axis was in the normal direction to the film.

This optical anisotropic element was attached to both sides of the split orientation type TN type liquid crystal cell prepared in Comparative Example 2, and further,
A polarizing film was attached to the outside. The direction of the transmission axis of the polarizing film was the same as the rubbing direction of the adjacent glass substrate, and the transmission axes of the two polarizing films were made orthogonal to each other to form a normally white mode alignment division type TN liquid crystal display element. .

The relationship between the transmittance and the voltage from the front of this TN type liquid crystal display device was the same as that in FIG. This liquid crystal display element was evaluated for viewing angle characteristics in the same manner as in Comparative Example 1. The result is shown in FIG.

From FIGS. 5, 8, 9 and 10, it can be seen that in Examples 1 and 2 of the present invention, the contrast spreads uniformly in all directions and the viewing angle characteristics are excellent.

[0043]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a liquid crystal display device of high quality display in which the viewing angle characteristics of the liquid crystal display device are improved and which is excellent in visibility. In addition, the present invention is applicable to STN
It goes without saying that excellent effects can be obtained even when applied to a simple matrix liquid crystal display element such as an LCD.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of a conventional TN type liquid crystal display element and a diagram illustrating a light transmission state when light is perpendicularly incident on a display surface.

FIG. 2 is a diagram illustrating a configuration of a conventional TN type liquid crystal display element and a light transmission state when light obliquely enters a display surface.

FIG. 3 is a diagram illustrating an example of a main refractive index of an optically anisotropic element used in the present invention.

FIG. 4 shows Example 1, Example 2, Comparative Example 1 and Comparative Example 2.
FIG. 3 is a diagram for explaining the relationship between the light transmittance from the front of the TN type liquid crystal display element and the voltage.

FIG. 5 is a diagram illustrating viewing angles in all directions with a contrast of 10 as a reference in the TN type liquid crystal display element of Comparative Example 1.

FIG. 6 is a diagram illustrating a rubbing process of TN type liquid crystal display devices of Example 1, Example 2 and Comparative Example 2.

FIG. 7 is a diagram illustrating rubbing directions of TN type liquid crystal display devices of Example 1, Example 2 and Comparative Example 2.

FIG. 8 is a diagram illustrating a viewing angle in all directions with a contrast of 10 as a reference of the TN type liquid crystal display element of Comparative Example 2;

FIG. 9 is a diagram illustrating viewing angles in all directions with a contrast of 10 as a reference of the TN type liquid crystal display element of Example 1.

FIG. 10 is a diagram illustrating an azimuth viewing angle with respect to contrast 10 of the TN type liquid crystal display element of Example 2;

[Explanation of symbols]

 A Polarizing film B Polarizing film PA Polarizing axis PB Polarizing axis L0 Incident light L1 Linearly polarized light that passed through the polarizing film A L2 Polarized light that passed through the TN liquid crystal cell (mainly elliptically polarized light) LC Liquid crystal in the TN liquid crystal cell was explained. thing

Claims (4)

[Claims] 1. A liquid crystal display device comprising a liquid crystal cell in which a liquid crystal is sandwiched between two electrode substrates and two polarizing elements arranged on both sides of the liquid crystal cell, wherein the alignment state of liquid crystal molecules in the liquid crystal cell. 2. A liquid crystal display element, characterized in that there are two or more regions different from each other and at least one optical anisotropic element is used between two polarizing elements. 2. The liquid crystal display element according to claim 1, wherein an optical axis of the optically anisotropic element is in a film normal direction. 3. The relationship between the refractive indices nx and ny orthogonal to each other in the film plane of the optically anisotropic element and the refractive index nz in the film normal direction is nx = ny> nz. The liquid crystal display device according to claim 2. 4. The liquid crystal display element according to claim 3, wherein the optical anisotropic element has a retardation in light of 632.8 nm of 50 nm to 1000 nm.