JPH05257138A - Two-layer type liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the visual angle characteristic at the time of not impressing a voltage to two pieces of liquid crystal cells without sacrificing the good characteristics at the time of impressing the voltage thereto by constituting the display device in such a manner that the inclination directions of liquid crystal molecules are opposite from each other when the voltage is impressed to the above-mentioned liquid crystal cells. CONSTITUTION:The inclination direction of the liquid crystal molecules when the voltage is impressed to the first liquid crystal 2 and the inclination direction of the liquid crystal molecules when the voltage is impressed to the second liquid crystal cell 3 are opposite from each other. The optical phase compensating films 40 which are laminated on this liquid crystal cell part 10 and are regarded to be optically negative uniaxial crystals improve the visual angle characteristics when the voltage is not impressed. The constitution of the substrate of the first liquid crystal cell 2 or the second liquid crystal 3 of the optical phase compensating film 40 which is regarded to be optically negative uniaxial crystal is possible as well. Further, the visual angle characteristic at the time of not impressing the voltage to the cells can also be improved by intersecting the optical axes of one set of the optically positive uniaxial crystals with each other with respect to the liquid crystal cell part 10 and laminating these crystals in such a manner that the optical axes thereof and the substrates of the liquid crystal cells parallel with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-layer liquid crystal display device, and in particular, when a voltage is applied to two liquid crystal cells, the tilt directions of liquid crystal molecules are opposite to each other, and The present invention relates to a two-layer type liquid crystal display device capable of improving viewing angle characteristics when no voltage is applied without sacrificing good characteristics when a voltage is applied, by stacking a dynamic phase compensation means.

[0002]

2. Description of the Related Art A liquid crystal having a negative dielectric anisotropy is used,
Liquid crystal display (EC
B liquid crystal display) can display completely black in the crossed Nicols and white in the parallel Nicols when no voltage is applied, so that the contrast can be increased and the threshold characteristics are sharp and gradation display is possible. Is also possible,
It is suitable for simple matrix full-color liquid crystal displays. However, an ECB having such high characteristics
Liquid crystal displays have not been put into practical use at the moment because they have the problems that it is difficult to obtain the molecular orientation of liquid crystal slightly tilted from the vertical and that the viewing angle dependence of the optical properties is large. ..

Regarding the method of aligning liquid crystal molecules slightly tilted from the vertical, the applicant of the present invention has proposed a method that can be easily realized by using a rubbing method. Furthermore, regarding the viewing angle dependence of optical characteristics when a voltage is applied, , A method of improving the ECB liquid crystal cell by stacking two layers so that the tilt directions of the liquid crystal molecules are opposite to each other when a voltage is applied.

[0004]

However, no improvement has been made to the viewing angle characteristics when no voltage is applied, and the viewing angle when no voltage is applied is not sacrificed without sacrificing good characteristics when a voltage is applied. EC that can improve characteristics
Realization of B liquid crystal cell was strongly desired.

[0005]

The present invention has been devised in view of the above problems, and is a two-layer liquid crystal display having a liquid crystal cell portion composed of a first liquid crystal cell and a second liquid crystal cell. , The tilt direction of the liquid crystal molecules enclosed in the first liquid crystal cell when a voltage is applied, and the second direction when a voltage is applied.
The optical phase compensating means is configured such that the tilt directions of the liquid crystal molecules enclosed in the liquid crystal cell are opposite to each other, and the liquid crystal cell section is regarded as an optically negative uniaxial crystal. Are stacked.

Further, the present invention is a two-layer type liquid crystal display having a liquid crystal cell portion comprising a first liquid crystal cell and a second liquid crystal cell, which is enclosed in the first liquid crystal cell when a voltage is applied. The tilting direction of the liquid crystal molecules and the tilting direction of the liquid crystal molecules sealed in the second liquid crystal cell when a voltage is applied are configured to be opposite to each other. The substrate of the second liquid crystal cell is characterized in that it serves as an optical phase compensating means which is optically regarded as a negative uniaxial crystal.

Further, according to the present invention, there is provided a first liquid crystal cell comprising a first transparent substrate having a pair of electrodes facing each other and a first liquid crystal material enclosed between the transparent substrates, and a pair of electrodes facing each other. A second liquid crystal cell composed of the second transparent substrate and a second liquid crystal material enclosed between the transparent substrates, and an optical phase compensating means optically regarded as a negative uniaxial crystal. A phase compensation film, wherein the first and second liquid crystal materials are liquid crystals having a negative dielectric constant anisotropy, and the first and second liquid crystal materials are sealed in the first liquid crystal cell when a voltage is applied. A two-layer structure in which the tilt direction of the liquid crystal molecules and the tilt direction of the second liquid crystal molecules enclosed in the second liquid crystal cell when a voltage is applied are opposite to each other. Type liquid crystal display device.

The present invention is a two-layer type liquid crystal display having a liquid crystal cell section consisting of a first liquid crystal cell and a second liquid crystal cell, which is enclosed in the first liquid crystal cell when a voltage is applied. The tilting direction of the liquid crystal molecules and the tilting direction of the liquid crystal molecules sealed in the second liquid crystal cell when a voltage is applied are configured to be opposite to each other. The optical axes of a pair of optically positive uniaxial crystals are orthogonal to each other, and optical phase compensating means for laminating the optical axes and the substrate of the liquid crystal cell are laminated.

[0009]

According to the present invention constructed as above, the tilt direction of the liquid crystal molecules when a voltage is applied to the first liquid crystal cell and the tilt direction of the liquid crystal molecules when a voltage is applied to the second liquid crystal cell. And are opposite to each other, and the optical phase compensating means, which is laminated with respect to the liquid crystal cell section and is regarded as an optically negative uniaxial crystal, improves the viewing angle characteristics when no voltage is applied. It is supposed to do. Further, in the present invention, the substrate of the first liquid crystal cell or the second liquid crystal cell may be an optical phase compensating means which is optically regarded as a negative uniaxial crystal.

Further, according to the present invention, a first liquid crystal cell having a pair of electrodes facing each other and a liquid crystal material having a negative dielectric anisotropy is sealed between the transparent substrates to form a first liquid crystal cell. A second transparent substrate having a pair of electrodes facing each other and a liquid crystal material having negative dielectric anisotropy enclosed between the transparent substrates
Of the liquid crystal cell, the tilt direction of the first liquid crystal molecules enclosed in the first liquid crystal cell when a voltage is applied, and the second liquid crystal cell enclosed in the second liquid crystal cell when a voltage is applied. The liquid crystal molecules are tilted in mutually opposite directions, and the optical phase compensating film, which is an optical phase compensating means optically regarded as a negative uniaxial crystal, has a viewing angle characteristic when no voltage is applied. Is designed to improve.

According to the present invention, a pair of optically positive uniaxial crystals are made to have their optical axes orthogonal to each other with respect to the liquid crystal cell section, and these optical axes are parallel to the substrate of the liquid crystal cell. It is possible to improve the viewing angle characteristics when no voltage is applied by stacking the layers.

[0012]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the structure of a two-layer type ECB cell 1. The two-layer type ECB cell 1 includes a liquid crystal cell section 10, an optical phase compensation film 40, and polarizers 50, 50. There is. The liquid crystal cell unit 10 is composed of a first liquid crystal cell 2 and a second liquid crystal cell 3. The first liquid crystal cell is
This cell uses a liquid crystal having a negative dielectric anisotropy and utilizes an electric field control birefringence effect (ECB effect). The first liquid crystal cell 2 includes a pair of first transparent substrates 21 and 21 facing each other.
And the first transparent electrodes 22 and 22 formed on the first transparent substrates 21 and 21, and the first liquid crystal material 23. The first transparent substrates 21 and 21 are made of float glass or polyester film, but any material can be used as long as it has high transparency and a flat surface. The first transparent electrodes 22 and 22 are for applying a voltage to the first liquid crystal material 23, and include a NESA film and an IT.
Although an O film can be used, any electrode member can be used as long as it has high transparency and low electric resistance. An alignment layer is formed in the first liquid crystal cell 2, and the alignment layer is formed of an In ₂ O ₃ film or SiO.
Vertically vapor-deposited on transparent substrate 21 or organic Si0
It is possible to employ the one in which (OCD) is spin-coated on the first substrate 21. Further, a vertical aligning agent such as DMOAP is used and a tilted vertical alignment is realized by using a rubbing machine or the like. In this tilted vertical alignment treatment, a tilting angle of liquid crystal molecules can be adjusted by combining a rotating rubbing roller and a horizontal moving table and applying an appropriate weight to the rubbing roller. Further, not only the rubbing method but also the oblique vertical alignment treatment can be performed by the oblique vapor deposition method. In this embodiment, EN-38 manufactured by Chisso Corporation is used as the first liquid crystal material 23, but any liquid crystal material having negative dielectric anisotropy can be used.

Similarly, the second liquid crystal cell 3 has a pair of second transparent substrates 31 and 31 facing each other (however, in the present embodiment, one second transparent substrate 31 is also used as the first transparent substrate 21). ), The second transparent electrodes 32 and 32 formed on the second transparent substrates 31 and 31, and the second liquid crystal material 3
It consists of 3.

In this embodiment, one of the first transparent substrate 21 and one of the second transparent substrates 31 are common. In this specification, one transparent substrate is the first transparent substrate 2
It includes a configuration that doubles as the first and second transparent substrates 31.

The second liquid crystal cell 3 has the same structure as the first liquid crystal cell 2 and has substantially the same characteristics. However, the tilt directions of the liquid crystal molecules when the voltage is applied to the first liquid crystal cell 2 and the second liquid crystal cell 3 are opposite to each other.

Therefore, when a voltage is applied to the first liquid crystal cell 2 and the second liquid crystal cell 3, if the viewing angle is taken in the tilt direction of the liquid crystal molecules of the first liquid crystal cell 2, the first liquid crystal cell 2 has a large viewing angle. The birefringence becomes smaller as it gets closer. Second to this
The liquid crystal cell 3 has a viewing angle in the direction opposite to the tilt direction of the liquid crystal molecules, and the birefringence is increased. For this reason, when the first liquid crystal cell 2 and the second liquid crystal cell 3 are stacked,
Bilayer type ECB cell 1 in which the viewing angle dependence of birefringence is suppressed
Overall, the optical characteristics will be compensated.

On the side opposite to the tilt direction of the liquid crystal molecules of the first liquid crystal cell 2 when a voltage is applied, the birefringence increases in the first liquid crystal cell 2 as the viewing angle increases. On the other hand, the second liquid crystal cell 3 has a small birefringence. Therefore, also in this case, the viewing angle dependence of the optical characteristics is compensated.

In this embodiment, the optical phase compensation film 4 is added to the first liquid crystal cell 2 and the second liquid crystal cell 3.
0 is stacked. Further, the first liquid crystal cell 2, the second liquid crystal cell 3 and the optical phase compensation film 40 are sandwiched, and the polarizers 50, 50 are opposed to each other. The optical phase compensating film 40 corresponds to an optical phase compensating means which is optically regarded as a negative uniaxial crystal. In this embodiment, the optical phase compensation film 40 is laminated on the upper part of the first liquid crystal cell 2, but it may be laminated on the lower part of the second liquid crystal cell 3. That is, the optical phase compensation film 4
0 may be arranged on the incident side or the emitting side of the liquid crystal cell unit 10. This optical phase compensation film 40 is called a retardation plate, and is a stretched polymer film whose birefringence is controlled with high precision. That is, the optical phase compensation film 40 is formed by uniaxially stretching a polymer film. The retardation in the optical phase compensation film 40 is represented by the product of the orientation refractive index given in the film forming process and the film thickness d.

The polarizers 50, 50 are also called polarizing plates, and are for passing only the polarized light component (linear polarized light) in a specific direction from natural light including polarized light components in all directions. is there. The polarizing plates 50, 50 are
A polarizing film on a film obtained by impregnating a polyvinyl alcohol film stretched in one direction with iodine is used, but other types of polarizing films can also be used.

Here, the function of the optical phase compensation film 40 will be described. In the above-described embodiment, if the optical phase compensation film 40 is not used, in the two-layer ECB cell 1, liquid crystal molecules are aligned substantially perpendicular to the substrate in the initial state when no voltage is applied. In such a molecular orientation state of liquid crystal, which is a positive uniaxial crystal, the optical axis is substantially perpendicular to the substrate, and therefore a liquid crystal cell is sandwiched between orthogonal Nicols and observed from the normal direction of the substrate. Birefringence does not occur, and almost perfect black can be displayed. However, if you tilt your viewing angle,
There is a problem in that the light is transmitted from the direction deviated from the optical axis, which causes birefringence and allows light to pass therethrough. That is, when viewed from the normal direction of the ECB liquid crystal cell, black is displayed, but when the viewing angle is changed, a black display is not produced, and there is a problem that the contrast is reduced depending on the viewing angle.

In order to solve this problem, it is effective to stack a substance optically regarded as a negative uniaxial crystal in the liquid crystal cell section 10. That is, when the optical axis of the optical phase compensation film 40, which is optically regarded as a negative uniaxial crystal, is aligned with the normal direction of the liquid crystal cell unit 10, the viewing angle is taken in the normal direction of the liquid crystal cell unit 10. However, there is no optical effect. When light travels in the liquid crystal cell unit 10 with a tilted viewing angle, birefringence occurs, and the phase of ordinary light is delayed compared with the phase of extraordinary light to cause retardation, but the light enters the optical phase compensation film 40. Then, the phase of the extraordinary light is delayed from the phase of the ordinary light, which is opposite to the phase of the liquid crystal layer, so that the phases of the emitted light are aligned again, and retardation does not occur as a whole. Therefore, the display remains black even if the viewing angle is changed.

Here, the retardation is an amount showing the optical path difference between ordinary light and extraordinary light, and in the case of a parallel aligned liquid crystal cell, if the refractive index anisotropy of the liquid crystal is delta n and the cell thickness is d, the voltage is The retardation R when not applied can be expressed as R = delta nd.

Instead of the optical phase compensator which is regarded as an optically negative uniaxial crystal, a set of optically positive uniaxial crystals are laminated so that their optical axes are orthogonal to each other, and A set of optically positive uniaxial crystals may be laminated on the liquid crystal cell unit 10 so that the crystal optical axis is parallel to the liquid crystal cell unit 10.

Further, the optical phase compensation film 40 is used as the first
The transparent substrate 21 or the second transparent substrate 31 can also be used.

Next, a simulation by numerical calculation of this embodiment will be described.

In this simulation, the molecular orientation of liquid crystal molecules when a voltage is applied is determined by continuum theory, and then Be
It was decided to calculate the optical characteristics by the rreman 4 × 4 matrix method. The coordinates are defined as shown in FIG. The normal direction of the cell substrate is the z axis, and the viewing angle direction is the polar angle α and the azimuth angle β. The tilt direction of the liquid crystal molecules was β = 45 °. The polarizer is a crossed Nicol, and the polarization directions are aligned with the x and y directions. Further, as the physical constants of the liquid crystal used in the simulation, those shown in Table 1 were used in consideration of EN-38.

The optical phase compensation film 40 is assumed to be a negative uniaxial crystal whose absolute value of refractive index anisotropy is equal to that of liquid crystal, and is laminated on the liquid crystal cell unit 10 with its optical axis parallel to the z axis. And The wavelength of light used for calculation is 550 nm unless otherwise specified.

The results of this simulation are shown in FIGS. 3 to 7.

FIG. 3 shows a comparison of polar angle dependence of transmittance in order to show the effect of optical phase compensation in a two-layer type ECB cell when no voltage is applied. However, the azimuth angle β is 45 degrees. As shown in FIG. 3, when optical phase compensation is not performed, there is a phenomenon that light is transmitted as the polar angle increases. In comparison with this, it is understood that when optical phase compensation is performed, almost no light is transmitted even if the polar angle becomes large, and therefore the transmittance hardly has a viewing angle dependency.

The viewing angle dependence of the transmittance when a voltage is applied is shown in FIGS. 4 to 7. The applied voltage is such that the transmittance when viewed from the direction normal to the liquid crystal cell is maximized, that is, the voltage at which the retardation of the liquid crystal cell becomes ½ wavelength.

FIG. 4 shows the transmittance of the one-layer type and two-layer type ECB liquid crystal cells when optical phase compensation is performed when the viewing angle is the tilt direction of the liquid crystal molecules, that is, the azimuth angle β is 45 degrees. This shows the polar angle dependence of. As shown in FIG. 4, it is understood that in the one-layer type ECB liquid crystal cell (ECB cell), the optical characteristics when a voltage is applied greatly depends on the viewing angle even if optical phase compensation is performed when a voltage is not applied. It 2 compared to this
It is understood that the layered ECB liquid crystal cell (D-ECB cell) has a good viewing angle characteristic even if optical phase compensation is performed when no voltage is applied.

FIG. 5 shows a one-layer type and a two-layer type E when optical phase compensation is performed when the polar angle α is 20 degrees.
It shows the azimuth angle dependence of the transmittance of the CB liquid crystal cell. As shown in FIG. 5, the single-layer ECB liquid crystal cell (ECB cell) had a transmittance of 100% when viewed from the normal direction of the liquid crystal cell when a voltage was applied, but the transmittance was changed by changing the viewing angle. It is understood that the rates vary greatly. In comparison, it is understood that the two-layer ECB liquid crystal cell (D-ECB) exhibits good viewing angle characteristics even if optical phase compensation is performed.

FIGS. 6 and 7 show a one-layer type and a two-type, respectively.
When optical phase compensation is performed on the layered ECB liquid crystal cell,
The viewing angle is the direction in which the liquid crystal molecules are tilted, that is, the azimuth angle β is 45
As a degree, the polar angle dependence of the transmittance at each wavelength is calculated. Here, red, green and blue have wavelengths of 65
0, 550 and 450 nm. 1 as shown in FIG.
The optical phase compensation of the layered ECB liquid crystal cell decreases the transmittance and becomes dark when the viewing angle is increased in the direction in which the liquid crystal molecules are tilted, that is, the direction in which the polar angle is positive. On the contrary, when the viewing angle is increased in the direction opposite to the direction in which the liquid crystal molecules are tilted, that is, the direction in which the polar angle is negative, the difference in retardation between wavelengths becomes large, and thus a phenomenon in which coloring occurs may be observed. To be understood. Compared with this, the two-layer ECB liquid crystal cell, as shown in FIG. 7, shows little change in transmittance even if the polar angle changes, and the difference in retardation between wavelengths does not increase, so that almost no coloring occurs. It turns out that it does not occur.

[0034]

The present invention configured as described above is a two-layer type liquid crystal display having a liquid crystal cell portion composed of a first liquid crystal cell and a second liquid crystal cell, and the first layer when a voltage is applied. The tilting direction of the liquid crystal molecules sealed in the liquid crystal cell and the tilting direction of the liquid crystal molecules sealed in the second liquid crystal cell when a voltage is applied are configured to be opposite to each other. It has a structure in which optical phase compensation means, which is optically regarded as a negative uniaxial crystal, is laminated to the cell part, so that light does not pass through even if the viewing angle is changed when no voltage is applied, so that a good black color is obtained. Can be displayed, and there is an excellent effect that the contrast with the white state when a voltage is applied is increased. The present invention does not sacrifice the good viewing angle characteristics when a voltage is applied, which the two-layer ECB liquid crystal cell has, and therefore has the effect of achieving high contrast even when the viewing angle is changed. Therefore, the present invention in which optical phase compensation is performed has an outstanding effect that it can provide a liquid crystal display having extremely good viewing angle characteristics regardless of a voltage application state.

The present invention is a two-layer type liquid crystal display having a liquid crystal cell section consisting of a first liquid crystal cell and a second liquid crystal cell, which is enclosed in the first liquid crystal cell when a voltage is applied. The tilting direction of the liquid crystal molecules and the tilting direction of the liquid crystal molecules sealed in the second liquid crystal cell when a voltage is applied are configured to be opposite to each other. A set of optically positive uniaxial crystals having their optical axes orthogonal to each other and laminating optical phase compensating means for making these optical axes parallel to the substrate of the liquid crystal cell. Therefore, even if the optical phase compensation by the negative uniaxial crystal cannot be realized, the optical phase compensation can be realized by using the positive uniaxial crystal, and it is possible to provide a liquid crystal display having an excellent viewing angle characteristic. Has the effect that .

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a two-layer liquid crystal cell of this example.

FIG. 2 is a diagram illustrating the definition of coordinates.

FIG. 3 is a diagram showing polar angle dependence of transmittance when no voltage is applied.

FIG. 4 is a diagram showing polar angle dependence of transmittance when voltage is applied.

FIG. 5 is a diagram showing the azimuth angle dependence of the transmittance when a voltage is applied.

FIG. 6 is a diagram showing polar angle dependence of transmittance when a voltage is applied.

FIG. 7 is a diagram showing polar angle dependence of transmittance when a voltage is applied.

FIG. 8 is a diagram showing various physical constants used for calculation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Two-layer type ECB cell 2 ... 1st liquid crystal cell 3 ... 2nd liquid crystal cell 10 ... Liquid crystal cell part 40 ... Optical phase compensation film 50 ... Polarizer

Claims (4)

[Claims] 1. A two-layer liquid crystal display having a liquid crystal cell section composed of a first liquid crystal cell and a second liquid crystal cell, wherein liquid crystal molecules enclosed in the first liquid crystal cell when a voltage is applied. And the inclination direction of the liquid crystal molecules enclosed in the second liquid crystal cell when a voltage is applied are configured to be opposite to each other. A two-layer liquid crystal display device, wherein optical phase compensating means regarded as negative uniaxial crystal is laminated. 2. A two-layer type liquid crystal display having a liquid crystal cell section consisting of a first liquid crystal cell and a second liquid crystal cell, wherein liquid crystal molecules sealed in the first liquid crystal cell when a voltage is applied. And the liquid crystal molecules enclosed in the second liquid crystal cell when a voltage is applied are arranged so that the tilt directions are opposite to each other, and the first liquid crystal cell or the second liquid crystal is formed. A two-layer liquid crystal display device, wherein a substrate of the cell serves as an optical phase compensating means which is optically regarded as a negative uniaxial crystal. 3. A first liquid crystal cell composed of a first transparent substrate having a pair of electrodes facing each other and a first liquid crystal material enclosed between the transparent substrates, and a second liquid crystal cell having a pair of electrodes facing each other. Second liquid crystal cell consisting of the transparent substrate and the second liquid crystal material enclosed between the transparent substrates, and an optical phase compensating film which is an optical phase compensating means optically regarded as a negative uniaxial crystal. And the first and second liquid crystal materials are liquid crystals having a negative dielectric anisotropy, and the first liquid crystal molecules enclosed in the first liquid crystal cell when a voltage is applied are A two-layer liquid crystal display, characterized in that the tilt direction and the tilt direction of the second liquid crystal molecule enclosed in the second liquid crystal cell when a voltage is applied are opposite to each other. apparatus. 4. A two-layer type liquid crystal display having a liquid crystal cell section composed of a first liquid crystal cell and a second liquid crystal cell, wherein liquid crystal molecules sealed in the first liquid crystal cell when a voltage is applied. And the inclination direction of the liquid crystal molecules enclosed in the second liquid crystal cell when a voltage is applied are opposite to each other. Optically uniaxial crystals having optical axes orthogonal to each other and optical phase compensating means laminated such that these optical axes are parallel to the substrate of the liquid crystal cell are laminated. Type liquid crystal display device.