JPH0424613A - Two-layer type liquid crystal display device - Google Patents

Abstract

PURPOSE:To compensate the dependency of optical characteristics on visual angles at the time of impressing voltage by forming the above device in such a manner that the inclination direction of the liquid crystal molecules sealed into a 1st liquid crystal cell when impressed with a voltage and the inclination direction of the liquid crystal molecules sealed into a 2nd liquid crystal cell when impressed with a voltage are reversed from each other. CONSTITUTION:The inclination directions of the liquid crystal molecules when the voltages are impressed respectively to the 1st liquid crystal cell 2 and the 2nd liquid crystal cell 3 are reversed from each other. The double refractiveness, therefore, increases with an increase in the visual angle in the 1st liquid crystal cell 2 if the visual angle is taken in the inclination direction of the liquid crystal molecules of the 1st liquid crystal 2 at the time of impressing the voltages to the 1st liquid crystal cell 2 and the 2nd liquid crystal cell 3. The 2nd liquid crystal cell 3 eventually assumes the visual angle in the direction reverse from the inclination direction of the liquid crystal molecules and has the larger double refractiveness. The dependency of the double refractiveness on the visual angles is suppressed in this way when the 1st liquid crystal cell 2 and the 2nd liquid crystal cell 3 are laminated. The optical characteristics are compensated as the whole of the two-layer type ECB cell 1.

Description

DETAILED DESCRIPTION OF THE INVENTION "Pre-industrial use" The present invention relates to a two-layer liquid crystal display device, and in particular,
The present invention relates to a two-layer liquid crystal display device in which the tilt directions of liquid crystal molecules become opposite to each other when a voltage is applied to two liquid crystal cells, and the optical characteristics have little visual dependence.

``Prior art'' A liquid crystal display that uses a liquid crystal with negative dielectric anisotropy and utilizes the electric field controlled birefringence effect (ECB effect) is completely black when no electric field is applied when used in crossed Nicols. When used in parallel nicols, it can display white, has sharp contrast threshold characteristics, and can also display gradations, making it a simple matrix type full-color liquid crystal. Suitable for display devices.

However, liquid crystal display devices that utilize the ECB effect have problems in that it is difficult to easily realize liquid crystal molecular orientation slightly tilted from the vertical, and that viewing angle is highly dependent.

Liquid crystals are positive uniaxial crystals. Therefore, the reason why the angle dependence of ECB-type Devi display devices that employ liquid crystals with negative dielectric constant anisotropy is large is that when viewed from the normal direction of the liquid crystal cell when no voltage is applied, the optical axis of the liquid crystal molecules is Birefringence does not occur because the view is parallel to the , but when viewed from an oblique direction, the birefringence is raw, and even when no voltage is applied, light is transmitted when it is in crossed nicols, and it is parallel nicols. This is because at ζ the light becomes elliptically polarized and does not pass through completely, resulting in darkness.

Regarding the above-mentioned inclined vertical alignment, the present applicant has proposed a new alignment method using a rubbing method, and a simple processing method has been realized. In order to reduce the viewing angle dependence, an ECB type liquid crystal display device was developed which can compensate for the viewing angle dependence when no voltage is applied by using a polymer film having birefringence.

[Problems to be Solved by the Invention] However, the method of compensating for viewing angle dependence using a polymer film having birefringence as described above can compensate for viewing angle dependence when no voltage is applied, but when a voltage is applied, There was a problem in that it was not possible to compensate for the viewing angle dependence of the image.

This viewing angle dependence will be explained in detail based on FIG. As shown in FIG. 3, within the plane in which the liquid crystal molecules are tilted, the viewing angle is defined as positive in the direction in which the liquid crystal molecules are tilted, and negative in the opposite direction. Since the liquid crystal molecules tilt when voltage is applied, the refractive index ellipse when viewed from the Z-axis direction is shown in Figure 3(c).
As the visual angle increases in the positive direction, the
), up to the tilt angle of the liquid crystal molecules, the ellipticity of the refractive index ellipse becomes small and the birefringence becomes small.Also, when the tilt angle of the liquid crystal molecules matches the viewing angle, that is, the optical axis When the viewing angle matches that of , the refractive index ellipse degenerates into a circle as shown in Figure 3(e), and the liquid crystal molecules no longer exhibit birefringence.As the viewing angle increases further, Figure 3(f) , as shown in (g), the ellipticity of the refractive index ellipse increases again and the birefringence increases.For this reason, as the viewing angle increases in the direction in which the liquid crystal molecules are tilted, the ellipticity of the refractive index ellipse increases. When the angle of inclination of the liquid crystal molecules and the direction of the viewing angle match, a complete light shielding state occurs.9 When the viewing angle further increases, a phenomenon occurs in which the light gradually becomes brighter again.

If the viewing angle is taken in the direction opposite to the direction in which the liquid crystal molecules are tilted, the ellipticity of the refractive index ellipse increases, as shown in Figures 3 (b) and (a), and birefringence increases. . There is a problem in that the retardation of this licked cell increases, causing phenomena such as fluctuations in transmittance and coloring. Therefore, if the retardation is set to 1/2 wavelength when viewed from the normal direction of the substrate (that is, the voltage is applied so that the transmitted light intensity is maximized), the viewing angle is taken in the direction in which the liquid crystal molecules are tilted. and,
The retardation of the liquid crystal cell becomes smaller and becomes darker. Conversely, if the viewing angle is taken in the direction opposite to the direction in which the liquid crystal molecules are tilted, the birefringence of the liquid crystal cell becomes large, and the difference in retardation depending on the wavelength becomes large, resulting in a problem that the image appears colored.

"Means for solving the problem" The present invention was devised in view of the problem described in -F, and is a two-layer liquid crystal display consisting of a first liquid crystal cell and a second liquid crystal cell, and a voltage The tilt direction of the liquid crystal molecules sealed in the first liquid crystal cell when voltage is applied is opposite to the tilt direction of the liquid crystal molecules sealed in the second liquid crystal cell when voltage is applied. It is configured.

The present invention provides a first liquid crystal cell comprising a first transparent substrate having a pair of opposing electrodes and a first liquid crystal material sealed between the transparent substrates; A second liquid crystal cell includes a second transparent substrate and a second liquid crystal material sealed between the transparent substrates, and the first and second liquid crystal materials have negative dielectric anisotropy. The tilt direction of the first liquid crystal molecules sealed in the first liquid crystal cell when a voltage is applied, and the tilt direction of the second liquid crystal molecules sealed in the second liquid crystal cell when a voltage is applied. The directions of inclination are opposite to each other.

Further, in the present invention, the first liquid crystal cell and the second liquid crystal cell are
They can also be configured to have equal retardation.

"Operation" The present invention configured as described above has two functions: the tilt direction of liquid crystal molecules when voltage is applied to the first liquid crystal cell, and the tilt direction of liquid crystal molecules when voltage is applied to the second liquid crystal cell. and are opposite to each other.

Further, the present invention provides a first liquid crystal cell including a first transparent substrate having a pair of opposing electrodes and a liquid crystal material having negative dielectric constant anisotropy sealed between the transparent substrates; A second liquid crystal cell is constructed by sealing a liquid crystal material having negative dielectric constant anisotropy between a second transparent substrate having an electrode and the transparent substrate, and a first liquid crystal cell when a voltage is applied. The tilt direction of the first liquid crystal molecules sealed in the second liquid crystal cell is opposite to the tilt direction of the second liquid crystal molecules sealed in the second liquid crystal cell when a voltage is applied.

The present invention can speed up the response recovery time to 1/4 in a two-layer ECB cell that has the same characteristics as a single-layer ECB cell when viewed from the cell normal direction.

"Example" An embodiment of the present invention will be described based on the drawings.

FIG. 1 shows the configuration of a two-layer ECB cell 1.
The two-layer ECB cell 1 consists of a first liquid crystal cell 2 and a second liquid crystal cell 3. The first liquid crystal cell uses a liquid crystal with negative dielectric constant anisotropy, and uses an electric field controlled birefringence effect (E
This is a cell that utilizes the CB effect). The first liquid crystal cell 2 includes a pair of opposing first substrates 21.21 and a first transparent electrode 2 formed on the first transparent substrates 21.21.
2.22, a first alignment layer 23.23, and a first liquid crystal material 24. The first transparent substrate 21.21 is 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 electrode 22.22 is for applying voltage to the first liquid crystal material 24,
Although NESAM or ITO films can be used, any electrode member can be used as long as it has high transparency and low electrical resistance.9 The first alignment layer 23 is made of In
2O3 film or SiO is vertically deposited on the first transparent substrate 21, or organic SiO (OCD) is deposited on the first substrate 21.
It is possible to adopt a spin code, etc. Further, a vertical alignment agent such as DMOAP is used, and a rubbing machine or the like is used to achieve oblique vertical alignment. In this tilted vertical alignment process, the tilt angle of the liquid crystal molecules can be adjusted by combining a rotating rubbing roller and a horizontal moving table and applying an appropriate weight 1 to the rubbing roller.

The oblique vertical alignment process can be performed not only by the rubbing method but also by an oblique vapor deposition method. In this embodiment, EN-38 manufactured by Chisso ■ is used as the first liquid crystal material 24.
Any liquid crystal material can be used as long as it has negative dielectric anisotropy.

Similarly, the second liquid crystal cell 3 includes a pair of opposing second transparent substrates 31 and 31 (however, in this embodiment, one of the second transparent substrates 31 is shared with the first transparent substrate 21). .)
A second transparent mold formed on this second transparent substrate 31.31 [i32.32, a second alignment layer 33.33,
It consists of a second liquid crystal material 34.

Note that in this embodiment, one of the first transparent substrates 21 and the second
One of the transparent substrates 31 is common. In this specification, one transparent substrate includes a structure that serves as the first transparent substrate 21 and the second transparent electrode 31.

The second liquid crystal cell 3 has a similar configuration to the first liquid crystal cell 2, and has almost the same characteristics. However, when a voltage is applied to each of the first liquid crystal cell 2 and the second liquid crystal cell 3, the tilt directions of the liquid crystal molecules 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 direction of inclination of the liquid crystal molecules of the first liquid crystal cell 2, the first liquid crystal cell 2 will have more complex as the viewing angle becomes larger. Refractive properties become smaller. In contrast, the second liquid crystal cell 3
The viewing angle falls in the direction opposite to the direction in which the liquid crystal molecules are tilted, and the birefringence increases. For this reason, when the first liquid crystal cell 2 and the second liquid crystal cell 3 are stacked, the viewing angle dependence of birefringence is suppressed, and the optical characteristics of the two-layer ECB cell 1 as a whole are compensated. become.

Further, on the side opposite to the direction in which the liquid crystal molecules of the first liquid crystal cell 2 are tilted when a voltage is applied, the birefringence of the first liquid crystal cell 2 increases 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.

Next, a simulation based on numerical calculation of this example will be explained.
The optical characteristics were calculated using the 4×4 matrix method. As for the coordinates, the two axes are the normal direction of the undefined 9-cell substrate as shown in FIG. 2, and the viewing angle direction is expressed as α and the azimuth angle β as much as possible. The tilt direction of liquid crystal molecules is β-45
The polarizers are crossed nicols, and the polarization directions are made to match in the X and y directions. Furthermore, the physical constants of the liquid crystal used in the simulation are shown in Table 1 in consideration of EN-38.
The one shown in was used.

The results of this simulation are shown in Figures 4 to 1.
This is Figure 2. FIG. 4 shows the dependence of transmittance on applied voltage in the normal direction of the cell. Note that the applied voltage is normalized by the threshold value when the pretilt angle is 0 degrees. In this embodiment, the viewing angle-dependent voltage is applied such that the transmittance in the normal direction of the substrate is 100%, that is, the retardation of the liquid crystal cell is 1/2 wavelength. And unless otherwise specified, the wavelength used was 5
50% m.

Here, retardation is the amount that indicates the optical path difference between ordinary light and extraordinary light. In the case of a parallel-aligned liquid crystal cell, if the refractive index anisotropy of the liquid crystal is An and the cell thickness is d, then when no voltage is applied, The retardation R is R=J n d . In the case of a vertically aligned liquid crystal cell, the retardation R becomes zero unless a voltage is applied. Furthermore, the retardation R of the liquid crystal cell can be changed by applying a voltage.
can be changed.

FIGS. 5 and 6 show the dependence of the transmittance on the azimuth angle β with α as a parameter as much as possible in a single-layer type and a two-layer type ECB cell, respectively.

Comparing the two, it can be seen that compared to the old ECB cell 1, the two-layer ECB cell 1 of this embodiment has less dependence of transmittance on β even if α becomes as large as possible; It can be seen that no decrease in transmittance is observed even when As a result, it can be seen that the two-layer ECB cell 1 of this example has improved viewing angle dependence compared to the old ECB cell 9. Figure 7 shows that the tilt direction ( That is, when the azimuth angle β is 45 degrees), the transmittance depends on the polar moon. As a result, the viewing angle dependence of the old type ECB cell 1 (ECB cell) is very large, but compared to this, the two-layer type ECB cell 1 (DECB cell) of this embodiment is
It is understood that the viewing angle dependence is considerably improved compared to the B cell (ECB cell). Furthermore, it can be seen that the characteristics are symmetrical with respect to the cell normal direction.

FIG. 8 shows the polar moon dependence of transmittance when the azimuth angle β is 135 degrees. Similarly to FIG. 7, the 2M type ECB cell 1 (D-ECB cell) of the present embodiment is
It is understood that the viewing angle dependence is considerably improved compared to cell B).

Figure 9 shows the tilt direction of the liquid crystal in the 1st old ECB cell.
That is, it shows the polar moon dependence of transmittance when the azimuth angle β is 45 degrees and each wavelength is used as a parameter. The wavelengths used in the calculation are 450% m for blue and 550% m for green.
Red is 650%m.

FIG. 10 shows that in the two-layer ECB cell 1 of this embodiment,
This shows the dependence of the transmittance on polar moon for each wavelength parameter.9 Comparing Figures 9 and 10, it can be seen that in the old ECB cell, the transmittance decreases in the direction in which the liquid crystal molecules are tilted. The display becomes dark. Furthermore, on the opposite side of the direction in which the liquid crystal molecules are tilted, the difference in retardation between wavelengths increases, resulting in coloration. On the other hand, in the second-older ECB cell 1 of this embodiment, the difference in retardation of each wavelength does not become large, so coloring is suppressed, and there is no large change in transmittance, so that a uniform display can be obtained.

Figure 11 shows the normal direction to the direction in which the liquid crystal is tilted (i.e., the azimuth angle β
This figure shows the dependence of the transmittance on the polar moon when each color is used as a parameter in an old model ECB cell (when 135 degrees).

FIG. 12 shows that in the two old ECB cells 1 of this embodiment,
This figure shows the polar moon dependence of transmittance when each color is used as a parameter.

Comparing FIG. 1j with FIG. 12, although no coloring is seen in either case, it is understood that the second old ECB cell 1 of this example has better viewing angle dependence.

By the way, in a liquid crystal cell, the response recovery time is 2 times the cell thickness.
It is known that it is proportional to the power of When comparing single-layer and double-layer ECB cells with the same retardation,
Since the cell thickness of a two-layer ECB cell is 1/2 of that of a single-layer type, the response recovery time is expected to be 1/4 faster.

"Effects" The present invention configured as described above has the following effects: the tilt direction of the liquid crystal molecules sealed in the first liquid crystal cell when a voltage is applied, and the tilt direction of the liquid crystal molecules sealed in the second liquid crystal cell when a voltage is applied. Since the tilt directions of the liquid crystal molecules are opposite to each other, there is an outstanding effect of being able to compensate for the viewing angle dependence of the optical properties when voltage is applied.

Furthermore, the present invention has the effect that viewing angle dependence of optical characteristics upon voltage application can be compensated for without impairing the advantages of the 1Iil type liquid crystal cell.

The present invention has the effect of speeding up the response recovery time to 1/4 in a two-layer ECB cell that has the same characteristics as the old type ECB cell when viewed from the cell normal direction.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention. FIG. 1 is a diagram showing the configuration of this embodiment, FIG. 2 is a diagram explaining the definition of coordinates, and FIG. 3 is a diagram explaining viewing angle dependence. , FIG. 4 to FIG. 12 are diagrams explaining the results of the simulation. 1 ・ ・ 2 ・ ・ 21 ・ 22 ・ 23 ・ 24 ・ 3 ・ ・ 31 ・ 32 ・ 33 ・ Two-layer ECB cell First liquid crystal cell First transparent substrate First transparent electrode First alignment layer First Liquid crystal material Second liquid crystal cell Second transparent substrate Second transparent electrode Second alignment layer 34 Second liquid crystal material

Claims (3)

[Claims] (1) A two-layer liquid crystal display consisting of a first liquid crystal cell and a second liquid crystal cell, in which the tilt direction of the liquid crystal molecules sealed in the first liquid crystal cell when a voltage is applied and the voltage A two-layer liquid crystal display device, characterized in that the directions of inclination of the liquid crystal molecules sealed in the second liquid crystal cell are opposite to each other when a voltage is applied. (2) A first device comprising a first transparent substrate having a pair of opposing electrodes and a first liquid crystal material sealed between the transparent substrates.
a second liquid crystal cell consisting of a second transparent substrate having a pair of opposing electrodes and a second liquid crystal material sealed between the transparent substrates, The liquid crystal material of No. 2 is a liquid crystal having negative dielectric constant anisotropy,
The first liquid crystal cell sealed in the first liquid crystal cell when a voltage is applied
The tilt direction of the liquid crystal molecules and the tilt direction of the second liquid crystal molecules sealed in the second liquid crystal cell when a voltage is applied are as follows.
A two-layer liquid crystal display device characterized in that the two-layer liquid crystal display device is configured to be opposite to each other. (3) The two-layer liquid crystal display device according to claim 1, wherein the first liquid crystal cell and the second liquid crystal cell have equal retardation.