JP2013029761A - Vertical alignment liquid crystal display and production method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vertical alignment liquid crystal display capable of preventing light omission in a pixel part with a simple configuration, and provide a production method for the same.SOLUTION: A passive-matrix vertical alignment liquid crystal display 100 comprises a first liquid crystal panel 31 and a second liquid crystal panel 32, and when voltage is applied, it displays a rectangular pixel in an area where a first electrode 311a, a second electrode 311b, a first electrode 321a and a second electrode 321b overlap with one another. In the vertical alignment liquid crystal display 100, the first liquid crystal panel 31 and the second liquid crystal panel 32 are configured so that a liquid crystal director direction n1 of the first liquid crystal layer 31 and a liquid crystal director direction n2 of the second liquid crystal layer 32 are opposite to each other and the liquid crystal director directions n1 and n2 make an angle of approximately ±45° to a side of the rectangular pixel.

Description

  The present invention relates to a vertical alignment type liquid crystal display device and a production method thereof.

  As a liquid crystal display device, a vertical alignment type liquid crystal display device (hereinafter also referred to as VA-LCD (Vertical Alignment-Liquid Crystal Display)) is known. In the VA-LCD, the liquid crystal molecules in the liquid crystal layer disposed between the upper and lower substrates are aligned substantially perpendicular to the main surface (opposing surface) of each substrate, and voltage is applied to the electrodes provided on the upper and lower substrates. Is applied, a voltage is applied to the liquid crystal layer, and the liquid crystal molecules are tilted in a direction substantially horizontal to the main surface of the substrate, thereby forming a pixel portion and enabling a predetermined display.

  VA-LCDs are widely used because they can provide high contrast. For example, when a liquid crystal display device is driven at a high duty so as to be applied in a passive matrix type, light leakage occurs in the pixel portion. There was a problem that.

  In high duty driving, normally, the OFF voltage is set lower than the threshold voltage at which the liquid crystal molecules start to fall, thereby preventing an increase in transmittance when the OFF voltage is applied. However, when an oblique electric field is generated between the upper and lower electrodes corresponding to the pixel edge portion, liquid crystal molecules are tilted at a voltage lower than the threshold voltage in a region where the oblique electric field is applied, and light leakage occurs at the pixel edge portion.

  As a method for suppressing such light leakage, the side corresponding to the pixel edge and the transmission axis (or absorption axis) of the polarizing plate are parallel or orthogonal to each other (or the liquid crystal molecules are aligned with respect to the side corresponding to the pixel edge). There is known a method of configuring a liquid crystal display device in such a manner that the tilt direction is ± 45 °. For example, in Patent Document 1, a liquid crystal display device is configured to satisfy the above relationship by forming hexagonal pixels with electrodes, and in Patent Document 2 using a zigzag electrode pattern. A technique for suppressing the above is disclosed.

JP 2011-028143 A JP 2009-156930 A

  However, the techniques disclosed in Patent Documents 1 and 2 have a problem that the electrode pattern becomes complicated.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a vertical alignment type liquid crystal display device capable of suppressing light leakage of a pixel portion with a simple configuration and a method for producing the same.

In order to achieve the above object, a liquid crystal display device according to the first aspect of the present invention provides:
A first liquid crystal layer, a pair of substrates arranged to face each other with the first liquid crystal layer interposed therebetween, and a first substrate formed on the first liquid crystal layer side surface of one of the pair of substrates. A first liquid crystal panel having one electrode and a first to second electrode formed on a surface of the other substrate on the first liquid crystal layer side;
A second liquid crystal layer, a pair of substrates arranged to face each other with the second liquid crystal layer interposed therebetween, and a second 2-layer formed on a surface of one of the substrates on the second liquid crystal layer side. A second liquid crystal panel having one electrode and a second-second electrode formed on a surface of the other substrate on the second liquid crystal layer side, and disposed under the first liquid crystal panel. Prepared,
A passive matrix type vertical alignment type liquid crystal display that displays a rectangular pixel in a region where the 1-1 electrode, the 1-2 electrode, the 2-1 electrode, and the 2-2 electrode overlap when a voltage is applied. A device,
The first liquid crystal panel and the second liquid crystal panel include an average inclination direction of liquid crystal molecules when a voltage is applied to the first liquid crystal layer and an average of liquid crystal molecules when a voltage is applied to the second liquid crystal layer. And the average inclination direction with respect to the sides of the rectangular pixels is approximately ± 45 °.
It is characterized by that.

In order to achieve the above object, a method for producing a liquid crystal display device according to the second aspect of the present invention comprises:
A first liquid crystal layer, a pair of substrates arranged to face each other with the first liquid crystal layer interposed therebetween, and a first substrate formed on the first liquid crystal layer side surface of one of the pair of substrates. A first liquid crystal panel having one electrode and a first to second electrode formed on a surface of the other substrate on the first liquid crystal layer side;
A second liquid crystal layer, a pair of substrates arranged to face each other with the second liquid crystal layer interposed therebetween, and a second 2-layer formed on a surface of one of the substrates on the second liquid crystal layer side. A second liquid crystal panel having one electrode and a second-second electrode formed on a surface of the other substrate on the second liquid crystal layer side, and disposed under the first liquid crystal panel. Prepared,
A passive matrix type vertical alignment type liquid crystal display that displays a rectangular pixel in a region where the 1-1 electrode, the 1-2 electrode, the 2-1 electrode, and the 2-2 electrode overlap when a voltage is applied. A production method of the device,
In the first liquid crystal panel and the second liquid crystal panel, an average inclination direction of liquid crystal molecules when a voltage is applied to the first liquid crystal layer and an average of liquid crystal molecules when a voltage is applied to the second liquid crystal layer And configured so that the average tilt direction with respect to the sides of the rectangular pixels is approximately ± 45 °.
It is characterized by that.

  According to the present invention, light leakage from the pixel portion can be suppressed with a simple configuration.

It is a schematic sectional drawing for demonstrating the structure of the liquid crystal display device which concerns on one Embodiment of this invention. It is a figure for demonstrating the relationship between a liquid crystal director direction and the transmission axis of a polarizing filter. (A) is a figure for demonstrating the relationship between the electrode of a 1st liquid crystal panel, and a liquid crystal director direction. (B) is a figure for demonstrating the relationship between the electrode of a 2nd liquid crystal panel, and a liquid crystal director direction. (C) is a figure for demonstrating the relationship between a liquid crystal director direction and a pixel edge part. It is a figure for demonstrating the effect of the liquid crystal display device which concerns on one Embodiment of this invention. It is a figure which shows the simulation result for pinpointing the range of the value of retardation. It is a figure which shows the simulation result of ON transmittance | permeability, front contrast, and response speed of the liquid crystal display device which concerns on one Embodiment of this invention, and various comparative examples. It is a figure which shows the simulation result of VT characteristic.

An embodiment according to the present invention will be described with reference to the drawings.
In the following description, it is assumed that the display surface direction of the liquid crystal display device (the direction of the viewer of the liquid crystal display device) of the predetermined component is “up” and the direction opposite to the display surface direction is “down”.

(Configuration of liquid crystal display device)
A liquid crystal display device 100 according to the present embodiment shown in FIG. 1 is a vertical alignment type liquid crystal display device having a multilayer panel structure, and includes a first polarizing filter 10, a second polarizing filter 20, a liquid crystal element 30, and a backlight. 40.

  The first polarizing filter 10 and the second polarizing filter 20 are arranged to face each other, and the liquid crystal element 30 is provided between them.

  The 1st polarizing filter 10 is located on the liquid crystal element 30, and is comprised by the polarizing plate, for example. The first polarizing filter 10 emits light incident from the front surface side or the back surface side as linearly polarized light along a transmission axis orthogonal to the absorption axis.

  The second polarizing filter 20 is located below the liquid crystal element 30 and is configured by, for example, a polarizing plate. The second polarizing filter 20 emits light incident from the front surface side or the back surface side as linearly polarized light along a transmission axis perpendicular to the absorption axis.

  As shown in FIG. 2, the first polarizing filter 10 and the second polarizing filter 20 have transmission axes (or absorption axes) of + 45 ° and −45 ° with respect to the liquid crystal director direction n1 or n2. Is arranged in crossed Nicols. The liquid crystal display device 100 in such an arrangement is a normally black mode. The liquid crystal director direction will be described in detail later.

The liquid crystal element 30 includes a first liquid crystal panel 31 and a second liquid crystal panel 32 disposed below the first liquid crystal panel 31.
The first liquid crystal panel 31 includes a first substrate unit 31a, a second substrate unit 31b, and a liquid crystal layer 31c including liquid crystal molecules 310c. The first substrate unit 31a and the second substrate unit 31b are arranged to face each other, and a liquid crystal layer 31c is provided between them.

The first substrate unit 31a is disposed on the liquid crystal layer 31c and includes a first substrate 310a, a first electrode 311a, and a first alignment film 312a.
The second substrate unit 31b is disposed below the liquid crystal layer 31c, and includes a second substrate 310b, a second electrode 311b, and a second alignment film 312b.

  The first substrate 310a and the second substrate 310b are transparent substrates such as a glass substrate and a plastic substrate, respectively, and transmit light.

Each of the first electrode 311a and the second electrode 311b is a transparent electrode that transmits light, and is formed from, for example, ITO (indium tin oxide) by a known method (for example, sputtering, vapor deposition, or etching). . The first electrode 311a and the second electrode 311b are disposed so as to face each other. The first electrode 311a is formed on the surface of the first substrate 310a on the first liquid crystal layer 31c side, and the second electrode 311b is formed on the surface of the second substrate 310b on the first liquid crystal layer 31c side. Here, “on the surface” includes a case where it is formed directly on the substrate surface and a case where it is formed via a predetermined member between the substrate surface and the electrode.
The 1st electrode 311a and the 2nd electrode 311b are respectively comprised from the transparent electrode formed in stripe form. Specifically, as shown in FIG. 3A, when the first electrode 311a is formed in a vertical stripe shape on the paper surface, the second electrode 311b is formed in a horizontal stripe shape on the paper surface (in the figure, the first The two electrodes 311b are represented by dotted lines). That is, in this case, the first electrode 311a is composed of a plurality of strip-shaped transparent electrodes r1 arranged at predetermined intervals in the left-right direction on the paper surface, and the second electrode 311b is arranged at predetermined intervals in the vertical direction on the paper surface. And a plurality of strip-shaped transparent electrodes c1.

  As will be described later, the second liquid crystal panel 32 has substantially the same configuration as the first liquid crystal panel 31, and the first electrode 321a and the second electrode 321b included in the second liquid crystal panel 32 are formed in the same manner as described above. The That is, as shown in FIG. 3B, the first electrode 321a is a plurality of strips arranged at a predetermined interval in the horizontal direction of the paper (the same direction as the arrangement direction of the first electrodes 311a of the first liquid crystal panel 31). The second electrode 321b is composed of a plurality of strip-shaped transparent electrodes c2 arranged at predetermined intervals in the vertical direction of the drawing (in the figure, the second electrode 321b is represented by a dotted line). did).

When a voltage is applied to both the first electrode 311a and the second electrode 311b, and both the first electrode 321a and the second electrode 321b, one transparent electrode r1 and one transparent electrode c1 in the first liquid crystal panel 31 are applied. 1 pixel e (dot) is formed in a region where one transparent electrode r2 and one transparent electrode c2 overlap in the second liquid crystal panel 32 (FIGS. 3A and 3B). ), An arbitrary one pixel is represented by a dot). One pixel e formed in this way is rectangular, and may be square or rectangular.
As described above, in the present embodiment, the first liquid crystal panel 31 and the second liquid crystal panel 32 include the intersection region of the first electrode 311a and the second electrode 311b (intersection region of the transparent electrodes r1 and c1) and the first electrode 321a. And the intersection region of the second electrode 321b (intersection region of the transparent electrodes r2 and c2) correspond to each other (that is, the pixel e is formed on both panels). Both panels may be configured such that all the intersecting regions correspond to each other, or may be configured such that a part of the intersecting regions correspond. That is, all display designs may be displayed in cooperation with both panels, or some display designs may be displayed in cooperation with both panels.
In the present embodiment, a voltage is applied to the first liquid crystal panel 31 and the second liquid crystal panel 32 by a passive drive method. Thus, the liquid crystal display device 100 is a so-called passive matrix liquid crystal display device.

  The first alignment film 312a and the second alignment film 312b are films in contact with the liquid crystal layer 31c, respectively, and are formed from, for example, polyimide by a known method (for example, flexographic printing). The first alignment film 312a is formed on the main surface (surface on the liquid crystal layer 310c side) of the first substrate 310a so as to cover the first electrode 311a. Similarly, the second alignment film 312b is formed on the main surface (surface on the liquid crystal layer 31c side) of the second substrate 310b so as to cover the second electrode 311b.

  The first alignment film 312a and the second alignment film 312b are vertical alignment films that regulate the alignment state of the liquid crystal layer 31c when no voltage is applied to the liquid crystal molecules 310c to be substantially perpendicular to the main surface (opposing surface) of the substrate. The liquid crystal molecules 310c are aligned substantially in one azimuth, and a predetermined pretilt angle of 90 ° is given to the liquid crystal molecules 310c of the liquid crystal layer 31c. The pretilt means that the liquid crystal molecules 310c are tilted from the vertical direction to a predetermined direction to some extent in order to define the direction in which the liquid crystal molecules 310c are tilted when a voltage is applied (a liquid crystal director direction described later). The pretilt angle is defined as an angle from the main surface of the substrate. As the substrate normal direction is 90 °, the pretilt angle decreases from 90 ° as the pretilt is applied.

  The first alignment film 312a and the second alignment film 312b are rubbed to form fine grooves. Thereby, the alignment direction of the liquid crystal molecules 310c of the liquid crystal layer 31c is regulated. Note that the alignment direction of the liquid crystal molecules 310c may be regulated by a known process such as an optical alignment process or a protrusion alignment process. In addition, an insulating film may be provided between the first electrode 31b and the first alignment film 31c and between the second electrode 32b and the second alignment film 32c, respectively, as necessary.

  The liquid crystal layer 31c is sandwiched between the first substrate unit 31a and the second substrate unit 31b. The first substrate unit 31a and the second substrate unit 31b are overlapped and fixed so as to face each other with a predetermined distance between them with a seal member (not shown) interposed therebetween. A liquid crystal material is confined in a sealed space formed by the first substrate unit 31a, the second substrate unit 31b, and the sealing member, and a liquid crystal layer 31c is formed. As the liquid crystal material, a material having a dielectric anisotropy Δε negative (Δε <0) and a refractive index anisotropy Δn at a wavelength of 589 nm of about 0.2 is used.

The second liquid crystal panel 32 includes a first substrate unit 32a, a second substrate unit 32b, and a liquid crystal layer 32c including liquid crystal molecules 320c. The first substrate unit 32a and the second substrate unit 32b are arranged to face each other, and a liquid crystal layer 32c is provided between them.
The first substrate unit 32a is disposed on the liquid crystal layer 32c and includes a first substrate 320a, a first electrode 321a, and a first alignment film 322a. The second substrate unit 32b is disposed under the liquid crystal layer 32c and includes a second substrate 320b, a second electrode 321b, and a second alignment film 322b.
The second liquid crystal panel 32 has substantially the same configuration as the first liquid crystal panel 31 and has substantially the same characteristics. For example, the first substrate unit 32 a of the second liquid crystal panel 32 corresponds to the first substrate unit 31 a of the first liquid crystal panel 31. Thus, each component of the second liquid crystal panel 32 corresponds to the same component among the components of the first liquid crystal panel 31. In FIG. 1, the liquid crystal molecules 310c and 320c are schematically represented by ellipses for convenience of explanation.

  The first liquid crystal panel 31 and the second liquid crystal panel 32 are stacked. Specifically, the first liquid crystal panel 31 and the second liquid crystal panel 32 are bonded by bonding the lower surface of the second substrate 310b of the first liquid crystal panel 31 and the upper surface of the first substrate 320a of the second liquid crystal panel 32 together. Laminated. Since a multi-layer structure is used in this manner, parallax occurs, so that the substrates on the bonding side (the second substrate 310b and the first substrate 320a) are preferably as thin as possible. For this reason, for example, after the first liquid crystal panel 31 is formed, the lower surface of the second substrate 310b is polished, and after the second liquid crystal panel 32 is formed, the upper surface of the first substrate 320a is polished, and then both are laminated or bonded together. These substrates are preferably thinner than the substrates that are not bonded to each other (the first substrate 310a of the first liquid crystal panel 31 and the second substrate 320b of the second liquid crystal panel 32). Instead of bonding in this way, the second substrate 310b of the first liquid crystal panel 31 and the first substrate 320a of the second liquid crystal panel 32 may be a single substrate common to both panels.

The first liquid crystal panel 31 and the second liquid crystal panel 32 have substantially the same configuration as described above, but are configured so that the liquid crystal director directions of the liquid crystal molecules are different from each other. Here, the “liquid crystal director direction” means an average inclination direction of liquid crystal molecules in the liquid crystal layer when a voltage is applied to one panel. That is, the liquid crystal director direction n1 of the liquid crystal molecules 310c and the liquid crystal director direction n2 of the liquid crystal molecules 320c are different from each other by 180 ° (see FIGS. 1 and 2).
As described above, when the liquid crystal director direction n1 is the viewing angle direction, the liquid crystal layer 31c is formed in the first liquid crystal panel 31 as the viewing angle increases (that is, as the viewpoint shifts from the substrate normal direction to the viewing angle direction). Birefringence is less likely to occur in the passing light. In this case, in the second liquid crystal panel 32, since the direction opposite to the liquid crystal director direction n2 is the viewing angle direction, birefringence is likely to occur in the light passing through the liquid crystal layer 32c. For this reason, according to the liquid crystal display device 100 which has the multilayer panel structure concerning this embodiment, viewing angle dependence can be suppressed.

Further, the first liquid crystal panel 31 and the second liquid crystal panel 32 are arranged such that the respective liquid crystal director directions n1 and n2 are approximately ± 45 ° (including just ± 45 °) with respect to the alignment direction of the transparent electrodes. It is configured. Specifically, as shown in FIG. 3C, the angle between the pixel edge ed corresponding to each side of the substantially square pixel e and the liquid crystal director directions n1 and n2 is approximately ± 45 °. It is configured as follows. Further, in the case of such a configuration, as can be seen with reference to FIGS. 2 and 3C, the side corresponding to the pixel edge ed and the transmission of the polarizing filter (the first polarizing filter 10 and the second polarizing filter 20). The axis (or absorption axis) has a parallel or orthogonal relationship.
For example, in a conventional VA-LCD with a monolayer orientation of a single-layer panel, if the liquid crystal director direction is set to ± 45 ° with respect to the pixel edge, light leakage at the pixel edge portion can be suppressed, but the viewing angle dependency is reduced. Since it becomes high, it was difficult to make such a setting. On the other hand, in the liquid crystal display device 100 according to the present embodiment, the liquid crystal director direction n1 of the first liquid crystal panel 31 and the liquid crystal director direction n2 of the second liquid crystal panel 32 are set to be opposite to each other as described above. Therefore, it is possible to suppress light leakage from the pixel edge portion while suppressing the viewing angle dependency. Further, the configuration is simple because it is not necessary to use a special electrode pattern.

  As described above, the first liquid crystal panel 31 and the second liquid crystal panel 32 have substantially the same configuration, but their characteristics (the composition of the transparent substrate, the refractive index anisotropy Δn of the liquid crystal, the thickness of the liquid crystal layer). It is also possible to adjust the viewing angle direction by making d) different from each other. In this case, in particular, the viewing angle direction may be adjusted by paying attention to the retardation (Δn · d) of the liquid crystal layer (retardation will be described later). Also in this case, as described later, the value of the total retardation R of the first liquid crystal panel 31 and the second liquid crystal panel 32 is set to 500 nm ≦ R ≦ 2000 nm.

  The backlight 40 is located under the second polarizing filter 20 and emits light in a planar shape to illuminate the liquid crystal element 30 and the like. The backlight 40 is configured by a combination of a light emitting diode and a light guide member, for example. The backlight 40 is appropriately used when the liquid crystal display device 100 performs bright display.

In the liquid crystal display device 100, when no voltage is applied, the liquid crystal molecules 310c and 320c are vertically aligned. Therefore, the light passing from the lower side of the second polarizing filter 20 has a polarization direction (electric field oscillation direction) depending on the liquid crystal layers 31c and 32c. Almost no change is made, and the second polarizing filter 20 cannot pass through the first polarizing filter 10 arranged in a crossed Nicols relationship. Thus, the liquid crystal display device 100 is in a normally black mode.
On the other hand, when a voltage was applied to the pair of electrodes (311a, 311b) of the first liquid crystal panel 31 and the pair of electrodes (321a, 321b) of the second liquid crystal panel 32, the voltages of the liquid crystal layers 31c, 32c were applied. In the region, the liquid crystal molecules 310c and 320c are tilted in the direction of the liquid crystal director and become substantially horizontal with the main surface of the substrate. Thereby, birefringence occurs in the light passing through the liquid crystal layers 31c and 32c, and the polarization direction changes, and the light passing through the liquid crystal layers 32c and 31c from the lower side of the second polarizing filter 20 passes through the first polarizing filter 10. To do. The liquid crystal display device 100 forms a pixel e by a region through which light passes (a region where the first electrode 311a and the second electrode 311b and the first electrode 321a and the second electrode 321b overlap in plan view when a voltage is applied). Is displayed.
In particular, in this embodiment, since the liquid crystal director direction n1 of the liquid crystal layer 31c and the liquid crystal director direction n2 of the liquid crystal layer 32c are set in opposite directions, the viewing angle dependency can be suppressed as described above. .

FIG. 4 shows a liquid crystal display device 100 and a liquid crystal display device having a configuration similar to that of the liquid crystal display device 100 and configured such that the angle between the liquid crystal director direction and the pixel edge ed is 0 ° or 90 ° (comparative example). The contrast result by simulation is shown. Here, the contrast is a ratio of luminance between OFF and ON in a certain display area. If the contrast is large, the display by the liquid crystal display device 100 is easy to see. Therefore, it is preferable that the contrast is large.
As shown in the figure, the contrast of the liquid crystal display device 100 is 500, which is larger than the contrast 250 of the comparative example, which is a favorable result. This result shows that the liquid crystal display device 100 configured so that the liquid crystal director directions n1 and n2 are approximately ± 45 ° with respect to the arrangement direction of the transparent electrodes as described above can suppress light leakage. . If light leakage can be suppressed, the brightness at the time of OFF decreases, and as a result, the contrast can be increased.

(About retardation of liquid crystal layer)
In the liquid crystal display device 100 capable of suppressing light leakage at the pixel edge portion as described above, the inventor of the present application further adds up the total retardation R of the first liquid crystal panel 31 and the second liquid crystal panel 32 (the retardation of the first liquid crystal layer 31c). It was found that high duty driving from 1/32 to 1/128 Duty becomes possible by setting the value of the sum of the retardation of the second liquid crystal layer 32c to 500 nm ≦ R ≦ 2000 nm. Here, the retardation of the liquid crystal layer is a product (Δn · d) of the thickness d of the liquid crystal layer and the refractive index anisotropy Δn of the liquid crystal.
Hereinafter, how the retardation is specified will be described.

  In VA-LCD, it is known that, in principle, the retardation should be ½ wavelength (λ / 2 (200 to 300 nm)) in order to maximize the transmittance. However, when the liquid crystal display device according to this embodiment is driven in a passive matrix type with a high duty, when the retardation is ½ wavelength, the steepness is low and the display becomes dark when ON. This is because in the passive drive, the ON-OFF voltage difference is limited (for example, as shown in FIG. 7, the OFF voltage is 2 V and the ON voltage is 2.5 V), and the liquid crystal molecules are difficult to tilt horizontally.

  In order to increase the refractive index and increase the transmittance while the voltage difference is limited, the retardation may be increased by increasing Δn or d. However, when a liquid crystal having a large Δn is used, problems such as a decrease in nematic phase-isotropic liquid phase transition temperature (Tni) and a decrease in response speed (increased viscosity) occur. Moreover, even if d is increased, the response speed is lowered.

  In the VA-LCD having a single-layer panel, it is difficult to increase the retardation for the above reason. Therefore, if the inventor adopts a VA-LCD having a multilayer panel structure as in this embodiment, the overall retardation is obtained as the sum of the retardations of each panel without forcibly increasing the retardation of each panel. Therefore, it was thought that high duty driving is possible.

FIG. 5 shows a simulation result for specifying the retardation.
Δn of the liquid crystal layers 31c and 32c is set to 0.2, and the sum of the thickness of the liquid crystal layer 31c and the thickness of the liquid crystal layer 32c is changed to 11, 10, 7.5, 5, 2.5, and 1.5 μm. Thus, the total retardation R of both panels is set to 2200, 2000, 1500, 1000, 500, and 300 nm, and the transmittance, contrast, and response speed at the ON time in each case are set to a predetermined simulation software (for example, manufactured by Shintech Co., Ltd.). Simulation software “LCD MASTER”). This result is a result in the case of 1/64 Duty and 1/9 Bias.

In the case of total retardation R = 2200, ON transmittance is 11% and contrast is 1500 (when OFF is set to 1), which is a good result, but the retardation is too large, and the response speed is as slow as 500 ms. . Conversely, when the retardation is set to a small value of R = 300, the response speed is very good at 5 ms, but the ON transmittance is 0.3% and the contrast is too small.
On the other hand, when 500 ≦ R ≦ 2000, the ON transmittance is 11% to 2%, the contrast is 1200 to 150, and the response speed is 300 to 15 ms. Thereby, in order to maintain good display quality, the total R (total of the first liquid crystal layer 31c and the second liquid crystal layer 32c) retardation R of both liquid crystal panels may be set to a condition of 500 nm ≦ R ≦ 2000 nm. I understood it.
Although there is no problem in maintaining the display quality, the response speed is slightly slow at 300 ms at R = 2000, and the ON transmittance is slightly low at 2% at R = 500. A value near 1000 may be set.

Here, as an example, simulation results of various characteristics of the liquid crystal display device 100 in which the layer thickness d of the first liquid crystal layer 31c is set to 2.7 μm and the layer thickness d of the second liquid crystal layer 32c is set to 2.7 μm are illustrated. It is shown in FIG. This result is a result in the case of 1/64 Duty and 1/9 Bias.
In this case, since Δn of the liquid crystal material is 0.2 (589 nm), the total retardation value of both liquid crystal panels is (0.2 × 2.7 (μm)) + (0.2 × 2.7). (Μm)) = 1080 nm and 500 nm ≦ R ≦ 2000 nm are satisfied.
As a comparative example, a liquid crystal display device having the same configuration as that of the liquid crystal display device 100 but having the same liquid crystal director direction in the upper and lower liquid crystal panels (comparative example 1) and the first liquid crystal panel 31c. Also, the simulation results of the single-layer monodomain structure liquid crystal display device (Comparative Example 2 and Comparative Example 3) in which either the second liquid crystal panel 32c is omitted are also shown in FIG. In Comparative Example 1, the layer thickness d of the first liquid crystal layer 31c is set to 2.7 μm, and the layer thickness d of the second liquid crystal layer 32c is set to 2.7 μm. In Comparative Example 2, the liquid crystal layer in the single-layer liquid crystal panel is set. The layer thickness was set to 2.7 μm, and in Comparative Example 3, the thickness of the liquid crystal layer in the single-layer liquid crystal panel was set to 5.4 μm.

  Focusing on the ON transmittance, the liquid crystal display device 100 having a large retardation value is 5%, the comparative example 1 is 5%, the comparative example 3 is 3%, because of the multilayer structure or the layer thickness d is large. It turns out that it is excellent in the transmittance | permeability compared with 1% of the comparative example 2 with small value. However, even if the comparative example 3 is excellent in the transmittance as described above, the response speed is slowed down to 500 ms by increasing d. On the other hand, the multi-layered liquid crystal display device 100 and Comparative Example 1 have a favorable response speed of 50 ms.

  As described above, compared with Comparative Examples 2 and 3 having a single layer structure, the liquid crystal display device 100 having a multilayer structure and Comparative Example 1 are superior in terms of ON transmittance and response speed. However, when focusing on contrast, the liquid crystal display device 100 is 500, the comparative example 1 is 300, and the liquid crystal display device 100 is superior to the comparative example 1. Further, as shown in the figure, when the contrast distribution C100 of the liquid crystal display device 100 is compared with the contrast distribution C1 of the comparative example 1, in the liquid crystal display device 100, the region Hi having a high contrast is obtained when the display surface is viewed from the front. A region Low that is distributed evenly (up and down) and left and right (to the object) and has low contrast is only scattered. On the other hand, in Comparative Example 1, it can be seen that the Hi region is uneven, and the Low region covers a wider range than the liquid crystal display device 100. Thus, it can be seen that the liquid crystal display device 100 configured such that the liquid crystal director direction is reversed between the upper and lower panels has a wider field of view than that of the first comparative example.

Here, the simulation result of the VT (voltage-transmittance) characteristic of the liquid crystal display device 100, Comparative Example 2, and Comparative Example 3 is shown in FIG.
As shown in the figure, it can be seen that the liquid crystal display device 100 can obtain the same VT characteristic as that of the comparative example 3 set to d = 5.4 μm by increasing the retardation in the multilayer structure. In other words, according to the liquid crystal display device 100, it is possible to improve the display quality without causing a decrease in response speed as in the comparative example 3 while increasing the ON transmittance while the voltage difference is limited due to passive driving. It can be seen that can be maintained.

(Regarding the production method of the liquid crystal display device 100)
A method for producing the liquid crystal display device 100 will be described.
First, a first substrate 310a and a second substrate 310b made of a transparent substrate are prepared, and a first electrode 311a and a second electrode 311b are formed on one surface of both substrates with ITO. As described above, the first electrode 311a and the second electrode 311b are orthogonal to each other and are formed in a dot matrix system.

  Next, a first alignment film 312a is formed on the first substrate 310a so as to cover the first electrode 311a. Similarly, a second alignment film 312b is formed on the second substrate 310b so as to cover the second electrode 311b. The first alignment film 312a and the second alignment film 312b thus formed are rubbed so as to be anti-parallel, for example, and adjusted to give a pretilt close to 90 °. Further, the liquid crystal director direction n1 is adjusted to be ± 45 ° with respect to the electrode arrangement direction (pixel edge ed of the pixel e). Thus, the first substrate unit 31a and the second substrate unit 31b are formed.

  Next, a sealing material (not shown) and a gap control material (not shown) are applied to either the first substrate unit 31a or the second substrate unit 31b, and the first substrate unit 31a, the second substrate unit 31b, Are stacked so that the electrode sides face each other. Then, a liquid crystal material having a negative dielectric anisotropy Δε (Δε <0) is injected between the first substrate unit 31a and the second substrate unit 31b to form the liquid crystal layer 31c, thereby forming the first liquid crystal. A panel 31 is created. The liquid crystal molecules 310c of the liquid crystal layer 31c are vertically aligned with the first alignment film 312a and the second alignment film 312b and given the pretilt.

Further, the second liquid crystal panel 32 is created in the same manner as the first liquid crystal panel 31. However, it is considered that the liquid crystal director directions are opposite to each other when the two panels are bonded.
Then, the first liquid crystal panel 31 and the second liquid crystal panel 32 are bonded together. At this time, in order to suppress parallax, the lower surface of the second substrate 310b of the first liquid crystal panel 31 is polished, the upper surface of the first substrate 320a of the second liquid crystal panel 32 is polished, and then both are bonded together. As described above, the second substrate 310b of the first liquid crystal panel 31 and the first substrate 320a of the second liquid crystal panel 32 may be a single substrate common to both panels.

  Next, the 1st polarizing filter 10 and the 2nd polarizing filter 20 are bonded together to the liquid crystal element 30 produced as mentioned above. For example, a neutral polarizing plate SKN-18243T manufactured by Polatechno Co., Ltd. is employed for the first polarizing filter 10 and the second polarizing filter 20. The first polarizing filter 10 and the second polarizing filter 20 are arranged in crossed Nicols so that each transmission axis (or absorption axis) has an angle of + 45 ° and −45 ° with respect to the liquid crystal director direction.

  The liquid crystal display device 100 is produced by disposing the backlight 40 below the second polarizing filter 20.

In addition, this invention is not limited by said embodiment and drawing. It goes without saying that changes (including deletion of components) can be added to the above embodiments and drawings.
In the above description, the liquid crystal display device 100 is a transmissive liquid crystal display device in which only the backlight 40 is provided below the second polarizing filter 20, but the present invention is not limited to this. A semi-reflective liquid crystal display device in which a semi-reflective layer made of a half mirror or the like is provided between the second polarizing filter 20 and the backlight 40 may be used. Further, instead of the semi-reflective layer, a reflective layer may be provided. In this case, the backlight 40 is unnecessary and a reflective liquid crystal display device is obtained. Moreover, in the above description, in order to make an understanding of this invention easy, description of the known technical matter which is not important was abbreviate | omitted suitably.

DESCRIPTION OF SYMBOLS 100 ... Liquid crystal display device 10 ... 1st polarizing filter 20 ... 2nd polarizing filter 30 ... Liquid crystal element 31 ... 1st liquid crystal panel 31a ... 1st board | substrate unit (310a ... 1st board | substrate, 311a ... 1st electrode, 312a ... 1st Alignment film)
31b ... second substrate unit (310b ... second substrate, 311b ... second electrode, 312b ... second alignment film)
31c ... Liquid crystal layer (310c ... Liquid crystal molecule)
32 ... 2nd liquid crystal panel 32a ... 1st board | substrate unit (320a ... 1st board | substrate, 321a ... 1st electrode, 322a ... 1st alignment film)
32b ... second substrate unit (320b ... second substrate, 321b ... second electrode, 322b ... second alignment film)
32c ... Liquid crystal layer (320c ... Liquid crystal molecule)
40 ... Backlight

Claims (4)

A first liquid crystal layer, a pair of substrates arranged to face each other with the first liquid crystal layer interposed therebetween, and a first substrate formed on the first liquid crystal layer side surface of one of the pair of substrates. A first liquid crystal panel having one electrode and a first to second electrode formed on a surface of the other substrate on the first liquid crystal layer side;
A second liquid crystal layer, a pair of substrates arranged to face each other with the second liquid crystal layer interposed therebetween, and a second 2-layer formed on a surface of one of the substrates on the second liquid crystal layer side. A second liquid crystal panel having one electrode and a second-second electrode formed on a surface of the other substrate on the second liquid crystal layer side, and disposed under the first liquid crystal panel. Prepared,
A passive matrix type vertical alignment type liquid crystal display that displays a rectangular pixel in a region where the 1-1 electrode, the 1-2 electrode, the 2-1 electrode, and the 2-2 electrode overlap when a voltage is applied. A device,
The first liquid crystal panel and the second liquid crystal panel include an average inclination direction of liquid crystal molecules when a voltage is applied to the first liquid crystal layer and an average of liquid crystal molecules when a voltage is applied to the second liquid crystal layer. And the average inclination direction with respect to the sides of the rectangular pixels is approximately ± 45 °.
A vertical alignment type liquid crystal display device. The total retardation value which is the sum of the retardation of the first liquid crystal layer and the retardation of the second liquid crystal layer is 500 nm or more and 2000 nm or less.
The vertical alignment type liquid crystal display device according to claim 1. The substrate on the second liquid crystal panel side of the first liquid crystal panel and the substrate on the first liquid crystal panel side of the second liquid crystal panel are one substrate shared by the first liquid crystal panel and the second liquid crystal panel. Composed of,
The vertical alignment type liquid crystal display device according to claim 1, wherein the liquid crystal display device is a vertical alignment type liquid crystal display device. A first liquid crystal layer, a pair of substrates arranged to face each other with the first liquid crystal layer interposed therebetween, and a first substrate formed on the first liquid crystal layer side surface of one of the pair of substrates. A first liquid crystal panel having one electrode and a first to second electrode formed on a surface of the other substrate on the first liquid crystal layer side;
A second liquid crystal layer, a pair of substrates arranged to face each other with the second liquid crystal layer interposed therebetween, and a second 2-layer formed on a surface of one of the substrates on the second liquid crystal layer side. A second liquid crystal panel having one electrode and a second-second electrode formed on a surface of the other substrate on the second liquid crystal layer side, and disposed under the first liquid crystal panel. Prepared,
A passive matrix type vertical alignment type liquid crystal display that displays a rectangular pixel in a region where the 1-1 electrode, the 1-2 electrode, the 2-1 electrode, and the 2-2 electrode overlap when a voltage is applied. A production method of the device,
In the first liquid crystal panel and the second liquid crystal panel, an average inclination direction of liquid crystal molecules when a voltage is applied to the first liquid crystal layer and an average of liquid crystal molecules when a voltage is applied to the second liquid crystal layer And configured so that the average tilt direction with respect to the sides of the rectangular pixels is approximately ± 45 °.
A method for producing a vertical alignment type liquid crystal display device.

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