JP2001318381A - Liquid crystal display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To overcome shortcomings of an IPS(in-plane switching) mode liquid crystal display panel i.e., having little margin for production due to comparatively large variation of white chromaticity caused by change of liquid crystal layer thickness and additionally having a low light modulation ratio due to high wavelength dependence. SOLUTION: The liquid crystal display panel, having normally black IPS mode construction in which the liquid crystal molecules exist in homogeneous aligning when no voltage is applied and exist in nearly 90 deg. twist aligning when voltage is applied, is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IPS (In-Plane Switching) type liquid crystal display panel exhibiting a wide viewing angle characteristic, and is particularly easy to produce because display unevenness hardly occurs. It relates to an excellent liquid crystal display panel.

[0002]

2. Description of the Related Art In recent years, liquid crystal display panels have begun to be used for display panels of monitors and televisions as display characteristics have been improved and screen sizes have been increased. In particular, IPS type liquid crystal display panels exhibiting a wide viewing angle characteristic have been introduced in high-end models of monitors and televisions. Such IP
The S type liquid crystal display panel is disclosed in, for example, Japanese Patent Application Laid-Open No. 10-260.
No. 431. Hereinafter, the conventional IPS type liquid crystal display panel described in the above publication will be briefly described.

FIG. 5 is a partial schematic sectional view showing a sectional structure of a conventional IPS type liquid crystal display panel. FIG.
6 is a schematic top view conceptually showing a planar structure of the liquid crystal display panel shown in FIG. 5 as viewed from above. The liquid crystal display panel shown in FIG. 5 includes an electrode substrate 10 provided with a pixel electrode 11 and a common electrode 12, a counter substrate 20, and the liquid crystal layer 1. The liquid crystal material used for the liquid crystal layer 1 is a nematic liquid crystal having a positive dielectric anisotropy. The thickness of the liquid crystal layer is about 3 μm, and the birefringence Δn is 0.09.
Therefore, Δn × d representing the retardation value is 27
0 (nm) and a wavelength of 540 nm near the center of visible light.
Is set to a value of one half. Also, the pixel electrode 11
The distance B between the electrode and the common electrode 12 is set to 15 μm.

[0004] An alignment film 2 is applied and formed on the surfaces of the electrode substrate and the opposing substrate which are in contact with the liquid crystal layer, and the alignment film 2 is applied to any of the substrates in the direction indicated by A in FIG. An orientation treatment has been performed. This alignment treatment is generally performed by a rubbing method, and the aligned alignment film strongly anchors the liquid crystal molecules 1a in contact. When no voltage is applied between the pixel electrode 11 and the common electrode 12, almost all the liquid crystal molecules 1a are aligned in the direction of A and are in a homogeneous alignment state. In FIG. 6, the alignment direction when no voltage is applied is inclined to the left by 3 ° from the vertical as an offset angle so that the liquid crystal molecules 1a rotate in the same direction when a voltage is applied.
That is, in the liquid crystal display panel shown in FIGS. 5 and 6, the angle between the alignment direction formed by the rubbing process on the alignment film 2 and the line of electric force generated between the pixel electrode 11 and the common electrode 12 is: It is almost right angle.

Next, when a voltage is applied between the pixel electrode 11 and the common electrode 12, the liquid crystal molecules 1a have a dielectric anisotropy. Try to align along. The arrangement direction of the liquid crystal molecules 1a is determined by the balance with the alignment force of the alignment film 2. At this time, the liquid crystal molecules 1a rotate counterclockwise in FIG. 6 due to the aforementioned offset angle. FIG. 5 shows the arrangement direction of the liquid crystal molecules 1a when a voltage is applied, and FIG. 6 shows the direction in which the liquid crystal molecules 1a rotate when a voltage is applied from the arrangement direction of the liquid crystal molecules 1a when no voltage is applied. I have.

[0006] The arrangement of the liquid crystal molecules 1a when the voltage is applied,
The light modulation rate is determined by the relationship with the polarization directions of the two polarizing plates 3 disposed outside the two substrates. In the IPS system, a normally black type is generally used, in which black display is performed when no voltage is applied and white display is performed when a voltage is applied, and high contrast is obtained. Note that, when a predetermined maximum voltage is applied between the pixel electrode 11 and the common electrode 12, the liquid crystal molecules 1a are arranged substantially along the lines of electric force C.

Here, since the thickness of the liquid crystal layer 1 is sufficiently smaller than the electrode spacing B, the lines of electric force C are generated substantially in parallel at both the upper part and the lower part of the liquid crystal layer 1. Therefore, the liquid crystal molecules 1a between the electrodes are all arranged in the same direction when a voltage is applied, except in the very vicinity of the alignment film 2 on the counter substrate 20 side. That is, the liquid crystal molecules in the liquid crystal layer are almost in a homogeneous alignment state even when a voltage is applied. In such a liquid crystal display panel, the thickness d of the liquid crystal layer and the birefringence Δn of the liquid crystal molecules are utilized by utilizing the birefringence of the liquid crystal molecules.
The light modulation is performed by inverting the phase of the light by setting the product Δn × d to approximately half the wavelength. That is, in this case, the thickness d of the liquid crystal layer, the birefringence Δn of the liquid crystal molecules, and the wavelength λ of the normally modulated light are expressed by the relational expression (2): Δn × d = １ ／ × λ (2 Satisfies.

[0008]

However, in the liquid crystal display panel having the structure of the above-mentioned prior art, there is no problem in black display when no voltage is applied, but the voltage is applied by directly utilizing the birefringence of the liquid crystal. The following problems occur when white display is performed by inverting the phase of light. That is, when the thickness d of the liquid crystal layer changes easily in production and unevenness in the display surface is likely to occur, the optimum wavelength is largely shifted, and the change in white chromaticity is relatively large. In addition, color unevenness in the display surface is likely to occur. Therefore, with respect to the thickness d of the liquid crystal layer, a margin in production is small, and it has been difficult to produce a high quality panel with high yield. Next, as shown in FIG. 7, in the conventional IPS mode liquid crystal display panel, V
The wavelength dependence of the -T characteristic (the relationship between the applied voltage and the transmittance) is large, and the wavelength ranges in which the maximum transmittance can be obtained during white display are R and G.
There is a problem that the luminous transmittance (light modulation rate), which differs for each wavelength of B and B and affects the entire visible light wavelength range, cannot be increased. Furthermore, the display panel is colored,
There was also a major problem that pure white display was not possible.

Accordingly, an object of the present invention is to solve such a conventional problem. Specifically, the present invention is easy to produce since display unevenness hardly occurs, and has a wide transmittance and excellent color display characteristics. An object of the present invention is to provide an IPS type liquid crystal display panel having a viewing angle.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an electrode substrate having a pixel electrode and a common electrode for at least one pixel, an opposing substrate, and an electrode substrate. A liquid crystal layer sandwiched therebetween, and a liquid crystal display panel of an in-plane switching mode having an alignment film provided on a surface of the electrode substrate and the counter substrate that is in contact with the liquid crystal layer, wherein liquid crystal molecules in the liquid crystal layer are: Provided is a liquid crystal display panel having a homogeneous arrangement when no voltage is applied, a twist arrangement of about 90 ° when a voltage is applied, and a normally black mode. In the liquid crystal display panel, when Δn is the birefringence of liquid crystal molecules and d is the thickness (nm) of the liquid crystal layer, the relational expression (1): Δn × d> 380 (nm) (1) Preferably, it is satisfied. Further, it is preferable that the orientation direction of the liquid crystal molecules when no voltage is applied is set in the range of 45 to 90 ° with respect to the direction of the horizontal electric field. Further, it is preferable that the thickness of the liquid crystal layer is at least half the distance between the pixel electrode and the common electrode. Further, it is preferable that the alignment force of the alignment film provided on the electrode substrate with respect to the liquid crystal molecules is weaker than the alignment force of the alignment film provided on the counter substrate with respect to the liquid crystal molecules.

In the liquid crystal display panel according to the present invention, the opposing substrate does not have an electrode for applying a lateral electric field, and a portion from the opposing substrate to at least a quarter of the thickness of the liquid crystal layer when a voltage is applied. A horizontal electric field is not applied to the liquid crystal molecules existing in the liquid crystal layer, and a horizontal electric field is applied to the liquid crystal molecules existing in a portion at least up to a quarter of the thickness of the liquid crystal layer from the electrode substrate. Is preferred. Further, each pixel is a region composed of the pixel electrode and the common electrode,
It is preferable to have at least two regions in which the direction of the lateral electric field when applying a voltage is different from each other. At this time, it is preferable that the intersection angle between the direction of the liquid crystal molecules having a homogeneous alignment when no voltage is applied and the horizontal electric field direction when the voltage is applied is 45 to 89 °.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to solve the above-mentioned problems, the present invention provides an electrode substrate having a pixel electrode and a common electrode for at least one pixel, an opposing substrate, and an electrode substrate between the electrode substrate and the electrode substrate. A liquid crystal display panel of a horizontal electric field type having a sandwiched liquid crystal layer, and an alignment film provided on a surface of the electrode substrate and the counter substrate that is in contact with the liquid crystal layer, wherein liquid crystal molecules in the liquid crystal layer have no voltage. Provided is a liquid crystal display panel having a homogenous arrangement at the time of application, a twist arrangement of about 90 ° at the time of applying a voltage, and a normally black mode. Therefore, the polarization axis of the polarizing plate provided on the electrode substrate side is orthogonal to the polarization axis of the polarizing plate provided on the counter substrate side. In the liquid crystal display panel, when Δn is the birefringence of liquid crystal molecules and d is the thickness (nm) of the liquid crystal layer, the relational expression (1): Δn × d> 380 (nm) (1) Preferably, it is satisfied. This is a condition for the visible light to rotate along the twist arrangement of the liquid crystal molecules. Also,
The upper limit of Δnxd may be about 1000, and preferably 380 to 480. On the other hand, Δn × d in the conventional IPS mode liquid crystal display panel is about 240 to 240.
It is about 300 nm, has a drawback that the range of d is narrow, and that the luminance change is sensitive to the fluctuation of d, and it is difficult to obtain a uniform display panel.

Preferably, the orientation direction of the liquid crystal molecules when no voltage is applied is set in the range of 45 to 90 ° with respect to the direction of the horizontal electric field. As described above, the orientation direction of the liquid crystal molecules when no voltage is applied can be controlled by a conventionally known method when performing the alignment treatment on the alignment film by the rubbing treatment.
Further, it is preferable that the thickness of the liquid crystal layer is at least half the distance between the pixel electrode and the common electrode. This is because the electric field does not act on the liquid crystal molecules near the opposing substrate, and a horizontal electric field acts on the liquid crystal molecules near the electrode substrate to obtain a twist arrangement. The upper limit may be about four times the distance between the pixel electrode and the common electrode.

It is preferable that an alignment force of the alignment film provided on the electrode substrate with respect to liquid crystal molecules is weaker than an alignment force of the alignment film provided on the counter substrate with respect to liquid crystal molecules. Specifically, at the time of the rubbing treatment, the orientation force can be adjusted by controlling the strength of the contact between the rubbing cloth and the orientation film, the rubbing density, and the like.

Next, in the liquid crystal display panel of the present invention, the counter substrate does not have an electrode for applying a horizontal electric field, and when a voltage is applied, at least a quarter of the thickness of the liquid crystal layer from the counter substrate. A horizontal electric field is not applied to the liquid crystal molecules existing in the portion up to and a horizontal electric field is applied to the liquid crystal molecules existing in a portion of at least a quarter of the thickness of the liquid crystal layer from the electrode substrate. It is preferred to configure. This is because the liquid crystal molecules are twisted when a voltage is applied. The lower limit may be about ８ of the thickness of the liquid crystal layer. Here, the upper limit is set to ４ because when an electric field acts too much on the center of the liquid crystal layer, the liquid crystal molecules take on a homogeneous arrangement instead of a twist arrangement. Further, in order to adjust the position in the thickness direction of the liquid crystal layer in which the alignment state of the liquid crystal molecules is different when a voltage is applied, specifically, the distance between the pixel electrode and the common electrode, the potential difference, and the like may be controlled.

Next, it is preferable that each pixel has at least two regions in which the alignment direction of liquid crystal molecules when no voltage is applied and the horizontal electric field direction when voltage is applied are different in relation to the pixel electrode and the common electrode. Conventionally, on an electrode substrate of an IPS type liquid crystal display panel, a pixel electrode and a common electrode are arranged substantially in parallel over each pixel. On the other hand, in the present invention, in one pixel, two or more regions in which directions of lines of electric force generated when a voltage is applied are different from each other are provided while arranging the pixel electrode and the common electrode substantially in parallel. This is shown in FIG. That is, the pixel electrode, which was conventionally linear, was slightly angled near its center. Thereby, there is an effect that the viewing angle can be further increased as compared with the conventional liquid crystal display panel. In this case, the intersection angle between the direction of the liquid crystal molecules when no voltage is applied and the direction of the horizontal electric field when the voltage is applied is 45 to 89 ° because light can be modulated and the liquid crystal molecules are not twisted in reverse. Is preferred. The control of the intersection angle can also be performed in the rubbing process as described above.

Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a partial schematic sectional view showing a sectional structure of an IPS type liquid crystal display panel according to an embodiment of the present invention. FIG. 2 is a schematic top view showing the planar structure of the liquid crystal display panel shown in FIG. As shown in FIGS. 1 and 2, the liquid crystal display panel of the present invention mainly includes an electrode substrate 10 on which a pixel electrode 11 and a common electrode 12 are formed, a counter substrate 20, and a liquid crystal layer 1. Here, a cyano-based nematic liquid crystal having a positive dielectric anisotropy was used for liquid crystal molecules to be filled in the liquid crystal layer 1, and no chiral agent was added. The thickness of the liquid crystal layer 1 was 8 μm, and Δn of the liquid crystal molecules was 0.055. Also, the pixel electrode 11
And the electrode interval B between the common electrodes 12 was 10 μm. That is, Δn × d = 440 nm, the Δn of the liquid crystal composition was set to be smaller, the thickness of the liquid crystal layer 1 was set to be considerably large, and the electrode interval B was set to be narrower than in the normal IPS mode.

As shown in FIG. 2, the planar structure is the same as that of the conventional IPS type liquid crystal display device except that the electrode interval B is narrowed. However, the alignment treatment of the electrode substrate and the counter substrate was performed under different conditions, and the alignment force with respect to the liquid crystal molecules was different between the upper and lower substrates. A polyimide alignment film 2 was applied to the surfaces of these substrates which were in contact with the liquid crystal layer, and was formed by curing. Thereafter, the surface of the alignment film 2 was subjected to an alignment treatment by a rubbing method. In this rubbing treatment, the contact between the alignment film 2 on the counter substrate 20 and the rubbing cloth was set strong, and the rubbing density was set high. On the other hand, the alignment treatment of the alignment film 2 of the electrode substrate 10 was performed such that both the contact with the rubbing cloth and the rubbing density were の of the counter substrate side. As a result, the liquid crystal molecules were strongly anchored to the alignment film of the counter substrate, and weakly anchored to the alignment film of the electrode substrate.

The rubbing directions of the upper and lower substrates are shown in FIG.
As shown in (2), the orientation was set to be 180 ° reverse, and a homogeneous orientation with a pretilt angle of about 2 ° was obtained. The polarizers 3 on the outer side of the electrode substrate 10 and the counter substrate 20 are set so that their polarization axes are perpendicular to each other so as to be in a normally black mode. They were arranged so that the indicated orientation directions A matched. With such a configuration, when no voltage is applied, the polarization axis on the incident side is aligned with the alignment direction A, that is, the arrangement direction of the liquid crystal molecules 1a, as described above, so that the birefringence of the liquid crystal is not affected. Thus, the light reaches the output-side polarizing plate 3 without changing the polarization state of the light. Here, since the polarization axes are orthogonal to each other, the light is absorbed and cut, and a black display is obtained. This mechanism is a conventional I
This is the same as the liquid crystal display panel of the PS system.

Next, when a predetermined maximum voltage is applied,
As shown in FIG. 1, the lines of electric force C are generated, and the liquid crystal molecules 1 a existing between the pixel electrode 11 and the common electrode 12 and located near the electrode substrate 10 are arranged along the electric field direction C shown in FIG. 1. Rotated. The predetermined maximum voltage is a voltage at which sufficient white luminance is obtained. However, since the thickness of the liquid crystal layer 1 is relatively large as compared with the electrode spacing B, the electric field is very weak in the vicinity of the counter substrate 20, and the anchoring force in this portion is set to be strong. Of the liquid crystal molecules 1a hardly moved. Therefore, when a voltage is applied, the liquid crystal molecules 1a are twist-arranged by twisting the liquid crystal molecules 1a of the liquid crystal layer 1 by about 90 ° (see FIGS. 1 and 2).
2 shows the arrangement direction of the liquid crystal molecules 1a when a voltage is applied. ). When light was incident in this state, the light in the visible light region was rotated so as to follow the twisted arrangement of the liquid crystal molecules 1a, and passed through the exit-side polarizing plate 3, resulting in white display.

In this case, the thickness d of the liquid crystal layer 1, the birefringence .DELTA.n of the liquid crystal molecules, and the wavelength .lambda. Of the normally modulated light are represented by the following formula (3), which is a Gouchtally equation: .DELTA.nxd = .SIGMA.3. / 2 × λ (3) According to this equation, the fluctuation of the optimum wavelength λ is 1 / √ in comparison with the conventional example, with respect to the fluctuation of the thickness d of the liquid crystal layer.
3, the fluctuation of the white chromaticity due to the fluctuation of the thickness d of the liquid crystal layer can be suppressed small, and the in-plane color unevenness hardly occurs. Further, since the wavelength dependency is reduced, the wavelength dependency of the VT characteristic is also reduced, and the wavelength range in which the maximum transmittance can be obtained during white display is relatively wide. Was good. Furthermore, for the same reason, coloring was little and good white display could be obtained. FIG. 3 shows the VT characteristic of the liquid crystal display panel according to the present embodiment. The difference due to the wavelength (color) is smaller than the VT characteristic of the conventional liquid crystal display panel shown in FIG. You can see that there is. Therefore, according to the present invention, a high-quality wide-viewing-angle liquid crystal display panel with a wide production margin can be produced with high yield.

Embodiment 2 Hereinafter, Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 4 is a schematic top view showing a planar structure of an electrode substrate of an IPS type liquid crystal display panel according to Embodiment 2 of the present invention. The configuration in the cross-sectional direction, the optical parameters, and the like were the same as in Example 1. As shown in FIG. 4, in the liquid crystal display panel according to the present embodiment, the pixel electrode 11 and the common electrode 12 are bent near the center thereof, and no offset angle is provided. It was perpendicular to the portion 12a.

With this configuration, two regions, ie, a region where the electric field direction is at 85 ° and a region where the electric field direction is at 95 ° with respect to the alignment direction A of the liquid crystal molecules (that is, in FIG. 85 ° to the right and 85 to the left
° region) was formed in one pixel. According to this configuration, when voltage is applied, a portion that is twisted 85 ° to the right and 8
There was a 5 ° twisted portion, and each portion had a different viewing angle characteristic. However, macroscopically, the viewing angle characteristics appear to be averaged, so that not only the contrast and gradation characteristics but also the viewing angle dependency including color change is reduced, and the IPS mode liquid crystal display panel is further improved. The viewing angle can be expanded.

[0024]

According to the present invention, the IPS mode of the normally black mode in which the liquid crystal molecules are in a homogeneous alignment when no voltage is applied and in an approximately 90 ° twist alignment when a voltage is applied is applied. A wide, wide viewing angle and high quality liquid crystal display panel can be realized.

[Brief description of the drawings]

FIG. 1 is a partial schematic cross-sectional view showing a cross-sectional structure of a liquid crystal display panel according to a first embodiment of the present invention.

FIG. 2 is a schematic top view showing a planar structure of an electrode substrate of the liquid crystal display panel shown in FIG.

FIG. 3 is a view illustrating V- of the liquid crystal display panel according to the first embodiment of the present invention.
Diagram showing T characteristics

FIG. 4 is a schematic top view showing a planar structure of an electrode substrate of a liquid crystal display panel according to a second embodiment of the present invention.

FIG. 5 is a partial schematic cross-sectional view showing a cross-sectional structure of a conventional IPS mode liquid crystal display panel.

6 is a schematic top view showing a planar structure of an electrode substrate of the IPS type liquid crystal display panel shown in FIG.

FIG. 7 is a diagram showing VT characteristics of a conventional IPS type liquid crystal display panel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal layer 1a Liquid crystal molecule 2 Alignment film 3 Polarizing plate 10 Electrode substrate 11 Pixel electrode 12 Common electrode 20 Counter substrate 21 Color filter A Alignment direction B Electrode spacing C Electric lines of force

Claims (8)

[Claims] 1. An electrode substrate having a pixel electrode and a common electrode for at least one pixel, a counter substrate, a liquid crystal layer sandwiched between the electrode substrate and the counter substrate, and a liquid crystal of the electrode substrate and the counter substrate. A liquid crystal display panel of a horizontal electric field type having an alignment film provided on a surface in contact with a layer, wherein liquid crystal molecules in the liquid crystal layer take a homogeneous arrangement when no voltage is applied and a twist arrangement of about 90 ° when a voltage is applied. ,
And a liquid crystal display panel in a normally black mode. 2. When the birefringence of the liquid crystal molecules is Δn and the thickness of the liquid crystal layer is d (nm), the relational expression (1): Δn × d> 380 (1) is satisfied. The liquid crystal display panel according to claim 1, wherein 3. An alignment direction of liquid crystal molecules when no voltage is applied,
3. The liquid crystal display panel according to claim 1, wherein the angle is set in a range of 45 to 90 degrees with respect to the direction of the horizontal electric field. 4. The liquid crystal display panel according to claim 1, wherein the thickness of the liquid crystal layer is at least half the distance between the pixel electrode and the common electrode. 5. The liquid crystal display device according to claim 1, wherein the alignment force of the alignment film provided on the electrode substrate is smaller than the alignment force of the alignment film provided on the counter substrate with respect to the liquid crystal molecules. A liquid crystal display panel according to any one of the above. 6. The opposing substrate has no electrode for applying a lateral electric field, and when a voltage is applied, the liquid crystal molecules present in at least a quarter of the thickness of the liquid crystal layer from the opposing substrate are reduced. 2. A horizontal electric field is not applied to the liquid crystal molecules, and a horizontal electric field is applied to liquid crystal molecules existing at least from the electrode substrate to a quarter of the thickness of the liquid crystal layer.
6. The liquid crystal display panel according to any one of items 1 to 5. 7. A pixel according to claim 1, wherein each pixel has at least two regions which are different from each other in a direction of a horizontal electric field when a voltage is applied. A liquid crystal display panel according to any one of the above. 8. The intersection angle between the direction of the liquid crystal molecules that take a homogeneous alignment when no voltage is applied and the direction of the horizontal electric field when a voltage is applied is 4.
The liquid crystal display panel according to claim 7, wherein the angle is 5 to 89 degrees.