JP2003029267A - Liquid crystal display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal panel having high response speed and wide visual field characteristics, in an IPS system liquid crystal display panel. SOLUTION: In the IPS system liquid crystal display panel, an alignment layer consisting of a polyimide having a fluorine-containing group in its side chain is formed on the surface of at least one substrate of an array substrate 1 and a color filter substrate 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel, and more particularly to an IPS type liquid crystal display panel in which liquid crystal is driven by applying an electric field substantially parallel to a substrate surface, which is a high quality liquid crystal display with fast response. It's about panels.

[0002]

2. Description of the Related Art In recent years, active matrix type liquid crystal displays using thin film transistors (TFTs) have been used in various fields such as displays for camcorders and displays for notebook computers, and have formed a large market. In particular, recently, application development as a monitor for personal computers and workstations is expected,
There is an increasing demand for a screen size having a diagonal of 13 to 14 inches or more. As the display mode of the TFT liquid crystal display, the twisted nematic (TN) mode is currently the mainstream, but for large-screen display applications, Japanese Patent Application Laid-Open No. 6-1608.
78, etc. are expected to have an in-plane switching (IPS) mode that applies an electric field almost parallel to the substrate surface and moves liquid crystal molecules parallel to the substrate surface due to its extremely wide viewing angle characteristics. Are gathering.

FIG. 2 is a diagram schematically showing the movement of liquid crystal molecules when displaying black and white in a conventional IPS mode liquid crystal display panel. 2 (a) and 2
(B) is a schematic diagram when an electric field is not applied and when an electric field is applied. As shown in FIG. 2, the IPS mode liquid crystal display panel operates by applying an electric field substantially parallel to the substrate surface. On the other hand, a conventional TN-mode liquid crystal display panel operates by applying electrodes to the upper and lower substrates and applying an electric field almost perpendicular to the substrate surface. The IPS-mode liquid crystal display panel and the TN-mode liquid crystal display panel have the same physical properties. The traits also differ in many ways. For example, regarding the response speed, it is generally considered that the IPS mode is slower than the TN mode. There are several possible causes for this, but one is the problem of the mode itself. As shown in FIG. 2A, when no electric field is applied, the liquid crystal molecules 8 are aligned substantially parallel to the pixel electrodes 3 without any twist between the array substrate 1 and the color filter substrate 2. When trying to display black and white, in the TN mode, the change from the horizontal direction to the vertical direction is about 90 °, whereas in the IPS mode, the change is about 45 ° as shown in FIG. 2B. Yes, this corresponds to the movement at the halftone level, which slows the response even in the TN mode.

Since the liquid crystal responds to an electric field, it is considered that the response can be speeded up by increasing the electric field strength. In the TN mode, since an electric field for moving liquid crystal molecules is generated between the upper and lower substrates, the electric field strength can be increased by reducing the distance between the substrates, that is, the cell gap.
It becomes possible to speed up the response. On the other hand, in the IPS mode, although the cell gap also affects the electric field strength, the electric field strength can be increased directly by narrowing the electrode interval.

[0005]

However, the conventional IPS mode liquid crystal display panel has the following problems. That is, in the IPS mode, the electrode portion generally does not transmit light, and the presence of the electrode portion leads to a reduction in aperture ratio. Therefore, there is a limit to improving the response speed by narrowing the electrode interval.

Further, in the IPS mode, since the viewing angle characteristics are emphasized, it is common to use a material system of a liquid crystal / alignment film having a low pretilt angle at the substrate interface, the anchoring of the interface is strong, and the interface is strong against an electric field. It is difficult to move,
The response speed becomes slow.

The present invention has been made in view of such problems of the conventional ones, and an object of the present invention is to provide a liquid crystal display panel having a fast response speed and a wide viewing angle.

[0008]

In a liquid crystal display panel according to the invention of claim 1 of the present application, liquid crystal is sandwiched between an array substrate and a color filter substrate facing the array substrate,
In a liquid crystal display panel for applying an electric field substantially parallel to the array substrate, at least one of the array substrate and the color filter substrate has a polyimide alignment film having a fluorine group in a side chain on its surface. , And that.

A liquid crystal display panel according to a second aspect of the present invention is the liquid crystal display panel according to the first aspect, wherein the liquid crystal contains 5% by weight or more of a cyano compound.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. Embodiment 1 of the present invention is one in which a polyimide alignment film having a fluorine group in a side chain is formed on the surface of a substrate, and the response speed of a liquid crystal display panel can be increased. .

FIG. 1 shows a plan view of a pixel portion of a liquid crystal display panel according to Embodiment 1 of the present invention. In the figure,
Reference numeral 1 is an array substrate, 3 is a pixel electrode, 4 is a common electrode, 11 is a signal wiring, and 12 is a scanning wiring.

As shown in FIG. 1, a pixel electrode 3 and a common electrode 4 are formed on an array substrate 1 in parallel with a signal wiring 11, and an electric field substantially parallel to the substrate surface is applied between these electrodes. It has become so. Generally, in a large-sized liquid crystal panel, the pixels have a vertically long shape.
The arrangement of the pixel electrode 3 and the common electrode 4 in the mode is
It is advantageous in terms of aperture ratio to extend the electrode in the signal wiring direction as shown in FIG. The signal wiring 11 and the scanning wiring 12 are both made of aluminum.

Next, after a polyimide alignment film having a fluorine group in a side chain is formed on the array substrate 1 and the color filter substrate facing the array substrate 1, a rubbing treatment with a rayon cloth is performed in a predetermined direction, and each is subjected to a rubbing treatment. Bonding is performed with a gap of 3.0 μm. After that, the liquid crystal is vacuum injected and IPS
Form a panel. The liquid crystal used did not contain a cyano compound, and had a refractive index anisotropy Δn of 0.09 and a dielectric anisotropy Δε of 10.5.

As shown in FIG. 2 (a), the liquid crystal is aligned without any twist between the array substrate 1 and the color filter substrate 2 when no electric field is applied, and its director direction 9
Forms an angle of 10 degrees with the signal wiring 11 as shown in FIG. Next, the polarizing plates 5 and 6 are attached to the top and bottom of the array substrate 1 and the color filter substrate 2, respectively, with their polarization axes orthogonal to each other and one polarization axis aligned with the director direction of the liquid crystal. Hereinafter, this liquid crystal display panel is referred to as liquid crystal panel A. Further, a liquid crystal display panel prepared by using a conventional polyimide alignment film containing no fluorine group instead of the polyimide alignment film having a fluorine group in its side chain in the liquid crystal panel A is referred to as a liquid crystal panel B.

A drive circuit is connected to the liquid crystal panel A and the response speed is measured. As a result, the rising response time τ _r is 1
8 msec, fall response time τ _d is 27 msec
Met. For the liquid crystal panel B, τ _r is 20 m
sec and τ _d were 29 msec.

A normal polyimide alignment film has an alkyl group in its side chain in order to generate a pretilt. The pretilt angle tends to increase as the alkyl chain is lengthened to increase the hydrophobicity. On the other hand, the fluorine group has the effect of lowering the surface energy and weakening the intermolecular interaction, and therefore acts to increase the hydrophobicity. As a result, it is considered that the pretilt angle becomes large, that is, it becomes difficult to receive the regulation force from the alignment film interface, and as a result, the response speed becomes faster.

As described above, in the liquid crystal display panel according to the first embodiment, the array substrate 1 and the color filter substrate 2 are used.
Since at least one of the substrates has a polyimide alignment film having a fluorine group on its side chain formed on the surface thereof, the response speed of the liquid crystal display panel can be increased.

Embodiment 2. In the liquid crystal display panel according to the first embodiment, the response speed can be increased by forming the polyimide alignment film having a fluorine group in the side chain on the surface of the substrate. In the second embodiment, the image sticking characteristic of the liquid crystal display panel is improved by further using the liquid crystal having 5% by weight of the cyano compound.

The plan view of the pixel portion of the liquid crystal display panel used in the second embodiment of the present invention is the same as that of the first embodiment. In the liquid crystal panel A produced by using the polyimide alignment film material containing a fluorine group in the side chain, Δ
A cyano compound having a physical property such as n, Δε and viscosity which is almost the same as that of the liquid crystal material used in the liquid crystal panels A and B is used.
A liquid crystal display panel was produced using a liquid crystal material containing wt%. Hereinafter, this liquid crystal display panel is referred to as a liquid crystal panel C. The response speed of the liquid crystal panel C was almost the same as that of the liquid crystal panel A.

Next, the burn-in characteristics of the liquid crystal panels A and C were evaluated. The evaluation method is to display a white and black stripe pattern for one hour and then check the presence or absence of an afterimage of the stripe pattern when the display is switched to full-scale halftone display. LCD panel A has a clear stripe pattern
An afterimage was seen even after 0 minute. On the other hand, in the liquid crystal panel C,
No afterimage was observed.

As described above, in the liquid crystal display panel according to the second embodiment, since the liquid crystal material containing 5% by weight of the cyano compound is used, the burn-in characteristic of the liquid crystal display panel can be improved.

[0022]

As described above, according to the liquid crystal display panel of the first aspect of the present invention, the liquid crystal is sandwiched between the array substrate and the color filter substrate facing the array substrate, and the array substrate is provided. In a liquid crystal display panel that applies an electric field substantially parallel to, at least one of the array substrate and the color filter substrate has a polyimide alignment film having a fluorine group in its side chain formed on its surface. Therefore, an excellent liquid crystal display panel having a high response speed can be provided. According to the liquid crystal display panel of claim 2 of the present invention, in the liquid crystal display panel of claim 1, the liquid crystal contains a cyano compound.
Since the content of the liquid crystal layer is not less than wt%, a liquid crystal display panel having no afterimage can be provided.

[Brief description of drawings]

FIG. 1 is a plan configuration diagram of a pixel portion of a liquid crystal display panel according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing movement of liquid crystal molecules when a black and white display is attempted in a conventional IPS mode liquid crystal display panel.

[Explanation of symbols]

3 pixel electrodes 4 common electrode 8 Liquid crystal molecules 9 Director direction of liquid crystal molecules 11 signal wiring 12 scanning wiring 13 thin film transistor

Claims (2)

[Claims] 1. A liquid crystal display panel in which a liquid crystal is sandwiched between an array substrate and a color filter substrate facing the array substrate, and an electric field substantially parallel to the array substrate is applied to the array substrate and the array substrate. A liquid crystal display panel, wherein at least one of the color filter substrates has a polyimide alignment film having a fluorine group in a side chain formed on the surface thereof. 2. The liquid crystal display panel according to claim 1, wherein the liquid crystal has a cyano compound in an amount of 5% by weight or more.