JP2004069870A - Orientation control film for liquid crystal, method for orienting liquid crystal using the same, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an orientation control film for a liquid crystal, which permits upsizing of a substrate and ensures uniform orientation, to provide a method for orienting the liquid crystal using the control film, and a liquid crystal display device. <P>SOLUTION: The liquid crystal display device is constructed by using an inorganic porous film composed of a porous SOG film as the orientation control film 3a for the liquid crystal, using the method for orienting the liquid crystal, which comprises laminating a glass substrate 1a with a transparent conductive film 2a attached thereon and a liquid crystal layer 5 via the orientation control film 3a for the liquid crystal and disposing the respective inorganic porous orientation control film 3a or 3b for the liquid crystal between a pair of the mutually opposing glass substrates 1a and 1b with the transparent conductive film 2a or 2b attached thereon and the liquid crystal layer 5 with the liquid crystal incorporated between the glass substrates 1a and 1b. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an alignment control film for liquid crystal, and further relates to a liquid crystal alignment method and a liquid crystal display device using the alignment control film.
[0002]
[Prior art]
FIG. 1 shows the structure of a TN type liquid crystal display panel, which is one of the mainstream liquid crystal display devices in recent years. Referring to FIG. 1, in the liquid crystal cell of this display panel, transparent conductive films 2a and 2b as positive and negative electrodes are respectively laminated on respective opposing surfaces of a pair of glass substrates 1a and 1b opposing each other, that is, inside. Next, alignment control films 3a and 3b are laminated on the inside of these electrodes, respectively, and a liquid crystal layer composed of a liquid crystal alone or a liquid crystal mixed with a dye is strictly sealed inside the two alignment control films. Is done. Then, the polarizing plates 4a and 4b are laminated on the glass substrates 1a and 1b on the side opposite to the facing surface, that is, on the outside, to constitute a liquid crystal display panel as a whole.
[0003]
In the above-mentioned TN type, a nematic liquid crystal having a positive dielectric anisotropy is used. When the liquid crystal cell is sealed, liquid crystal molecules are aligned in parallel by the alignment control films 3a and 3b. Twist 90 ° on the parallel plane (horizontal plane in FIG. 1) of the membranes 3a and 3b. That is, the liquid crystal molecules aligned in parallel as described above gradually tilt in a parallel plane between the two alignment control films so that the liquid crystal molecules near the alignment control film 3a and the liquid crystal molecules near the alignment control film 3b are orthogonal to each other. It is oriented in a twisted state.
[0004]
In the liquid crystal display panel configured as described above, if no voltage is applied between the transparent conductive films 2a and 2b, light passing through the polarizing plate 4a on the light source side becomes linearly polarized light and enters the liquid crystal layer. Then, the light vector is rotated by the twisted liquid crystal molecules in the liquid crystal layer, and passes through the polarizing plate 4b placed orthogonal to the polarizing plate 4a. On the other hand, when a voltage equal to or higher than a certain threshold value is applied, the liquid crystal molecules are homeotropically aligned, that is, vertically aligned, and thus lose the ability to rotate the light vector of the incident light from the polarizing plate 4a. Light is blocked by the polarizing plate 4b.
[0005]
The principle of the liquid crystal display device is to transmit and block incident light as described above, and the alignment treatment of liquid crystal molecules is important. In this alignment treatment, it is required to ensure uniformity of alignment of liquid crystal molecules.
[0006]
As a method for such an alignment treatment, a parallel alignment method called a rubbing method has been conventionally known. In this method, for example, a coating of a polyimide resin, which is an organic polymer, is applied on a substrate and baked, and then the surface of the coating is rubbed in a certain direction using a cloth roll or a brush.
[0007]
However, in the rubbing method, friction is applied to a laminated structure of at least three layers of a glass substrate, a transparent conductive film electrode adhered to the glass substrate, and an alignment control resin film. Dust generated by abrasion of brushes and friction machines and fragmentation of constituent materials of each layer is likely to be generated. In order to prevent the processing environment from deteriorating due to such dust, a cleaning step for removal is newly required. There is also a problem that uneven alignment may occur during friction by the rubbing method. Furthermore, the static electricity generated during the friction process causes the destruction of the TFT element, partially lowers the charge retention rate on the surface of the alignment control film, and causes the sticking of foreign substances adhered by electrostatic adsorption. I sometimes go. In addition to these, when the lamination shape is complicated, the rubbing conditions are different between the step-shaped portion and the flat-shaped portion, so that the alignment regulating force and the tilt angle are biased, and as a result, the alignment uniformity is obtained with high accuracy. It becomes difficult. In addition, since the rubbing step is often performed with the rubbing angle always constant, the pixel may need to be divided and aligned.
[0008]
As an alternative to the above-mentioned rubbing method, oblique evaporation method or rotary double vacuum evaporation method in which an oxide such as SiO ₂ or CrO is evaporated from a direction appropriately inclined with respect to the normal to the surface of the glass substrate to obtain a slant orientation, Instead of a glass substrate, a polymer film stretching method in which a polymer having a long main chain is stretched by about 200% to perform orientation treatment in the stretching direction, and a Langmuir film method besides these methods.
[0009]
[Problems to be solved by the invention]
By the way, in recent years, as the size of the display screen and the size of the solar cell increase, the tendency of the substrate to increase in size is remarkable.
[0010]
However, in the above-described oblique evaporation method and the rotary double vacuum evaporation method, there is a problem in mass productivity because the surface of the alignment control film formed by these is delicate and easily damaged, and even in the polymer film stretching method, There is a problem in that the types of long main chain polymers are limited.In addition, the Langmuir method requires large equipment for large-area substrates and has a limitation in improving the processing speed. The response to the change is not perfect. Rather, the ability to cope with a large-sized substrate is at present less than that of the rubbing method.
[0011]
There is also a method of aligning liquid crystal molecules in a random direction by using an organic polymer film having a fine structure such as a porous or mesh-like structure without performing rubbing (Japanese Patent Laid-Open No. 6-18890). Has the disadvantage of being low.
[0012]
In view of the above problems, the present invention provides a liquid crystal alignment control film capable of coping with an increase in the size of a substrate and ensuring uniformity of alignment, a liquid crystal alignment method using the control film, and a liquid crystal display device. The challenge is to do that.
[0013]
[Means for Solving the Problems]
In order to solve the above problems, the alignment control film for liquid crystal of the present invention is formed as an inorganic porous film. As the inorganic porous film, a film having pores of about nanometers is desirably used, so that a uniform orientation treatment can be performed without using a mechanical means such as a rubbing method. In addition, such an inorganic porous film can be easily formed regardless of the size of the film formation area, so that it can be applied to a large substrate.
[0014]
A preferred example of the inorganic porous film is a porous SOG film having a heat resistance temperature of about 400 ° C. or higher, which is about the same as that of a glass substrate, that is, an inorganic porous film formed using a Spin on Glass coating method. be able to.
[0015]
Furthermore, the liquid crystal alignment method in which the substrate with the transparent conductive film and the liquid crystal layer are laminated via the liquid crystal alignment control film made of the inorganic porous film makes it possible to perform both uniform alignment processing and large-sized substrates.
[0016]
Then, the above-mentioned inorganic porous liquid crystal alignment control film is interposed between a pair of substrates with a transparent conductive film opposed to each other and a liquid crystal layer formed by enclosing liquid crystal between the two substrates, thereby forming a liquid crystal display device. When configured, this device has high performance corresponding to an increase in the size of the substrate while ensuring uniform alignment of liquid crystal molecules.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
A method for manufacturing a liquid crystal display device including the inorganic porous alignment control film of the present invention will be described using the TN type liquid crystal display panel of FIG.
[0018]
Before forming the alignment control film of the present liquid crystal display panel, a transparent conductive film 2a is formed as an anode layer or a cathode layer on the surface of the liquid crystal element glass substrate 1a. At this time, an indium tin oxide (ITO) film can be used as a constituent material of the transparent conductive film 2a. In addition to the ITO film, tin oxide (SnO ₂ ), indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), cadmium oxide (CdO), and cadmium oxide-tin oxide (Cd ₂ SnO ₂ ) combining these materials ₄ ) A transparent conductive film such as cadmium oxide-zinc oxide (CZT) or indium oxide-zinc oxide (IZO) can be used. Further, a transparent conductive film that has been patterned according to the display format of the liquid crystal may be used.
[0019]
Then, spin rotation is performed on the transparent conductive film 2a using a porous silica material precursor solution containing hexamethyldisiloxane or hexamethyldisilazane having water repellency (for example, ISM-1.5 manufactured by ULVAC, Inc.). The film is formed by applying by spin coating at several 1500 rpm. To the porous silica material precursor solution used here, in addition to a water-repellent substance such as hexamethyldisiloxane or hexamethyldisilazane, alcohol or butyl acetate may be added as an additive as necessary. . Next, the above-mentioned transparent electrode film 2a with the spin coat film is fired together with the glass substrate 1a to which these are adhered, so that the solvent, water, acid or alkali catalyst or surface activity in the above-mentioned porous silica material precursor solution is obtained. While evaporating the agent and the like, an orientation control film 3a made of a porous SOG film is formed. At this time, the thickness of the orientation control film 3a is about 300 nm, but it is desirable to form the orientation control film 3a in the range of 50 nm to 2 μm by controlling the number of revolutions during spin coating.
[0020]
The baking conditions described above are not particularly limited as long as they can evaporate a solvent, water, acid, ammonia, or the like, and can obtain a porous SOG film. At a temperature of about 50 to 350 ° C. to mainly evaporate the solvent, and then to a temperature at which the surfactant or other organic substance can be evaporated in air of, for example, about 1 to 10 ⁵ Pa (for example, 200 ５００500 ° C.) for a period of time during which the structure of the resulting porous membrane is not destroyed. Of course, when oxidation or the like becomes a problem, it is necessary to perform treatment in an inert gas composed of He gas, Ar gas, N ₂ gas, or the like.
[0021]
The thus-formed laminated structure of the glass substrate 1a, the transparent conductive film 2a, and the alignment control film 3a, and a similar laminated structure (the glass substrate 1b, the transparent conductive film 2b, and the alignment control film 3b) are transparent. The conductive films 2a and 2b are configured to form a pair as positive and negative electrodes. Then, the liquid crystal layer 5 is arranged symmetrically with respect to the axis of symmetry so that the distance between the substrates 1a and 1b of both laminated structures becomes 50 μm. Furthermore, the liquid crystal display panel is formed by sandwiching the outer sides of the symmetrically arranged and opposed laminated structures 1a to 3a and 1b to 3b by polarizing plates 4a and 4b orthogonal to each other.
[0022]
The orientation of the thus obtained liquid crystal display simple panel was confirmed. As a result, the orientation control films 3a and 3b made of the porous SOG film are formed as porous films opened in a direction perpendicular to the opposing surfaces of the substrates 1a and 1b, whereby the liquid crystal molecules are removed from the surface of the substrate. It was confirmed that the film was vertically oriented in the normal direction.
[0023]
【The invention's effect】
As is clear from the above description, since the alignment control film for liquid crystal of the present invention is formed using an inorganic porous film such as a porous SOG film using a silica material, it has a heat resistance temperature of 400 ° C. or more. It is a porous film and has a uniform porous structure throughout the film, so that uniformity of alignment of liquid crystal molecules can be ensured, unlike a rubbing method or the like as a mechanical method. In addition, the formation of the inorganic porous film can be easily performed regardless of the size of the film formation area by a combination of a wet method and a firing method at a low degree of vacuum, so that it can be applied to a large substrate. .
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing a liquid crystal display panel.
1a 1b Glass substrate 2a 2b ITO film 3a 3b Porous alignment control film 4a 4b Polarizer 5 Liquid crystal layer

Claims (4)

An alignment control film for a liquid crystal, comprising an inorganic porous film. 2. The liquid crystal alignment control film according to claim 1, wherein the inorganic porous film is formed of a porous SOG film. A liquid crystal alignment method, comprising laminating a substrate with a transparent conductive film and a liquid crystal layer via an alignment control film for liquid crystal comprising the inorganic porous film. A liquid crystal display device, wherein the inorganic porous liquid crystal alignment control film is interposed between a pair of substrates with a transparent conductive film facing each other and a liquid crystal layer in which liquid crystal is sealed between the two substrates. .

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