JP4119708B2 - Method for producing alignment control film for liquid crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an alignment control film for liquid crystal.
[0002]
[Prior art]
FIG. 1 shows the structure of a TN liquid crystal display panel which is one of the mainstream liquid crystal display devices in recent years. Referring to FIG. 1, a liquid crystal cell of this display panel is formed by laminating transparent conductive films 2a and 2b as positive and negative electrodes, respectively, on each facing surface side of a pair of glass substrates 1a and 1b facing each other, that is, inside. Next, alignment control films 3a and 3b are laminated inside these electrodes, respectively, and a liquid crystal layer 5 made of liquid crystal alone or a liquid crystal mixed with a dye is tightly sealed inside these alignment control films. Composed. And the polarizing plates 4a and 4b are laminated | stacked on the opposite side to the said opposing surface in the glass substrates 1a and 1b, ie, an outer side, and comprise a liquid crystal display panel as a whole.
[0003]
In the TN type as described above, nematic liquid crystal with positive dielectric anisotropy is used, and when encapsulated in a liquid crystal cell, liquid crystal molecules are aligned in parallel by the alignment control films 3a and 3b, and the alignment direction is controlled. The film 3a and 3b is twisted by 90 ° on the parallel plane (horizontal plane in FIG. 1). That is, the liquid crystal molecules aligned in parallel as described above are gradually inclined in the parallel plane between the two alignment control films so as to be orthogonal to each other in the vicinity of the alignment control film 3a and in the vicinity of the alignment control film 3b. 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, the 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 higher than a certain threshold is applied, the liquid crystal molecules are in a homeotropic alignment, that is, a vertical alignment, and therefore the ability to rotate the light vector of incident light from the polarizing plate 4a is lost. The light is blocked by the polarizing plate 4b.
[0005]
It is the principle of the liquid crystal display device that transmits and blocks the incident light as described above, and the alignment treatment of the liquid crystal molecules is important. In this alignment treatment, it is desired to ensure the alignment uniformity of the liquid crystal molecules.
[0006]
Conventionally, a parallel alignment method called a rubbing method is known as such an alignment treatment method. In this method, for example, a polyimide resin-based paint, which is an organic polymer, is applied on a substrate and baked, and then the surface of the coating film is rubbed (rubbed) in a certain direction using a cloth roll or a brush.
[0007]
However, the rubbing method rubs against a laminated structure of at least three layers of a glass substrate, a transparent conductive film electrode attached to the glass substrate, and an alignment control resin film. Dust generated due to wear of brushes and friction machines and fragmentation of constituent materials of each layer is likely to occur. In order to prevent the processing environment from being deteriorated by such dust, a cleaning process for removal is newly required. Another problem is that there is a risk of orientation unevenness during rubbing. Furthermore, static electricity generated during the friction process causes damage to the TFT element, and also partially reduces the charge retention rate on the surface of the orientation control film, or causes seizure of foreign matter adhered by electrostatic adsorption. Sometimes. In addition to these, when the laminated shape is complicated, the rubbing conditions are different between the stepped shape portion and the flat shape portion, so that the orientation regulating force and the tilt angle are biased, and as a result, the uniformity of the orientation is obtained with high accuracy. It becomes difficult. Further, since the rubbing process is often performed with the rubbing angle kept constant, pixel divisional alignment may be required.
[0008]
As an alternative to the rubbing method described above, an oxide such as SiO ₂ or CrO is vapor-deposited from a direction inclined with respect to the normal of the glass substrate surface, and an oblique vapor deposition method or a rotary double vacuum vapor deposition method for obtaining a tanned orientation, In place of the glass substrate, there is a polymer film stretching method in which an orientation treatment in this stretching direction is performed using a film obtained by stretching a polymer having a long main chain by about 200%, and Langmuir film method is also used.
[0009]
[Problems to be solved by the invention]
By the way, in recent years, with the progress of larger displays and larger solar cells, the trend toward larger substrates is remarkable.
[0010]
However, in the oblique deposition method and the rotary double vacuum deposition method described above, there is a difficulty in mass productivity because the surface of the orientation control film formed by these is delicate and easily damaged, and in the polymer film stretching method, There is a problem that the types of long main chain polymers are limited, and the Langmuir method also requires a large apparatus for large-area substrates and has a limitation in improving the processing speed. Response to conversion is not perfect. Rather, the ability to handle large substrates is not as good as the rubbing method.
[0011]
In addition, there is a method (Japanese Patent Laid-Open No. 6-18890) in which liquid crystal molecules are oriented in a random direction by an organic polymer film having a fine structure such as a porous or network structure without rubbing. Has the disadvantage of being low.
[0012]
In view of the above problems, an object of the present invention is to provide a method for producing an alignment control film for liquid crystal that can cope with an increase in the size of a substrate and can ensure alignment uniformity.
[0013]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention , the alignment control film for liquid crystal is formed as an inorganic porous film. As the inorganic porous film, a film having pores on the order of nanometers is desirably used, whereby uniform alignment treatment can be performed without depending on mechanical means such as a rubbing method. Such an inorganic porous film can be easily formed regardless of the size of the film formation area, and thus can be applied to a large substrate.
[0014]
And as said inorganic porous film, the porous SOG film | membrane which has a heat resistant temperature of 400 degreeC or more comparable as a glass substrate, ie, the inorganic porous film formed using the Spin on Glass coating method, is made into a suitable example. be able to.
That is, the method for producing an alignment control film for liquid crystal according to the present invention includes a step of applying a porous silica material precursor solution by spin coating on a transparent conductive film of a substrate with a transparent conductive film, Baking the formed substrate, and forming an orientation control film made of a porous SOG film while evaporating the solvent , water, catalyst and surfactant contained in the porous silica material precursor solution. is doing.
The porous silica material precursor solution may contain water-repellent hexamethyldisiloxane or hexamethyldisilazane.
Also, an alcohol or butyl acetate Le may be added as an additive to the porous silica material precursor solution.
Furthermore, the calcination process may be treated at a temperature of 50 to 350 ° C. in air was mainly evaporate the solvent to evaporate the surfactant other organic matter then with 1 to 10 5 ^Pa in the air It is preferable to process at the temperature of 200-500 degreeC.
Further, an inert gas may be used instead of the air.
[0015]
Furthermore, the liquid crystal alignment method of laminating a substrate with a transparent conductive film and a liquid crystal layer through the above alignment control film for liquid crystal composed of an inorganic porous film enables both uniform alignment processing and large-size substrate compatibility.
[0016]
A liquid crystal display device is formed by interposing the inorganic porous liquid crystal alignment control film between a pair of substrates with a transparent conductive film facing each other and a liquid crystal layer formed by sealing liquid crystal between the two substrates. 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]
DETAILED DESCRIPTION OF THE INVENTION
A method for producing an alignment control film for liquid crystal according to the present invention will be described using the TN type liquid crystal display panel of FIG.
[0018]
Prior to the formation of the alignment control film of the present liquid crystal display panel, the transparent conductive film 2a is formed as an anode layer or a cathode layer on the surface of the glass substrate 1a for liquid crystal elements. 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 a combination of these cadmium oxide-tin oxide (Cd ₂ SnO) ₄ ) Transparent conductive films such as cadmium oxide-zinc oxide (CZT) and indium oxide-zinc oxide (IZO) can be used. The transparent conductive film may be patterned according to the liquid crystal display format.
[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. In addition to water-repellent substances such as hexamethyldisiloxane and hexamethyldisilazane, alcohol or butyl acetate may be added as an additive to the porous silica material precursor solution used here, if necessary. . Next, the transparent electrode film 2a with the spin coat film is baked together with the glass substrate 1a to which the transparent electrode film 2a is attached, and the solvent, water, acid or alkali catalyst, or surface activity in the porous silica material precursor solution is baked. The orientation control film 3a made of a porous SOG film is formed while evaporating the agent and the like. At this time, the film thickness of the orientation control film 3a is about 300 nm, but it is desirable to form the film in the range of 50 nm to 2 μm by controlling the number of rotations during spin coating.
[0020]
The firing treatment conditions described above are not particularly limited as long as the solvent, water, acid, ammonia, or the like can be evaporated, and a porous SOG film can be obtained. At a temperature of about 50 to 350 ° C. to mainly evaporate the solvent, and then, for example, a temperature at which a surfactant or other organic substance can be evaporated in air of about 1 to 10 ⁵ Pa (for example, 200 (~ 500 ° C) may be heat-treated for a time during which the resulting porous membrane structure is not destroyed. Of course, when oxidation or the like becomes a problem, it is necessary to treat all in an inert gas composed of He gas, Ar gas, N ₂ gas or the like.
[0021]
The laminated structure of the glass substrate 1a, the transparent conductive film 2a, and the orientation control film 3a thus formed, and the same laminated structure (the glass substrate 1b, the transparent conductive film 2b, and the orientation 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 stacked structures is 50 μm. Further, the liquid crystal display panel is formed by sandwiching the outer sides of the laminated structures 1a to 3a and 1b to 3b arranged symmetrically in this manner and sandwiched by polarizing plates 4a and 4b orthogonal to each other.
[0022]
The orientation of the liquid crystal display simple panel thus obtained 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 facing surfaces of the substrates 1a and 1b, whereby the liquid crystal molecules are formed on the substrate surface. It was confirmed that the film was vertically aligned in the normal direction.
[0023]
【The invention's effect】
As is apparent from the above description , according to the method for producing an alignment control film for liquid crystal of the present invention, it is formed using an inorganic porous film such as a porous SOG film using a silica material. The porous film has a heat-resistant temperature and has a uniform porous structure throughout the film, and this can ensure the uniformity of the alignment of liquid crystal molecules, unlike the rubbing method that is a mechanical method. . 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 low-vacuum baking method, and thus 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 polarizing plate 5 liquid crystal layer

Claims (5)

Applying a porous silica material precursor solution by spin coating on the transparent conductive film of the substrate with the transparent conductive film; and
A step of firing the substrate formed in the step and forming an orientation control film made of a porous SOG film while evaporating the solvent , water, catalyst, and surfactant contained in the porous silica material precursor solution. A method for producing an alignment control film for liquid crystal comprising:   2. The method for producing an alignment control film for liquid crystal according to claim 1, wherein the porous silica material precursor solution contains hexamethyldisiloxane or hexamethyldisilazane having water repellency. The method of creating the porous silica material precursor solution for liquid crystal alignment layer according to claim 2, characterized in that the addition of alcohol or butyl acetate Le as additives. The calcination treatment is 200 that can be treated at a temperature of 50 to 350 ° C. in air was mainly evaporate the solvent to evaporate the surfactant other organic matter then with 1 to 10 5 ^Pa in the air The method for producing an alignment control film for liquid crystal according to any one of claims 1 to 3, wherein the treatment is performed at a temperature of 500 ° C.   The method for producing an alignment control film for liquid crystal according to claim 4, wherein an inert gas is used instead of the air.

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