JPH07128669A - Liquid crystal display panel and its production - Google Patents

Abstract

PURPOSE:To eliminate the need for a rubbing treatment and to prevent the nonuniformity of orientation. CONSTITUTION:This liquid crystal display panel has a pair of substrates 3 provided with electrodes 2 on opposite surfaces, a liquid crystal 1 which is clamped between a pair of these substrates 3 and has a chiral nematic phase and org. high polymer films 5 while are formed on the opposite surfaces of a pair of the substrates 3 and are elastomers. The org. high polymer films 5 which are elastomers are applied on the opposite surfaces of at least one substrate of a pair of the substrates 3 provided with the electrodes 2 on the opposite surfaces and after the liquid crystal 1 having the chiral nematic phase is clamped between the opposite surfaces of a pair of the substrates 3 and 3, the liquid crystal 1 is heated to a nematic phase-isotropic transition point (NI point) or above and is then cooled down to room temp. As a result, the production without executing the rubbing treatment is possible and the production of the liquid crystal display panel free from the nonuniform orientation of the liquid crystal is possible by heating the liquid crystal to the NI point of the liquid crystal or above.

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 its manufacturing method.

[0002]

2. Description of the Related Art A liquid crystal display panel in which scanning electrodes and signal electrodes are arranged in a matrix and liquid crystal is filled between the electrodes to form a large number of pixels to display an image is well known. Conventionally used liquid crystal has been a twisted nematic type (TN type) liquid crystal. When a TN type liquid crystal is used, it is usual to form a thin film of polyimide on an electrode and rub it to use it as a liquid crystal alignment film. However, such a TN liquid crystal cell has a problem that the viewing angle is narrow.

In recent years, a proposal for expanding the viewing angle has been proposed by Toko and Kobayashi (SID93 digest, pages 622 to 625). In this method, after forming a polyimide alignment film on a pair of electrodes, a chiral nematic liquid crystal is injected into the liquid crystal cell without rubbing and maintaining a constant gap. The chiral pitch of the chiral nematic liquid crystal is set to four times the cell thickness, so that the liquid crystal spontaneously twists about 90 degrees in the cell. Here, it is possible to switch the light by applying a voltage to the polarizing plates arranged on both sides of the cell in parallel or at right angles.

[0004]

However, in the liquid crystal display cell according to Toko et al., Which is not rubbed, the liquid crystal must be injected into the cell in an isotropic phase, and the entire liquid crystal cell is heated above the isotropic phase temperature. It is not realistic because of the drawback that equipment is required and the drawback that the time of the injection process increases because of heating and cooling during injection. When a method of injecting a liquid crystal in a nematic phase, which has been conventionally used in manufacturing a TN liquid crystal display panel for the liquid crystal cell that is not rubbed, is used, the liquid crystal is partially aligned due to the flow of the liquid crystal at the time of injection. However, there was a defect that the uniformity was poor with the naked eye. Further, even if the liquid crystal cell thus oriented by flow was kept in the isotropic phase for several hours, the non-uniformity was not completely eliminated.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a liquid crystal display panel in which liquid crystal display cells which are not rubbed have less uneven alignment and a manufacturing method thereof. And

[0006]

The liquid crystal display panel of the present invention comprises:
A pair of substrates provided with electrodes on opposite surfaces, a liquid crystal having a chiral nematic phase sandwiched between the pair of substrates, and an organic polymer film which is an elastomer formed on the opposite surfaces of the pair of substrates. There is. The liquid crystal used in the liquid crystal display panel of the present invention has a chiral nematic phase having a positive dielectric anisotropy, and has a region in which the major axis direction of liquid crystal molecules is microscopically aligned in a uniform direction. There are a plurality of liquid crystal molecules, the liquid crystal molecule major axis directions are different between the respective regions, and the liquid crystal molecules exhibit a twisted alignment state between the pair of substrates in each region. It has a disclination line.

The method of manufacturing a liquid crystal display panel according to the present invention is
An organic polymer film, which is an elastomer, is applied to the facing surface of at least one of the pair of substrates provided with electrodes on the facing surface, and a liquid crystal having a chiral nematic phase is sandwiched between the pair of substrates. It is characterized in that the material is heated to a nematic phase-isotropic phase transition point (NI point) or higher and then cooled to room temperature.

[0008]

In the liquid crystal display panel of the present invention, an organic polymer film, which is an elastomer, is formed on the opposing surfaces of a pair of substrates that are in contact with the liquid crystal. In such a liquid crystal display panel, it is possible to eliminate the alignment disorder due to the flow generated when the liquid crystal is sandwiched between the two electrodes at room temperature by heating.

It is considered that the alignment disorder due to the flow is caused by the liquid crystal adsorbing on the surface of the alignment film along the flow direction and deforming the alignment film. In the conventional configuration, since the surface of the alignment film is deformed, even if the liquid crystal cell is heated above the nematic phase-isotropic phase transition point (NI point) of the liquid crystal,
This alignment disorder remains. However, the organic polymer film, which is an elastomer used as an alignment film in the liquid crystal display panel of the present invention, has a low elastic modulus and allows the molecular chains to move to some extent, and therefore elastically deforms even when the liquid crystal is injected. , The liquid crystal orientation disorder due to the flow is unlikely to occur.

Further, by heating the liquid crystal above the nematic phase-isotropic phase transition point (NI point) to make it an isotropic liquid,
The liquid crystal substance randomly moves in Brownian motion.
At this time, when the liquid crystal is sandwiched between the electrodes, a slight deformation of the molecular chains of the alignment film caused by the flow of the liquid crystal is eliminated, and the molecular chains are randomly arranged. Therefore, in the liquid crystal display panel of the present invention, non-uniformity that can be observed with the naked eye due to alignment disorder due to flow does not occur.

[0011]

1 is a sectional view of an embodiment of the liquid crystal display panel of the present invention. The liquid crystal display panel is manufactured by sandwiching the liquid crystal 1 between the substrates 3 having the transparent electrode 2 on the surface in contact with the liquid crystal 1. This liquid crystal display panel has a polarizing plate 4 on the surface of the substrate 3 which is not in contact with the liquid crystal 1. In the liquid crystal display panel of this embodiment, the transmittance of light passing through the polarizing plate 4 and the liquid crystal 1 and yet another polarizing plate 4 is changed by the magnitude of the electric field applied to the liquid crystal 1 as in the conventional one. is there. The arrangement method of the two polarizing plates 4 is most preferably parallel or vertical. The liquid crystal display panel has an organic polymer film 5 which is an elastomer on the transparent electrode 2 of the substrate 3.

As the liquid crystal 1, a chiral nematic liquid crystal obtained by adding a small amount of a chiral agent to the nematic liquid crystal is used. As the nematic liquid crystal and the chiral agent, known materials used in twisted nematic (TN) liquid crystal display panels and super twisted nematic (STN) liquid crystal display panels can be used as they are. Examples of chiral agents include CB15 and C15 manufactured by BDH, CN, R811, S811, R1011 and S10 manufactured by Merck.
11, Chisso CM-19, CM, CM-20, CM
-21, CM-22, etc. can be used. The (liquid crystal layer thickness / pitch) of the liquid crystal 1 used is preferably about 0.1 to 0.75, and 0.25 is optimal because the liquid crystal display panel has less coloring.

The substrate 3 may be transparent to visible light. That is, as the substrate 3, glass, acrylic resin,
Known transparent substances such as polycarbonate resin, polyether sulfone, and polyarylate can be used. Although the thickness of the substrate 3 is not particularly specified, it is 1.1 mm to 500 mm.
It is generally about μm. The transparent electrode 2 made of tin oxide or ITO (indium tin oxide) is formed on the substrate 3 by means such as vapor deposition, sputtering, and CVD. Further, an organic polymer film 5 which is an elastomer is formed on this surface.

The organic polymer film 5, which is an elastomer, may be of any type, but is preferably thermoplastic since it is easy to make the orientation uniform by heating. Here, the elastomer refers to an elastomer having an elongation of 100% or more and substantially recovering its original shape when an external force is removed. Further, the organic polymer film 5 which is an elastomer is optimally one containing at least one selected from polystyrene, polyolefin, polyurethane, polyester and polyvinyl chloride.

The organic polymer 5 which is an elastomer
Must maintain their properties as an elastomer in the operating temperature range. The operating temperature range varies depending on the application of the liquid crystal display panel, but is generally about 0 ° C to 60 ° C. The organic polymer film 5 which is an elastomer is produced by applying the solution on the substrate 3 having the transparent electrode 2 and then removing the solvent. As a coating method, a known method such as a spin coating method, a printing method, or a dipping method can be used. The organic polymer film 5 which is an elastomer formed on the substrate 3 needs to be heated in order to remove the solvent.
The heating temperature varies depending on the solvent, but when N-methylpyrrolidone is used as the solvent, heating on a hot plate at 100 ° C. for 1 minute is sufficient. The film thickness of the organic polymer film 5 that is an elastomer is not particularly limited. However, it is optimal that the film thickness is 20 nm or more and 200 nm or less. If the film thickness is less than 20 nm, the film cannot cover the entire surface uniformly, and if it is thicker than 200 nm, the voltage drop due to the film becomes large, and the display quality as a liquid crystal display panel deteriorates.

The organic polymer film 5 which is an elastomer is formed on the surface of the substrate 3 having the transparent electrode 2. An insulating layer may be formed between the electrode 2 and the polymer film 5 serving as an alignment film to prevent a short circuit between the upper and lower substrates. Although the insulating layer may be made of any material, for example, silicon oxide and titanium oxide are excellent in insulating property and transparency. The organic polymer film 5 which is an elastomer should not have uniaxial orientation. When the organic polymer film 5 which is an elastomer has uniaxial orientation, a plurality of regions in which the long axes of liquid crystal molecules are oriented in a uniform direction are not present, which is not preferable. Therefore, the organic polymer film 5 that is the produced elastomer
Does not require an alignment treatment such as a rubbing treatment. 2 having an organic polymer film 5 which is an elastomer and a transparent electrode 2
The liquid crystal 1 is sandwiched between the substrates 3 with an appropriate gap maintained so that the polymer films 5 serving as the alignment films on the substrates 3 face each other. A known method such as a vacuum injection method or a liquid crystal dropping method can be used as the sandwiching method. In order to keep the distance between the two substrates 3 constant,
Generally, spherical particles of glass or synthetic resin are arranged between the substrates 3. Further, it is preferable to bond the two substrates 3 with an adhesive before or at the same time as the liquid crystal 1 is sandwiched. Epoxy resin is often used as the adhesive.

Further, in this way, the liquid crystal 1 is interposed between the substrates 3.
After sandwiching, the substrate 3 holding the liquid crystal 1 is held above the NI point of the liquid crystal. The holding time is not particularly limited, but when using a hot air dryer, about 2 hours is sufficient. If the liquid crystal display panel is kept at a high temperature for a long time, the liquid crystal may be partially decomposed, which is not preferable. Now, the polarizing plate 4 is attached to the surface of the substrate 3 of the liquid crystal display panel thus manufactured so that the polarization axes thereof are orthogonal to each other. Light is incident from the lower substrate 3 and observed from above the upper substrate 3. FIG. 2 is a perspective view showing a microscopic alignment state in a pixel at an off voltage when the liquid crystal display panel of this embodiment is driven. Reference numeral 6 in FIG. 2 represents the molecular long axis (director) of the liquid crystal molecule. There were a plurality of regions (domains) 7, 8, 9, 10 having different directors 6 at the substrate interface, and the disclination line 11 generated due to the different directions of the director 6 between the domains was observed. In a normal liquid crystal display panel, since the alignment film on the substrate is rubbed, only one domain in which the direction of the director 6 of the liquid crystal is the same is seen in the pixel.
In the case of this embodiment, since the organic polymer film 5 which is an elastomer is not subjected to the rubbing treatment, it is considered that the liquid crystal molecules are in an amorphous state and are aligned, and a plurality of domains are generated. In each domain, the liquid crystal molecules are in a twisted alignment state between the upper and lower substrates according to the set value of d / p. In this embodiment, since d / p is set to 0.25, the liquid crystal molecules are twisted and aligned by 90 ° between the upper and lower substrates. In this case, it is considered that the incident light is emitted with its polarization direction changed by 90 ° due to the birefringence effect of the liquid crystal layer.

Next, when an on-voltage is applied, the liquid crystal molecules in each domain change from the twist alignment state to the splay alignment state, so that a disclination line due to the deformation also occurs in the liquid crystal layer (bulk). . Within the domain, the liquid crystal molecules are oriented so that the directors are parallel to the direction of the electric field, and incident light propagates in the liquid crystal layer in a substantially linearly polarized state, and is cut by the exit side polarizing plate to obtain a dark state. But,
Disclination does not disappear completely.

The organic polymer film 5 which is an elastomer
The liquid crystal display panel having is excellent in liquid crystal orientation,
No non-uniform alignment of the liquid crystal 1 in the flow direction due to liquid crystal injection was observed. In the above description, the liquid crystal display panel in which the liquid crystal layer thickness divided by the liquid crystal pitch is 0.25 is used as the liquid crystal material, but the liquid crystal layer thickness / liquid crystal pitch is not limited to this. is not.

In the above description, the transmissive liquid crystal display panel is taken as an example, but the present invention can be applied to a reflective liquid crystal display panel having a reflective layer on one substrate. Specific examples will be described below. (Example 1) A N-methylpyrrolidone solution of a polyurethane elastomer (trade name: Paraprene 22S, made by Nippon Polyurethane Co., Ltd.) was applied on a surface having an electrode on a glass substrate having a circular electrode with an area of 2 cm ² using ITO. It was dried to prepare a film having a film thickness of 70 nm. This paraprene 2
When a film having a thickness of 50 μm was prepared by 2S and the elongation was measured at room temperature, it was 200% or more, and it was almost returned to the original length when the tension was removed.

Further, the two substrates on which the paraprene 22S film was formed were combined so that the alignment films face each other.
The distance between the substrates is kept at 5.0 μm and the periphery of the substrates is sealed with epoxy resin except at one place, and then NI is applied by a vacuum injection method.
Nematic liquid crystal (brand name LIXON660
4, manufactured by Chisso Petrochemical Co., Ltd.) was sealed between the substrates to produce a liquid crystal display panel. The liquid crystal injected here was obtained by adding a chiral agent (trade name R811, manufactured by E. Merck) so that the pitch of the liquid crystal was 20 μm. This liquid crystal panel was kept at 120 ° C. for 1 hour in a hot air dryer and then cooled to room temperature.

This liquid crystal panel was sandwiched between two polarizing plates arranged so that their polarization axes were orthogonal to each other. Furthermore, when a rectangular wave of 5 V and 60 Hz was applied to this liquid crystal display panel, light was not transmitted through the electrode portions, and light was transmitted through the other portions. Further, the liquid crystal display panel having the organic polymer film, which is a polyurethane elastomer, had a good liquid crystal alignment property, and no alignment nonuniformity of the liquid crystal in the flow direction due to liquid crystal injection was observed. (Example 2) A toluene solution of polystyrene elastomer (trade name Califlex TR, manufactured by Shell Chemical Co., Ltd.) was applied on a surface having an electrode on a glass substrate having a circular electrode having an area of 2 cm ² using ITO and dried. , Film thickness 70n
m film was prepared. 50μm with this Califlex TR
Film was prepared and its elongation was measured at room temperature.
When the tension was removed, it returned to almost the original length.

Further, the two substrates having the califlex TR film formed thereon were combined so that the alignment films face each other. After keeping the space between the substrates at 5.0 μm and sealing the periphery of the substrates with epoxy resin except at one place, a nematic liquid crystal with a NI point of 64 ° C. (product name LIXON6
604, manufactured by Chisso Petrochemical Co., Ltd.) was sealed between the substrates to produce a liquid crystal display panel. The liquid crystal injected here was obtained by adding a chiral agent (trade name R811, manufactured by E. Merck) so that the pitch of the liquid crystal was 20 μm. This liquid crystal panel was kept at 120 ° C. for 1 hour in a hot air dryer and then cooled to room temperature.

This liquid crystal panel was sandwiched between two polarizing plates arranged so that their polarization axes were orthogonal to each other. Furthermore, when a rectangular wave of 5 V and 60 Hz was applied to this liquid crystal display panel, light was not transmitted through the electrode portions, and light was transmitted through the other portions. Further, the liquid crystal display panel having the organic polymer film which is a polystyrene elastomer had a good liquid crystal alignment property, and no liquid crystal alignment nonuniformity due to the liquid crystal injection was observed. (Example 3) A N-methylpyrrolidone solution of a polyurethane elastomer (trade name Elastollan E1080, manufactured by Nippon Elastollan) was applied onto a surface having electrodes on a glass substrate having a circular electrode with an area of 2 cm ² using ITO. Then, it was dried to form a film having a film thickness of 70 nm. A film having a thickness of 50 μm was prepared using Elastollan E1080, and the elongation was measured at room temperature to find that it was 400% or more, and the length returned to the original value when the tension was removed.

Further, the two substrates having the Elastollan E1080 film formed thereon were combined so that the alignment films face each other. After keeping the space between the substrates at 5.0 μm and sealing the periphery of the substrates with epoxy resin except at one place, a nematic liquid crystal with NI point of 64 ° C. (product name LIXON
6604, manufactured by Chisso Petrochemical Co., Ltd.) was sealed between the substrates to manufacture a liquid crystal display panel. The liquid crystal injected here was obtained by adding a chiral agent (trade name R811, manufactured by E. Merck) so that the pitch of the liquid crystal was 20 μm. This liquid crystal panel was kept at 120 ° C. for 1 hour in a hot air dryer and then cooled to room temperature.

This liquid crystal panel was sandwiched between two polarizing plates arranged so that their polarization axes were orthogonal to each other. Furthermore, when a rectangular wave of 5 V and 60 Hz was applied to this liquid crystal display panel, light was not transmitted through the electrode portions, and light was transmitted through the other portions. Further, the liquid crystal display panel having the organic polymer film, which is a polyurethane elastomer, had a good liquid crystal alignment property, and no alignment nonuniformity of the liquid crystal in the flow direction due to liquid crystal injection was observed. (Comparative Example 1) A polyimide varnish (trade name LQ-S100, manufactured by Hitachi Chemical Co., Ltd.) N- was formed on a surface of an electrode on a glass substrate having a circular electrode with an area of 2 cm ² using ITO.
A methylpyrrolidone solution was applied and the solvent was removed using a hot plate, followed by curing at 250 ° C for 1 hour to give a film thickness of 70
A film of nm was prepared. When a film having a thickness of 50 μm was prepared from this polyimide and the elongation was measured, the elongation was 5% or less.

Further, the two substrates having the polyimide film formed thereon were combined so that the alignment films face each other. After keeping the distance between the substrates at 5.0 μm and sealing the periphery of the substrates with epoxy resin except at one place, the NI point 64 was applied by the vacuum injection method.
A nematic liquid crystal (trade name: LIXON6604, manufactured by Chisso Petrochemical) at ℃ was sealed between the substrates to manufacture a liquid crystal display panel. The liquid crystal injected here was a chiral agent (trade name: R811, manufactured by E. Merck) with a liquid crystal pitch of 20 μm.
What was added so that it became so. This liquid crystal panel was not kept at a high temperature.

This liquid crystal panel was sandwiched between two polarizing plates arranged so that their polarization axes were orthogonal to each other. Further, when a rectangular wave of 5 V and 60 Hz was applied to this liquid crystal display panel, light was not transmitted through the electrode portions, and light was transmitted through the other portions. However, it was possible to observe streaks along the flow of liquid crystal at the time of injection both when the voltage was OFF and when it was ON. Therefore, when the voltage was turned off, the color was colored along the lines, and even when the voltage was turned on, uniform black display was not obtained. Comparative Example 2 A polyimide varnish having a glass transition point of 266 ° C. of a cured product (trade name LQ) was formed on a surface of an electrode on a glass substrate having a circular electrode with an area of 2 cm ² using ITO.
-S100, Hitachi Chemical Co., Ltd.) N-methylpyrrolidone solution was applied, and the solvent was removed using a hot plate.
The film was cured at 50 ° C. for 1 hour to form a film having a film thickness of 70 nm.

Further, the two substrates having the polyimide film formed thereon were combined so that the alignment films face each other. After keeping the distance between the substrates at 5.0 μm and sealing the periphery of the substrates with epoxy resin except at one place, the NI point 64 was applied by the vacuum injection method.
A nematic liquid crystal (trade name: LIXON6604, manufactured by Chisso Petrochemical) at ℃ was sealed between the substrates to manufacture a liquid crystal display panel. The liquid crystal injected here was a chiral agent (trade name: R811, manufactured by E. Merck) with a liquid crystal pitch of 20 μm.
What was added so that it became so. This liquid crystal panel was kept at 120 ° C. for 1 hour in a hot air dryer and then cooled to room temperature.

This liquid crystal panel was sandwiched between two polarizing plates arranged so that their polarization axes were orthogonal to each other. Furthermore, when a rectangular wave of 5 V and 60 Hz was applied to this liquid crystal display panel, light was not transmitted through the electrode portions, and light was transmitted through the other portions. However, it was possible to observe streaks along the flow of liquid crystal at the time of injection both when the voltage was OFF and when it was ON. Therefore, a uniform black display was not obtained even when the voltage was turned on.

Examples 1 to 3 and Comparative Examples 1 and 2
The liquid crystal orientation was investigated for the purpose of comparative examination of the liquid crystal panels. The orientation was judged by whether or not an orientation defect was observed by visual observation with no voltage applied. The results are shown in Table 1.

[0032]

[Table 1]

[0033]

INDUSTRIAL APPLICABILITY The liquid crystal display panel of the present invention can be manufactured without rubbing treatment, and the
By heating above the point, it becomes possible to manufacture a liquid crystal display panel in which the alignment of the liquid crystal is not uniform.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a liquid crystal display panel of the present invention.

FIG. 2 is a perspective view showing a microscopic alignment state in a pixel of the liquid crystal display panel of FIG.

[Explanation of symbols]

 1 liquid crystal 2 transparent electrode 3 substrate 4 polarizing plate 5 organic polymer film which is an elastomer 6 molecular long axis of liquid crystal molecule 7 domain 8 domain 9 domain 10 domain 11 disclination line

Claims (4)

[Claims] 1. A pair of substrates provided with electrodes on opposing surfaces, a liquid crystal having a chiral nematic phase sandwiched between the pair of substrates, and an organic polymer which is an elastomer formed on the opposing surfaces of the pair of substrates. A liquid crystal display panel having a film. 2. The liquid crystal display panel according to claim 1, wherein the organic polymer film which is an elastomer is thermoplastic. 3. The liquid crystal display panel according to claim 1, wherein the organic polymer film which is an elastomer does not have uniaxial orientation. 4. A liquid crystal having a chiral nematic phase is applied between the pair of substrates by coating an organic polymer film, which is an elastomer, on at least one of the pair of substrates provided with electrodes on the opposite faces. After sandwiching the liquid crystal, the liquid crystal is heated to a nematic phase-isotropic phase transition point (NI point) or higher, and then cooled to room temperature, which is a method for manufacturing a liquid crystal display panel.