JP2000267103A - Alignment film, method of manufacturing the same, and liquid crystal display device - Google Patents

Abstract

(57) [Summary] [Object] To provide an alignment film for liquid crystal display by irradiating a linear or partially polarized ultraviolet light to a photoreactive polymer material and a method for producing the same. A polymer having a photosensitive structural unit represented by Chemical Formula 1 or Chemical Formula 2 in a main chain structure is coated on a substrate to form a film. In the film, the photosensitive component is isotropic,
When light from an ultraviolet lamp is irradiated through a polarizer with linear polarization or partial polarization, photocrosslinking reaction of a photosensitive component in only a specific direction is promoted, and a highly crosslinked anisotropic film is formed. When the liquid crystal molecules come into contact with the polymer material film, the liquid crystal molecules are arranged by the interaction, and can form a liquid crystal alignment film. Since the liquid crystal can be aligned with a relatively small amount of irradiation energy by using the polymer material, an alignment film effective for a liquid crystal display device having excellent heat resistance can be provided without extending the alignment processing time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal panel having excellent heat resistance by irradiating a photosensitive polymer film with linearly or partially polarized ultraviolet rays having a relatively small energy amount. The present invention provides a polymer film for orienting a sealed liquid crystal, and is useful for improving a method of manufacturing a liquid crystal display.

[0002]

2. Description of the Related Art Conventionally, in order to align a liquid crystal enclosed in a liquid crystal panel, as shown in FIG. 2, a surface of a polymer compound 22 such as polyimide applied to a substrate 21 is wound around a cloth in which nylon or polyester fibers are planted. Rubbing with a drum (rubbing roll) 23 to form an extremely fine groove on the surface,
Alternatively, an alignment film produced by a method of stretching orientation or a method of oblique vapor deposition of silicon oxide (SiO) obtained by obliquely depositing silicon oxide (SiO) on a substrate has been used.
In such a precedent, the method of physically rubbing the surface of a polymer compound with a planted cloth causes discharge due to fine dust or static electricity, and has been a problem in a liquid crystal panel manufacturing process. In addition, the oblique deposition method of SiO has problems that it is difficult to maintain the uniformity of the deposition angle and the film thickness on the substrate, and the process becomes large. recent years,
In order to solve the above-mentioned problems, attention has been paid to a technique of aligning liquid crystals by irradiating light as a method for producing a non-rubbing alignment film. This liquid crystal photo-alignment technology is a decomposition type,
It is roughly classified into dimerization type, isomerization type, etc. In each case, by irradiating linearly polarized light to the formed photosensitive material, the photoreaction in only a specific direction progresses, and the film itself becomes anisotropic. It controls the orientation of the liquid crystal. A polyimide-based material has been reported as a photodecomposition type alignment film. Polyimide has been used for liquid crystal alignment films, and has high reliability in printability and cell electrical characteristics.However, it is inherently stable to light, has low photosensitivity, and utilizes decomposition reactions. There is a problem that the thermal stability of the liquid crystal alignment becomes insufficient. As a light dimerization type alignment film, polyvinyl cinnamate (PVCi) has been reported. However, low thermal stability is a problem in practical use. In PVCi, the light irradiation energy amount (313n
m) to 200 mJ / cm ² , but it is necessary to have an energy amount of ^{20 to} 30 J / cm ^{2 to} obtain a thermally stable film. 3D15
(1998). In addition, even an azo polymer used for a photoisomerization type alignment film has a thickness of up to 1000 mJ.
2B05 (1998) that liquid crystal alignment can be achieved with a relatively small amount of energy of about ² / cm ²
However, compounds showing photoisomerization have low stability to heat and light and are not practically usable.

[0003]

The polyimide rubbing alignment film is simple, but physically rubs the surface of the substrate to generate static electricity and dust, which hinders the liquid crystal display assembly process. On the other hand, in the case of optical alignment, when a large area of mother glass is irradiated collectively in a liquid crystal production line, the energy density is reduced, and the alignment processing time becomes longer with materials developed so far. Although it is possible to increase the energy density by increasing the size of the light source, there is a problem that the device becomes large and impractical.

[0004]

In view of the above problems, the present invention provides a liquid crystal alignment film using a polymer having at least one kind of a structure exhibiting photocrosslinkability represented by Chemical Formula 1 or 2 in the main chain. And a method for producing the same.

Embedded image

Embedded image However, in Chemical Formulas 1 and 2, Ar is p (m)-
A phenylene group and / or a p (m) -biphenylene group, R ₁ and R ₂ are a hydrogen group, a methyl group and / or a nitrile group. The photo-alignment material in the present invention includes a photo-crosslinkable aromatic acid component having an unsaturated bond, and a polyether, an aliphatic polyester, and an aliphatic polyester having a reactive group at both terminals for improving film forming properties. It can be synthesized by coupling with a polycarbonate or a long-chain alkylene component. As a basic synthesis method, melt polycondensation, solution polycondensation, interfacial polycondensation and the like can be used. The polymer needs to include a double bond for photocrosslinking and exhibiting liquid crystal alignment. For this purpose, p (m) -phenylenebis (acrylic acid), p (m) -phenylenebis (cyanobutadienecarboxylic acid), p (m) -phenylenebis (cyanoacrylic acid), 4 (3) -Hydroxycinnamic acid, p (m)-
Biphenylene bis (acrylic acid), p (m) -Biphenylene bis (cyanobutadiene carboxylic acid), p (m)-
Biphenylene bis (cyanoacrylic acid) or the like is used. Examples of components for improving film forming properties include polyalkylene glycols having a hydroxy group at both ends, such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and propylene oxide-ethylene oxide copolymer glycols, and amination at both ends. Polyalkylene oxides, such as polyethylene oxide, polypropylene oxide, polytetramethylene oxide, propylene oxide-ethylene oxide copolymer, and polyalkyl adipate as a polyester system, polyalkylene octanoate,
Examples thereof include aliphatic polyesters such as polyalkylene sebacate and aliphatic polycarbonates. By irradiating this polymer material with a linearly or partially polarized ultraviolet ray, an aromatic acid component having a photocrosslinkable unsaturated bond is crosslinked as shown in Reaction Formula 1, and an alignment having excellent heat resistance. A film may be formed. According to this solution, problems in the related art such as generation of defects due to fine dust and static electricity in the case of physically rubbing the surface of the polymer compound and prolongation of the alignment processing time in optical alignment are solved. .

Embedded image

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to FIG. A polymer coating film 12 is formed by applying (spin coating or casting) the solution of the above-described polymer material on the substrate 11. At the time of film formation, the aromatic acid component having an unsaturated bond is not oriented in a specific direction.
When the film is irradiated with a linearly or partially polarized ultraviolet ray L, the aromatic acid component having an unsaturated bond oriented in a direction parallel to the direction of electric field oscillation or the direction of the largest electric field oscillation of the irradiated ultraviolet ray is directed in the vertical direction. The photoreaction is promoted more than the aromatic acid component having an unsaturated bond, and an anisotropic film in which a crosslinking reaction in only a specific direction has progressed. Due to this crosslinking reaction, the polymer chains are fixed, and a film excellent in heat resistance without anisotropy being destroyed by heat treatment. In order to promote the crosslinking of the aromatic acid component having an unsaturated bond, light having a wavelength suitable for the reaction of this portion is irradiated. This wavelength varies depending on the structure represented by Formula 1 or 2,
Generally 200-500 nm, especially 250-45 nm.
The effectiveness of 0 nm is often high. When the liquid crystal molecules come into contact with the surface of the alignment film, the liquid crystal molecules are aligned in a direction perpendicular to the direction of the electric field vibration of the irradiated ultraviolet light or the direction of the largest electric field vibration. In the case of using the high-pressure mercury lamp, the polymer material of the present invention represented by the chemical formula 7 is 15 mJ / cm ^2.
It was confirmed by experiments that liquid crystal alignment was possible with a relatively small irradiation energy amount (313 nm).

Embedded image When the liquid crystal is oriented in the direction of electric field oscillation of irradiated ultraviolet light or in a direction perpendicular to the direction of the largest electric field oscillation, a pretilt angle does not appear, so that an alignment defect occurs in a TN (twisted nematic) type cell and is not suitable as an alignment film However, it can be sufficiently used as an alignment film of an IPS (in-plane switching) mode liquid crystal display device that does not require a pretilt angle. In the polymer material of the present invention, orientation is developed by promoting a crosslinking reaction of an aromatic acid component having an unsaturated bond in only a specific direction. Further, the heat resistance and strength of the film depend on the bridging strength of the aromatic acid component having an unsaturated bond.
On the other hand, the film-forming property depends on the content of a component for improving the film-forming property in the polymer material. From such a viewpoint, the content of the aromatic acid component having an unsaturated bond is desirably 10% by weight or more.

As described above, in the photo-alignment film and the method of manufacturing the same according to the present invention, the liquid crystal alignment excellent in heat resistance can be achieved by irradiating linearly polarized light or partially polarized ultraviolet light. Since a process such as rubbing the surface is not required, static electricity, dust and the like are not generated, and since the alignment function of the liquid crystal is expressed with a relatively small irradiation energy amount, without lengthening the alignment processing time, Particularly, an alignment film effective for an IPS mode liquid crystal display device can be provided.

A method for synthesizing a raw material compound of a polymer material will be described below. n-butyl-p-phenylenebisacrylate 1 mol, hexamethylene glycol 2-6 mo
1, polytetramethylene glycol 0.5-1.5mo
1 (molecular weight 1200), tetrabutyl titanate 0.9
5 mol and 0.74 mol of tridecyl phosphite are put into a reaction vessel, and 150 ° C. (1 hour) and 180 ° C. (0.
5 hours), followed by reaction at 220 ° C. under reduced pressure, and distilling off n-butanol and excess hexamethylene glycol produced by transesterification to reduce the content of the aromatic acid component having an unsaturated bond to 30 wt. %, 25wt%, 20
Polymer 1, Polymer 2 and Polymer 3 in wt% were obtained.

[0008]

EXAMPLES Example 1 Polymer 1 was dissolved in dichloroethane and spin-coated to a thickness of about 100 nm on a substrate covered with ITO (indium tin oxide). On the substrate,
Irradiated with 1.5 mW / cm ² (313 nm) polarized ultraviolet light at room temperature for 5 to 180 seconds from the direction perpendicular to the horizontal plane. By preparing two such substrates and filling them with a liquid crystal ZLI2061 [manufactured by Merck Japan Ltd.], a thickness of 4.
A TN type liquid crystal cell of 5 μm was assembled. When this liquid crystal cell was observed under crossed Nicols and parallel Nicols, clear light and dark were observed in the liquid crystal cell with an irradiation time of 10 seconds or more, and the orientation of liquid crystal molecules was confirmed. Further, the prepared cell was heated at 100 ° C.
Was heated in a constant temperature bath for 1.5 hours, and then cooled to room temperature. Observation of the heat-treated liquid crystal cell under crossed Nicols and parallel Nicols confirmed that the liquid crystal cell having an irradiation time of 10 seconds or more maintained the liquid crystal alignment performance before the heat treatment. The results are summarized in Table 1. In Table 1, the numbers at the top indicate the irradiation energy (mJ / cm ² ), ○ indicates good orientation, Δ indicates insufficient orientation, and × indicates poor orientation.

[Table 1]

Example 2 Polymer 2 was dissolved in dichloroethane and spin-coated to a thickness of about 100 nm on a substrate covered with ITO (indium tin oxide). The substrate was irradiated with polarized ultraviolet light of 1.5 mW / cm ² (313 nm) from a direction perpendicular to a horizontal plane at room temperature for 10 seconds. By preparing two such substrates and filling the liquid crystal ZLI2061, a TN type liquid crystal cell having a thickness of 4.5 μm was assembled. When this liquid crystal cell was observed under crossed Nicols and parallel Nicols, clear contrast was observed, and the orientation of the liquid crystal molecules was confirmed.

Example 3 A polymer 3 was dissolved in dichloroethane and spin-coated to a thickness of about 100 nm on a substrate covered with ITO (indium tin oxide). The substrate was irradiated with polarized ultraviolet light of 1.5 mW / cm ² (313 nm) from a direction perpendicular to a horizontal plane at room temperature for 10 seconds. By preparing two such substrates and filling the liquid crystal ZLI2061, a TN type liquid crystal cell having a thickness of 4.5 μm was assembled. When this liquid crystal cell was observed under crossed Nicols and parallel Nicols, clear contrast was observed, and the orientation of the liquid crystal molecules was confirmed.

Comparative Example 1 Polyvinylcinnamate
6 thinner (manufactured by Nissan Chemical Industries, Ltd.), spin-coated on a substrate covered with ITO (indium tin oxide),
Preliminary baking was performed at 90 ° C. for 30 seconds to obtain a coating film having a thickness of about 100 nm. 1.5 mW / cm ² (313 nm) is applied to the substrate.
Was irradiated at room temperature from the direction perpendicular to the horizontal plane for 300 seconds. A liquid crystal ZLI is prepared by fabricating two such substrates.
Filling with 2061, TN of 4.5 μm thickness
Type liquid crystal cell was assembled. This liquid crystal cell is crossed Nicols,
When observed under parallel Nicols, although clear light and dark were observed, the prepared cell was placed in a thermostat at 100 ° C. for 1.5 hours.
After heating for a period of time and cooling to room temperature, the liquid crystal cell was observed under crossed Nicols and parallel Nicols, and it was confirmed that the liquid crystal alignment was disturbed.

[0012]

As described above, according to the photo-alignment film and the method of manufacturing the same of the present invention, the liquid crystal alignment is possible by irradiating linearly polarized light or partially polarized ultraviolet light. Since a process such as physically rubbing the substrate surface is not required and static electricity, dust and the like are not generated, defects generated in a liquid crystal display assembling process are significantly reduced. In addition, since the liquid crystal can be aligned with a relatively small amount of irradiation energy, it is possible to provide an alignment film which is excellent in heat resistance and effective for a liquid crystal display device without lengthening the alignment processing time.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a method for manufacturing an alignment film according to the present invention.

FIG. 2 is an example showing a conventional method for manufacturing an alignment film.

[Explanation of symbols]

 11: substrate 12: polymer coating film L: natural light

Claims (5)

[Claims] 1. A step of applying a polymer having a structural unit represented by the chemical formula 1 or 2 in a structure on a substrate, and irradiating the applied polymer with linearly or partially polarized light. An alignment film and a method for manufacturing the alignment film, wherein the alignment film is manufactured in a step including: Embedded image Embedded image In the chemical formulas 1 and 2, Ar is a p (m) -phenylene group and / or p (m) -biphenylene group substituted at the para or meta position, and R ₁ and R ₂ are a hydrogen group, a methyl group and And / or a nitrile group. 2. A step of applying a polymer or copolymer having at least one of the structural units represented by Chemical Formula 3, Chemical Formula 4, Chemical Formula 5 and Chemical Formula 6 on a substrate, and An alignment film produced by a process including an operation of irradiating a polymer with linearly or partially polarized light, and a method for producing the alignment film. Embedded image Embedded image Embedded image Embedded image However, in Chemical Formula 3, Chemical Formula 4, Chemical Formula 5, and Chemical Formula 6, Ar _{1 to} Ar ₄ are p (m) -phenylene group and / or p (m) -biphenylene group, R _{1 to} R ₈ are hydrogen group, methyl X and Y are aliphatic polyesters, aliphatic polyethers, and / or aliphatic polycarbonates, and n and m are 1 to 12. 3. A copolymer comprising a component having at least one of the structural units represented by the chemical formulas 3, 4, 5, and 6 in the structure and a component comprising a polyalkylene oxide is provided on a substrate. It is characterized in that it is produced in a step of applying, and a step including an operation of irradiating linearly polarized light or partially polarized light to the applied polymer,
An alignment film and a method of manufacturing the same. 4. The method according to claim 1, 2 or 3.
3. The method for manufacturing an alignment film according to claim 1, wherein the method includes heating and cooling the substrate. 5. The method according to claim 1, 2 or 3.
5. A liquid crystal display device produced by the production method according to claim 4, wherein liquid crystal alignment is achieved by an alignment film.