JP3341042B2 - Method for producing tilt alignment film for liquid crystal and liquid crystal cell using tilt alignment film for liquid crystal obtained by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal cell using a tilt alignment film for a liquid crystal having high productivity in which any tilt angles can be designed, by irradiating a resin film containing a photoisomerization reaction structural unit with non-polarized light in an oblique direction. SOLUTION: A resin film containing a photoisomerization reaction structural unit is irradiated with non-polarized light in an oblique direction to form a tilt alignment film for a liquid crystal. The resin film used contains a photoisomerization reaction structural unit, and the photoisomerization reaction structural unit preferably has at least one double bond selected from N=N and C=C bonds and causes geometrical photoisomerization reaction by irradiation of light. As for the photoisomerization reaction structural unit having N=N bonds, for example, azobenzene and azopyridine can be used. As for the photoisomerization reaction structural unit having Cr=C bonds, for example, stilbene and stilbazole can be used. As for the resin containing the photoisomerization reaction structural unit, any of vinyl polymers, ring-opened polymers or the like can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a tilt alignment film for liquid crystal and a liquid crystal cell using the tilt alignment film for liquid crystal obtained by the manufacturing method.

[0002]

2. Description of the Related Art Since liquid crystals exhibit optical anisotropy, by using their birefringence, dichroism and optical rotatory power, devices such as display or recording devices and optical devices such as polarization and light interference can be used. It can be used for various optical elements based on characteristics. In addition, a liquid crystal is sandwiched between two substrates provided with transparent electrodes to form a liquid crystal cell composed of a large number of pixels, and a voltage is applied to the liquid crystal layer, whereby a liquid crystal display based on switching of liquid crystal alignment is performed. The device is realized. In order to optimize the optical characteristics of such a liquid crystal display device, it is essential to align and orient the liquid crystal in a uniform direction.
For this purpose, a method of chemically or physically treating a substrate surface is known (J. Cognard, Mol. Cryst. Liq. Cry.
st., Spplement 1, p1 (1982)).

For example, in order to obtain a homogeneous alignment of liquid crystal which is parallel to the substrate surface and is uniformly aligned in one direction, the surface of the substrate is coated with a polymer resin film such as polyimide, and this is coated in one direction with a cloth or the like. A rubbing method of rubbing is known. This method is widely used for producing an alignment film for liquid crystal which is indispensable for constructing a liquid crystal cell.

The orientation of the liquid crystal includes an out-of-plane orientation which is an orientation in a direction (polar angle direction) included in a plane perpendicular to the substrate surface, and a direction (azimuth direction) in a plane parallel to the substrate surface. ), There is an in-plane orientation, and furthermore, an orientation having both of them, that is, an orientation in a certain latitude and longitude direction. The angle between the alignment direction of the liquid crystal molecules and the surface of the substrate is called a pretilt angle. Control of the alignment having both out-of-plane alignment and in-plane alignment has the same meaning as the control of the pretilt angle. Regardless of whether the operation mode is twisted nematic (TN) or super twisted nematic (STN), in order to manufacture a high-quality liquid crystal display device, the pretilt angle is controlled so that the voltage inside the liquid crystal cell is turned off when the voltage is not applied. Angle between the liquid crystal alignment direction of the substrate and the substrate surface is an inclination angle other than 0 degrees or 90 degrees (this is called a tilt angle in the present specification, and a liquid crystal alignment film having a tilt angle is tilted for a liquid crystal. (Referred to as a film). It is said that an optimum tilt angle exists according to various operation modes. Therefore, there is a need for a tilt alignment film for liquid crystal that generates an arbitrary tilt angle.

Conventionally, the above-described rubbing method is used industrially because a rubbing process is performed in a fixed direction to give a tilt angle whose direction is fixed. In addition to the rubbing method, methods for generating a tilt angle include an oblique vapor deposition method (JP-A-56-68626) and a Langmuir-Blodgett method of providing a polymer monomolecular film on a substrate surface (JP-A-62-195622). Gazette) has been proposed.

As another method for controlling the liquid crystal alignment, a liquid crystal alignment control method utilizing a photochemical reaction on a substrate surface is known. In this method, a molecular layer or a polymer layer containing a molecule that undergoes an isomerization reaction by the action of light is provided on a substrate surface, and the layer is irradiated with linearly polarized light to perform alignment control (Ichimura , Surface, 32, 671 (1994)
reference). By irradiating the above-mentioned molecular layer or polymer layer with linearly polarized light, a change in the molecular structure or molecular orientation is induced to change the orientation of the liquid crystal, and the direction defined by the polarization axis of the linearly polarized light. The liquid crystal can be aligned at a time, and homogeneous alignment control can be easily realized (Kawanishi et al., Polym. Mater. Sci. Eng., 66, p263 (19
92)). In addition, a method has been proposed in which a film formed by dissolving and dispersing a dichroic dye in polyimide is irradiated with linearly polarized light to form an alignment film for liquid crystal (Gibbon et al., Nature, 351;
p49 (1991)). However, in these, the tilt angle is not controlled.

[0007] On the other hand, cinnamic acid derivatives (M. Schadt et al., Jpn. J. Appl. Phys., 74, p2071 (1992)) and coumarin derivatives (M. Schadt et al., Nature, 381, p212 (M. Schadt et al.) 1996)), a liquid crystal alignment treatment method comprising irradiating linearly polarized light to a polymer film having a side chain. Another method is to irradiate the polyimide film with linear ultraviolet light to form an alignment film for liquid crystal (Hasegawa et al., J. Photopolym. Sci. Tec.
hnol., 2, p241 (1995)). Alternatively, a method of irradiating an excimer laser to the surface of a polymer film to form a periodic striped pattern on the surface has been reported (JP-A-2-19621).
No. 9, etc.).

It is well known that these light irradiation methods give a homogeneous orientation, but as a method for giving a tilt angle, a polymer film having a cinnamic acid derivative in a side chain is irradiated obliquely with linearly polarized light (Y .limura, T. Satoh and S. Kobaya
shi: J. Photopolym.Sci.Technol., 8, p257 (1995)), irradiating a polymer film having a coumarin derivative in the side chain with linearly polarized light obliquely (M. Schadt et al., Nature, 381, 212 (1996)) ,
Irradiate the polyimide film obliquely with polarized laser light (MH
asegawa et al., J. Photopolym.Sci.Technol., 2, p241 (1995))
It is known. Each of these uses linearly polarized light and irradiates the light obliquely to the substrate.

The rubbing treatment gives a homogeneous orientation while generating a tilt angle relatively easily. However, since the orientation direction is limited to one direction, it is difficult to give a fine and multiaxial orientation state. Or impossible. For this reason, an alignment division method which has been proposed as a method for improving the viewing angle dependency in a liquid crystal display device in particular.
(JP-A-62-159119, JP-A-63-10
In Japanese Patent No. 6624), one pixel is divided into a plurality of parts and different pretilt angles and directions of liquid crystal alignment are set for each area. However, it is difficult to perform this by a rubbing method and lacks productivity. Also, other physical methods have a significant lack of productivity, as follows. That is, the oblique deposition method requires a vacuum system, and multiaxial orientation is impossible. In the Langmuir-Blodgett method, it is indispensable to raise the water surface spread film, and similarly, multiaxial orientation cannot be performed.

On the other hand, the method of controlling the liquid crystal alignment by the action of light gives a liquid crystal alignment state by exposing a large area of the substrate at a time, and also diverts photolithography technology. This is an excellent method in principle because of providing divided pixels. However, there are the following problems in applying this method to an alignment film for liquid crystal. In other words, in order to use polarized light, a polarizing element is generally required, so that the effective light amount is reduced to reduce productivity, and that a pretilt angle over a wide range from 90 degrees to 0 degrees cannot be arbitrarily set. , And so on.

[0011]

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing a tilt alignment film for a liquid crystal, which does not require the use of a polarizing element at the time of manufacture, is high in productivity, and can be set to an arbitrary tilt angle. An object of the present invention is to provide a liquid crystal cell using a tilt alignment film for liquid crystal obtained by the method.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, when the non-polarized light is irradiated on the photoisomerization-reactive molecule, the non-polarized light is irradiated. Of molecules having a transition moment in the direction perpendicular to the direction of incidence selectively absorb light and isomerize, resulting in preferential generation of molecules having a transition moment in the direction corresponding to the direction of incidence. As a result, the present invention has been completed.

That is, according to the present invention, there is provided a method for producing a tilt alignment film for liquid crystal, which comprises irradiating a non-polarized light to a resin film containing a photoisomerization reaction constituent unit from an oblique direction. . Further, according to the present invention, a tilt alignment film for liquid crystal is produced, wherein non-polarized light is irradiated from an oblique direction to a resin film containing a photoisomerization reaction constituent unit and causing liquid crystal vertical alignment. A method is provided. Further, according to the present invention, the substrate on which the tilt alignment film for liquid crystal obtained by any one of the above manufacturing methods is formed and the substrate on which the alignment film for liquid crystal, which may be the same as or different from the substrate, are opposed. There is provided a liquid crystal cell which is arranged and sandwiches liquid crystal between these substrates.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The tilt alignment film for liquid crystal of the present invention is formed by irradiating a non-polarized light from an oblique direction to a resin film containing a photoisomerization reaction constituent unit. The resin film used in the present invention contains a photoisomerization reaction structural unit. The photoisomerization reaction structural unit includes N = N bond and C =
Having at least one double bond selected from a C bond,
Those which cause a photogeometric isomerization reaction by light irradiation are preferably used. Examples of the photoisomerization reaction structural unit having an N = N bond include azobenzene, azopyridine, and azonaphthalene. Examples of the photoisomerization reaction structural unit having a CＣC bond include stilbene, stilbazole, stilbazolium, chalcone, cinnamic acid, cinnamylideneacetic acid, and the like.

The resin containing the photoisomerization constitutional unit may be any of a vinyl polymer, a redox polymer, a condensation polymer, and an addition polymer. The tilt angle is significantly affected by the side chain structure as well as the main chain structure of the polymer. Also,
In order to generate a large tilt angle, it is particularly preferable that the resin film before light irradiation causes liquid crystal vertical alignment. In order to cause liquid crystal vertical alignment, it is appropriate to introduce a suitable substituent into the photoisomerization reaction structural unit, and the substituent has a carbon number of 1 to 8
A straight chain alkyl group, a straight chain alkenyl group having 1 to 8 carbon atoms, a straight chain alkoxy group having 1 to 8 carbon atoms, a straight chain alkenyloxy group having 1 to 8 carbon atoms,
Cyclohexyl group, cyclohexenyl group, fluoro group,
Examples include a trifluoromethyl group and a trifluoromethoxy group.

The substrate used in the present invention, which is required to provide a film made of the above resin, may be any substrate coated with such a resin, and may be transparent or opaque, but constitutes a liquid crystal cell. At least one of the two substrates needs to be transparent. As a transparent substrate, a sheet of silica glass, hard glass, quartz, various plastics or the like, or a metal oxide such as silicon oxide, tin oxide, indium oxide, aluminum oxide, titanium oxide, chromium oxide, zinc oxide, etc. Alternatively, a material coated with silicon nitride, silicon carbide, or the like is used. As the opaque substrate, a substrate obtained by attaching a metal layer or a metal oxide layer to the surface of a metal or glass or plastic sheet is used.

The tilt alignment film for liquid crystal of the present invention is formed by irradiating the above resin film with light.
Light irradiation on a resin film having a photoisomerization reactive unit will be described. The resin solution is formed into a thin film on a substrate by a coating method such as spin coating, casting coating, and screen printing. The thickness of the resin film is in the range from 5 nm to 1000 nm, more preferably in the range from 10 nm to 500 nm. Since the orientation of the liquid crystal is mainly controlled by the orientation of the photoisomerization residue in the surface layer of the resin film, it is meaningless to control the tilt orientation of the liquid crystal even if the thickness is larger than the above range.

In order to obtain a uniform tilt alignment of the liquid crystal, a resin film having photoisomerization ability and exhibiting vertical alignment is irradiated with non-polarized light obliquely to the film surface. As a light source, an ultra-high pressure mercury lamp, a xenon lamp, a fluorescent lamp, a mercury / xenon lamp, or the like can be used. Light from a light source is incident on the resin film at a certain angle from a perpendicular to the resin film surface. The angle between the perpendicular and the incident direction is 5 to 60 degrees, more preferably 10 to 45 degrees. The amount of irradiation energy per unit area greatly depends on characteristics of resin, irradiation wavelength, and the like, but is from 10 mJ / cm ² to 10 J
/ Cm ² , more preferably 50 mJ / cm ² to 2
J / cm ² .

The tilt angle generated in this way is stable at room temperature, but in order to prevent the tilt angle from changing even in a heating state or a light irradiation state, a thermosetting agent or a photocuring agent must be used. It may be used together. For example,
A photocrosslinking agent having two azide groups is dissolved in a resin, and 436
A cross-linked structure is formed by irradiating light obliquely with a wavelength of nm and then irradiating vertically with ultraviolet light for photo-crosslinking.
This makes it possible to stabilize the tilt angle.

According to the present invention, a liquid crystal cell can be formed using a substrate having the above-described tilt alignment film for liquid crystal. In this case, a substrate provided with a transparent electrode such as ITO is used as the substrate. After the resin film is formed on the surface of the substrate, the light irradiation treatment is performed. Hereinafter, a liquid crystal cell can be prepared by a known method using the substrate with a liquid crystal tilt alignment film. The display operation mode of the liquid crystal cell is T
N or STN. A substrate on which a tilt alignment film for a liquid crystal having a large tilt angle is formed has a vertical alignment (ve
It can be suitably used for producing a (rtically aligned) liquid crystal cell.

[0021]

According to the method for producing a tilt alignment film for liquid crystal of the present invention, since a tilt alignment film for liquid crystal is prepared by using light from a normal light source, a polarizing element is not required for the production and the amount of light is reduced. Exposure operation is possible without any problems, and the productivity is high. Further, the tilt alignment film for liquid crystal obtained by the present invention can set an arbitrary tilt angle by selecting a resin structure, and a liquid crystal cell using this can be used for various liquid crystal display devices.

[0022]

Next, the present invention will be described in more detail by way of examples.

Example 1 1-Hydroxy-4'-fluoroazobenzene and carbonic acid
1- (2-hydroxyethyl)-obtained from tylene
4'-fluoroazobenzene is converted to methacrylic acid chloride
Esterification in the presence of triethylamine with 1
-(2-methacryloyloxyethyl) -4'-fluoro
Azobenzene was obtained. This monomer is
Azobisisobutyronitrile as polymerization initiator in
Polymerized, weight average molecular weight 1.1 × 10⁵The poly (1-
(2-methacryloyloxyethyl) -4-fluoroazo
Benzene). As a result of thermal analysis, this homopolymer
The glass transition temperature was 98 degrees. Next, this homopoly
Dissolved in toluene, and the solution was placed on a glass plate.
A thin film was formed by pin coating. This thin film is a nematic liquid
Crystal (NPC-02) with vertical orientation.
I accepted. Next, after heating the thin film to 100 degrees,
After returning to the temperature, it was taken out of the extra-high pressure mercury lamp. And
Light having a wavelength of 436 nm is applied to this thin film per unit area.
Irradiation energy 5 J / cm²And perpendicular to the film surface
Irradiation at an angle of 20 degrees from the direction
A substrate with a crystal orientation film was obtained. Two pieces obtained as above
Nematic liquid crystal cell using a substrate with a liquid crystal alignment film
Created. Also, in the above, irradiation per unit area
Change the amount of energy, and in the same way nematic liquid crystal cell
It was created. For each of the nematic liquid crystal cells created above
The tilt angle by the crystal rotation method.
I asked. As a result, the irradiation energy amount was 5 J /
cm ², 10J / cm², 20J / cm²At the time
The tilt angles were 80 degrees, 75 degrees, and 70 degrees, respectively.
In the above, the incident angle was changed, and
Obtain a substrate with an alignment film for crystallization and use these
A crystal cell was prepared, and the tilt angle was determined. As a result, the incident angle
An angle between 35 and 45 degrees from the direction perpendicular to the film surface
When changing each of them, the irradiation energy per unit area
Energy amount 10J / cm²And the tilt angle is 60
Degrees, 57 degrees.

Example 2 Example 2 was repeated in the same manner as in Example 1 except that light having a wavelength of 365 nm was irradiated at an irradiation energy amount of 0.3 J / cm ² per unit area and an incident angle of 20 ° from a direction perpendicular to the film surface. A nematic liquid crystal cell was prepared in the same manner using the two substrates with an alignment film for liquid crystal obtained in this manner, and the tilt angle was measured to be 7 degrees.

Example 3 1- (2-Hydroxyethyl) -4'-cyclohexylazobenzene obtained from 1-hydroxy-4'-cyclohexylazobenzene and ethylene carbonate is esterified with methacrylic acid chloride in the presence of triethylamine. 1- (2-methacryloyloxyethyl)-
4'-Cyclohexylazobenzene was obtained. This monomer was polymerized in tetrahydrofuran using azobisisobutyronitrile as a polymerization initiator, and the weight average molecular weight was 3.1.
× 10 ⁵ of poly (1- (2-methacryloyloxyethyl) -4'-cyclohexyl azobenzene) was obtained. As a result of thermal analysis, the glass transition temperature of this homopolymer was 49
Degree. This homopolymer was dissolved in toluene, and the solution was spin-coated on a glass plate to form a thin film. It was confirmed that this thin film exhibited vertical alignment with a nematic liquid crystal (NPC-02). Next, the thin film was heated to 100 ° C., returned to room temperature, and taken out of the ultrahigh pressure mercury lamp. Then, a wavelength of 436 nm is applied to this thin film.
Of irradiation energy of 10 J / cm per unit area
^{In step 2} , irradiation was performed at an angle of 20 degrees from the direction perpendicular to the film surface to obtain a substrate with a liquid crystal alignment film according to the present invention.
A nematic liquid crystal cell was prepared using the two substrates with an alignment film for liquid crystal obtained as described above. The tilt angle of this nematic liquid crystal cell was determined by the crystal rotation method. As a result, the tilt angle was 72 degrees. In the above, changing the incident angle to 35 degrees,
In the same manner, a substrate with a liquid crystal alignment film was obtained, and a nematic liquid crystal cell was prepared using these substrates, and the tilt angle was determined. As a result, the tilt angle was 67 degrees.

Example 4 The procedure of Example 3 was repeated except that the light having a wavelength of 365 nm was irradiated at an incident energy of 0.5 J / cm ² per unit area and at an incident angle of 20 ° from the direction perpendicular to the film surface. A nematic liquid crystal cell was prepared in the same manner using the two substrates with an alignment film for liquid crystal obtained above, and the tilt angle was measured to be 1.1 degrees.

Example 5 Poly (1- (2-methacryloyloxyethyl) azobenzene) having a weight average molecular weight of 1.7 × 10 ⁵ was similarly synthesized by radical polymerization. As a result of thermal analysis, the glass transition temperature of this homopolymer was 88 degrees. This homopolymer was dissolved in toluene, and the solution was spin-coated on a glass plate to form a thin film. It was confirmed that this thin film exhibited vertical alignment with a nematic liquid crystal (NPC-02). Next, the thin film was heated to 100 ° C., returned to room temperature, and taken out of the ultrahigh pressure mercury lamp. And
The thin film is irradiated with light having a wavelength of 436 nm at an irradiation energy amount of 0.3 J / cm ² per unit area at an angle of 20 degrees from the vertical direction with respect to the film surface. With this, a substrate was obtained. A nematic liquid crystal cell was prepared using the two substrates with a liquid crystal alignment film thus obtained, and the tilt angle was determined by a crystal rotation method. As a result, the tilt angle was 83.4 degrees.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-284421 (JP, A) JP-A-2-55330 (JP, A) JP-A-9-5747 (JP, A) JP-A 8- 292432 (JP, A) JP-A-6-287453 (JP, A) JP-A-3-179424 (JP, A) JP-A-2-113221 (JP, A) WO 96/37807 (WO, A1) ( 58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1337

Claims (3)

(57) [Claims] 1. A liquid containing a photoisomerization reaction structural unit , and
A method for producing a tilt alignment film for liquid crystal, comprising irradiating a non-polarized light directly from a diagonal direction to a resin film that causes crystal vertical alignment . 2. The photoisomerization reaction unit has an N = N bond and
And at least one double bond selected from C = C bonds
And exhibit a photogeometric isomerization reaction, and
2. The method for producing a tilt alignment film for a liquid crystal according to claim 1, wherein the liquid crystal causes direct alignment . 3. The method according to claim 1, wherein
A substrate on which the obtained tilt alignment film for liquid crystal is formed, and
Forming an alignment film for liquid crystal which may be the same or different from
Substrates facing each other, and hold the liquid crystal between these substrates.
Liquid crystal cell.