JPH10293210A - Optical film manufacturing method - Google Patents

Abstract

(57) [Problem] To provide a method for producing an optical film excellent in optical performance, mechanical performance and heat resistance. SOLUTION: A discotic liquid crystalline material is cooled at a cooling rate of 100 from a temperature range showing a discotic nematic phase.
After quenching at a rate of at least ℃ / min, it is subjected to a photocrosslinking reaction to obtain an optical film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical film having excellent optical performance, mechanical performance and heat resistance.

[0002]

2. Description of the Related Art Films in which discotic liquid crystals are hybrid-aligned are expected to be used as compensators for various liquid crystal displays because of their unique alignment structures.
For example, JP-A-8-50206 and JP-A-8-206
No. 334,621 discloses a twisted nematic (T
N) As a viewing angle compensator for a TFT-LCD using cells,
JP-A-8-327822 discloses a color compensation and viewing angle compensating plate for an OCB mode display, and JP-A-9-21914 discloses a color compensating and viewing angle compensating plate for a display using a hybrid nematic cell. Has been proposed.

[0003] Discotic liquid crystals are disc-shaped liquid crystals. The shape is in contrast to the rod-like nematic liquid crystal used in the driving liquid crystal cell in the liquid crystal display.
Therefore, it has a potentially high capability in compensating the driving liquid crystal cell.

[0004] The hybrid orientation is an orientation in which the orientation direction (director) of the liquid crystal changes in the film thickness direction.
The alignment direction of the liquid crystal molecules in the driving liquid crystal cell changes in the film thickness direction. If the hybrid structure of the discotic liquid crystal can be controlled in accordance with the change, very high compensation is possible.

In order to obtain a hybrid alignment film of discotic liquid crystal, liquid crystal materials and processing conditions are optimized. First, an ideal alignment is realized in a liquid crystal state, and then a liquid crystal is formed to have a mechanical strength as a film. It is necessary to perform a fixing treatment of the alignment structure formed in the state. It is very important that the fixing treatment does not destroy the alignment structure in the liquid crystal state. When the alignment structure changes during the fixing process, the alignment does not match the liquid crystal alignment in the liquid crystal cell to be compensated, and the compensation performance is greatly reduced. As a method for fixing a discotic liquid crystal, see Japanese Patent Application Laid-Open No. 8-5020.
In Japanese Patent Application Laid-Open No. 6-334, a method of performing photo-crosslinking in a heat treatment atmosphere after heat treatment using a material having a polymerizable group as a liquid crystal material, and in Japanese Patent Application Laid-Open No. 8-334621, a state change such as vitrification is caused by cooling to be fixed. A method is disclosed.

In the former method using photocrosslinking, light is applied to a material in a discotic nematic liquid crystal state having fluidity. In general, when the photocrosslinking reaction proceeds in a discotic nematic phase having high fluidity, the physical properties of the liquid crystalline material change with the crosslinking. Since the liquid crystal molecules tend to change to a thermodynamically stable alignment state following the change, the optical performance of the film after cross-linking may be significantly inferior to that before cross-linking. Here, the change in physical properties refers to the presence or absence of the ability to form a liquid crystal phase, a decrease in liquid crystallinity, a change in viscosity and elastic constant, and the like. The hybrid alignment by the discotic liquid crystal is formed under a delicate balance between the liquid crystalline material and the atmosphere at the film interface, and even a slight change in physical properties greatly affects the alignment form. Therefore, in the conventional production method in which the orientation may be impaired with a change in physical properties, there are many problems left as a method for producing an optical compensation film or the like that requires extremely strict control. .

On the other hand, in the case of the fixing method using a state change such as vitrification, the change in the orientation structure before and after the state change hardly occurs. In this regard, the fixing method by photocrosslinking in the above-mentioned heat treatment atmosphere is used. It is better. In the state change, unlike the phase change, the alignment structure of the liquid crystal does not basically change. However, when compared with the fixing method using photocrosslinking, the film strength and heat resistance after the fixing were not sufficient, and there was a possibility that the film could not withstand use in a severe environment.

[0008]

SUMMARY OF THE INVENTION In view of the above problems, the present inventors have made intensive studies on a method for fixing an alignment structure formed in a liquid crystal state without damaging it, and as a result, have finally reached the present invention. Specifically, it has been found that a state in which the fluidity of liquid crystal molecules is extremely restricted is created without disturbing the alignment structure in the liquid crystal state, and the object can be achieved by performing a photocrosslinking treatment thereafter.

[0009]

That is, the first aspect of the present invention is as follows.
The present invention relates to a method for producing an optical film, comprising quenching a discotic liquid crystal material from a temperature range showing a discotic nematic phase at a cooling rate of 100 ° C./min or more, and subjecting it to a photocrosslinking reaction.

A second aspect of the present invention is that after the discotic liquid crystalline material is heat-treated in a temperature region exhibiting a discotic nematic phase to achieve hybrid alignment, the material is cooled from the temperature region at a cooling rate of 100 ° C./min or more. The present invention relates to a method for producing an optical film, comprising quenching and then subjecting to a photocrosslinking reaction to fix the hybrid orientation.

A third aspect of the present invention is to provide a discotic liquid crystalline material having a columnar phase and / or a crystalline phase in a region having a lower temperature than the discotic nematic phase, and a columnar phase or a crystalline phase having a columnar phase or a crystalline phase from a temperature region exhibiting the discotic nematic phase. Cooling rate 100 ° C /
The present invention relates to a method for producing the above-mentioned first and second optical films, wherein the supercooled state of the discotic nematic phase is formed by quenching in more than one minute to form a photocrosslinking reaction in the supercooled state.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for producing an optical film of the present invention is characterized by a method for fixing an alignment, which impairs a unique alignment structure obtained in a liquid crystal state, specifically, a hybrid alignment of a discotic liquid crystal. Without this, sufficient immobilization can be achieved. Hereinafter, the present invention will be described in detail.

First, a discotic liquid crystalline material that can be used in the present invention will be described. The main component of the material is a discotic liquid crystal compound or the liquid crystal composition. Generally, a discotic liquid crystal is a liquid crystal expressed by a molecule having a mesogen having a disk shape with high planarity. The characteristic of the discotic liquid crystal is that the refractive index in an extremely small region in the liquid crystal layer has a negative uniaxial property, and the refractive index in a certain plane is constant as shown in FIG. The direction perpendicular to the plane is the optical axis, and the refractive index in the optical axis direction is ne.
In this case, no> ne. In the present invention, a director refers to a unit vector that specifies the average optical axis alignment direction of molecules present in the vicinity of each point of the liquid crystal material layer. Depending on the orientation, the refractive index characteristics and thus the optical characteristics of the obtained structure are determined. The discotic liquid crystal is C.I. According to Destrade et al., The discotic nematic phase (ND phase) depends on the orientational order of the molecule.
discotic nematic, Dho phase (h
exagonal ordered column
phase), Dhd phase (hexagonal di)
ordered columnar phase),
D rd phase (rectangular disorder)
(red column phase) and Dob phase (oblique column phase) (C. Destrade et. al.).
al. Mol. Cryst. Liq. Cryst. 10
6, 121 (1984)).

In the present invention, a compound or a composition having at least a discotic nematic phase must be used as a discotic liquid crystalline material in order to obtain hybrid alignment. A discotic liquid crystal material having no discotic nematic phase as a liquid crystal phase and having the above-mentioned columnar phase (Dho phase, Dhd phase, Dob phase) has a high degree of order between molecules, so that hybrid deformation cannot be obtained. In the present invention, the term “hybrid alignment” means an alignment structure in which the angle between the director of the discotic liquid crystal and the plane of the alignment substrate described later differs between the vicinity of the upper interface and the vicinity of the lower interface of the optical film.
The angle is not particularly limited, as long as the angle between the director of the discotic liquid crystal and the film plane near the upper and lower interfaces of the obtained film is different from each other. Preferably, in the vicinity of one interface of the film, the angle is approximately 60 to 90 degrees as an absolute value, and more preferably approximately 80 to 90 degrees.
The angle in the vicinity of the other interface is approximately 0 to 50 degrees, and more preferably approximately 0 to 10 degrees as the absolute value. A preferred hybrid orientation structure is a structure in which the angle between the director and the plane of the film changes in the thickness direction of the film from the vicinity of one interface of the film to the vicinity of the other interface.

Further, in the present invention, it is necessary that a state having extremely low fluidity can be obtained upon cooling from the liquid crystal state. Therefore, considering the behavior during cooling, a discotic liquid crystalline compound having a columnar phase and / or a crystalline phase in a temperature range lower than the discotic nematic phase or a material composed of the liquid crystalline composition is preferable. However, at the time of film production, a clear transition from a discotic nematic phase to a higher-order phase may lead to destruction of the oriented structure. Therefore, as described later, after achieving a uniform hybrid orientation in the discotic nematic phase, the liquid crystal is made to lose the fluidity without disturbing the orientation in the discotic nematic phase by quenching. The liquid crystal film thus obtained is in a supercooled state, and can lose fluidity without disturbing the alignment. Note that the supercooled state referred to in the present invention means that, although the columnar phase or the crystal phase is thermally stable at a certain temperature, these phases cannot appear due to the heat history, and the columnar phase or the crystal phase It refers to a state of staying in a discotic nematic phase having a lower degree of order. The present invention is characterized in that a photocrosslinking reaction is performed in this supercooled state.

Representative examples of the discotic liquid crystal satisfying the above requirements are described below. These are examples, and the scope of the present invention is not limited to these.

[0017]

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[0018]

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As a specific example, in the above general formula, R ₁
To R ₆ are all

[0020]

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The compounds all R ₁ to R ₆ is a substituent of group A, such as, the overall R ₁ to R ₆ is

[0022]

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(A product obtained by the introduction reaction of two types of substituents is usually a mixture of molecules in which the introduction positions and ratios of the respective substituents are different. The same applies to the following composition examples represented by the average number of moles), and all of R _{1 to} R ₆ are

[0024]

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[0025]

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[0026]

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As a specific example, in the above general formula, R ₁
To R ₆ are all

[0028]

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A compound in which all of R _{1 to} R ₆ are a substituent of Group A, and all of R _{1 to} R ₆ are

[0030]

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[0031]

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As exemplified above, the liquid crystal compound or composition constituting the discotic liquid crystal material used in the present invention has photopolymerizability with a portion exhibiting liquid crystal properties (called a mesogen). It has at least an acrylic group and a methacryl group. The mesogen and the photopolymerizable substituent may be present in one molecule or may be present in different molecules. A typical example of the latter is a composition of a normal discotic liquid crystal compound having no polymerizable group and a photopolymerizable monomer such as an ordinary acrylic monomer having no liquid crystal property, and the composition is as described above. This is the case when it has properties.

In the present invention, one or more of the above discotic liquid crystalline compounds or compositions are used as the main constituent components of the discotic liquid crystalline material.

The discotic liquid crystal material used in the present invention contains a photoinitiator in addition to the discotic liquid crystal compound or composition as described above. The photoinitiator is not particularly limited, and the following known photoinitiator compounds can be usually used.

For example, benzyl, benzoyl ether, benzoin isobutyl ether, benzoin isopropyl ether, benzophenone, benzoyl benzoic acid, methyl benzoyl benzoate, 4-benzoyl-4'-methyldiphenyl sulfide, benzyl methyl ketal, dimethylaminomethyl benzoate, 2- n-butoxyethyl-4-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, 3,3'-dimethyl-4-
Methoxybenzophenone, methylobenzoylformate, 2-methyl-1- (4- (methylthio) phenyl)
-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one, 1- (4-dodecylphenyl) -2-hydroxy-2 -Methylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, 2
-Hydroxy-2-methyl-1-phenylpropane-1
-One, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 2-chlorothioxanthone, 2,4-diethylthioxanthone 2,4
-Diisopropylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 1-chloro-4-propoxythioxanthone and the like. These photoinitiators can be used alone or in combination of two or more.

However, it is necessary not to lose the liquid crystallinity of the liquid crystalline material by the addition of the photoinitiator.
The addition amount of the photoinitiator is usually 0.2 to 10% by weight or less, more preferably 0.5 to 10% by weight, based on the liquid crystal compound or the composition.
It is at most 6% by weight, more preferably 1 to 6% by weight.
If the amount of the photoinitiator is less than 0.2% by weight, a sufficient crosslinking reaction may not proceed. If it exceeds 10% by weight, the liquid crystallinity may be lost. In addition to the photoinitiator, a sensitizer can be further added as long as the effect of the present invention is not impaired.

In order to obtain an optical film in which the hybrid alignment is fixed uniformly using the discotic liquid crystalline material as described above, the following substrate and each step will be taken. First, a substrate (hereinafter, referred to as an alignment substrate) will be described.

In the present invention, in order to obtain hybrid alignment, it is desirable to perform an alignment treatment by sandwiching the discotic liquid crystal material layer above and below at different interfaces. If the upper and lower sides are sandwiched by the same interface, the orientation at the upper and lower interfaces of the material layer becomes the same, and it becomes difficult to obtain hybrid orientation.

As a specific embodiment, a lower surface of the discotic liquid crystal material layer is in contact with the alignment substrate, and an upper interface is in contact with air by using one alignment substrate and the air interface. Although hybrid alignment can be formed using substrates having different interfaces at the top and bottom, it is preferable to use one alignment substrate and an air interface from the viewpoint of the manufacturing process.

The alignment substrate that can be used in the present invention includes:
It is desirable that the substrate has anisotropy so that the direction in which the liquid crystal tilts (the direction obtained when the director is projected onto the alignment substrate) can be defined. If the orientation substrate cannot define the direction in which the liquid crystal is inclined at all, only a structure inclined in a random orientation can be obtained (the projection vector of the director onto the substrate becomes disordered).

As the oriented substrate that can be used in the present invention, specifically, one having the following in-plane anisotropy is desirable. That is, polyimide, polyamide imide, polyamide, polyether imide, polyether ether ketone, polyether ketone, polyketone sulfide, polyether sulfone, polysulfone, polyphenylene sulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyacetal, Polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol, polypropylene, cellulosic plastics, epoxy resin, phenolic resin, etc. plastic film substrate and uniaxially stretched film substrate, aluminum, iron, copper etc. with slit grooves on the surface Metal substrate, alkali glass, borosilicate glass, furin etched into slits on the surface A glass substrate such as glass, etc. are used as the substrate.

In the present invention, the above-mentioned various substrates obtained by subjecting the above-mentioned substrate to a surface treatment such as a hydrophilic treatment or a hydrophobic treatment may be used. Further, a rubbing plastic film substrate subjected to a rubbing treatment on the plastic film substrate, or a plastic film subjected to a rubbing treatment, for example, a rubbing polyimide film, the above various substrates having a rubbing polyvinyl alcohol film and the like, and an oblique deposition film of silicon oxide. The various substrates described above can be used.

Among the above-mentioned various alignment substrates, a substrate having a rubbing polyimide film, a rubbing polyimide substrate, a rubbing polyetheretherketone substrate, a rubbing polyetheretherketone substrate, which is suitable for forming discotic liquid crystals in a hybrid alignment, is used. Rubbing polyethersulfone substrate, rubbing polyphenylene sulfide substrate, rubbing polyethylene terephthalate substrate, rubbing polyethylene naphthalate substrate, rubbing polyarylate substrate, and cellulose-based plastic substrate.

As a means for disposing the discotic liquid crystalline material on the alignment substrate, coating is usually used. The application of the discotic liquid crystalline material can be performed using a discotic liquid crystalline material solution in which the material is dissolved in various solvents, or a material in a molten state,
From the viewpoint of the process, it is preferable to apply a solution in which the solution in which the discotic liquid crystalline material is dissolved in a solvent is used to apply the solution on an alignment substrate.

The solution application will be described. As the solvent, although it depends on the type of the liquid crystalline material, usually, halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, tritrichloroethylene, tetrachloroethylene, chlorobenzene, orthodichlorobenzene, phenol, para Phenols such as chlorophenol, aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene and 1,2-dimethoxybenzene, acetone, ethyl acetate, t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene Glycol monomethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethyl cellosolve, butyl cellosolve, 2-pyrrolidone,
N-methyl-2-pyrrolidone, pyridine, triethylamine, dimethylformamide, dimethylacetamide,
Acetonitrile, butyronitrile, carbon disulfide and the like and a mixed solvent thereof are used.

The concentration of the solution depends on the solubility of the liquid crystalline material and the final thickness of the intended optical film and cannot be unconditionally determined, but is usually used in the range of 1 to 60% by weight. Preferably, it is used in the range of 3 to 40% by weight.

As a method of applying the discotic liquid crystalline material solution on the alignment substrate, a spin coating method, a roll coating method, a printing method, a dipping and pulling method, a curtain coating method (die coating method) and the like can be adopted.

After the application, the solvent is removed, and a layer of a liquid crystalline material having a uniform thickness is first formed on the substrate. The conditions for removing the solvent are not particularly limited, and it is sufficient that the solvent can be substantially removed and the liquid crystal material layer does not flow or fall off.
Usually, the solvent is removed by air drying at room temperature, drying on a hot plate, drying in a drying furnace, or blowing hot or hot air. The thickness of the liquid crystalline material after drying depends on the application and cannot be unconditionally determined, but is usually 0.1 μm to 20 μm,
Preferably, it is in the range of 0.3 μm to 10 μm, more preferably 0.5 μm to 7 μm.

The purpose of this coating / drying step is to first form a layer of discotic liquid crystal material uniformly on the substrate, and the liquid crystal material layer has not yet formed a hybrid orientation. In order to perform hybrid alignment, the following heat treatment is performed.

The heat treatment is performed at a temperature at which the discotic liquid crystalline material exhibits a discotic nematic phase or at a temperature higher than the temperature. In other words, the liquid crystal material is oriented in the discotic nematic phase, or once in an isotropic liquid state higher than the temperature range in which the liquid crystal phase is exhibited, the temperature is lowered to the temperature range in which the discotic nematic phase is exhibited, and the liquid crystal material is oriented. Two methods can be used.

The temperature of the heat treatment depends on the liquid crystal material, and cannot be specified unconditionally. However, it is usually 50 ° C. to 200 ° C., preferably 80 ° C. to 170 ° C., more preferably 100 ° C. to 15 ° C.
It is in the range of 0 ° C.

Although the time required for the liquid crystal to form a sufficient alignment varies depending on the discotic liquid crystalline material, it cannot be said unconditionally, but it is usually 5 seconds to 2 hours, preferably 10 seconds to 40 minutes. More preferably, it is in the range of 20 seconds to 20 minutes. If the time is shorter than 5 seconds, the temperature of the liquid crystalline material layer may not rise to a predetermined temperature and the alignment may be insufficient. On the other hand, when the time is longer than 2 hours, productivity is undesirably reduced. By the above heat treatment, a discotic liquid crystalline material layer having a uniform hybrid alignment formed on the alignment substrate can be obtained.

Next, in the present invention, quenching is performed in order to change from a state showing a fluid discotic nematic phase to a state without fluidity without disturbing the hybrid orientation. If careless cooling operation is performed, the orientation may be disturbed. In particular, in the present invention, since it is preferable to use a liquid crystalline material having a columnar phase and / or a crystalline phase, there is a great possibility that these phases will appear and the hybrid alignment will be completely destroyed by a normal cooling operation. Therefore, by rapidly cooling from a temperature region showing a discotic nematic phase, the liquid crystal material hybrid-aligned in the temperature region is formed in a supercooled state of the discotic nematic phase. By this quenching operation, the alignment structure formed in the temperature region can be stably maintained.

The cooling rate is usually 100 ° C./min or more, preferably 500 ° C./min or more, more preferably 1000 ° C./min.
/ Min or more. If the cooling rate is slower than 100 ° C / min,
The alignment structure obtained in a liquid crystal state may be destroyed.
Further, there is a fear that a supercooled state cannot be obtained. Note that the cooling rate in the present invention means a rate from a state showing a discotic nematic phase to a state where an oriented structure formed in this state can be stably maintained.
Specifically, for example, when a material having a columnar phase and / or a crystalline phase in a region lower than the discotic nematic phase is used as the liquid crystal material, the columnar phase or the crystalline region is shifted from the temperature range showing the discotic nematic phase. It means the rate at which the crystal phase reaches a stable temperature range. Therefore, the cooling by the quenching operation is to perform an operation of lowering the temperature from a temperature range where a discotic nematic phase is usually exhibited to a temperature near room temperature, but the discotic liquid crystal property capable of maintaining a stable phase as described above at or above room temperature or below room temperature. When using a material, it is not limited to these. The method for obtaining such a rapid cooling rate is not particularly limited, but after the heat treatment, it can be performed by a method such as blowing cold air, putting into cold water, or increasing the rate of removal from the heat treatment furnace. In addition, it is usually sufficient to reduce the quenching operation to about room temperature atmosphere,
It is preferable to lower the temperature to at least the transition temperature from the discotic nematic phase to the higher order phase. Note that the transition temperature here refers to the temperature at which the transition from the discotic nematic phase to the higher-order phase occurs when cooled at a sufficiently low rate, but when such a measurement is difficult due to strong monotropic liquid crystallinity. Refers to a temperature at which a transition from a higher-order phase to a discotic nematic phase occurs when the temperature is raised.

Next, an optical film is obtained on an alignment substrate by fixing a liquid crystal material layer having a hybrid alignment in a state obtained by rapid cooling, for example, a supercooled state, by a photocrosslinking reaction. be able to.

The wavelength of the light to be irradiated in the photocrosslinking reaction is not particularly limited, and ultraviolet light, visible light, infrared light (heat ray), and electron beam can be used as needed. Usually, ultraviolet light is used. Its light sources include low-pressure mercury lamps (germicidal lamps, fluorescent chemical lamps, black lights), high-pressure discharge lamps (high-pressure mercury lamps, metal halide lamps), and short arc discharge lamps (ultra-high pressure mercury lamps, xenon lamps, mercury xenon lamps), etc. Is mentioned. Among them, ultraviolet light from a high-pressure mercury lamp is the most common and can be preferably used in the present invention.
When a suitable sensitizer is contained in the discotic liquid crystal material, or when the material itself has a sensitizing effect, a light source in the visible light region can be used.

Although the amount of light emitted from the light source as described above depends on the type of discotic liquid crystalline material and the amount of the photoinitiator to be added, it cannot be determined unconditionally, but is usually 20 to 5000.
mJ / cm ² , preferably 50 to 3000 mJ / c
m ² , more preferably 100 to 2000 mJ / cm ²
Range.

After the photocrosslinking reaction, aging by heat, which is a known means, may be performed in order to react a small amount of unreacted polymerizable groups. Aging is usually 60 ° C ~ 2
It is carried out at a temperature of 00 ° C, preferably 80 ° C to 160 ° C.

The optical film produced by the above steps may be used as it is on an alignment substrate for various optical applications, or may be used by providing an overcoat layer with a transparent resin or the like on the surface of the optical film. Is also good. It can also be used in combination with other films. In the present invention, the alignment substrate is used to align the discotic liquid crystalline material. However, if the characteristics of the alignment substrate are inconvenient for the optical application to be used, the alignment substrate is peeled off after the photocrosslinking reaction. May be removed. Further, only the optical film on the alignment substrate may be transferred to another substrate by a known method.

The optical film obtained by the above-described production method is very excellent in optical performance and durability. Therefore, it can be applied to various optical uses, and in particular, as an optical compensation film for a liquid crystal display, it can exhibit characteristics not found in other materials. Such a liquid crystal display can be classified by the liquid crystal orientation of the cell used.
N (Twisted Nematic) mode, OCB
(Optically Compensated Bir
environment) mode, STN (Super
Twisted Nematic mode, HAN (H
ybridgeAligned Nematic) mode,
VAN (Vertically Aligned Ne)
magnetic) mode, SH (Super Homeot)
(ropic) mode.

[0061]

EXAMPLES Examples will be described below, but the present invention is not limited to these examples. In addition, each analysis method used in the Example is as follows. A series of operations was performed in a yellow room where ultraviolet light was cut. (Chemical structure determination) It was measured by 400 MHz ¹ H-NMR (JNM-GX400 manufactured by JEOL Ltd.). (Observation by optical microscope) Olympus polarizing microscope BX-5
Orthoscope observation and conoscopic observation were performed using 0. The liquid crystal phase was identified by observing the texture while heating on a Mettler hot stage (FP-80). (Ellipsometry) The measurement was performed using an ellipsometer DVA-36VWLD manufactured by Mizojiri Optical Industrial Co., Ltd. (Measurement of refractive index) Abbe refractometer Type- manufactured by Atago Co., Ltd.
Performed using 4T. (Measurement of film thickness) A high-precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory Co., Ltd. was mainly used. In addition, a method of measuring the thickness of the film from the data of the refractive index and the interference wave measurement (JASCO Corporation UV / visible / near infrared spectrophotometer V-570) was also used.

(Example 1)

[0063]

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A discotic liquid crystalline material of the formula (1) was synthesized. This material showed a discotic nematic phase at a temperature of 80 ° C. or higher, and the columnar phase was a stable phase between room temperature and 80 ° C. The liquid crystal phase existed at least up to 160 ° C., but at a temperature higher than 160 ° C., thermal polymerization of the material occurred, so that an isotropic phase transition temperature could not be confirmed. For 10 g of this liquid crystalline material, a photoinitiator Ir
gacure-184 (manufactured by CIBA-GEIGY) was added in an amount of 0.4 g, and 90 g of N-methylpyrrolidone was added to prepare a coating solution. This solution was applied to a glass substrate having a 10 cm square rubbing polyimide film by a spin coating method. Then, it was dried on a hot plate at 70 ° C. and heat-treated in an oven at 130 ° C. for 10 minutes to align the liquid crystal. After the heat treatment, a vat filled with ion-exchanged water was prepared, and a sample was taken out of the oven, poured into water, and rapidly cooled. At least 10 seconds after the introduction into the water, the temperature of the sample was 40 ° C. or lower (the cooling rate was 540 ° C./min at the latest). Thus, a supercooled liquid crystal material layer in which the liquid crystal material was uniformly hybrid-aligned was obtained on the alignment substrate (film 1a). The thickness of the liquid crystal material layer in a supercooled state was 1.5 μm. The retardation was measured using this sample. The sample was tilted along the rubbing direction of the substrate as shown in FIG. 2, and the relationship between the tilt angle and apparent retardation was examined, and the result of line a in FIG. 2 was obtained. The fact that the retardation change is asymmetric depending on the tilt direction and the absence of a tilt angle at which the retardation value becomes zero do not exist indicate that the hybrid orientation is obtained. Note that the pencil code of the material layer was as weak as 6B. Next, a photocrosslinking reaction was performed on the liquid crystal material layer (film 1a) in a supercooled state at room temperature using a high-pressure mercury lamp. Exposure is 800
mJ / cm ² . The optical film (film 1b) obtained by the photocrosslinking reaction was subjected to detailed optical measurement in the same manner as described above. As a result, the result indicated by line b in FIG. 1 was obtained. Do you get it. The pencil hardness of the optical film was 2H, which was much higher than that before crosslinking. The optical film obtained as described above is
The sample was placed on an N test cell and arranged as shown in FIG. 3, and the viewing angle dependence of the contrast ratio was measured. The TN cell had a 90 ° left-hand twist and a retardation of 490 nm when no voltage was applied. As shown in FIG. 4, the viewing angle was significantly widened by mounting the optical film.

(Comparative Example 1) The same procedure as in Example 1 was performed up to the orientation by heat treatment, and a film was produced by changing the operation after cooling as follows. After the heat treatment was completed, the sample was taken out of the oven and quickly placed on a hot plate at 130 ° C. Next, on a hot plate, while the liquid crystalline material is in a state of exhibiting a discotic nematic phase,
Exposure was performed at 800 mJ / cm ^{2 using} a high-pressure mercury lamp. The retardation of the obtained (film 1c) was measured, and the result of line c in FIG. 2 was obtained. Compared to the lines a and b in FIG. 2, the retardation value was generally lower, and the left-right asymmetry in the figure was smaller. This indicates that the anisotropy based on the liquid crystal alignment is small, and indicates that an undesired change in the alignment of the liquid crystal has occurred during the crosslinking operation. When the viewing angle dependence of the contrast ratio was measured in the same manner as in Example 1, the effect of enlarging the viewing angle was small as shown in FIG. The test cells, their driving conditions, and the arrangement of the films were exactly the same as in Example 1.

(Embodiment 2)

[0067]

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A discotic liquid crystalline material represented by the formula (2) a, b, c was prepared. Orientation ratio of each material a: b: c
Was 40:30:30 by weight. Formula (2) -a is a discotic liquid crystalline compound having an acrylic group, Formula (2) -b is a non-polymerizable discotic liquid crystalline compound,
Formula (2) -c is a non-liquid crystal polymerizable compound. This material exhibited a discotic nematic phase in the temperature range from 60C to 160C. When the temperature was gradually lowered from the temperature range showing the liquid crystal phase, precipitation of a microcrystalline structure was observed at 60 ° C. To 10 g of the liquid crystal material, 0.2 g of biimidazole (produced by Kurokin Kasei Co., Ltd.) as a photoinitiator and 0.05 g of Michler's ketone as a sensitizer were added. This liquid crystalline material was dissolved in triethylene glycol dimethyl ether to prepare a 15% by weight solution. Next, this solution was applied to a glass substrate having a 10 cm square rubbing polyimide film by spin coating, and dried on a 70 ° C hot plate. The heat treatment was performed on a Mettler hot stage, and at the same time, a polarizing microscope observation was performed.
However, in order to prevent a slight progress of photocrosslinking due to the light source of the microscope, a filter capable of cutting ultraviolet light and near ultraviolet light was used. As a result of observation, when treated at 140 ° C,
A uniform hybrid orientation was obtained in about 2 minutes after the schlieren texture. The in-plane retardation was measured using a Berek compensator attached to the microscope and found to be 74 nm. After a heat treatment at 140 ° C. for 5 minutes, the sample was quickly pressed against an aluminum plate placed at room temperature and rapidly cooled. At least 40 seconds after the start of cooling, the temperature of the sample was 40 ° C or lower (the cooling rate was 150 ° C /
Min). The liquid crystal phase after cooling did not show any particular disorder in the orientation, and the in-plane retardation was 77 nm, which was slightly different from that before cooling. Subsequently, exposure was performed at 600 mJ / cm ^{2 using} a high-pressure mercury lamp to perform a crosslinking reaction.
The in-plane retardation after crosslinking was 72 nm, which was not much different from that before crosslinking. The thickness of the liquid crystal layer was 1.8 μm as measured by a step-type stylus meter. The pencil cord was weaker than 6B before crosslinking, but had a hardness of about HB after crosslinking.

(Comparative Example 2) A heat treatment was performed in the same manner as in Example 2. Next, ultraviolet rays were irradiated in a heat treatment atmosphere. The in-plane retardation during the heat treatment at 140 ° C. was 74 nm, but the ultraviolet rays were irradiated at 600 mJ / cm while heating at 140 ° C. with the hot stage lid open.
^In the case of ² hits, the in-plane retardation after light irradiation is 12
nm.

(Embodiment 3)

[0071]

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A composition comprising formulas (3) a and b was prepared. This composition is a high-order phase which is considered to be a crystalline phase or a columnar phase at room temperature.
It had the property of transforming into a discotic nematic phase at ℃. This composition was used as a discotic liquid crystalline material, and 0.1 g of Irgacur was added to 10 g of the composition.
e-907 (manufactured by CIBA-GEIGY) was added to prepare a butyl cellosolve solution having a solute concentration of 10% by weight. Using this solution, a film was produced by a continuous process. The solution was applied over a length of 10 m to a rubbing polyimide film having a width of 25 cm (a rubbed Dupont Kapton film having a thickness of 100 μm) by a roll coater, and dried with hot air at 70 ° C. Then 12
After heat treatment at 0 ° C. for 5 minutes, the mixture was cooled to obtain a supercooled state of the liquid crystal material layer. The cooling rate was increased by blowing air at about 25 ° C. near the outlet of the heat treatment furnace. At least 10 seconds after leaving the heat treatment furnace outlet, the temperature of the film was 30 ° C. or less (cooling rate was 540 ° C./min or more). Subsequently, light irradiation by a high-pressure mercury lamp was performed to completely fix the liquid crystal alignment. Exposure is 300mJ / c
m ² , the temperature of the sample chamber was about 40 ° C. Thus, an optical film was obtained on the rubbing polyimide film. In addition, since the polyimide film lacked transparency and had a problem depending on the application when used as an optical film, the optical film was transferred to an optical grade polyether sulfone via an adhesive. The operation was performed by laminating the polyethersulfone subjected to the adhesion treatment and the optical film on the rubbing polyimide film so that the adhesion layer and the optical film were in contact with each other, and then peeling off the rubbing polyimide film. Optical measurement was performed in detail on the optical film on the polyether sulfone after the release transfer operation. As a result, a uniform hybrid orientation was obtained in the optical film, and the film thickness was 5.2 μm.
m, the in-plane retardation was 50 nm. When the heat resistance of the optical film was examined, at least 20
Up to 0 ° C., the alignment structure of the liquid crystal was stable. Above 200 ° C., deformation of the polyethersulfone film occurred.

(Embodiment 4)

[0074]

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A discotic liquid crystalline material of the formula (4) was prepared. This liquid crystalline material showed a discotic nematic phase at a temperature of 100 ° C. or higher, and at a temperature lower than that, the columnar phase was a stable phase. 0.2 g of Irgacure-90 is added to 10 g of the discotic liquid crystal material.
7 (manufactured by CIBA-GEIGY) and a solute concentration of 10
A weight percent butyl cellosolve solution was prepared. Using this solution, a film was produced by a continuous process. The solution was applied over a length of 10 m to a rubbing polyethylene terephthalate film having a width of 25 cm (a 75 μm-thick Rumirror film manufactured by Toray Co., Ltd.) by a roll coater, and dried with hot air at 70 ° C. Next, the film was heat-treated at 150 ° C. for 5 minutes, and was cooled by transporting the film from a furnace to a room temperature atmosphere to obtain a supercooled state of the liquid crystal material layer. The speed of the film passing through the outlet of the heat treatment furnace was 5 m / min. At least 2 after leaving the heat treatment furnace
After 0 seconds, the temperature was below 40 ° C. (cooling rate 3
30 ° C./min or more). Subsequently, light irradiation by a high-pressure mercury lamp was performed to completely fix the liquid crystal alignment. Exposure is 5
00 mJ / cm ² and the temperature of the sample chamber was about 40 ° C.
Thus, an optical film was obtained on the rubbing polyimide film. Since the polyethylene terephthalate film used as the substrate has birefringence, there is a problem in using the optical film as it is formed on the film for optical applications depending on the application. Then, the optical film was transferred to an optical grade triacetyl cellulose film (manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 80 μm via an ultraviolet curing adhesive. For the operation, an adhesive was applied on the optical film, and a triacetyl cellulose film was laminated thereon. Next, the adhesive was cured by ultraviolet irradiation, and then the rubbing polyethylene terephthalate film was peeled off to transfer the optical film. Optical measurement was performed in detail on the optical film on the triacetyl cellulose film after the release transfer operation. As a result, a uniform hybrid orientation was obtained, the film thickness was 0.9 μm, and the in-plane retardation was 20 nm.

(Comparative Example 4) A heat treatment was performed in the same manner as in Example 4. After the heat treatment, cooling was performed at a cooling speed of 0.5 m / min at a passage speed at the outlet of the heat treatment furnace. One minute after leaving the heat treatment furnace, the temperature of the film was 80 ° C. (the cooling rate was about 70 ° C./min). Then, a photocrosslinking reaction was performed under the same conditions as in Example 4. The liquid crystal material layer after the reaction had a microcrystalline structure, and many defects were observed.

[0077]

According to the production method of the present invention, an optical film excellent in optical performance, mechanical strength and heat resistance can be easily produced. In the present invention, the cooling after the heat treatment is important, but since it is easy to cope with the equipment, there is no great burden on the cost. The optical film produced by the present invention makes it possible to supply a high-performance film to the optical field, particularly to the liquid crystal display field, and has an extremely high industrial value.

[Brief description of the drawings]

FIG. 1 is a view for explaining a unique refractive index distribution and a director of a discotic liquid crystal.

FIG. 2 shows a result of measuring an apparent retardation by tilting a liquid crystalline film as formed on a substrate along a rubbing direction of the substrate. The figure explaining the direction which inclines a film in the figure was shown. In addition, the direction of inclination of the director of the liquid crystal in the figure is a schematic representation based on the results obtained in this measurement. Line 1a Liquid crystalline material thin film in supercooled state of Example 1 Line 1b Optical film obtained after photocrosslinking of Example 1 Line 1c Film obtained in Comparative Example 1

FIG. 3A is a perspective view of the liquid crystal display device used in Example 1 and Comparative Example 1, and FIG. 3A is an axial arrangement of components (a and b).
(C) is a diagram illustrating an azimuth angle φ and a viewing angle θ. Reference Signs List 1 upper polarizing plate 2 TN liquid crystal cell 3 upper electrode substrate having rubbing polyimide film 4 lower electrode substrate having rubbing polyimide film 5 lower polarizing plate 6 optical film formed on glass substrate having rubbing polyimide film 7 discotic liquid crystal Film (film 1b or film 1c) 8 Substrate (glass substrate having a rubbing polyimide film) 9 Transmission axis of upper polarizing plate 10 Rubbing direction of upper electrode substrate 11 Rubbing direction of lower electrode substrate 12 Transmission axis of lower polarizing plate 13, 13 '' Rubbing direction of substrate

FIG. 4 is a view angle characteristic obtained in Example 1. The curve in the figure is an equal contrast curve with a contrast of 50. The three concentric circles represent viewing angles θ = 20 degrees, 40 degrees, and 60 degrees, respectively, and the crosses indicated by dotted lines represent azimuth angles φ = 0, 90 degrees, and 1
Represents 80 degrees and 270 degrees. Dotted line No film (when there is no member 6 in FIG. 3) Solid line When film 1b is used

FIG. 5 is a view angle characteristic obtained in Comparative Example 1. The curve in the figure is an equal contrast curve with a contrast of 50. Dotted line No film (when there is no member 6 in FIG. 2) Solid line When film 1c is used

Claims (3)

[Claims] 1. A method for cooling a discotic liquid crystalline material from a temperature range showing a discotic nematic phase to a cooling rate of 100
A method for producing an optical film, comprising quenching at a rate of at least ° C / min and subjecting it to a photocrosslinking reaction. 2. After a discotic liquid crystalline material is heat-treated in a temperature region exhibiting a discotic nematic phase to achieve hybrid alignment, a cooling rate of 1 from said temperature region.
A method for producing an optical film, comprising quenching at a rate of at least 00 ° C./min, and then subjecting it to a photocrosslinking reaction to fix the hybrid orientation. 3. A discotic liquid crystalline material having a columnar phase and / or a crystalline phase in a temperature range lower than the discotic nematic phase, and a temperature range in which the columnar phase or the crystal phase is stable from the temperature range showing the discotic nematic phase. 3. The optical film according to claim 1, wherein the optical film is rapidly cooled at a cooling rate of 100 ° C./min or more to form a supercooled state of a discotic nematic phase, and then subjected to a photocrosslinking reaction in the supercooled state. Manufacturing method.