JPH10307208A - Production of optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical film having excellent optical performance, dyanamical performance and heat resistance performance by rapidly cooling a discotic liquid crystalline material having a chiral discotic nematic phase at a cooling rate of a specific value or above from a temp. region where its liquid crystal phase is exhibited, then subjecting the material to a photocrosslinking reaction. SOLUTION: The discotic liquid crystalline material having the chiral discotic nematic phase is rapidly cooled at the cooling rate of >=100 deg.C/min from the temp. region where its liquid crystal phase is exhibited and is then subjected to the photocrosslinking reaction. The discotic liquid crystalline material is otherwise heat treated in the temp. region where its liquid crystal phase is exhibited to achieve twist orientation and thereafter, the material is rapidly cooled at the cooling rate of >=100 deg.C/min from the temp. region and is then subjected to the crosslinking reaction to immobilize the twist orientation. Namely, the condition in which the flow property of liquid crystal molecules is extremely limited is creased without the disturbance of the orientation structure formed in the temp. region where the chiral discotic nematic liquid crystal phase is exhibited and thereafter, the photocrosslinking reaction is executed.

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 Liquid crystals in a driving liquid crystal cell form a complicated alignment. One of the major features is that most of the liquid crystal cells use a twisted structure, which is a unique alignment structure of liquid crystal, to realize a display with high contrast. For such a liquid crystal cell, twist alignment is effective as a compensation means in order to perform advanced optical compensation, and various compensation films in which a liquid crystalline polymer is twisted have been developed.

[0003] Recently, discotic liquid crystals have attracted attention as compensation means as described above because of their unique molecular skeleton. Discotic liquid crystal is a disc-shaped liquid crystal, and has a shape different from a rod-shaped nematic liquid crystal used in a driving liquid crystal cell. Therefore, a discotic liquid crystal is a liquid crystal having a potentially high ability in optically compensating the liquid crystal cell. By using this discotic liquid crystal, a compensation film exhibiting an unprecedented compensation effect has been developed.

For example, JP-A-8-50206 and JP-A-8-334621 disclose, as a viewing angle compensation film for a TFT-LCD using a twisted nematic (TN) cell, a film in which discotic liquid crystals are hybrid-aligned. Have been.

For a cell having a twisted structure,
Also, since the compensating means having a twisted orientation can expect a higher compensation effect, an optical film in which a discotic liquid crystal is twisted has been developed.

For example, in Japanese Patent Application Laid-Open No. 9-26572,
An optical film that achieves uniform twist alignment by introducing a chiral substituent into a discotic liquid crystal or using a composition with a chiral component is disclosed. The development of this film has made it possible to further greatly improve the viewing angle of a twisted nematic liquid crystal display and the like.

In general, as a method for obtaining a film as described above using a material exhibiting liquid crystallinity, it is necessary to optimize a liquid crystal material and processing conditions, and first, to realize an ideal alignment in a liquid crystal state. Next, an immobilization treatment must be performed in order to have a mechanical strength as a film. JP-A-9-
In Japanese Patent No. 26572, the film is fixed by utilizing a state change such as vitrification. With this fixing method, although the optical characteristics can be sufficiently satisfied, as evident from the optical compensation effect, the film strength and heat resistance cannot be said to be sufficient, and there is a fear that the film cannot withstand use in a severe environment. was there.

As a method for immobilizing a discotic liquid crystal, for example, a method using photocrosslinking as disclosed in JP-A-8-50206 is considered to be effective. In this publication, light irradiation is performed on a material in a temperature region exhibiting a fluid discotic nematic phase. In general, when the photo-crosslinking reaction proceeds in a discotic nematic phase with high fluidity, the physical properties of the liquid crystal, such as the ability to form a liquid crystal phase, the decrease in liquid crystallinity, changes in viscosity and elastic constant, etc. are caused by crosslinking. Very easy to happen.

The control of the twisted orientation of the discotic liquid crystal is achieved under a delicate balance between the liquid crystal and the atmosphere at the film interface, and even a slight change in physical properties greatly affects the orientation. I do. Therefore, in the conventional method in which the alignment may be impaired due to a change in physical properties, there is a problem as a method for producing a discotic liquid crystal optical film having a twisted alignment that requires very strict alignment control. There was a situation that has been left.

[0010]

In view of the above-mentioned problems, the present inventors have conducted intensive studies on a method for fixing a twisted orientation formed in a temperature region exhibiting a chiral discotic nematic phase without impairing it. Reached. Specifically, a situation in which the fluidity of liquid crystal molecules is extremely restricted is created without disturbing the alignment structure formed in the temperature region exhibiting a chiral discotic nematic liquid crystal phase, and then the photo-crosslinking reaction is performed. I found that it could be reached.

[0011]

That is, the first aspect of the present invention is as follows.
Is a method for producing an optical film, comprising quenching a discotic liquid crystalline material having a chiral discotic nematic phase from a temperature range exhibiting the liquid crystal phase at a cooling rate of 100 ° C./min or more, and then subjecting the material to a photocrosslinking reaction. About the law. In the second aspect of the present invention, a discotic liquid crystalline material having a chiral discotic nematic phase is heat-treated in a temperature region exhibiting the liquid crystal phase to achieve twist alignment, and then cooled from the temperature region at a cooling rate of 100 ° C. / The present invention relates to a method for producing an optical film, wherein the optical film is quenched in minutes or more and then subjected to a photocrosslinking reaction to fix the twist orientation. In the third aspect of the present invention, a discotic liquid crystalline material having a columnar phase and / or a crystalline phase in a lower temperature region than a chiral discotic nematic phase is used. The above-described first and second aspects, wherein a rapid cooling is performed at a cooling rate of 100 ° C./min or more in a stable temperature range to form a supercooled state of a chiral discotic nematic phase, and then a photocrosslinking reaction is performed in the supercooled state. The present invention relates to a method for producing a second optical film. A fourth aspect of the present invention is the second aspect, wherein the twist orientation is a twist orientation in which the magnitude of a projection vector of the director of the discotic liquid crystal onto the film plane changes in the film thickness direction of the film. And a method for producing a third optical film.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The method for producing an optical film of the present invention is characterized by a method for fixing an orientation, and a unique orientation structure obtained in a liquid crystal state, specifically, sufficient fixation without impairing a twisted orientation by a discotic liquid crystal. Can be achieved. Hereinafter, the present invention will be described in detail.

In the present invention, the twist orientation refers to two arbitrary planes such as the front and back surfaces of the film and the inner surface of the film.
The projection direction of the director of the discotic liquid crystal on one surface does not overlap with the projection direction of the director of the discotic liquid crystal on the other surface. The preferred twist orientation in the present invention is that the projection of the discotic liquid crystal into the film surface of the director of the discotic liquid crystal monotonically increases, that is, changes the direction of rotation from one surface to the other surface in the thickness direction of the film. It is a structure that is rotated without. In the present invention, the term “director” means a unit vector that specifies the average alignment direction of the optical axis of molecules present near each point of the liquid crystal material layer. As the twist-oriented structure as described above, a structure as shown in FIG. 1 in which the director and the film plane are substantially parallel to each other, and the magnitude of the projection vector of the director onto the film plane changes in the film thickness direction. For example, there is a structure as shown in FIG. The present invention is suitable for fixing a structure in which the orientation is easily disturbed as described above, and is particularly suitable for those having a unique twisted orientation structure as shown in FIG. 2 in which the orientation is easily disturbed. The effect can be exhibited.

In the orientation structure shown in FIG. 2, the angle between the director of the discotic liquid crystal and the plane of the film is different between the vicinity of one interface of the film and the vicinity of the other interface. Preferably, the angle ranges from approximately 60 degrees to 90 degrees as an absolute value, and more preferably approximately 80 degrees to 90 degrees as an absolute value. In the vicinity of the opposite interface, the absolute value is approximately 0 degree to 50 degrees. Less than,
More preferably, it is approximately 0 degrees or more and 30 degrees or less.

In the present invention, the rotation axis of the twist is taken in the normal direction of the film plane, and the torsion angle is defined by the rotation angle of the component of the director in the in-plane direction of the film. Where the director is oriented substantially normal to the film plane, such as within 0.1 degrees, preferably within 0.5 degrees, and more preferably within 1 degree, the torsion angle is considered to be absent.
In the torsional orientation, the direction of the in-plane component of the director usually changes monotonically with the movement in the thickness direction of the film.

Next, the discotic liquid crystalline material which 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. Discotic liquid crystal is C.I. Destr
Ade et al. disclose a discotic nematic phase (ND phase discotic nematic phase) depending on the orientational order of the molecules.
magnetic), Dho phase (hexagonal orde)
red column phase), Dhd phase (h
exagonal disordered column
nar phase), Drd phase (rectangula)
r disordered columnar pha
se), Dob phase (oblique column)
(C. Destr)
adeet al. Mol. Cryst. Liq. Cr
yst. 106, 121 (1984)).

In the present invention, a discotic liquid crystalline compound having at least a chiral discotic nematic phase or a material composed of the liquid crystalline composition is used to obtain a desired twisted orientation. The chiral discotic nematic phase is a liquid crystal phase in which a twisted structure is added to the discotic nematic phase. In a discotic liquid crystalline material having no columnar phase (Dho phase, Dhd phase, Dob phase or a liquid crystal phase having a twisted structure added thereto) having no chiral discotic nematic phase as a liquid crystal phase, , It is difficult to obtain a uniform twisted orientation.

Further, in the present invention, it is necessary that a state of remarkably low fluidity can be obtained upon cooling from a temperature range exhibiting a chiral discotic nematic phase. Therefore, when considering the behavior at the time of cooling, a discotic liquid crystal compound having a columnar phase and / or a crystal phase in a temperature range lower than the chiral discotic nematic phase or a material composed of the liquid crystal composition is more suitable. . However, at the time of production, a clear transition from a chiral discotic nematic phase to a higher-order phase may lead to the destruction of the orientation structure. Therefore, as described later, after achieving a uniform torsional orientation in the chiral discotic nematic phase, the liquid crystal is lost by quenching without disturbing the orientation in the chiral discotic nematic phase. 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 on a discotic liquid crystalline material in a supercooled state in which the twisted alignment is formed.

Next, as the discotic liquid crystal constituting the discotic liquid crystal material having a chiral discotic nematic phase used in the present invention, a portion exhibiting a liquid crystal phase (called a mesogen), for example, an acryl group or a methacryl group, etc. And at least a chiral substituent that induces a twist orientation. The mesogen, the photopolymerizable substituent, and the chiral substituent may be present in one molecule or may be present in different molecules. The photopolymerizable substituent and the chiral substituent need not necessarily be present in the discotic liquid crystal molecule. Typical examples of the latter include, for example, discotic liquid crystals having no polymerizable substituents, photopolymerizable compounds, such as ordinary acrylic monomers having no liquid crystallinity, and optically active compounds having chiral substituents. A composition having the above-mentioned properties as a composition.

The discotic liquid crystal material used in the present invention includes a discotic liquid crystal having a chiral substituent and a photopolymerizable substituent, a discotic liquid crystal having a chiral substituent, and a discotic liquid crystal having a photopolymerizable substituent. Composition comprising at least a chic liquid crystal and a discotic liquid crystal having no chiral substituent and polymerizable substituent, a composition comprising at least a photopolymerizable compound and an optically active compound having a chiral substituent chiral Composition comprising at least a discotic liquid crystal having a substituent and a photopolymerizable compound Composition comprising at least a discotic liquid crystal having a polymerizable substituent and an optically active compound having a chiral substituent Is essential as a main component. Examples of the discotic liquid crystal that can be used in the present invention will be described below. However, the present invention is not limited to these.

[0021]

Embedded image

The above general formula (I), (II) or (II)
In I), R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R
₆ is a substituent selected from the following group A, group B or group C. However, in the liquid crystal material described above, the general formula (I), (II) or (III) having at least one or more substituents selected from group A and / or group C. At least one discotic liquid crystal represented by the formula: In the above-mentioned liquid crystalline material, the compound represented by the general formula (I), (II) or (II) having one or more kinds of substituents selected from Group B is used.
It contains at least one discotic liquid crystal represented by I).

[0023]

Embedded image

[0024]

Embedded image

[0025]

Embedded image

[0026]

Embedded image

[0027]

Embedded image

More specifically, the following compounds can be exemplified. In the general formula (I), R _{1 to} R
The whole of ₆ ,

Embedded image (Where x + y + z = 6.0, x> 1.0, z> 0 (molar composition ratio), m is an integer of 2 or more and 14 or less, and n is 2
An integer of 18 or more and l is an integer of 2 or more and 9 or less)
(The product obtained by the introduction reaction of two or more substituents is usually a mixture of molecules in which the introduction positions and the ratios of the respective substituents are different, and the above designation constitutes 1 mol of the compound. The same applies to the following, which is represented by the average mole number of each unit.)

In the general formula (I), R _{1 to} R ₆ are all

Embedded image (However, x + y + 2z = 6.0, x> 1.0, 0 <z ≦
1.0 (molar composition ratio), m is an integer of 2 or more and 14 or less, and n is an integer of 2 or more and 18 or less),

In the general formula (I), all of R _{1 to} R ₆ are

Embedded image (Where x + y + z = 6.0, x> 1.0, z> 0 (molar composition ratio), m is an integer of 2 or more and 14 or less, and n is 2
Which is an integer of 18 or more).

In the general formula (I), each of R _{1 to} R ₆ is

Embedded image (Where m is an integer of 2 to 14) and each of R _{1 to} R ₆ is

[0032]

Embedded image Wherein l is an integer of 2 or more and 9 or less,

In the general formula (II), R _{1 to} R ₆
Of the whole

Embedded image (Where x + y + z = 6.0, x> 1.0, z> 0 (molar composition ratio), m is an integer of 2 or more and 14 or less, and n is 2
An integer of 18 or more and l is an integer of 2 or more and 9 or less)
A compound represented by

In the general formula (II), all of R _{1 to} R ₆ are

Embedded image (However, x + y + 2z = 6.0, x> 1.0, 0 <z ≦
1.0 (molar composition ratio), m is an integer of 2 or more and 14 or less, n is an integer of 2 or more and 18 or less, and the third substituent is a linking group.

In the general formula (II), all of R _{1 to} R ₆ are

Embedded image (Where x + y + z = 6.0, x> 1.0, z> 0 (molar composition ratio), m is an integer of 2 or more and 14 or less, and n is 2
Which is an integer of 18 or more).

In the general formula (II), each of R _{1 to} R ₆ is

Embedded image (Where m is an integer of 2 to 14) and each of R _{1 to} R ₆ is

[0037]

Embedded image Wherein l is an integer of 2 or more and 9 or less,

In the general formula (III), all of R _{1 to} R ₆ are

Embedded image (Where x + y + z = 6.0, x> 1.0, z> 0 (molar composition ratio), m is an integer of 2 or more and 14 or less, and n is 2
An integer of 18 or more and l is an integer of 2 or more and 9 or less)
A compound represented by

In the general formula (III), all of R _{1 to} R ₆ are

Embedded image (However, x + y + 2z = 6.0, x> 1.0, 0 <z ≦
1.0 (molar composition ratio), m is an integer of 2 or more and 14 or less, and n is an integer of 2 or more and 18 or less),

In the general formula (III), all of R _{1 to} R ₆ are

Embedded image (Where x + y + z = 6.0, x> 1.0, z> 0 (molar composition ratio), m is an integer of 2 or more and 14 or less, and n is 2
Which is an integer of 18 or more).

In the general formula (III), each of R _{1 to} R ₆ is

Embedded image (Where m is an integer of 2 to 14) and each of R _{1 to} R ₆ is

[0042]

Embedded image (Where l is an integer of 2 or more and 9 or less).

Here, when a bifunctional substituent is used, the resulting discotic liquid crystal becomes an oligomer composition or a polymer composition in which mesogens are linked.
The chirality of the chiral substituent component in the liquid crystal is not particularly limited, and may be an S-form or an R-form. However,
Since the S-body and the R-body give twists in opposite directions, one of them is selected depending on the application. The S-form and the R-form may be mixed, but one must be present in excess of the other. When both the S-form and the R-form are equal in amount, a twist orientation cannot be obtained. In addition, since the amount of the chiral substituent component is approximately proportional to the magnitude of the twist, a twist orientation having a desired twist angle can be obtained by controlling the amount of the chiral substituent.

In the present invention, one kind or two or more kinds of the above discotic liquid crystals are used as constituents of the liquid crystalline material. The discotic liquid crystalline material used in the present invention contains a photoinitiator in addition to the discotic liquid crystal as described above. The photoinitiator is not particularly limited, and usually the following compounds can be 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-butoxy Ethyl-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-
Phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropane-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 to prevent the liquid crystallinity of the liquid crystal material from being lost by the addition of the photoinitiator.
The addition amount of the photoinitiator is usually 0.2 to
It is 10% by weight, preferably 0.5 to 6% by weight, more preferably 1 to 6% by weight. If the amount 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 twisted orientation is fixed by using the discotic liquid crystalline material described above, it is desirable to perform each step using a substrate described below.

First, a substrate (hereinafter, referred to as an alignment substrate) will be described. The alignment substrate is desirably a substrate having anisotropy so that a director of the liquid crystal at the substrate interface can be defined. If the orientation of the liquid crystal cannot be specified at all, it is difficult to obtain a uniform orientation in the film plane. However, the orientation substrate to be used depends on the liquid crystal material and the intended orientation structure (the structural characteristics imparted in addition to the twist orientation, and cannot be described in a unified manner. Here, the above-described twist orientation structure has been described. A description will be given of an oriented substrate suitable for forming a unique twisted orientation in which the magnitude of the vector of the director projected onto the film plane changes in the film thickness direction. Those having such in-plane anisotropy can be mentioned.

For example, 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 and other plastic film substrates and uniaxially stretched film substrates, aluminum, iron with slit-shaped grooves on the surface, Metal substrates such as copper, alkali glass with a slit-shaped surface etched, borosilicate glass , Glass substrate, such as flint glass, and the like. Further, in the present invention, the above various substrates obtained by subjecting the above 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 oriented substrates, more preferred substrates include a substrate having a rubbing polyimide film, a rubbing polyimide substrate, a rubbing polyetheretherketone substrate, a rubbing polyetheretherketone substrate, a rubbing polyethersulfone substrate, and a rubbing polyphenylenesulfide. Substrates, rubbing polyethylene terephthalate substrates, rubbing polyethylene naphthalate substrates, rubbing polyarylate substrates, and cellulose-based plastic substrates can be exemplified.

In the present invention, a discotic liquid crystalline material is applied on the above-mentioned alignment substrate, and then undergoes a uniform alignment process and a fixing process.

The discotic liquid crystalline material can be applied by using a discotic liquid crystalline material solution in which the material is dissolved in various solvents or in a state in which the material is melted. It is preferable to apply the solution using the solution in which the discotic liquid crystalline material is dissolved.

The solution application will be described. The solvent is usually a halogenated hydrocarbon such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, tritrichloroethylene, tetrachloroethylene, chlorobenzene, orthodichlorobenzene, phenol, parachloroform, although it depends on the type of the liquid crystal material. Phenols such as phenol, 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 etc., and the like mixed solvents used.

The concentration of the solution cannot be determined unconditionally because it depends on the solubility of the liquid crystalline material and the thickness of the optical film finally intended, but it is usually 1 to 60% by weight, preferably 3% by weight.
It is used in the range of ４０40% by weight. Note that a surfactant may be added to the solution for the purpose of improving the coatability of the solution as long as the effect of the present invention is not impaired.

As a method for 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 crystal 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 dried liquid crystalline material 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 and drying step is to first form a layer of discotic liquid crystal material uniformly on the substrate, and the discotic liquid crystal molecules in the liquid crystal material layer form a twisted orientation. I haven't. In order to orient the liquid crystalline material, the following heat treatment is performed.

The heat treatment is performed in a temperature range showing a chiral discotic nematic phase of the discotic liquid crystalline material or at a temperature higher than the temperature range. That is, the liquid crystal material is oriented in the chiral discotic nematic phase, or once in an isotropic liquid state at a higher temperature than the temperature range exhibiting the chiral discotic nematic phase, and then in a temperature range exhibiting the chiral discotic nematic phase. And the orientation can be reduced.

The temperature of the heat treatment depends on the liquid crystalline material, and cannot be specified unconditionally.
Perform at 0 ° C.

Although the time required for the liquid crystal to be sufficiently oriented depends on the discotic liquid crystal material, it cannot be said unconditionally, but it is usually performed in the range of 5 to 2 hours, preferably 10 seconds. ４０40 minutes, more preferably 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. If it is longer than 2 hours,
It is not preferable because productivity is reduced. By the above heat treatment, a discotic liquid crystal material layer having a desired orientation, that is, a twist orientation, can be uniformly formed on the orientation substrate.

Next, in the present invention, quenching is performed for the purpose of changing the twist orientation obtained as described above from a liquid crystal state having fluidity to a state having no fluidity without disturbing the twist orientation. If careless cooling operation is performed, the orientation may be disturbed. In particular, in the present invention, the columnar phase and / or
Alternatively, since it is preferable to use a liquid crystalline material having a crystalline phase, there is a possibility that these phases may appear and the twist orientation may be completely destroyed by a normal cooling operation. Then, by rapidly cooling from a temperature region exhibiting a chiral discotic nematic phase, a liquid crystal material twist-oriented in the temperature region is formed in a supercooled state. By this quenching operation, the twisted orientation structure formed in the temperature region can be stably maintained. The cooling rate is usually at least 100 ° C / min, preferably at least 500 ° C / min, more preferably at least 1000 ° C / min. Cooling rate is 1
If the temperature is lower than 00 ° C./min, the supercooled state cannot be obtained, and the orientation structure obtained in the chiral discotic nematic phase may be destroyed. Note that the cooling rate in the present invention means a rate from a state where a discotic nematic phase is exhibited to a state where the 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 at a lower temperature than the chiral discotic nematic phase is used as the liquid crystalline material, the columnar phase shifts from the temperature region exhibiting the chiral discotic nematic phase. It means the rate at which the phase or crystalline 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 chiral discotic nematic phase is usually exhibited to a temperature near room temperature, but a discotic liquid crystal capable of maintaining the above-mentioned stable phase at room temperature or higher or lower than room temperature. The use of a conductive material is not limited to this. 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. As described above, the quenching operation is usually sufficient to lower the temperature to about room temperature, but it is preferable to lower the temperature to at least the transition temperature from the chiral discotic nematic phase to the higher order phase. The transition temperature here refers to the temperature at which the transition from a chiral discotic nematic phase to a higher-order phase occurs when cooled at a sufficiently low rate, but such a measurement is difficult because of its strong monotropic liquid crystallinity. In such a case, it refers to a temperature at which a transition from a higher-order phase to a chiral 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 obtained by rapid cooling, for example, a twisted alignment in a supercooled state, by a photocrosslinking reaction. Can be.

The wavelength of the light 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 the discotic liquid crystal material and the amount of the photoinitiator added, it cannot be unconditionally determined, 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, the reaction may be performed as it is, or aging by heat, which is a known means, may be performed to react a small amount of unreacted polymerizable groups. Aging is usually performed at 60 ° C to 200 ° C, preferably at 80 ° C to 16 ° C.
Perform at 0 ° C.

The optical film produced by the above steps may be used as it is on an alignment substrate for various optical applications, or an overcoat layer made of a transparent resin or the like may be provided on the surface of the optical film. . It can also be used in combination with other films. In the present invention,
Although the alignment substrate is used to align the discotic liquid crystalline material, if the characteristics of the alignment substrate are inconvenient for the optical application to be used, the alignment substrate may be peeled off and removed after the photocrosslinking reaction. . Further, only the optical film formed 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 excellent in optical performance, mechanical performance and heat resistance. It can be applied to various optical applications, and among other things, it can exhibit characteristics not found in other materials as an optical compensation film for liquid crystal displays. Among such liquid crystal displays, a so-called TF combining a TFT liquid crystal and a driving liquid crystal cell of a twisted nematic type that is becoming mainstream at present.
The application to a T liquid crystal display is particularly significant.

[0067]

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. (Film Thickness Measurement) 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)

[0069]

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A discotic liquid crystal containing (R) -3-methyladipic acid unit of the formula (1) was synthesized. (R) -3
-Methyladipic acid used Aldrich reagent. The liquid crystal of the formula (1) showed a chiral discotic nematic phase at a temperature of 75 ° C. or higher, and the columnar phase was a stable phase between room temperature and 75 ° C. The chiral discotic nematic phase was present at least up to 160 ° C., but at temperatures higher than 160 ° C., thermal polymerization occurred, so that an isotropic phase transition temperature could not be confirmed.

The photo initiator Irga was added to 10 g of the liquid crystal.
cure907 (manufactured by CIBA-GEIGY)
g was added to obtain a discotic liquid crystal material. 90 g of N-methylpyrrolidone was added to the material to prepare a solution of a liquid crystalline material. This solution was applied to a glass substrate having a 10 cm square rubbing polyimide film by a spin coating method. Then dried on a hot plate at 80 ° C,
Heat treatment was performed in a 140 ° C. oven for 5 minutes. After the heat treatment, the sample was taken out of the oven, immediately put into water at room temperature and rapidly cooled. At least 20 seconds after the introduction into the water, the temperature was 40 ° C. or lower (the cooling rate was about 300 ° C./min). In this way, a liquid crystalline material was uniformly aligned on a glass substrate having a film of rubbing polyimide, and a supercooled film 1a maintaining the alignment was obtained. The pencil hardness of this film was as low as 6B.

When the optical measurement was performed in detail on the film 1a, a structure as shown in FIG. 2 was obtained in which the projection vector of the director onto the substrate changed in the film thickness direction while having a twisted structure. I knew it was there. Next, as a result of performing ellipsometry with an ellipsometer, an apparent retardation of 48 nm and an apparent twist angle of 90 degrees (left twist) were obtained.

Next, in a state where the film 1a in a supercooled state is formed on a glass substrate having a rubbing polyimide film, light is applied to the film 1a with a high-pressure mercury lamp at room temperature.
The surface was irradiated to obtain a photo-crosslinked optical film 1b.
The exposure amount was 800 mJ / cm ² . The pencil hardness of the film 1b was HB. When an optical measurement was performed on the film 1b in the same manner as above, an apparent retardation of 45 nm and an apparent twist angle of 90 degrees (left-hand twist) were obtained, which were almost the same as those before crosslinking.

(Embodiment 2)

[0075]

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[0076]

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[0077]

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Compounds of formula (2) a, b, c, d were prepared. Mixing ratio (weight ratio) of each compound a: b: c: d = 4
The composition was mixed at 0: 40: 18: 2 to obtain a composition. Equation (2) −
a is a discotic liquid crystal having an acrylic group, formula (2)
-B is a non-polymerizable discotic liquid crystal, formula (2) -c is a non-liquid crystal polymerizable compound, and formula (2) -d is a chiral non-liquid crystal compound. The chiral group was obtained from natural menthol (manufactured by Aldrich). This composition is:
A chiral discotic nematic phase was exhibited in a temperature range of at least 80 ° C to 160 ° C. When the temperature was gradually lowered from the temperature range where the chiral discotic nematic phase was exhibited, precipitation of a microcrystalline structure was observed at 60 ° C.
When the temperature was raised from a state in which microcrystals were present, the phase changed to a chiral discotic nematic phase at 80 ° C.

To 10 g of the above liquid crystalline composition, 0.2 parts of biimidazole (manufactured by Kurokin Kasei Co., Ltd.) was used as a photoinitiator.
g, 0.05 g of Michler's ketone is added as a sensitizer,
A discotic liquid crystal material was used. This liquid crystalline material was dissolved in butyl cellosolve to prepare a 12% by weight solution.

Next, the solution was applied by a roll coater to a rubbing polyphenylene sulfide film having a width of 25 cm (a rubbed film of 100 μm-thick Tolerina film made by Toray Co., Ltd.) over a length of 20 m. After the application, it was dried with hot air at 70 ° C., and heat-treated at 130 ° C. for 3 minutes to uniformly twist and orient. After the heat treatment, a rapid cooling operation was performed to obtain a liquid crystal material layer in a supercooled state. In the quenching operation, the cooling rate was increased by blowing air at about 25 ° C. near the outlet of the heat treatment furnace. By this quenching operation, the temperature was reduced to 40 ° C. or less at least 10 seconds after the heat treatment (the cooling rate was about 540 ° C./min).

Subsequently, light irradiation with a high-pressure mercury lamp was performed to completely fix the orientation. Exposure is 300mJ
/ Cm ² , and the sample chamber temperature was about 40 ° C. Thus, the optical film 2 was obtained on the rubbing polyphenylene sulfide.

Since the polyphenylene sulfide film lacks transparency and has a problem in some applications, the film 2 was transferred to an optical grade polyether sulfone via an adhesive. The operation was performed by laminating the adhesive-treated polyether sulfone and the film 3 on the rubbing polyimide film so that the adhesive layer and the film 3 were in contact with each other, and then peeling off the rubbing polyimide film.

The optical measurement of the film 2 on the polyether sulfone after the release transfer operation was performed in detail. As a result, a structure (FIG. 2) having a twisted structure and in which the magnitude of the vector projected on the substrate of the director changes in the film thickness direction was obtained. The film thickness was 2.4 μm, the apparent retardation was 80 nm, and the twist angle was 60 degrees (right twist). The director was in a direction substantially parallel to the film surface on the interface side with the adhesive, and in a direction substantially perpendicular to the film surface on the air side interface. When the heat resistance of this film was examined, the alignment structure of the liquid crystal was maintained up to 200 ° C. Above 200 ° C., deformation of the polyethersulfone film occurred.

(Example 3)

[0085]

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[0086]

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A composition (weight ratio 96.8: 3.2) consisting of formulas (3) a and b was prepared. The chiral unit in the formula (3) b was obtained from (R) -1-chloro-2-octanediol (manufactured by Japan Energy). In this composition, the stable phase at room temperature was a higher-order phase which seems to be a crystalline phase or a columnar phase. By increasing the temperature, 40
It had the property of changing to a chiral discotic nematic phase at ℃. 0.1 g of I per 10 g of this composition
rgacure-907 (manufactured by CIBA-GEIGY)
Was added to obtain a liquid crystalline material.

Using the above materials, an optical film was prepared by the following steps. As the substrate, a substrate obtained by rubbing a silicon-treated triacetyl cellulose film (thickness: 80 μm) by rubbing the silicone-treated surface in one direction with a cloth was used.

Using two substrates (20 cm square), the above-mentioned liquid crystalline material was sandwiched between the substrates while being heated to 60 ° C. The rubbing directions of the two substrates are 90
The angle of degree was formed. The thickness of the liquid crystal material layer was adjusted by passing the sample between nip rolls set at an appropriate nip pressure, to a thickness of about 5 μm.

The liquid crystalline material sandwiched between the triacetyl loin films is treated in an oven at 100 ° C. for 10 minutes to uniformly align the liquid crystal material, and then cooled to room temperature, and the liquid crystalline material is cooled to a supercooled state of a chiral discotic nematic phase. And Cooling reduced the temperature to below 40 ° C. at least 15 seconds after removal from the oven (cooling rate approximately 240 ° C./min). Then, irradiation was carried out with a high-pressure mercury lamp at 100 mJ / cm ² to effect crosslinking.

The optical film 3 thus obtained was subjected to detailed optical measurements while being sandwiched between two upper and lower triacetyl cellulose films. The obtained film 3 had an orientation structure as shown in FIG. The retardation and the twist angle were measured by the wave guide method. As a result, values of a retardation of 480 nm and a twist angle of 90 degrees were obtained.

(Embodiment 4)

[0093]

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A discotic liquid crystal of the formula (4) was prepared. As a raw material of the chiral unit, natural naproxen (manufactured by Aldrich) was used. This discotic liquid crystal exhibited a chiral discotic nematic phase at a temperature of 85 ° C. or higher, and a columnar phase was a stable phase at a temperature lower than 85 ° C. To 10 g of the liquid crystal, 0.2 g of Irgacure-907 (manufactured by CIBA-GEIGY) was added to obtain a discotic liquid crystal material. Then
A butyl cellosolve solution having a solute concentration of 10% by weight was prepared.

This solution was applied to a soda glass substrate (30 cm).
Corner, thickness 1.1 mm) by spin coating,
After drying at 60 ° C., it was heat-treated in an oven at 140 ° C. for 10 minutes. After uniform orientation by heat treatment, the liquid crystal material was cooled to room temperature, and the liquid crystalline material on the soda glass substrate was placed in a supercooled state. At least one minute after removal from the oven, the temperature was below 40 ° C. (cooling rate was about 100 ° C./min). The film 4a on the soda glass substrate in a supercooled state had a property of selectively reflecting red light. Central wavelength of cholesteric selective reflection is 640n
m, the band width was about 40 nm. The film thickness is about 10
μm and a structure in which the helical cycle was repeated about 26 times was obtained. The pencil hardness of the film was very weak at 6B or less.

Next, the film 4a in the supercooled state was irradiated with light of 400 mJ / cm ² by a high-pressure mercury lamp to cause a crosslinking reaction to proceed. The optical film 4b obtained by photocrosslinking had selective reflection with a center wavelength of 640 nm as in the case before crosslinking. The pencil hardness of the film is B
Met. Further, in the film 4b, there was almost no difference in selective reflection characteristics in the range of room temperature to 150 ° C.

[0097]

By using the production method of the present invention, an optical film having excellent optical performance, mechanical strength, and heat resistance can be produced. 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 schematic view of a twist alignment structure according to the present invention. FIG. 9 is a schematic diagram particularly illustrating the orientation structure of the optical film 3 obtained in Example 3.

FIG. 2 is a schematic view of a twist alignment structure according to the present invention. FIG. 2 is a schematic view of an oriented structure formed by a film 1a and an optical film 1b in a supercooled state obtained in Example 1. The arrow in the figure indicates the direction of the director of the liquid crystal. Although there is no distinction between the front and the rear, the director is indicated by a single arrow for convenience.

Claims (4)

[Claims] 1. A discotic liquid crystalline material having a chiral discotic nematic phase is quenched at a cooling rate of 100 ° C./min or more from a temperature range where the liquid crystal phase is exhibited.
A method for producing an optical film, which is subjected to a photocrosslinking reaction. 2. A discotic liquid crystalline material having a chiral discotic nematic phase is heat-treated in a temperature region exhibiting the liquid crystal phase to achieve twist alignment, and then cooled at a cooling rate of 100 ° C./min or more from the temperature region. A method for producing an optical film, comprising quenching and then subjecting to a photocrosslinking reaction to fix the twist orientation. 3. A discotic liquid crystalline material having a columnar phase and / or a crystalline phase at a temperature lower than that of a chiral discotic nematic phase, and a columnar phase or a crystalline phase at a temperature at which a columnar phase or a crystalline phase is stabilized from a temperature range exhibiting a chiral discotic nematic phase. 3. The method according to claim 1, wherein the region is rapidly cooled at a cooling rate of 100 ° C./min or more to form a supercooled state of a chiral discotic nematic phase, and then subjected to a photocrosslinking reaction in the supercooled state. Manufacturing method of optical film. 4. A twist alignment in which the magnitude of a vector of a director of a discotic liquid crystal projected onto a film plane changes in the film thickness direction of the film. Manufacturing method of optical film.