JP2001281445A - Optical anisotropic element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical anisotropic element with the strictly controlled aligned tilt angle and the alignment direction of discotic liquid crystalline molecules. SOLUTION: In the optical anisotropic element having an alignment layer and an optical anisotropic layer containing the discotic liquid crystalline molecules fixed in an aligned state on a transparent substrate in this order, the discotic liquid crystalline molecules are essentially vertically aligned with the alignment layer. After the vertical aligning of the discotic liquid crystalline molecules, the alignment direction of the discotic liquid crystalline molecules is controlled by light irradiation from a single direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment film and an optically anisotropic layer containing discotic liquid crystal molecules fixed in a substantially vertically aligned state on a transparent support. The present invention relates to an optically anisotropic element having this order and a method of manufacturing the same.

[0002]

2. Description of the Related Art A liquid crystal display device comprises a liquid crystal cell, a polarizing plate, and an optical compensation sheet (retardation plate) provided between the liquid crystal cell and the polarizing plate. The liquid crystal cell is composed of rod-like liquid crystal molecules,
It consists of two substrates for enclosing it and an electrode layer for applying a voltage to the rod-like liquid crystalline molecules. An alignment film (double-sided alignment film) is provided on the two substrates to align the encapsulated rod-like liquid crystal molecules. The alignment film of the liquid crystal cell is generally obtained by providing a polymer thin film such as polyimide or polyvinyl alcohol on a substrate and rubbing (rubbing) the cloth uniformly with a cloth. The optical compensation sheet is a birefringent film having a function of removing coloring of a liquid crystal screen. As the optical compensation sheet, a resin film whose birefringence is increased by stretching is commonly used.

It has been proposed to use, as an optical compensation sheet, an optically anisotropic element obtained by fixing the orientation of liquid crystal molecules, instead of a stretched film having a birefringence. Liquid crystal molecules have various alignment forms. Therefore,
By fixing the orientation of the liquid crystal molecules, an optically anisotropic element having optical performance that cannot be obtained with a stretched film having a birefringence can be obtained. JP-A-3-87
No. 720 discloses an optical compensation sheet using a film having a twisted nematic orientation. The liquid crystal molecules used in the optical compensation sheet described in the publication are rod-like liquid crystal molecules similar to the compounds used in the liquid crystal cell. JP-A-5-215921 discloses an optical compensation sheet in which a rod-shaped liquid crystal compound exhibiting liquid crystallinity when cured is sealed between two substrates subjected to an alignment treatment.

However, the properties of liquid crystal molecules and alignment films required in the optical compensation sheet are completely different from the requirements in the liquid crystal cell. For example, rod-like liquid crystal molecules used in a liquid crystal cell are insufficient in the effect of improving the viewing angle required for an optical compensation sheet. Further, in the optical compensatory sheet, it is necessary to fix and use the liquid crystal molecules in an oriented state. The rod-like liquid crystal molecules used in a liquid crystal cell have poor alignment state stability. Further, the rod-like liquid crystal molecules used in the liquid crystal cell are formed on a single substrate (support).
Simply coating on the alignment film (single-sided alignment film) provided thereon does not provide sufficient alignment. In a liquid crystal cell, an alignment film (double-sided alignment film) can be provided on each of the two substrates in order to seal rod-like liquid crystalline molecules between the two substrates. As described in JP-A-5-215921,
When a structure of a double-sided alignment film similar to a liquid crystal cell is adopted for the optical compensation sheet, the total weight of the liquid crystal display device increases. For the above reasons, research and development of liquid crystal molecules and alignment films used in the optical compensation sheet have been advanced independently of liquid crystal molecules and alignment films used in liquid crystal cells.

As for liquid crystal molecules, it has been proposed in recent optical compensation sheets to use discotic liquid crystal molecules instead of rod-shaped liquid crystal molecules. When discotic liquid crystal molecules are used for the optical compensation sheet, the viewing angle of the liquid crystal display device can be significantly improved. Also,
Discotic liquid crystalline molecules are more excellent in stability of alignment state than rod-like liquid crystalline molecules. JP-A-8-27
No. 284 proposes to introduce a polymerizable group into discotic liquid crystal molecules and to stably fix the alignment state by a polymerization reaction. With respect to the alignment film of the optical compensation sheet, a method of controlling the alignment of liquid crystal molecules only with a single-sided alignment film has been proposed on the premise that discotic liquid crystal molecules are used. JP-A-7-14640
No. 9 discloses a technique in which an SiO obliquely deposited film is used as a one-sided alignment film instead of an alignment film obtained by rubbing. JP-A-7-281028 discloses that
A technique using a rubbed polyimide film as a single-sided alignment film is disclosed.

[0006] S described in Japanese Patent Application Laid-Open No. 7-146409
When the iO obliquely deposited film is used as a single-sided alignment film, rubbing debris is not generated, so that an optical compensation sheet with few alignment defects (high optical purity) can be obtained. However, the SiO obliquely deposited film is not suitable for mass production. When mass-producing an optical compensatory sheet, it is necessary to continuously form an alignment film on a long transparent support. It is technically difficult to form a vapor deposition film continuously in a long shape. Moreover, the optical compensation sheet formed in a long shape is used by cutting along the optical axis direction. Therefore, if the optical axis direction does not coincide with the longitudinal direction of the long sheet, a portion to be discarded due to cutting occurs. When the angle difference between the optical axis direction and the longitudinal direction increases, the area of the discarded portion increases. With an alignment film used for a conventional optical compensatory sheet, strict adjustment in the optical axis direction was extremely difficult.

Japanese Patent Application Laid-Open No. 10-42820 discloses an optical compensatory sheet using an alignment film to which an alignment function is given by light irradiation. An alignment film to which an alignment function is given by light irradiation has a problem that the alignment function is weak and unstable. In the optical compensation sheet, since the alignment state of the liquid crystal compound is fixed and used, in principle, the stability of the alignment function is required as compared with the case of the liquid crystal cell. In addition, since the optical compensation sheet preferably has a single-sided alignment film configuration, in principle, a stronger alignment function is required as compared with a liquid crystal cell having a double-sided alignment film configuration. However, Japanese Patent Application Laid-Open
According to the description of Japanese Patent No. 42820, when discotic liquid crystalline molecules are used, an alignment film to which an alignment function is unexpectedly imparted by light irradiation can be advantageously used in an optical compensation sheet.

Japanese Patent Application Laid-Open No. 2000-75131 discloses an optical compensatory sheet in which discotic liquid crystal molecules are substantially vertically aligned using an alignment film provided with an alignment function by light irradiation. That is, the alignment film to which the alignment function is given by light irradiation is also effective when the discotic liquid crystal molecules are substantially vertically aligned.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optically anisotropic element in which the tilt angle and the alignment direction of discotic liquid crystalline molecules are strictly controlled.
Another object of the present invention is to provide a method for manufacturing an optically anisotropic element in which the orientation tilt angle and orientation direction of discotic liquid crystalline molecules can be easily controlled.

[0010]

The object of the present invention has been attained by the following optically anisotropic elements (1) to (4) and the following method for producing an optically anisotropic element (5). (1) An optically anisotropic element having, in this order, an alignment film and an optically anisotropic layer containing discotic liquid crystal molecules fixed in an aligned state on a transparent support, The liquid crystal molecules are substantially vertically aligned by the alignment film, and the alignment direction of the discotic liquid crystal molecules is controlled by light irradiated from a single direction after the vertical alignment of the discotic liquid crystal molecules. Optical anisotropic element. (2) The optically anisotropic element according to (1), wherein the discotic liquid crystalline molecules are fixed in an aligned state by polymerization. (3) The optically anisotropic element according to (1), wherein the alignment film contains a photosensitive polymer. (4) The optically anisotropic element according to (3), wherein the photosensitive polymer has, in a side chain, a group having a function of aligning discotic liquid crystal molecules substantially vertically.

(5) A step of providing an alignment film made of a photosensitive polymer on a transparent support; a step of providing a layer containing a discotic liquid crystal molecule having a polymerizable group and a photopolymerization initiator on the alignment film. A step of aligning the discotic liquid crystal molecules substantially vertically; a step of irradiating light from a single direction to control an alignment direction of the discotic liquid crystal molecules; and a step of irradiating light to discotic liquid crystal molecules. A method for producing an optically anisotropic element, comprising a step of forming an optically anisotropic layer by polymerizing molecules. In this specification, that the discotic liquid crystalline molecules are substantially vertically aligned means that the average tilt angle of the discotic liquid crystalline molecules is 50 to 90 degrees. The average tilt angle of the discotic liquid crystal molecules means the average angle between the disc surface of the discotic liquid crystal molecules and the surface of the support (or the surface of the alignment film). That is, the vertical alignment in the present specification means a homogeneous alignment of discotic liquid crystalline molecules.

[0012]

According to the present invention, when discotic liquid crystal molecules are used, even in the case of an alignment film formed by light irradiation that has a weak and unstable alignment function, the discotic liquid crystal molecules can be fixed in an aligned state. However, as a result of research conducted by the present inventors, it is difficult to strictly control both the orientation tilt angle and the orientation direction of discotic liquid crystalline molecules in an alignment film formed by light irradiation. The present inventor has succeeded in strictly controlling both the orientation tilt angle and the orientation direction of discotic liquid crystalline molecules by improving the manufacturing procedure of the alignment film and the optically anisotropic element by light irradiation. . In the present invention, an alignment film having a normal (irradiation unnecessary) alignment function and an alignment function by light irradiation is used. First, the discotic liquid crystalline molecules are substantially vertically aligned by a normal alignment function. Next, the orientation direction of the discotic liquid crystalline molecules is controlled by light irradiation. By employing such a two-stage alignment treatment, the alignment tilt angle and alignment direction of the discotic liquid crystalline molecules can be strictly controlled.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In an optically anisotropic element, a first step of providing an alignment film made of a photosensitive polymer on a transparent support;
A second step of rubbing the alignment film; a third step of providing a layer containing a discotic liquid crystal molecule having a polymerizable group and a photopolymerization initiator on the alignment film; and substantially heating the discotic liquid crystal molecule by heating. 4th orientation perpendicular to
Step: a fifth step of irradiating light from a single direction to control the orientation direction of the discotic liquid crystal molecules, and forming an optically anisotropic layer by irradiating light to polymerize the discotic liquid crystal molecules It is preferable to manufacture by the 6th process.

[Transparent Support] As the transparent support, a plastic film, a glass (quartz glass) plate or a metal film is used. A plastic film is preferably used. Examples of plastic film materials include:
Cellulose ester (eg, triacetyl cellulose),
Includes polycarbonate, polyarylate, polysulfone and polyethersulfone. For mass production,
The transparent support is preferably formed in a long shape (roll shape). The thickness of the transparent support is preferably from 20 to 500 μm, more preferably from 50 to 200 μm. An undercoat layer containing a hydrophilic polymer (eg, gelatin, polyvinyl alcohol) may be provided between the transparent support and the alignment film. The thickness of the undercoat layer is preferably from 0.1 to 2 μm, more preferably from 0.2 to 1 μm.

[Alignment Film] An alignment film to which an alignment function is given by light irradiation from a single direction is formed using a photochromic compound or a photosensitive polymer. A photochromic compound is a compound that changes its chemical structure by the action of light, thereby changing its behavior (for example, color tone) with respect to light. Generally, those changes are reversible. Photochromic compounds conventionally proposed for liquid crystal cells include azobenzene compounds (K. Ichimura et al., Langmu
ir, vol. 4, page 1214 (1988); K. Aokiet al., Langm
uir, vol. 8, page 1007 (1992); Y. Suzuki et al., L
angmuir, vol. 8, page 2601 (1992); K. Ichimura et a
l., Appl. Phys. Lett., vol. 63, No. 4, page 449 (1
993); N. Ishizuki, Langmuir, vol. 9, page 3298 (19
93); N. Ishizuki, Langmuir, vol. 9, page 857 (199
3)), hydrazono-β-ketoester compound (S. Yamam
ura et al., Liquid Crystals, vol. 13, No. 2, page
189 (1993)), stilbene compounds (Kunihiro Ichimura et al., Journal of Polymers, Vol. 47, No. 10, p. 771 (1990)) and spiropyran compounds (K. Ichimura et al., Chemistry Le.
tters, page 1063 (1992); K. Ichimura et al., Thin
Solid Films, vol. 235, page 101 (1993)).

Photochromic compounds containing a double bond structure consisting of C = C, C = N or N = N are particularly preferred. The photochromic compound having a double bond structure is
The following (1) and (2) essential elements and the following (3) to
It consists of optional elements of (5). (1) Double bond structure consisting of C = C, C = N or N = N (2) Cyclic structure present on both sides (need not be directly connected) of the bond of (1) above (3) Arbitrary ( A linking group between 1) and (2); (4) a substituent of any carbon atom of (1); (5) a substituent of a cyclic structure of any (2). , Trans is preferable to cis. Two or more double bond structures may be present in the molecule. It is preferable that the plurality of double bond structures have a conjugate relationship. Examples of the cyclic structure (2) include a benzene ring, a naphthalene ring, and a nitrogen-containing heterocyclic ring (eg, a pyridinium ring, a benzopyridinium ring). In the case of a nitrogen-containing heterocyclic ring, it is preferable that a carbon atom (not a nitrogen atom) constituting the ring be bonded to a carbon atom or a nitrogen atom of the double bond structure of (1). A benzene ring is particularly preferred.

Examples of the linking group (3) include -NH- and -CO-. However, it is preferable that (1) and (2) are directly connected without the connecting group of (3).
Examples of the substituent in the above (4) include an aryl group (eg, phenyl) and cyano. However, there is no substituent of (4), and the carbon atom contained in the double bond structure is unsubstituted except for the bond with (2) (-CH = CH- or -CH = N
-) Is preferable. Examples of the substituent of the above (5) include an alkoxy group (eg, methoxy, hexyloxy),
Examples include cyano, an alkyl group (eg, butyl, hexyl) and an alkylamino group (eg, dimethylamino). When the cyclic structure of (2) is a benzene ring, the substituent is preferably bonded to the para position. In addition, as described later, when a photochromic compound is used by chemically bonding to a polymer, a functional group for chemically bonding to the polymer is introduced into the photochromic compound as a substituent of (5).

It is necessary to use the photochromic compound fixed to the surface of the support by some means. It is particularly preferred that the photochromic compound is chemically bonded to the polymer and immobilized. The polymer chemically bonded to the photochromic compound is a hydrophilic polymer (eg, gelatin, polyvinyl alcohol, poly (meth)
Acrylate). Polyvinyl alcohol is particularly preferably used. The reaction between the photochromic compound and the polymer is determined according to the type of the polymer (particularly, the type of the functional group). In the case of a polymer having a hydroxyl group such as polyvinyl alcohol, a reaction between an acid halide and a hydroxyl group can be used.

The polymer used for the alignment film preferably further has a group having a function of substantially vertically (homogeneously) aligning the discotic liquid crystalline molecules. In order to align the discotic liquid crystalline molecules substantially vertically, it is important to lower the surface energy of the alignment film. Specifically, the surface energy of the alignment film is reduced by the functional groups of the polymer, and thereby the discotic liquid crystal molecules are in a standing state. As the functional group that lowers the surface energy of the alignment film, a hydrocarbon group having 10 or more carbon atoms is effective. In order to make the hydrocarbon group exist on the surface of the alignment film, it is preferable to introduce the hydrocarbon group into a side chain rather than the main chain of the polymer. The hydrocarbon group is an aliphatic group, an aromatic group, or a combination thereof. The aliphatic group may be cyclic, branched, or linear. The aliphatic group is preferably an alkyl group (may be a cycloalkyl group) or an alkenyl group (may be a cycloalkenyl group). The hydrocarbon group may have a substituent that does not show strong hydrophilicity, such as a halogen atom. The hydrocarbon group preferably has 10 to 100 carbon atoms, and preferably has 10 to 6 carbon atoms.
It is more preferably 0 and most preferably 10 to 40. The main chain of the polymer preferably has a polyvinyl alcohol structure.

A modified polyvinyl alcohol having a hydrocarbon group having 10 or more carbon atoms can align discotic liquid crystal molecules substantially vertically (homogeneously). The hydrocarbon group is an aliphatic group, an aromatic group, or a combination thereof. The aliphatic group may be cyclic, branched, or linear. The aliphatic group is preferably an alkyl group (may be a cycloalkyl group) or an alkenyl group (may be a cycloalkenyl group). The hydrocarbon group may have a substituent that does not show strong hydrophilicity, such as a halogen atom. The number of carbon atoms in the hydrocarbon group is preferably 10 to 100, more preferably 10 to 60, and more preferably 10 to 60.
Most preferably, it is from 40 to 40. The modified polyvinyl alcohol having a hydrocarbon group contains 2 to 80 mol% of a repeating unit having a hydrocarbon group having 10 or more carbon atoms.
And more preferably 3 to 70 mol%.

A preferred modified polyvinyl alcohol is represented by the following formula (PV). (PV)-(VAl) x- (HyC) y- (VAc) z- (P)
q-wherein, VAl is a vinyl alcohol repeating unit; HyC is a repeating unit having a hydrocarbon group having 10 or more carbon atoms; VAc is a vinyl acetate repeating unit; and P is a photochromic compound. X is 20 to 95 mol% (preferably 25 to 90 mol%); y is 0
Is from 0 to 80 mol% (preferably from 2 to 70 mol%); z is from 0 to 30 mol% (preferably from 2 to 20 mol%); and q is from 0 to 30 mol% (preferably from 2 to 70 mol%). 20 mol%). Preferred repeating unit having a hydrocarbon group having 10 or more carbon atoms (HyC)
Is represented by the following formulas (HyC-I) and (HyC-II).

[0022]

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In the formula, L ¹ represents —O—, —CO—, —SO
₂ -, - NH-, an alkylene group, an arylene group and a divalent linking group selected from their combinations; L
² is a single bond or -O -, - CO -, - SO 2 -,
-NH-, a divalent linking group selected from an alkylene group, an arylene group and a combination thereof;
¹ and R ² are each a hydrocarbon group having 10 or more carbon atoms. Examples of the divalent linking group formed by the above combination are shown below.

[0024] L1: -O-CO- L2: -O -CO- alkylene group -O- L3: -O-CO- alkylene group -CO-NH- L4: -O-CO- alkylene group -NH-SO ₂ -Arylene group-O-L5: -arylene group-NH-CO-L6: -arylene group-CO-O-L7: -arylene group-CO-NH-L8: -arylene group-O-L9: -O-CO -NH-arylene group -NH-CO-

Preferred repeating units (X) chemically bonded with a photochromic compound are represented by the following formulas (PI) and (P-II).

[0026]

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Wherein L ¹ is —O—, —CO—, —SO
₂ -, - NH-, an alkylene group, an arylene group and a divalent linking group selected from their combinations; L
² is a single bond or -O -, - CO -, - SO 2 -,
-NH-, a divalent linking group selected from an alkylene group, an arylene group and a combination thereof;
¹ and Z ² are each a monovalent photosensitive group derived from a photochromic compound. Examples of the divalent linking group formed by the above combination are those represented by the formula (HyC-
Same as (I) and (HyC-II). Examples of the monovalent photosensitive group (Z) derived from the photochromic compound are shown below.

[0028]

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[0029]

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[0030]

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The degree of polymerization of the polymer used for the alignment film is 20
0 to 5000, preferably 300 to 30
00 is preferred. The molecular weight of the polymer is 90
00 to 200,000, preferably 1300
More preferably, it is 0 to 130,000. Two or more polymers may be used in combination. In forming the alignment film, a rubbing treatment is preferably performed. The rubbing treatment is performed by rubbing the surface of the film containing the polymer several times with paper or cloth in a certain direction.

After the discotic liquid crystal molecules are oriented substantially vertically using the orientation film, light is irradiated from a single direction to control the orientation direction of the discotic liquid crystal molecules. X-rays, electron beams, ultraviolet rays, visible light rays, or infrared rays (heat rays) are used as the irradiation light. It is particularly preferred to use ultraviolet light or visible light. As a light source,
A low pressure mercury lamp, a high pressure discharge lamp or a short arc discharge lamp is preferably used. When the discotic liquid crystal molecules are polymerized using a photopolymerization initiator (described later), it is preferable to use light having a wavelength different from the photosensitive wavelength of the photopolymerization initiator. For that purpose, it is preferable to use a filter for selecting light having an appropriate wavelength.

The light is irradiated on the film in one direction as much as possible. The single direction means a single direction in the film plane (the direction in which the direction of light is projected on the film plane),
It also includes directions that are horizontal or perpendicular to the film plane. Exposure is more preferably from preferably 50 to 6000 mJ / cm ^2, a 100 to 2000 mJ / cm ^2. In order to provide an alignment control function to the alignment film in a short time, it is preferable to irradiate light while heating. The heating temperature is preferably from 40 to 250 ° C.

[Optical Anisotropic Layer] The optically anisotropic layer is formed from discotic liquid crystalline molecules. In the optically anisotropic layer,
Using the above-mentioned alignment film, the disc surface of the discotic liquid crystalline molecules is substantially perpendicular to the alignment film (50 to 9).
(An average inclination angle in a range of 0 degree). It is preferable that the discotic liquid crystalline molecules be fixed in the optically anisotropic layer while maintaining a vertical (homogeneous) alignment state. More preferably, the discotic liquid crystalline molecules are fixed by a polymerization reaction.

Discotic liquid crystalline molecules are described in various literatures (C. Destrade et al., Mol. Crysr. Liq. Cryst., V
ol. 71, page 111 (1981); edited by The Chemical Society of Japan, quarterly chemistry review, No. 22, Liquid Crystal Chemistry, Chapter 5, Chapter 10, Section 2
(1994); B. Kohne et al., Angew. Chem. Soc. Chem. C
omm., page 1794 (1985); J. Zhang et al., J. Am. Che
m. Soc., vol. 116, page 2655 (1994)). Regarding the polymerization of discotic liquid crystalline molecules,
It is described in JP-A-8-27284. In order to fix the discotic liquid crystal molecules by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystal molecules. However, when a polymerizable group is directly connected to the disc-shaped core, it becomes difficult to maintain an oriented state in the polymerization reaction. Therefore, a linking group is introduced between the discotic core and the polymerizable group. Therefore, the discotic liquid crystalline molecule having a polymerizable group is preferably a compound represented by the following formula.

D (-LQ) _{n wherein} D is a discotic core; L is a divalent linking group; Q is a polymerizable group; and n is an integer from 4 to 12 is there. An example of the discotic core (D) of the above formula is shown below. In each of the following examples, LQ (or QL) means a combination of a divalent linking group (L) and a polymerizable group (Q). Triphenylene (D4) is particularly preferred.

[0037]

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[0038]

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[0039]

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[0040]

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[0041]

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[0042]

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[0043]

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[0044]

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[0045]

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In the above formula, the divalent linking group (L) is
Alkylene group, alkenylene group, arylene group, -CO
It is preferably a divalent linking group selected from the group consisting of-, -NH-, -O-, -S- and a combination thereof. The divalent linking group (L) is an alkylene group, an alkenylene group, an arylene group, -CO-, -NH-, -O-
And a group obtained by combining at least two divalent groups selected from the group consisting of and -S-.
The divalent linking group (L) is most preferably a group obtained by combining at least two divalent groups selected from the group consisting of an alkylene group, an alkenylene group, an arylene group, -CO- and -O-. The alkylene group preferably has 1 to 12 carbon atoms. The alkenylene group preferably has 2 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbon atoms. The alkylene group, alkenylene group and arylene group may have a substituent (eg, an alkyl group, a halogen atom, a cyano, an alkoxy group, an acyloxy group). Examples of the divalent linking group (L) are shown below. The left side is bonded to the discotic core (D), and the right side is bonded to the polymerizable group (Q). AL represents an alkylene group or an alkenylene group, and AR represents an arylene group.

L1: -AL-CO-O-AL- L2: -AL-CO-O-AL-O- L3: -AL-CO-O-AL-O-AL- L4: -AL-CO-O -AL-O-CO-L5: -CO-AR-O-AL-L6: -CO-AR-O-AL-O-L7: -CO-AR-O-AL-O-CO-L8: -CO -NH-AL-L9: -NH-AL-O-L10: -NH-AL-O-CO-L11: -O-AL-L12: -O-AL-O-L13: -O-AL-O- CO-

L14: -O-AL-O-CO-NH-AL-L15: -O-AL-S-AL-L16: -O-CO-AL-AR-O-AL-O-CO-L17: -O-CO-AR-O-AL-CO-L18: -O-CO-AR-O-AL-O-CO-L19: -O-CO-AR-O-AL-O-AL-OC
O-L20: -O-CO-AR-O-AL-O-AL-OA
L-O-CO-L21: -S-AL-L22: -S-AL-O-L23: -S-AL-O-CO-L24: -S-AL-S-AL-L25: -S-AR -AL-

When an asymmetric carbon atom is introduced into AL (alkylene group or alkenylene group), a discotic liquid crystal molecule can be twisted in a helical manner.
Examples of AL * containing an asymmetric carbon atom are given below. The left side is the disc-shaped core (D) side, and the right side is the polymerizable group (Q) side. The carbon atom (C) marked with * is an asymmetric carbon atom. The optical activity may be either S or R.

AL * 1: -CH ₂ CH ₂ -C * HCH _{3
-CH 2 CH 2 CH 2 - AL} * 2: -CH 2 CH 2 CH 2 -C * HCH 3 -CH
_{2 CH 2 - AL * 3:} -CH 2 -C * HCH 3 -CH 2 CH 2 CH
_{2 CH 2 - AL * 4:} -C * HCH 3 -CH 2 CH 2 CH 2 CH 2
_{CH 2 - AL * 5: -CH} 2 CH 2 CH 2 CH 2 -C * HCH 3
_{-CH 2 - AL * 6: -CH} 2 CH 2 CH 2 CH 2 CH 2 -C * H
_{CH 3 - AL * 7: -C} * HCH 3 -CH 2 CH 2 CH 2 CH 2
_{- AL * 8: -CH 2 -C} * HCH 3 -CH 2 CH 2 CH
_{2 - AL * 9: -CH 2} CH 2 -C * HCH 3 -CH 2 CH
_{2 - AL * 10: -CH 2} CH 2 CH 2 -C * HCH 3 -CH
_{2 - AL * 11: -CH 2} CH 2 CH 2 CH 2 -C * HCH 3
- AL * 12: -C * HCH 3 -CH 2 CH 2 CH 2 - AL * 13: -CH 2 -C * HCH 3 -CH 2 CH 2 - AL * 14: -CH 2 CH 2 -C * HCH 3 _{-CH 2 - AL * 15: -CH} 2 CH 2 CH 2 -C * HCH 3 -

[0051] _{AL * 16: -CH 2 -C *} HCH 3 - AL * 17: -C * HCH 3 -CH 2 - AL * 18: -C * HCH 3 -CH 2 CH 2 CH 2 CH 2
_{CH 2 CH 2 - AL * 19} : -CH 2 -C * HCH 3 -CH 2 CH 2 CH
_{2 CH 2 CH 2 - AL *} 20: -CH 2 CH 2 -C * HCH 3 -CH 2 CH
_{2 CH 2 CH 2 - AL *} 21: -CH 2 CH 2 CH 2 -C * HCH 3 -CH
_{2 CH 2 CH 2 - AL *} 22: -C * HCH 3 -CH 2 CH 2 CH 2 CH 2
_{CH 2 CH 2 CH 2 - AL} * 23: -CH 2 -C * HCH 3 -CH 2 CH 2 CH
₂ CH ₂ CH ₂ CH ₂ -AL * 24: -CH ₂ CH ₂ -C * HCH ₃ -CH ₂ CH
_{2 CH 2 CH 2 CH 2 -} AL * 25: -CH 2 CH 2 CH 2 -C * HCH 3 -CH
_{2 CH 2 CH 2 CH 2 -} AL * 26: -C * HCH 3 - (CH 2) 8 - AL * 27: -CH 2 -C * HCH 3 - (CH 2) 8 - AL * 28: -CH 2 _{-C * HCH 2 CH 3 - AL} * 29: -CH 2 -C * HCH 2 CH 3 -CH 2 - AL * 30: -CH 2 -C * HCH 2 CH 3 -CH 2 CH
₂ −

AL * 31: -CH ₂ -C * HCH ₂ CH _{3
-CH 2 CH 2 CH 2 CH 2} - AL * 32: -CH 2 -C * H (n-C 3 H 7) -CH 2
_{CH 2 - AL * 33: -CH} 2 -C * H (n-C 3 H 7) -CH 2
_{CH 2 CH 2 CH 2 - AL} * 34: -CH 2 -C * H (OCOCH 3) -CH 2
_{CH 2 - AL * 35: -CH} 2 -C * H (OCOCH 3) -CH 2
_{CH 2 CH 2 CH 2 - AL} * 36: -CH 2 -C * HF-CH 2 CH 2 - AL * 37: -CH 2 -C * HF-CH 2 CH 2 CH 2 C
_{H 2 - AL * 38: -CH} 2 -C * HCl-CH 2 CH 2 - AL * 39: -CH 2 -C * HCl-CH 2 CH 2 CH 2
_{CH 2 - AL * 40: -CH} 2 -C * HOCH 3 -CH 2 CH 2 - AL * 41: -CH 2 -C * HOCH 3 -CH 2 CH 2 C
_{H 2 CH 2 - AL * 42} : -CH 2 -C * HCN-CH 2 CH 2 - AL * 43: -CH 2 -C * HCN-CH 2 CH 2 CH 2
_{CH 2 - AL * 44: -CH} 2 -C * HCF 3 -CH 2 CH 2 - AL * 45: -CH 2 -C * HCF 3 -CH 2 CH 2 CH
₂ CH ₂ −

The polymerizable group (Q) in the above formula is determined according to the type of the polymerization reaction. Examples of the polymerizable group (Q) are shown below.

[0054]

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[0055]

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[0056]

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The polymerizable group (Q) is an unsaturated polymerizable group (Q1
To Q7), an epoxy group (Q8) or an aziridinyl group (Q9), more preferably an unsaturated polymerizable group, and more preferably an ethylenically unsaturated polymerizable group (Q
1 to Q6) are most preferred. In the above formula, n is an integer of 4 to 12. Specific numbers are determined according to the type of discotic core (D).
The combination of a plurality of L and Q may be different, but is preferably the same. Two or more discotic liquid crystal molecules may be used in combination. For example, a molecule having an asymmetric carbon atom in the divalent linking group and a molecule having no asymmetric carbon atom can be used in combination. Further, a molecule having a polymerizable group (Q) and a molecule having no polymerizable group (Q) in the above formula (a molecule having a hydrogen atom or an alkyl group instead of Q) may be used in combination. It is particularly preferable to use a molecule having an asymmetric carbon atom and having no polymerizable group in combination with a molecule having a polymerizable group and having no asymmetric carbon atom. Molecules having an asymmetric carbon atom and no polymerizable group substantially function as chiral agents more than discotic liquid crystal molecules.

Instead of introducing an asymmetric carbon atom into the divalent linking group (L) of the discotic liquid crystal molecule, a compound having an asymmetric carbon atom and having optical activity (chiral agent) is added to the optically anisotropic layer. Even if added, the discotic liquid crystalline molecules can be twisted and aligned in a helical manner. As the compound containing an asymmetric carbon atom, various natural or synthetic compounds can be used. The same or similar polymerizable group as the discotic liquid crystalline molecule may be introduced into the compound containing an asymmetric carbon atom. When a polymerizable group is introduced, the discotic liquid crystal molecules are aligned substantially vertically (homogeneously) and then fixed, and at the same time, the compound containing an asymmetric carbon atom is also optically anisotropic by the same or similar polymerization reaction. It can be fixed in layers.

The optically anisotropic layer is formed of a discotic liquid crystal molecule and the above-mentioned liquid crystal alignment promoter, and further, if necessary, a compound containing an asymmetric carbon atom, or a polymerizable initiator or other additives described below (for example, , A cellulose ester) on the alignment film. As a solvent used for preparing the coating solution, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-
Dimethylformamide), sulfoxide (eg, dimethylsulfoxide), heterocyclic compound (eg, pyridine), hydrocarbon (eg, benzene, hexane), alkyl halide (eg, chloroform, dichloromethane), ester (eg, methyl acetate, butyl acetate) ), Ketones (eg, acetone, methyl ethyl ketone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination. The application of the coating solution can be performed by a known method (eg, an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a die coating method, a bar coating method).

Discotic liquid crystal molecules that are substantially vertically (homogeneously) aligned are fixed while maintaining the alignment state. The immobilization is preferably performed by a polymerization reaction of the polymerizable group (Q) introduced into the discotic liquid crystalline molecule. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. Photopolymerization reactions are preferred. Examples of photopolymerization initiators include α-carbonyl compounds (U.S. Pat.
670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in US Pat. No. 2,722,512), and polynuclear quinone compounds (described in US Pat. No. 304612)
Nos. 7 and 2951758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in U.S. Pat. No. 3,549,367), an acridine and phenazine compound (Japanese Unexamined Patent Publication No.
-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat.
12970).

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight of the solid content of the coating solution.
More preferably, it is 5 to 5% by weight. Light irradiation for the polymerization of discotic liquid crystalline molecules preferably uses ultraviolet light. The irradiation energy is 20 mJ /
cm ^{2 to} 50 J / cm ² , preferably 10
More preferably, it is 0 to 800 mJ / cm ² . Light irradiation may be performed under heating conditions to promote the photopolymerization reaction. The thickness of the optically anisotropic layer is 0.1 to 5
It is preferably 0 μm, more preferably 1 to 30 μm, and most preferably 5 to 20 μm. When two optical compensation sheets are used in the liquid crystal display device, the thickness may be half the thickness of the optically anisotropic layer required when using one sheet. The average tilt angle of the discotic liquid crystalline molecules in the optically anisotropic layer is 50 to 90 degrees. The angle of inclination is preferably as uniform as possible. However, if the tilt angle changes continuously along the thickness direction of the optically anisotropic layer, there is no problem even if there is a slight change.

[Liquid crystal display device] The optically anisotropic element of the present invention is advantageously used as an optical compensation sheet for a liquid crystal display device. This is particularly effective in a liquid crystal display device using an STN type liquid crystal cell. The STN-type liquid crystal display device includes an STN-type liquid crystal cell, a pair of optical compensation sheets disposed on both sides of the liquid crystal cell, an optical compensation sheet disposed on one side of the liquid crystal cell, and a pair of polarizing plates disposed on both sides thereof. Become. The relationship between the alignment direction of the rod-like liquid crystal molecules in the liquid crystal cell and the alignment direction of the discotic liquid crystal molecules is determined by the director of the liquid crystal cell closest to the optical compensation sheet (the long axis direction of the rod-like molecules) and the liquid crystal. The director of the discotic liquid crystalline molecules of the optical compensation sheet closest to the cell (the normal direction of the disk-shaped core plane) is oriented substantially in the same direction (less than ± 10 °) when viewed from the normal direction of the liquid crystal cell. It is preferable to arrange them such that The transparent support of the optical compensation sheet can also function as a protective film on the liquid crystal cell side of the polarizing film. In such a case, the transparent support is arranged so that the slow axis (the direction in which the refractive index is maximized) and the transmission axis of the polarizing film are substantially perpendicular or substantially parallel (less than ± 10 °). Is preferred.

[0063]

EXAMPLES Example 1 (Formation of Undercoat Layer) A transparent polyethersulfone film having a thickness of 170 μm was used as a transparent support. On one side of the transparent support, a gelatin subbing layer having a thickness of 0.5 μm was provided.

(Synthesis of Photoisomerized Polymer) Degree of Polymerization 500
The fully saponified polyvinyl alcohol and 4- (4-hexylphenylazo) phenoxyacetyl chloride were heated in a mixed solvent of dimethylformamide and benzene for 2 hours to introduce 8% by weight of azobenzene units into the polyvinyl alcohol. The obtained polymer and 4-phenylbenzoic acid chloride were heated in a mixed solvent of dimethylformamide and benzene for 3 hours to introduce 8% by weight of phenylbenzoic acid units. Thus, a photoisomerized polymer was synthesized.

(Formation of Alignment Film)
The mixture to which 5% by weight of glutaraldehyde was added was dissolved in a mixed solvent of water and methanol to obtain a 2.5% by weight solution. The solution was coated on a gelatin subbing layer and dried. Next, a rubbing treatment was performed to form an alignment film.

(Formation of Optically Anisotropic Layer) A photopolymerization initiator (Irgacure 90) was added to the following discotic liquid crystalline molecules.
7, Nippon Kayaku Co., Ltd.) was dissolved in 2-butanone to prepare a 10% by weight solution. The solution was applied on the alignment film, dried, and heated at 90 ° C. for 5 minutes to align the discotic liquid crystal molecules. While maintaining a temperature of 90 ° C., parallel light of 400 nm was irradiated from a high-pressure mercury lamp of 500 W at an incident angle of 60 degrees and an azimuth angle of 45 degrees for 5 minutes. Further, a parallel light of 365 nm was irradiated from a high-pressure mercury lamp of 500 W for 10 seconds to cool. Thus, an optically anisotropic element was produced.

[0067]

Embedded image

(Evaluation of Optically Anisotropic Element) When the optically anisotropic element was sandwiched between two orthogonal polarizers and the light transmittance was examined, the longitudinal direction of the support and the axis of the orthogonal polarizer were determined. When the length direction of the support was at an angle of 45 degrees with respect to the axis of the orthogonal polarizer, almost no light was transmitted. From the above results, it was found that the discotic liquid crystalline molecules were aligned in the direction of light irradiation on azobenzene used for the alignment film. Further, when the optically anisotropic element was left for three days and then observed again, the same state was maintained.

Comparative Example 1 (Formation of Alignment Film) A mixture obtained by adding 0.5% by weight of glutaraldehyde to the photoisomerized polymer synthesized in Example 1 was dissolved in a mixed solvent of water and methanol. , 2.5% by weight. The solution was coated on the gelatin subbing layer of Example 1 and dried. Next, heat to 85 ° C.
365 nm parallel light (non-polarized light) from a 00W high-pressure mercury lamp
Was irradiated at an incident angle of 60 degrees and an azimuth angle of 45 degrees for 5 minutes. After the light irradiation, the film was cooled to form an alignment film.

(Formation of Optically Anisotropic Layer) A mixture of the discotic liquid crystal molecules used in Example 1 and 0.1% by weight of a photopolymerization initiator (Irgacure 907, manufactured by Nippon Kayaku Co., Ltd.) was added. , 2-butanone to prepare a 10% by weight solution. The solution is applied on the alignment film, dried, and
For 5 minutes to align the discotic liquid crystalline molecules. While maintaining a temperature of 90 ° C., a parallel light of 365 nm was irradiated from a high-pressure mercury lamp of 500 W for 5 seconds for cooling. Thus, an optically anisotropic element was produced.

(Evaluation of Optically Anisotropic Element) When the optically anisotropic element was sandwiched between two orthogonal polarizers and the light transmittance was examined, the longitudinal direction of the support and the axis of the orthogonal polarizer were determined. When the length direction of the support was at an angle of 45 degrees with respect to the axis of the orthogonal polarizer, almost no light was transmitted. From the above results, it was found that the discotic liquid crystalline molecules were aligned in the direction of light irradiation on azobenzene used for the alignment film.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/1347 G02F 1/1347 4H027 F term (Reference) 2H049 BA12 BA46 BB03 BB62 BC04 BC05 BC09 BC22 2H088 EA44 HA01 HA03 HA15 HA16 HA18 MA20 2H089 QA16 TA14 TA15 2H090 HB07Y HB08Y JB02 JB03 LA06 LA09 MA01 MB01 MB06 2H091 FA08X FA08Z FA11X FA11Z LA30 4H027 BA08 BA11

Claims (5)

[Claims] 1. An optically anisotropic element comprising, on a transparent support, an alignment film and an optically anisotropic layer containing discotic liquid crystal molecules fixed in an aligned state in this order, The discotic liquid crystalline molecules are substantially vertically aligned by the alignment film, and the orientation of the discotic liquid crystalline molecules is controlled by light irradiated from a single direction after the vertical alignment of the discotic liquid crystalline molecules. An optically anisotropic element comprising: 2. The optically anisotropic element according to claim 1, wherein the discotic liquid crystal molecules are fixed in an aligned state by polymerization. 3. The optically anisotropic element according to claim 1, wherein the alignment film contains a photosensitive polymer. 4. The optically anisotropic element according to claim 3, wherein the photosensitive polymer has, in a side chain, a group having a function of substantially vertically aligning discotic liquid crystalline molecules. 5. A step of providing an alignment film made of a photosensitive polymer on a transparent support; a step of providing a layer containing a discotic liquid crystal molecule having a polymerizable group and a photopolymerization initiator on the alignment film; Aligning the discotic liquid crystal molecules substantially vertically; irradiating light from a single direction to control the alignment direction of the discotic liquid crystal molecules; and irradiating light to the discotic liquid crystal molecules To form an optically anisotropic layer by polymerizing the polymer.