JP2002072210A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide viewing angle liquid crystal display device having a liquid crystal cell of a vertical alignment mode. SOLUTION: The liquid crystal display device consists of a liquid crystal cell holding rod-like liquid crystal molecules homogeneously aligned between two sheets of electrode substrates with 0 deg. twist angle of the liquid crystal molecules and two sheets of polarizing films arranged on the both sides of the liquid crystal cell. The liquid crystal display device is characterized by having an optical compensation sheet, composed of an optically anisotropic layer containing discotic compounds arranged on a transparent supporting body, arranged between the liquid crystal cell and at least one of the polarizing films and by having a retardation value of the liquid crystal cell, in the state of voltage application between the two sheets of the electrode substrates of the liquid crystal cell, and the sum total of retardation values of the optical compensation sheets satisfying an inequality 1<=(ΣRRF)/RLC(ON)<1.5 (in the inequality, RLC(ON) expresses the retardation value of the liquid crystal cell in the state of the voltage application to the liquid crystal cell, and ΣRRF expresses the sum total of the retardation values of the optical compensation sheets).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display comprising a polarizing film and a liquid crystal cell of a horizontal alignment mode.

[0002]

2. Description of the Related Art A liquid crystal display (LCD) is a CRT (Ca
Compared to a thode ray tube, it has the major advantages of being thinner, lighter, and consuming less power. The liquid crystal display device includes a liquid crystal cell and a pair of polarizing plates disposed on both sides of the liquid crystal cell. The liquid crystal cell is composed of rod-like liquid crystal molecules, two substrates for enclosing the same, and an electrode layer for applying a voltage to the rod-like liquid crystal molecules. The combination of the substrate and the electrode layer is called an electrode substrate. In order to align the enclosed rod-like liquid crystal molecules, an alignment film is provided on the two substrates. Further, in order to increase the viewing angle of the liquid crystal cell, an optical compensation sheet (retardation plate) is often provided between the liquid crystal cell and the polarizing plate. As the optical compensation sheet, a stretched birefringent film has been conventionally used.

It has been proposed to use an optical compensatory sheet having an optically anisotropic layer containing a discotic compound on a transparent support instead of a stretched birefringent film. The optically anisotropic layer is formed by orienting the discotic compound and fixing the orientation state. Discotic compounds generally have large birefringence. In addition, the discotic compound has various orientation forms. Therefore, by using a discotic compound, an optical compensatory sheet having optical properties that cannot be obtained with a conventional stretched birefringent film can be produced. Regarding an optical compensation sheet using a discotic compound, JP-A-6-214116, US Pat. No. 5,583,679,
No. 5,646,703 and West German Patent Publication 391162.
It is described in each specification of No. 0A1.

In a liquid crystal cell of a horizontal alignment mode, rod-like liquid crystal molecules are substantially horizontally aligned when no voltage is applied, and substantially vertically when a voltage is applied. The horizontal alignment mode is
It is also called a parallel alignment mode or a homogeneous alignment mode. A liquid crystal cell of a horizontal alignment mode has been proposed for a long time. Recently, ECB (Electrically Controlle
2. Description of the Related Art A liquid crystal cell of a horizontal alignment mode is used in a d-birefringence type liquid crystal display device. The ECB type liquid crystal display device is described in JP-A-5-203946.

[0005] The horizontal alignment mode is characterized in that the viewing angle is wide and the response speed is fast as compared with general liquid crystal modes (TN mode, STN mode). However, the viewing angle characteristics have room for further improvement. In order to further improve the liquid crystal display device in the horizontal alignment mode, it is conceivable to use an optical compensation sheet in the same manner as in a general liquid crystal mode. However, the conventional optical compensation sheet made of a stretched birefringent film has an insufficient optical compensation function for a liquid crystal display device in a horizontal alignment mode. As described above, it has been proposed to use an optical compensatory sheet having an optically anisotropic layer containing a discotic compound and a transparent support instead of the stretched birefringent film. JP-A-11-316378 discloses a horizontal alignment mode liquid crystal display device using an optical compensation sheet containing a discotic compound. By using the optical compensatory sheet containing the discotic compound, the viewing angle characteristics of the liquid crystal display device in the horizontal alignment mode are remarkably improved.

[0006]

As described above, it is known that the use of an optical compensation sheet improves the viewing angle characteristics of a liquid crystal display device in a horizontal alignment mode.
In order to obtain high-quality display, further improvement in viewing angle characteristics is desired. An object of the present invention is to provide a liquid crystal display device having a wide viewing angle, comprising a liquid crystal cell of an arbitrary horizontal alignment mode and an optical compensation sheet for optically compensating the liquid crystal cell corresponding to the liquid crystal cell. .

Means for Solving the Problems The present inventor has proposed a liquid crystal cell having a retardation value in which a voltage equal to or higher than a threshold voltage is applied between two electrode substrates of a liquid crystal cell in a horizontal alignment mode. Between the retardation values of the optical compensation sheet,
By satisfying the specific relationship, it has been found that a liquid crystal display device having an unprecedented wide viewing angle can be provided.

The present invention is directed to a liquid crystal cell having horizontally oriented rod-like liquid crystal molecules sandwiched between two electrode substrates so that the twist angle of the liquid crystal molecules is 0 °, and disposed on both sides of the liquid crystal cell. A liquid crystal display device comprising two polarizing films, wherein an optically anisotropic layer containing a discotic compound is provided on a transparent support between the liquid crystal cell and at least one polarizing film. The total value of the retardation value of the liquid crystal cell and the retardation value of the optical compensation sheet in a state where a sheet is disposed and a voltage is applied between the two electrode substrates of the liquid crystal cell is expressed by the following formula (I). A liquid crystal display device characterized by satisfying. (I) 1 ≦ (ΣR _RF ) / R _{LC (ON)} <1.5 In the formula, R _{LC (ON)} is a retardation value of the liquid crystal cell when a voltage is applied to the liquid crystal cell, and ΔR _RF Is
This is the total retardation value of the optical compensation sheet.

Further, the present invention provides a liquid crystal cell having horizontally oriented rod-like liquid crystal molecules sandwiched between two electrode substrates and having a twist angle of the liquid crystal molecules of 0 °, and a liquid crystal cell having both sides of the liquid crystal cell. A liquid crystal display device comprising two polarizing films disposed, wherein an optically anisotropic layer containing a discotic compound is provided on a transparent support between a liquid crystal cell and at least one polarizing film. A compensation sheet is disposed, and the total value of the retardation value of the liquid crystal cell and the retardation value of the optical compensation sheet when a voltage is applied between the two electrode substrates of the liquid crystal cell is represented by the following formula (I). There is also an ECB type liquid crystal display device characterized by satisfying the following. (I) 1 ≦ (ΣR _RF ) / R _{LC (ON)} <1.5 In the formula, R _{LC (ON)} is a retardation value of the liquid crystal cell when a voltage is applied to the liquid crystal cell, and ΔR _RF Is
This is the total retardation value of the optical compensation sheet.

In each of the liquid crystal display devices of the present invention, it is preferable that the angle between the disc surface of the discotic compound and the transparent support changes in the depth direction of the optically anisotropic layer. . In this specification, “substantially perpendicular” or “substantially parallel” means that the angle is within a range of less than ± 5 ° from a strict angle. This range is preferably less than ± 4 °, more preferably less than ± 3 °, and most preferably less than ± 2 °. In this specification, the term “slow axis (slo
w axis) ”indicates the direction in which the refractive index is the maximum, and“ the fast axis (f
"ast axis)" means the direction in which the refractive index is minimum, and "transmission axis" means the direction in which the transmittance is maximum.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a liquid crystal display and an optical compensation sheet will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically showing the orientation of a liquid crystalline compound in a horizontally aligned liquid crystal cell. As shown in FIG. 1, the horizontal alignment liquid crystal cell includes an upper substrate (24a) and a lower substrate (24b).
A structure in which a liquid crystal compound (21) is sealed in between.
The liquid crystal compound (21) used in the horizontal alignment liquid crystal cell is:
Generally, it has a positive dielectric anisotropy. The upper substrate (24a) and the lower substrate (24b) of the liquid crystal cell have alignment films (22a, 22b) and electrode layers (23a, 23b), respectively. The alignment film has a function of aligning the rod-like liquid crystal molecules (21a to 21e). RD is the rubbing direction of the alignment film. The electrode layer has a function of applying a voltage to the rod-like liquid crystal molecules (21a to 21j). When the applied voltage of the horizontal alignment liquid crystal cell is low, the rod-like liquid crystal molecules (21a to 21j) are substantially horizontally aligned as shown in off of FIG. However, they are not completely horizontally oriented but slightly inclined (pretilted) in a certain direction. This is because the rod-like liquid crystal molecules (21a to 21a)
21j) are all inclined in a fixed direction (pre-tilt direction). As shown in on in FIG. 1, when the applied voltage is high, the rod-like liquid crystal molecules (21a to 211j) are oriented more vertically than in the off state. However, the substrate (24
a, 24b) Near rod-like liquid crystal molecules (21a, 21j)
Remain almost in the horizontal direction, and the rod-like liquid crystalline molecules (21d to 21g) at the center of the liquid crystal cell are oriented almost vertically.

FIG. 2 is a schematic view showing an optical compensatory sheet used in the liquid crystal display device of the present invention. As shown in FIG. 2, the optical compensation sheet is a laminate of a transparent support (33) and an optically anisotropic layer (31). The optical compensation sheet shown in FIG. 2 has an alignment film (32) between the transparent support (33) and the optically anisotropic layer (31). The discotic compounds (31a to 31e) contained in the optically anisotropic layer (31) are planar molecules. The discotic compounds (31a to 31e) have only one plane in the molecule, that is, a disc surface. The disk surface is inclined with respect to the surface of the transparent support (33). The angle (tilt angle) between the disk surface and the support surface increases as the distance between the disk-shaped compound and the alignment film increases. The average inclination angle is preferably in the range of 15 to 65 °. When the inclination angle is changed as shown in FIG. 2, the viewing angle expanding function of the optical compensation sheet is significantly improved. In addition, the optical compensatory sheet with the changed tilt angle has a display image inversion,
There is also a function of preventing the occurrence of gradation change or coloring. Normal (NL) of the disk surface of the disk-shaped compounds (31a to 31e)
Is orthogonal to the transparent support surface (PL), and has an antiparallel relationship with the rubbing direction (RD) of the alignment film (32).

FIG. 3 is a schematic diagram showing a horizontal alignment type liquid crystal display device according to the present invention. The liquid crystal display device shown in FIG.
Horizontal alignment liquid crystal cell (20), optically anisotropic layers 31A and 31B arranged on both sides of the liquid crystal cell, transparent supports 33A and 3
3B, the polarizing films 34A and 34B, and the backlight (B
L). The horizontal alignment liquid crystal cell (20) corresponds to the liquid crystal cell shown in FIG. The upper and lower rubbing directions (RD2, RD3) of the liquid crystal cell (20) are opposite (anti-parallel).
It is. The rubbing directions (RD1, RD4) of the discotic compound of the optically anisotropic layers (31A, 31B) are in an antiparallel relationship with the rubbing directions (RD2, RD3) of the facing liquid crystal cells. As described above, the rubbing directions (RD1, RD4) of the discotic compound are antiparallel to the average direction in which the normal of the disc surface is orthogonally projected onto the transparent support surface. Then, the two polarizing films (34A, 34B) have in-plane transmission axes (TA1, T2).
A2) are arranged so as to be orthogonal to each other (crossed Nicols).

FIG. 4 is a conceptual diagram showing the relationship of optical compensation in a horizontal alignment type liquid crystal display device. As shown in FIG. 4, in the liquid crystal display device according to the present invention, the horizontal alignment liquid crystal cell (20) is provided with an optically anisotropic layer (31) containing a discotic compound.
A, 31B) compensate optically. Optically anisotropic layer (31
A, 31B) Rubbing direction of the discotic compound (RD1,
RD4) is changed to the rubbing direction of the liquid crystal cell (RD2, RD
3), the liquid crystal molecules of the horizontal alignment liquid crystal cell (20) and the optically anisotropic layer (31) are set.
A, 31B) correspond to the discotic compounds (a to c, e to
g) to optically compensate.

As described above, a liquid crystal display device can be manufactured by arranging a horizontal alignment liquid crystal cell, an optical compensation sheet, and a polarizing film. In the liquid crystal display device of the present invention, the retardation value of the liquid crystal cell when a voltage equal to or higher than the threshold voltage of the liquid crystal cell is applied between the two electrode substrates, and the retardation value of the optical compensation sheet. When the total value satisfies the relationship of the following formula (I), a liquid crystal display device having excellent viewing angle characteristics can be obtained. (I) 1 ≦ (ΣR _RF ) / R _{LC (ON)} <1.5 In the formula, R _{LC (ON)} is a retardation value of the liquid crystal cell when a voltage is applied to the liquid crystal cell, and ΔR _RF Is
This is the total retardation value of the optical compensation sheet.

Hereinafter, the details of the liquid crystal display device of the present invention will be described. [Retardation] The optical compensatory sheet of the present invention comprises an optically anisotropic layer containing a discotic compound provided on a transparent support. Retardation value of optical compensation sheet (R _RF )
Is defined by the following formula (II). (II) R _RF = (nx _RF −ny _RF ) × d In the _RF equation, nx _RF is the refractive index in the slow axis direction in the plane of the optical compensation sheet, and ny _RF is the phase advance in the plane of the optical compensation sheet. The index of refraction in the axial direction, and d _RF is the thickness of the optical compensation sheet in nm.

The retardation value (R) of the liquid crystal cell when a voltage equal to or higher than the threshold value is applied to the liquid crystal cell.
_{LC (ON)} ) is defined by the following formula (III). (III) R _{LC (ON)} = (nx _{LC (ON)} −ny _{LC (ON)} ) × d In the _LC equation, nx _{LC (ON)} is the refractive index in the slow axis direction in the liquid crystal cell plane when voltage is applied. Ny _{LC (ON)} is the refractive index in the fast axis direction in the liquid crystal cell plane when voltage is applied, and d _LC is
This is the thickness of the liquid crystal cell held between two substrates in nm. The retardation value (R _{LC (ON)} ) of a liquid crystal cell is calculated by measuring the refractive index ellipse of one liquid crystal molecule in a cell when a voltage higher than the threshold voltage is applied between two electrode substrates of the liquid crystal cell. It is determined by measuring the retardation from the normal direction of the substrate, considering the body.

[Liquid Crystal Cell] The liquid crystal cell used in the liquid crystal display device of the present invention is called a horizontal alignment mode liquid crystal cell. The liquid crystal cell in the horizontal alignment mode is also called a parallel alignment mode or a homogeneous alignment mode. In the liquid crystal cell in the horizontal alignment mode, the rod-like liquid crystal molecules are substantially horizontally aligned when no voltage is applied, and substantially vertically when a voltage is applied. The twist angle of the rod-like liquid crystal molecules in the liquid crystal cell in the horizontal alignment mode is 0 °, which is distinguished from the liquid crystal cell in the TN mode or STN mode.

[Polarizing Film] An iodine-based polarizing film,
There are a dye-based polarizing film using a dichroic dye and a polyene-based polarizing film. The iodine-based polarizing film and the dye-based polarizing film are generally manufactured using a polyvinyl alcohol-based film. The transmission axis of the polarizing film corresponds to a direction perpendicular to the stretching direction of the film. Generally, a polarizing film is used in a liquid crystal display device as a polarizing plate having a transparent protective film provided on both sides thereof. A cellulose acetate film is used as a transparent protective film.

[Liquid Crystal Display Device] The liquid crystal display device of the present invention comprises the above-described horizontal alignment mode liquid crystal cell and two polarizing films disposed on both sides thereof. In the liquid crystal display device of the present invention, when using a polarizing plate provided with a protective film on both sides of the polarizing film, an optical compensation sheet, or one sheet disposed between the liquid crystal cell and one of the polarizing plates, or Two sheets are arranged between the liquid crystal cell and both polarizing plates. If necessary, an optical compensation sheet may be additionally provided at the same position. Further, in the liquid crystal display device of the present invention, an optical compensation sheet can be used as a protective film on the liquid crystal cell side among the two protective films provided on both sides of the polarizing film. Then, of the two protective films provided on the polarizing film, a protective film made of a cellulose acetate film is used as the protective film on the side opposite to the liquid crystal cell. When the protective film on the liquid crystal cell side provided on the polarizing film is used as the optical compensation sheet, the protective film on the liquid crystal cell side of one polarizing film may be used as the optical compensation sheet, or both polarizing films may be used on the liquid crystal cell side. May be used as an optical compensation sheet. Further, if necessary, an optical compensation sheet may be additionally provided.

[Transparent Support] A glass plate or a polymer film, preferably a polymer film, is used as the transparent support of the optical compensation sheet. A cellulose ester film is often used as the polymer film. Transparent support means that the light transmittance is 80% or more. As a transparent support, generally,
Optically isotropic polymer films are used. Specifically, the optical isotropy means that the retardation is 10 nm.
Is preferably less than 5 nm, more preferably less than 5 nm. In the optically isotropic transparent support, the retardation (Rth) in the thickness direction is preferably less than 10 nm, more preferably less than 5 nm. The in-plane retardation (Re) and the thickness direction retardation (Rth) of the transparent support are defined by the following formulas. Re = (nx−ny) × d Rth = [{(nx + ny) / 2} −nz] × d where nx and ny are in-plane refractive indices of the transparent support, and nz is the thickness of the transparent support. Is the refractive index in the direction, and d is the thickness of the transparent support.

As the transparent support, an optically anisotropic polymer film can be used if necessary. That is, in some cases, the optical anisotropy of the optically anisotropic layer is added to the optical anisotropy of the transparent support to correspond to the optical anisotropy of the liquid crystal cell (optical compensation). The retardation value of the optically anisotropic transparent support is preferably from 0 to 300 nm,
The thickness is more preferably 0 to 200 nm, and most preferably 0 to 100 nm. The retardation (Rth) in the thickness direction of the optically anisotropic transparent support is 10
To 1000 nm, preferably 10 to 40 nm.
0 nm is more preferable, and 10 to 300 nm
Is more preferable.

In the case of an optically anisotropic support, a synthetic polymer (eg, polycarbonate, polysulfone, polyethersulfone, polyacrylate, polymethacrylate, norbornene resin) is generally used. However, the use of a retardation increasing agent (a birefringence increasing agent), a decrease in the degree of acetylation of cellulose acetate, or the production of a film by a cooling dissolution method described in European Patent No. 0911656 A2 may cause an optical anisotropy. A cellulose ester film having high (high retardation) properties can also be produced. To obtain an optically anisotropic transparent support,
A stretching process may be performed on the polymer film. However, the polymer film is stretched in the longitudinal direction of the roll in the manufacturing process without performing a stretching process. Depending on the optical anisotropy of the liquid crystal cell or the optically anisotropic layer, even if it is an optical anisotropy caused by natural stretching in such a manufacturing process, it may function as a transparent support having optical anisotropy. is there.

The transparent support comprising a polymer film is
It is preferably formed by a solvent casting method.
Further, the thickness of the transparent support is preferably from 10 to 500 μm, more preferably from 50 to 200 μm. In order to improve the adhesion between the transparent support and a layer provided thereon (adhesion layer, alignment film or optically anisotropic layer), the transparent support is subjected to surface treatment (eg, glow discharge treatment, corona discharge treatment, ultraviolet light ( UV) treatment, flame treatment). An ultraviolet absorber may be added to the transparent support. An adhesive layer (undercoat layer) may be provided on the transparent support. The adhesion layer is described in JP-A-7-333433. The thickness of the adhesion layer is preferably from 0.1 to 2 μm, more preferably from 0.2 to 1 μm.

[Alignment Film] The alignment film has a function of defining the alignment direction of the discotic compound of the optically anisotropic layer. The alignment film may be formed by rubbing an organic compound (preferably a polymer), obliquely depositing an inorganic compound, forming a layer having microgrooves, or using a Langmuir-Blodgett method (L
B film) to accumulate organic compounds (eg, ω-tricosanoic acid, dioctadecylmethylammonium chloride, methyl stearylate). Further, an alignment film in which an alignment function is generated by application of an electric field, a magnetic field, or light irradiation is also known. The alignment film is preferably formed by rubbing a polymer. Polyvinyl alcohol is a preferred polymer. Modified polyvinyl alcohol to which a hydrophobic group is bonded is particularly preferred. Since the hydrophobic group has an affinity for the discotic compound in the optically anisotropic layer, the discotic compound can be uniformly oriented by introducing the hydrophobic group into polyvinyl alcohol. The hydrophobic group is bonded to the main chain terminal or side chain of polyvinyl alcohol. The hydrophobic group is preferably an aliphatic group having 6 or more carbon atoms (preferably an alkyl group or an alkenyl group) or an aromatic group. When a hydrophobic group is bonded to the main chain terminal of polyvinyl alcohol, it is preferable to introduce a linking group between the hydrophobic group and the main chain terminal. Examples of the linking group include -S-, -C (CN) R ^1- ,
-NR ² -, - CS- and a combination thereof. R ¹ and R ² are each a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (preferably, an alkyl group having 1 to 6 carbon atoms).

When a hydrophobic group is introduced into the side chain of the polyvinyl alcohol, a part of the acetyl group (—CO—CH ₃ ) of the vinyl acetate unit of the polyvinyl alcohol is replaced with an acyl group (−) having 7 or more carbon atoms. CO-R ³ ). R ³ is an aliphatic group or an aromatic group having 6 or more carbon atoms. Commercially available modified polyvinyl alcohol (eg,
MP103, MP203, R1130, Kuraray Co., Ltd.
May be used. The saponification degree of (modified) polyvinyl alcohol used for the alignment film is preferably 80% or more. The degree of polymerization of (modified) polyvinyl alcohol is 2
It is preferably at least 00. The rubbing treatment is performed by rubbing the surface of the alignment film several times with paper or cloth in a certain direction. It is preferable to use a cloth in which fibers having uniform length and thickness are uniformly planted. The alignment film is indispensable in the production of the optically anisotropic layer in which the discotic compound is oriented, but is not essential in the optical compensation sheet. Therefore, after the discotic compound in the optically anisotropic layer is oriented, if the discotic compound in the oriented state is fixed, only the optically anisotropic layer is transferred to another transparent support to form an optical compensation sheet. Is also possible. When the alignment film is provided between the transparent support and the optically anisotropic layer, it is preferable to provide an adhesion imparting means (such as an undercoat layer) between the transparent support and the alignment film.

[Optically Anisotropic Layer] The optically anisotropic layer contains a discotic compound. The optically anisotropic layer is preferably a layer containing a discotic compound having negative uniaxiality and being obliquely oriented. In the discotic compound, as shown in FIG. 2, the angle between the disc surface of the discotic compound and the transparent support surface changes in the depth direction of the optically anisotropic layer (hybrid orientation). Is preferred. The optical axis of the discotic compound exists in the direction normal to the disc surface. The discotic compound has birefringence in which the refractive index in the disc surface direction is larger than the refractive index in the optical axis direction. The optically anisotropic layer is preferably formed by orienting the discotic compound by the above-mentioned orientation film and fixing the discotic compound in the oriented state. The discotic compound is preferably fixed by a polymerization reaction. Note that the optically anisotropic layer has no direction in which the retardation value becomes zero. In other words, the minimum value of the retardation of the optically anisotropic layer is a value exceeding 0.

Discotic compounds are described in various references (C. Destrad
e et al., Mol. Crysr. Liq. Cryst., vol. 71, page 1
11 (1981); edited by The Chemical Society of Japan, quarterly chemistry review, No. 2
2. Liquid Crystal Chemistry, Chapter 5, Chapter 10, Section 2 (1994); BK
ohne et al., Angew. Chem. Soc. Chem. Comm., page 1
794 (1985); J. Zhang et al., J. Am. Chem. Soc., Vo.
l. 116, page 2655 (1994)). The polymerization of the discotic compound is described in JP-A-8-27284. In order to fix the discotic compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic compound. 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 compound having a polymerizable group is preferably a compound represented by the following formula (IV).

(IV) D (-LP) _{n wherein} D is a discotic core; L is a divalent linking group, P is a polymerizable group, and n is 4 to 12 Is an integer. Examples of the disc-shaped core (D) are shown below. In each of the following examples, LP (or PL) means a combination of a divalent linking group (L) and a polymerizable group (P).

[0029]

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[0030]

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[0031]

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[0032]

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[0033]

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[0034]

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[0035]

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[0036]

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[0037]

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In the formula (IV), the divalent linking group (L)
Is an alkylene group, alkenylene group, arylene group,-
It is preferably a divalent linking group selected from the group consisting of CO-, -NH-, -O-, -S- and a combination thereof. The divalent linking group (L) is an alkylene group, an arylene group, -CO-, -NH-, -O- and -S-
The divalent linking group is preferably a combination of at least two divalent groups selected from the group consisting of The divalent linking group (L) is an alkylene group, an arylene group,-
Most preferably, it is a divalent linking group obtained by combining at least two divalent groups selected from the group consisting of CO- and -O-. The alkylene group has 1 to 1 carbon atoms.
It is preferably 2. The alkenylene group preferably has 2 to 12 carbon atoms. The arylene group preferably has 6 to 10 carbon atoms.

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 a polymerizable group (P).
To join. AL represents an alkylene group or an alkenylene group, and AR represents an arylene group. In addition, the alkylene group, alkenylene group, and arylene group may have a substituent (eg, an alkyl 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-AR-O-AL-CO-L17: -O-CO-AR-O-AL-O-CO-L18: -O-CO-AR-O-AL -O-AL-OC
O-L19: -O-CO-AR-O-AL-O-AL-OA
L-O-CO-L20: -S-AL-L21: -S-AL-O-L22: -S-AL-O-CO-L23: -S-AL-S-AL-L24: -S-AR -AL-

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

[0042]

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[0043]

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[0044]

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[0045]

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[0046]

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[0047]

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The polymerizable group (P) is an unsaturated polymerizable group (P
1, P2, P3, P7, P8, P15, P16, P1
7) or an epoxy group (P6, P18), more preferably an unsaturated polymerizable group,
Ethylenically unsaturated polymerizable groups (P1, P7, P8, P1
5, P16, P17). In the formula (IV), n is an integer of 4 to 12. Specific numbers are determined according to the type of the disc-shaped core (D). The combination of a plurality of L and P may be different, but is preferably the same. The optically anisotropic layer can be formed by applying a coating liquid containing a discotic compound and, if necessary, a polymerizable initiator and optional components on the alignment film.

The oriented discotic compound is fixed while maintaining the oriented state. The immobilization is preferably performed by a polymerization reaction. 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.
369670), acyloin ethers (described in US Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in US Pat. No. 272251)
No. 2), polynuclear quinone compounds (US Pat. No. 304)
Nos. 6127 and 2951758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (described in US Pat. No. 3,549,367), an acridine and phenazine compound (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,221,970).

The amount of the photopolymerization initiator used is preferably 0.01 to 20% by mass of the solid content of the coating solution.
More preferably, the content is 5 to 5% by mass. The light irradiation for the polymerization of the discotic compound is preferably performed using ultraviolet light. Irradiation energy is 20 to 5000 mJ / c
m ² , preferably 100 to 800 mJ / c.
m ² is more preferable. Light irradiation may be performed under heating conditions to promote the photopolymerization reaction.
A protective layer may be provided on the optically anisotropic layer. As described above, the optical compensation sheet used in the present invention can be manufactured.

[Adjustment of Retardation Value]
Sheet retardation value (R_RF) Is the following formula (II)
Defined by (II) R_RF= (Nx_RF-Ny_RF) × d_RF Then, a voltage is applied to the liquid crystal cell measured as described above.
The retardation value of the liquid crystal cell (R
_{LC (ON)}) And the retardation value of the optical compensation sheet
Total value (ΣR_RF) Satisfies the following formula (I).
The liquid crystal display device of the present invention can be manufactured. (I) 1 ≦ (ΣR_RF) / R_{LC (ON)}<1.5 When using a plurality of optical compensation sheets, each light
By summing the retardation values of the school compensation sheet
R_RFCan be requested. Simple to satisfy this relationship
The most suitable method is to apply the letter
Solution value (R _{LC (ON)}) To satisfy the above equation
Adjust the retardation value of the optical compensation sheet
I just need.

The retardation value of the optical compensation sheet is
It is proportional to the thickness of the optically anisotropic layer. Therefore, when the optically anisotropic layer is applied, an optical compensatory sheet satisfying the relationship of the above formula (I) can be produced by adjusting the thickness thereof. If the retardation value (R _RF ) of the optical compensation sheet prepared by changing the thickness of the optically anisotropic layer is checked in advance, the retardation value (R
_{LC (ON)} ), the thickness of the optically anisotropic layer can be easily determined, and the liquid crystal display device of the present invention satisfying the relationship of the above formula (I) can be easily manufactured. . Further, the adjustment of the retardation value of the optical compensation sheet may be adjusted not only by changing the thickness of the optically anisotropic layer, but also by changing the type of the discotic compound, or the retardation of the transparent support. The value may be adjusted.

[0053]

The retardation value of the horizontal alignment mode liquid crystal cell is determined by the type of rod-like liquid crystal molecules to be enclosed and the thickness of the rod-like liquid crystal molecule layer sandwiched between a pair of electrode substrates. Further, the retardation value ( _{RLC (ON)} ) in a state where a voltage is applied between the two electrode substrates of the liquid crystal cell can be easily obtained by measurement. Of the liquid crystal display device of the present invention, the relationship between the retardation value of the liquid crystal cell in a state where a voltage is applied to the liquid crystal cell and _{(R LC (ON)),} the sum of the retardation value of the optical compensation sheet and (.SIGMA.R _RF) However, by satisfying the relationship of the following formula (I), a liquid crystal display device with high contrast over a wide viewing angle and little inversion can be obtained. Further, the retardation value of the optical compensation sheet used in the liquid crystal display device of the present invention can be easily changed by changing the type of the discotic molecule used, the retardation of the transparent support, or the thickness of the optically anisotropic layer. Can be adjusted. Therefore, it is possible to easily obtain a liquid crystal display device having a wide viewing angle in which an arbitrary horizontally aligned liquid crystal cell is compensated by the optical compensation sheet corresponding to the liquid crystal cell. (I) 1 ≦ (ΣR _RF ) / R _{LC (ON)} <1.5

[0054]

[Example 1] (Production of liquid crystal cell) A coating liquid for an alignment film (SE7210, manufactured by Nissan Chemical Industries, Ltd.) was applied to a glass substrate with an ITO electrode using a spin coater, and the solvent was dried. . 25
By firing at 0 ° C. for 2 hours, an alignment film was formed. A rubbing treatment was performed on the surface of the alignment film. The two glass substrates thus obtained were opposed to each other in an arrangement in which the rubbing directions were parallel, and the cell gap was set to 3 μm. A liquid crystal compound (ZLI-1132, manufactured by Merck) was injected into the cell gap to prepare a liquid crystal cell. The retardation value of the liquid crystal cell when no voltage was applied was 370 nm, and when a voltage of 5.0 V was applied between the two electrode substrates, the retardation value was 6 nm.
It was 8 nm.

(Preparation of Transparent Support) A 0.1 μm-thick gelatin undercoat layer was formed on a 100 μm-thick triacetyl cellulose film. On the gelatin undercoat layer,
A coating solution having the following composition was applied at 28 ml / m ² using a # 16 wire bar coater. Drying was performed with hot air at 60 ° C. for 60 seconds, and further with hot air at 90 ° C. for 150 seconds to form an alignment film.

<< Composition of Alignment Layer Coating Solution >>変 性 The following modified polyvinyl alcohol 10 parts by weight Water 371 parts by weight Methanol 119 parts by weight Glutaraldehyde (crosslinked Agent) 0.5 parts by mass ────────────────────────────────────

[0057]

Embedded image

(Preparation of Optical Compensation Sheet) On an alignment film formed on a transparent support, 10.0 g of the following discotic (liquid crystalline) compound was added to ethylene oxide-modified trimethylolpropane triacrylate (V # 360, 1.0 g of cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co., Ltd.)
20 g, and 0.30 g of a photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) were added, and a coating solution obtained by dissolving this in methyl ethyl ketone so as to have a solid concentration of 35% by mass was used using a bar coater having a wire diameter of 80 μm. And applied. This was heated in a thermostat at 130 ° C. for 5 minutes, and then irradiated with UV light having an illuminance of 250 mW / cm ² for 1.5 seconds with a UV irradiator to polymerize the discotic compound. Then, it was left to cool to room temperature. Thus, an optically anisotropic layer was formed, and an optical compensation sheet was produced. The thickness of the formed optically anisotropic layer was 1.4 μm.

[0059]

Embedded image

(Fabrication of Liquid Crystal Display Device) The two rubbing directions of the prepared liquid crystal cell in the horizontal alignment mode and the rubbing direction of the optical compensation sheet are antiparallel, and two optical compensation sheets are provided on both sides of the liquid crystal cell. Stuck together. Furthermore, a liquid crystal display device was manufactured by laminating two polarizing plates such that the transmission axes of the polarizing plates were in a crossed Nicols arrangement and the transmission axes of the polarizing plates were at 45 ° to the rubbing direction of the liquid crystal cell. .

Example 2 (Preparation of Liquid Crystal Cell) A liquid crystal cell was prepared in the same manner as in the liquid crystal cell prepared in Example 1, except that the cell gap was set to 2 μm. The retardation value of the liquid crystal cell when no voltage was applied was 250 nm, and the retardation value when a voltage of 5.0 V was applied between the two electrode substrates was 3 nm.
It was 2 nm.

(Preparation of Optical Compensation Sheet) As the transparent support, the support prepared in Example 1 is used. On the alignment film formed on the transparent support, 10.0 g of the discotic (liquid crystalline) compound used in Example 1 was added to ethylene oxide-modified trimethylolpropane triacrylate (V # 36).
1.0 (manufactured by Osaka Organic Chemical Co., Ltd.), 0.20 g of cellulose acetate butyrate (CAB531-0.2, manufactured by Eastman Chemical Company), and a photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy) 30 g was added, and this was dissolved in methyl ethyl ketone so that the solid concentration became 25% by mass.
Was applied using a bar coater. After heating this in a thermostat at 130 ° C. for 5 minutes, the illuminance was 250
The disk-shaped compound was polymerized by irradiating with UV light of mW / cm ² for 1.5 seconds. Then, it was left to cool to room temperature. Thus, an optically anisotropic layer was formed, and an optical compensation sheet was produced. The thickness of the formed optically anisotropic layer was 1.0 μm.

(Fabrication of Liquid Crystal Display Device) Two rubbed optical compensatory sheets were provided on both sides of the liquid crystal cell in such a manner that the rubbing direction of the produced liquid crystal cell in the horizontal alignment mode was antiparallel to the rubbing direction of the optical compensatory sheet. Stuck together. Furthermore, a liquid crystal display device was manufactured by laminating two polarizing plates such that the transmission axes of the polarizing plates were in a crossed Nicols arrangement and the transmission axes of the polarizing plates were at 45 ° to the rubbing direction of the liquid crystal cell. .

Comparative Example 1 The liquid crystal cell in the horizontal alignment mode prepared in Example 1 and a uniaxially stretched polycarbonate film having a retardation value of 34 nm were arranged so that the rubbing direction of the liquid crystal cell was perpendicular to the slow axis of the polycarbonate film. Then, two polycarbonate films were bonded to both sides of the liquid crystal cell. Furthermore, a liquid crystal display device was manufactured by laminating two polarizing plates such that the transmission axes of the polarizing plates were in a crossed Nicols arrangement and the transmission axes of the polarizing plates were at 45 ° to the rubbing direction of the liquid crystal cell. .

Comparative Example 2 (Preparation of Optical Compensation Sheet) An optical compensation sheet was prepared in the same manner as in Example 1 except that a bar coater having a wire diameter of 120 μm was used for coating the optically anisotropic layer. The thickness of the formed optically anisotropic layer was 2.0 μm. (Fabrication of Liquid Crystal Display Device) The two rubbing directions of the liquid crystal cell in the horizontal alignment mode fabricated in Example 1 and the rubbing direction of the optical compensatory sheet were antiparallel, and two optical compensatory sheets were provided on both sides of the liquid crystal cell. Were pasted together. Furthermore, a liquid crystal display device was manufactured by laminating two polarizing plates such that the transmission axes of the polarizing plates were in a crossed Nicols arrangement and the transmission axes of the polarizing plates were at 45 ° to the rubbing direction of the liquid crystal cell. .

(Optical Characteristics of Liquid Crystal Display) Examples 1 and 2
And in the liquid crystal display devices manufactured in Comparative Examples 1 and 2,
The retardation value of the liquid crystal cell and the retardation value of the optical compensation sheet when a voltage is applied are shown in Table 1 below.

[0067]

[Table 1] Table 1-Liquid crystal liquid crystal cell and optical compensation sheet retardation value display _{R LC (ON) R RF ΣR} RF example 1 68 nm 35 nm 70 nm example 2 32 nm 16 nm 32 nm Comparative example 1 68 nm 34 nm 68 nm Comparative example 2 68nm 55nm 110nm ─────────── ─────────────────────────

(Viewing Angle Characteristics of Liquid Crystal Display) Example 1,
A voltage of 55 Hz was applied between the two electrode substrates of the liquid crystal cells of the liquid crystal display devices manufactured in Comparative Example 1 and Comparative Examples 1 and 2, and the white display was set to 1.0 V and the black display was set to 5.0 V, and the luminance was measured using a measuring instrument ( EZ-Contrast 160D, manufactured by ELDIM), and the contrast characteristics were calculated. Brightness ratio (white display /
(Black display) was used as the contrast ratio, and the viewing angle at which a top / bottom / left / right contrast ratio of 10: 1 was obtained was measured. The results are summarized in Table 2 below.

[0069]

[Table 2] Table 2 LCD front view contrast device 12:00 6: 3 3: 9 Example 1 55 51 65 64 150 Example 2 52 50 62 60 160 Comparative Example 1 35 28 41 38 155 Comparative Example 2 37 36 45 42 120 ──────────────────────────

[0070]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing the orientation of a liquid crystalline compound in a horizontally aligned liquid crystal cell.

FIG. 2 is a schematic diagram showing an optical compensation sheet according to the present invention.

FIG. 3 is a schematic diagram showing a horizontal alignment type liquid crystal display device according to the present invention.

FIG. 4 is a conceptual diagram showing a relationship of optical compensation in a horizontal alignment type liquid crystal display device.

[Explanation of symbols]

 Reference Signs List 20 horizontal alignment liquid crystal cell 21 liquid crystal compound 21 a to 21 j rod-like liquid crystal molecule 22 a, 22 b alignment film 23 a, 13 b electrode layer 24 a upper substrate 24 b lower substrate 31 optically anisotropic layer 31 a to 31 e discotic compound 32 alignment film 33 transparent support Body 34 Polarizing film NL Normal direction of the disk surface of the discotic compound PL Direction of normal projection of the normal of the disk surface to the transparent support surface RD Rubbing direction TA In-plane transmission axis BL Backlight a to c, e to g Relationship

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H049 BA02 BA06 BA42 BB03 BB49 BC04 BC05 BC22 2H088 HA03 HA16 JA09 KA05 KA07 KA17 KA18 KA26 KA29 LA06 MA07 2H091 FA08X FA08Z FA11X FA11Z FB02 FD08 KA09 HA10 HA10

Claims (3)

[Claims] 1. A liquid crystal cell having horizontally oriented rod-like liquid crystal molecules sandwiched between two electrode substrates so that the twist angle of the liquid crystal molecules is 0 °, and disposed on both sides of the liquid crystal cell. A liquid crystal display device comprising two polarizing films, wherein an optical compensation sheet in which an optically anisotropic layer containing a discotic compound is provided on a transparent support is disposed between a liquid crystal cell and at least one polarizing film. And the sum of the retardation value of the liquid crystal cell and the retardation value of the optical compensation sheet in a state where a voltage is applied between the two electrode substrates of the liquid crystal cell satisfies the following formula (I). A liquid crystal display device characterized by the following: (I) 1 ≦ (ΣR _RF ) / R _{LC (ON)} <1.5 [where R _{LC (ON)} is a value of a liquid crystal cell in a state where a voltage is applied to the liquid crystal cell. The retardation value; and ΔR
_RF is the sum of the retardation values of the optical compensation sheet]. 2. A liquid crystal cell in which a horizontally oriented rod-like liquid crystal molecule is sandwiched between two electrode substrates so that a twist angle of the liquid crystal molecule is 0 °, and arranged on both sides of the liquid crystal cell. A liquid crystal display device comprising two polarizing films, wherein an optical compensation sheet in which an optically anisotropic layer containing a discotic compound is provided on a transparent support is disposed between a liquid crystal cell and at least one polarizing film. And the sum of the retardation value of the liquid crystal cell and the retardation value of the optical compensation sheet in a state where a voltage is applied between the two electrode substrates of the liquid crystal cell satisfies the following formula (I). ECB type liquid crystal display device characterized by the following: (I) 1 ≦ (ΣR _RF ) / R _{LC (ON)} <1.5 [where R _{LC (ON)} is a liquid crystal in a state where a voltage is applied to a liquid crystal cell. The retardation value of the cell; and ΔR
_RF is the sum of the retardation values of the optical compensation sheet]. 3. The liquid crystal according to claim 1, wherein an angle between the disc surface of the discotic compound and the transparent support changes in a depth direction of the optically anisotropic layer. Display device.