JPH09297216A - Optically anisotropic film, its production and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optically anisotropic material which improves characteristics in the angle of visual field of a liquid crystal display device, to provide the production method of this material, and to provide a liquid crystal display device having excellent characteristics in the angle of visual field in which the optical anisotropic material is used. SOLUTION: This optically anisotropic film is produced by mixing a polymer and a discotic liquid crystal, and the phase of the discotic liquid crystal is separated from the phase of the polymer. The average particle size of the discotic liquid crystal in the phase separation state ranges 20 to 600nm. The retardation of the optical anisotropic film measured along the normal direction (with 546nm measurement wavelength) ranges -200 to 200nm. Further, the film is obtd. by stretching a film produced from a mixture of the polymer and the discotic liquid. The obtd. film is used for a liquid crystal display device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical anisotropic film used for a non-linear optical element, a liquid crystal display device (hereinafter sometimes referred to as LCD), a method for producing the same, and an optical anisotropic film. The liquid crystal display device used.

[0002]

2. Description of the Related Art Liquid crystal displays have excellent characteristics such as low voltage drive and light weight, and are widely used in personal computers, word processors and the like.
As a result of commercialization of a panel that drives each pixel with a thin film transistor or a diode, a TFT (Thin Film)
Transister) -TN (Twisted Ne)
The liquid crystal display (Matic) has characteristics that it can respond faster and has a wider viewing angle than the STN liquid crystal display, and is becoming the mainstream at present. But T
Even in the N system, there is a problem in that the vertical viewing angle is insufficient and the tendency becomes more remarkable when gradation display is performed.

The above problems are caused by the fact that liquid crystal molecules have different refractive indexes in the major axis direction and the minor axis direction (refractive index anisotropy).
It is considered that the liquid crystal molecules are tilted and aligned when a voltage is applied, and the optical characteristics are asymmetrical in the vertical direction of the screen. In order to reduce the angle dependence of the contrast and display color of a TN liquid crystal display due to the refractive index anisotropy of liquid crystal molecules, Japanese Patent Laid-Open No. 4-346312 discloses a negative refractive index anisotropy on a TN cell. A method of stacking cholesteric liquid crystal cells having, a method of using a film in which a polymer liquid crystal exhibiting a cholesteric phase is oriented and then rapidly cooled below a glass transition temperature to fix the orientation, and Japanese Patent Laid-Open No. 6-166534 discloses Japanese Patent Laid-Open No. 6-214116 proposes a method using a discotic liquid crystal that is tilted. Further, JP-A-6-214116 discloses that a low-molecular liquid crystal is dispersed in a polymer matrix,
A method for aligning a liquid crystal by applying an electric field or a magnetic field to perform an alignment operation is also disclosed. However, the method using the cholesteric liquid crystal cell for compensation is not preferable because the entire panel becomes heavy and thick, and at the same time, the manufacturing cost becomes high. Further, in the method using a polymer compound having a cholesteric phase, since the cholesteric phase structure is fixed by quenching below the glass transition point, it is necessary to use one having a glass transition temperature sufficiently higher than room temperature. However, there is a problem that the alignment treatment requires a considerably high temperature, which is not preferable in manufacturing. Furthermore, when a polymer compound is used, since the temperature dependence of the refractive index anisotropy is smaller than that of a liquid crystal cell, when the temperature at which the panel is used changes, the refractive index anisotropy of the compensating film, There occurs a problem that the refractive index anisotropy of the liquid crystal cell is shifted and the effect of improving the viewing angle is reduced. Further, when the discotic liquid crystal is tilt-aligned, when a discotic liquid crystal having a large refractive index anisotropy is directly coated on the substrate, in order to obtain an optical anisotropic film with a large area and uniform optical characteristics, the film There was a problem that the thickness accuracy was a problem and it was not suitable for mass production. Further, in the system described in JP-A-6-214116 in which a low molecular weight liquid crystal is mixed with a polymer matrix, it is necessary to further fix the orientation of the low molecular weight liquid crystal by photocrosslinking.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical anisotropic body which improves the viewing angle characteristics of a liquid crystal display device, a method for producing the same, and a liquid crystal having excellent viewing angle characteristics using the optical anisotropic body. It is to provide a display device.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that the polymer (hereinafter, the polymer is sometimes referred to as a matrix polymer or simply matrix). It was found that the discotic liquid crystal is oriented and the optically anisotropic film is obtained with good yield by mixing the discotic liquid crystal, forming a film, phase-separating the discotic liquid crystal from the matrix, and stretching the film. The present invention has been completed. That is, the present invention is [1] an optically anisotropic film obtained by mixing a polymer and a discotic liquid crystal, wherein the discotic liquid crystal is phase-separated from the polymer, and the domain of the phase-separated discotic liquid crystal is Is in the range of 20 to 600 nm, and the retardation (measurement wavelength 546 nm) of the optically anisotropic film measured from the normal direction is -200 to 200 nm. . The present invention also relates to [2] the method for producing an optically anisotropic film according to [1], which comprises stretching a film obtained by mixing a polymer and a discotic liquid crystal. Furthermore, the present invention provides [3]
The present invention relates to a liquid crystal display device using the optically anisotropic film as described in [1] above.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the optically anisotropic film of the present invention, the discotic liquid crystal is phase-separated from the polymer matrix, and the discotic liquid crystal (hereinafter sometimes abbreviated as liquid crystal) part forms a domain.

The average particle size of the domains of the discotic liquid crystal is 20 to 600 nm, preferably 30 to 400 nm. The average particle size of the domains is obtained by observing an optically anisotropic film with a transmission electron microscope (hereinafter, sometimes referred to as TEM), directly measuring individual particle sizes, and obtaining a number average of the obtained particle sizes. It is determined by finding the value.

In the optically anisotropic film of the present invention, visible light may be scattered at the interface between the domains. In the optically anisotropic film of the present invention, it is preferable that internal scattering due to scattering at these interfaces is small. This is because the scattered light generally changes its polarization state, and thus the optical characteristics may deteriorate in the case of an optically anisotropic film having a large internal scattering.

The orientation of the liquid crystal can be controlled by the shape of the domain. For example, when the domain shape is a spheroid, the liquid crystal is uniaxially aligned, and when the three axes have different lengths,
The orientation of the liquid crystal becomes biaxial orientation. Further, when it is desired to obtain the tilted alignment of the liquid crystal, it is exemplified that the axis of the ellipsoid is tilted from the film normal direction. It is effective to control the shape of these domains by a stretching operation described later.

The retardation value of the optically anisotropic film of the present invention as seen from the film normal direction (measurement wavelength 54
6 nm) is -200 to 200 nm, preferably -100 to 100 nm. The optical axis of the optically anisotropic film of the present invention may be parallel to the film normal direction,
It may be inclined from the normal direction. An example of the tilt angle when tilted from the normal direction is 10 to 50 °,
More preferably, it is 20 to 40 °.

Next, the matrix polymer will be described. In the present invention, as the matrix of the optically anisotropic film, one having a small polymer retardation is preferably used. The retardation by the polymer is measured by the Senarmont method (measured by light having a wavelength of 546 nm) on the polymer film produced under the same conditions as the optically anisotropic film except that the liquid crystal is not contained. The retardation of the polymer is preferably 100 nm or less, more preferably 50 nm or less, and particularly preferably 30 nm or less.

The retardation of the matrix is the product Δn of the birefringence Δn of the matrix polymer and the thickness d of the film.
It is represented by d. If the thickness of the film is reduced to reduce the retardation, handling of the film becomes difficult, which is not preferable, and the film thickness has a lower limit. It is preferable to reduce the birefringence of the matrix in order to reduce the retardation. Generally, the birefringence Δn due to the orientation of the polymer is represented by the following mathematical formula 1 using the intrinsic birefringence Δn ₀ of the polymer and the orientation function f.

## EQU1 ## Δn = Δn ₀ × f As a method of reducing the birefringence of a polymer, a polymer having a small intrinsic birefringence is used, or a polymer having a positive intrinsic birefringence is mixed with a polymer having a negative birefringence. Examples thereof include a method of reducing apparent intrinsic birefringence and a method of reducing the orientation function.

As the polymer having a small intrinsic birefringence, polymethacrylic acid derivatives such as polymethyl methacrylate, poly-n-butyl methacrylate, poly-t-butyl methacrylate and polyglycol methacrylate; polyacrylic acid; polymethyl acrylate; Polyacrylic acid derivatives such as acrylates, polyvinyl acetate, polyvinyl butyrate, polyoxymethylphenylsilylene, norbornene-ethylene copolymer (manufactured by Mitsui Petrochemical Co., Ltd .: APEL, etc.), norbornene-containing resin (Nihon Gosei) Made by Rubber Co., Ltd .: Trade name ART
ON, etc.), amorphous polyolefin (manufactured by Nippon Zeon Co., Ltd .: trade name ZEONEX, etc.), polyester resin for optical use (manufactured by Kanebo Co., Ltd.), acryl-butadiene-styrene copolymer (manufactured by Toray Industries, Ltd .: trade name Toyolac) Transparent grade). Among them, polymethyl methacrylate, poly-n-butyl methacrylate, poly-t-butyl methacrylate, norbornene-ethylene copolymer, polyester resin for optical use, amorphous polyolefin, and acryl-butadiene-styrene copolymer are preferable.

Next, when a polymer having a positive intrinsic birefringence and a polymer having a negative intrinsic birefringence are mixed and used as a matrix of the optically anisotropic film, the film has a positive intrinsic birefringence. Examples of the polymer include polyvinyl chloride, polyvinylidene fluoride, vinylidene fluoride / ethylene trifluoride copolymer, polyethylene oxide, polyphenylene oxide, polycarbonate, and the like. Examples include methyl methacrylate and polystyrene.

A polymer having a positive or negative intrinsic birefringence, and a mixture ratio (weight ratio) of a combination of compatible polymers and an apparent intrinsic birefringence of polyphenylene oxide and polystyrene is 20: 80-3
0:70, 30:70 to 40:60 for polyethylene oxide and polymethyl methacrylate, 5:95 to 15:85 for vinylidene fluoride / ethylene trifluoride copolymer and polymethyl methacrylate, polyvinylidene fluoride and polymethyl methacrylate Then 15:85 to 25: 7
5. 1 for polyvinyl chloride and polymethyl methacrylate
5:85 to 25:75. Among these, a combination of polyphenylene oxide and polystyrene, which are easily soluble in a solvent, and a combination of polyethylene oxide and polymethyl methacrylate are preferable.

As a method for reducing the orientation function, there is a method in which the discotic liquid crystal is stretched while being heated at a temperature not lower than the glass transition temperature and not higher than the melting temperature of the mixed film. Suitable polymers for the method include:
Examples include polycarbonate, polysulfone, polyarylate, polyether sulfone, cellulose diacetate, cellulose triacetate, polystyrene, ethylene vinyl alcohol copolymer, polyethylene terephthalate, polyethylene naphthalate, etc., preferably polycarbonate,
Examples include polysulfone, cellulose acetate, polyethylene terephthalate, and polystyrene.

Additives may be added to these matrix polymers for the purpose of imparting mechanical strength or improving the adhesiveness when they are laminated to an LCD panel. The kind and amount of the additive are not particularly limited as long as they do not impair the object of the present invention.

Examples of the discotic liquid crystal used in the present invention include compounds represented by the following general formulas (1) to (14) and exhibiting a discotic liquid crystal phase.

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[Chemical 6]

[Chemical 7]

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[Chemical 12]

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Embedded image[In the above formulas (1) to (14), A₁, A_Two, A_Three,
A_Four, A_Five, A₆, A₇, A ₈Each independently, charcoal
Hydrocarbon or heterocyclic compound group having a prime number of 1 to 22, the following
A group consisting of the compound of formula (15) or (16)
You. M is Si, Al, Fe, Cu, Zn, Sn, C
atomic group of o, Pb, Mg, Ni or VO or hydrogen
Is shown.

Embedded image (In formula (15), X is -O-, -S-, -COO-, or -OCO-, j is 1 or 0, k is an integer of 0 to 10, and m is 0 or 1 and Ar
₁ is a phenylene group, biphenylene notation, naphthalenyl group,
Anthracenyl group, cyclohexyl group, pyridine-diyl group, pyrimidine-diyl group, p is 0 or 1, R ₁ is halogen, cyano group or 1 to 2 carbon atoms
0 is an alkyl group, an alkoxy group, an alkylthio group, an aromatic compound group, or a heterocyclic compound group, and n is an integer of 0 to 6. )

Embedded image(In formula (16), X is the same as the definition in formula (15).
It is. j'is 1 or 0 and k'is 0 to 10
Is an integer, m'is 0 or 1, and Ar is _Two, A
r_ThreeAre each independently a phenylene group, biphenylene
Note, naphthalenyl group, anthracenyl group, cyclohexyl
Group, pyridine-diyl group, pyrimidine-diyl group
And p ′ and p ″ are each independently 0 or 1. L
Is -CH_Two-O-, -O-CH_Two-, -COO-,-
OCO-, -CH_Two-CH_Two-, -CH = N- or-
N is a divalent group represented by CH-, and q is 0 or 1.
It is. R_TwoIs a halogen, a cyano group, or 1 to 2 carbon atoms
0 alkyl group, alkoxy group, alkylthio group, aromatic
Group compound group or heterocyclic compound group, n'from 0 to
It is an integer of 3. )]

A in the above formulas (1) to (14)₁, A_Two,
A_Three, A_Four, A_Five, A₆, A₇, A ₈To each independently
Methyl as the corresponding hydrocarbon group having 1 to 22 carbon atoms
Group, ethyl group, propyl group, butyl group, pentyl group,
Xyl group, heptyl group, octyl group, decyl group, lauri
And the like. As the heterocyclic compound group, 2-
Examples include thienyl, 2-pyrrolyl, and 2-pyridyl groups.
Is shown.

A in the equation (15) or (16)
Examples of r ₁ , Ar ₂ and Ar ₃ each independently include a phenylene group, biphenylene group, naphthalenyl group, anthracenyl group, cyclhexylene group, pyridine-diyl group, pyrimidine-diyl group and the like. Preferably 1,4
A phenylene group, a 1,4-cyclohexylene group and a pyridine-2,5-diyl group.

Examples of R ₁ and R ₂ are each independently a halogen, a cyano group, an alkyl group having 1 to 20 carbon atoms, an alkoxy group, an alkylthio group, an aromatic compound group or a heterocyclic compound group. Here, as the alkyl group having 1 to 20 carbon atoms, a methyl group, an ethyl group, a propyl group,
Examples thereof include a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group and a lauryl group. It may also contain optically active carbon. A methyl group, an ethyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group and an octyl group are preferable.

The alkoxy group having 1 to 20 carbon atoms includes methoxy group, ethoxy group, propoxy group, butoxy group, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group, decyloxy group, lauryloxy group. And so on. It may also contain optically active carbon. A methoxy group, an ethoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group and an octyloxy group are preferable. As the alkylthio group, a methylthio group, an ethylthio group, a propylthio group, a butylthio group, a pentylthio group, a hexylthio group, a heptylthio group, an octylthio group, a decylthio group,
Examples thereof include a laurylthio group, and a methylthio group, an ethylthio group, a butylthio group, a pentylthio group, a hexylthio group, a heptylthio group and an octylthio group are preferable.

As the aromatic compound group, phenyl group, 4
-C ₁ -C ₁₂ alkoxyphenyl group (C ₁ -C ₁₂ indicates that it has 1 to 12 carbon atoms, and the same shall apply hereinafter), 4-C ₁ -C ₁₂ alkylphenyl group, 1- Examples thereof include a naphthyl group and a 2-naphthyl group. As the heterocyclic compound group, 2-thienyl group, 2-pyrrolyl group, 2
Examples thereof include a-, 3- or 4-pyridyl group.

X is independently -O- or -S.
-, -COO- or -OCO- is exemplified, but from the viewpoint of ease of synthesis, either -O- or -OCO- group is preferable.

In the discotic liquid crystal used in the present invention, formulas (1) to (1) to
A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , in (14),
A ₆ , A ₇ , and A ₈ may be groups having different structures, but A ₁ , A ₂ ,
A ₃ , A ₄ , A ₅ , A ₆ , A ₇ and A ₈ are preferably the same.

The discotic liquid crystal used in the present invention is
Those exhibiting a discotic nematic phase or column arrangement are preferred. The temperature range showing the nematic phase or the smectic phase is preferably −30 ° C. to 200.
C., more preferably −30 to 150 ° C., particularly preferably −30 ° C. to 120 ° C. A liquid crystal that satisfies the above temperature range may be used alone, or two or more kinds of liquid crystals may be mixed and used in order to keep the temperature range within the above range.

Next, the method for producing the optically anisotropic film of the present invention will be described. As a method of mixing the discotic liquid crystal and the matrix polymer, a method of mixing in a solution state is preferable in order to uniformly mix them. Specifically, a method in which a polymer is suspended or dissolved in a solvent and a discotic liquid crystal is suspended or dissolved therein and mixed is mentioned. The polymer used in the present invention preferably has a high solubility in a solvent. Regarding the mixing ratio of the liquid crystal and the matrix polymer, if the ratio of the liquid crystal is too large, the mechanical strength of the film is lowered and the productivity is lowered, and if the ratio is too small, the optical properties are deteriorated. Therefore, the concentration of the liquid crystal [weight of liquid crystal / (sum of weight of liquid crystal and matrix polymer)] is preferably 1 to 50% by weight, and more preferably 2 to 40% by weight.

As a film forming method of a discotic liquid crystal and a matrix polymer, a solvent casting method of dissolving the discotic liquid crystal or matrix polymer in a solvent and casting, an extrusion molding method of kneading in a solid state and extruding from a die or the like to form a film. Examples thereof include a calendering method in which a film is kneaded in a solid state and then a calendar roll is used, and a press molding method in which a film is pressed by a press or the like is used. The thickness of the film after film formation is not particularly limited, but if it is too thin, mechanical strength and degree of polarization are adversely affected, so a certain thickness is required. Since the evaporation rate of is slowed and productivity is deteriorated, it is necessary to make it thin to some extent. The thickness of the film after film formation is 20 to 500 μm
Is preferable, and more preferably 70 to 300 μm.

In the method for producing an optically anisotropic film of the present invention, examples of the film stretching method include a tenter stretching method, a roll-to-roll stretching method and a roll-to-roll compression stretching method. The tenter stretching method and the inter-roll stretching method are preferable from the viewpoint of uniformity of the film surface. In the optically anisotropic film of the present invention, as a stretching method for tilting the optical axis from the normal direction, a method of rolling the film between two rolls having different peripheral speeds and stretching while applying shear, Examples include a method of applying shear along a roll having a small curvature. There are no particular restrictions on the draw ratio or draw speed.

The heating temperature is appropriately selected depending on the softening temperature of the matrix polymer used and the transition temperature of the liquid crystal.

[0031]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The structure of the liquid crystal compound was confirmed by elemental analysis, infrared absorption spectrum and H-NMR spectrum, and the molecular weight was confirmed by gel permeation chromatography (GPC). The retardation of the optically anisotropic film or matrix alone is
Polarization microscope [Nikon Corporation, OPTIPHOTO2-
POL] using the Senarmont method. The wavelength of the measurement light is 546 nm. The retardation when the film was tilted was measured by mounting a tilting jig on the microscope. The liquid crystal display device of the present invention was evaluated by mounting the optically anisotropic film of the present invention on a TN type liquid crystal display device and visually evaluating it.

Example 1 A discotic liquid crystal represented by the following formula (17) was mixed with polymethylmethacrylate (trade name: Sumipex MHF manufactured by Sumitomo Chemical Co., Ltd.) and dissolved in methylene chloride to prepare a methylene chloride solution. A film is obtained by casting this solution on a glass substrate surface-treated with a silane coupling agent. The obtained film is stretched by passing it between two rolls having a heater and a different peripheral speed, to obtain an optically anisotropic film. When the obtained optically anisotropic film was mounted on a TN type liquid crystal display device, the viewing angle was widened as compared with when it was not used.

Embedded image (In the formula, R is —OC ₅ H _11. )

[0033]

According to the present invention, the optically anisotropic film is
Since it can be mass-produced with high accuracy, and the viewing angle characteristics of the liquid crystal display device can be improved by using the optically anisotropic film, it is of great industrial value.

Claims (6)

[Claims] 1. An optically anisotropic film formed by mixing a polymer and a discotic liquid crystal, wherein the discotic liquid crystal is phase-separated from the polymer, and the average particle size of domains of the phase-separated discotic liquid crystal. Is in the range of 20 to 600 nm, and the retardation (measurement wavelength 546 nm) of the optically anisotropic film measured from the normal direction is -200.
An optically anisotropic film having a thickness of about 200 nm. 2. The optically anisotropic film according to claim 1, which has a polymer retardation (measurement wavelength 546 nm) of 100 nm or less. 3. The optically anisotropic film according to claim 2, wherein the polymer is a polymer in which a polymer having a positive intrinsic birefringence and a polymer having a negative birefringence are compatible with each other. 4. The optical anisotropic film according to claim 1, 2 or 3, wherein an optical axis of the optical anisotropic film is inclined from a normal line direction of the optical anisotropic film. 5. A film obtained by mixing a polymer and a discotic liquid crystal is stretched.
The method for producing an optically anisotropic film according to 2, 3, or 4. 6. A liquid crystal display device using the optically anisotropic film according to any one of claims 1 to 4.