JPH08278406A - Optically anisotropic film, its production and liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide an optically anisotropic film and its production method having a characteristic approximate to a wave length dispersion characteristic and a temp. characteristic of a retardation of a liquid crystal display cell which is combined to use and to provide a liquid crystal display device using the optically anisotropic film and excellent in display characteristic, especially a STN(super twisted nematic) type liquid crystal display or a ECB(electric field controlling birefringence) type liquid crystal display device inexpensively and without a complicated process. CONSTITUTION: In the optically anisotropic film, the value of the retardation of the optically anisotropic body film at 80 deg.C is 60-97% of the value of the retardation at 30 deg.C, and a αvalue defined by general formula α=RF/RD is over 1.06. In the formula, RF is the value of the retardation measured by a hydrogen F ray (wave length 486nm) and RD is the value of the retardation measured by a sodium D ray (wave length 589nm).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical anisotropy used for a super twist nematic (hereinafter sometimes referred to as STN) type or electric field control birefringence (hereinafter sometimes referred to as ECB) type liquid crystal display device. The present invention relates to a body film, a method for producing the body film, and a liquid crystal display device using the optically anisotropic film.

[0002]

2. Description of the Related Art A retardation film is obtained by uniaxially stretching a transparent thermoplastic polymer film and compensates for coloration of a liquid crystal display element, particularly an STN type liquid crystal display element or an ECB type liquid crystal display element, and has a display quality. It is used as an optical compensator (color compensator) for improving A liquid crystal display device using a retardation film has advantages such as light weight, thinness, and low cost. 2. Description of the Related Art Recently, so-called car navigation systems in which a liquid crystal display device is mounted on an automobile or the like to display image information such as a map have been widely used. Therefore, high-speed display is required under high temperature conditions. A relatively inexpensive ST for this system
There has been a demand for using an N-type liquid crystal display device, and a liquid crystal cell having an improved response speed has been developed. In this case, ST
The liquid crystal material used in the N cell has a large wavelength dispersion characteristic of birefringence, and since the wavelength dispersion characteristic is different from the retardation film made of polycarbonate which is mainly used at present, it is not possible to sufficiently compensate the coloring. There is a problem that the display quality is deteriorated and the retardation (retardation) of the liquid crystal cell and the retardation film is different at a high temperature, and the display quality at a high temperature is deteriorated.

That is, it has wavelength dispersion characteristics that match the wavelength dispersion characteristics of the birefringence of the liquid crystal material used in the STN type liquid crystal display device of high speed response, and also matches the temperature change of the retardation of the liquid crystal cell. There is a demand for a retardation film having a variable retardation. The effect of temperature is explained as follows. As the temperature rises, the retardation decreases with the relaxation of the alignment of liquid crystal molecules and polymers, but the relaxation of the orientation of the low-molecular liquid crystals that are generally used in liquid crystal cells is better than that of the polymers used in retardation films. Since it is larger than the orientation relaxation and the change in retardation is large, the retardation of both that had been optimized at room temperature deviates from the optimum condition at high temperature, resulting in incomplete color compensation of the liquid crystal cell and coloring. Occurs and the display characteristics deteriorate.

As a method for improving the wavelength dispersion of the retardation film, Japanese Patent Laid-Open No. 5-107413 discloses a retardation film using polysulfone having a high wavelength dispersion. Similarly, JP-A-6-174923 discloses the use of polyarylate having high wavelength dispersion. However, in both cases, polysulfone or polyarylate having high wavelength dispersion has a high glass transition temperature in order to fix the orientation by stretching, and thus the retardation hardly changes in the operating temperature range. Therefore, it was difficult to change the phase difference by following the temperature change of the retardation of the liquid crystal cell. Further, since the wavelength dispersion characteristic of retardation differs depending on the liquid crystal material used for the liquid crystal cell, it may be necessary to control the wavelength dispersion of the retardation film.
JP-A-5-27119 and JP-A-6-13022
Japanese Unexamined Patent Publication No. 27 discloses that chromatic dispersion is controlled by a combination of optical anisotropic bodies having different chromatic dispersion values. However, in either case, there is no description about the compensation function in the high temperature region due to the temperature change of retardation.

Next, in JP-A-4-500284, a side chain type liquid crystal polymer having a linear or cyclic main chain is used to obtain the same temperature dependence and temperature dependence as those of liquid crystal molecules used in a liquid crystal cell. A retardation film having wavelength dependence is exemplified. It is disclosed that an aligned liquid crystal polymer film can be obtained by forming a liquid crystal polymer on the alignment film or applying an external field such as an electric field or a magnetic field to the liquid crystal polymer film. In order to fix the orientation of the liquid crystal polymer, it is necessary to cool it below the glass transition temperature after orientation, and it is necessary to use a material having a glass transition temperature higher than the operating temperature. It cannot be said that the amount of the foundation that follows the temperature change is sufficient. Further, when heated above the glass transition temperature, there is a problem that the orientation is disturbed and the retardation is changed. Further, in JP-A-5-257013, liquid crystal molecules are dispersed in a polymer film and stretched together with the polymer film.
A retardation film having the same dependence and wavelength dependence on liquid crystal molecules used in a liquid crystal cell is described. However, there is no description of specifically preferable rate of temperature change, wavelength dispersion ability, and what kind of physical property and structure of liquid crystal should be dispersed to what extent.

Further, in Example 6 of Japanese Patent Publication No. 7-13683, there is shown an example in which a liquid crystal compound is blended with polyvinyl chloride to enhance wavelength dispersion. A substance having a low point cannot be used due to deformation and deterioration of optical properties within the temperature range of use. Further, there is no description about the compensation function in the high temperature region due to the temperature change of retardation. In addition, JP-A-7-130
No. 23, there is disclosed a method of adjusting wavelength dispersion by adding a plasticizer to polycarbonate or polyarylate, but there is no description about a compensating function in a high temperature region due to temperature change of retardation. in this way,
An optical anisotropic body whose retardation changes according to the temperature change of the retardation of the liquid crystal cell (hereinafter also referred to as a temperature-compensated optical anisotropic body), and a wavelength dispersion of the retardation of the liquid crystal cell Shows chromatic dispersion close to
Moreover, there is no known specific description of those having excellent optical characteristics.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optically anisotropic film having characteristics similar to wavelength dispersion characteristics and temperature characteristics of retardation of a liquid crystal display cell used in combination, and the optical anisotropic body. A method for producing a film and a liquid crystal display device excellent in display characteristics at high temperature using the optically anisotropic film, particularly an STN type liquid crystal display device or an ECB type liquid crystal display device, which is inexpensive and does not require complicated steps. To provide.

[0008]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have used an optically anisotropic film obtained by mixing a polymer and a liquid crystal material for an optical compensation layer. As a result, the inventors have found that a liquid crystal display device can be obtained which has less deterioration in display characteristics even when used at high temperature and has a faster response speed than in the case of room temperature, and thus completed the present invention.

That is, the present invention comprises the following inventions. [1] The retardation value at 80 ° C. of the optically anisotropic film is 6 of the retardation value at 30 ° C.
An optically anisotropic film having a value of 0 to 97% and an α value defined by the following general formula (1) exceeding 1.06.

## EQU3 ## α = R _F / R _D (1) [where, R _F is the value of the retardation measured with hydrogen F line (wavelength 486 nm), and R _D is sodium D line (wavelength 589 nm) ) Is the value of the retardation measured in (). ]

[2] The optically anisotropic film is transparent or
A liquid crystal compound is mixed with a semitransparent polymer.
The ratio of the compound is 2 with respect to the weight sum of the liquid crystal compound and the polymer.
Optics according to [1], characterized in that
Anisotropic film. [3] A transparent or semitransparent polymer represented by the following general formula (2)
Abbe number (ν _D) Is less than 31
The optically anisotropic film according to claim 2, which is a characteristic.

Ν _D = (n _D −1) / (n _F −n _C ) [where n _C , n _D , and n _F are the C line (wavelength 656 nm) and D line (of the Fraunhofer line, respectively) Wavelength 589n
m) Refractive index for F line (wavelength 486 nm). [4] α defined by the general formula (1) described in [1] above
The value of is, when the liquid crystal compound is uniaxially aligned alone,
3. The optically anisotropic film according to claim 2, which has a value of more than 1.06.

[5] An optical anisotropic body as described in [2], [3] or [4], characterized in that the polymer and the liquid crystal compound are mixed and formed into a film, and then the film is uniaxially stretched while being heated. Film manufacturing method. [6] An optically anisotropic film formed by uniaxially stretching a polymer having an Abbe number (ν _D ) of less than 31, and the retardation value at 80 ° C. is 60 to 97% of the retardation value at 30 ° C. A composite optical anisotropic film formed by laminating an optical anisotropic film. [7] A polymer film having an Abbe number (ν _D ) of less than 31, and a film obtained by mixing a polymer and a liquid crystal compound are laminated, and then the laminated film is uniaxially stretched [6 ] The manufacturing method of the composite optical anisotropic film of description. [8] A liquid crystal display device using the optically anisotropic film according to [1], [2], [3], [4] or [6].

Next, the present invention will be described in detail. The retardation value at 80 ° C. of the optically anisotropic film of the present invention is 60 to 97 of the retardation value at 30 ° C.
%, Preferably 70 to 95%, more preferably 75 to 93%. When the rate of temperature change is less than 60%, the mechanical strength of the film becomes small, and when it exceeds 97%, the temperature dependence of the retardation of the liquid crystal display cell cannot be sufficiently compensated, which is not preferable. In addition, the term “compensation” as used herein means an optical anisotropic film for adjusting the display hue in a liquid crystal display device of a type that performs color expression by the phase difference, in addition to canceling the phase difference that the liquid crystal cell itself has. Including using.

It is essential that the optically anisotropic film of the present invention exhibits the above temperature dependence of retardation and, at the same time, exhibits a high retardation and wavelength dispersion. For this purpose, when the α value defined in the general formula (1) is used as an index of chromatic dispersion, an index showing chromatic dispersion exceeding 1.06 is used.

In order to obtain an optically anisotropic film having a high wavelength dispersion, it can be realized by using a liquid crystal compound having a high wavelength dispersion of refractive index or a polymer having a high wavelength dispersion. As a liquid crystal compound having a high wavelength dispersion, the retardation shown when the liquid crystal compound is uniaxially aligned has an α value of 1 in the general formula (1).
The liquid crystal material or polymer having an Abbe number of more than 06 has an Abbe number (ν _D , which may hereinafter be simply referred to as Abbe number) of 3.
A material smaller than 1 is exemplified.

For the optically anisotropic film of the present invention, it is possible to use a material having a birefringence property, in which the birefringence is reversibly decreased / increased as the temperature rises / falls. As such a material, a polymer having a low glass transition temperature or a softening temperature is cross-linked, a polymer having a high glass transition temperature or a softening temperature mixed with a low molecular compound, or a polymer having a high glass transition temperature or a softening temperature. A mixture of a liquid crystal compound is exemplified. Among these, a mixture of a polymer having a high glass transition temperature or a high softening temperature with a liquid crystal compound is preferable because it exhibits excellent properties.

The temperature change rate of the retardation of the optically anisotropic film of the present invention can be selected so as to be optimum according to the temperature change rate of the liquid crystal display cell to be compensated. That is, when the temperature change rate of the liquid crystal display cell is large, the temperature change rate of the optical anisotropic film is also increased accordingly, and when the temperature change rate of the liquid crystal display cell is small, the optical anisotropic film The temperature change rate may be reduced accordingly. In order to adjust the rate of temperature change of retardation of the optically anisotropic film, a liquid crystal having a different isotropic phase transition temperature is used when a liquid crystal compound is mixed with a polymer (hereinafter, sometimes referred to as matrix or matrix polymer). Examples of the method include mixing compounds, mixing liquid crystal compounds having different rates of temperature change, changing the mixing ratio of the matrix polymer and the liquid crystal compound, or using matrix polymers having different intrinsic birefringence.

As another aspect of the optically anisotropic film of the present invention, the optically anisotropic film formed by uniaxially stretching a polymer having a high wavelength dispersion and the retardation value at 80 ° C. are 3
There is also a composite type structure in which optically anisotropic films having a retardation value at 0 ° C. of 60 to 97% are laminated.
The polymer having high wavelength dispersion is not particularly limited as long as the Abbe number is smaller than 31.

In the present invention, the ratio of the polymer and the liquid crystal compound in the film obtained by mixing the polymer with the liquid crystal compound is 2 to 50% by weight based on the total weight of the liquid crystal compound and the polymer. Yes, 5 to 30% by weight is more preferable, and 5 to 20% by weight is further preferable. The ratio is 2
If it is less than 50% by weight, the retardation due to the liquid crystal compound is small, and if it exceeds 50% by weight, the strength of the obtained film becomes small, which is not preferable.

The retardation value of the optically anisotropic film of the present invention when viewed from the front at room temperature varies depending on the liquid crystal cell, the display system and the number of sheets used, but is 50 to 2
000 nm is preferably used, and 100 to 180
It is more preferably 0 nm.

Examples of the type of liquid crystal compound used in the present invention include low molecular weight liquid crystals, liquid crystal oligomers and high molecular weight liquid crystals. From the viewpoint of compatibility with matrix polymers, low molecular weight liquid crystals or liquid crystal oligomers are preferably used.

The liquid crystal compound used in the present invention preferably exhibits a nematic phase or a smectic phase. The temperature range showing the nematic or smectic phase is
Preferably -30 ° C to 200 ° C, more preferably -3.
The temperature is 0 to 150 ° C, particularly preferably -30 ° C to 120 ° C. A liquid crystal compound satisfying the above temperature range may be used alone, or two or more kinds of liquid crystal compounds may be mixed and used in order to keep the temperature range within the above range.

Examples of the low molecular weight liquid crystal include those represented by the following general formula (1).

Embedded image Wherein, R ₁ is an alkyl group or an alkoxy group having 1 to 6 carbon atoms. Ar ₁ , Ar ₂ and Ar ₃ are each independently 1,4-phenylene group, 1,4-cyclohexylene group, pyridine-2,5-diyl group, pyrimidine-2,5.
A diyl group or a derivative of these groups. Sp ₁ ,
Sp ₂ is independently -COO-, -OCO-, -N.
CH -, - CHN -, - CH 2 -CH 2 -, - CH 2 -
_{O -, - O-CH 2} -, - N = N -, - C≡C-, single bond (. Ar ₁ and Ar ₂ or Ar ₂ and Ar _3, corresponds to the direct binding), or the following It is a group represented by the general formula (2). ]

Embedded image [In the formula, k ₁ is 0 or an integer of ₁ (corresponding to direct bonding of Ar ₂ and B ₁ when k ₁ is 0). B
₁ is a hydrogen atom, a cyano group, a halogen, an alkyl group or an alkoxy group having 1 to 6 carbon atoms, an acrylate group or a methacrylate group. ]

Examples of the liquid crystal oligomer include a side chain type liquid crystal oligomer and a main chain type liquid crystal oligomer, and examples of the high molecular weight liquid crystal include a side chain type high molecular weight liquid crystal and a main chain type high molecular weight liquid crystal. From the viewpoint of compatibility, a side chain type liquid crystal oligomer or a side chain type polymer liquid crystal is preferable.
Examples of the side chain type liquid crystal oligomer or the side chain type liquid crystal polymer include those having at least one repeating unit represented by the following general formula (3).

[Chemical 3][In the formula, A is represented by the following general formula (4) or (5).
Group. In the general formula (4), -Si-O- is general
It is a main chain of the formula (3), and even if it is cyclic,
Good. In the general formula (5), -C-CH₂− Is a general formula
The main chain of (3), the COO group is Sp₃Bind to. one
When A in the general formula (3) is the general formula (4), R₂Is carbon
Is an alkyl group or phenylene group of the number 1 to 6,
In the formula (3), when A is the general formula (5), R ₂Is the carbon number
1 to 6 alkyl or alkoxy groups. General formula
Ar in (3)_Four, Ar_Five, Ar₆Are each German
1,4-phenylene group, 1,4-cyclohexylene
Group, pyridine-2,5-diyl group, pyrimidine-2,5
A diyl group or a derivative of these groups. Sp₃Is
It is an alkyl group or an alkoxy group having 2 to 8 carbon atoms.
Sp_Four, Sp _FiveAre independently -COO-, -OCO
-, -NCH-, -CHN-, -CH ₂-CH₂-,-
CH₂-O-, -O-CH₂-, -N = N-, -C≡C
-, Single bond (Ar_FourAnd Ar_Five, Or Ar_FiveAnd Ar₆But
It corresponds to the direct connection. ), Or the general formula
It is a group represented by (2). k₂Is an integer of 0 or 1
Yes (k₂When is 0 Ar_FiveAnd B₂Be bound directly
Corresponds to. ). B₂Is a hydrogen atom, cyano group, halogen
An alkyl group or an alkoxy group having 1 to 6 carbon atoms,
It is an acrylate group or a methacrylate group. ]

[0024]

[Chemical 4]

Embedded image

The total number of repeating units represented by the general formula (3) is preferably 4 or more and 2 in the side chain type liquid crystal oligomer.
It is 1 or less, and more preferably 4 or more and 10 or less. Examples of these side chain type liquid crystal oligomers include linear ones and cyclic ones, but cyclic ones are preferable. Next, in the polymer liquid crystal, the total number of repeating units represented by the general formula (3) is preferably 50 or more and 20,000 or less, and more preferably 50 or more and 10,000 or less.
These low molecular weight liquid crystals, side chain type liquid crystal oligomers or side chain type polymer liquid crystals may be used alone or in combination. The side chain type liquid crystal oligomer or the side chain type liquid crystal polymer does not have to have a single side chain group, and may be a copolymer having different side chains.

Light scattering of the optically anisotropic film of the present invention is preferably small. A factor that influences the light scattering is the mismatch of the refractive index between the liquid crystal compound and the matrix. Adjusting the refractive index of the matrix is not preferable because it may change the mechanical characteristics and the characteristics such as solubility in a solvent, so that it is preferable to mainly adjust the refractive index of the liquid crystal. The refractive index of the liquid crystal used in the present invention for ordinary light is preferably 1.4 to 1.6.

Next, the matrix polymer will be described. The matrix polymer has an Abbe number smaller than 31 when mixed with a liquid crystal compound, and is not opaque.
Alternatively, the addition of the liquid crystal compound is not particularly limited as long as it does not cause opacity and appearance / optical defects.

When the liquid crystal compound is uniaxially aligned alone
The α value defined by the general formula (1) shown above exceeds 1.06
If the matrix polymer was mixed with a liquid crystal compound
In this case, the α value defined in general formula (1) exceeds 1.06.
However, it is not opaque, or by adding a liquid crystal compound.
If it does not cause opacity and appearance / optical defects,
Not determined. In this case, the performance of the added liquid crystal compound
From the perspective of effective use, matrix poly
For polymers, it is preferable to use polymers with low birefringence.
Yes. Birefringence Δn due to polymer orientation is generally
Intrinsic birefringence Δn ₀And the orientation function f,
Represented as

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 intrinsic birefringence. A method of reducing the apparent intrinsic birefringence and a method of reducing the orientation function are exemplified.

As the polymer having a small intrinsic birefringence, polymethacrylic acid derivatives such as polymethylmethacrylate, poly-n-butylmethacrylate, poly-t-butylmethacrylate and polyglycolmethacrylate, polyacrylic acid, polymethylacrylate and polyethyl. Examples thereof include polyacrylic acid derivatives such as acrylate, polyvinyl acetate, polyvinyl butyrate, polyoxymethylphenylsilylene, and the like. Among these, polymethyl methacrylate, poly-n-butyl methacrylate and poly-t-butyl methacrylate 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 mixture has a positive intrinsic birefringence. Examples of the polymer include polyvinyl chloride, polyvinylidene fluoride, vinylidene fluoride / trifluoroethylene copolymer, polyethylene oxide, polyphenylene oxide, and polycarbonate.Polymers having negative intrinsic birefringence include poly Examples include methyl methacrylate and polystyrene.

As a polymer having positive or negative intrinsic birefringence, a mixing ratio (weight ratio) of a combination of compatible polymers and a reduction in apparent intrinsic birefringence is 20: polyphenylene oxide and polystyrene. 80-3
0:70, 30: 70-40: 60 for polyethylene oxide and polymethylmethacrylate, 5: 95-15: 85 for vinylidene fluoride / trifluoroethylene copolymer and polymethylmethacrylate, polyvinylidene fluoride and polymethylmethacrylate. Then 15:85 to 25: 7
5, 1 for polyvinyl chloride and polymethylmethacrylate
Examples are 5:85 to 25:75. Of these, combinations of polyphenylene oxide and polystyrene, which are easily soluble in a solvent, and combinations of polyethylene oxide and polymethylmethacrylate are preferred.

As a method for reducing the orientation function, there is a method in which a polymer mixed with a liquid crystal compound is stretched while being heated at a glass transition temperature or a softening temperature or higher. Examples of the polymer suitable for the method include polycarbonate, polysulfone, polyarylate, polyether sulfone, cellulose diacetate, cellulose triacetate, polystyrene, ethylene vinyl alcohol copolymer, polyethylene terephthalate, polyethylene naphthalate, and the like. Is polycarbonate, polysulfone, cellulose acetate, polyethylene terephthalate,
An example is polystyrene.

When the α value defined by the general formula (1) when the liquid crystal compound is uniaxially aligned alone is less than 1.06, the α value of the entire optically anisotropic film is increased, It is necessary to use a polymer having a high α value and an intrinsic birefringence as a matrix polymer, or to combine it with an optically anisotropic film having a high α value. Abbe number is 31
Examples of smaller higher polymers include polysulfone,
Examples are polyarylate, polyethylene sulfide or their derivatives.

It is preferable that the polymer mixed with the liquid crystal compound does not cause changes in optical properties with time or changes in shape under the maximum use temperature condition in the use form. Therefore, the glass transition temperature or the softening temperature of the polymer mixed with the liquid crystal compound has a preferable lower limit value. Further, in order to obtain the optically anisotropic film of the present invention, when the step of stretching the film at a glass transition temperature or a softening temperature or higher is included, the glass transition temperature or the softening temperature of the polymer mixed with the liquid crystal compound is high. If it is too much, it is not industrially preferable, so that there is a preferable upper limit. From the above, the glass transition temperature or softening temperature required for the polymer mixed with the liquid crystal compound is preferably 70 ° C to 250 ° C,
0 ° C to 180 ° C is more preferable.

Here, a plasticizer may be added in order to lower the glass transition temperature or the softening temperature of the polymer mixed with the liquid crystal compound or to increase the impact resistance. The type and amount of the plasticizer are not particularly limited as long as they do not impair the object of the present invention. Further, in order to lower the apparent glass transition temperature or softening temperature, the stretching may be performed in a state where the amount of residual solvent is large or in a state where the solvent is swollen. The type and content of the solvent are whitening during stretching,
There is no particular limitation as long as appearance and optical defects such as foaming and stretching unevenness do not occur.

Further, additives such as a rubber component may be used for the purpose of imparting mechanical strength to the matrix polymer. The kind and amount of additives such as rubber component are not particularly limited as long as they do not impair the object of the present invention.

Next, a method for producing the optically anisotropic film of the present invention will be described. The optically anisotropic film is produced by uniaxially stretching a polymer film prepared by mixing a liquid crystal compound. Any known film forming method may be used in the film forming step. For example, a solvent casting method of dissolving a liquid crystal and a matrix polymer in a solvent and casting, an extrusion molding method of kneading in a solid state to form an extruded film from a die, a calendar method of kneading in a solid state and then forming a film with a calendar roll, press, etc. An example is a press molding method for forming a film with. Among them, the solvent casting method or the extrusion molding method in which the liquid crystal compound and the polymer are mixed in a solution or a molten state is preferable from the viewpoint of uniform mixing of the liquid crystal compound and the polymer. Among these, the solvent casting method is more preferable because it is excellent in film thickness accuracy. The thickness of the film after film formation is not particularly limited, but is preferably 20 to 300 μm, and more preferably 70 to 300 from the viewpoint of handling and cost of the film.
It is 200 μm.

The method for uniaxially stretching the film is as follows.
Any known method may be used. Examples thereof include a tenter stretching method, a roll-to-roll stretching method, a roll-to-roll compression stretching method, and the like. From the viewpoint of the uniformity of retardation in the film plane and the like, a method of uniaxially stretching by a roll stretching method or a tenter stretching method is preferable. Moreover, you may perform the process which widens the viewing angle by raising the refractive index of the thickness direction of an optically anisotropic film by a well-known method.

As a method for producing the composite optically anisotropic film according to one aspect of the present invention, a laminated film obtained by laminating a polymer film having an Abbe number smaller than 31 and a mixed film of the polymer and liquid crystal compound is used. Uniaxially stretching,
Alternatively, a method in which a polymer film having an Abbe number smaller than 31 and a mixed film of a polymer and a liquid crystal compound are individually stretched to form an optically anisotropic film, and then the films are bonded to each other are exemplified. The above-mentioned film can be used as the film obtained by mixing the polymer and the liquid crystal compound, and in this case, the film having an α value of 1.06 or less can also be used. When a laminated film of a polymer stretched film having an Abbe number smaller than 31 and a polymer-liquid crystal compound mixed film is simultaneously stretched, a polymer stretched film having an Abbe number smaller than 31 and a polymer-liquid crystal compound The mixed film of 1 may be laminated or may not be laminated. When laminating, an adhesive can be used. The above-mentioned uniaxial stretching method can be used for stretching the laminated film.

The film of the present invention may be provided with an ordinary transparent hard coat layer or gas barrier layer on one side or both sides for the purpose of protecting the surface and ensuring adhesiveness of the adhesive.

The liquid crystal display device of the present invention is a liquid crystal display device having a liquid crystal display cell, at least one optical anisotropic film of the present invention, and at least one polarizing film.
Particularly, in the case of the STN type liquid crystal display device, the liquid crystal display cell has a twist angle of 18 between the substrates having electrodes.
An example is a cell made of a low-molecular liquid crystal having a super-twisted nematic orientation of 0 to 360 °. In the liquid crystal display device of the present invention, there is no particular limitation on the place or number of the optically anisotropic film, and it may be anywhere between the polarizing film and the liquid crystal display cell. Further, the absorption axis of the polarizing film, the rubbing direction of the liquid crystal display cell, and the angle formed by the stretching axis of the optically anisotropic film are determined so that the contrast, the viewing angle characteristics, and the display color tone are optimized.

[0042]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. The retardation of the obtained optically anisotropic film was measured by a Senarmont method while keeping the optically anisotropic film at 30 ° C. or 80 ° C. using a hot stage with a polarizing microscope [TFM-120ATF manufactured by Oak Manufacturing Co., Ltd.]. Was measured using. R _F and R _D values are 400 nm, 480 nm, 550
The retardation values at nm, 600 nm, and 800 nm were measured and extrapolated from these values. The temperature dependence of the retardation was determined by measuring the retardation while heating the obtained optically anisotropic film on a hot stage.

Example 1 Polycarbonate [manufactured by Teijin Ltd., trade name: Panlite C1400]: cyclic siloxane liquid crystal oligomer (indicating a nematic phase, having a nematic / isotropic phase transition temperature of 130)
℃, polystyrene equivalent number average molecular weight 1600, α value in horizontal orientation = 1.08) were mixed in a weight ratio of 85:15 and dissolved in methylene chloride so that the total amount was 20% by weight. did. This solution was cast on glass from an applicator with a 0.5 mm gap and air dried.
This film was stretched 2.0 times at 150 ° C. at a rate of 50% / min using a tensile tester (Toyo Seiki Co., Ltd., Strograph-T). At this time, R _{F at} 30 ° C. =
400 nm, α value = 1.07, R _F = 3 at 80 ° C.
A film having a thickness of 68 nm and an α value of 1.07 was obtained. (80 ° C
In was R _F) = 0.92 in R _F) / (30 ℃. When the obtained optically anisotropic film was mounted on an STN type liquid crystal display device and the display characteristics from room temperature to 80 ° C. were visually confirmed, good black and white display was exhibited even when the temperature was increased from room temperature.

Example 2 Polymethylmethacrylate [Sumitomo Chemical Co., Ltd., trade name MHF]: Cyclic siloxane liquid crystal oligomer (indicating a nematic phase, nematic / isotropic phase transition temperature is 130)
℃, polystyrene equivalent number average molecular weight 1600, α value in horizontal orientation = 1.08) were mixed in a weight ratio of 85:15 and dissolved in methylene chloride so that the total amount was 20% by weight. did. This solution was cast on glass from an applicator with a 0.5 mm gap and air dried.
This film was stretched at 100 ° C. at a rate of 33% / min using a tensile tester (Toyo Seiki Co., Ltd., Strograph-T) .2.
It was stretched to 0 times. At this time, R _F = 405 at 30 ° C.
nm, α value = 1.08, R _F = 372n at 80 ° C.
A film having m and α value of 1.08 was obtained. It was = 0.92 (R _F at 30 ℃) / (R _F at 80 ° C.). When the obtained optically anisotropic film was mounted on an STN type liquid crystal display device and the display characteristics from room temperature to 80 ° C. were visually confirmed, good black and white display was exhibited even when the temperature was increased from room temperature.

Example 3 Polycarbonate [manufactured by Teijin Ltd., trade name Panlite C]
1400]: cyclic siloxane-based liquid crystal oligomer (showing a nematic phase, a nematic / isotropic phase transition temperature is 130 ° C.
And a polystyrene-converted number average molecular weight of 1600 and an α value in horizontal orientation = 1.08) were mixed in a weight ratio of 85:15 and dissolved in methylene chloride so that the total amount was 20% by weight. . This solution was cast on glass from an applicator with a 0.5 mm gap and air dried. Using a tensile tester (manufactured by Toyo Seiki Co., Ltd., Strograph-T), this film was tested at 100 ° C. at a rate of 33% / min to 1.4.
It was stretched twice. R _F = 150 nm, α value = 1.
11 Polysulfone and stretching axis are attached in parallel, and 30 ℃
To obtain a multilayer optically anisotropic film having R _F = 400 nm, α value = 1.07, R _F = 370 nm at 80 ° C., and α value = 1.07. / (3 (R _F at 80 ° C.)
R _F ) = 0.94 at 0 ° C. When the obtained optically anisotropic film was mounted on an STN type liquid crystal display device and the display characteristics from room temperature to 80 ° C. were visually confirmed, good black and white display was exhibited even when the temperature was increased from room temperature.

Comparative Example 1 A 20 wt% methylene chloride solution of polycarbonate [manufactured by Teijin Ltd., trade name: Panlite C1400] was added to 0.5
It was cast on glass from an applicator with a mm gap and air dried. This film was stretched 2.0 times at 170 ° C. at a rate of 33% / min using a tensile tester (Toyo Seiki Co., Ltd., Strograph-T). At this time, R _{F at} 30 ° C. = 394 nm, α value = 1.06, R at 80 ° C.
A film having an _F value of 394 nm and an α value of 1.06 was obtained.
(R _{F at} 80 ° C.) / (R _{F at} 30 ° C.) =
It was 1.000. The obtained optically anisotropic film is S
When mounted on a TN type liquid crystal display device and visually confirming the display characteristics from room temperature to 80 ° C., a good black and white display was shown at room temperature, but when the temperature was raised from room temperature to 80 ° C., the display characteristics deteriorated.

Comparative Example 2 A polysulfone film (manufactured by Sumitomo Bakelite, trade name Sumilite FS-1200) was shredded and dissolved in methylene chloride to give a 20% by weight solution. This solution
It was cast on glass from an applicator with a 0.5 mm gap and air dried. 33% at 210 ° C of this film using a tensile tester (Toyo Seiki Co., Ltd. Strograph-T)
The film was stretched 2.0 times at a speed of 1 / min. At this time, a film having R _F = 427 nm at 30 ° C., α value = 1.11 and R _F = 427 nm at 80 ° C. and α value = 1.11. (R _F at 80 ℃) / (R _F at 30 ° C.)
= 1.000. When the obtained optically anisotropic film was mounted on an STN type liquid crystal display device and the display characteristics from room temperature to 80 ° C were visually confirmed, a good black and white display was shown at room temperature, but the temperature was raised from room temperature to 80 ° C. Then, the display characteristics deteriorate.

Comparative Example 3 Polyvinyl chloride [manufactured by Wako Pure Chemical Industries, Ltd .: degree of polymerization: about 110]
0]: Liquid crystals (α value = 1.09 in horizontal alignment) mainly containing the compound of the structural formula shown below are mixed in a weight ratio of 3: 1 and the total is 20% by weight. So that it was dissolved in tetrahydrofuran. This solution was cast on a glass from an applicator with a 0.5 mm gap, air-dried, and then dried in a vacuum dryer at room temperature.

[Chemical 6]This film is tested by a tensile tester (made by Toyo Seiki Co., Ltd.
Graph-T) at 100 ° C. at a rate of 50% / min.2.
It was stretched to 0 times. R at 30 ° C at this time_F= 503
nm and α value = 1.06. Adhere this to the glass plate
After sticking with the agent, the temperature rises to 80 ° C_F= 4
Even if the temperature drops to 00 nm and returns to 30 ° C, R _F= 400 nm
It remained. After this, go up and down between 80 ℃ and 30 ℃
R even if warmed_FThe value of was unchanged. [(80 ° C
R in_F) / (R at 30 ° C_F) = 1.0
0]. This film is not attached to a glass plate
If the temperature is raised to 80 ° C as it is, it shrinks and the retardation is almost
It became zero. After sticking to the above glass plate,
The optically anisotropic film that has been subjected to the temperature rising process is displayed on the STN type liquid crystal surface.
Mounted on a display device to visually check display characteristics from room temperature to 80 ° C
, It showed a good black and white display at room temperature.
However, the display characteristics deteriorate when the temperature is raised from room temperature to 80 ° C.
It

[0049]

The optically anisotropic film of the present invention has characteristics close to the wavelength dispersion characteristics and temperature characteristics of the retardation of the liquid crystal display cell used in combination. By using the optically anisotropic film, excellent display characteristics at high temperature,
And a liquid crystal display device using a liquid crystal material having a high wavelength dispersion and capable of high-speed response, particularly an STN type liquid crystal display device or an ECB
Type liquid crystal display device can be obtained at low cost without requiring complicated steps.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masato Kuwahara 6 Kitahara, Tsukuba-shi, Ibaraki Sumitomo Chemical Co., Ltd.

Claims (8)

[Claims] 1. The retardation value at 80 ° C. of the optically anisotropic film is 60 to 97% of the retardation value at 30 ° C., and the α value defined by the following general formula (1) is 1. An optically anisotropic film characterized by exceeding 0.06. ## EQU1 ## α = R _F / R _D (1) [wherein, R _F is the value of the retardation measured with hydrogen F line (wavelength 486 nm), and R _D is sodium D line (wavelength 589 nm) ) Is the value of the retardation measured in (). ] 2. An optically anisotropic film comprising a transparent or semitransparent polymer mixed with a liquid crystal compound, wherein the ratio of the liquid crystal compound is 2 to 50 relative to the weight sum of the liquid crystal compound and the polymer.
The optical anisotropic film according to claim 1, wherein the optical anisotropic film is in a weight percentage. 3. The optically anisotropic film according to claim 2, wherein the Abbe number (ν _D ) defined by the following general formula (2) of the transparent or semitransparent polymer is smaller than 31. [Mathematical formula-see original document] ν _D = (n _D -1) / (n _F -n _C ) [where n _C , n _D , and n _F are the C line (wavelength 656 nm) and the D line (of the Fraunhofer line, respectively) Wavelength 589n
m) Refractive index for F line (wavelength 486 nm). ] 4. The optically anisotropic film according to claim 2, wherein the value of α defined by the general formula (1) when the liquid crystal compound is uniaxially aligned is more than 1.06. . 5. The method for producing an optically anisotropic film according to claim 2, 3 or 4, wherein the polymer and the liquid crystal compound are mixed to form a film, and the film is uniaxially stretched while being heated. 6. An optically anisotropic film obtained by uniaxially stretching a polymer having an Abbe number (ν _D ) of less than 31, and the retardation value at 80 ° C. is 60 to 97% of the retardation value at 30 ° C. A composite optical anisotropic film formed by laminating the optical anisotropic film as described above. 7. A polymer film having an Abbe's number (ν _D ) of less than 31, and a film obtained by mixing a polymer and a liquid crystal compound are laminated, and then the laminated film is uniaxially stretched. The method for producing the composite optical anisotropic film according to claim 6. 8. A liquid crystal display device using the optically anisotropic film according to claim 1.