JP2005520209A - Optical compensation film, polarizing plate and image display device - Google Patents

Abstract

Polymer having retardation value Re (= (nx−ny) × d) in the range of 0 to 100 nm and retardation value Rth (= {(nx + ny) / 2−nz} × d) in the range of 70 to 500 nm Disclosed is an optical compensation sheet comprising a film and an optically anisotropic layer containing a liquid crystalline compound thereon. The polymer film is made of a polymer having a photoelastic coefficient of 10 × 10 ⁻¹² m ² / N or less and a moisture permeability measured by a JIS Z0208 test method of 1 g / m 2 · 24 hrs or less and 70 to 500 nm. Also disclosed are polarizing plates and devices comprising the optical compensation film.

Description

  The present invention relates to an optical compensation film that is lightweight and excellent in durability, a polarizing plate using the same, and an image display device.

  A liquid crystal display device has excellent features such as thinness, light weight, and low power consumption compared to a CRT, and is widely used in notebook computers, monitors, televisions, PDAs, mobile phones, car navigation systems, video cameras, and the like. However, in the TN mode, which is currently the mainstream of liquid crystal display devices, there is a problem of viewing angle characteristics such as a change in display color and contrast depending on the viewing direction in principle. In order to improve this viewing angle characteristic and realize a liquid crystal display device with high display quality, in Japanese Patent No. 2587398, an optical compensation film in which a discotic liquid crystal is hybrid-aligned is inserted between a polarizing plate and a liquid crystal cell. It is described to do. However, this method has a problem that the liquid crystal display device itself becomes thick due to the optical compensation film and the adhesive. In JP-A-7-191217 and European Patent 0911656A2, an optical compensation film in which an optically anisotropic layer made of a discotic liquid crystal is coated on a transparent support is used as a protective film on one side of a polarizing film. It is described that by using an elliptically polarizing plate, the viewing angle can be improved without increasing the thickness of the liquid crystal display device.

  However, when these optical compensation films are used in a severe environment such as high temperature and high humidity, stress and distortion are generated, and a phase difference is likely to be generated at the location. It has been found that this phase difference causes frame-like light leakage (increased transmittance) in the liquid crystal display device, and the display quality of the liquid crystal display device is lowered. In particular, in the case of a large liquid crystal display device of 17 inches or more, it is difficult to completely eliminate light leakage. Further, it has been proposed that a liquid crystal display device having a simpler structure is obtained by bonding the optical compensation film to a polarizing film to function as a protective film for the polarizing film. However, when the optical compensation film functions as a protective film for the polarizing film, in addition to the above-mentioned problems, the optical compensation film transmits moisture when used at a high temperature and high humidity. There may be a problem of deteriorating optical characteristics. Therefore, the optical compensation film is required to have durability that does not deteriorate optical characteristics even under severe use conditions such as high temperature and high humidity, and does not allow moisture to permeate.

  The present invention has been made in view of the above problems, and when used in an image display device, contributes to an improvement in viewing angle, and even when the image display device is used under severe conditions, light leakage, etc. An object of the present invention is to provide an optical compensation film and a polarizing plate that contribute to reducing the deterioration of display quality due to the above. Another object of the present invention is to provide an optical compensation film and a polarizing plate excellent in durability with little change in optical properties that occur when used under severe conditions. It is another object of the present invention to provide an image display device having a wide viewing angle and excellent durability in which deterioration of display quality due to light leakage that occurs when used under severe conditions is reduced.

  As a result of examining the cause of the change in the optical characteristics of the optical compensation film that causes light leakage, the present inventors have obtained the knowledge that the following two are the causes. One is the severe use conditions (high temperature and high humidity) of the image display device, the polymer film expands or contracts, and the optical properties of the optical compensation film change, and the other is the backlight of the image display device. Is a temperature distribution in the plane of the optical compensation film, and the optical characteristics change due to the thermal distortion.

  As a result of further investigation based on this knowledge, it was found that the change in the optical characteristics of the optical compensation film is related to the photoelastic coefficient and the moisture permeability, and the present invention was completed through further investigation. .

In one aspect, the present invention provides a Re retardation value defined by the following formula (I) in the range of 0 to 100 nm and an Rth retardation value defined by the following formula (II) in the range of 70 to 500 nm. It has a certain polymer film and an optically anisotropic layer containing a liquid crystal compound thereabove, and the polymer film has a photoelastic coefficient of 10 × 10 ⁻¹² m ² / N or less, and according to JIS Z0208 test method. An optical compensation film comprising a polymer having a measured moisture permeability of 1 g / m 2 · 24 hrs or less;
(I) Re = (nx−ny) × d
(II) Rth = {(nx + ny) / 2−nz} × d
In the formula, nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the plane of the polymer film, respectively, and nz is the refractive index in the thickness direction of the polymer film.

  As a preferred embodiment, the optical compensation film in which the polymer has a specific gravity of 1.20 or less; the optical compensation film in which the polymer is a cyclic polyolefin-based polymer; and the cyclic polyolefin-based polymer is selected from tetracyclododecenes A polymer obtained by ring-opening polymerization of a monomer, or a polymer obtained by hydrogenating a ring-opening copolymer of a monomer selected from tetracyclododecenes and a monomer obtained from norbornene The optical compensation film; the optical compensation film containing an aromatic compound having at least two aromatic rings; and the aromatic compound being a compound having at least one 1,3,5-triazine ring. Optical compensation film; the polymer film contains thermally conductive particles The optical compensation film having a thermal conductivity of 1 W / (m · K) or more; a polymer having a heat conductive layer containing heat conductive particles on at least one surface of the polymer film, and the polymer having the heat conductive layer The optical compensation film having a thermal conductivity of 1 W / (m · K) or more; the optical compensation film wherein the liquid crystal compound is selected from a discotic liquid crystal compound; the polymer film is a stretched polymer film The optical compensation film is provided.

  In another aspect, the present invention includes a polarizing film having two surfaces, and two protective films provided on each of the two surfaces, wherein at least one of the two protective films is the polymer film. A polarizing plate is provided.

  In another aspect, the present invention is sandwiched between two polarizing plates, a liquid crystal cell sandwiched between the two polarizing plates, and one of the two polarizing plates and the liquid crystal cell. An image display device comprising the optical compensation film is provided.

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, the present invention will be described in detail. In the present specification, “to” indicates a range including numerical values described before and after the values as a minimum value and a maximum value, respectively.

[Optical compensation film]
The optical compensation film of the present invention has a polymer film and an optically anisotropic layer containing a liquid crystal compound thereon. Hereinafter, various materials that can be used for the optical compensation film of the present invention and methods for producing the same will be described.

The polymer used for the polymer film has a photoelastic coefficient of 10 × 10 ⁻¹² m ² / N or less at a wavelength of 633 mm and a moisture permeability measured by the JIS Z0208 test method of 1 g / m ² · 24 hrs or less. is there. When a polymer having a photoelastic coefficient and moisture permeability within the above ranges is used, a change in optical characteristics caused when used in a high temperature and high humidity environment can be reduced, and an optical compensation film having excellent durability can be obtained. The photoelastic coefficient of the polymer used in the present invention is preferably 7 × 10 ⁻¹² m ² / N. The moisture permeability of the polymer used in the present invention is preferably 0.6 g / m ² · 24 hrs.

  In the present invention, the moisture permeability is measured using a JIS Z0202 test method in which the polymer to be measured is a film having a thickness of 300 μm, and the temperature is 40 ° C. and the relative humidity is 90%.

  The specific gravity of the polymer used in the present invention is preferably 1.2 or less. When a polymer having a specific gravity within the above range is used, the weight can be reduced while maintaining the optical characteristics within a desired range, which contributes to weight reduction of the polarizing plate and the image display device.

  Preferable specific examples of the polymer having the photoelastic coefficient and moisture permeability within the above ranges include acrylic resins (for example, polymethyl methacrylate), cyclic polyolefins (for example, Arton G, Arton F, commercially available from JSR, and Nippon Zeon). ZEONOR 1020R, 1060R, 1420R, 1600R, ZEONEX 480, 480R, 280R, 490R, E48R, E28R, RS820) and the like. Of these, cyclic polyolefins are preferred. Among cyclic polyolefins, particularly preferred are polymers comprising as a constituent a ring-opening polymer of tetracyclododecenes or a polymer obtained by hydrogenating a ring-opening copolymer of tetracyclododecenes and norbornenes. . That is, tetracyclododecene (also known as dimethano-1,4,5,8-octahydro-1,2,3, which is described in detail in JP-B-2-9619 and JP-A-9-263627. 4,4a, 5,8,8a-naphthalene) ring-opening polymers or tetracyclododecenes and norbornene (also known as bicyclo- [2 · 2 · 1] -heptene-2) s The polymer obtained by hydrogenation is particularly preferable because it has extremely low hygroscopicity and is excellent in transparency, moldability and water resistance. The ratio of the tetracyclododecene skeleton in this polymer is usually 50 mol% or more, preferably 80 mol% or more, particularly preferably 90 mol% or more from the viewpoint of heat resistance, and the molecular weight of the polymer is the ring opening. It can be controlled by adding olefin or cycloolefin at the time of polymerization, but it is generally 1,000 to 500,000, preferably 10,000 to 100,000.

  The polymer film can be produced using a solution casting method or a melt film forming method. From the viewpoint of the film surface, it is preferable to use the solution casting method, but the melt film forming method using no solvent is excellent in terms of productivity and cost.

  In the solution casting method, a film is produced using a solution (dope) in which a polymer is dissolved in an organic solvent. Drying by the solution casting method is largely divided into drying on the drum (or band) surface and drying during film conveyance. When drying on the drum (or band) surface, it is preferable to dry slowly at a temperature that does not exceed the boiling point of the solvent being used (when the boiling point is exceeded, bubbles are formed). Further, drying during film transport is preferably performed at a glass transition temperature of the polymer ± 30 ° C., and more preferably ± 20 ° C.

  The polymer film, together with the optically anisotropic layer described later, needs to adjust the retardation within a predetermined range in order to perform optical compensation of the image display device. Further, in order to prevent light leakage of the image display device due to heat, stress, or strain and maintain display quality, the thickness, thermal conductivity, thermal expansion coefficient, etc. of the polymer film are set in appropriate ranges.

  Hereafter, the preferable range of the various characteristics of the polymer film used for this invention is demonstrated. In addition, since the characteristics of the polymer film produced by the solution casting method change depending on the residual amount of the solvent used for preparing the polymer solution as described later, the preferable range of the residual amount of the solvent is also described below. To do.

In the present invention, the Re retardation value and the Rth retardation value of the polymer film are defined by the following formulas (I) and (II), respectively.
(I) Re = (nx−ny) × d
(II) Rth = {(nx + ny) / 2−nz} × d

  In the formula, nx and ny are the refractive indexes in the slow axis direction and the fast axis direction, respectively, in the plane of the polymer film, nz is the refractive index in the thickness direction of the polymer film, and d is the thickness of the polymer film. Represent.

  In the present invention, the Re retardation value of the polymer film is adjusted to a range of 0 to 100 nm, and the Rth retardation value is adjusted to a range of 70 to 500 nm.

  When two optical compensation films of the present invention are used in a TN mode liquid crystal display device, the Rth retardation value of the polymer film is preferably 70 to 250 nm, and when one optical compensation film is used, a polymer is used. The Rth retardation value of the film is more preferably 150 to 400 nm.

  When two optical compensation films of the present invention are used in an OCB mode liquid crystal display device, the polymer film preferably has a Re retardation value of 30 to 50 nm and an Rth retardation value of 150 to 200 nm. When one compensation film is used, the polymer film preferably has a Re retardation value of 50 to 100 nm and an Rth retardation value of 300 to 500 nm.

  In the present invention, in order to adjust the Re retardation value and the Rth retardation value of the polymer film, it is preferable to use a retardation control agent described later. The retardation control agent can be dissolved and / or dispersed in the polymer and contained in the film.

  The retardation controlling agent is used for adjusting the retardation of the polymer film to a desired range. As the retardation control agent, an aromatic compound having at least two aromatic rings is preferably used. In the present specification, the term “aromatic ring” is used to mean an aromatic heterocycle in addition to an aromatic hydrocarbon ring. As the aromatic compound, a retardation control agent for a cellulose ester film comprising a discotic compound described in JP-A No. 2001-166144 is preferable. The molecular weight of the retardation control agent is preferably 300 to 800.

  The retardation control agent is preferably used in an amount of 0.01 to 20% by weight, more preferably 0.05 to 15% by weight, and more preferably 0.1 to 10% by weight based on the weight of the polymer. More preferably it is used. Two or more kinds of compounds may be used in combination.

The polymer film used in the present invention preferably has a thermal conductivity of 1 W / (m · K) or more. When the thermal conductivity is in the above range, the temperature distribution generated in the plane of the optical compensation film can be made uniform, and this can significantly reduce the change in optical characteristics and the light leakage of the display device. The higher the value of the thermal conductivity, the better. However, in the method of adding the high thermal conductivity particles described later, it is generally 10 W / (m · K) or less. In the present invention, the thermal conductivity of the polymer film refers to a value measured as follows. That is, a polymer film is sandwiched between a TO-3 type heater case and a copper plate, and 10% of the film thickness is compressed. Next, power is applied to the copper heater case for 5 minutes, and the temperature difference between the copper heater case and the copper plate is measured. The measured temperature difference value can be used in the following equation to calculate the thermal conductivity.
Thermal conductivity {W / (m · K)} = {power (W) × thickness (m)} / {temperature difference (K) × measurement area (m ² )}

  In order to control the thermal conductivity of the polymer film, it is preferable to contain highly thermally conductive particles in the polymer film. Moreover, in order to control thermal conductivity, you may provide the heat conductive layer containing a highly heat conductive particle separately in the one surface of a polymer film. The heat conductive layer may be provided by co-casting a polymer containing highly heat conductive particles with the polymer, or may be provided by applying a coating solution containing the particles on the surface of the polymer film. Examples of the high thermal conductive particles that can be used include aluminum nitride, silicon nitride, boron nitride, magnesium nitride, silicon carbide, aluminum oxide, silicon oxide, zinc oxide, magnesium oxide, carbon, diamond, and metal. In order not to impair the transparency of the film, it is preferable to use transparent particles. The average particle size of the high thermal conductivity particles is preferably in the range of 0.05 to 80 μm, and more preferably in the range of 0.1 to 10 μm. Further, spherical particles may be used, or acicular particles may be used.

  The addition amount of the high thermal conductivity particles to the polymer film is preferably in the range of 5 to 100% by weight based on the weight of the polymer. When the addition amount is less than 5% by weight, the improvement in heat conduction is poor, and when it exceeds 50% by weight, the productivity tends to deteriorate and the polymer film tends to become brittle.

The polymer film used in the present invention preferably has a hygroscopic expansion coefficient of 30 × 10 ⁻⁵ /% RH or less, more preferably 15 × 10 ⁻⁵ /% RH or less, and more preferably 10 × 10 ⁻⁵ /%. More preferably, it is% RH or less. When the hygroscopic expansion coefficient is in the above range, even when used under high humidity, the polymer film can be prevented from being distorted, and the frame-shaped light leakage (increased transmittance) when used under high humidity. Can be prevented. In addition, although the one where a hygroscopic expansion coefficient is smaller is preferable, it is a value of 1.0 * 10 < ^-5 > /% RH or more normally.

The hygroscopic expansion coefficient indicates the amount of change in the sample length when the relative humidity is changed at a constant temperature. Specifically, a sample having a width of 5 mm and a length of 20 mm was cut out from the produced polymer film, and one end was fixed and suspended in an atmosphere of 25 ° C. and 20% RH (R ₀ ). A weight of 0.5 g is hung on the other end and left for 10 minutes to measure the length (L ₀ ). Next, with the temperature kept at 25 ° C., the humidity is set to 80% RH (R ₁ ), and the length (L ₁ ) is measured. The hygroscopic expansion coefficient can be calculated from the measured value according to the following formula. The measurement is performed 10 samples for the same sample, and the average value is adopted.
Hygroscopic expansion coefficient [/% RH] = {(L ₁ −L ₀ ) / L ₀ } / (R ₁ −R ₀ )

  According to the study by the present inventors, it has been found that in order to reduce the dimensional change due to moisture absorption of the polymer film, the free volume in the polymer film may be reduced. In the solution casting method, the amount of the solvent used for preparing the polymer solution (dope) remaining in the film after film formation has a great influence on the size of the free volume. The smaller the amount of residual solvent, the smaller the dimensional change. A general method for reducing the residual solvent is to cast the dope and form a film, and then dry the film at a high temperature and for a long time. descend. The amount of residual solvent is preferably in the range of 0.01 to 1% by weight, more preferably in the range of 0.02 to 0.07% by weight, and in the range of 0.03 to 0.05% by weight. Most preferably. The amount of residual solvent in the polymer film can be measured using a gas chromatograph (GC18A, manufactured by Shimadzu Corporation) after dissolving a certain amount of sample in chloroform.

  The elastic modulus of the polymer film is preferably 3000 MPa or less, and more preferably 2500 MPa or less.

  In order to reduce the distortion of the polymer film, it is effective to enhance the plane orientation of the polymer molecules by stretching the polymer film. It is also effective for adjusting the retardation of the polymer film. In order to enhance the plane orientation of the polymer molecules, biaxial stretching is preferred. Biaxial stretching includes simultaneous biaxial stretching and sequential biaxial stretching, but sequential biaxial stretching is preferred from the viewpoint of continuous production, and after casting the dope, the film is peeled off from the band or drum, After stretching in the width direction (longitudinal method), the film is stretched in the longitudinal direction (width direction). Methods for stretching in the width direction are described in, for example, JP-A-62-115035, JP-A-4-152125, 4-284221, 4-298310, and 11-48271. Yes. Stretching is performed at room temperature or under heating conditions. The heating temperature is preferably not higher than the glass transition temperature of the film.

  When a polymer film is produced by a solution casting method, it can be stretched in a step of drying the film after film formation. This is particularly effective when the solvent remains. In the case of stretching in the longitudinal direction, for example, the film can be continuously stretched by adjusting the speed of the film conveyance roller so that the winding speed is higher than the film peeling speed. In the case of stretching in the width direction, the film can be stretched by conveying the film while holding the film with a tenter and gradually widening the tenter. After the film is dried, it can be stretched using a stretching machine (preferably uniaxial stretching using a long stretching machine). The stretch ratio of the film (the ratio of the increase due to stretching relative to the original length) is preferably 5 to 15%, more preferably 10 to 40%, and most preferably 15 to 35%. .

  The steps from casting to post-drying may be performed in an air atmosphere or an inert gas atmosphere such as nitrogen gas.

  The polymer film used in the present invention can be stored and transported in a wound state after being produced. The winding machine used may be a commonly used winding machine, and can be wound by a winding method such as a constant tension method, a constant torque method, a taper tension method, or a program tension control method with a constant internal stress. .

  The polymer film used in the present invention is preferably subjected to a surface treatment in order to provide an optically anisotropic layer containing a liquid crystalline compound described later. Specific examples include corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment, and ultraviolet irradiation treatment. It is also preferable to provide an undercoat layer as described in JP-A-7-333433.

  From the viewpoint of maintaining the flatness of the film, the temperature during the surface treatment is preferably Tg (glass transition temperature) or less of the polymer, specifically 170 ° C. or less.

  The surface energy of the polymer film used in the present invention is preferably 55 mN / m or more, and more preferably 60 mN / m to 75 mN / m. The surface energy of the solid can be determined by a contact angle method, a wet heat method, and an adsorption method as described in “Basics and Applications of Wetting” (issued by Realize 1989.12.10). The polymer film of the present invention is suitable for measuring the surface energy by the contact angle method. Specifically, in the present invention, it can be calculated from the contact angle of two types of droplets whose surface energy is known. The contact angle of the droplet on the polymer film is the angle between the tangent line drawn on the droplet and the film surface at the intersection of the droplet surface and the film surface. There are two angles between the film surface and such tangents, but the angle containing the droplet is defined as the contact angle.

  The optical compensation film of the present invention is produced by laminating an optically anisotropic layer formed from a liquid crystalline compound on a produced polymer film. The surface-treated polymer film and the optical film provided thereon are prepared. An alignment film is preferably provided between the anisotropic layer. The alignment film functions to align the liquid crystal compound used in a certain direction. Therefore, although an alignment film is necessary for producing the optical compensation film of the present invention, the alignment film may be omitted if the liquid crystalline compound is fixed in the alignment state after alignment. That is, the alignment film is not an essential component of the optical compensation film, and only the optically anisotropic layer on the alignment film with the alignment state fixed is transferred onto the polymer film to produce the optical compensation film. Is also possible.

  The alignment film contributes to controlling the alignment direction of the liquid crystal compound. The alignment film is an organic compound (eg, ω-tricosanoic acid) formed by rubbing treatment of an organic compound (preferably a polymer), oblique deposition of an inorganic compound, formation of a layer having a microgroove, or Langmuir-Blodgett method (LB film). , Dioctadecylmethylammonium chloride, methyl stearylate). Furthermore, an alignment film in which an alignment function is generated by application of an electric field, application of a magnetic field, or light irradiation is also known. In the present invention, the alignment film is preferably formed by a rubbing treatment of a polymer.

  As the alignment film, a polyvinyl alcohol derivative is preferable. Of these, modified polyvinyl alcohol having a hydrophobic group bonded thereto is particularly preferred. The alignment film can be formed from one type of polymer, but can also be formed by rubbing a layer composed of two types of crosslinked polymers. As the at least one polymer, it is preferable to use either a polymer that can be crosslinked by itself or a polymer that is crosslinked by a crosslinking agent. The alignment film is formed by introducing a functional group into a polymer having a functional group or a reaction between polymers by light, heat, pH change, or the like, or by using a cross-linking agent having a high reaction activity. It can be produced by introducing a bond derived from a crosslinking agent and crosslinking between the polymers.

  The alignment film can be cross-linked by applying an alignment film coating solution containing the polymer or a mixture of the polymer and a cross-linking agent onto the polymer film, followed by heating or the like as desired. Since it is only necessary to ensure the durability of the final product (optical compensation film), the crosslinking treatment may be performed at any stage after the alignment film is coated on the polymer film and before the optical compensation film is obtained. In consideration of the orientation of the layer (optically anisotropic layer) made of the liquid crystalline compound formed on the alignment film, it is also preferable to perform sufficient crosslinking after aligning the liquid crystalline compound on the alignment film. Generally, the alignment film is crosslinked by applying an alignment film coating solution on a polymer film and drying by heating. It is preferable that the heating temperature of the coating solution is set to be low so that the alignment film is sufficiently cross-linked at the stage of the heat treatment when forming the optically anisotropic layer described later. As the alignment film, those described in Japanese Patent No. 2587398 are preferable.

  The thickness of the alignment film is preferably 0.1 to 10 μm. Heating and drying can be performed at a heating temperature of 20 to 110 ° C. In order to form sufficient crosslinking, the heating temperature is preferably in the range of 60 to 100 ° C, and preferably in the range of 80 to 100 ° C. The drying time is 1 minute to 36 hours, preferably 5 to 30 minutes. The pH is also preferably set to an optimum value for the cross-linking agent to be used. When glutaraldehyde is used as the cross-linking agent, it is preferably in the range of pH 4.5 to 5.5, particularly pH 5. preferable.

  As the rubbing treatment, a treatment method widely adopted as a liquid crystal alignment treatment process of the LCD can be used. That is, it is a method of aligning the liquid crystalline compound by rubbing the surface of the alignment film in a certain direction using paper, gauze, felt, rubber, nylon, polyester fiber or the like. Generally, it can be carried out by rubbing the alignment film several times using a cloth or the like in which fibers having uniform length and thickness are flocked on average.

  In the present invention, the optically anisotropic layer formed from the liquid crystalline compound is preferably formed on an alignment film provided on the polymer film.

  The liquid crystalline compounds used in the optically anisotropic layer include rod-like liquid crystalline compounds and discotic liquid crystalline compounds, which may be high-molecular liquid crystals or low-molecular liquid crystals. This includes those that are no longer shown. Among these, a discotic liquid crystalline compound is preferable.

  The optically anisotropic layer is produced by applying and aligning a coating liquid containing a liquid crystalline compound and, if necessary, a monomer, a polymerization initiator, a surfactant, and the like on the alignment film. The thickness of the optically anisotropic layer is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, and most preferably 1 to 10 μm.

  In the present invention, the optically anisotropic layer described in Japanese Patent No. 2587398 is preferably applied as the optically anisotropic layer.

  It is preferable to use a discotic liquid crystalline compound for the optically anisotropic layer. The discotic liquid crystalline compound includes a discotic liquid crystal. The optically anisotropic layer is composed of a discotic liquid crystalline compound, a polymerization initiator described later, and optional additives (eg, plasticizer, monomer, surfactant, cellulose ester, 1,3,5-triazine compound, chiral agent). ) Containing a liquid crystal composition (coating liquid) is applied on the alignment film, and the discotic liquid crystalline compound is aligned.

  Examples of discotic liquid crystalline compounds include C.I. Destrade et al., Mol. Cryst. 71, 111 (1981), benzene derivatives, research report of C. Destrade et al., Mol. Cryst. 122, 141 (1985), Physics lett, A, 78, 82 ( 1990), Torxene derivatives described in B. Kohne et al., Angew. Chem. 96, 70 (1984), cyclohexane derivatives described in JMLehn et al., J. Chem. Commun. , P. 1794 (1985), J. Zhang et al., J. Am. Chem. Soc. 116, 2655 (1994), Asacrown and phenylacetylene macrocycles etc. Can be mentioned. In addition, the discotic liquid crystalline compounds generally have a structure in which these are used as a mother nucleus at the center of a molecule, and a linear alkyl group, alkoxy group, substituted benzoyloxy group, etc. are radially substituted as their side chains. Is also included and exhibits liquid crystallinity. However, the molecule itself is not limited to these as long as it has negative uniaxiality and can give a certain orientation.

  In the present invention, the optically anisotropic layer formed from the discotic liquid crystalline compound does not necessarily need to be the final compound. For example, a low molecular weight discotic liquid crystalline compound is formed by heat, light, And the like, which are polymerized or cross-linked by reaction with heat, light, etc., resulting in high molecular weight and loss of liquid crystallinity. In order to fix the discotic liquid crystalline compound by polymerization, it is necessary to bond a polymerizable group as a substituent to the discotic core of the discotic liquid crystalline compound. However, if a polymerizable group is directly connected to the disk-shaped core, the alignment state may be disturbed by polymerization, and in order to prevent this, a spacer (linking group) is introduced between the disk-shaped core and the polymerizable group. Is preferred. Preferred examples of the discotic liquid crystalline compound are described in JP-A-8-50206, and the polymerization of the discotic liquid crystalline compound is described in JP-A-8-27284.

  In the present invention, the angle (inclination angle) between the disc surface of the discotic liquid crystalline compound and the polymer film surface differs in the depth direction of the optically anisotropic layer. That is, the tilt angle changes with the increase in the distance from the bottom surface of the optically anisotropic layer, and the changes include continuous increase, continuous decrease, intermittent increase, intermittent decrease, continuous increase and continuous. Although a change including a decrease and an intermittent change including an increase and a decrease can be given, the intermittent change includes a region where the inclination angle does not change in the middle of the thickness direction. Even if the tilt angle includes a region where the tilt angle does not change, the tilt angle preferably increases or decreases as a whole. Further, it is preferable that the inclination angle increases as a whole, and it is particularly preferable that the inclination angle changes continuously.

  The tilt angle of the disk-shaped unit on the alignment film side can be generally adjusted by selecting a discotic liquid crystalline compound or a material for the alignment film, or by selecting a rubbing treatment method. Further, the inclination angle of the disk-like unit on the surface side (air side) can be adjusted by selecting a discotic liquid crystalline compound or another compound used together with the discotic liquid crystalline compound. Examples of the compound used together with the discotic liquid crystalline compound include a plasticizer, a surfactant, a polymerizable monomer and a polymer. Further, the degree of change in the tilt angle can be adjusted by the same selection as described above.

  The optically anisotropic layer may contain other additives in addition to the discotic liquid crystalline compound. The plasticizer, surfactant, and polymerizable monomer that can be used with the discotic liquid crystalline compound are compatible with the discotic liquid crystalline compound, change the tilt angle of the discotic liquid crystalline compound, or align it. Any compound can be used as long as it does not inhibit Among these, polymerizable monomers (eg, compounds having a vinyl group, a vinyloxy group, an acryloyl group, and a methacryloyl group) are preferable. The amount of the compound added is generally preferably 1 to 50% by weight and more preferably 5 to 30% by weight with respect to the discotic liquid crystalline compound. Moreover, the adhesiveness between an alignment film and an optically anisotropic layer can be improved by mixing and using a monomer with 4 or more reactive functional groups.

  As the polymer used together with the discotic liquid crystalline compound, any polymer can be used as long as it is compatible with the discotic liquid crystalline compound and can change the tilt angle of the discotic liquid crystalline compound. A cellulose ester can be mentioned as an example of a polymer. Preferable examples of the cellulose ester include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose and cellulose acetate butyrate. In general, the amount of the polymer added is preferably 0.1 to 10% by weight, and preferably 0.1 to 8% by weight with respect to the disk-like liquid crystalline compound so as not to disturb the alignment of the disk-like liquid crystalline compound. More preferably, it is 0.1 to 5% by weight.

  In the present invention, the optically anisotropic layer is generally formed by applying a solution obtained by dissolving a discotic liquid crystalline compound and other compounds in a solvent onto an alignment film, drying, and then heating to a discotic nematic phase formation temperature. Then, it is obtained by maintaining the alignment state (discotic nematic phase) and cooling. Alternatively, the optically anisotropic layer may be formed by applying a solution obtained by dissolving a discotic liquid crystalline compound and another compound (for example, a polymerizable monomer, a photopolymerization initiator) in a solvent onto the alignment film, and then drying. It is obtained by heating to a discotic nematic phase formation temperature, followed by polymerization (by irradiation with UV light or the like) and further cooling.

  The discotic nematic liquid crystal phase-solid phase transition temperature of the discotic liquid crystalline compound used in the present invention is preferably 70 to 300 ° C, particularly preferably 70 to 170 ° C.

  In the present invention, it is preferable to maintain and fix the aligned liquid crystal compound. 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, and a photopolymerization reaction is preferred. Examples of the photopolymerization initiator include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatic acyloin. Compound (described in US Pat. No. 2,722,512), polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US Pat. No. 3,549,367) Acridine and phenazine compounds (JP-A-60-105667, U.S. Pat. No. 4,239,850) and oxadiazole compounds (U.S. Pat. No. 4,212,970).

  The amount of the photopolymerization initiator used is preferably 0.01 to 20% by weight, more preferably 0.5 to 5% by weight, based on the solid content of the coating solution.

  Light irradiation for the polymerization of the liquid crystalline compound is preferably performed using ultraviolet rays.

The irradiation energy is preferably from ^{20mJ / cm 2 ~50J / cm 2} , more preferably from 20~5000mJ / cm ^2, even more preferably in the range of 100 to 800 mJ / cm ^2. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.

  As described above, the optical compensation film of the present invention can be produced by providing the optically anisotropic layer on the polymer film. A protective layer may be provided on the optically anisotropic layer. The optical compensation film of the present invention can be used as a member of a polarizing plate or a member of an image display device. In particular, when used in a liquid crystal display device, it contributes to an improvement in viewing angle. Further, even when the image display device is used under severe conditions (external force load, high temperature, high humidity), it contributes to reducing the deterioration of display quality due to light leakage or the like. Moreover, when it uses for a polarizing plate and an image display apparatus, it contributes to the thinning and weight reduction. In particular, the optical compensation film of the present invention is preferably used alone or in the form of a polarizing plate bonded to a polarizing film for an image display device, particularly a transmissive liquid crystal display device.

  Hereinafter, embodiments in which the optical compensation film of the present invention is applied to a polarizing plate and an image display device will be described.

[Polarizer]
One embodiment of the polarizing plate of the present invention is a polarizing plate comprising a polarizing film and two transparent protective films disposed on both sides thereof, and at least one of the transparent protective films is a polarizing film having the optical compensation film of the present invention It is a board. The optical compensation film of the present invention can be used as only one protective film, and the optical compensation film of the present invention can be used as both protective films. In an embodiment in which only one protective film is used, a normal cellulose acetate film can be used for the other protective film.

  In the present invention, any of an iodine polarizing film, a dye polarizing film using a dichroic dye, and a polyene polarizing film can be used as the polarizing film. The iodine-based polarizing film and the dye-based polarizing film can be generally produced using a polyvinyl alcohol film.

  Further, the durability (resistance to heat and humidity) of the protective film is important for the durability of the polarizing plate. That is, depending on the use conditions (under high humidity) of the image display device, the polarization ability may be reduced due to moisture entering the polarizing film. In the present invention, a polymer film made of a polymer having a moisture permeability within a predetermined range is used as the polymer film of the optical compensation film. The polymer film constituting the optical compensation film of the present invention is a polymer obtained by hydrogenating a ring-opening polymer of tetracyclododecenes or a ring-opening copolymer of tetracyclododecenes and norbornenes. If it becomes, moisture permeability is remarkably low, and it is more preferable as a protective film of a polarizing plate.

[Image display device]
One embodiment of the image display device of the present invention includes two polarizing plates, a liquid crystal cell sandwiched between the two polarizing plates, and an optical compensation of the present invention sandwiched between the polarizing plate and the liquid crystal cell. An image display device having at least one film, preferably a liquid crystal display device, more preferably a transmissive liquid crystal display device. The polarizing plate includes a polarizing film and two transparent protective films disposed on both sides thereof. One optical compensation film of the present invention may be disposed between the liquid crystal cell and one polarizing plate, or two optical compensation films may be disposed between the liquid crystal cell and both polarizing plates. The liquid crystal cell carries a liquid crystal between two electrode substrates.

  The optical compensation film of the present invention can be used in combination with various modes of liquid crystal cells, for example, in combination with TN mode or OCB mode liquid crystal cells.

  The present invention will be described more specifically with reference to the following examples. The materials, reagents, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[Example 1]
(Production of polymer film)
A composition consisting of 100 parts by weight of “ZEONOR 1020R” (manufactured by ZEON Corporation) and 200 parts by weight of methylene chloride was put into a mixing tank and stirred while heating to prepare a polymer solution. A composition comprising 16 parts by weight of a retardation control agent represented by the following formula and 100 parts by weight of methylene chloride was charged into another mixing tank, and stirred while heating to prepare a retardation control agent solution.
A dope was prepared by mixing 474 parts by weight of this polymer solution with 63 parts by weight of the retardation controlling agent solution and stirring sufficiently. The addition amount of the retardation control agent was 5.5 parts by weight with respect to 100 parts by weight of the polymer.

  The obtained dope was cast using a band casting machine, a film having a residual solvent amount of 15% by weight was uniaxially stretched at a magnification of 120% under the condition of 150 ° C., and the polymer film (PF− 01) was produced.

  With respect to this polymer film (PF-01), the Re retardation value and the Rth retardation value at a wavelength of 550 nm were measured by an ellipsometer (M-150, manufactured by JASCO Corporation). The results are shown in Table 1.

  Furthermore, the film thickness of the produced polymer film was measured with a digital film thickness meter (K-402B, manufactured by Anritsu Corporation) at 100 points in an area of 1 square meter (1 m × 1 m). The average value was 62.0 μm, and the standard deviation was 1.5 μm.

(Preparation of alignment film)
Next, after the corona treatment was performed on the produced polymer film, from 10 parts by weight of modified polyvinyl alcohol represented by the following structural formula, 371 parts by weight of water, 119 parts by weight of methanol, and 0.5 part by weight of glutaraldehyde (crosslinking agent). The coating solution of the composition is applied with a # 16 wire bar coater (coating amount 28 mL / m ² ), dried for 60 seconds with hot air at 60 ° C., and further for 150 seconds with hot air at 90 ° C. An alignment film was provided on the film.

(Production of optical compensation film)
The polymer film provided with the alignment film was rubbed in the direction of 45 ° with respect to the longitudinal direction. 41.01 g of a discotic liquid crystalline compound represented by the following structural formula, 4.06 g of ethylene oxide modified trimethylolpropane triacrylate (V # 360, manufactured by Osaka Organic Chemical Co., Ltd.), cellulose acetate butyrate (CAB551-0) 0.23 g, manufactured by Eastman Chemical Co., Ltd. 0.23 g, cellulose acetate butyrate (CAB531-1, manufactured by Eastman Chemical Co.) 0.90 g, photopolymerization initiator (Irgacure 907, manufactured by Ciba Geigy Co.) 1.35 g, increased A coating solution prepared by dissolving 0.45 g of a sensitizer (Kayacure DETX, manufactured by Nippon Kayaku Co., Ltd.) in 102 g of methyl ethyl ketone was applied with a # 3 wire bar (application amount: 5 mL / m ² ).

This was affixed to a metal frame and heated in a thermostatic bath at 130 ° C. for 2 minutes to align the discotic liquid crystalline compound. Next, using a 120 W / cm high pressure mercury lamp at 130 ° C., UV irradiation was performed for 1 minute to polymerize the discotic liquid crystalline compound. Then, it stood to cool to room temperature and produced the optical compensation film (KH-01).

[Example 2]
(Production of polymer film)
A composition comprising 150 parts by weight of “ZEONOR 1020R” (manufactured by ZEON Corporation) and 350 parts by weight of methylene chloride was put into a mixing tank and stirred while heating to prepare a polymer solution. 36 parts by weight of the same retardation control agent solution as in Example 1 was mixed with 474 parts by weight of this polymer solution, and the dope was prepared by sufficiently stirring. The addition amount of the retardation control agent was 3.5 parts by weight with respect to 100 parts by weight of the polymer.

  The obtained dope was cast using a band casting machine, and after the film surface temperature on the band reached 40 ° C., it was dried with warm air of 70 ° C. for 1 minute, and the film was peeled off from the band. . Next, this film was dried with a drying air at 140 ° C. for 10 minutes to produce a polymer film (PF-02; thickness: 50 μm) having a residual solvent amount of 0.3 wt%.

  About the produced polymer film (PF-02), it carried out similarly to the polymer film of Example 1, and measured the optical characteristic. The results are shown in Table 1.

(Preparation of polymer film provided with alignment film)
After the produced polymer film was subjected to corona treatment, a polymer film provided with an alignment film was produced in the same manner as in Example 1.

(Production of optical compensation film)
A rubbing treatment was performed in parallel with the longitudinal direction of the polymer film provided with the alignment film, and 41.001 g of the discotic liquid crystalline compound used in Example 1, ethylene oxide-modified trimethylolpropane triacrylate (V # 360, Osaka Organic Chemical ( 4.06 g, photopolymerization initiator (Irgacure 907, Ciba Geigy) 1.35 g, and sensitizer (Kayacure DETX, Nippon Kayaku Co., Ltd.) 0.45 g were dissolved in 102 g of methyl ethyl ketone. The coating solution was applied with a # 3.6 wire bar (amount of application: 6.3 mL / m ² ).

  This was heated in a constant temperature zone of 130 ° C. for 2 minutes to align the discotic liquid crystalline compound. Next, UV irradiation was performed for 1 minute using a 120 W / cm high pressure mercury lamp in an atmosphere of 60 ° C. to polymerize the discotic liquid crystalline compound. Then, it stood to cool to room temperature, the optically anisotropic layer was formed, and the optical compensation film (KH-02) of this invention was produced.

[Example 3]
(Production of polymer film)
A composition consisting of 100 parts by weight of “ZEONOR 1020R” (manufactured by ZEON Corporation), 300 parts by weight of methylene chloride (first solvent), and 30 parts by weight of boron nitride powder was put into a mixing tank, stirred while heating, The ingredients were dissolved and a polymer solution was prepared. 36 parts by weight of the retardation controlling agent solution used in Example 1 was mixed with 474 parts by weight of this polymer solution, and the dope was prepared by sufficiently stirring. The addition amount of the retardation control agent was 3.5 parts by weight with respect to 100 parts by weight of the polymer.

Using the obtained dope, a polymer film (PF-03) of the present invention was produced in the same manner as in Example 2 (thickness: 50 μm).
It was 1.2 W / (m * K) when the heat conductivity of the obtained polymer film (PF-03) was measured. The optical properties were measured in the same manner as in Example 1. The results are shown in Table 1.

(Preparation of alignment film)
After the produced polymer film was subjected to corona treatment, a polymer film provided with an alignment film was produced in the same manner as in Example 1.

(Production of optical compensation film)
An optical compensation film (KH-03) of the present invention was produced in the same manner as in Example 2 except that the polymer film PF-03 was used.

[Comparative Example 1]
(Production of polymer film)
A composition consisting of 100 parts by weight of a polycarbonate resin (Pure Ace: Teijin Chemicals) and 350 parts by weight of methylene chloride was put into a mixing tank and stirred while heating to prepare a polymer solution (dope).

  The obtained dope was cast using a band casting machine, and after the film surface temperature on the band reached 40 ° C., it was dried with warm air of 40 ° C. for 1 minute, and the film was peeled off from the band. . Next, the film was stretched 25% in the direction perpendicular to the transport direction by tenter stretching under the condition of 150 ° C., dried for 10 minutes, and further stretched 25% in the transport direction with a residual solvent amount of 7.0% by weight. Thus, a comparative polymer film (PFH-1; thickness 80 μm) was produced. The optical properties of the produced polymer film (PFH-1) were measured. The results are shown in Table 1.

(Preparation of alignment film)
After the produced polymer film was subjected to corona treatment, a polymer film provided with an alignment film was produced in the same manner as in Example 1.

(Production of optical compensation film)
A comparative optical compensation film (KHH-1) was produced in the same manner as in Example 1 except that the polymer film of Comparative Example 1 was used.

[Example 4]
A polarizing film is prepared by adsorbing iodine to a stretched polyvinyl alcohol film, and a corona treatment is applied to the polymer film side of the optical compensation film (KH-01) prepared in Example 1, and a polyvinyl alcohol adhesive is applied. The lever was attached to one side of the polarizing film. In addition, a commercially available cellulose triacetate film (Fujitac TD80UF, manufactured by Fuji Photo Film Co., Ltd.) is saponified and attached to the opposite side of the polarizing film using a polyvinyl alcohol adhesive, and the polarizing plate (PP −01).

  Except that (KH-02), (KH-03) and (KHH-1) were used as polymer films, the polarizing plates (PP-02), (PP-03) and comparative examples of the present invention were the same. A polarizing plate (PPH-1) was produced.

[Example 5]
A pair of polarizing plates provided in a liquid crystal display device (AQUAS LC-20C1-S, manufactured by Sharp Corporation) using a TN type liquid crystal cell is peeled off, and a polarizing plate (PP-02) prepared in Example 4 is used instead. ) Are attached to the viewer side and the backlight side one by one with an adhesive so that the optical compensation film side becomes the liquid crystal cell side, and the TN type liquid crystal display device (LCD-02) of the present invention was produced. . The transmission axis of the polarizing plate on the observer side and the transmission axis of the polarizing plate on the backlight side are orthogonal to each other, and the rubbing direction of the liquid crystal cell and the rubbing direction of the optically anisotropic layer are arranged in antiparallel.

  A TN type LCD-03 was produced in the same manner except that the polarizing plate (PP-03) produced in Example 4 was used instead of the polarizing plate (PP-02).

About the produced liquid crystal display device LCD-02 and LCD-03, the viewing angle was measured in eight steps from black display (L1) to white display (L8) using a measuring machine (EZ-Contrast 160D, manufactured by ELDIM). . The results are shown in Table 2. The numbers in Table 2 indicate a range in which the contrast ratio is 10 or more and there is no black-side gradation inversion (inversion between L1 and L2).

(Evaluation of frame-shaped light leakage)
Under the environmental conditions of temperature 25 ° C. and relative humidity 60%, a backlight was placed on the manufactured liquid crystal panels LCD-02 and 03 and lighted continuously for 5 hours. The leak was evaluated. As a result, no frame-like light leakage occurred.

[Example 6]
A polyimide film was provided as an alignment film on a glass substrate with an ITO electrode, and a rubbing treatment was performed. The two obtained glasses are faced so that the rubbing directions are parallel to each other, a cell gap is set to 6 μm, a liquid crystal compound having a Δn of 0.1396 (ZLI1132, manufactured by Merck) is injected, and a bend-aligned liquid crystal is injected. A cell was produced. The polarizing plate (PP-01) produced in Example 4 was sandwiched between the bend alignment cells and the optical anisotropic layer side was the liquid crystal cell side, and the rubbing direction of the liquid crystal cell and the rubbing direction of the optical anisotropic layer were Were bonded so as to be antiparallel to each other, thereby producing an OCB mode liquid crystal cell LCD-01.

  An OCB-mode LCD-04 was produced in the same manner except that the polarizing plate PPH-1 was used instead of the polarizing plate PP-01.

A rectangular wave voltage of white display 2V and black display 5V is applied to this liquid crystal display device at 55 Hz, and from a black display (L1) to a white display (L8) using a measuring instrument (EZ-Contrast 160D, manufactured by ELDIM). The viewing angle was measured in 8 steps. The results are shown in Table 3. The numbers in Table 2 indicate a range in which the contrast ratio is 10 or more and there is no black-side gradation inversion (inversion between L1 and L2).

(Evaluation of frame-shaped light leakage)
Under the environmental conditions of a temperature of 25 ° C. and a relative humidity of 60%, a backlight is placed on the manufactured liquid crystal panels LCD-01 and 04 and they are lit continuously for 5 hours. The leak was evaluated. As a result, the frame-shaped light leakage did not occur in the LCD-01 of the present invention, but the frame-shaped (especially top and bottom) light leakage occurred on the LCD-04 of the comparative example, resulting in poor image quality. It was.

  The present invention contributes to the improvement of the viewing angle when used in an image display device, and even when used under severe conditions, the display quality of an image by the image display device is reduced due to light leakage or the like. It is possible to provide an optical compensation film and a polarizing plate that contribute to the reduction. In addition, the present invention can provide an optical compensation film and a polarizing plate excellent in durability, with little change in optical properties that occur when used under severe conditions. In addition, the present invention can provide an image display device that has a wide viewing angle and has excellent durability in which deterioration in display quality due to light leakage that occurs when used under severe conditions is reduced.

Claims (13)

A polymer film having a Re retardation value defined by the following formula (I) in the range of 0 to 100 nm and an Rth retardation value defined by the following formula (II) in the range of 70 to 500 nm; And an optically anisotropic layer containing a liquid crystal compound, and the polymer film has a photoelastic coefficient of 10 × 10 ⁻¹² m ² / N or less and a moisture permeability measured by a JIS Z0208 test method of 1 g / m 2. -An optical compensation film made of a polymer of 24 hrs or less and 70 to 500 nm;
(I) Re = (nx−ny) × d
(II) Rth = {(nx + ny) / 2−nz} × d
In the formula, nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the plane of the polymer film, respectively, nz is the refractive index in the thickness direction of the polymer film, and d is the thickness. 2. The optical compensation film according to claim 1, wherein the specific gravity of the polymer is 1.20 or less. The optical compensation film according to claim 1, wherein the polymer is a cyclic polyolefin-based polymer. A polymer obtained by ring-opening polymerization of a monomer selected from tetracyclododecenes, or a ring-opening copolymer of a monomer selected from tetracyclododecenes and a monomer obtained from norbornene The optical compensation film according to claim 3, which is a polymer obtained by hydrogenation reaction. The optical compensation film according to claim 1, wherein the polymer film contains an aromatic compound having at least two aromatic rings. The optical compensation film according to claim 5, wherein the aromatic compound is a compound having at least one 1,3,5-triazine ring. The optical compensation film according to claim 1, wherein the polymer film contains thermally conductive particles and has a thermal conductivity of 1 W / (m · K) or more. A heat conductive layer containing heat conductive particles is provided on at least one surface of the polymer film, and the heat conductivity of the polymer film having the heat conductive layer is 1 W / (m · K) or more. 6. The optical compensation film according to any one of 6. The optical compensation film according to claim 1, wherein the liquid crystal compound is a compound selected from discotic liquid crystal compounds. The optical compensation film according to claim 1, wherein the polymer film is a stretched polymer film. A polarizing film having two surfaces and two protective films provided on each of the two surfaces, wherein at least one of the two protective films is defined in any one of claims 1 to 10. A polarizing plate which is a polymer film. The polarizing plate is sandwiched between two polarizing plates, a liquid crystal cell sandwiched between the two polarizing plates, and one of the two polarizing plates and the liquid crystal cell. And an optical compensation film defined by the above. The apparatus according to claim 12, wherein the liquid crystal cell is in a TN-mode or an OCS-mode.