JP2004004642A - Optical film and picture display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical film capable of realizing easy-to-view display having a high contrast ratio over a wide range. <P>SOLUTION: In the optical film obtained by laminating a phase difference film on one surface of a polarizing plate constituted by laminating a transparent protective film on both surfaces of a polarizer so that the absorption axis of the polarizing plate and the lagging axis of the phase difference film may be orthogonal or parallel, the phase difference film is set so that an Nz value expressed by Nz=(nx<SB>1</SB>-nz<SB>1</SB>)/(nx<SB>1</SB>-ny<SB>1</SB>) may satisfy 0.4 to 0.6 and an in-plane phase difference Re<SB>1</SB>=(nx<SB>1</SB>-ny<SB>1</SB>)×d<SB>1</SB>may be 200 to 350nm when it is assumed that a direction where an in-plane refractive index on a film surface is maximum is an X-axis, a direction perpendicular to the X-axis is a Y-axis and the thickness direction of the film is a Z-axis, the refractive indexes in the respective axial directions are nx<SB>1</SB>, ny<SB>1</SB>and nz<SB>1</SB>and the thickness of the film is d<SB>1</SB>(nm). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical film in which a polarizing plate and a retardation film are laminated. Further, the present invention relates to an image display device such as a liquid crystal display device, a PDP, and a CRT using the optical film. In particular, the optical film of the present invention is suitable for a liquid crystal display device operating in a so-called IPS mode.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a liquid crystal display device, a so-called TN mode liquid crystal display device in which liquid crystals having positive dielectric anisotropy are twisted horizontally between substrates facing each other has been mainly used. However, in the TN mode, birefringence occurs due to liquid crystal molecules in the vicinity of the substrate due to the driving characteristics of the liquid crystal molecules, resulting in light leakage, making it difficult to perform perfect black display. On the other hand, in the IPS mode liquid crystal display device, in the non-driving state, the liquid crystal molecules have a homogeneous alignment substantially parallel to the substrate surface, so that light passes through the liquid crystal layer without substantially changing its polarization plane. As a result, by arranging the polarizing plates above and below the substrate, almost complete black display can be achieved in a non-driven state.
[0003]
However, in the IPS mode, although almost complete black display can be achieved in the panel normal direction, when the panel is observed from a direction deviated from the normal direction, the panel is deviated from the optical axis direction of polarizing plates disposed above and below the liquid crystal cell. In the direction, there is a problem that the viewing angle becomes narrow as a result of light leakage inevitable due to the characteristics of the polarizing plate.
[0004]
In order to solve this problem, a polarizing plate is used in which a geometrical axis shift of the polarizing plate which occurs when obliquely observed is compensated by a retardation film. A polarizing plate capable of obtaining such an effect has been disclosed (for example, see Patent Documents 1 and 2). However, it is difficult to realize a sufficiently wide viewing angle with a conventionally known retardation film.
[0005]
In the polarizing plate described in Patent Document 1, a retardation film is used as a protective film for a polarizer. However, although the polarizing plate provides good viewing angle characteristics in a normal use environment, the protective film directly laminated due to a dimensional change of the polarizer under high temperature or high humidity also deforms. Therefore, the retardation value of the retardation film used for the protective film deviates from a desired value, and there is a problem that the effect cannot be stably maintained.
[0006]
On the other hand, in Patent Document 2, a retardation film is laminated on a polarizing plate using a triacetyl cellulose film (TAC film) generally used as a protective film. In this case, since no stress is applied directly to the retardation film, the retardation value of the retardation film is stable. However, since there is a retardation value that cannot be ignored in the TAC film, it is difficult to design a retardation film that compensates for the axial misalignment. Further, similarly to the above, the dimensional change of the polarizer at high temperature or high humidity causes a change in the retardation value of the TAC film, so that the desired purpose cannot be achieved.
[0007]
[Patent Document 1]
JP-A-4-305602
[0008]
[Patent Document 2]
JP-A-4-371903
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide an optical film in which a polarizing plate and a retardation film are laminated, and when applied to an image display device, an optical film capable of realizing an easily viewable display having a high contrast ratio over a wide range. I do.
[0010]
Still another object of the present invention is to provide an optical film capable of securing a stable retardation value even under high temperature or high humidity.
[0011]
Another object of the present invention is to provide an image display device using the optical film, which can realize an easy-to-see display having a high contrast ratio over a wide range, particularly a liquid crystal display device operating in an IPS mode.
[0012]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above problems, and as a result, have found the following optical films, and have completed the present invention.
[0013]
That is, the present invention is an optical film laminated such that the absorption axis of the polarizing plate and the slow axis of the retardation film are orthogonal or parallel,
In the retardation film, the direction in which the in-plane refractive index in the film plane is the maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refraction in each axial direction. Rate nx ₁ , Ny ₁ , Nz ₁ , Film thickness d ₁ (Nm),
Nz = (nx ₁ -Nz ₁ ) / (Nx ₁ -Ny ₁ ) Satisfies 0.4 to 0.6,
And in-plane retardation Re ₁ = (Nx ₁ -Ny ₁ ) × d ₁ Is 200 to 350 nm.
[0014]
In the optical film of the present invention, when the polarizing plate is arranged in a crossed Nicols state, light leakage in a direction shifted from the optical axis can be eliminated by the specific retardation film. In particular, an IPS mode liquid crystal display device has a function of compensating for a decrease in contrast in an oblique direction of a liquid crystal layer. The Nz value of the retardation film is 0.4 to 0.6, and the in-plane retardation is 200 to 350 nm. The Nz value is preferably at least 0.45, more preferably at least 0.48, from the viewpoint of enhancing the compensation function. On the other hand, the Nz value is preferably 0.55 or less, more preferably 0.52 or less. In-plane retardation Re ₁ Is preferably 230 nm or more and more preferably 250 nm or more from the viewpoint of enhancing the compensation function. On the other hand, the in-plane retardation Re ₁ Is preferably 300 nm or less, more preferably 280 nm or less. Retardation film thickness d ₁ Is not particularly limited, but is usually about 40 to 100 μm, preferably 50 to 70 μm.
[0015]
As the optical film, on one side of a polarizing plate obtained by laminating a transparent protective film on both surfaces of a polarizer, those laminated such that the absorption axis of the polarizing plate and the slow axis of the retardation film are orthogonal or parallel. preferable.
[0016]
In the optical film, the transparent protective film has (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in a side chain, and (B) a substituted and / or unsubstituted phenyl group and a nitrile group in a side chain. It is preferable to contain a thermoplastic resin.
[0017]
The transparent film containing a mixture of the thermoplastic resins (A) and (B) as a main component has a stable dimension even when the polarizer undergoes dimensional change at high temperature or high humidity and receives the stress. A phase difference value can be secured. That is, it is possible to obtain an optical film in which a phase difference hardly occurs even in an environment of high temperature and high humidity and little change in characteristics.
[0018]
In the optical film, the transparent protective film has a direction in which the in-plane refractive index in the film plane is the maximum, the X axis, the direction perpendicular to the X axis is the Y axis, and the thickness direction of the film is the Z axis. The axial refractive index is nx ₂ , Ny ₂ , Nz ₂ , Film thickness d ₂ (Nm),
In-plane retardation Re ₂ = (Nx ₂ -Ny ₂ ) × d ₂ Is 20 nm or less,
And the thickness direction retardation Rth = ｛(nx ₂ + Ny ₂ ) / 2-nz ₂ ) × d ₂ ) Is preferably 30 nm or less.
[0019]
The in-plane retardation of the transparent protective film is 20 nm or less, more preferably 10 nm or less, and the thickness direction retardation is 30 nm or less, more preferably 20 nm or less. As described above, by reducing the residual retardation of the transparent protective film of the polarizer, the design of the laminated retardation film becomes easy, and an optical film having a high compensation effect by the retardation film can be obtained. Transparent protective film thickness d ₂ Is not particularly limited, but is generally 500 μm or less, preferably 1 to 300 μm. In particular, the thickness is preferably 5 to 200 μm.
[0020]
Further, in the optical film, it is preferable that the transparent protective film is a stretched film. Generally, the strength of a film material can be improved by stretching, and more robust mechanical properties can be obtained. Many materials cannot be used as a protective film for a polarizer because a retardation is generated by stretching. A transparent film containing a mixture of the thermoplastic resins (A) and (B) as a main component can satisfy the in-plane retardation and the thickness direction retardation even when stretched. The stretching treatment may be either uniaxial stretching or biaxial stretching. In particular, a biaxially stretched film is preferable.
[0021]
Further, the present invention relates to an image display device using the optical film.
[0022]
Further, according to the present invention, the image display device is an IPS mode liquid crystal display device,
The optical film is arranged on the cell substrate on the viewing side,
On the cell substrate on the side opposite to the viewing side, a polarizing plate formed by laminating a transparent protective film on both surfaces of the polarizer is arranged, and the extraordinary refractive index of the liquid crystal substance in the liquid crystal cell in the state where no voltage is applied. The present invention relates to a liquid crystal display device, wherein a direction and an absorption axis of the polarizing plate are in a parallel state.
[0023]
Further, according to the present invention, the image display device is an IPS mode liquid crystal display device,
A polarizing plate formed by laminating a transparent protective film on both sides of the polarizer is arranged on the cell substrate on the viewing side,
On the cell substrate on the side opposite to the viewing side, the optical film is disposed, and in a state where no voltage is applied, the direction of the extraordinary refractive index of the liquid crystal material in the liquid crystal cell and the absorption axis of the optical film are orthogonal to each other. And a liquid crystal display device.
[0024]
In the IPS mode liquid crystal display device, the transparent protective film of the polarizing plate comprises (A) a thermoplastic resin having a substituted or unsubstituted imide group in a side chain, and (B) a substituted or unsubstituted phenyl group and a nitrile in a side chain. It preferably contains a thermoplastic resin having a group.
[0025]
In the IPS mode liquid crystal display device, the transparent protective film has an X-axis in a direction in which the in-plane refractive index in the film plane is maximum, a Y-axis in a direction perpendicular to the X-axis, and a Z-axis in a thickness direction of the film. And the refractive index in each axial direction is nx ₂ , Ny ₂ , Nz ₂ , Film thickness d ₂ (Nm),
In-plane retardation Re ₂ = (Nx ₂ -Ny ₂ ) × d ₂ Is 20 nm or less,
And the thickness direction retardation Rth = ｛(nx ₂ + Ny ₂ ) / 2-nz ₂ ) × d ₂ ) Is preferably 30 nm or less.
[0026]
In the IPS mode liquid crystal display device, the transparent protective film is preferably a biaxially stretched film.
[0027]
As the image display device of the present invention, an IPS mode liquid crystal display device is preferable. This has conventionally occurred in an IPS mode liquid crystal display device by disposing an optical film obtained by laminating the polarizing plate of the present invention and a retardation film having a specific retardation value on one of the surfaces of an IPS mode liquid crystal cell. Light leakage during black display can be reduced. Such an IPS mode liquid crystal display device has a high contrast ratio in all directions, and can realize a wide viewing angle and easy-to-view display.
[0028]
In particular, when a transparent protective film containing a mixture of the thermoplastic resins (A) and (B) as a main component is used as the transparent protective film of the polarizing plate disposed on the liquid crystal cell surface, a wide viewing angle is obtained. This is suitable for obtaining a liquid crystal display device capable of securing a stable phase difference.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an optical film and an image display device of the present invention will be described with reference to the drawings. As shown in FIG. 1, in the optical film of the present invention, a retardation film 2 is laminated on a polarizing plate 1. As the polarizing plate, a polarizer can be used as it is, or a transparent protective film can be laminated and used. FIG. 1 shows an example in which a retardation film 2 is laminated on one surface of a polarizing plate 1 in which a transparent protective film 1b is laminated on both surfaces of a polarizer 1a. The absorption axis of the polarizing plate 1 and the slow axis of the retardation film 2 are laminated so as to be orthogonal or parallel. It is preferable that the absorption axis of the polarizing plate 1 and the slow axis of the retardation film 2 are laminated in parallel from the point of the continuous bonding step at the time of lamination.
[0030]
As the retardation film, the Nz value and the in-plane retardation Re ₁ Those satisfying the values can be used without particular limitation. For example, a birefringent film of a polymer film, an alignment film of a liquid crystal polymer and the like can be mentioned.
[0031]
Examples of the high-molecular polymer include polyolefins such as polycarbonate and polypropylene, polyesters such as polyethylene terephthalate and polyethylene naphthalate, alicyclic polyolefins such as polynorbornene, polyvinyl alcohol, polyvinyl butyral, polymethyl vinyl ether, polyhydroxyethyl acrylate, and hydroxy. Ethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyarylate, polysulfone, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallylsulfone, polyvinyl alcohol, polyamide, polyimide, polyvinyl chloride, cellulose polymer, or a binary polymer of these , Ternary copolymers, graft copolymers, blends, etc. It is. The retardation film controls the refractive index in the thickness direction by a method of biaxially stretching the polymer film in the plane direction, a method of uniaxially or biaxially stretching in the plane direction, and a method of stretching also in the thickness direction. It can be obtained by: Further, it can be obtained by, for example, a method in which a heat-shrinkable film is adhered to a high-molecular polymer film, and the polymer film is subjected to a stretching treatment and / or a shrinking treatment under the action of the shrinkage force caused by heating to be inclinedly oriented.
[0032]
Examples of the liquid crystalline polymer include various types of main chain and side chain in which a conjugated linear atomic group (mesogen) imparting liquid crystal orientation is introduced into the main chain and side chain of the polymer. Can be Specific examples of the main-chain type liquid crystalline polymer include a structure in which a mesogen group is bonded by a spacer portion that imparts flexibility, such as a nematic-oriented polyester-based liquid crystalline polymer, a discotic polymer, and a cholesteric polymer. . Specific examples of the side-chain type liquid crystalline polymer include polysiloxane, polyacrylate, polymethacrylate or polymalonate having a main chain skeleton, and a paraffin-imparting paraffin having a conjugated atomic group as a side chain. And those having a mesogen moiety composed of a substituted cyclic compound unit. The alignment film of these liquid crystalline polymers is, for example, a rubbed surface of a thin film of polyimide or polyvinyl alcohol formed on a glass plate, or a liquid crystalline polymer on an alignment-treated surface such as obliquely deposited silicon oxide. It is preferable that the liquid crystal polymer is oriented by developing and heat-treating the above solution, particularly, the liquid crystal polymer is inclined and oriented.
[0033]
The polarizer is not particularly limited, and various types can be used. Examples of the polarizer include a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, and a dichromatic dye such as iodine or a dichroic dye. And uniaxially stretched by adsorbing a hydrophilic substance, or a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride. Among these, a polarizer composed of a polyvinyl alcohol-based film and a dichroic substance such as iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.
[0034]
A polarizer obtained by dyeing a polyvinyl alcohol-based film with iodine and uniaxially stretching can be produced, for example, by dyeing polyvinyl alcohol by immersing it in an aqueous solution of iodine, and stretching the film to 3 to 7 times its original length. If necessary, it can be immersed in an aqueous solution of potassium iodide or the like which may contain boric acid, zinc sulfate, zinc chloride or the like. Further, if necessary, the polyvinyl alcohol-based film may be immersed in water and washed with water before dyeing. By washing the polyvinyl alcohol-based film with water, dirt on the surface of the polyvinyl alcohol-based film and an anti-blocking agent can be washed off. is there. Stretching may be performed after dyeing with iodine, may be performed while dyeing, or may be stretched and then dyed with iodine. Stretching can be performed in an aqueous solution of boric acid or potassium iodide or in a water bath.
[0035]
The material for forming the transparent protective film provided in the polarizer is not particularly limited, but (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in a side chain, and (B) a substituted and / or substituted side chain in a side chain. Alternatively, a resin containing a thermoplastic resin having an unsubstituted phenyl group and a nitrile group can be preferably used. As described above, the transparent protective film containing the thermoplastic resins (A) and (B) hardly causes a phase difference even when subjected to stress due to a dimensional change of the polarizer, and has an in-plane even when stretched. Phase difference Re ₂ And the thickness direction retardation Rth can be controlled to be small. A transparent protective film containing such thermoplastic resins (A) and (B) is described in, for example, WO 01/37007. The transparent protective film may contain other resins even when the thermoplastic resins (A) and (B) are the main components.
[0036]
The thermoplastic resin (A) has a substituted and / or unsubstituted imide group in a side chain, and the main chain is an arbitrary thermoplastic resin. The main chain may be, for example, a main chain composed of only carbon, or an atom other than carbon may be inserted between carbons. It may also be composed of atoms other than carbon. The main chain is preferably a hydrocarbon or a substitute thereof. The main chain is obtained, for example, by addition polymerization. Specifically, for example, it is polyolefin or polyvinyl. The main chain is obtained by condensation polymerization. For example, it can be obtained by an ester bond, an amide bond and the like. The main chain is preferably a polyvinyl skeleton obtained by polymerizing a substituted vinyl monomer.
[0037]
As a method for introducing a substituted and / or unsubstituted imide group into the thermoplastic resin (A), any conventionally known method can be adopted. For example, a method of polymerizing the monomer having the imide group, a method of polymerizing various monomers to form a main chain, and then introducing the imide group, and a method of grafting the compound having the imide group to a side chain are exemplified. Can be As the substituent of the imide group, a conventionally known substituent capable of substituting hydrogen of the imide group can be used. For example, an alkyl group and the like can be mentioned.
[0038]
The thermoplastic resin (A) is a binary or higher multi-component copolymer containing a repeating unit derived from at least one olefin and at least one repeating unit having a substituted and / or unsubstituted maleimide structure. It is preferred that The olefin / maleimide copolymer can be synthesized from an olefin and a maleimide compound by a known method. The synthesis method is described in, for example, JP-A-5-59193, JP-A-5-195801, JP-A-6-136058 and JP-A-9-328523.
[0039]
Examples of the olefin include isobutene, 2-methyl-1-butene, 2-methyl-1-pentene, 2-methyl-1-hexene, 2-methyl-1-heptene, 2-methyl-1-heptene, Examples thereof include 1-isooctene, 2-methyl-1-octene, 2-ethyl-1-pentene, 2-ethyl-2-butene, 2-methyl-2-pentene, and 2-methyl-2-hexene. Of these, isobutene is preferred. These olefins may be used alone or in combination of two or more.
[0040]
As the maleimide compound, maleimide, N-methylmaleimide, N-ethylmaleimide, Nn-propylmaleimide, Ni-propylmaleimide, Nn-butylmaleimide, Ns-butylmaleimide, Nt-butyl Maleimide, Nn-pentylmaleimide, Nn-hexylmaleimide, Nn-heptylmaleimide, Nn-octylmaleimide, N-laurylmaleimide, N-stearylmaleimide, N-cyclopropylmaleimide, N-cyclo Butylmaleimide, N-cyclopentylmaleimide, N-cyclohexylmaleimide, N-cycloheptylmaleimide, N-cyclooctylmaleimide and the like. Among these, N-methylmaleimide is preferred. These maleimide compounds may be used alone or in combination of two or more.
[0041]
In the olefin / maleimide copolymer, the content of the olefin repeating unit is not particularly limited, but is about 20 to 70 mol%, preferably 40 to 60 mol%, more preferably, of the total repeating units of the thermoplastic resin (A). 45 to 55 mol%. The content of the repeating unit having a maleimide structure is about 30 to 80 mol%, preferably 40 to 60 mol%, and more preferably 45 to 55 mol%.
[0042]
The thermoplastic resin (A) contains a repeating unit of the olefin and a repeating unit of a maleimide structure, and can be formed by only these units. In addition to the above, repeating units of other vinyl monomers may be contained at a ratio of 50 mol% or less. Other vinyl monomers include acrylic acid monomers such as methyl acrylate and butyl acrylate, methacrylic acid monomers such as methyl methacrylate and cyclohexyl methacrylate, and vinyl ester monomers such as vinyl acetate. And vinyl ether monomers such as methyl vinyl ether, acid anhydrides such as maleic anhydride, and styrene monomers such as styrene, α-methylstyrene and p-methoxystyrene.
[0043]
The weight average molecular weight of the thermoplastic resin (A) is not particularly limited. ³ ~ 5 × 10 ⁶ It is about. The weight average molecular weight is 1 × 10 ⁴ More preferably, 5 × 10 ⁵ The following is preferred. The glass transition temperature of the thermoplastic resin (A) is at least 80 ° C, preferably at least 100 ° C, more preferably at least 130 ° C.
[0044]
Further, a glutarimide-based thermoplastic resin can be used as the thermoplastic resin (A). The glutarimide resin is described in JP-A-2-153904 and the like. The glutarimide resin has a glutarimide structural unit and a methyl acrylate or methyl methacrylate structural unit. The other vinyl monomer can be introduced into the glutarimide resin.
[0045]
The thermoplastic resin (B) is a thermoplastic resin having a substituted and / or unsubstituted phenyl group and a nitrile group in a side chain. The main chain of the thermoplastic resin (B) can be the same as that of the thermoplastic resin (A).
[0046]
Examples of the method of introducing the phenyl group into the thermoplastic resin (B) include a method of polymerizing a monomer having the phenyl group, a method of polymerizing various monomers to form a main chain, and then introducing a phenyl group; Examples include a method of grafting a compound having a phenyl group to a side chain. As the substituent of the phenyl group, a conventionally known substituent capable of substituting hydrogen of the phenyl group can be used. For example, an alkyl group and the like can be mentioned. The method for introducing a nitrile group into the thermoplastic resin (B) may be the same as the method for introducing a phenyl group.
[0047]
The thermoplastic resin (B) is a binary or ternary or more multi-component copolymer containing a repeating unit (nitrile unit) derived from an unsaturated nitrile compound and a repeating unit (styrene unit) derived from a styrene-based compound. It is preferred that they are united. For example, an acrylonitrile-styrene copolymer can be preferably used.
[0048]
As the unsaturated nitrile compound, any compound having a cyano group and a reactive double bond can be mentioned. Examples thereof include α-substituted unsaturated nitriles such as acrylonitrile and methacrylonitrile, and nitrile compounds having an α, β-disubstituted olefinically unsaturated bond such as fumaronitrile.
[0049]
Styrene compounds include any compound having a phenyl group and a reactive double bond. Examples include unsubstituted or substituted styrene compounds such as styrene, vinyltoluene, methoxystyrene, and chlorostyrene, and α-substituted styrene compounds such as α-methylstyrene.
[0050]
Although the content of the nitrile unit in the thermoplastic resin (B) is not particularly limited, it is about 10 to 70% by weight, preferably 20 to 60% by weight, more preferably 20 to 50% by weight, based on the total repeating units. is there. Particularly, 20 to 40% by weight and 20 to 30% by weight are preferable. The styrene unit is about 30 to 80% by weight, preferably 40 to 80% by weight, and more preferably 50 to 80% by weight. Particularly, 60 to 80% by weight and 70 to 80% by weight are preferable.
[0051]
The thermoplastic resin (B) contains the nitrile unit and the styrene-based unit, and can be formed by only these units. In addition to the above, a repeating unit of another vinyl monomer may be contained in a proportion of 50 mol% or less. Examples of other vinyl monomers include those exemplified for the thermoplastic resin (A), olefin repeating units, maleimide, substituted maleimide repeating units, and the like. Examples of the thermoplastic resin (B) include an AS resin, an ABS resin, and an ASA resin.
[0052]
The weight average molecular weight of the thermoplastic resin (B) is not particularly limited. ³ ~ 5 × 10 ⁶ It is about. Preferably 1 × 10 ⁴ 5 × 10 or more ⁵ It is as follows.
[0053]
The ratio between the thermoplastic resin (A) and the thermoplastic resin (B) is adjusted according to the retardation required for the transparent protective film. In general, the mixing ratio is preferably such that the content of the thermoplastic resin (A) is 50 to 95% by weight, more preferably 60 to 95% by weight, of the total amount of the resin in the film. And more preferably 65 to 90% by weight. The content of the thermoplastic resin (B) is preferably 5 to 50% by weight, more preferably 5 to 40% by weight, and still more preferably 10 to 35% by weight of the total amount of the resin in the film. %. The thermoplastic resin (A) and the thermoplastic resin (B) are mixed by hot melt kneading them.
[0054]
As a material for forming a transparent protective film other than the above, a material having excellent transparency, mechanical strength, heat stability, moisture shielding property, isotropy, and the like is preferable. For example, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, and styrene such as polystyrene and acrylonitrile / styrene copolymer (AS resin). Polymers, polycarbonate polymers and the like. In addition, polyethylene, polypropylene, polyolefin having a cyclo- or norbornene structure, polyolefin-based polymers such as ethylene-propylene copolymer, vinyl chloride-based polymers, amide-based polymers such as nylon and aromatic polyamide, imide-based polymers, and sulfone-based polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Blends of polymers and the like are also examples of polymers forming the transparent protective film. The transparent protective film can also be formed as a cured layer of a thermosetting resin or an ultraviolet curing resin such as an acrylic, urethane, acrylic urethane, epoxy or silicone resin.
[0055]
The surface of the transparent protective film on which the polarizer is not adhered (the surface on which the coating layer is not provided) has been subjected to a hard coat layer, an antireflection treatment, a sticking prevention, and a treatment for diffusion or antiglare. Is also good.
[0056]
The hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate, for example, by applying a suitable ultraviolet-curable resin such as an acrylic resin or a silicone resin to a cured film having excellent hardness and sliding properties, etc., as a transparent protective film. It can be formed by a method of adding to the surface of. The anti-reflection treatment is performed for the purpose of preventing the reflection of external light on the polarizing plate surface, and can be achieved by forming an anti-reflection film or the like according to the related art. In addition, the anti-sticking treatment is performed for the purpose of preventing adhesion to an adjacent layer.
[0057]
The anti-glare treatment is performed for the purpose of preventing external light from being reflected on the surface of the polarizing plate and hindering the visibility of light transmitted through the polarizing plate, and is, for example, a roughening method using a sand blast method or an embossing method. The transparent protective film can be formed by giving a fine uneven structure to the surface of the transparent protective film by an appropriate method such as a method of mixing transparent fine particles or the like. As the fine particles to be contained in the formation of the surface fine uneven structure, for example, a conductive material composed of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and the like having an average particle size of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles that may be used and organic fine particles made of a crosslinked or uncrosslinked polymer or the like are used. When forming the fine surface unevenness structure, the amount of the fine particles to be used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, per 100 parts by weight of the transparent resin forming the fine surface unevenness structure. The anti-glare layer may also serve as a diffusion layer (such as a viewing angle expanding function) for diffusing light transmitted through the polarizing plate to increase the viewing angle or the like.
[0058]
The anti-reflection layer, anti-sticking layer, diffusion layer, anti-glare layer and the like can be provided on the transparent protective film itself, or can be separately provided as an optical layer separately from the transparent protective film.
[0059]
For the bonding treatment between the polarizer and the transparent protective film, an isocyanate-based adhesive, a polyvinyl alcohol-based adhesive, a gelatin-based adhesive, a vinyl-based latex-based, an aqueous-based polyester, or the like is used.
[0060]
The method of laminating the retardation film and the polarizing plate is not particularly limited, and the lamination can be performed with an adhesive layer or the like. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited, and for example, an acrylic polymer, a silicone-based polymer, a polyester, a polyurethane, a polyamide, a polyether, and a polymer having a fluorine-based or rubber-based polymer as a base polymer are appropriately selected. Can be used. In particular, an acrylic adhesive having excellent optical transparency, exhibiting appropriate wettability, cohesiveness and adhesive adhesive properties and having excellent weather resistance and heat resistance can be preferably used.
[0061]
Each layer such as an optical film and a pressure-sensitive adhesive layer, for example, by a method such as a method of treating with a UV absorber such as a salicylic acid ester compound or a benzophenol compound, a benzotriazole compound or a cyanoacrylate compound, or a nickel complex salt compound. A material having an ultraviolet absorbing ability may be used.
[0062]
The optical film of the present invention is suitably used for an IPS mode liquid crystal display device. An IPS mode liquid crystal display device includes a pair of substrates sandwiching a liquid crystal layer, an electrode group formed on one of the pair of substrates, and a liquid crystal composition material layer having dielectric anisotropy sandwiched between the substrates. A liquid crystal comprising: an alignment control layer formed opposite to the pair of substrates to align the molecular alignment of the liquid crystal composition material in a predetermined direction; and a driving unit for applying a driving voltage to the electrode group. With cells. The electrode group has an arrangement structure in which a parallel electric field is mainly applied to an interface between the alignment control layer and the liquid crystal composition material layer.
[0063]
As shown in FIGS. 2 and 3, the optical film 3 of the present invention is disposed on the viewing side or light incident side of the liquid crystal cell. The optical film 3 preferably has the retardation film 1 side as the liquid crystal cell 4 side. The polarizing plate 1 is arranged on the opposite side of the liquid crystal cell 4 on which the optical film 3 is arranged. The absorption axis of the polarizing plate 1 arranged on both sides of the cell substrate 4 and the absorption axis of the optical film 3 (the polarizing plate 1) are arranged orthogonally. The polarizing plate 1 is a polarizer 1a similar to that used for the optical film 3 and has a transparent protective film 2b laminated on both surfaces.
[0064]
When the optical film 3 is arranged on the viewing side of the IPS mode liquid crystal cell 4 as shown in FIG. 2, the polarizing plate 1 is applied with no voltage to the cell substrate 4 on the side opposite to the viewing side (light incident side). In this state, it is preferable to arrange the liquid crystal cell 4 such that the direction of the extraordinary light refractive index of the liquid crystal material in the liquid crystal cell 4 and the absorption axis of the polarizing plate 1 are in parallel.
[0065]
When the optical film 3 is disposed on the light incident side of the IPS mode liquid crystal cell 4 as shown in FIG. 3, the polarizing plate 1 is disposed on the cell substrate 4 on the viewing side, It is preferable to arrange the liquid crystal material in 4 such that the direction of the extraordinary light refractive index of the liquid crystal material and the absorption axis of the optical film 3 are orthogonal to each other.
[0066]
The optical film and the polarizing plate can be used by laminating other optical layers in practical use. The optical layer is not particularly limited. For example, the optical layer may be used for forming a liquid crystal display device such as a reflection plate, a semi-transmission plate, and a retardation plate (including a wavelength plate such as や or ４). One or two or more optical layers can be used. In particular, a reflective polarizing plate or a transflective polarizing plate in which a reflecting plate or a transflective reflecting plate is further laminated on a polarizing plate, and a polarizing plate in which a brightness enhancement film is further laminated on a polarizing plate are preferable.
[0067]
The reflection type polarizing plate is provided with a reflection layer on a polarizing plate, and is used to form a liquid crystal display device of a type that reflects incident light from a viewing side (display side) and displays the reflected light. There is an advantage that the built-in light source can be omitted, and the liquid crystal display device can be easily made thinner. The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is provided on one surface of the polarizing plate via a transparent protective layer or the like as necessary.
[0068]
Specific examples of the reflective polarizing plate include those in which a reflective layer formed by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum to one surface of a transparent protective film that has been matted as necessary. Further, there may be mentioned, for example, a transparent protective film in which fine particles are contained to form a fine surface unevenness structure, and a reflective layer having a fine unevenness structure is formed thereon. The reflective layer having the above-mentioned fine uneven structure has an advantage of diffusing incident light by irregular reflection, preventing directivity and glare, and suppressing unevenness in brightness and darkness. Further, the transparent protective film containing fine particles also has an advantage that the incident light and the reflected light thereof are diffused when transmitting the light, and the unevenness of light and darkness can be further suppressed. The reflective layer having a fine uneven structure reflecting the fine uneven structure on the surface of the transparent protective film is formed by, for example, making the metal transparent by an appropriate method such as a vacuum evaporation method, an ion plating method, an evaporation method such as a sputtering method, or a plating method. It can be carried out by a method of directly attaching to the surface of the protective layer.
[0069]
The reflection plate can be used as a reflection sheet or the like in which a reflection layer is provided on an appropriate film according to the transparent film instead of the method of directly applying the reflection plate to the transparent protective film. Since the reflective layer is usually made of a metal, the use form in which the reflective surface is covered with a transparent protective film, a polarizing plate, or the like is intended to prevent a decrease in the reflectance due to oxidation and, as a result, a long-lasting initial reflectance. It is more preferable to avoid separately providing a protective layer.
[0070]
The transflective polarizing plate can be obtained by forming a transflective reflective layer such as a half mirror that reflects and transmits light with the reflective layer. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell. When a liquid crystal display device or the like is used in a relatively bright atmosphere, an image is displayed by reflecting incident light from the viewing side (display side). In a relatively dark atmosphere, a liquid crystal display device of a type that displays an image using a built-in light source such as a backlight built in the back side of a transflective polarizing plate can be formed. That is, the transflective polarizing plate can save energy for use of a light source such as a backlight in a bright atmosphere, and is useful for forming a liquid crystal display device of a type that can be used with a built-in light source even in a relatively dark atmosphere. It is.
[0071]
An elliptically polarizing plate or a circularly polarizing plate in which a retardation plate is further laminated on a polarizing plate will be described. When changing linearly polarized light to elliptically or circularly polarized light, changing elliptically or circularly polarized light to linearly polarized light, or changing the polarization direction of linearly polarized light, a phase difference plate or the like is used. In particular, a so-called quarter-wave plate (also referred to as a λ / 4 plate) is used as a retardation plate that changes linearly polarized light into circularly polarized light or converts circularly polarized light into linearly polarized light. A half-wave plate (also referred to as a λ / 2 plate) is generally used to change the polarization direction of linearly polarized light.
[0072]
The elliptically polarizing plate compensates (prevents) coloring (blue or yellow, etc.) caused by birefringence of the liquid crystal layer of the liquid crystal display device, and is effectively used for a monochrome display without the coloring. Further, the one in which the three-dimensional refractive index is controlled is preferable because coloring which occurs when the screen of the liquid crystal display device is viewed from an oblique direction can be compensated (prevented). The circularly polarizing plate is effectively used, for example, when adjusting the color tone of an image of a reflection type liquid crystal display device that displays an image in color, and also has an antireflection function.
[0073]
A polarizing plate obtained by laminating a polarizing plate and a brightness enhancement film is usually used by being provided on the back side of a liquid crystal cell. The brightness enhancement film reflects linearly polarized light of a predetermined polarization axis or circularly polarized light of a predetermined direction when natural light is incident due to reflection from a backlight or a back side of a liquid crystal display device, and has a property of transmitting other light. A polarizing plate obtained by laminating a brightness enhancement film and a polarizing plate, while transmitting light from a light source such as a backlight to obtain a transmission light in a predetermined polarization state, is reflected without transmitting light other than the predetermined polarization state. You. The light reflected on the surface of the brightness enhancement film is further inverted through a reflection layer or the like provided on the rear side thereof and re-incident on the brightness enhancement film, and a part or all of the light is transmitted as light of a predetermined polarization state to thereby obtain brightness. In addition to increasing the amount of light transmitted through the enhancement film, it is also possible to improve the luminance by supplying polarized light that is hardly absorbed by the polarizer to increase the amount of light that can be used for liquid crystal display image display and the like. In other words, when light is incident through the polarizer from the back side of the liquid crystal cell with a backlight or the like without using a brightness enhancement film, light having a polarization direction that does not match the polarization axis of the polarizer is almost completely polarized. Is absorbed by the polarizer and does not pass through the polarizer. That is, although it depends on the characteristics of the polarizer used, about 50% of the light is absorbed by the polarizer, and accordingly, the amount of light available for liquid crystal image display and the like decreases, and the image becomes darker. The brightness enhancement film is such that light having a polarization direction as absorbed by the polarizer is once reflected by the brightness enhancement film without being incident on the polarizer, and further inverted through a reflection layer or the like provided behind the same. The brightness enhancement film transmits only the polarized light whose polarization direction has been changed so that the polarization direction of the light reflected and inverted between the two can pass through the polarizer. Since the light is supplied to the polarizer, light from a backlight or the like can be efficiently used for displaying an image on the liquid crystal display device, and the screen can be brightened.
[0074]
A diffusion plate may be provided between the brightness enhancement film and the above-mentioned reflection layer or the like. The light in the polarization state reflected by the brightness enhancement film goes to the reflection layer and the like, but the diffuser provided uniformly diffuses the light passing therethrough, and at the same time, eliminates the polarization state and becomes a non-polarization state. That is, the diffuser returns the polarized light to the original natural light state. The light in the non-polarized state, that is, the light in the natural light state is repeatedly directed to the reflection layer and the like, reflected through the reflection layer and the like, again passed through the diffusion plate and re-incident on the brightness enhancement film. Thus, while maintaining the brightness of the display screen by providing a diffusion plate that returns polarized light to the original natural light state between the brightness enhancement film and the reflective layer, etc., at the same time, reducing unevenness in the brightness of the display screen, A uniform and bright screen can be provided. It is considered that by providing such a diffusion plate, the number of repetitions of the reflection of the first incident light is moderately increased, and a uniform bright display screen can be provided in combination with the diffusion function of the diffusion plate.
[0075]
The brightness enhancement film has a property of transmitting linearly polarized light having a predetermined polarization axis and reflecting other light, such as a multilayer thin film of a dielectric or a multilayer laminate of thin films having different refractive index anisotropy. Such as those shown (manufactured by 3M, D-BEF, etc.), those having an oriented film of cholesteric liquid crystal polymer and its oriented liquid crystal layer supported on a film substrate (manufactured by Nitto Denko Corporation, PCF350, Merck, Transmax, etc.), Appropriate ones such as those exhibiting the characteristic of reflecting one of the left-handed or right-handed circularly polarized light and transmitting the other light can be used.
[0076]
Therefore, in the brightness enhancement film of the type that transmits linearly polarized light having the predetermined polarization axis, the transmitted light is incident on the polarization plate as it is, with the polarization axis aligned, thereby efficiently transmitting the light while suppressing the absorption loss by the polarization plate. Can be done. On the other hand, in a brightness enhancement film of the type that emits circularly polarized light, such as a cholesteric liquid crystal layer, it can be directly incident on a polarizer, but from the viewpoint of suppressing absorption loss, the circularly polarized light is linearly polarized through a retardation plate. It is preferable that the light is incident on a polarizing plate. By using a quarter-wave plate as the retardation plate, circularly polarized light can be converted to linearly polarized light.
[0077]
A retardation plate that functions as a quarter-wave plate in a wide wavelength range such as a visible light region exhibits, for example, a retardation layer that functions as a quarter-wave plate for light-color light having a wavelength of 550 nm and other retardation characteristics. It can be obtained by a method of superimposing a retardation layer, for example, a retardation layer functioning as a half-wave plate. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be composed of one or more retardation layers.
[0078]
The cholesteric liquid crystal layer is also configured such that two or three or more cholesteric liquid crystal layers are superimposed on each other to reflect circularly polarized light in a wide wavelength range such as a visible light region. Based on this, it is possible to obtain circularly polarized light transmitted in a wide wavelength range.
[0079]
Further, the polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers as in the above-mentioned polarized light separating type polarizing plate. Therefore, a reflective elliptically polarizing plate or a transflective elliptically polarizing plate obtained by combining the above-mentioned reflective polarizing plate, semi-transmissive polarizing plate, and retardation plate may be used.
[0080]
The optical film and the polarizing plate on which the optical layers are laminated can also be formed by a method in which the optical films are laminated in advance in the process of manufacturing a liquid crystal display device or the like. It has the advantage of being excellent in stability and assembly work and can improve the manufacturing process of a liquid crystal display device and the like. Appropriate bonding means such as an adhesive layer can be used for lamination. When bonding the above-mentioned polarizing plate and other optical layers, their optical axes can have an appropriate arrangement angle according to the target retardation characteristics and the like.
[0081]
The formation of the liquid crystal display device can be performed according to a conventional method. A liquid crystal display device is generally formed by appropriately assembling components such as an illumination system as necessary and incorporating a drive circuit, but is not particularly limited except that the optical film is used in the present invention. , According to the prior art. As for the liquid crystal cell, in addition to the above-described IPS mode, any type such as a VA type and a π type can be used.
[0082]
As the liquid crystal display device, an appropriate liquid crystal display device such as an illumination system or a device using a reflector can be formed. Further, when forming the liquid crystal display device, for example, a suitable component such as a diffusion plate, an anti-glare layer, an anti-reflection film, a protection plate, a prism array, a lens array sheet, a light diffusion plate, a backlight, etc. Two or more layers can be arranged.
[0083]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.
[0084]
The retardation film, the refractive indices nx, ny, and nz were measured by an automatic birefringence measuring device (manufactured by Oji Scientific Instruments, automatic birefringence meter KOBRA21ADH), and Nz and in-plane retardation Re were measured. ₁ Was calculated. The same measurement was performed for the transparent protective film, and the in-plane retardation Re was measured. ₂ And the thickness direction retardation Rth were calculated.
[0085]
Example 1
(Transparent protective film)
75 parts by weight of an alternating copolymer of isobutene and N-methylmaleimide (N-methylmaleimide content 50 mol%) and 25 parts by weight of an acrylonitrile-styrene copolymer having an acrylonitrile content of 28% by weight It was dissolved in methylene to obtain a solution having a solid content of 15% by weight. This solution was spread on a glass plate, cast on a polyethylene terephthalate film, allowed to stand at room temperature for 60 minutes, and then peeled off from the film. After drying at 100 ° C. for 10 minutes, it was dried at 140 ° C. for 10 minutes and further at 160 ° C. for 30 minutes to obtain a 100 μm-thick transparent protective film. In-plane retardation Re of transparent protective film ₂ Was 4 nm, and the thickness direction retardation Rth was 4 nm.
[0086]
(Polarizer)
A polarizing plate was prepared by laminating the transparent protective film on both sides of a film (polarizer: 20 μm) obtained by adsorbing iodine on a polyvinyl alcohol-based film and using an adhesive.
[0087]
(Optical film)
By stretching the polycarbonate film, a thickness of 65 μm and an in-plane retardation Re are obtained. ₁ Was 260 nm and Nz = 0.5. This retardation film and the polarizing plate were laminated using an adhesive such that the slow axis of the retardation film and the absorption axis of the polarizing plate were in a parallel state to produce an optical film.
[0088]
(Liquid crystal display)
As shown in FIG. 2, the optical film was laminated with an adhesive so that the retardation film side of the optical film was on the viewing side of the IPS mode liquid crystal cell. On the other hand, a polarizing plate was laminated on the surface on the opposite side of the liquid crystal cell with an adhesive to produce a liquid crystal display device. The polarizing plate on the viewing side was laminated so that the direction of the extraordinary light refractive index of the liquid crystal composition in the liquid crystal cell was perpendicular to the absorption axis of the polarizing plate when no voltage was applied. Further, the absorption axis of the polarizing plate and the absorption axis of the optical film were arranged to be orthogonal to each other.
[0089]
(Evaluation)
In this liquid crystal display device, when the contrast ratio in the direction of inclination of 70 degrees from the normal direction in the azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 50. The measurement of the contrast ratio was performed using EZ Contrast (manufactured by ELDIM). After the liquid crystal display device was charged for 200 hours under the conditions of 60 ° C. and 95% RH, in-plane unevenness of black display was visually observed, and almost no unevenness was observed.
[0090]
Example 2
The transparent protective film produced in the same manner as in Example 1 was stretched 1.5 times at 160 ° C. in the MD direction, and then 1.5 times at 160 ° C. in the TD direction. This stretched film has a thickness of 45 μm and an in-plane retardation Re. ₂ Was 4 nm, and the thickness direction retardation Rth was 12 nm.
[0091]
A polarizing plate and an optical film were produced in the same manner as in Example 1 except that this transparent protective film was used. Further, a liquid crystal display device was manufactured in the same manner as in Example 1. In this liquid crystal display device, when the contrast ratio in a direction of inclination of 70 degrees from the normal direction in an azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 40. After the liquid crystal display device was charged for 200 hours under the conditions of 60 ° C. and 95% RH, in-plane unevenness of black display was visually observed, and almost no unevenness was observed.
[0092]
Example 3
A polarizing optical film was produced by directly laminating the retardation film made of polycarbonate prepared in Example 1 on a polarizer such that the slow axis was parallel to the absorption axis of the polarizer. The polarizing optical film thus produced was laminated with an adhesive in the same manner as in Example 1 such that the retardation film side was on the viewing side of the IPS mode liquid crystal cell. On the other hand, the polarizing plate used in Example 1 was laminated on the opposite surface with an adhesive to produce a liquid crystal display device.
[0093]
In this liquid crystal display device, when the contrast ratio in the direction of inclination of 70 degrees from the normal direction in the azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 50. After the liquid crystal display device was charged for 200 hours under the conditions of 60 ° C. and 95% RH, in-plane unevenness of black display was visually observed. Was observed.
[0094]
Example 4
(Transparent protective film)
65 parts by weight of a glutarimide copolymer comprising N-methylglutarimide and methyl methacrylate (N-methylglutarimide content: 75% by weight, acid content: 0.01 meq / g or less, glass transition temperature: 147 ° C.), and acrylonitrile And an acrylonitrile-styrene copolymer having a styrene content of 28% by weight and a styrene content of 72% by weight, respectively, and melt-kneading the resulting resin composition into a T-die melt extruder, A 135 μm thick film was obtained. This film was stretched 1.7 times at 160 ° C. in the MD direction, and then stretched 1.8 times at 160 ° C. in the TD direction. The thickness of the obtained biaxially stretched transparent film is 55 μm, and the in-plane retardation Re is ₂ = 1 nm and thickness direction retardation Rth = 3 nm.
[0095]
A polarizing plate and an optical film were produced in the same manner as in Example 1 except that this transparent protective film was used. Further, a liquid crystal display device was manufactured in the same manner as in Example 1. In this liquid crystal display device, when the contrast ratio in the direction of inclination of 70 degrees from the normal direction in the azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 55. After the liquid crystal display device was charged for 200 hours under the conditions of 60 ° C. and 95% RH, in-plane unevenness of black display was visually observed, and almost no unevenness was observed.
[0096]
Comparative Example 1
A polarizing plate was prepared by laminating a triacetyl cellulose film as a transparent protective film on both sides of a film (polarizer: 20 μm) obtained by adsorbing iodine on a polyvinyl alcohol-based film and stretching. The triacetyl cellulose film has a thickness of 80 μm and an in-plane retardation Re. ₂ Was 4 nm, and the thickness direction retardation Rth was 45 nm.
[0097]
This polarizing plate was laminated on both surfaces of an IPS mode liquid crystal cell similar to that of Example 1 with an adhesive to produce a liquid crystal display device. The polarizing plates disposed on both sides of the liquid crystal cell were disposed such that the polarization axes were orthogonal to each other.
[0098]
In this liquid crystal display device, when the contrast ratio was measured in a direction at an inclination of 70 degrees from the normal direction in an azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate, the contrast ratio was 9.
[0099]
Comparative Example 2
The polarizing plate used in Example 1 was laminated on both sides of the same IPS mode liquid crystal cell as in Example 1 with an adhesive to produce a liquid crystal display device. The polarizing plates disposed on both sides of the liquid crystal cell were disposed such that the polarization axes were orthogonal to each other.
[0100]
In this liquid crystal display device, when the contrast ratio in the direction of inclination of 70 degrees from the normal direction in the azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 20.
[0101]
Comparative Example 3
A retardation film having an in-plane retardation of 100 nm and Nz = 0.5, obtained by stretching a polycarbonate film on the polarizing plate prepared in Example 1, was applied to the retardation film of the retardation film and the absorption of the polarizing plate. A polarizing optical film was produced by laminating using an adhesive so that the axes were in a parallel state. The polarizing optical film thus produced was laminated with an adhesive in the same manner as in Example 1 such that the retardation film side was on the viewing side of the IPS mode liquid crystal cell. On the other hand, the polarizing plate used in Example 1 was laminated on the opposite surface with an adhesive to produce a liquid crystal display device.
[0102]
In this liquid crystal display device, when the contrast ratio in the direction of inclination of 70 degrees from the normal direction in the azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 15.
[0103]
Comparative Example 4
A retardation film having an in-plane retardation of 260 nm and Nz = 1.0, obtained by stretching a polycarbonate film on the polarizing plate prepared in Example 1, was applied to the slow axis of the retardation film and the absorption of the polarizing plate. A polarizing optical film was produced by laminating using an adhesive so that the axes were in a parallel state. The polarizing optical film thus produced was laminated with an adhesive in the same manner as in Example 1 such that the retardation film side was on the viewing side of the IPS mode liquid crystal cell. On the other hand, the polarizing plate used in Example 1 was laminated on the opposite surface with an adhesive to produce a liquid crystal display device.
[0104]
In this liquid crystal display device, when the contrast ratio in the direction of inclination of 70 degrees from the normal direction in the azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 8.
[0105]
Comparative Example 5
The retardation film having an in-plane retardation of 120 nm and Nz = 1.0 obtained by stretching the polycarbonate film on the polarizing plate prepared in Example 1 was applied to the retardation film of the retardation film and the absorption of the polarizing plate. A polarizing optical film was produced by laminating using an adhesive so that the axes were in a parallel state. The polarizing optical film thus produced was laminated with an adhesive in the same manner as in Example 1 such that the retardation film side was on the viewing side of the IPS mode liquid crystal cell. On the other hand, the polarizing plate used in Example 1 was laminated on the opposite surface with an adhesive to produce a liquid crystal display device.
[0106]
In this liquid crystal display device, when the contrast ratio in the direction of inclination of 70 degrees from the normal direction in the azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 8.
[0107]
Reference Example 1
A polarizing plate was prepared by laminating a triacetyl cellulose film as a transparent protective film on both sides of a film (polarizer: 20 μm) obtained by adsorbing iodine on a polyvinyl alcohol-based film and stretching. Polarization optics by laminating the polycarbonate retardation film prepared in Example 1 on the polarizing plate using an adhesive so that the slow axis of the retardation film and the absorption axis of the polarizing plate are in a parallel state. A film was prepared. The polarizing optical film thus produced was laminated with an adhesive in the same manner as in Example 1 such that the retardation film side was on the viewing side of the IPS mode liquid crystal cell. On the other hand, the polarizing plate used in Example 1 was laminated on the opposite surface with an adhesive to produce a liquid crystal display device.
[0108]
In this liquid crystal display device, when the contrast ratio in the direction of inclination of 70 degrees from the normal direction in the azimuth direction of 45 degrees with respect to the optical axis of the orthogonal polarizing plate was measured, the contrast ratio was 4. After the liquid crystal display device was charged for 200 hours under the conditions of 60 ° C. and 95% RH, in-plane unevenness of black display was visually observed. Was observed.
[Brief description of the drawings]
FIG. 1 is an example of a cross-sectional view of an optical film of the present invention.
FIG. 2 is a conceptual diagram of the liquid crystal display device of the present invention.
FIG. 3 is a conceptual diagram of the liquid crystal display device of the present invention.
[Explanation of symbols]
1 Polarizing plate
1a Polarizer
1b Transparent protective film
2 Retardation film
3 Optical film
4 IPS mode liquid crystal cell

Claims (11)

In an optical film laminated such that the absorption axis of the polarizing plate and the slow axis of the retardation film are orthogonal or parallel,
In the retardation film, the direction in which the in-plane refractive index in the film plane is the maximum is the X axis, the direction perpendicular to the X axis is the Y axis, the thickness direction of the film is the Z axis, and the refraction in each axial direction. When the ratio is nx ₁ , ny ₁ , nz ₁ , and the film thickness d ₁ (nm),
Nz value represented by _{Nz = (nx 1 -nz 1)} / (nx 1 -ny 1) is satisfied 0.4-0.6,
The optical film and the in-plane retardation _{Re 1 = (nx 1 -ny 1} ) × d 1 , characterized in that it is 200 to 350 nm. An optical film that is laminated on one side of a polarizing plate obtained by laminating a transparent protective film on both surfaces of a polarizer such that the absorption axis of the polarizing plate and the slow axis of the retardation film are orthogonal or parallel. The optical film according to claim 1, wherein: The transparent protective film contains (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in a side chain, and (B) a thermoplastic resin having a substituted and / or unsubstituted phenyl group and a nitrile group in a side chain. 3. The optical film according to claim 2, wherein: The direction in which the in-plane refractive index of the transparent protective film is in the plane of the film is the X-axis, the direction perpendicular to the X-axis is the Y-axis, and the thickness direction of the film is the Z-axis. Is nx ₂ , ny ₂ , nz ₂ , and the thickness d ₂ (nm) of the film,
The in-plane retardation Re ₂ = (nx ₂ −ny ₂ ) × d ₂ is 20 nm or less;
The optical film according to claim 2, wherein a thickness direction retardation Rth = ｛(nx ₂ + ny ₂ ) / 2-nz ₂ ) × d ₂ ) is 30 nm or less. The optical film according to claim 2, wherein the transparent protective film is a stretched film. An image display device using the optical film according to claim 1. The image display device is an IPS mode liquid crystal display device,
The optical film according to any one of claims 1 to 5, is arranged on the cell substrate on the viewing side,
On the cell substrate on the side opposite to the viewing side, a polarizing plate formed by laminating a transparent protective film on both sides of the polarizer is arranged, and the extraordinary refractive index of the liquid crystal substance in the liquid crystal cell in the state where no voltage is applied. A liquid crystal display device, wherein the direction and the absorption axis of the polarizing plate are in parallel. The image display device is an IPS mode liquid crystal display device,
A polarizing plate formed by laminating a transparent protective film on both sides of the polarizer is arranged on the cell substrate on the viewing side,
The optical film according to any one of claims 1 to 5, is arranged on the cell substrate on the side opposite to the viewing side, and the direction of the extraordinary light refractive index of the liquid crystal substance in the liquid crystal cell in a state where no voltage is applied. A liquid crystal display device wherein the absorption axis of the optical film is orthogonal. The transparent protective film of the polarizing plate contains (A) a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and (B) a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain. 9. The liquid crystal display device according to claim 7, wherein: The direction in which the in-plane refractive index of the transparent protective film is in the plane of the film is the X-axis, the direction perpendicular to the X-axis is the Y-axis, and the thickness direction of the film is the Z-axis. Is nx ₂ , ny ₂ , nz ₂ , and the thickness d ₂ (nm) of the film,
The in-plane retardation Re ₂ = (nx ₂ −ny ₂ ) × d ₂ is 20 nm or less;
10. The liquid crystal display device according to claim 7, wherein a thickness direction retardation Rth = ｛(nx ₂ + ny ₂ ) / 2-nz ₂ ) × d ₂ ) is 30 nm or less. The liquid crystal display device according to any one of claims 7 to 10, wherein the transparent protective film is a stretched film.

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