JP2008146003A - Retardation film containing acrylic resin and styrene resin - Google Patents

Abstract

An object of the present invention is to obtain a retardation film used in various types of liquid crystal display devices including an IPS mode having excellent optical characteristics, productivity, and heat resistance.
A retardation film containing an acrylic resin and a styrene resin.
[Selection figure] None

Description

  The present invention relates to a retardation film having excellent optical properties, productivity, heat resistance, and ultraviolet absorption.

  A retardation film is a film having retardation (phase difference) and having a function of converting a polarization state of light, and exhibiting a function by changing an arbitrary polarization to another arbitrary polarization state. It is. For example, liquid crystal molecules in a liquid crystal display have optical anisotropy, so that linearly polarized light is not maintained when light passes through the liquid crystal cell, light leaks, and contrast degradation or hue change occurs when viewed from an oblique direction. This causes display problems. In order to improve this, a retardation film is used. That is, in this case, the function is expressed by returning the light deviated from the linearly polarized light after passing through the liquid crystal cell to the linearly polarized light.

By the way, with the recent expansion of the thin display market represented by liquid crystal televisions, there is an increasing demand for obtaining clearer images at a lower price. An IPS mode liquid crystal display device that has been put into practical use for this purpose and is highly expected in the future (Patent Document 1).
Unlike the other modes, the IPS mode is called an IPS (In-Plane Switching) mode because an electric field is applied almost parallel to the substrate. In the liquid crystal display device of the IPS mode, since the liquid crystal molecules have a homogeneous alignment substantially parallel to the substrate surface in the non-driven state, the light passes through the liquid crystal layer with almost no change in the polarization plane. As a result, by disposing polarizing plates above and below the substrate, almost complete black display is possible in a non-driven state.

  However, even in a liquid crystal display device using the IPS mode, when viewed from a specific oblique direction, gradation inversion, coloring, and contrast decrease may occur, and the viewing angle may be reduced in that direction. . Therefore, like other liquid crystal display methods, it is necessary to perform optical compensation using a retardation film to expand the viewing angle.

  As described above, in the IPS mode, since the liquid crystal molecules have a homogeneous alignment substantially parallel to the substrate surface, a film having a high refractive index in the direction perpendicular to the substrate surface is used for the optical compensation. It is effective (see, for example, FIG. 3 of Patent Document 4 and “Optical Film for Display” (CMC Publishing, 2004), page 104).

Other than the IPS mode liquid crystal display device, it may be effective to use a film having a high refractive index in a direction perpendicular to the display surface.
For example, in Patent Document 6, in a VA mode liquid crystal display device, a retardation film having a high refractive index in a direction perpendicular to a substrate surface using polystyrene which is a polymer having negative birefringence. (Negative A plate) is prepared and optical compensation is described. Moreover, positive typification such as polyethylene terephthalate, polycarbonate, polysulfane, and polyethersulfone is described. In a liquid crystal display device using a resin having intrinsic birefringence for the liquid crystal cell substrate (Patent Document 7), the substrate itself has optical anisotropy, unlike the case of using glass for the substrate. There is a need to compensate. Specifically, such a substrate has a larger refractive index in a direction parallel to the substrate surface than a refractive index in a direction perpendicular to the substrate surface, and thus a direction perpendicular to the display surface of the display device. It is effective to use a film having a high refractive index.

  Therefore, a retardation film used in various types of liquid crystal display devices including an IPS mode liquid crystal display device uses a material having negative birefringence or a material having positive birefringence. In order to increase the refractive index in a direction perpendicular to the substrate surface, a special treatment is applied to the substrate.

For example, as a method of producing a retardation film used in an IPS mode liquid crystal display device, a film having a positive birefringence such as a polycarbonate film or a cycloolefin film such as norbornene is used. A method is known in which a heat-shrink film is adhered and subjected to a stretching treatment and / or a shrinkage treatment under the action of the shrinkage force caused by heating to perform tilt orientation (Patent Document 2).
However, this method has a problem in productivity because it includes not only a single film processing step but also a heat shrink film bonding step and a peeling step. That is, when a positive birefringent material is used, there is a disadvantage that the productivity is inferior.

  Attempts have also been made to use negative birefringent materials for use in IPS mode liquid crystal displays. For example, a method of using fine particles such as strontium carbonate having negative optical anisotropy (Patent Document 3) or using a styrene polymer as a polymer having negative intrinsic birefringence (Patent Document 4) has been devised. Yes. In the former, in order to obtain negative birefringence (especially when the refractive index in the thickness direction is increased), it is necessary to blend a large amount of fine particles. There was a problem in productivity in handling in the process. Further, since the latter has a high absolute value of the photoelastic coefficient because it is a styrene-based resin, there is a problem that when used in a display device, the image quality deteriorates due to changes in temperature and humidity, or is not stable.

  Similarly, as a method of using a styrene resin as a polymer having negative intrinsic birefringence, a method of stretching and using a polymer film containing a styrene resin and a polycarbonate resin (Patent Document 5). However, in this method, since the two resins are basically not completely compatible, phase separation occurred under the usage environment of the display, and there was a problem in transparency and optical stability. Also, the photoelastic coefficient was not practically sufficient.

  By the way, the retardation film is sometimes used also as a polarizing plate protective film (Patent Document 8), and has an ultraviolet absorption equivalent to that of triacetyl cellulose (TAC) that has been widely used as a conventional polarizing plate protective film. May be required.

  Under such circumstances, a retardation film excellent in optical characteristics, productivity, and ultraviolet absorption is desired. In other words, it can be manufactured by simply stretching the film, without special treatment such as adhesion / peeling of another film or addition of special fine particles, and does not cause phase separation, the absolute value of the photoelastic coefficient is small, There is a need for a retardation film having negative birefringence.

JP 7-261152 A JP 2006-106180 A JP 2005-156863 A Japanese Patent Laid-Open No. 10-54982 JP-A-2005-31621 JP-T-2006-514754 JP 60-177320 A JP 2006-58825 A

An object of this invention is to provide the retardation film which is excellent in an optical characteristic, productivity, heat resistance, and an ultraviolet absorptivity.
Furthermore, an object of the present invention is to improve the stability of display in various liquid crystal display devices using such a phase difference film.

  The present inventors have found that a film containing an acrylic resin and a styrene resin has a small absolute value of a photoelastic coefficient, a negative birefringence, and a heat resistance without special treatment. The present inventors have found that it is excellent and does not cause phase separation, and have completed the present invention.

  According to the present invention, it is possible to provide a retardation film that is excellent in optical characteristics, productivity, heat resistance, and ultraviolet absorption and can be suitably used for various types of liquid crystal display devices.

Hereinafter, the present invention will be described in detail.
1. Description of Acrylic Resin In the present invention, the acrylic resin refers to a resin containing 50% by mass or more of an acrylic monomer. Here, the acrylic monomer refers to acrylic acid, methacrylic acid and derivatives thereof.

Specific examples of the acrylic resin include methacrylic acid esters such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, and methyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, and 2-ethylhexyl acrylate. Examples thereof include those obtained by polymerizing one or more monomers selected from acrylic acid esters such as these, and may be homopolymers thereof or copolymers with other monomers.
Among these, a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and another monomer is preferable.

Examples of monomers copolymerizable with methyl methacrylate include other alkyl methacrylates, acrylic alkyl esters; styrene and o-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, Nuclear alkyl-substituted styrene such as p-tert-butylstyrene; aromatic vinyl compounds such as α-alkyl-substituted styrene such as α-methylstyrene and α-methyl-p-methylstyrene; vinyl cyanide such as acrylonitrile and methacrylonitrile And maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; unsaturated carboxylic acid anhydrides such as maleic anhydride; and unsaturated acids such as acrylic acid, methacrylic acid and maleic acid.
These may be used alone or in combination of two or more.

Among these monomers that can be copolymerized with methyl methacrylate, alkyl acrylates are particularly preferred because of their excellent thermal decomposition resistance and high fluidity during molding of methacrylic resins obtained by copolymerizing these. .
The copolymerization ratio of the acrylic acid alkyl esters when methyl methacrylate is copolymerized with the alkyl alkyl esters is preferably 0.1% by mass or more from the viewpoint of heat decomposability, and from the viewpoint of heat resistance. It is preferable that it is 15 mass% or less. The content is more preferably 0.2% by mass or more and 14% by mass or less, and particularly preferably 1% by mass or more and 12% by mass or less.

  Among the alkyl acrylates, methyl acrylate and ethyl acrylate can remarkably improve the fluidity at the time of molding described above even when copolymerized with methyl methacrylate in a small amount of 0.1 to 1% by mass. Therefore, it is preferable.

  In the present invention, a heat-resistant acrylic resin can be used as the acrylic resin. Specific examples of heat-resistant acrylic resins include methacrylic acid esters and / or acrylic acid esters and aromatic vinyl compounds such as α-alkyl-substituted styrenes such as α-methylstyrene and α-methyl-p-methylstyrene; acrylonitrile Vinyl cyanides such as methacrylonitrile; maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; unsaturated carboxylic acid anhydrides such as maleic anhydride; unsaturated acids such as acrylic acid, methacrylic acid and maleic acid And a copolymer thereof.

Preferable heat-resistant acrylic resins include methyl methacrylate-maleic anhydride-styrene copolymers. In particular, methyl methacrylate units in the copolymer are 40 to 90% by mass, and maleic anhydride units are 3 to 20%. Heat resistance, light, and styrene unit copolymerization ratio (styrene unit / maleic anhydride unit) 1 to 3 times by mass%, styrene unit 7-40 mass%, and maleic anhydride unit copolymerization ratio It is preferable from the point of elastic modulus. More preferably, the methyl methacrylate unit in the copolymer is 40 to 90% by mass, the maleic anhydride unit is 5 to 19% by mass, and the styrene unit is 10 to 40% by mass, and particularly preferably in the copolymer. The methyl methacrylate unit is 45 to 88% by mass, the maleic anhydride unit is 6 to 15% by mass, and the styrene unit is 16 to 40% by mass.
For the production of such a heat-resistant acrylic resin, a method described in JP-B 63-1964 can be used.

  Acrylic resins that can be suitably used in the present invention are methyl methacrylate / methyl acrylate copolymer, methyl methacrylate / ethyl acrylate copolymer, and methyl methacrylate / maleic anhydride / styrene copolymer. In particular, a methyl methacrylate / methyl acrylate copolymer is preferable in that both fluidity and heat resistance during molding are well balanced.

  As the acrylic resin of the present invention, two or more types having different molecular weights and compositions can be used at the same time.

The acrylic resin preferably has a weight average molecular weight of 50,000 to 200,000. The weight average molecular weight is preferably 50,000 or more from the viewpoint of the strength of the molded product, and preferably 200,000 or less from the viewpoint of molding processability and fluidity. A more preferable range is 70,000 to 150,000.
In the present invention, isotactic polymethacrylate and syndiotactic polymethacrylate can be used simultaneously.

As a method for producing an acrylic resin, for example, generally used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, and anionic polymerization can be used. It is preferable to avoid mixing of foreign substances as much as possible. From this viewpoint, bulk polymerization and solution polymerization without using a suspending agent or an emulsifier are preferable.
When solution polymerization is performed, a solution prepared by dissolving a mixture of monomers in an aromatic hydrocarbon solvent such as toluene or ethylbenzene can be used. In the case of polymerization by bulk polymerization, the polymerization can be started by irradiation with free radicals generated by heating or ionizing radiation as is usually done.

As the initiator used for the polymerization reaction, any initiator used in radical polymerization can be used. For example, azo compounds such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butyl peroxide- An organic peroxide such as 2-ethylhexanoate can be used.
In particular, when polymerization is carried out at a high temperature of 90 ° C. or higher, solution polymerization is generally used. Therefore, a peroxide, azobis, which has a 10-hour half-life temperature of 80 ° C. or higher and is soluble in the organic solvent used. Initiators and the like are preferred. Specifically, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, Examples thereof include 1-azobis (1-cyclohexanecarbonitrile) and 2- (carbamoylazo) isobutyronitrile.
These initiators are preferably used in the range of 0.005 to 5 wt%.

As the molecular weight modifier used as necessary in the polymerization reaction, any one used in radical polymerization can be used, and for example, mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate are particularly preferable. It is mentioned as a thing.
These molecular weight regulators are added in a concentration range such that the polymerization degree of the acrylic resin is controlled within a preferable range.

2. Description of Styrenic Resin The styrene resin in the present invention refers to a resin containing 50% by mass or more of a styrene monomer. Here, the styrene monomer means a monomer having a styrene skeleton in its structure.

  Specific examples of styrenic monomers include styrene as well as o-methyl styrene, m-methyl styrene, p-methyl styrene, 2,4-dimethyl styrene, ethyl styrene, p-tert-butyl styrene, etc. Styrene; Vinyl aromatic compound monomers such as α-alkyl-substituted styrene such as α-methylstyrene and α-methyl-p-methylstyrene are exemplified, and a typical one is styrene.

  Styrenic resins include those obtained by copolymerizing styrene monomer components with other monomer components. Examples of the copolymerizable monomer include methyl methacrylate such as methyl methacrylate, cyclohexyl methacrylate, methylphenyl methacrylate, isopropyl methacrylate; methyl acrylate, ethyl acrylate, Unsaturated carboxylic acid alkyl ester monomers such as alkyl acrylates such as butyl acrylate, 2-ethylhexyl acrylate and cyclohexyl acrylate; methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid Unsaturated carboxylic acid monomers such as cinnamic acid; unsaturated dicarboxylic acid anhydride monomers such as maleic anhydride, itaconic acid, ethyl maleic acid, methyl itaconic acid, chloromaleic acid; acrylonitrile, methacrylate Unsaturated nitrile monomers such as rhonitrile; 1,3-butadiene, 2-methyl- Conjugated dienes such as 1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and the like, and copolymerizing two or more of these Is also possible.

Styrenic resins that can be suitably used in the present invention are styrene / acrylonitrile copolymers, styrene / methacrylic acid copolymers, and styrene / maleic anhydride copolymers because of their high heat resistance.
In addition, styrene / acrylonitrile copolymer, styrene / methacrylic acid copolymer, and styrene / maleic anhydride copolymer are highly compatible with acrylic resins, so they are highly transparent and cause phase separation during use. It is also preferable from the viewpoint of obtaining a film in which the transparency does not decrease. From such a viewpoint, it is particularly preferable when a polymer containing methyl methacrylate as a monomer component is used as the acrylic resin.

In the case of a styrene-acrylonitrile copolymer, the copolymer ratio of acrylonitrile in the copolymer is preferably 1 to 40% by mass. A more preferable range is 1 to 30% by mass, and an especially preferable range is 1 to 25%. A copolymer ratio of acrylonitrile in the copolymer of 1 to 40% by mass is preferable because of excellent transparency.
In the case of a styrene-methacrylic acid copolymer, the copolymer ratio of methacrylic acid in the copolymer is preferably 0.1 to 50% by mass. A more preferable range is 0.1 to 40% by mass, and a further preferable range is 0.1 to 30% by mass. When the copolymer ratio of methacrylic acid in the copolymer is 0.1% by mass or more, the heat resistance is excellent, and when it is in the range of 50% by mass or less, the transparency is excellent, which is preferable.
In the case of a styrene-maleic anhydride copolymer, the maleic anhydride copolymer ratio in the copolymer is preferably 0.1 to 50% by mass. A more preferable range is 0.1 to 40% by mass, and a further preferable range is 0.1 to 30% by mass. If the maleic anhydride content in the copolymer is 0.1% by mass or more, the heat resistance is excellent, and if it is in the range of 50% by mass or less, the transparency is excellent, which is preferable.

  Among these, a styrene-methacrylic acid copolymer and a styrene-maleic anhydride copolymer are particularly preferable from the viewpoint of heat resistance.

As the styrenic resin, a plurality of types having different compositions, molecular weights, and the like can be used in combination.
The styrene resin can be obtained by a known anion, block, suspension, emulsion or solution polymerization method. Further, in the styrene resin, the unsaturated double bond of the benzene ring of the conjugated diene or styrene monomer may be hydrogenated. The hydrogenation rate can be measured by a nuclear magnetic resonance apparatus (NMR).

3. Description of Resin Composition Containing Acrylic Resin and Styrene Resin as Retardation Film Material The retardation film of the present invention is produced using a resin composition containing an acrylic resin and a styrene resin. The ratio of the acrylic resin at this time is 0.1 to 0.1 mass of acrylic resin with respect to 100 parts by mass of the total amount of acrylic resin and styrene resin from the viewpoint of photoelastic coefficient, heat resistance, and retardation control. The content is preferably 99.9 parts by mass, more preferably 1 to 90 parts by mass, and particularly preferably 5 to 85 parts by mass.

Other resin components other than the acrylic resin and the styrene resin can be added to the resin composition used as the material of the retardation film of the present invention as long as the effect is not impaired. Other resin components at this time include polyolefins such as polyethylene and polypropylene; polyamides, polyphenylene sulfides, polyether ether ketones, polyesters, aliphatic polyester resins, polysulfones, polyphenylene oxides, polyimides, polyether imides, polyacetors. And thermoplastic resins such as phenol; and thermosetting resins such as phenol resin, melamine resin, silicone resin, and epoxy resin. One or more of these resin components can be used.
Moreover, it is preferable that the ratio of another resin component is 20 mass parts or less with respect to 100 mass parts of total amounts of acrylic resin and styrene resin.

Furthermore, arbitrary additives can be mix | blended with the resin composition used as the material of the retardation film of this invention according to various objectives within the range which does not impair the effect of this invention. The type of additive is not particularly limited as long as it is generally used for blending resins and rubber-like polymers. Inorganic fillers such as silicon dioxide; Pigments such as iron oxide; Lubricants such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene bisstearamide; Mold release agents; Paraffinic process oil, naphthene Softeners and plasticizers such as process oils, aromatic process oils, paraffins, organic polysiloxanes, mineral oils; antioxidants such as hindered phenol antioxidants and phosphorus heat stabilizers; hindered amines Flame retardants; antistatic agents; reinforcing agents such as organic fibers, glass fibers, carbon fibers, and metal whiskers; colorants; ultraviolet absorbers, other additives, or mixtures thereof.
These additives are preferably added in an amount of 0.01 to 50 parts by mass with respect to 100 parts by mass of the total amount of the acrylic resin and the styrene resin.

The vapor pressure (P) at 20 ° C. of the additive is preferably 1.0 × 10 ⁻⁴ Pa or less because of excellent molding processability. A more preferable range is a vapor pressure (P) of 1.0 × 10 ⁻⁶ Pa or less, and a particularly preferable range is a vapor pressure (P) of 1.0 × 10 ⁻⁸ Pa or less. Here, being excellent in moldability means that, for example, the adhesion of the additive to the roll is small during film formation. When the additive adheres to the roll, for example, it adheres to the surface of the molded body and deteriorates the appearance and optical characteristics, so that it is not preferable as an optical material.

  The melting point (Tm) of the additive is preferably 80 ° C. or higher because of excellent molding processability. A more preferable range is a melting point (Tm) of 130 ° C. or higher, and a particularly preferable range is a melting point (Tm) of 160 ° C. or higher.

  When the additive is heated from 23 ° C. to 260 ° C. at a rate of 20 ° C./min, the additive mass reduction rate is preferably 50% or less because of excellent molding processability. A more preferable range is a mass reduction rate of 15% or less, and a particularly preferable range is a mass reduction rate of 2% or less.

Among the additives as described above, an ultraviolet absorber is particularly preferable because it has an effect of reducing the absolute value of the photoelastic coefficient of the resin composition to which the ultraviolet absorber is added.
However, it is not preferable to add a large amount of an ultraviolet absorber because the absolute value of the photoelastic coefficient of the resin composition increases. Therefore, it is preferable that the addition amount of a ultraviolet absorber is 0.1-10 mass parts with respect to a total of 100 mass parts of acrylic resin and styrene resin, More preferably, it is 0.1-2 mass parts. It is particularly preferably 0.1 to 1.5 parts by mass or less.
The content of the ultraviolet absorber can be determined by measuring proton NMR with a nuclear magnetic resonance apparatus (NMR) and obtaining from the ratio of integral values of peak signals, or by extracting from a resin with a good solvent and then using a gas chromatograph ( It can be quantified by a method such as GC).

In addition, the retardation film of the present invention can also serve as a polarizing plate protective film. In this case, ultraviolet rays equivalent to triacetyl cellulose (TAC), which has been conventionally used as a polarizing plate protective film. Absorptivity is required (for example, according to KONIKA TECHNICICAL REPORT VOL.16 (2003), regarding the ultraviolet transmittance of the polarizing plate protective film, it is necessary that the transmittance at a wavelength of 380 nm is 10% or less. Therefore, it is effective to add a UV absorber.
The addition amount at this time is 0.1 to 5 parts by mass with respect to a total of 100 parts by mass of the acrylic resin and the styrene resin from the balance between the ultraviolet absorption effect and the reduction in optical characteristics, mechanical characteristics, and heat resistance. It is preferable that
When the film also serves as a polarizing plate protective film, the retardation film of the present invention may be directly attached to a polarizing film or the like (for example, a stretched film of polyvinyl alcohol dyed with iodine or a dye).

  Examples of ultraviolet absorbers include benzotriazole compounds, triazine compounds, benzoate compounds, benzophenone compounds, oxybenzophenone compounds, phenol compounds, oxazole compounds, and malonic ester compounds. , Cyanoacrylate compounds, lactone compounds, salicylic acid ester compounds, benzoxazinone compounds, and the like. Preferred are benzotriazole-based compounds and benzotriazine-based compounds. These may be used alone or in combination of two or more.

The vapor pressure (P) at 20 ° C. of the ultraviolet absorber is preferably 1.0 × 10 −4 Pa or less, like other additives, because of excellent molding processability. More preferably, the vapor pressure (P) is 1.0 × 10 −6 Pa or less, and particularly preferably, the vapor pressure (P) is 1.0 × 10 −8 Pa or less.
The melting point (Tm) of the ultraviolet absorber is preferably 80 ° C. or higher, like other additives, because of excellent molding processability. More preferably, the melting point (Tm) is 130 ° C. or more, and the melting point (Tm) is particularly preferably 160 ° C. or more.
In addition, the mass reduction rate when the ultraviolet absorber is heated from 23 ° C. to 260 ° C. at a rate of 20 ° C./min is 50% or less, as in the case of other additives, so that the moldability is excellent. Therefore, it is preferable. A more preferable range is a mass reduction rate of 15% or less, and a particularly preferable range is a mass reduction rate of 2% or less.

  The manufacturing method of the resin composition used as the material of the retardation film in the present invention is not particularly limited, and a known method can be used. For example, using a kneading machine such as a single screw extruder, twin screw extruder, Banbury mixer, brabender, various kneaders, etc., resin components, hydrolysis inhibitors and other components as necessary And can be manufactured by melt-kneading.

Materials become resin composition of the retardation film of the present invention, the absolute value of the photoelastic coefficient is 0 Pa ^-1 or more, preferably 5.0 × 10 ^-12 Pa ^-1 or less. The photoelastic coefficient is a coefficient representing the ease with which birefringence changes due to an external force, and is described in various documents (for example, Chemical Review, No. 39, 1998 (published by the Academic Publishing Center)). In the present invention, it is defined by the following formula.
C = Δn / σ Δn = n1-n2
(Wherein, C: photoelastic coefficient, σ: stretching stress [Pa], Δn: birefringence in the plane direction when stress is applied, n1: refractive index for light having a polarization plane in a direction parallel to the stretching direction, n2: Refractive index for light having a polarization plane in the direction perpendicular to the stretching direction)

  The closer the absolute value of the photoelastic coefficient is to zero, the smaller the change in birefringence due to external force, which means that the change in birefringence designed for each application is small, and the optical characteristics are excellent.

Absolute values 0 or more photoelastic coefficient, still more preferably 4.5 × 10 ^-12 Pa ^-1 or less, 0 or more, and particularly preferably 4.0 × 10 ^-12 Pa ^-1 or less.

  In the resin composition used as the material of the retardation film of the present invention, such control of the photoelastic coefficient can be performed by the blending ratio of the resin components to be blended. That is, it can be controlled by the blending ratio of the acrylic resin and the styrene resin of the resin composition.

4). Description of retardation film molding method The retardation film molding method of the present invention is not particularly limited. Injection molding, sheet molding, blow molding, injection blow molding, inflation molding, extrusion It can be formed into a film by a known method such as molding, foam molding or cast molding, and a secondary processing molding method such as pressure forming or vacuum forming can also be used. Of these, extrusion molding and cast molding are preferably used. At this time, for example, an unstretched film can be extruded using an extruder or the like equipped with a T die, a circular die, or the like. When obtaining a molded product by extrusion molding, it is possible to use a material in which various resin components, additives, and the like are previously melt-kneaded, or to perform molding via melt-kneading at the time of extrusion molding. In addition, an unstretched film can be cast-molded by dissolving the various resin components using a solvent common to the various resin components, for example, a solvent such as chloroform and methylene dichloride, and then solidifying by casting and solidifying.

  Further, if necessary, the unstretched film can be uniaxially stretched in the mechanical flow direction, uniaxially stretched in the direction perpendicular to the mechanical flow direction, and a sequential biaxial stretching method of roll stretching and tenter stretching, A biaxially stretched film can also be produced by stretching by a simultaneous biaxial stretching method by tenter stretching, a biaxial stretching method by tuber stretching, or the like.

5. Description of optical properties of retardation film The retardation film of the present invention preferably has a high refractive index in a direction perpendicular to the film surface. That is, the thickness direction retardation (Rth) is preferably a negative value. For example, in the IPS mode liquid crystal display device as described above, since the liquid crystal molecules have a homogeneous alignment substantially parallel to the substrate surface, the optical compensation is performed in a direction perpendicular to the film surface. This is because it is effective to use a film having a high refractive index.

  Specifically, the retardation (Rth) in the thickness direction of the retardation film of the present invention is preferably −2000 to −10 nm, more preferably −1500 to −20 nm, and particularly preferably −1000 to −1000. 30 nm.

In the present invention, retardation in the plane direction (Re), retardation in the thickness direction (Rth), and Nz are defined as follows.
Re = (nx−ny) × d,
Rth = [(nx + ny) / 2−nz] × d
Nz = (nx−nz) / | (nx−ny) |
(Where nx is the main refractive index in the x direction when x is the direction in which the refractive index is maximum in the film plane (slow axis direction), ny is the direction perpendicular to the x direction in the film plane (advanced) The main refractive index in the y direction when the phase axis direction) is y, nz: the main refractive index in the film thickness direction, and d: the film thickness (nm).)

  By utilizing such a retardation, the retardation film of the present invention can be applied to various types of optical compensation films for liquid crystal display devices such as IPS mode, ¼ wavelength plates, ½ wavelength plates. It is used as a retardation film.

  Further, the retardation film of the liquid crystal display device is required to further improve the image quality by performing not only optical compensation of the liquid crystal cell but also optical compensation of the polarizing plate and other members. Therefore, it is desired that the retardation can be controlled in a wide range.

  The retardation control of the retardation film is usually performed by controlling the stretching conditions of the film. This is because the retardation is caused by the degree of molecular orientation due to stretching of the film and the thickness of the film itself. When Re is set to 10 nm or more and Rth is set to -10 nm or less, uniaxial stretching with a high stretching ratio and biaxial stretching with greatly different stretching ratios in the mechanical flow direction and the direction orthogonal to the mechanical flow direction are preferably used. In the case of uniaxial stretching, the stretching ratio is preferably 10% or more, more preferably 30% or more, and most preferably 50% or more. In the case of biaxial stretching, the ratio (MD direction / TD direction) of the draw ratio between the mechanical flow direction (MD direction) and the direction orthogonal to the mechanical flow direction (TD direction) is 0.67 or less or 1.5 Preferably, it is preferably 0.55 or less, or 1.8 or more, and most preferably 0.5 or less or 2 or more.

  The draw ratio as described above is a standard for obtaining the target retardation, and various drawing conditions can be applied to obtain the target retardation. However, from the viewpoint of heat resistance and strength, the draw ratio is preferably 0.1% or more and 1000% or less in at least one of the mechanical flow direction and the direction orthogonal to the mechanical flow direction. It is more preferably 2% or more and 600% or less, and particularly preferably 0.3% or more and 300% or less. By designing in this range, a retardation film preferable in heat resistance and strength can be obtained.

  In the present invention, the thickness of the retardation film is preferably 0.1 μm or more from the viewpoint of handling properties, and preferably 300 μm or less from the viewpoint of thinning required in the technical field. For the same reason, the range of 0.2 to 250 μm is more preferable, and the range of 0.3 to 200 μm is particularly preferable.

In the present invention, the retardation film is preferably a negative uniaxial optical element whose refractive index distribution satisfies ny <nx = nz. Ideally, a negative uniaxial optical element whose refractive index distribution satisfies ny <nx = nz has an optical axis in one direction in the plane. In the present invention, nx = nz includes not only the case where nx and nz are completely the same, but also the case where ny and nz are substantially the same. Here, “when nx and nz are substantially the same” means that the absolute value of nx−nz (= Nz × Re / d) is 1.0 × 10 ⁻³ or less. The definitions of Nz, Re, and d are as described above.
A phase difference film satisfying such a relationship is called a negative A plate, and is a liquid crystal panel generated due to a phase difference value of a polarizing plate or a component disposed between the polarizing plate and the liquid crystal cell ( It is used to reduce light leakage in an oblique direction in black display of a liquid crystal display device).

  When the retardation film of the present invention is used as a negative A plate, the in-plane retardation (Re) is 40 nm to 1100 nm, preferably 40 nm to 500 nm, more preferably 50 nm to 300 nm. By setting the above range, the functions of the optical elements can be exhibited synergistically, the contrast ratio in the oblique direction of the liquid crystal display device can be increased, and the color shift amount in the oblique direction can be reduced.

  When the retardation film of the present invention is used as a negative A plate, a preferable Nz coefficient is −0.5 or more and 0 or less, more preferably −0.4 or more and 0 or less, and particularly preferably −0. 3 or less and 0 or less. The Nz coefficient of an ideal negative A plate is 0. The closer the Nz coefficient is to 0, the higher the contrast ratio in the oblique direction of the liquid crystal display device, and the smaller the color shift amount in the oblique direction.

In the present invention, it is also preferable that the phase difference film satisfies nx = ny <nz. A phase difference film satisfying such a relationship is called a positive C plate. A negative uniaxial optical element. Ideally, a negative uniaxial optical element whose refractive index distribution satisfies nx = ny <nz has an optical axis in one direction in the plane. In the present invention, nx = ny includes not only the case where nx and ny are completely the same, but also the case where nx and ny are substantially the same. Here, “when nx and ny are substantially the same” means that the absolute value of nx−ny = (Re / d) is 1.0 × 10 ⁻³ or less. The definitions of Re and d are as described above.

  When the retardation film of the present invention is used as a positive C plate, the in-plane retardation (Re) is less than 40 nm, preferably 20 nm or less, more preferably 10 nm or less. The theoretical limit value of the in-plane retardation (Re) of the positive C plate is 0 nm.

  When the retardation film of the present invention is used as a positive C plate, the preferred thickness direction retardation (Rth) is -20 nm or less, more preferably -60 nm or less, and particularly preferably -90 nm or less. . By setting the above range, the function of the phase difference film is exhibited synergistically, the contrast ratio in the oblique direction of the liquid crystal display device can be increased, and the color shift amount in the oblique direction can be reduced.

6). Description of Polarizing Plate Protective Film Since the retardation film of the present invention has high mechanical strength, it can also be used as a protective film for various optical elements. In particular, since the retardation film of the present invention has optical anisotropy, it can be suitably used as a polarizing plate protective film. The case where the retardation film of this invention is used as a polarizing plate protective film below is demonstrated.

A polarizing plate can be produced by laminating the retardation film of the present invention on a polarizing film as a polarizing plate protective film. In the present invention, it is preferable to laminate a retardation film on one surface of the polarizing film and to laminate a protective film having optical isotropy on the other surface.
Usually, since the protective film aims at protecting the polarizing film, an optically isotropic film such as a triacetyl cellulose film is used.
On the other hand, in the present invention, the optically anisotropic retardation film of the present invention is laminated as a protective film on one surface, and the optically isotropic protective film is laminated on the other surface. To do. As a result, the protective film on one side also serves as a retardation film, so that a retardation film made of a polycarbonate resin or a cycloolefin resin that is usually affixed on the protective film of the polarizing plate is omitted. Further, it is possible to reduce the thickness of the polarizing plate and improve the productivity.
Moreover, since there is no process which adhere | attaches another retardation film on a protective film, it is excellent in productivity.

    When a retardation film having a Re of 10 nm or more is used as a retardation film laminated on one surface, it functions as a quarter-wave plate, a half-wave plate, other retardation films, and a protective film. Will have both

  The optically isotropic protective film laminated on the other surface of the polarizing film preferably has a smaller Re, preferably Re is 10 nm or less, more preferably 8 nm or less, and even more preferably 5 nm or less.

In the present invention, as an optically isotropic protective film laminated on the other surface, it is preferable to use a film obtained by molding a resin composition containing an acrylic resin and not containing a styrene resin. . In the present invention, the “resin composition containing an acrylic resin and not containing a styrene resin” also includes an acrylic resin.
Here, the definition of acrylic resin is as above-mentioned.

  Specific examples of the acrylic resin include methacrylic acid alkyl ester such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, 2-acrylic acid 2- Examples thereof include those obtained by polymerizing one or more monomers selected from acrylic acid alkyl esters such as ethylhexyl.

Among these, a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and other monomers is particularly preferable.
Examples of monomers copolymerizable with methyl methacrylate include other alkyl alkyl methacrylates, alkyl acrylates, aromatic vinyl compounds such as styrene, vinyl toluene and α-methyl styrene; acrylonitrile, methacrylonitrile, etc. Vinyl cyanides; maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; unsaturated carboxylic acid anhydrides such as maleic anhydride; unsaturated acids such as acrylic acid, methacrylic acid and maleic acid . These may be used alone or in combination of two or more.

Among these monomers that are copolymerizable with methyl methacrylate, alkyl acrylates are particularly excellent in heat decomposability and have high fluidity during the molding of methacrylic resins obtained by copolymerizing these. Therefore, it is preferable.
The amount of alkyl acrylates used when methyl acrylate is copolymerized with methyl methacrylate is preferably 0.1% by mass or more from the viewpoint of heat decomposability, and 15 from the viewpoint of heat resistance. It is preferable that it is below mass%. More preferably, it is 0.2-14 mass%, and it is especially preferable that it is 1-12 mass%.
As the alkyl acrylates, methyl acrylate and ethyl acrylate are preferable because the effect of improving the fluidity during the molding process described above can be obtained even by copolymerizing with a small amount of methyl methacrylate.

  The mass average molecular weight of the acrylic resin is preferably 50,000 to 200,000. The mass average molecular weight is preferably 50,000 or more from the viewpoint of the strength of the molded product, and preferably 200,000 or less from the viewpoint of molding processability and fluidity. A more preferable range is 70,000 to 150,000. In the present invention, isotactic polymethacrylate and syndiotactic polymethacrylate can be used simultaneously.

As a method for producing an acrylic resin, for example, generally used polymerization methods such as cast polymerization, bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, and anionic polymerization can be used. It is preferable to avoid mixing of foreign substances as much as possible. From this viewpoint, bulk polymerization and solution polymerization without using a suspending agent or an emulsifier are preferable. Specifically, the method described in Japanese Patent Publication No. 63-1964 can be used.
When solution polymerization is performed, a solution prepared by dissolving a mixture of monomers in an aromatic hydrocarbon solvent such as toluene or ethylbenzene can be used. In the case of polymerization by bulk polymerization, the polymerization can be started by irradiation with free radicals generated by heating or ionizing radiation as is usually done.

As the initiator used for the polymerization reaction, any initiator used in radical polymerization can be used. For example, azo compounds such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butyl peroxide- An organic peroxide such as 2-ethylhexanoate can be used.
In particular, when polymerization is carried out at a high temperature of 90 ° C. or higher, solution polymerization is generally used. Initiators and the like are preferred. Specifically, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, Examples thereof include 1-azobis (1-cyclohexanecarbonitrile) and 2- (carbamoylazo) isobutyronitrile. These initiators can be used in the range of 0.005 to 5 mass%, for example.

  As the molecular weight regulator used as necessary in the polymerization reaction, any of those used in radical polymerization can be used, for example, mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate, and the like. It is mentioned as preferable. These molecular weight regulators are added in a concentration range such that the polymerization degree of the acrylic resin (d) is controlled within a preferable range.

  The acrylic resin used in the present invention is preferably a copolymer having a methacrylate unit and / or an acrylate unit, an aromatic vinyl compound unit, and a compound unit represented by the following general formula [1].

  General formula [1]

（ＸはＯまたは、Ｎ−Ｒを示す。Ｏは酸素原子、Ｎは窒素原子、Ｒは水素原子、アルキル基、アリ−ル基またはシクロアルカン基である）

(X represents O or N—R. O is an oxygen atom, N is a nitrogen atom, R is a hydrogen atom, an alkyl group, an aryl group, or a cycloalkane group)

  As the methacrylic acid ester and / or acrylic acid ester copolymerized with the compound represented by the general formula [1], methyl methacrylate is preferable. Examples of the aromatic vinyl compound include α-alkyl-substituted styrene such as α-methylstyrene and α-methyl-p-methylstyrene, and styrene is preferable.

  As the compound represented by the general formula [1], a compound in which X = O, that is, maleic anhydride is preferable. Furthermore, from the viewpoint of heat resistance and photoelastic coefficient, the methyl methacrylate unit in the copolymer is 40 to 90% by mass, the styrene unit is 5 to 40% by mass, the maleic acid unit is 5 to 20% by mass, and It is preferable that the copolymerization ratio of the styrene unit to the copolymerization ratio of the maleic acid unit is 1 to 3 times. More preferably, the methyl methacrylate unit in the copolymer is 40 to 90% by mass, the maleic anhydride unit is 5 to 19% by mass, and the styrene unit is 10 to 40% by mass, and particularly preferably in the copolymer. The methyl methacrylate unit is 45 to 88% by mass, the maleic anhydride unit is 6 to 15% by mass, and the styrene unit is 16 to 40% by mass.

Another preferred example of the acrylic resin is a copolymer containing a methacrylic ester and / or an acrylic ester unit, an aromatic vinyl compound unit, and an acid anhydride unit having a 6-membered ring structure. This copolymer containing an acid anhydride unit having a 6-membered ring structure is suitable for an optical material because it has excellent heat resistance and the design of a molded product obtained therefrom is easy to design.
As the methacrylic acid ester and / or acrylic acid ester which is the first monomer component of the copolymer containing an acid anhydride unit having a 6-membered ring structure, methyl methacrylate is preferable, and the second monomer component is Examples of the aromatic vinyl compound include α-alkyl-substituted styrene such as α-methylstyrene and α-methyl-p-methylstyrene, and styrene is preferable.
Further, the acid anhydride unit having a 6-membered ring structure, which is the third unit of the copolymer containing an acid anhydride unit having a 6-membered ring structure, includes an unsaturated carboxylic acid monomer and, if necessary, an unsaturated carboxylic acid. After the acid alkyl ester monomer and other monomer components are polymerized to form a copolymer, the copolymer is heated in the presence or absence of a suitable catalyst to remove alcohol and / or Alternatively, it can be produced by carrying out an intramolecular cyclization reaction by dehydration. In this case, typically, the carboxyl group of the unsaturated carboxylic acid unit of 2 units is dehydrated by heating the copolymer, or the alcohol group from the adjacent unsaturated carboxylic acid unit and unsaturated carboxylic acid alkyl ester unit is 1 unit of an acid anhydride unit having a 6-membered ring structure is generated.
Examples of the unsaturated carboxylic acid monomer for producing a 6-membered ring acid anhydride unit include methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, cinnamic acid, and the like. Examples of the carboxylic acid alkyl ester monomer include methyl methacrylate and methyl acrylate.
A copolymer containing an acid anhydride unit having a 6-membered ring structure is disclosed in JP-B-02-26641, JP-A-2006-266543, JP-A-2006-274069, JP-A-2006-274071, and JP-A-2006-274071. The composition ratio can be determined, manufactured, and evaluated with reference to the methods described in JP 2006-283013 A and JP 2005-162835 A.

  The melt index (ASTM D1238; I condition) of the acrylic resin used in the present invention is preferably 10 g / 10 min or less from the viewpoint of the strength of the protective film obtained by molding the acrylic resin. More preferably, it is 6 g / 10 minutes or less, More preferably, it is 3 g / 10 minutes or less.

The optically isotropic protective film laminated on the other surface of the polarizing film in the present invention can contain an aliphatic polyester resin in addition to the acrylic resin.
Examples of the aliphatic polyester-based resin include a polymer mainly composed of aliphatic hydroxycarboxylic acid and a polymer mainly composed of aliphatic polyvalent carboxylic acid and aliphatic polyhydric alcohol. .
Specific examples of the polymer having an aliphatic hydroxycarboxylic acid as a main component include polyglycolic acid, polylactic acid, poly-3-hydroxybutyric acid, poly-4-hydroxybutyric acid, poly-4-hydroxyvaleric acid, poly-3-hydroxy Hexanoic acid and polycaprolactone are exemplified, and specific examples of the polymer mainly comprising an aliphatic polyvalent carboxylic acid and an aliphatic polyvalent alcohol include polyethylene adipate, polyethylene succinate, Examples include polybutylene adipate and polybutylene succinate. These aliphatic polyester resins can be used alone or in combination of two or more.

  Among these aliphatic polyester-based resins, polymers having hydroxycarboxylic acid as a main constituent component are preferable, and polylactic acid-based resins are particularly preferably used. These (e) components can use 1 or more types.

  Examples of the polylactic acid-based resin include polymers having L-lactic acid and / or D-lactic acid as main constituent components.

In the polylactic acid-based resin, the constituent molar ratio of the L-lactic acid unit and the D-lactic acid unit is preferably 100% for both the L-form and the D-form, and either the L-form or the D-form is preferably 85% or more. More preferably, one is 90% or more, and still more preferably one is 94% or more. In the present invention, poly-L lactic acid mainly composed of L-lactic acid and poly-D lactic acid mainly composed of D-lactic acid can be used simultaneously.
The polylactic acid-based resin may be copolymerized with a lactic acid derivative monomer other than L-form or D-form, or other components copolymerizable with lactide. Examples of such components include dicarboxylic acids and polyhydric alcohols. , Hydroxycarboxylic acid, lactone and the like. The polylactic acid resin can be polymerized by a known polymerization method such as direct dehydration condensation or ring-opening polymerization of lactide. If necessary, the molecular weight can be increased using a binder such as polyisocyanate.
The mass average molecular weight range of the polylactic acid-based resin is preferably 30,000 or more from the viewpoint of mechanical properties, and more preferably 1,000,000 or less from the viewpoint of workability. More preferably, it is 50,000-500,000, Most preferably, it is 100,000-280,000.

  In addition, the polylactic acid-based resin may contain 0.1 to 30% by mass of a copolymer component other than lactic acid as long as the object of the present invention is not impaired. Examples of such other copolymer component units include polyvalent carboxylic acids, polyvalent alcohols, hydroxycarboxylic acids, and lactones. Specifically, oxalic acid, malonic acid, succinic acid, glutaric acid, Adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, fumaric acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium sulfone Polyvalent carboxylic acids such as isophthalic acid; ethylene glycol, propylene glycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol, decandiol, 1,4-cyclohexanedimethanol -Nole, neopentyl glycol, glycerin, trimethyl -Rupropane, pentaerythritol, bisphenol A, aromatic polyhydric alcohol obtained by addition reaction of bisphenol with ethylene oxide, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol And polyhydric alcohols such as polytetramethylene glycol; hydroxy such as glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid, hydroxybenzoic acid Carboxylic acids; lactones such as glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, and δ-valerolactone can be used. These copolymer components can be used alone or in combination of two or more.

  As a method for producing an aliphatic polyester-based resin, a known polymerization method can be used. In particular, for a polylactic acid-based resin, a direct polymerization method from lactic acid, a ring-opening polymerization method via lactide, or the like can be employed. .

  In the present invention, when the optically isotropic protective film contains an acrylic resin and an aliphatic polyester resin, the ratio (part by mass) of the acrylic resin is the sum of the acrylic resin and the aliphatic polyester resin. The amount is preferably 0.1 to 99.9 parts by mass, more preferably 50 to 99.9 parts by mass with respect to 100 parts by mass based on the photoelastic coefficient, strength, heat resistance, and haze value. 60 to 95 parts by mass is particularly preferable. When it is 50 parts by mass or more, the haze value in a moist heat atmosphere becomes small, which is preferable. When the haze value is small or the change is small, it can be suitably used for display applications.

  The proportion (parts by mass) of the aliphatic polyester resin is 0.1 to 0.1 parts in terms of the photoelastic coefficient, strength, heat resistance, and haze value with respect to 100 parts by mass of the total amount of the acrylic resin and the aliphatic polyester resin. It is preferably 99.9 parts by mass, more preferably 0.1 to 50 parts by mass, and particularly preferably 5 to 40 parts by mass. When it is 50 parts by mass or less, the haze value in a moist and heat atmosphere is preferably reduced. When the haze value is small or the change is small, it can be suitably used for display applications.

  In the present invention, the thickness of the protective film having optical isotropy is preferably 0.1 μm or more from the viewpoint of handling properties, and preferably 300 μm or less from the viewpoint of thinning. For the same reason, the range of 0.2 to 250 μm is more preferable, and the range of 0.3 to 200 μm is particularly preferable.

  It is preferable to use an optically isotropic adhesive for laminating the polarizing film, the retardation film, and the protective film. Examples of such an adhesive include polyvinyl alcohol adhesives and urethane adhesives. , Epoxy adhesives, acrylic adhesives and the like. When the adhesive property between the polarizing film and the protective film is poor, it is preferable that the protective film is appropriately bonded with the polarizing film after an easy adhesion treatment such as a corona treatment, a primer treatment or a coating treatment.

  Optically isotropic protection obtained by laminating the retardation film of the present invention on one side of a polarizing film and molding a resin composition containing an acrylic resin and no styrene resin on the other side When films are laminated, defects such as warpage and curl due to characteristic differences between resins and abnormalities due to stress due to differences in hygroscopicity are reduced.

  In addition to the acrylic resin, other resins can be added to the optically isotropic protective film laminated on the other surface of the polarizing film in the present invention as long as the effect is not impaired. Other resin components at this time include polyolefins such as polyethylene and polypropylene; polyamides, polyphenylene sulfides, polyether ether ketones, polyesters, aliphatic polyester resins, polysulfones, polyphenylene oxides, polyimides, polyether imides, polyacetors. And thermoplastic resins such as phenol; and thermosetting resins such as phenol resin, melamine resin, silicone resin, and epoxy resin. One or more of these resin components can be used.

In the present invention, the polarizing film is not particularly limited. For example, a polarizing film obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched resin film is preferable.
Such a polarizing film can be manufactured using a well-known method, for example, can be manufactured by the method described in Unexamined-Japanese-Patent No. 2002-174729 etc. Specifically, it is as follows.
As the resin constituting the polarizing film, a polyvinyl alcohol resin is preferable, and a polyvinyl alcohol resin obtained by saponifying a polyvinyl acetate resin is preferable. Here, examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of other monomers copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. Further, the saponification degree of the polyvinyl alcohol-based resin is preferably 85 to 100 mol%, more preferably 98 to 100 mol%. This polyvinyl alcohol-based resin may be further modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used. The degree of polymerization of the polyvinyl alcohol-based resin is preferably 1000 to 10,000, and more preferably 1500 to 10,000.

For example, a polarizing film is a step of producing a film from a resin and uniaxially stretching, a step of dyeing a stretched polyvinyl alcohol-based resin film with a dichroic dye, and adsorbing iodine or a dichroic dye, two-color It can be manufactured through a step of treating a polyvinyl alcohol-based resin film adsorbed with a functional dye with an aqueous boric acid solution and a step of washing with water after the treatment with an aqueous boric acid solution.
Uniaxial stretching may be performed before dyeing with a dichroic dye, may be performed simultaneously with dyeing with a dichroic dye, or may be performed after dyeing with a dichroic dye. When uniaxial stretching is performed after dyeing with a dichroic dye, uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. It is also possible to perform uniaxial stretching in a plurality of stages.
Uniaxial stretching may be performed uniaxially between rolls having different peripheral speeds, or may be uniaxially stretched using a thermal roll. Moreover, the dry-type extending | stretching which extends | stretches in air | atmosphere may be sufficient, and the wet extending | stretching which extends | stretches in the state swollen with the solvent may be sufficient. The draw ratio is usually about 4 to 8 times.

In order to dye the resin film with the dichroic dye, for example, the resin film may be immersed in an aqueous solution containing the dichroic dye. Here, examples of the dichroic dye include iodine and dichroic dyes.
When iodine is used as the dichroic dye, a method of immersing and dyeing a resin film in an aqueous solution containing iodine and potassium iodide can be employed. The iodine content in this aqueous solution is preferably about 0.01 to 0.5 parts by mass per 100 parts by mass of water, and the potassium iodide content is 0.5 to 10 parts by mass per 100 parts by mass of water. It is preferable that it is a grade. The temperature of this aqueous solution is preferably about 20 to 40 ° C., and the immersion time in this aqueous solution is preferably about 30 to 300 seconds.
When a dichroic dye is used as the dichroic dye, a method of immersing and dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing the dichroic dye can be employed. The content of the dichroic dye in this aqueous solution is preferably about 1 × 10 ⁻³ to 1 × 10 ⁻² parts by mass per 100 parts by mass of water. This aqueous solution may contain an inorganic salt such as sodium sulfate. The temperature of this aqueous solution is preferably about 20 to 80 ° C., and the immersion time in this aqueous solution is preferably about 30 to 300 seconds.

  The boric acid treatment after dyeing with the dichroic dye is performed by immersing the dyed resin film in an aqueous boric acid solution. The boric acid content in the boric acid aqueous solution is preferably about 2 to 15 parts by mass, more preferably about 5 to 12 parts by mass per 100 parts by mass of water. When iodine is used as the dichroic dye, the aqueous boric acid solution preferably contains potassium iodide. The content of potassium iodide in the boric acid aqueous solution is preferably about 2 to 20 parts by mass, more preferably 5 to 15 parts by mass per 100 parts by mass of water. The immersion time in the boric acid aqueous solution is preferably about 100 to 1200 seconds, more preferably about 150 to 600 seconds, and further preferably about 200 to 400 seconds. Moreover, it is preferable that the temperature of boric-acid aqueous solution is 50 degreeC or more, More preferably, it is 50-85 degreeC.

The resin film after the boric acid treatment is preferably washed with water. The washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol-based resin film in water. After washing with water, a drying process is appropriately performed to obtain a polarizing film. The water temperature in the water washing treatment is preferably about 5 to 40 ° C., and the immersion time is preferably about 2 to 120 seconds. It is preferable that the drying process performed after that is performed using a hot air dryer or a far-infrared heater. The drying temperature is preferably 40 to 100 ° C. The treatment time in the drying treatment is preferably about 120 seconds to 600 seconds.
The final film thickness is preferably 5 to 200 [mu] m, more preferably 10 to 150 [mu] m, and particularly preferably 15 to 100 [mu] m from the viewpoint of easy handling of the film and the requirement for thinning the display.

  It is preferable to use an optically isotropic adhesive for laminating the polarizing film with the retardation film or the protective film. Examples of the adhesive include a polyvinyl alcohol adhesive, a urethane adhesive, and an epoxy adhesive. Examples thereof include an adhesive and an acrylic adhesive. When the adhesion between the polarizing film and the resin film is poor, the film is bonded to the polarizing film after appropriately applying an easy adhesion treatment such as a corona treatment, a plasma treatment, or a coating treatment.

  The retardation film of the present invention can be subjected to surface functionalization treatment such as antireflection treatment, transparent conductive treatment, electromagnetic wave shielding treatment, and gas barrier treatment.

The retardation film of the present invention is useful for improving the image quality of IPS mode liquid crystal display devices used for various displays such as televisions, personal computers, mobile phones, car navigation systems, medical equipment, and industrial equipment.
Moreover, the circularly-polarizing plate which bonded the retardation film of this invention and the polarizing film can reduce the internal reflection of a display apparatus when it is used for a reflection type liquid crystal display or an organic EL display, and is useful.

[Example]
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples.
First, the evaluation methods used in the present invention and examples will be described.
<1> Evaluation Method <1-1> Measurement of Retardation (Re, Rth, Nz) Measurement was performed using a retardation measurement device “RETS-100” manufactured by Otsuka Electronics Co., Ltd.
<1-2> Measurement of photoelastic coefficient: Cut out a film to 5 cm × 1 cm, chuck it so that the distance between chucks is 3 cm, and measure the retardation while performing a tensile test at a speed of 0.1 mm / min. The retardation was measured using an apparatus (RETS-100), and the birefringence in the plane direction was measured.
A graph plotting the values measured in this way with the birefringence (Δn) as the y-axis and the tensile stress (σ) as the x-axis is obtained, the inclination of the initial straight line portion is obtained, and this is used as the optical elastic modulus. .
<1-3> Measurement of glass transition temperature (DSC method)
The measurement was performed using a differential scanning calorimeter “Pyris 1” manufactured by Perkin Elmer.
<1-4> Measurement of light transmittance The spectral spectrum was measured using U-3310 manufactured by Hitachi, Ltd., and the transmittance at 380 nm was determined.
<1-5> Measurement of warpage of polarizing plate The polarizing plate is cut into a square of 200 mm × 200 mm and placed on a horizontal and flat base so that the center of the film is in contact with the base, and an atmosphere of 23 ° C. and 50% RH. The film was left at rest for 72 hours, and the height at which the four corners of the cut film were warped from the table was calculated as an average.
<1-6> Measurement of durability of polarizing plate at high temperature and high humidity The degree of polarization before and after being held at 60 ° C. and 90% RH for 1000 hours is obtained according to the following formula, and the degree of polarization retention is calculated using this value. And durability was evaluated.
Degree of polarization (%) = {[(H ₂ −H ₁ ) / (H ₂ + H ₁ )] × ½} × 100
Here, H ₂ is a value (parallel transmittance) measured using a spectrophotometer in a state in which the orientation directions of the two polarizing plates are aligned in the same direction, and H ₁ is the two polarizations. It is a value (orthogonal transmittance) measured in a state where the orientation directions of the plates are superposed so as to be orthogonal to each other. Shimadzu UV-3150 spectrophotometer was used for the measurement of the degree of polarization.
The degree of polarization retention is a value obtained by multiplying 100 by the value obtained by dividing the degree of polarization after the retention test at 60 ° C. and 90% RH by the degree of polarization before the test. The larger the value, the better the durability.
In the measurement of the degree of polarization, when both the in-plane retardation (Re) of the first surface and the second surface is 10 nm or more, the influence of circularly polarized light becomes strong and is not suitable for the evaluation of the present invention. I didn't do it. For the same reason, when the in-plane retardation (Re) of either the first surface or the second surface is 10 nm or less, Re is 10 nm when the two polarizing plates are overlapped. Evaluation was performed by superimposing the following layers on the inside.

<2> Preparation of Raw Material <2-1> Methyl methacrylate / methyl acrylate copolymer (P-1)
1,1-di-t-butylperoxy-3,3,5-trimethyl was added to a monomer mixture consisting of 89.2 parts by weight of methyl methacrylate, 5.8 parts by weight of methyl acrylate, and 5 parts by weight of xylene. 0.0294 parts by mass of cyclohexane and 0.115 parts by mass of n-octyl mercaptan were added and mixed uniformly.
This solution is continuously supplied to a sealed pressure resistant reactor having an internal volume of 10 liters, polymerized with stirring at an average temperature of 130 ° C. and an average residence time of 2 hours, and then continuously sent to a storage tank connected to the reactor. The volatile matter was removed under a certain condition, and this was continuously transferred to an extruder in a molten state, and a methyl methacrylate / methyl acrylate copolymer (P-1) pellet was obtained by the extruder. .
The copolymer (P-1) has a methyl acrylate copolymerization ratio of 6.0% by mass, a melt flow rate value of 230 ° C. and a load of 3.8 kg measured in accordance with ASTM-D1238. Was 1.0 g / 10 min.

<2-2> Styrene / methacrylic acid copolymer (P-2)
Continuous solution polymerization was carried out using all the equipment made of stainless steel. 75.2% by mass of styrene, 4.8% by mass of methacrylic acid, and 20% by mass of ethylbenzene were used as a preparation liquid, and 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane was used as a polymerization initiator. This mixed solution was continuously supplied at a rate of 1 l / hr to a completely mixed polymerization reactor equipped with a stirrer having an internal volume of 2 l and polymerized at 136 ° C. A polymerization liquid containing 49% solids was continuously taken out, first preheated to 230 ° C., then kept at 230 ° C., and supplied to a devolatilizer with a reduced pressure of 20 Torr. It discharged continuously from the gear pump at the lower part of the volatilizer, and this was continuously transferred to the extruder in a molten state, and styrene / methacrylic acid copolymer (P-2) pellets were obtained with the extruder.
The obtained copolymer (P-2) was colorless and transparent. As a result of composition analysis by neutralization titration of this polymer, the copolymerization ratio of styrene was 92% by mass, and the copolymerization ratio of methacrylic acid was 8.1%. %Met. The melt flow rate measured at 230 ° C. under a load of 3.8 kg measured in accordance with ASTM-D1238 was 5.1 g / 10 min.

<2-3> Styrene / maleic anhydride copolymer (P-3)
Continuous solution polymerization was carried out using all the equipment made of stainless steel. A total of 100 parts by mass was prepared at a ratio of 91.7 parts by mass of styrene and 8.3 parts by mass of maleic anhydride. (However, both are not mixed.) 5 parts by mass of methyl alcohol and 0.03 part by mass of 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane as a polymerization initiator are mixed with styrene, It was set as the 1st preparation liquid. This first preparation solution was 0.95 kg / hr. Was continuously fed to a jacketed complete mixing polymerization machine having an internal volume of 4 L.
On the other hand, maleic anhydride heated to 70 ° C. was used as the second preparation liquid at 0.10 kg / hr. Was fed to the same polymerization machine at a speed of When the polymerization conversion rate became 54%, the polymerization solution was continuously removed from the polymerization machine, first preheated to 230 ° C., kept at 230 ° C., and supplied to a devolatilizer reduced to 20 torr, with an average retention of 0 After 3 hours, it was continuously discharged from the lower gear pump of the devolatilizer, and this was continuously transferred to the extruder in a molten state, and the styrene / maleic anhydride copolymer (P- The pellet of 3) was obtained.
The obtained styrene / maleic anhydride copolymer (P-3) was colorless and transparent. As a result of composition analysis by neutralization titration of this polymer, the copolymerization ratio of styrene was 85% by mass, and the copolymer of maleic anhydride units. The polymerization rate was 15% by mass. The melt flow rate measured at 230 ° C. under a load of 2.16 kg measured according to ASTM-D1238 was 2.0 g / 10 min. The photoelastic coefficient (unstretched) was 4.1 × 10 −12 Pa −1.
<2-4> Polystyrene resin (P-4)
As a general polystyrene resin, HF77 which is a standard grade made by PS Japan Co., Ltd. was prepared.
<2-5> Aliphatic polyester resin (P-5)
Polylactic acid (Kargildau 4032D) was used.
<2-6> UV absorber (U-1)
A benzotriazole-based compound (U-1) (Asahi Denka Co., Ltd., ADK STAB LA-31 (melting point (Tm): 195 ° C.) was prepared. Using Rigaku Denki Co., Ltd., ThermoPlus TG8120, It was 0.03% when the mass reduction | decrease rate at the time of heating up at a speed | rate of 20 degree-C / min from 23 degreeC to 260 degreeC was measured.

[Examples 1 to 22, Comparative Examples 1 to 4]
Using the resin composition having the composition shown in Tables 1 to 3, the T-die mounting extruder manufactured by Technobel (KZW15TW-25MG-NH type / width 150 mm T die mounting / lip thickness 0.5 mm) in-cylinder resin temperature, An unstretched film was obtained by adjusting the temperature to the conditions shown in Tables 1 to 3 and performing extrusion molding. The flow (extrusion direction) of the film was defined as the MD direction, and the direction perpendicular to the MD direction was defined as the TD direction.
And an unstretched film is cut out so that a width | variety may be set to 50 mm, uniaxial stretching (between chucks: 50 mm, chuck movement speed: 500 mm / min) is performed using the tension test machine on the conditions shown in Tables 1-3, and uniaxial stretching A film was obtained.
Further, the uniaxially stretched film was cut out to have a width of 50 mm, and uniaxial stretching (between chucks: 50 mm, chuck moving speed: 500 mm / min) was performed using a tensile tester under the conditions shown in Tables 1 to 3. The biaxially stretched film of 1-22 and Comparative Examples 1-4 was obtained.

Table 1 shows the optical characteristics of the retardation films of Examples 1 to 9 and Comparative Examples 1 to 3.
In each of the phase difference films of Examples 1 to 9, Rth became a negative value when Re was set to ¼ wavelength of 550 nm and around ½ wavelength. Furthermore, in these retardation films, it can be seen that Rth can be controlled in a wide range from -382 to -77 nm by controlling the composition of the material, stretching conditions, and the like.
This shows that the retardation film of the present invention can cope with various optical compensation conditions as well as an IPS mode liquid crystal display device.

In addition, the retardation films of Examples 1 to 9 have a glass transition temperature of about 120 ° C. or higher and have sufficient heat resistance to withstand practical use. Further, the absolute value of the photoelastic coefficient is 2 × 10 ⁻¹² Pa ⁻¹ or less, and a styrenic resin (polystyrene resin) which is a typical negative birefringent material such as Comparative Example 2 or Comparative Example 3. It can be seen that excellent optical stability of 1/3 or less of the absolute value of the photoelastic coefficient of

In addition, in the retardation films of Examples 7 to 9, the absolute value of the photoelastic coefficient is 1 × 10 ⁻¹² Pa ⁻¹ or less, which is lower than that of the retardation film of Example 6 having the same resin composition. It was. This is presumably because the ultraviolet absorber acted to cancel the photoelastic coefficient of the resin component. Although the glass transition temperature tended to be slightly lower than that in the case where no UV absorber was added (Example 6) due to the addition of the UV absorber, it was still 125 ° C. or higher and was sufficient to withstand practical use. Heat resistance.
Furthermore, in the retardation films of Examples 7 to 9, the light transmittance at 380 nm was about 1% by the addition of the ultraviolet absorber. This value satisfies the level generally required for a polarizing plate protective film, and it can be seen that the retardation film of the present invention is also useful as a polarizing plate protective film.

Table 2 shows the optical characteristics of the retardation films of Examples 10 to 17 and Comparative Example 4.
In the retardation films of Examples 10 to 17, the in-plane retardation Re was changed widely (140 to 1039 nm) by controlling the stretching conditions and the like. In any case, the Rth was designed to be a negative value. We were able to. In addition, the retardation films of Examples 10 to 17 had a smaller absolute value of the photoelastic coefficient than that of the retardation film made of polystyrene resin (Comparative Example 4).
In each of the retardation films of Examples 10 to 17, the in-plane retardation (Re = (nx−ny) × d) is a positive value, and nx−nz (= Nz × Re / d). Since the absolute value of is less than 1.0 × 10 ⁻³ , the relationship of ny <nx = nz was satisfied, and it could be used as a negative A plate. Thus, it was confirmed that the optical characteristics can be designed so that the retardation film of the present invention can be used as a negative A plate.

Table 3 shows the optical characteristics of the retardation films of Examples 18 to 22.
In each of the retardation films of Examples 18 to 22, the thickness direction retardation (Rth = [(nx + ny) / 2−nz] × d) is a negative value, and nx−ny (= Re / d). ) Is 1.0 × 10 ⁻³ or less, it satisfies the relationship of nx = ny <nz and can be used as a positive C plate. As described above, it was confirmed that the optical characteristics can be designed so that the retardation film of the present invention can be used as a positive C plate.

[Examples 23 to 36, Comparative Example 5]
(Manufacture of polarizing film)
Polyvinyl acetate was saponified (degree of saponification 98 mol%), molded, and the resulting polyvinyl alcohol film (thickness 75 μm) was composed of 1000 parts by mass of water, 7 parts by mass of iodine, and 105 parts by mass of potassium iodide. The film was immersed in an aqueous solution for 5 minutes to adsorb iodine to the film. Next, this film was stretched uniaxially in the machine direction 5 times in a 4% by mass boric acid aqueous solution at 40 ° C., and then dried in a tension state to obtain a polarizing film.
(Manufacture of protective film for comparison)
i) Acrylic resin protective film (Reference Examples 1 and 2)
In the same manner as in Examples 1 to 22 and Comparative Examples 1 to 4, the protective films of Reference Examples 1 and 2 were produced using the resin compositions shown in Table 4 under the conditions shown in Table 4.
Table 4 shows the film thickness and in-plane retardation of Reference Examples 1 and 2.
ii) Triacetyl cellulose protective film (Reference Example 3)
As a typical example of a conventional polarizing plate protective film, a triacetyl cellulose-based protective film was produced as follows.
21 parts by mass of triacetyl cellulose, 2 parts by mass of triphenyl phosphate (plasticizer) and 1 part by mass of biphenyl diphenyl phosphate (plasticizer), 62 parts by mass of methylene chloride, 12 parts by mass of methanol A dope was prepared by dissolving in 2 parts by mass of n-butanol. The dope was cast on an endless metal support to form a film on the support. The film was dried on the support until the amount of the organic solvent in the film was 60% by mass, and the film was peeled off from the support.
The tenter was used to fix the lateral dimensions of the film, and in that state, the film was dried from both sides for 3 minutes until the amount of organic solvent in the film was 15% by mass (primary drying). After the film was peeled off from the support, the elongation in the longitudinal dimension of the film after the primary drying of the film was 4.5%. Furthermore, the film was dried using a roller until the amount of the organic solvent in the film was 0.5% by mass (secondary drying). The obtained film was wound up, and finally the surface was saponified to produce a triacetyl cellulose film having a thickness of 81 μm. The in-plane retardation of this film was 6 nm (Table 4).
iii) Cycloolefin-based protective film (Reference Example 4)
As a typical example of the polarizing plate protective film of the prior art, a cycloolefin resin film, which is an amorphous polyolefin resin, was produced as follows.
Addition polymerization of ethylene and norbornene was performed as a cyclic polyolefin to produce an ethylene-norbornene random copolymer (ethylene content: 65 mol%, MFR: 30 g / 10 min, number average molecular weight: 68000). 100 parts by mass of the resin obtained here was dissolved in a mixed solvent of 80 parts by mass of cyclohexane, 80 parts by mass of toluene, and 80 parts by mass of xylene, and a film having a thickness of 75 μm was produced by a casting method. The in-plane retardation of this film was 5 nm (Table 4).
iv) Heat-resistant acrylic resin-based protective film (Reference Example 5)
According to the method described in Japanese Patent Publication No. 63-1964, a methyl methacrylate-maleic anhydride-styrene copolymer was obtained.
The composition of the resulting methyl methacrylate-maleic anhydride-styrene copolymer was 74% by weight methyl methacrylate, 10% by weight maleic anhydride, and 16% by weight styrene, and the copolymer melt flow rate value ( ASTM-D1238; 230 ° C., 3.8 kg load) was 1.5 g / 10 min. This methyl methacrylate-maleic anhydride-styrene copolymer was molded and stretched under the conditions shown in Table 4 to produce a protective film of Reference Example 5.
Table 4 shows the film thickness and in-plane retardation of Reference Example 5.

(Manufacture of polarizing plates)
Using a 10% aqueous solution of a polyvinyl alcohol-based resin as an adhesive, Examples 9, 10 and 21, the retardation film of Test Example 1 and the protective films of Reference Examples 1 to 5 on both surfaces of the polarizing film are shown in Table 4. A polarizing plate was obtained by pasting together in the combination shown in FIG.

Tables 4 and 5 show the warpage and polarization degree retention of the polarizing plates of Examples 23 to 36 and Comparative Example 5.
From Tables 4 and 5, it was confirmed that the polarizing plate using the retardation film of the present invention as a protective film had little warpage and excellent durability at high temperature and high humidity. In particular, the warpage of the polarizing plates of Examples 23 to 25 which are common to Comparative Example 5 is smaller than that of the polarizing plate of Comparative Example 5 in that the film of Reference Example 3 is used as the protective film for the first surface. It is considered that this is because the retardation film of the present invention used as the protective film for the second surface has a function capable of hydrogen bonding and has an interaction with moisture.

The retardation film of the present invention is excellent in optical properties, productivity, and heat resistance, and can be suitably used as a retardation film used in various types of liquid crystal display devices including the IPS mode.
Moreover, the polarizing plate which bonded the retardation film and polarizing film of this invention can be used suitably as a reflection type liquid crystal display and a circularly-polarizing plate for organic electroluminescent displays.

Claims (14)

  A retardation film containing an acrylic resin and a styrene resin.   The retardation film according to claim 1, comprising 0.1 to 99.9 parts by mass of an acrylic resin with respect to 100 parts by mass of the total amount of the acrylic resin and the styrene resin.   The retardation film according to claim 1, wherein the acrylic resin is a methyl methacrylate / methyl acrylate copolymer.   The retardation film according to claim 1, wherein the styrene resin is a styrene / methacrylic acid copolymer.   The retardation film according to claim 1, wherein the styrene resin is a styrene / maleic anhydride copolymer.   The retardation film according to claim 1, wherein the retardation film has an in-plane retardation (Re) of 40 to 1100 nm and an Nz coefficient of −0.5 or more and 0 or less. The retardation film according to claim 6, wherein Re is 40 to 1100 nm and ny <nx = nz is satisfied.
In the formula, nx: main refractive index in the x direction when the direction in which the refractive index is maximum in the film plane (slow axis direction) is x, ny: a direction perpendicular to the x direction in the film plane (fast phase) Y is the main refractive index in the y direction, where y is the axial direction), and nz is the main refractive index in the film thickness direction.   The retardation film according to claim 1, wherein the retardation film has an in-plane retardation (Re) of less than 40 nm and a thickness direction retardation (Rth) of −20 nm or less. The retardation film according to claim 8, wherein Re is less than 40 nm and nx = ny <nz is satisfied.
In the formula, nx: main refractive index in the x direction when the direction in which the refractive index is maximum in the film plane (slow axis direction) is x, ny: a direction perpendicular to the x direction in the film plane (fast phase) Y is the main refractive index in the y direction, where y is the axial direction), and nz is the main refractive index in the film thickness direction.   The retardation film according to any one of claims 1 to 9, which is for an IPS mode liquid crystal display device.   The retardation film according to claim 1, which is for a liquid crystal display device using a liquid crystal cell substrate formed of a resin having positive intrinsic birefringence.   It is a polarizing plate by which a protective film is bonded together on both surfaces of a polarizing film, Comprising: At least one of this protective film is a retardation film as described in any one of Claims 1-11.   It is a polarizing plate by which a protective film is bonded on both surfaces of a polarizing film, and one of the protective films is the retardation film according to any one of claims 1 to 11, and the other is an acrylic resin. The polarizing plate according to claim 12, which is a film obtained by molding a resin composition containing no styrene resin.   It is a polarizing plate by which a protective film is bonded together on both surfaces of a polarizing film, Comprising: Both of this protective film are the retardation films described in any one of Claims 1-11.