JP4068120B2 - Optical compensation film - Google Patents

Description

The present invention relates to an optical compensation film .

In recent years, with the expansion of the display market, there has been an increasing demand for clearer images. Therefore, there is a demand for an optical material imparted with higher optical properties, not just a transparent material.
One of such advanced optical characteristics is birefringence. In general, a polymer has birefringence because the refractive index differs between the molecular main chain direction and the direction perpendicular thereto. Depending on the application, it is required to strictly control this birefringence. For example, in the case of a protective film used for a polarizing plate of a liquid crystal, a polymer material molded body having a smaller birefringence is required even if the total light transmittance is the same. A typical example is a film made of triacetylcellulose. On the other hand, by using this birefringence, it is possible to change linearly polarized light into circularly polarized light (1/4 wavelength plate, etc.) or compensate for the birefringence of liquid crystal (optical compensation film, such as retardation film). It becomes. Polycarbonate is well known as such a birefringent optical material.

In recent years, liquid crystal displays have become larger, and accordingly, it is necessary to increase the size of polymer optical elements such as retardation films. However, when the optical element is enlarged, the bias of the external force is generated. Therefore, when the optical element is made of a material that easily changes birefringence due to the external force, a distribution of birefringence occurs and the contrast becomes non-uniform. .
The ease of occurrence of birefringence change due to external force is expressed by a photoelastic coefficient. However, since the above-mentioned polycarbonate has a large photoelastic coefficient, a birefringent optical material having a small photoelastic coefficient instead of these is eagerly desired.

  As a retardation film containing a styrene resin, a retardation film made of a styrene-acrylonitrile copolymer is known (Patent Document 1). However, this film has a large photoelastic coefficient and is not satisfactory as a retardation film.

  Blend of styrene-acrylonitrile copolymer and acrylic resin (Non-patent Document 1), Blend of styrene-methacrylic acid copolymer and acrylic resin (Patent Document 2), Styrene-maleic anhydride copolymer and acrylic A blend of resin based resins (Non-Patent Document 2) itself is known. However, these blends are not used for optical materials.

  As a resin composition for an optical material containing a styrene-maleic anhydride copolymer, a resin composition comprising a styrene-maleic anhydride copolymer and a polycarbonate is known (Patent Document 3). However, this resin composition is a combination of resins having a positive photoelastic coefficient, and the absolute value of the photoelastic coefficient is large.

  As a film focusing on the positive / negative of intrinsic birefringence, a retardation film made of a resin having intrinsic birefringence of positive and negative (Patent Document 4) is also known. However, what is specifically disclosed in Patent Document 4 is a film made of a combination of resins having a positive photoelastic coefficient, and has a large photoelastic coefficient.

In addition, a retardation film made of a resin having positive and negative photoelastic coefficients is also known (Patent Document 5). However, in this retardation film, in order to provide birefringence necessary for the retardation film, the photoelastic coefficient is a large resin as a positive resin (60 × 10 ⁻⁸ cm ² / N
(= 60 × 10 ⁻¹² Pa ⁻¹ or more). Therefore, there is a problem that materials that can be used are limited, and other optical characteristics cannot be freely designed.

  Furthermore, recently, there is a demand for controlling not only the in-plane retardation of the retardation film but also the retardation in the thickness direction in order to obtain a higher image quality of the liquid crystal screen. And in the case of the phase difference film for horizontal electric field (IPS) mode liquid crystal displays which attracted attention in recent years, it is preferable that the thickness direction retardation is a negative value. However, a film made of triacetyl cellulose or polycarbonate, which is a general optical film, or a retardation film disclosed in Patent Document 5, has a positive retardation in the thickness direction. Therefore, in addition to a small absolute value of the photoelastic coefficient, an optical film having a negative retardation in the thickness direction is demanded.

JP 05-257014 A JP-A-56-98251 JP-A-7-233296 Japanese Patent Laid-Open No. 2002-40258 JP 2004-212971 A T.Nishimoto, POLYMER, vol.30, p.1279-1285, 1989 D.Chopra, Society of Plastics Engineers. Annual Technical Conference, 59th, vol.2, p.2326-2330, 2001

An object of the present invention is to provide an optical compensation film that exhibits high birefringence and has a small change in birefringence due to an external force, that is, a small absolute value of a photoelastic coefficient.
Furthermore, the present invention aims to provide an optical compensation film Thickness direction retardation is negative.

As a result of intensive studies on the birefringence of the resin composition, the present inventors have unified the positive and negative of the intrinsic birefringence of the resin as the main component, so that the resin composition can be obtained without using a resin having a large photoelastic coefficient. It has been found that high birefringence can be imparted to an object.
Furthermore, the present inventors have found that if the intrinsic birefringence of the resin as the main component is negative, the thickness direction retardation when the resin composition is made into a film can be made negative.
Based on the above knowledge, the present inventors include a resin (a) having a positive photoelastic coefficient and a negative intrinsic birefringence, and a resin (b) having a negative photoelastic coefficient and a negative intrinsic birefringence. It has been found that the resin composition can realize high birefringence and a small absolute value of photoelastic coefficient, and that the retardation in the thickness direction becomes negative when it is formed into a film , thereby completing the present invention.

The present invention is as follows.
Styrene-acrylonitrile copolymer having a positive photoelastic coefficient when unstretched at 23 ° C. and a negative intrinsic birefringence and an acrylonitrile content of 1 to 40% by mass, a methacrylic acid content of 0.1 to 50% by mass methacrylic acid copolymers and maleic anhydride content is 0.1 to 50 wt% styrene - - styrene resin (a) is selected from the group consisting of maleic acid anhydride copolymer, styrene is
An optical compensation film comprising a resin composition containing an acrylic resin (b) having a negative photoelastic coefficient when unstretched at 23 ° C. and a negative intrinsic birefringence,
The total content of the resin (a) and the resin (b) in the resin composition is 80% by mass or more,
The optical compensation film whose mass ratio ((a) / (b)) of resin (a) and resin (b) in the said resin composition is 20 / 80-80 / 20.

According to the present invention, it is possible to provide an optical compensation film that exhibits high birefringence and a small absolute value of the photoelastic coefficient. Moreover, the retardation of the optical compensation film can be controlled to a desired value by molding and stretching under specific conditions.
Therefore, when used in a liquid crystal display device or the like, an optical compensation film having a small distribution of birefringence caused by the bias of external force and excellent contrast uniformity can be obtained.

Hereinafter, the present invention will be specifically described.
The resin composition constituting the optical compensation film of the present invention is a styrene-acrylonitrile copolymer having a positive photoelastic coefficient when unstretched at 23 ° C., a negative intrinsic birefringence, and an acrylonitrile content of 1 to 40% by mass. polymers, styrene content of methacrylic acid is 0.1 to 50 wt% - methacrylic acid copolymer and maleic anhydride content is 0.1 to 50 wt% styrene - the group consisting of maleic anhydride copolymer And an acrylic resin (b) whose photoelastic coefficient when unstretched at 23 ° C. is negative and whose intrinsic birefringence is negative.

The “photoelastic coefficient” in the present invention is a coefficient representing the ease with which birefringence changes due to external force, and is defined by the following equation.
C _R [Pa ⁻¹ ] = Δn / σ _R
Here, σ _R is extensional stress [Pa], Δn is birefringence when stress is applied, and Δn is defined by the following equation.
Δn = n ₁ −n ₂
Here, n ₁ is the refractive index in the direction parallel to the stretching direction, and n ₂ is the refractive index in the direction perpendicular to the stretching direction.
The closer the value of the photoelastic coefficient is to zero, the smaller the change in birefringence due to external force, which means that the birefringence designed for each application is less likely to change due to external force.

In addition, “inherent birefringence” in the present invention is a value representing the magnitude of birefringence depending on orientation, and is defined by the following equation.
Intrinsic birefringence = npr−nvt
Here, npr is a refractive index in a direction parallel to the alignment direction of the polymer aligned with uniaxial order, and nvt is a refractive index in a direction perpendicular to the alignment direction.

  That is, in the present invention, a resin having a negative intrinsic birefringence means that when light is incident on a layer formed by orienting polymers constituting the resin in a uniaxial order, the light is refracted in the orientation direction. A resin whose rate is smaller than the refractive index of light in a direction perpendicular to the orientation direction.

The resin (a) will be described.
In the present invention, as the resin (a), scan styrene - acrylonitrile copolymer, styrene - methacrylic acid copolymer, styrene - used styrene resin selected from the group consisting of maleic anhydride copolymer. These styrenic resins are preferable because they have properties required for optical materials such as heat resistance and transparency.
Moreover, since styrene-acrylonitrile copolymer, styrene-methacrylic acid copolymer, and styrene-maleic anhydride copolymer are highly compatible with a polymer containing methyl methacrylate as a monomer component, resin ( It is particularly preferable when a polymer containing methyl methacrylate as a monomer component is used as b).

Styrene - For acrylonitrile copolymer, acrylonitrile content in the copolymer Ru 1 to 40% by mass. A more preferable range is 1 to 30% by mass, and an especially preferable range is 1 to 25%. When the content of acrylonitrile in the copolymer is 1 to 40% by mass, it is preferable because of excellent transparency.
Styrene - For methacrylic acid copolymers, methacrylic acid content in the copolymer is Ru 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 methacrylic acid 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.
Styrene - If maleic anhydride copolymer, maleic acid content in the copolymer is Ru 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.

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

The photoelastic coefficient of the resin (a) when not stretched at 23 ° C. is preferably 60 × 10 ⁻¹² Pa ⁻¹ or less, more preferably 30 × 10 ⁻¹² Pa ⁻¹ or less, and 6 × It is particularly preferably 10 ⁻¹² Pa ⁻¹ or less. When the photoelastic coefficient of the resin (a) is in this range, an optical film having a small photoelastic coefficient and a desired Rth can be obtained.

The resin (b) will be described.
In the present invention, an acrylic resin is used as the resin (b).
In the present invention, the acrylic resin refers to a polymer containing acrylic acid, methacrylic acid or a derivative thereof as a monomer component.

  Among these acrylic resins, in particular, a polymer containing an acrylic acid alkyl ester or a methacrylic acid alkyl ester as a monomer component is highly compatible with a styrene resin, and therefore a styrene resin is used as the resin (a). Particularly preferred when used.

  Specific examples of the acrylic resin containing an alkyl acrylate or alkyl methacrylate as a monomer component include methacrylic acid alkyl esters such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, and methyl methacrylate; methyl acrylate, Examples include those obtained by polymerizing one or more monomers selected from alkyl acrylates such as ethyl acrylate, butyl acrylate, isopropyl acrylate, and 2-ethylhexyl acrylate.

The acrylic resin containing an alkyl acrylate ester or an alkyl methacrylate ester as a monomer component includes those obtained by copolymerization of monomers other than methacrylic acid alkyl esters and acrylic acid alkyl esters.
Acrylic acid alkyl esters, methacrylic San'a alkyl ester can be copolymerized with methacrylic acid alkyl esters, as the monomer other than the acrylic acid alkyl ester, styrene, vinyl toluene, aromatic vinyl compounds such as α- 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 Etc. These may be used alone or in combination of two or more.
When monomer components other than methacrylic acid alkyl ester and acrylic acid alkyl ester are copolymerized, the copolymerization ratio is preferably less than 50% by mass with respect to methacrylic acid alkyl ester and acrylic acid alkyl ester. More preferably, it is 40 mass% or less, Most preferably, it is 30 mass% or less. Less than 50% by mass is preferable because optical properties such as total light transmittance are excellent.

Among polymers containing an alkyl acrylate ester or an alkyl methacrylate ester as a monomer component, a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate and another monomer is heat resistant and transparent. It is preferable because it has properties required for optical materials such as optical properties.
As the monomer copolymerized with methyl methacrylate, acrylic acid alkyl esters are particularly preferable because they are excellent in thermal decomposition resistance and have high fluidity during molding of a methacrylic resin obtained by copolymerization thereof. The amount of alkyl acrylates used when copolymerizing alkyl methacrylates with methyl methacrylate is preferably 0.1% by mass or more from the viewpoint of thermal decomposition resistance, and 15 masses from the viewpoint of heat resistance. % Or less is preferable. 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 are preferable because only a small amount of methyl acrylate is copolymerized with a small amount of methyl methacrylate because the effect of improving the fluidity during the molding process described above can be obtained remarkably.

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 the 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. For optical applications, it is preferable to avoid contamination of minute foreign substances as much as possible. From this viewpoint, bulk polymerization or solution polymerization without using a suspending agent or an emulsifier is 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 in the polymerization reaction, any initiator used in radical polymerization can be used. For example, azo compounds such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butylperoxy 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 common, so that the 10-hour half-life temperature is 80 ° C. or higher and a peroxide that is soluble in the organic solvent used, An azobis initiator is preferred. Specifically, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, cyclohexane peroxide, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, 1, Examples thereof include 1-azobis (1-cyclohexanecarbonitrile) and 2- (carbamoylazo) isobutyronitrile.
These initiators are preferably used, for example, in the range of 0.005 to 5% by mass.

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 are particularly preferable. As mentioned.
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.

The resin (b) is preferably a methyl methacrylate homopolymer, a methyl methacrylate-methyl acrylate copolymer, or a methyl methacrylate-ethyl acrylate copolymer, with a good balance between fluidity and heat resistance during molding. In particular, a methyl methacrylate-methyl acrylate copolymer is preferable because it has both.
As the resin (b), a plurality of types of acrylic resins having different compositions and molecular weights can be used in combination.

The photoelastic coefficient when the resin (b) is unstretched at 23 ° C. is preferably −60 × 10 ⁻¹² Pa ⁻¹ or more, more preferably −30 × 10 ⁻¹² Pa ⁻¹ or more. It is particularly preferably -6 × 10 ⁻¹² Pa ⁻¹ or higher. When the photoelastic coefficient of the resin (b) is in this range, an optical film having a small photoelastic coefficient and a desired Rth can be obtained.

Next, the resin composition for optical materials constituting the optical compensation film of the present invention will be described.
It is preferable that the resin (a) and the resin (b) are compatible. The compatibility can be realized by appropriately selecting the compositions (including the copolymer composition) of the resins (a) and (b), the blending ratio, the kneading temperature, the kneading pressure, the cooling temperature, the cooling rate, and the like. The miscible is described in detail in “High Performance Polymer Alloy” (edited by the Society of Polymer Science, published by Maruzen Co., Ltd. in 1991). When the resin (a) and the resin (b) are compatible, it becomes possible to increase the total light transmittance of a film obtained by molding a resin composition containing the resin (a) and the resin (b).
From such a viewpoint, in the present invention, as the resin (a), a styrene-acrylonitrile copolymer having an acrylonitrile content of 1 to 40% by mass, and a styrene-methacrylic acid having a methacrylic acid content of 0.1 to 50% by mass. copolymers and maleic anhydride content is 0.1 to 50 wt% styrene - styrene resin selected from the group consisting of maleic anhydride copolymer, combining acrylic resin as the resin (b). By using such a combination of the resin (a) and the resin (b), it is possible to produce a highly stable optical element that does not cause phase separation during use and decrease transparency.

In the optical science material resin composition, by adjusting the content and mass ratio of the resin (a), the resin (b), it is possible to control the photoelastic coefficient.
The content of the resin (a) in the resin composition for an optical material constituting the optical compensation film of the present invention is particularly preferably 20 to 80 parts by mass. The content of the resin (b) is particularly preferably 20 to 80 parts by mass.
In the present invention, the total content of the resin (a) and resin (b) is state, and are more than 80% by weight relative to the resin composition, it is good preferable is 90 mass% or more.
Further, in the present invention, the mass ratio of the resin (a) and resin (b) ((a) / (b)) is a 2 0/80 to 80/20, the resin (a), the resin (b) Although it depends on the type, it is favorable preferable is 40 / 60-60 / 40.

The resin composition for an optical material constituting the optical compensation film of the present invention contains 0.1 to 10 parts by mass of the ultraviolet absorber (c) with respect to 100 parts by mass in total of the resins (a) and (b). Is more preferably 0.1 to 2 parts by mass, and particularly preferably 0.1 to 1.5 parts by mass.

  By adding such an amount of the ultraviolet absorber (c), the photoelastic coefficient and the spectral transmittance can be controlled within preferable ranges. However, when a large amount of the ultraviolet absorber (c) is added, the photoelastic coefficient is increased, which is not preferable as an optical material.

  The content of the ultraviolet absorber (c) is 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).

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

The vapor pressure (P) at 20 ° C. of the ultraviolet absorber (c) is preferably 1.0 × 10 ⁻⁴ Pa or less because of excellent moldability. 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. Here, being excellent in moldability means that, for example, when a film is formed, there is little adhesion of a low molecular compound to a roll. When a low molecular weight compound adheres to the roll, it also adheres to the film surface and deteriorates the appearance and optical properties, which is not preferable as an optical material.

  The melting point (Tm) of the ultraviolet absorber (c) is preferably 80 ° C. or higher because of excellent moldability. More preferably, the melting point (Tm) is 130 ° C. or more, and the melting point (Tm) is particularly preferably 160 ° C. or more.

  Moreover, since it is excellent in molding processability when the ultraviolet absorber (c) is 50% or less when the temperature is increased at a rate of 20 ° C./min from 23 ° C. to 260 ° C., 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 resin composition constituting the optical compensation film of the present invention can contain a polymer other than the resin (a) component and the component (b) as long as the object of the present invention is not impaired. Polymers other than resin (a) and resin (b) include rubber components such as olefin elastomers, styrene elastomers, acrylic rubbers; polyolefins such as polyethylene and polypropylene, polyamides, polyphenylene sulfide resins, and polyether ether ketone resins. And thermoplastic resins such as polyester, polysulfone, polyphenylene oxide, polyimide, polyetherimide, and polyacetal; and thermosetting resins such as phenol resin, melamine resin, silicone resin, and epoxy resin.

  Furthermore, arbitrary additives can be mix | blended with the resin composition of this invention according to the objective within the range which does not impair the effect of this invention remarkably. Such additives are not particularly limited as long as they are generally used for blending resins and rubber-like polymers. For example, inorganic fillers; pigments such as iron oxides; lubricants such as stearic acid, behenic acid, zinc stearate, calcium stearate, magnesium stearate, ethylene bisstearamide; mold release agents; paraffinic process oil, naphthenic process Softeners and plasticizers such as oils, aromatic process oils, paraffins, organic polysiloxanes and mineral oils; antioxidants such as hindered phenolic antioxidants and phosphorus heat stabilizers; hindered amine light stabilizers, benzos Examples include triazole ultraviolet absorbers, benzophenone ultraviolet absorbers; flame retardants; antistatic agents; reinforcing agents such as organic fibers, glass fibers, carbon fibers, and metal whiskers; coloring agents; and other additives.

The method for producing the resin composition for an optical material constituting the optical compensation film of the present invention is not particularly limited, and a known method can be used. For example, using a melt kneader such as a single-screw extruder, twin-screw extruder, Banbury mixer, Brabender, various kneaders, etc., the resin (a) and the resin (b), and if necessary, the above other components are added. The resin composition can be produced by melt kneading.

Next, the optical compensation film will be described.
The molding method is not particularly limited, and a known method can be used. For example, it can be molded by methods such as injection molding, sheet molding, blow molding, injection blow molding, inflation molding, extrusion molding, foam molding, etc., and secondary processing molding methods such as compressed air molding and vacuum molding can also be used. Can do.

In the present invention, the film means a film having a thickness of 300 μm or less . In the present invention, the thickness of the film is preferably 1 μm or more, more preferably 5 μm or more .

The optical compensation film of the present invention is preferably formed by a technique such as extrusion molding or cast molding. For example, an unstretched film or sheet can be extruded by using an extruder or the like equipped with a T die, a circular die, or the like. When a molded product is obtained by extrusion molding, a material obtained by melting and kneading the resin (a) and the resin (b) in advance can be used, or molding can be performed through melt-kneading at the time of extrusion molding. In addition, the resin (a) and the resin (b) are dissolved in a solvent common to the resin (a) and the resin (b), for example, a solvent such as chloroform and methylene dichloride. The film can also be cast.

Furthermore, if necessary, the unstretched film can be uniaxially stretched in the mechanical flow direction and uniaxially stretched in the direction orthogonal to the mechanical flow direction. Moreover, successive biaxial stretching method of roll stretching and tenter stretching, simultaneous biaxial stretching method using a tenter stretching, it is also possible to produce biaxially stretched fill beam by stretching the biaxial stretching method using a tubular stretching. The stretching is preferably performed in the range of (Tg−20 ° C.) to (Tg + 50 ° C.) based on the glass transition temperature (Tg).

The draw ratio is preferably 0.1 to 1000% in either direction, more preferably 0.2 to 600%, and particularly preferably 0.3 to 300%. By designing in this range, a molded article for an optical element that is preferable in terms of birefringence, heat resistance and strength can be obtained.
Here, the draw ratio is the draw-fill beam obtained shrunk at a temperature above 50 ° C. than the glass transition temperature, it can be obtained by the following expression. The glass transition temperature can be determined by a DSC method or a viscoelastic method.
Stretch ratio (%) = [(length before shrinkage / length after shrinkage) −1] × 100

By performing biaxial stretching at different stretching ratios in the mechanical flow direction and the direction orthogonal to the mechanical flow direction, a film having high strength and a high in-plane retardation value can be obtained. Such a film having a small photoelastic coefficient and a high retardation value is suitably used as a retardation film.
On the other hand, a film having high strength and a low in-plane retardation value can be obtained by performing biaxial stretching at substantially the same stretch ratio in the mechanical flow direction and the direction orthogonal to the mechanical flow direction. Such a film having a small photoelastic coefficient and a low retardation value is suitably used as a polarizing plate protective film.

The optical compensation film of the present invention can be used by laminating two or more films having different properties such as retardation, and a polymer film other than the present invention is laminated on the optical compensation film of the present invention. You can also.

The optical compensation film of the present invention preferably has an absolute value of photoelastic coefficient at 23 ° C. of 0 to 5 × 10 ⁻¹² Pa ⁻¹ . The absolute value of the photoelastic coefficient is more preferably 0 to 4 × 10 ⁻¹² Pa ⁻¹ , further preferably 0 to 3.5 × 10 ⁻¹² Pa ⁻¹ , and 0 to 3.0. It is particularly preferable that it is 10 × 10 ⁻¹² Pa ⁻¹ or less.
If the photoelastic coefficient of the optical compensation film is within this range, the change in birefringence due to an external force is small, so that when this is used for a large liquid crystal display device or the like, contrast and screen uniformity are excellent.

The optical compensation film of the present invention, the weight ratio of the composition and resin of the resin composition for optical material (a) and resin (b), Thickness, and by designing within the preferred range stretch ratio, etc., the in-plane retardation (Re), thickness direction retardation (Rth), and Nz coefficient can be controlled.
Here, in-plane retardation (Re), thickness direction retardation (Rth), and Nz are defined by the following equations.
_{Re = (n x -n y)} × d
_{Rth = ((n x + n} y) / 2) -n z) × d
_{Nz = (n x -n z)} / | (n x -n y) |
(Wherein, n _x: main refractive index in the x direction when the direction in which the refractive index is maximized in the molding in the body surface was x, n _y: when a direction perpendicular to the x-direction in the molding in the body surface is y (The main refractive index in the y direction, _nz : the main refractive index in the thickness direction of the molded body, and d: the thickness (nm) of the molded body.)

The preferred Re value of the optical compensation film in the present invention is 0 to 400 nm, more preferably 5 to 350 nm, and particularly preferably more than 20 and 350 or less.
When the optical compensation film of the present invention is used as a quarter wavelength plate, the absolute value of Re is preferably 100 nm or more and 180 nm or less, more preferably 120 nm or more and 160 nm or less, and further preferably 130 nm or more and 150 nm or less. .
When the optical compensation film of the present invention is also used as a half-wave plate, the absolute value of Re is preferably 240 or more and 320 nm or less, more preferably 260 or more and 300 nm or less, and further preferably 270 or more and 290 nm. It is as follows.

The absolute value of Re / Rth of the optical compensation film of the present invention is preferably 3 or less, more preferably 0.1 to 2, and further preferably 0.2 to 1.5. The absolute value of Re / Rth can be adjusted by the draw ratio in the MD and TD directions, the film thickness, and the mass ratio of the resin (a) and the resin (b).
In the present invention, it is possible to design Rth of the optical compensation film to a negative value, but by designing Rth to a negative value, a preferable optical compensation film for a liquid crystal display can be obtained. Particularly, it is preferable for a horizontal electric field (IPS) mode liquid crystal display. A preferable Rth value is −400 nm to −1 nm, more preferably −350 nm to −5 nm, and particularly preferably −300 nm to −10 nm. The value of Rth can be adjusted by the draw ratio in the MD and TD directions, the film thickness, and the mass ratio of the resin (a) and the resin (b).

The Nz coefficient of the optical compensation film of the present invention is preferably −5 to 0, more preferably −3 to 0, and particularly preferably −1.5 to 0. By designing in this range, a preferable optical compensation film for a liquid crystal display can be obtained. Particularly, it is preferable for a horizontal electric field (IPS) mode liquid crystal display. The Nz coefficient can be adjusted by the stretching ratio in the MD and TD directions, the film thickness, and the mass ratio of the resin (a) and the resin (b).

The optical compensation film of the present invention preferably has a total light transmittance of 80% or more, more preferably 85% or more, further preferably 87% or more, and particularly preferably 90% or more. preferable.
Such total light transmittance is adjusted by adjusting the composition of resin (a) and resin (b) (including copolymer composition), blending ratio, kneading temperature, kneading pressure, cooling temperature, cooling rate, etc. This can be achieved by compatibilizing the components of the material resin composition.

The optical compensation film of the present invention preferably has a spectral transmittance at 380 nm of 5% or less. The lower the spectral transmittance at 380 nm in the ultraviolet region, the more preferable it can be used as an optical film, preventing the deterioration of the polarizer and liquid crystal element. The spectral transmittance at 380 nm is more preferably 3% or less, and the spectral transmittance at 380 nm is particularly preferably 2.5% or less.
Therefore, the optical compensation film of the present invention preferably has a spectral transmittance at 380 nm of 5% or less, and the absolute value of the photoelastic coefficient is 0 to 4 × 10 ⁻¹² Pa ^−1. In this case, the absolute value of the photoelastic coefficient is more preferably ⁰ to 3.5 × 10 ⁻¹² / Pa ⁻¹ , and particularly preferably ^{0 to} 3.0 × 10 ⁻¹² Pa ⁻¹ .

The optical compensation 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, and can be usefully used as a surface functionalized substrate.

Since the optical compensation 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 optical compensation film of the present invention can be optically anisotropic, it can be suitably used as a polarizing plate protective film. Below, the case where the molded object for optical elements of this invention is used as a polarizing plate protective film is demonstrated.

A polarizing plate can be produced by laminating the polarizing plate protective film of the present invention on a polarizing film. In the present invention, it is preferable to laminate a protective film having Re of 10 nm or more on one surface of the polarizing film and to laminate a protective film having Re of 10 nm or less 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.
In contrast, in a preferred embodiment of the present invention, the protective film having optical anisotropy of the present invention is laminated on one surface, and the protective film having optical isotropy is laminated on the other surface. As a result, the protective film on one side also serves as an optically anisotropic film. It is possible to omit the isotropic film and reduce the thickness of the polarizing plate.
Moreover, since there is no process which adhere | attaches another optical anisotropic film on a protective film, it is excellent in productivity.

Moreover, it is preferable that Re of the protective film laminated | stacked on one surface of a polarizing film is 10 nm or more, More preferably, it is 20-1000 nm, More preferably, it is 30-900 nm.
The protective film having Re of 10 nm or more laminated on one surface has functions as an optical compensation retardation film, a quarter wavelength plate, a half wavelength plate, and other retardation films.

  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, it is preferable to use a film made of an acrylic resin (d) as an optically isotropic protective film laminated on the other surface.

  Specific examples of the acrylic resin (d) include methacrylic acid alkyl ester such as cyclohexyl methacrylate, t-butyl cyclohexyl methacrylate, methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate, acrylic What polymerized 1 or more types of monomers chosen from acrylic acid alkylesters, such as acid 2-ethylhexyl, is preferable.

Among these, a homopolymer of methyl methacrylate or a copolymer with 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 (d) 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 the acrylic resin (d), 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 the introduction of minute foreign substances as much as possible. From this viewpoint, bulk polymerization or solution polymerization without using a suspending agent or an emulsifier is preferable. Specifically, the method described in JP-B 63-1964 and the like 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 in the polymerization reaction, any initiator used in radical polymerization can be used. For example, azo compounds such as azobisisobutylnitrile, benzoyl peroxide, lauroyl peroxide, t-butylperoxy- 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, 1,1 -Azobis (1-cyclohexanecarbonitrile), 2- (carbamoylazo) isobutyronitrile and the like can be mentioned. 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 one used in general radical polymerization can be used, for example, mercaptan compounds such as butyl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-ethylhexyl thioglycolate, and the like. Particularly preferred. 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.

  As the acrylic resin (d) used in the present invention, a copolymer obtained by copolymerizing a methacrylic acid ester and / or an acrylic acid ester, an aromatic vinyl compound and a compound represented by the following general formula [1] Is preferred.

（ＸはＯまたは、Ｎ−Ｒを示す。Ｏは酸素原子、Ｎは窒素原子、Ｒは水素原子またはアルキル基である）

(X represents O or N—R. O is an oxygen atom, N is a nitrogen atom, R is a hydrogen atom or an alkyl 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 styrenes 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 The ratio of styrene units to maleic acid units is preferably 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.

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

The acrylic resin (d) can contain an aliphatic polyester resin (e).
Examples of the aliphatic polyester-based resin (e) include a polymer having an aliphatic hydroxycarboxylic acid as a main constituent, and a polymer having an aliphatic polyvalent carboxylic acid and an aliphatic polyhydric alcohol as main constituents. It is done.
Specific examples of the polymer having an aliphatic hydroxycarboxylic acid as a main constituent include polyglycolic acid, polylactic acid, poly-3-hydroxybutyric acid, poly-4-hydroxybutyric acid, poly-4-hydroxyvaleric acid, poly-3-hydroxyhexane Examples of the polymer mainly composed of an aliphatic polyvalent carboxylic acid and an aliphatic polyhydric alcohol include polyethylene adipate, polyethylene succinate, polybutylene adipate, and polybutylene succinate. Etc. These aliphatic polyester resins (e) can be used alone or in combination of two or more.

  Among these aliphatic polyester resins (e), a polymer containing hydroxycarboxylic acid as a main constituent component is preferable, and a polylactic acid resin is 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 lactic acid derivative monomers other than L-form or D-form or other components copolymerizable with lactide. Examples of such components include dicarboxylic acids, polyhydric alcohols, hydroxycarboxylic acids. Examples include acids and lactones. The polylactic acid resin can be polymerized by a known polymerization method such as direct dehydration condensation or ring-opening polymerization of lactide. Moreover, it can also be made high molecular weight using binders, such as polyisocyanate, as needed.
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, polyhydric alcohols, hydroxycarboxylic acids, lactones, and the like. 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 sulfoisophthalic acid Polyvalent carboxylic acids such as ethylene glycol, propylene glycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol, decanediol, 1,4-cyclohexanedimethanol, neopentylglycol, glycerin, trimethyl Aromatic propane, pentaerythritol, bisphenol A, polyhydric alcohols such as aromatic polyhydric alcohol obtained by addition reaction of bisphenol with ethylene oxide, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; glycolic acid, 3- Hydroxycarboxylic acids such as hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid, hydroxybenzoic acid; glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, Lactones such as 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 the aliphatic polyester resin (e), a known polymerization method can be used. In particular, for a polylactic acid resin, a direct polymerization method from lactic acid, a ring-opening polymerization method via lactide, or the like is employed. be able to.

  In the present invention, the ratio (part by mass) of the acrylic resin (d) in the resin composition comprising the acrylic resin (d) and the aliphatic polyester resin (e) is the acrylic resin (d) and the aliphatic polyester resin. It is preferable that it is 0.1-99.9 mass parts with respect to 100 mass parts of total amounts of resin (e) from the point of a photoelastic coefficient, intensity | strength, heat resistance, and a haze value, and 50-99.9 mass parts. More preferably, it is particularly preferably 60 to 95 parts by mass. When it is 50 parts by mass or more, the haze value in a moist heat atmosphere is lowered, which is preferable. When the haze value is small or the change is small, it can be suitably used for display applications and the like.

  The ratio (parts by mass) of the aliphatic polyester resin (e) is 100 parts by mass of the total amount of the acrylic resin (d) and the aliphatic polyester resin (b), the photoelastic coefficient, strength, heat resistance, It is preferable that it is 0.1-99.9 mass part from the point of a haze value, It is more preferable that it is 0.1-50 mass part, It is especially preferable that it is 5-40 mass part. When the amount is 50 parts by mass or less, the haze value in a moist heat atmosphere is preferably reduced. When the haze value is small or the change is small, the present invention can be suitably used for display applications.

In the present invention, the thickness of the protective film is preferably 0.1 μm or more from the viewpoint of handling properties, and is 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.
For the bonding of the polarizing film and the protective film, it is preferable to use an optically isotropic adhesive. Examples of such an adhesive include a polyvinyl alcohol-based adhesive, a urethane-based adhesive, an epoxy-based adhesive, Examples include acrylic adhesives. When the adhesion 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.

  When a protective film using the molded article for an optical element of the present invention is used on one side of the polarizing plate and a protective film made of an acrylic resin (d) is used on the other side, warping or curling due to a characteristic difference between the resins. Such problems as described above, and abnormalities due to stress due to the difference in hygroscopicity are reduced.

The polarizing film used for such a polarizing plate is not particularly limited, but for example, a polarizing film in which a dichroic dye is adsorbed and oriented 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. Moreover, it is preferable that the saponification degree of a polyvinyl alcohol-type resin is 85-100 mol%, More preferably, it is 98-100 mol%. This polyvinyl alcohol-based resin may be further modified, and for example, polyvinyl formal and 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 process of producing a film from a resin and uniaxially stretching the film, a process of dyeing a stretched polyvinyl alcohol-based resin film with a dichroic dye, and adsorbing iodine or a dichroic dye, a dichroic dye Can be produced through a step of treating the polyvinyl alcohol-based resin film adsorbed with boric acid aqueous solution and a step of washing with water after the treatment with boric acid aqueous 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.
For uniaxial stretching, rolls having different peripheral speeds may be uniaxially stretched or uniaxially stretched using a hot 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 using a dichroic dye 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 water washing treatment is performed, for example, by immersing a boric acid-treated polyvinyl alcohol 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.

Next, the present invention will be described specifically by way of examples.
The evaluation methods used in the present invention and examples will be described.
(1) Evaluation method (I) Measurement of photoelastic coefficient, judgment of intrinsic birefringence positive / negative (measurement of photoelastic coefficient)
A birefringence measuring apparatus described in detail in Macromolecules 2004, 37, 1062-1066 is used. A film tensioning device is disposed in the laser beam path, and a birefringence is measured while applying a tensile stress at 23 ° C. to a test piece of a resin or resin composition having a width of 7 mm. The strain rate during stretching is 20% / min (chuck interval: 30 mm, chuck moving speed: 6 mm / min.
The values measured in this way are plotted with the birefringence (Δn) as the y-axis and the extension stress (σ _R ) as the x-axis. The elastic modulus (C _R ) is calculated. The smaller the absolute value of the slope is, the closer the photoelastic coefficient is to 0, indicating a preferable optical characteristic.
(Intrinsic birefringence positive / negative judgment)
Stretching is performed while applying an extensional stress within the range of the glass transition temperature or higher and the glass transition temperature + 50 ° C. or lower, rapidly solidified, and npr-nvt at 23 ° C. is measured. When npr-nvt is negative, it is determined that the intrinsic birefringence is negative, and when npr-nvt is positive, the intrinsic birefringence is positive.

(II) Measurement of total light transmittance Measurement is performed in accordance with ASTM D1003.
(III) Measurement of molecular weight Using GPC (GPC-8020 manufactured by Tosoh Corporation, detection RI, column Shodex K-805, 801 linked by Showa Denko), the solvent was chloroform, the measurement temperature was 40 ° C., and converted to a standard commercial polystyrene. Determine the weight average molecular weight.
(IV) Measurement of acrylonitrile content (styrene-acrylonitrile) copolymer was formed into a film using a hot press machine, and the absorbance at 1603 cm ^-1 and 2245 cm ^-1 of the film was measured using FT-410 manufactured by JASCO Corporation. taking measurement. Are obtained in advance, (styrene - acrylonitrile) acrylonitrile content of the copolymer and 1603cm ^-1, by using the relationship between the absorbance ratio of the 2245 cm ^-1,
The acrylonitrile content in the (styrene-acrylonitrile) copolymer is determined.
(V) In-plane retardation (Re), thickness direction retardation (Rth) and Nz coefficient (measurement of in-plane retardation (Re))
The thickness d (nm) of the film is measured using a thickness gauge. This value is input to a birefringence measuring apparatus RETS-100 manufactured by Otsuka Electronics Co., Ltd., a sample is placed so that the measurement surface is perpendicular to the measurement light, and in-plane retardation (Re ) Is measured and calculated.
(Thickness direction retardation (Rth), measurement of Nz)
The average refractive index n of the optical film is measured at 23 ° C. using a Metricon laser refractometer Model 2010. And average refractive index n and film thickness d (nm) are inputted into Otsuka Electronics Co., Ltd. birefringence measuring apparatus RETS-100, and thickness direction retardation (Rth) and Nz coefficient are measured and calculated at 23 ° C. .
(VI) Measurement of spectral transmittance The spectral spectrum is measured using U-3310 manufactured by Hitachi, Ltd., and the transmittance at 380 nm is obtained.
(VII) Measurement of warping 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 in an atmosphere of 23 ° C. and 50% RH. It is allowed to stand for 72 hours, and is calculated by averaging the height at which the four corners of the cut film are warped from the table.
(VIII) 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 was obtained according to the following formula, and the degree of polarization holding rate was calculated using this value to obtain durability. Assess sex.
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. The degree of polarization is measured using a Shimadzu UV-3150 spectrophotometer.
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.

(2) Preparation of raw materials (I) Resin having positive photoelastic coefficient and negative intrinsic birefringence (a)
1) Styrene-acrylonitrile copolymer (a-1)
A monomer mixture composed of 72% by mass of styrene, 13% by mass of acrylonitrile, and 15% by mass of ethylbenzene was continuously fed into a complete mixing reactor equipped with a stirrer, and a polymerization reaction was performed at 150 ° C. and a residence time of 2 hours.
The obtained polymerization solution was continuously supplied to an extruder, and unreacted monomers and a solvent were collected by the extruder to obtain styrene-acrylonitrile copolymer (a-1) pellets.
The obtained styrene-acrylonitrile copolymer (a-1) was colorless and transparent, and as a result of compositional analysis by neutralization titration, the styrene content was 80% by mass, the acrylonitrile content was 20% by mass, and 220 ° C. in accordance with ASTM-D1238. The melt flow rate value at 10 kg load was 13 g / 10 min. The photoelastic coefficient (unstretched) was 5.0 × 10 ⁻¹² Pa ⁻¹ and the intrinsic birefringence was negative.

2) Styrene-methacrylic acid copolymer (a-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 are used as a preparation liquid, and 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane is used as a polymerization initiator. This prepared solution was added at 1 L / hr. The mixture was continuously fed at a rate of 1 liter to a completely mixed polymerization reactor equipped with a stirrer with an internal volume of 2 L, and polymerization was carried out at 136 ° C.
A polymerization liquid containing 49% of solid content is continuously taken out, first preheated to 230 ° C., kept at 230 ° C., and supplied to a devolatilizer depressurized to 20 torr. It discharged continuously from the gear pump at the lower part of the volatilizer.
The obtained styrene-methacrylic acid copolymer (a-2) was colorless and transparent, and as a result of compositional analysis by neutralization titration, the styrene content was 92 mass% and the methacrylic acid content was 8 mass%. The melt flow rate value measured at 230 ° C. under a load of 3.8 kg measured in accordance with ASTM-D1238 was 5.2 g / 10 minutes. Moreover, the photoelastic coefficient (unstretched) is 4.8 × 10 ⁻¹² Pa ^−1.
The intrinsic birefringence was negative.

3) Styrene-maleic anhydride copolymer (a-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, the two are not mixed.) 5 parts by mass of methyl alcohol and 0.03 parts by mass of 1,1-tert-butylperoxy-3,3,5-trimethylcyclohexane as a polymerization initiator are mixed with styrene. It was set as the preparation liquid. 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. To the same polymerization machine at a speed of 1, and polymerization is carried out at 111 ° C. 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. After 3 hours, it was continuously discharged from the lower gear pump of the devolatilizer to obtain a styrene-maleic anhydride copolymer (a-3). The obtained styrene-maleic anhydride copolymer (a-3) was colorless and transparent, and as a result of compositional analysis by neutralization titration, the styrene content was 85% by mass and the maleic anhydride unit was 15% by mass. The melt flow rate value 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) is 4.1 × 10 ^−1.
2 Pa ⁻¹ and intrinsic birefringence was negative.

(II) Resin having negative photoelastic coefficient and negative intrinsic birefringence (b)
1) Methyl methacrylate-methyl acrylate copolymer (b-1)
1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane 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 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 L, polymerized with stirring at an average temperature of 130 ° C. and an average residence time of 2 hours, and then continuously supplied to a storage tank with deaeration equipment connected to the reactor. To remove volatiles. Furthermore, it transferred to the extruder in the molten state continuously, and the pellet of the (methyl methacrylate-methyl acrylate (b-1) copolymer was obtained with the extruder.
The methyl methacrylate-methyl acrylate copolymer (b-1) obtained had a methyl acrylate content of 6.0% by mass, a weight average molecular weight of 145,000, and 230 ° C. measured according to ASTM-D1238. The melt flow rate value at a load of 3.8 kg was 1.0 g / 10 min. Moreover, the photoelastic coefficient (unstretched) was −4.2 × 10 ⁻¹² Pa ⁻¹ and the intrinsic birefringence was negative.

2) Methyl methacrylate-methyl acrylate copolymer (b-2)
1,1-di-t-butylperoxy-3,3,3 was added to a monomer mixture consisting of 93.2 parts by weight of methyl methacrylate, 2.3 parts by weight of methyl acrylate, and 3.3 parts by weight of xylene. Add 0.03 parts by weight of trimethylcyclohexane and 0.12 parts by weight of n-octyl mercaptan and mix uniformly. This solution was continuously supplied to a sealed pressure-resistant reactor having an internal volume of 10 L, polymerized with stirring at an average temperature of 130 ° C. and an average residence time of 2 hours, and then continuously sent to a reservoir connected to the reactor, Volatiles were removed under certain conditions. Furthermore, it transferred to the extruder in the molten state continuously, and the pellet of the methyl methacrylate-methyl acrylate copolymer (b-2) was obtained.
The methyl methacrylate-methyl acrylate copolymer (b-2) obtained had a methyl acrylate content of 2.0%, a weight average molecular weight of 102,000, and 230 ° C. measured in accordance with ASTM-D1238. The melt flow value with an 8 kg load was 2.0 g / 10 min. The photoelastic coefficient (unstretched) was −4.4 × 10 ⁻¹² Pa ⁻¹ and the intrinsic birefringence was negative.
(III) UV absorber (c)
A benzotriazole-based compound (c-1) (Asahi Denka Co., Ltd., ADK STAB LA-31 (melting point (Tm): 195 ° C.) was used. Rigaku Denki Co., Ltd., ThermoPlus TG8120, 23 It was 0.03% when the mass reduction | decrease rate at the time of heating up from 20 degreeC to 260 degreeC at the speed | rate of 20 degree-C / min was measured.
(IV) Polycarbonate As a comparative example, polycarbonate (WONDERLITE PC-110 manufactured by Asahi Kasei Co., Ltd.) was used. The photoelastic coefficient (unstretched) of this polycarbonate is 70 × 10 ⁻¹² Pa ^−.
1 and the intrinsic birefringence was positive.
(V) Acrylic resin (d)
1) Methyl methacrylate / methyl acrylate copolymer (d-1)
The aforementioned methyl methacrylate / methyl acrylate copolymer (b-1) was used as the methyl methacrylate / methyl acrylate copolymer (d-1).
2) Heat-resistant acrylic resin (d-2)
A methyl methacrylate-maleic anhydride-styrene copolymer was obtained by the method described in Japanese Patent Publication No. 63-1964.
The composition of the obtained methyl methacrylate-maleic anhydride-styrene copolymer (d-2) was 74% by mass of methyl methacrylate, 10% by mass of maleic anhydride, and 16% by mass of styrene. The rate value (ASTM-D1238; 230 ° C., 3.8 kg load) was 1.6 g / 10 min.
(VI) Aliphatic polyester resin (e)
Polylactic acid (e-1) (Cargildau 4032D) was used.

[Examples 1 and 3 to 5 and Comparative Examples 1 to 4, 9, and 12]
Using the resin composition having the blending ratio shown in Table 1, using a Technobel T-die mounting extruder (KZW15TW-25MG-NH type / width 150 mmT die mounting / lip thickness 0.5 mm), screw rotation speed, extruder An unstretched film was obtained by adjusting the resin temperature in the cylinder and the temperature of the T die and performing extrusion molding.

Table 1 shows the composition of each unstretched film, extrusion molding conditions, film thickness, and photoelastic coefficient. For comparison, the photoelastic coefficient of a commercially available TAC (triacetylcellulose) film (trade name TACPHAN, manufactured by LOFO High Tech Film, positive photoelastic coefficient, intrinsic birefringence is positive) is shown as Comparative Example 4.
The unstretched films of the present invention (Examples 1 and 3 to 5) all had a small absolute value of the photoelastic coefficient and high transparency. In contrast, an unstretched film (Comparative Example 3) obtained from a polycarbonate conventionally used for a retardation film and a TAC film (Comparative Example 4) used as a protective film for a polarizing plate are photoelastic. The absolute value of the coefficient was very large. In addition, the films (Comparative Examples 1, 2, 9, and 12) each using the resin (a) and the resin (b) independently have absolute photoelastic coefficients as compared with Examples 1 and 3 to 5 in which both are mixed. The value was great.

[Example 2 and Comparative Examples 5, 6, and 7]
Using a Technobel T-die mounting extruder (KZW15TW-25MG-NH type / width 150 mm T-die mounting / lip thickness 0.5 mm), adjusting the screw rotation speed, the resin temperature in the cylinder of the extruder, and the temperature of the T die An unstretched film was obtained by 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.
Next, the width of the obtained unstretched film was cut out to 50 mm, and uniaxial stretching (between chucks: 50 mm, chuck moving speed: 500 mm / min) was performed using a tensile tester. Example 2 and Comparative Example 5 A uniaxially stretched film of ~ 7 was obtained.

Table 2 shows the composition, extrusion molding conditions, stretching conditions, and film characteristics of each uniaxially stretched film. For comparison, a commercially available TAC (triacetylcellulose) film (trade name TACPHAN, manufactured by LOFO High Tech Film) has a photoelastic coefficient of 10 × 10 ^−12.
The photoelastic coefficient of Pa ⁻¹ and positive birefringence is shown as Comparative Example 4.
The uniaxially stretched film of the present invention (Example 2) had a small absolute value of the photoelastic coefficient, and the uniaxially stretched films of Comparative Examples (Comparative Examples 5 to 6) had a large absolute value of the photoelastic coefficient.
Further, the uniaxially stretched film of the present invention (Example 2) exhibited birefringence sufficient for use as a retardation film, and the Rth value was also negative.

[Examples 6 to 25, Comparative Examples 13 to 15]
Using the resin composition having the composition shown in Table 3, using a T-die mounting extruder (BT-30-C-36-L type / width 400 mm T-die mounting / lip thickness 0.8 mm) manufactured by Plastic Engineering Laboratory, An unstretched film was obtained by adjusting the screw rotation speed, the resin temperature in the cylinder of the extruder, and the temperature of the T die to perform extrusion molding.
Uniaxial stretching of the film flow (extrusion direction) (MD direction) relative to the unstretched film was performed using a roll type longitudinal stretching machine manufactured by Ichikin Kogyo Co., Ltd. In order to obtain the target set draw ratio, the rotation speeds of the two rolls (low speed side roll / high speed side roll) were changed and the rolls were continuously stretched between the rolls.
Subsequently, the direction (TD direction) perpendicular to the MD direction of the obtained longitudinally uniaxially stretched film was continuously performed using a tenter stretching machine manufactured by Ichikin Kogyo Co., Ltd. Stretching was performed by changing the distance between the tenter chucks at a flow rate of 2 m / min in order to obtain a target set stretching ratio.

Table 3 shows the composition, extrusion molding conditions, stretching conditions, and film characteristics of each film.
The films of Examples 6 to 25 all had a small absolute value of the photoelastic coefficient, a high total light transmittance, and high birefringence when stretched (Examples 7 to 17 and 19 to 25). On the other hand, the films of Comparative Examples 13 to 15 each using the resin (a) and the resin (b) independently had a larger absolute value of the photoelastic coefficient than the films of Examples 6 to 25 in which both were blended.
And from the results of Examples 6 to 9, Examples 12 to 14, Examples 15 to 17, and Examples 18 and 19, the values of the birefringence (nx-ny), Re, and Rth of the film also depend on the stretching conditions. It was confirmed that it changed greatly. Thereby, in this invention, it has confirmed that Re and Rth were controllable by adjusting extending | stretching conditions.
Furthermore, from the comparison between Examples 20 to 22 and Examples 23 to 25, the photoelastic coefficient is obtained by adding about 1 part by mass of the ultraviolet absorber to 100 parts by mass in total of the resin (a) and the resin (b). It was confirmed that ultraviolet rays can be shielded without greatly affecting the resistance.

[Examples 26 to 30]
Using the resin composition having the composition shown in Table 4, using a T-die mounting extruder (BT-30-C-36-L type / width 400 mm T-die mounting / lip thickness 0.8 mm) manufactured by Plastic Engineering Laboratory, An unstretched film was obtained by adjusting the screw rotation speed, the resin temperature in the cylinder of the extruder, and the temperature of the T die to perform extrusion molding.
Next, the obtained unstretched film is cut out so that the length becomes 1/2 of the distance between chucks of the tenter inlet, and uniaxially stretched in the direction (TD direction) perpendicular to the film flow (extrusion direction). , Using a tenter stretching machine manufactured by Ichikin Kogyo Co., Ltd. Stretching was performed by changing the distance between the tenter chucks at a flow rate of 2 m / min in order to obtain a target set stretching ratio.

Table 4 shows the composition, extrusion molding conditions, stretching conditions, and film characteristics of each uniaxially stretched film.
As for the uniaxially stretched film of Examples 26-30, all had a small absolute value of a photoelastic coefficient, and Nz value was near zero.
Moreover, from the result of Examples 27-30, it has confirmed that the value of the photoelastic coefficient of a film also increased as the compounding quantity of resin (a) in the resin composition which comprises a film increased. Thereby, in this invention, it has confirmed that the photoelastic coefficient of a resin composition was controllable by adjusting the compounding quantity of resin (a) and resin (b).

[Examples 31 to 41, Comparative Example 16]
(Production of protective films of Examples 31 to 34 and Test Examples 1 to 3)
Biaxial stretching was performed in the same manner as in Examples 6 to 25 using the resin composition having the composition shown in Table 5, and polarizing plate protective films of Examples 31 to 34 and Test Examples 1 to 3 were produced. Table 5 shows the molding, stretching conditions, film thickness, and Re.

(Production of triacetyl cellulose-based protective film (TAC-1))
As a representative example of a conventional polarizing plate protective film, a triacetyl cellulose-based 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) were dissolved in 62 parts by mass of methylene chloride, 12 parts by mass of methanol and 2 parts by mass of n-butanol. A dope was prepared. 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 lateral dimension of the film was fixed using a tenter, and in this state, the film was dried from both sides for 3 minutes until the amount of the 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 reached 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 80 μm. The in-plane retardation of this film was 5 nm.
(Production of cycloolefin-based protective film (COP-1))
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.
As a cyclic polyolefin, addition polymerization of ethylene and norbornene was performed to produce an ethylene-norbornene random copolymer (ethylene content: 65 mol%, MFR: 31 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 80 μm was produced by a casting method. The in-plane retardation of this film was 6 nm.
(Manufacture of polarizing film)
Polyvinyl acetate is saponified (saponification degree: 98 mol%), molded, and the resulting polyvinyl alcohol film (thickness 75 μm) is an aqueous solution comprising 1000 parts by mass of water, 7 parts by mass of iodine and 105 parts by mass of potassium iodide 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.
(Production of polarizing plates of Examples 35 to 41 and Comparative Example 16)
Using a 10% aqueous solution of a polyvinyl alcohol-based resin as an adhesive, the protective films of Examples 31 to 34 and Test Examples 1 to 3 were bonded to both surfaces of the polarizing film in the combinations shown in Table 6 to obtain a polarizing plate.

Table 6 shows the warpage and polarization degree retention of the polarizing plates of Examples 35 to 41 and Comparative Example 16.
From Table 6, it was confirmed that the polarizing plate using the optical compensation film of the present invention as a protective film had little warpage and excellent durability at high temperature and high humidity.

In particular, the optical compensation film liquid crystal display of the present invention, a plasma display, an organic EL display, a field emission display, or a polarizing plate protective film used for displays such as rear projection television, 1/4-wavelength plate, 1/2-wave plate or the like it can be used for the phase difference plate, suitably as a liquid crystal optical compensation fill beam such as a viewing angle control film.
In particular, the optical compensation film of the present invention can be suitably used as a retardation film for an IPS mode liquid crystal display device in which the thickness direction retardation is desired to be a negative value.

Claims (12)

Styrene-acrylonitrile copolymer having a positive photoelastic coefficient when unstretched at 23 ° C. and a negative intrinsic birefringence and an acrylonitrile content of 1 to 40% by mass, a methacrylic acid content of 0.1 to 50% by mass methacrylic acid copolymers and maleic anhydride content is 0.1 to 50 wt% styrene - - styrene resin (a) is selected from the group consisting of maleic acid anhydride copolymer, styrene is
An optical compensation film comprising a resin composition containing an acrylic resin (b) having a negative photoelastic coefficient when unstretched at 23 ° C. and a negative intrinsic birefringence,
The total content of the resin (a) and the resin (b) in the resin composition is 80% by mass or more,
The optical compensation film whose mass ratio ((a) / (b)) of resin (a) and resin (b) in the said resin composition is 20 / 80-80 / 20.   The optical compensation film of Claim 1 which contains 0.1-10 mass parts of ultraviolet absorbers (c) with respect to 100 mass parts of said resin compositions. 3. The optical compensation film according to claim ¹ , wherein a photoelastic coefficient at 23 ° C. is −4 × 10 ⁻¹² to 4 × 10 ⁻¹² Pa ⁻¹ . 4. The optical compensation film according to claim 3, wherein the photoelastic coefficient at 23 ° C. is −4 × 10 ⁻¹² to 4 × 10 ⁻¹² Pa ⁻¹ and the spectral transmittance at 380 nm is 5% or less.   The optical compensation film according to any one of claims 1 to 4, which is a film formed by extrusion molding.   The optical compensation film according to any one of claims 1 to 4, which is a film formed by cast molding.   A retardation film using the optical compensation film according to claim 1.   The retardation film according to claim 7, wherein the thickness direction retardation (Rth) is −300 to −1 nm.   The retardation film according to claim 7 or 8, wherein an absolute value of a ratio (Re / Rth) of in-plane retardation (Re) and thickness direction retardation (Rth) is 3 or less. N _z factor, the phase difference film according to any one of claims 7-9 is -5 to 0.   The polarizing plate protective film using the optical compensation film of any one of Claims 1-6.   A polarizing plate comprising the protective film according to claim 11, wherein a protective film having a Re of 10 nm or more is laminated on one surface of the polarizing film, and a protective film made of an acrylic resin and having a Re of 10 nm or less is laminated on the other surface. .