JP2012159545A - Optical film and polarizing plate having the same, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film for a polarizing plate formed of an olefin-based resin which has high mechanical strength, is hard to cause rupture or the like, and can reduce the thickness, and to provide a polarizing plate having the same, and a liquid crystal display device.SOLUTION: In the optical film F for the polarizing plate formed of the olefin-based resin, the degree of the crystallinity is 35% or more, the in-plane retardation value Rat a wavelength of 590 nm is in a range of 0-400 nm, the thickness-direction retardation value Rat a wavelength of 590 nm is 0-400 nm, and the olefin-based resin is preferably a polypropylene-based resin.

Description

  The present invention relates to an optical film, a polarizing plate provided with the optical film, and a liquid crystal display device, and more particularly to an optical film for a polarizing plate made of an olefin resin, a polarizing plate provided with the optical film, and a liquid crystal display device.

  A liquid crystal display device has characteristics such as low power consumption, operation at a low voltage, and light weight and thinness. Therefore, the liquid crystal display device is used in various display devices by taking advantage of these characteristics. The liquid crystal display device is composed of many materials such as a liquid crystal cell, a polarizing plate, a retardation film, a condensing sheet, a diffusion film, a light guide plate, and a light reflecting sheet. Therefore, improvements aimed at productivity, weight reduction, brightness improvement, and the like are actively performed by reducing the number of constituent films or reducing the thickness of the film or sheet.

  On the other hand, a liquid crystal display device is required to have a product that can withstand severe durability conditions depending on applications. For example, a liquid crystal display device for a car navigation system may have a high temperature and humidity in a vehicle in which the liquid crystal display device is placed, and the temperature and humidity conditions are severe as compared with a monitor for a normal television or personal computer. For such applications, polarizing plates that are highly durable are also required.

  The polarizing plate usually has a structure in which a transparent protective film is laminated on one side or both sides of a polarizing film made of a polyvinyl alcohol-based resin having a dichroic dye adsorbed and oriented. The polarizing film is produced by a method in which a polyvinyl alcohol-based resin film is subjected to longitudinal uniaxial stretching and dyeing with a dichroic dye, then treated with boric acid to cause a crosslinking reaction, and then washed with water and dried. As the dichroic dye, iodine or a dichroic organic dye is used. A polarizing plate is formed by laminating a protective film on one or both sides of the polarizing film thus obtained, and is used by being incorporated in a liquid crystal display device.

  As the protective film, a cellulose acylate resin film typified by triacetyl cellulose is often used, and its thickness is usually in the range of about 30 to 120 μm. In addition, an adhesive composed of an aqueous solution of a polyvinyl alcohol-based resin is often used for laminating the protective film.

  However, a polarizing plate in which a protective film made of triacetyl cellulose is laminated on one side or both sides of a polarizing film on which a dichroic dye is adsorbed and oriented via an adhesive made of an aqueous solution of a polyvinyl alcohol-based resin, under wet heat conditions When used for a long time, there is a problem that the polarizing performance is deteriorated or the protective film and the polarizing film are easily peeled off.

  Therefore, a method has been proposed in which at least one of the protective films is formed of a resin material other than the cellulose acylate resin. For example, in a polarizing plate in which protective films are laminated on both surfaces of a polarizing film, a technique is known in which at least one of the protective films is made of a polypropylene resin that is a kind of olefin resin (see, for example, Patent Document 1). ). Olefin-based resins, particularly polypropylene-based resins, are relatively inexpensive compared to other resins, so that the production cost of the protective film can be reduced. In addition, since the polypropylene-based resin has high flexibility, the film thickness can be reduced by stretching or the like. For this reason, it is possible to reduce the thickness of the polarizing plate to which the protective film is bonded.

  By the way, as an index indicating the crystallinity of molecules constituting the film, there is a crystallinity obtained by X-ray diffraction. Conventionally, an optical compensation resin film for a polarizing plate having a crystallinity of 0.15 or less is known (for example, see Patent Document 2). The smaller the degree of crystallinity, the smaller the proportion of crystals and the less likely light scattering occurs on the crystal surface. Therefore, according to the optical compensation resin film of Patent Document 2, light leakage due to light scattering can be prevented, and the contrast of the display image can be improved. Furthermore, a cyclic olefin random copolymer having a crystallinity by the X-ray crystal diffraction method in the range of 0 to 10% is also known (for example, see Patent Document 3).

JP 2007-334295 A (Claims 1-3, paragraphs 0009-0018) International Publication No. 2007/125797 (Claim 1, paragraphs 0117, 0156 to 0207) JP-A-62-252406 (Claim 1)

  In the examples of Patent Document 2, cycloolefin resins, polycarbonate resins, and cellulose ester resins are used as materials for optical films having a crystallinity of 0.15 or less. In the comparative example, an optical film having a degree of crystallinity exceeding 0.15 is disclosed. However, polycarbonate resin or cellulose ester resin is used as the material, and no olefin resin is used. .

  On the other hand, the inventors have been researching optical films using olefin-based resins that are cheaper and more flexible than conventional resin materials. In this process, in an optical film made of an olefin resin, the mechanical strength is low when the crystallinity is 0.15 (15%) or less as in Patent Document 2, and therefore, when the film is thinned, It has been found that the supporting force is not sufficient, so that it is difficult even to form a film, or even if it can be formed into a film, it becomes a “fragile” film that is easily broken. Therefore, it is difficult to use such an olefin resin having a low crystallinity as a protective film or retardation film for a polarizing plate.

  An object of the present invention is to provide an optical film having high mechanical strength, an polarizing plate provided with the same, and a liquid crystal display device in an optical film made of an olefin resin.

  According to the optical film of the present invention, the above-described problem is solved by being an optical film for a polarizing plate made of an olefin resin and having a crystallinity of 35% or more.

  In this case, the crystallinity is more preferably 45% or more.

In the above case, in-plane retardation value _{R o} at the wavelength 590nm, which is defined by the following formula in the range of 0～400Nm, and the thickness direction retardation _{R th} at the wavelength 590nm is in the range of 0～400Nm Is preferred.
_{R o = (n x -n y} ) × d
_Rth = (( _nx + _ny ) / 2- _nz ) * d
_(Wherein, n _x, n y, _{n z} is the main axis x of the respective refractive index ellipsoid, y, represents the refractive index in the z-direction, and _n x, is _{n y} a refractive index of the optical film plane direction, ( _nz represents the refractive index in the thickness direction of the optical film, and d represents the thickness (nm) of the film.)

  The optical film is preferably a non-oriented film or a biaxially stretched film.

  Furthermore, it is preferable that the optical film is a biaxially stretched film and the film thickness is in the range of 5 to 40 μm.

  The olefin resin is preferably a polypropylene resin.

  Moreover, according to the polarizing plate of this invention, the said subject is solved by providing the optical film in any one of said, and the polarizing film bonded by the said optical film.

  In this case, the optical film is preferably a protective film made of a non-oriented film.

  Alternatively, the optical film may be a retardation film made of a biaxially stretched film.

  The said subject is solved by providing the polarizing plate in any one of said, and the liquid crystal cell on which the said polarizing plate was bonded according to the liquid crystal display device of this invention.

  According to the optical film of the present invention, since the degree of crystallinity is 35% or higher, the mechanical strength is higher than that of a conventional optical film for a polarizing plate having a low degree of crystallinity, and breakage or the like is unlikely to occur. For this reason, in the liquid crystal display device provided with such an optical film, durability is improved because the liquid crystal display device is hardly damaged. In addition, since the optical film is formed of an olefin resin, it can be made thinner than the conventional optical film. This makes it possible to reduce the thickness of the polarizing plate provided with the optical film and the liquid crystal display device provided with the polarizing plate.

  Moreover, according to the polarizing plate and the liquid crystal display device of the present invention, since such an optical film having high mechanical strength is provided, the film is hardly broken and the durability is improved. In addition, by providing an optical film made of an olefin-based resin that can be thinned, it is possible to reduce the thickness of the polarizing plate and the liquid crystal display device.

It is the perspective view which showed typically the measuring method of X-ray diffraction intensity. It is the graph which isolate | separated the peak from the diffraction pattern. It is a cross-sectional schematic diagram of the polarizing plate in one Embodiment of this invention. It is a cross-sectional schematic diagram of the liquid crystal display device using a polarizing plate. It is a graph which shows the X-ray-diffraction pattern of the optical film of Example 1 (unstretched film). It is a graph which shows the X-ray-diffraction pattern of the optical film of Example 2 (biaxially stretched film). 6 is a graph showing an X-ray diffraction pattern of a sample of Comparative Example 1. 6 is a graph showing an X-ray diffraction pattern of a sample of Comparative Example 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited by the member, arrangement | positioning, etc. which are demonstrated below, These members etc. can be suitably changed in accordance with the meaning of this invention.

(Optical film)
The optical film of the present invention is an optical film made of an olefin resin and has a crystallinity of 35% or more.

  A method for measuring the degree of crystallinity in the present invention will be described with reference to FIG. The crystallinity of the present invention is calculated from the area obtained by irradiating the optical film F with X-rays, measuring the X-ray diffraction intensity, obtaining a diffraction pattern. FIG. 1 is a perspective view schematically showing a method for measuring the X-ray diffraction intensity by the transmission-imaging method. When a diffraction pattern obtained by irradiating a point O in the plane from the normal direction of the optical film F with X-rays is recorded on an imaging plate or the like, various diffraction patterns can be obtained depending on the crystallinity constituting the optical film F. it can.

  Next, the method for calculating the crystallinity in the present invention will be specifically described. First, X-rays are irradiated perpendicularly to the surface of the optical film F from the normal direction of the surface of the optical film F. The X-ray transmitted through the optical film F is diffracted in a direction that satisfies Bragg's law, and a concentric X-ray diffraction image having an angle of 2θ with the extension line of the incident X-ray is set as an imaging plate. I is shown above. The integrated intensity of each diffraction line is calculated from this X-ray diffraction image, and an X-ray diffraction pattern profile is created with the vertical axis representing the X-ray diffraction intensity and the horizontal axis representing 2θ.

Next, as shown in FIG. 2, a profile in the range of 2θ = 5 to 30 ° is used in this X-ray diffraction pattern, a base line connecting both ends is drawn there, and the background from the diffraction pattern and the base line is drawn. Calculate the curve. Then, a peak obtained by subtracting the background from the diffraction pattern is set as a separation peak, and a peak peculiar to crystalline is a crystalline peak, and a peak peculiar to amorphous is a non-crystalline peak. In the case of an unstretched product such as an unstretched film, the degree of crystallinity is calculated by the following formula from the values of the crystalline peak area and the non-crystalline peak area.
Crystallinity (%) = {(crystalline peak area) / (crystalline peak area + noncrystalline peak area)} × 100
On the other hand, in the case of a stretched product such as a uniaxially stretched film or a biaxially stretched film, the above formula cannot be strictly applied when calculating the degree of crystallinity due to crystal orientation. Therefore, the crystallinity in this case is calculated by the following formula. In the following formula, the crystallinity is calculated on the assumption that all but non-crystal is crystal.
Crystallinity (%) = {1− (noncrystalline peak area / (crystalline peak area + noncrystalline peak area))} × 100

  As a specific method of X-ray diffraction measurement, for example, a 10 cm × 10 cm film sample is cut out, an X-ray beam is obtained from CuKα rays using a Rigaku X-ray diffractometer RotaFlex RU200B, and the film is irradiated with the diffraction beam. Is recorded as a diffraction pattern on the imaging plate.

  The upper limit of the crystallinity of the optical film F is not particularly defined as long as it is 35% or more, but it is 99.9% or less as a theoretical upper limit of the crystallinity, and 95% or less as a practical limit value. . If the degree of crystallinity is less than 35%, the degree of crystallization of the resin constituting the optical film F is low and the mechanical strength is low, so that there is a disadvantage that breakage and the like are likely to occur. The degree of crystallinity may be 35% or more, preferably 40% or more, and more preferably 45% or more.

  The optical film F having a degree of crystallinity exceeding approximately 60% can be obtained by using a new material called a nano-oriented crystal. Nano-oriented crystals have small crystal particles and high orientation in the direction of elongation, and are particularly excellent in properties such as mechanical strength, heat resistance, and transparency as compared with conventional oriented crystal materials. Nano-oriented crystals are obtained by stretching the polymer melt at a strain rate higher than the critical elongation strain rate, and after cooling the polymer melt into an oriented melt state, cooling crystallization while maintaining this oriented melt state. Can be manufactured.

The crystal size of the nano-oriented crystal is 300 nm or less, preferably 100 nm or less, more preferably 20 nm or less. Furthermore, the number density of the crystals of the nano-oriented crystal is 40 μm ⁻³ or more, preferably 10 ³ μm ⁻³ or more, more preferably 10 ⁵ μm ⁻³ or more. The nano-oriented crystal has a high degree of crystallinity but a small crystal size, and therefore has little light scattering on the crystal surface and high transparency.

  Regarding this nano-oriented crystal and its production method, Japanese Patent Application Laid-Open No. 2008-248039 and 'Elongational crystallographic of isopropionic polypropylene forms nano-orientated crystals with 10-44. "High performance by polymer elongation crystallization" (Polymer 2010, 59, July, p. 492-496).

  For the purpose of adjusting the crystallinity of the optical film F, a nucleating agent may be added to the olefin resin in the production of the nano-oriented crystal. Examples of the nucleating agent include 3,6-dichlorophthalic anhydride, 4,5-dichlorophthalic anhydride, 3,6-dibromophthalic anhydride, 3,4-dibromophthalic anhydride, 3-chloro-5-fluoroanhydride Examples include phthalic acid, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, and tetraiodophthalic anhydride. Among these compounds, mention may be made of dihalogen-substituted phthalic anhydrides such as 3,6-dichlorophthalic anhydride and 3,4-dibromophthalic anhydride.

  In the case of the above-described nano-oriented crystal, a nano nucleating agent can also be used as the nucleating agent. The nano nucleating agent is a fine nucleating agent having a number average particle size of 0.1 μm or less (more preferably 50 nm or less). The addition amount of the nanonucleating agent is preferably 0.1 to 0.5% by weight. Examples of the nanonucleating agent include sodium-2,2′-methylene-bis (4,6-di-tert-butylphenyl) phosphate, sodium-bis (4-tert-butylphenyl) phosphate, 1,3 , 2,4-Dibenzylidenesorbitol, 1,3,2,4-di (p-methylbenzylidene) sorbitol, 1,3,2,4-di (p-ethylbenzylidene) sorbitol, 1,3-p-chloro Examples thereof include benzylidene-2,4-p-methylbenzylidene sorbitol, 1,3,4,4-di (p-chlorobenzylidene) sorbitol and the like.

Next, the retardation value of the optical film F will be described. The optical film F is in the range plane retardation value _{R o} at the wavelength 590nm is 0～400Nm, and the thickness direction retardation _{R th} at the wavelength 590nm are those preferably in the range of 0～400Nm. When the in-plane retardation value _Ro and the thickness direction retardation value _Rth exceed 400 nm, the retardation is excessively manifested, which is not preferable as the optical film F. As will be described later, a polarizing film protective film or retardation film is particularly preferable. When the optical film F is used, display unevenness or the like is likely to occur.

Here, the in-plane slow axis direction of the refractive index of the optical film F n _x, plane fast axis direction of the refractive index n _y of the optical film _F, the refractive index in the thickness direction of the retardation layer n _z, When the thickness of the film is d, the in-plane retardation value _Ro and the thickness direction retardation value _Rth can be expressed by the following equations.
_{R 0 = (n x -n y} ) × d (1)
_Rth = [( _nx + _ny ) / 2- _nz ] * d (2)

The thickness direction retardation value R _th is the in-plane retardation value R ₀ , the retardation value R ₄₀ measured by tilting the slow axis by 40 °, the film thickness d, and the average refractive index n of the film. with _0, obtains the _{n x, n y, n z} numerically from equation (1) and equation (4) to (7), these can be calculated by substituting the equation (2). For reference, the _Nz coefficient = can be calculated from Equation (3). The same applies to other descriptions in the present specification.
N _z factor _{= (n x -n z) /} (n x -n y) (3)
_{R 40 = (n x -n y} ') × d / cos (φ) (4)
_{(N x + n y + n} z) / 3 = n 0 (5)
here,
φ = sin ⁻¹ [sin (40 °) / n ₀ ] (6)
_{ny ′} = _ny × _nz / [ _ny ² × sin ² (φ) + _nz ² × cos ² (φ)] ^1/2 (7)

In the commercially available phase difference measuring apparatus, the numerical calculation shown here is automatically performed in the apparatus, and the in-plane retardation value R ₀ and the thickness direction retardation value R _th are automatically displayed. There are many things. An example of such a measuring device is KOBRA-WPR (manufactured by Oji Scientific Instruments).

  Next, the olefin resin constituting the optical film F will be described. Examples of the olefin resin include a cyclic olefin resin obtained by polymerizing a cyclic olefin monomer such as norbornene or another cyclopentadiene derivative using a polymerization catalyst, or a chain olefin monomer such as ethylene or propylene as a polymerization catalyst. A chain olefin-based resin polymerized using Of these, the cyclic olefin-based resin is non-crystalline and thus has a low crystallinity and is not optimal for the present invention. On the other hand, the chain olefin resin is more preferable than the cyclic olefin resin because it is crystalline and has a high crystallinity.

Here, as cyclic olefin resin, the following resin can be illustrated, for example.
(1) A resin obtained by performing ring-opening metathesis polymerization from cyclopentadiene and olefins using norbornene or a derivative thereof obtained by Diels-Alder reaction as a monomer, followed by hydrogenation;
(2) A resin obtained by performing ring-opening metathesis polymerization using dicyclopentadiene and olefins or methacrylates as a monomer by tetracyclododecene or a derivative thereof obtained by Diels-Alder reaction, followed by hydrogenation;
(3) A resin obtained by performing ring-opening metathesis copolymerization in the same manner using two or more selected from norbornene, tetracyclododecene and derivatives thereof and other cyclic olefin monomers, followed by hydrogenation;
(4) A resin obtained by addition-copolymerizing an aromatic compound having a vinyl group to norbornene, tetracyclododecene or a derivative thereof.

  Examples of chain olefin resins include polyethylene resins and polypropylene resins. Among these resin materials, the adhesiveness with the polarizing film is relatively good, the film formed has high flexibility and can be thinned, the raw material is inexpensive and the production cost is low, etc. Therefore, a polypropylene resin is preferable. The polypropylene resin may be composed of a propylene homopolymer or a copolymer of polypropylene and another comonomer.

Examples of the comonomer copolymerized with propylene include ethylene and α-olefins having 4 to 20 carbon atoms. In this case, the following compounds can be given as specific examples of the α-olefin. 1-butene, 2-methyl-1-propene (above C ₄ ); 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene (above C ₅ ); 1-hexene, 2-ethyl- 1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene ₆ ); 1-heptene, 2-methyl-1-hexene, 2,3-dimethyl-1-pentene, 2-ethyl-1-pentene, 2-methyl-3-ethyl-1-butene (above C ₇ ); 1-octene, 5-methyl-1-heptene, 2-ethyl-1-hexene, 3,3-dimethyl-1-hexene, 2-methyl-3-ethyl-1-pentene, 2,3,4-trimethyl- 1-pentene, 2-propyl-1-pentene, , 3-diethyl-1-butene (or _C 8); 1-nonene _(C 9); 1-decene _(C 10); 1-undecene _(C 11); 1-dodecene _(C 12); 1-tridecene ( C ₁₃ ); 1-tetradecene (C ₁₄ ); 1-pentadecene (C ₁₅ ); 1-hexadecene (C ₁₆ ); 1-heptadecene (C ¹⁷ ); 1-octadecene (C ₁₈ ); 1-nonadecene (C ₁₉₎ )etc. Of these, α-olefins having 4 to 12 carbon atoms are preferred. From the viewpoint of copolymerizability, 1-butene, 1-pentene, 1-hexene and 1-octene are particularly preferable, and 1-butene and 1-hexene are particularly preferable.

  The copolymer may be a random copolymer or a block copolymer. Preferable copolymers include propylene / ethylene copolymers and propylene / 1-butene copolymers. In the propylene / ethylene copolymer and the propylene / 1-butene copolymer, the ethylene unit content and the 1-butene unit content are, for example, 616 of “Polymer Analysis Handbook” (published by Kinokuniya, 1995). It can obtain | require by performing an infrared (IR) spectrum measurement by the method described in the page.

  From the viewpoint of improving the transparency and workability of the optical film F, it is preferable to use propylene as a main component and a random copolymer with any unsaturated hydrocarbon, and among them, a copolymer with ethylene is preferable. When a copolymer is used, the copolymerization ratio of unsaturated hydrocarbons other than propylene is advantageously in the range of 1 to 10% by weight, and the more preferable copolymerization ratio is in the range of 3 to 7% by weight. Is within. It is preferable to set the unit of unsaturated hydrocarbons other than propylene to 1% by weight or more because the processability and transparency of the optical film F are improved. On the other hand, when the ratio exceeds 10% by weight, the melting point of the resin is lowered and the heat resistance is deteriorated, which is not preferable. In addition, when setting it as the copolymer of a 2 or more types of comonomer and polypropylene, it is preferable that the total content of the unit derived from all the comonomer contained in the copolymer is 1 to 10 weight%.

The polypropylene resin can be produced by a method of homopolymerizing propylene using a known polymerization catalyst or a method of copolymerizing propylene and another copolymerizable comonomer. Examples of known polymerization catalysts include the following catalysts.
(1) Ti—Mg-based catalyst comprising a solid catalyst component containing magnesium, titanium and halogen as essential components;
(2) A catalyst system in which a solid catalyst component containing magnesium, titanium, and halogen as essential components is combined with an organoaluminum compound and, if necessary, a third component such as an electron donating compound;
(3) Metallocene catalysts, etc.

  Among these catalyst systems, the catalyst system shown in (2) is common. More specifically, the organoaluminum compound is preferably triethylaluminum, triisobutylaluminum, a mixture of triethylaluminum and diethylaluminum chloride, tetraethyldialumoxane, or the like. As the electron donating compound, cyclohexylethyldimethoxysilane, tert-butylpropyldimethoxysilane, tert-butylethyldimethoxysilane, dicyclopentyldimethoxysilane and the like are preferable.

  On the other hand, examples of the solid catalyst component shown in (1) include catalyst systems described in JP-A-61-218606, JP-A-61-287904, JP-A-7-216017, and the like. Examples of the metallocene catalyst shown in (3) include catalyst systems described in Japanese Patent No. 2587251, Japanese Patent No. 2627669, Japanese Patent No. 2668732, and the like.

  Polypropylene resin uses, for example, a solution polymerization method using an inert solvent typified by a hydrocarbon compound such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, and a liquid monomer as a solvent. It can be produced by a bulk polymerization method, a gas phase polymerization method in which a gaseous monomer is polymerized as it is, or the like. Polymerization by these methods may be carried out batchwise or continuously.

  The stereoregularity of the polypropylene resin may be any of isotactic, syndiotactic, and atactic. From the viewpoint of heat resistance, syndiotactic or isotactic is preferable.

  The melt flow rate (MFR) of the polypropylene resin is preferably in the range of 0.1 to 200 g / 10 minutes, particularly 0.5 to 50 g / 10 minutes. The MFR value is a value measured at a temperature of 230 ° C. and a load of 21.18 N in accordance with JIS K 7210. By using a polypropylene resin having an MFR in this range, a uniform film can be obtained without imposing a large load on the extruder.

  This polypropylene resin may be blended with known additives as long as the effects of the present invention are not impaired. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an antifogging agent, and an antiblocking agent. Examples of the antioxidant include phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, hindered amine light stabilizers, and the like. As the antioxidant, for example, a composite antioxidant having a unit having both a phenol-based antioxidant mechanism and a phosphorus-based antioxidant mechanism in one molecule can be used. Examples of the UV absorber include UV absorbers such as 2-hydroxybenzophenone and hydroxyphenylbenzotriazole, and benzoate UV blockers. The antistatic agent may be polymer type, oligomer type or monomer type. Examples of the lubricant include higher fatty acid amides such as erucic acid amide and oleic acid amide, higher fatty acids such as stearic acid, and salts thereof. Examples of the nucleating agent include a sorbitol nucleating agent, an organic phosphate nucleating agent, and a polymer nucleating agent such as polyvinylcycloalkane. As the anti-blocking agent, fine particles having a spherical shape or a shape close thereto can be used regardless of inorganic type or organic type. A plurality of these additives may be used in combination.

  The olefin-based resin can be formed into an optical film F by forming a film by an arbitrary method and performing a stretching treatment as necessary. The optical film F is preferably transparent and substantially free of in-plane retardation when used as a protective film 25 or a retardation film 23 described later. The optical film F having substantially no in-plane retardation is, for example, an extrusion molding method from a molten resin, a solvent casting method in which a resin dissolved in an organic solvent is cast on a flat plate, and the solvent is removed to form a film. Etc.

(Unstretched film)
Hereinafter, a method for producing the optical film F that is an unstretched film by an extrusion method will be described in detail. In extrusion molding, an olefin resin is melt-kneaded by rotation of a screw in an extruder and extruded from a T die into a sheet. The temperature of the molten sheet to be extruded is about 180 to 300 ° C. If the temperature of the molten sheet at this time is less than 180 ° C., the spreadability is not sufficient, the thickness of the resulting film becomes non-uniform, and retardation unevenness tends to occur in the film. Moreover, when the temperature exceeds 300 ° C., the resin is easily deteriorated or decomposed, and bubbles may be generated in the molten sheet or carbides may be contained.

The extruder may be a single screw extruder or a twin screw extruder. For example, when using a single-screw extruder is the ratio between the length L and the diameter D of the screw L / D of about 24 to 36, the screw groove in the spatial volume V ₁ and the resin metering section of the screw groove in the resin supply section The compression ratio V ₁ / V _2, which is the ratio to the space volume V ₂ , is about 1.5 to 4, and a screw having a full flight type, a barrier type or a Maddock type kneading part is used. it can. Barrier type in which L / D is 28 to 36 and compression ratio V ₁ / V ₂ is 2.5 to 3.5 from the viewpoint of suppressing deterioration and decomposition of the olefin resin and uniformly melting and kneading. It is preferable to use a screw.

  Moreover, in order to suppress deterioration and decomposition | disassembly of an olefin resin as much as possible, it is preferable to make the inside of an extruder into a nitrogen atmosphere or a vacuum. Furthermore, in order to remove the volatile gas generated when the olefin resin is deteriorated or decomposed, it is also preferable to provide an orifice of about 1 mmφ to 5 mmφ at the tip of the extruder to increase the resin pressure at the tip of the extruder. Increasing the resin pressure at the leading end of the extruder by installing an orifice means increasing the back pressure at the leading end, thereby improving the stability of extrusion. The diameter of the orifice to be used is more preferably 2 mmφ or more and 4 mmφ or less.

  The T-die used for extrusion preferably has no fine steps or scratches on the surface of the resin flow path, and its lip portion is plated or coated with a material having a low coefficient of friction with the molten olefin resin. Further, a sharp edge shape with a lip tip polished to 0.3 mmφ or less is preferable. Examples of the material having a small friction coefficient include tungsten carbide type and fluorine type special plating. By using such a T-die, it is possible to suppress the generation of eyes and simultaneously suppress the die line, so that a resin film having excellent appearance uniformity can be obtained. In the T-die, the manifold has a coat hanger shape and preferably satisfies the following condition (i) or (ii), and more preferably satisfies the condition (iii) or (iv).

(I) When the lip width of the T die is less than 1500 mm: the thickness direction length of the T die> 180 mm,
(Ii) When the lip width of the T die is 1500 mm or more: the thickness direction length of the T die> 220 mm,
(Iii) When the lip width of the T die is less than 1500 mm: the length in the height direction of the T die> 250 mm,
(Iv) When the lip width of the T die is 1500 mm or more: Length in the height direction of the T die> 280 mm.

  By using a T die that satisfies such conditions, the flow of the molten olefin-based resin inside the T die can be adjusted, and the lip portion can be extruded while suppressing thickness unevenness. It is possible to obtain an optical film F that is excellent in accuracy and has a more uniform retardation.

  In addition, it is preferable to attach a gear pump via an adapter between an extruder and a T die from a viewpoint of suppressing the extrusion fluctuation | variation of an olefin resin. In order to remove foreign substances in the olefin resin, it is preferable to attach a leaf disk filter.

  The optical film F includes a metal roll (also referred to as a chill roll or a casting roll) and an elastic body that rotates by pressing the molten sheet extruded from the T die in the circumferential direction of the metal roll. It can obtain by pinching between and cooling and solidifying. In this case, the touch roll may be one in which an elastic body such as rubber is directly on the surface, or may be one in which the surface of the elastic body roll is covered with an outer cylinder made of a metal sleeve. When using a touch roll in which the surface of the elastic roll is covered with an outer cylinder made of a metal sleeve, cooling is usually performed by directly sandwiching a molten sheet of olefin resin between the metal cooling roll and the touch roll. . On the other hand, in the case of using a touch roll whose surface is an elastic body, a biaxially stretched film of a thermoplastic resin may be interposed between the molten sheet of olefin resin and the touch roll to sandwich the pressure.

  When the olefin resin molten sheet is cooled and solidified by being sandwiched between the cooling roll and the touch roll as described above, the surface temperature of the cooling roll and the touch roll may be lowered to rapidly cool the molten sheet. preferable. For example, it is preferable to adjust the surface temperature of both rolls to a range of 0 ° C. or higher and 30 ° C. or lower. When these surface temperatures exceed 30 ° C., it takes time to cool and solidify the molten sheet, so that the crystal component in the olefin resin grows, and the resulting film may be inferior in transparency. . On the other hand, when the surface temperature of the roll is lower than 0 ° C., the surface of the metal cooling roll is dewed and water droplets are attached, and the appearance of the resulting film tends to be deteriorated.

  Since the surface state of the metal cooling roll to be used is transferred to the surface of the optical film F, the thickness accuracy of the obtained optical film F may be reduced if the surface has irregularities. Therefore, it is preferable that the surface of the metal cooling roll is in a mirror surface state as much as possible. Specifically, the roughness of the surface of the metal cooling roll is preferably 0.4 S or less, more preferably 0.05 S to 0.2 S, expressed as a standard sequence of the maximum height. .

  The touch roll that forms the nip portion with the metal cooling roll has a surface hardness of 65 to 80 as a value measured by a spring type hardness test (A type) defined in JIS K 6301. It is preferable that it is 70-80. By using such a surface hardness touch roll, it becomes easy to maintain a uniform linear pressure applied to the molten sheet, and a bank (resin) of the molten sheet is provided between the metal cooling roll and the touch roll. It becomes easy to form into a film without causing a stagnation.

  The pressure (linear pressure) when sandwiching the molten sheet is determined by the pressure for pressing the touch roll against the metal cooling roll. The linear pressure is preferably 50 N / cm or more and 300 N / cm or less, and more preferably 100 N / cm or more and 250 N / cm or less. By setting the linear pressure within the above range, it becomes easy to produce the optical film F while maintaining a constant linear pressure without forming a bank.

  When sandwiching a biaxially stretched film of a thermoplastic resin together with a molten sheet of an olefinic resin between a metal cooling roll and a touch roll, the thermoplastic resin constituting the biaxially stretched film is composed of an olefinic resin and Any resin that does not strongly heat-seal can be used. Specific examples include polyester, polyamide, polyvinyl chloride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and polyacrylonitrile. Among these, polyesters that have little dimensional change due to humidity, heat, and the like are most preferable. The thickness of the biaxially stretched film is usually about 5 to 50 μm, preferably 10 to 30 μm.

  The distance (air gap) from the lip of the T die to the pressure between the metal cooling roll and the touch roll is preferably 200 mm or less, and more preferably 160 mm or less. The molten sheet extruded from the T-die is stretched from the lip to the roll, and orientation tends to occur. By shortening the air gap as described above, a film having a smaller orientation can be obtained. The lower limit of the air gap is determined by the diameter of the metal cooling roll to be used, the diameter of the touch roll, and the tip shape of the lip to be used, and is usually 50 mm or more.

  The processing speed when producing the optical film F is determined by the time required for cooling and solidifying the molten sheet. When the diameter of the metal cooling roll to be used is increased, the distance at which the molten sheet is in contact with the cooling roll becomes longer, so that production at a higher speed is possible. Specifically, when a 600 mmφ metal cooling roll is used, the processing speed is about 5 to 20 m / min at the maximum.

  The molten sheet sandwiched between the metal cooling roll and the touch roll is cooled and solidified by contact with the roll. And after slitting an edge part as needed, it is wound up by a winder and turns into a roll film. In addition, in order to protect the surface of the optical film F during winding up to use of the optical film F, a surface protective film made of another thermoplastic resin is bonded to both sides of the optical film F during winding. You may wind up in the state. When a molten sheet of an olefin resin is sandwiched between a metal cooling roll and a touch roll together with a biaxially stretched film made of a thermoplastic resin, the biaxially stretched film is used as one surface protective film. You can also.

  The unstretched optical film F has a thickness of usually 20 to 200 μm, preferably 20 to 120 μm. When the thickness of the optical film F is less than 20 μm, the handling properties tend to be inferior, and even when the thickness exceeds 200 μm, the handling properties may decrease due to the increased rigidity of the film.

The optical film F needs to be excellent in transparency. Specifically, the haze value measured according to JIS K 7361 is 10% or less, preferably 7% or less. When the haze value exceeds 10%, when the obtained polarizing plate is applied to a liquid crystal display device, white luminance tends to decrease and the screen tends to become dark. In addition, the haze value measured according to JIS K 7361 is defined by the following formula.
(Diffuse transmittance / total light transmittance) × 100 (%)
An unstretched film can be manufactured by the above process. JP, 2007-253377, A can be referred to for details of this manufacturing method.

(Biaxially stretched film)
The optical film F may be a stretched film in addition to the unstretched film described above. A biaxially stretched film is suitable as the stretched film. A uniaxially stretched film is not suitable as the optical film F because the phase difference tends to increase because the molecules are oriented in the stretch direction. On the other hand, since the biaxially stretched film is stretched in the biaxial direction, the molecules are not biased and oriented only in one direction, and the phase difference is hardly exhibited excessively.

  A biaxially stretched film can be produced by subjecting the unstretched film obtained in the above process to stretching. By this stretching treatment, a thin optical film F with high mechanical strength can be obtained. As the stretching method, longitudinal stretching that stretches in the film longitudinal direction (MD) of the unstretched film and lateral stretching that stretches in a direction substantially perpendicular to the longitudinal direction (TD) are performed. Biaxial stretching may be simultaneous biaxial stretching that simultaneously stretches in two stretching directions, or sequential biaxial stretching that stretches in one direction and then stretches in the other.

(1) Longitudinal stretching Examples of the longitudinal stretching method include a method of stretching an unstretched film by a difference in rotational speed between two or more rolls, and a long span stretching method. The long span stretching method is a method in which a longitudinal stretching machine having two pairs of nip rolls and an oven disposed therebetween is used to stretch the unstretched film in the oven by a difference in rotational speed between the two pairs of nip rolls. . In order to obtain the optical film F with high optical uniformity, the long span longitudinal stretching method is particularly advantageous. Of the longitudinal stretching methods, a method using an air floating oven is particularly preferable.

  After the longitudinal stretching, the longitudinally stretched film is once wound up in a roll shape and used for the next lateral stretching. The longitudinal draw ratio is not limited, but is usually 1.01 to 2 times, and in order to obtain an optical film excellent in optical uniformity, it is preferably 1.05 to 1.8 times.

(2) Lateral stretching Next, lateral stretching will be described. Next, transverse stretching is performed on the longitudinally stretched film obtained in the longitudinal stretching step. The transverse stretching of this embodiment is composed of the following three steps.
(2-1) A step of preheating the film at a preheating temperature equal to or higher than the melting point of the olefin resin (preheating step);
(2-2) Step of stretching the film in the transverse direction at a stretching temperature lower than the preheating temperature (lateral stretching step);
(2-3) A step of heat-setting the horizontally stretched film stretched in the transverse direction (heat setting step).

  As a typical transverse stretching method, there is a tenter method. The tenter method is a method in which a film in which both ends in the film width direction are fixed with a chuck is stretched in an oven with a wide chuck interval. In the tenter method, each step is performed in each zone. In this case, the oven temperature of the zone which performs a preheating process (Y1), the zone which performs a horizontal extending process (Y2), and the zone which performs a heat setting process (Y3) uses the apparatus which can adjust temperature independently.

(2-1) Preheating process A preheating process is a process performed before the process of extending | stretching a film to a horizontal direction, and is a process of heating a film to the temperature of sufficient height to extend | stretch a film. The preheating temperature means the atmospheric temperature in the zone where the oven preheating process is performed, and is a temperature equal to or higher than the melting point of the olefin resin of the film to be stretched. Although the specific temperature of a preheating process is based also on melting | fusing point of an olefin resin, it is 90-180 degreeC normally, Preferably it is temperature in the range of 110-160 degreeC, More preferably, it is 135-145 degreeC.

(2-2) Transverse stretching step The transverse stretching step is a step of stretching the film in the lateral direction (width direction). The stretching temperature in this transverse stretching step is lower than the preheating temperature. By stretching the preheated film at a temperature lower than that of the preheating step, the film can be stretched uniformly in the transverse direction, and as a result, an optical film F having excellent optical axis uniformity can be obtained. . The stretching temperature is preferably 5 to 20 ° C lower than the preheating temperature in the preheating step, and more preferably 7 to 15 ° C.

The draw ratio by the drawing treatment is preferably 50 to 300%, particularly 100 to 250%, more preferably 150 to 200%. When the draw ratio is less than 50%, the mechanical strength of the optical film F is not improved so much, which is not preferable. On the other hand, if the draw ratio exceeds 300%, the film thickness becomes too thin and, on the contrary, it becomes easy to break or the handling property is lowered, which is not preferable. In addition, the draw ratio here is calculated | required using the following numerical formula.
Stretch ratio (%) = 100 × {(Length after stretching) − (Length before stretching)} / (Length before stretching)

(2-3) Heat setting step The heat setting step is a step of passing the film through the atmosphere at a predetermined temperature in the oven while maintaining the film width at the end of the drawing step, and the optical drawing in the transverse drawing step. It is carried out in order to effectively ensure the stability of the optical characteristics of the film F. In this heat setting step, the film is passed through a zone having a predetermined heat setting temperature while maintaining the width of the optical film F in the transverse stretching step as it is. The heat setting temperature in the heat setting process means the ambient temperature in the zone where the heat setting process of the oven is performed. In order to efficiently suppress the shake of the optical axis of the film, the heat setting temperature is preferably within a range from a temperature 5 ° C. lower than the stretching temperature in the stretching step to a temperature 30 ° C. higher than the stretching temperature.

  The residence time of the optical film F in the heat setting step is preferably 10 to 120 seconds, more preferably 30 to 90 seconds, and still more preferably 30 to 60 seconds. A residence time means the time when the optical film F exists in the zone which performs the heat setting process of a tenter stretching machine. If the residence time in the heat setting step is less than 10 seconds, the thermal stability of the optical film F finally obtained may be insufficient. Further, when the residence time exceeds 120 seconds, there is a problem that productivity is lowered.

  The step of transverse stretching may further include a heat relaxation step. The thermal relaxation step is a step of removing unnecessary strain (residual strain) by stretching the film to a predetermined width in the transverse stretching step and then narrowing the chuck interval by several% (usually 0.5 to 7%). It is. Normally, in the tenter method, the thermal relaxation step is performed in a thermal relaxation zone between the stretching zone and the heat setting zone and capable of setting the temperature independently of the other zones.

  A biaxially stretched film can be obtained by the above steps. JP, 2007-286615, A can be referred to for details of this extending method.

  Since the optical film F obtained in this way has been subjected to stretching treatment, it has higher mechanical strength than an unstretched film and is not easily broken.

  Moreover, since the optical film F extends | stretches in a biaxial direction, it is thin compared with an unstretched film. Specifically, the film thickness of the stretched optical film F is 0.7 to 0.25 times the thickness when the film thickness of the unstretched film is 1. The specific film thickness is usually 4 to 140 μm, and 5 to 40 μm is particularly preferable from the viewpoint of thinning. Thus, the optical film F with a thin film thickness of less than 40 μm is difficult to realize when a cellulose acetate resin is used as in Patent Document 1, and the olefin resin is biaxially stretched as in the present invention. Can be obtained.

(Polarizing plate 20)
Next, a polarizing plate using the optical film F of the present invention will be described. FIG. 3 is a drawing showing a polarizing plate in one embodiment of the present invention, and shows a schematic sectional view of the polarizing plate. As shown in FIG. 3A, the polarizing plate 20 includes at least a polarizing film 21 and a retardation film 23 laminated on one surface of the polarizing film 21. The polarizing film 21 and the protective film 25 are bonded and laminated via an adhesive layer (not shown). Alternatively, as another embodiment, as illustrated in FIG. 3B, the polarizing plate 20 may include a polarizing film 21 and a protective film 25 laminated on one surface of the polarizing film 21. As another embodiment, as shown in FIG. 3C, a protective film 25, a polarizing film 21, and a retardation film 23 may be laminated in this order as the polarizing plate 20. Hereinafter, each layer constituting the polarizing plate 20 will be described.

(1) Polarizing film 21
The polarizing film 21 is a film having a function of converting natural light into linearly polarized light. As the polarizing film 21, a film obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film can be used. As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. As the polyvinyl acetate resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, polyvinyl acetate and Examples thereof include copolymers with other copolymerizable monomers. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group.

  The saponification degree of the polyvinyl alcohol resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can also be used. The degree of polymerization of the polyvinyl alcohol resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

  A film obtained by forming such a polyvinyl alcohol resin is used as a raw film of the polarizing film 21. The method for forming a polyvinyl alcohol-based resin is not particularly limited, and can be formed by a known method. Although the thickness of a polyvinyl alcohol-type raw film is not specifically limited, For example, it is about 10-150 micrometers.

  The polarizing film 21 usually has a step of uniaxially stretching such a polyvinyl alcohol resin film, a step of adsorbing a dichroic dye by dyeing the polyvinyl alcohol resin film with a dichroic dye, and a dichroic dye It is manufactured through a step of treating the adsorbed polyvinyl alcohol-based resin film with a boric acid aqueous solution and a step of washing with water after the treatment with the boric acid aqueous solution.

  Uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before dyeing with the dichroic dye, simultaneously with dyeing, or after dyeing. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before boric acid treatment or during boric acid treatment. Moreover, uniaxial stretching can also be performed in several steps. For uniaxial stretching, a method of stretching uniaxially between rolls having different peripheral speeds, a method of stretching uniaxially using a hot roll, or the like can be adopted. Further, the uniaxial stretching may be dry stretching in which stretching is performed in the air, or may be wet stretching in which stretching is performed in a state where a polyvinyl alcohol-based resin film is swollen using a solvent such as water. The draw ratio is usually about 3 to 8 times.

  The polyvinyl alcohol resin film can be dyed with a dichroic dye by, for example, a method of immersing the polyvinyl alcohol resin film in an aqueous solution containing the dichroic dye. Specifically, iodine or a dichroic dye is used as the dichroic dye. In addition, it is preferable to perform the process which a polyvinyl alcohol-type resin film swells by immersing in water before a dyeing process.

  When iodine is used as the dichroic dye, a method of dyeing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide is usually employed. The content of iodine in this aqueous solution is usually about 0.01 to 1 part by weight per 100 parts by weight of water, and the content of potassium iodide is usually about 0.5 to 20 parts by weight per 100 parts by weight of water. It is. The temperature of the aqueous solution used for dyeing is usually about 20 to 40 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 20 to 1,800 seconds.

On the other hand, 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 a water-soluble dichroic dye is usually employed. The content of the dichroic dye in this aqueous solution is usually about 1 × 10 ⁻⁴ to 10 parts by weight, preferably about 1 × 10 ⁻³ to 1 part by weight per 100 parts by weight of water. This aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing assistant. The temperature of the aqueous dichroic dye solution used for dyeing is usually about 20 to 80 ° C. Moreover, the immersion time (dyeing time) in this aqueous solution is usually about 10 to 1,800 seconds.

  The boric acid treatment after dyeing with a dichroic dye can be performed by immersing the dyed polyvinyl alcohol-based resin film in a boric acid-containing aqueous solution. The boric acid content in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The content of potassium iodide in the boric acid-containing aqueous solution is usually about 0.1 to 15 parts by weight, preferably about 5 to 12 parts by weight per 100 parts by weight of water. The immersion time in the boric acid-containing aqueous solution is usually about 60 to 1,200 seconds, preferably about 150 to 600 seconds, and more preferably about 200 to 400 seconds. The temperature of the boric acid-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C., more preferably 60 to 80 ° C.

  The polyvinyl alcohol resin film after the boric acid treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing a boric acid-treated polyvinyl alcohol resin film in water. The temperature of water in the water washing treatment is usually about 5 to 40 ° C., and the immersion time is usually about 1 to 120 seconds.

  After washing with water, a drying process is performed to obtain the polarizing film 21. The drying process can be performed using a hot air dryer or a far infrared heater. The temperature of a drying process is about 30-100 degreeC normally, Preferably it is 50-80 degreeC. The drying time is usually about 60 to 600 seconds, preferably 120 to 600 seconds.

  In this way, the polyvinyl alcohol-based resin film is subjected to uniaxial stretching, dyeing with a dichroic dye, and boric acid treatment, and the polarizing film 21 is obtained. The thickness of the polarizing film 21 can be about 2-40 micrometers, for example.

(2) Retardation film 23 (optical film F)
The retardation film 23 is an optical compensation film having an optical compensation function that widens the viewing angle when bonded to the liquid crystal cell 40. In the present invention, the optical film F described above can be preferably used as the retardation film 23. That is, the protective film 25 is made of an olefin resin, and a retardation film using the optical film F is preferable. The olefin-based resin can contain an additive as long as transparency and adhesiveness with the polarizing film 21 are not impaired.

  The retardation film 23 is preferably a biaxially stretched unstretched film obtained by forming an olefin resin into a film. In this case, in addition to appropriately adjusting the stretching ratio and the stretching speed so as to obtain a desired retardation value, various temperatures such as preheating temperature, stretching temperature, heat set temperature, cooling temperature during stretching, and the like What is necessary is just to select a pattern suitably.

  The thickness of the retardation film 23 is not particularly limited, but is preferably in the range of 4 to 140 μm. When the thickness of the retardation film 23 is less than 4 μm, it is difficult to handle the film, and it is difficult to express a predetermined retardation value. On the other hand, the thickness of the retardation film 23 is 140 μm. When exceeding, there are cases where processability is inferior, transparency is lowered, or the weight of the obtained polarizing plate 20 is increased. In particular, from the viewpoint of thinning, the thickness of the retardation film 23 is preferably in the range of 5 to 40 μm.

As the retardation film 23, various materials can be appropriately selected according to the mode of the applied liquid crystal cell. Examples of the retardation film 23 include a positive B plate (a positive biaxial retardation film). The positive B plate can be produced by stretching an unstretched film formed of a resin in the biaxial direction. The positive B plate, the in-plane slow axis direction of the refractive index of the film n _x, the in-plane fast axis direction of the refractive index of the film n _y, the refractive index in the thickness direction of the film is taken as n _z , “N _z > n _x > n _y ”. Plane retardation value _{R o} is preferably 0~400nm at the wavelength 590nm of the phase difference film 23, more preferably from 30 to 150 nm. The _{N z} coefficient is in the range of 1.1 to 7, especially preferably in the range of 1.4 to 5. From these ranges, the value of the optical characteristic may be appropriately selected according to the viewing angle characteristic required for the applied liquid crystal display device.

  The optical axis when laminating the polarizing film 21 and the retardation film 23 (positive B plate) is 0 ± 0.5 °, preferably 0, with respect to the absorption axis of the polarizing film 21. It is preferable that the angle is or 90 ± 0.5 °, preferably 90 °.

(3) Protective film 25 (optical film F)
The protective film 25 is a film that is laminated on the outside of the polarizing film 21 and protects the surface of the polarizing film 21. In the present invention, the above-described optical film F can be preferably used as the protective film 25. That is, the protective film 25 is made of an olefin resin, and a protective film using the optical film F is preferable. The olefin-based resin can contain an additive as long as transparency and adhesiveness with the polarizing film 21 are not impaired.

  As the protective film 25, an olefin-based resin formed into a film shape may be used without being stretched, or may be subjected to a stretching treatment. By using it as it is unstretched, since the thickness of the protective film 25 becomes large, performances, such as abrasion resistance of the protective film 25, improve, and handling property also improves. Moreover, since it is not necessary to perform an extending | stretching process in an unstretched film, it becomes possible to reduce the manufacturing cost of a film. On the other hand, when the stretching process is performed, the thickness of the protective film 25 is reduced, so that the polarizing plate 20 can be thinned and the mechanical strength of the protective film 25 is improved by the stretching process. In addition, a extending | stretching process is biaxial stretching extended | stretched both in a film longitudinal direction (MD) and the direction (TD) substantially perpendicular | vertical to this.

  A functional film having various functions can also be used as the protective film 25. Examples of such a functional film include an antiglare film. As an anti-glare film, the thing in which the hard-coat layer which has a fine uneven | corrugated shape on the surface can be mentioned. Such a hard coat layer is formed by a method of forming a coating film containing organic fine particles or inorganic fine particles on the surface of the base film, or after forming a coating film containing or not containing organic fine particles or inorganic fine particles. The film can be manufactured by a method (for example, an embossing method) or the like that presses the film against the uneven surface of a roll having an uneven shape.

  Furthermore, the protective film 25 having functionality is not limited to the above-described anti-glare film, and may be other functional films. For example, a film having functions such as antireflection, low reflection, antifouling, and antistatic may be used.

[Anti-reflective / low-reflective properties (anti-reflective / low-reflective film)]
In general, the antireflection film is formed by stretching a low refractive index layer that is also an antifouling layer and at least one layer having a higher refractive index than that of the low refractive index layer (that is, a high refractive index layer or a medium refractive index layer). It is formed by being provided on a resin film such as unstretched cellulose acetate.

  As a multilayer film in which transparent thin films of inorganic compounds (metal oxides, etc.) with different refractive indexes are laminated, colloid by chemical vapor deposition (CVD) method, physical vapor deposition (PVD) method, metal compound sol / gel method such as metal alkoxide And a method of forming a thin film by post-treatment (ultraviolet irradiation: JP-A-9-157855, plasma treatment: JP-A-2002-327310) after forming the metal oxide particle film.

  On the other hand, various antireflection films have been proposed as antireflection films having high productivity, in which a thin film in which inorganic particles are dispersed in a matrix is laminated. Moreover, the antireflection film which consists of an anti-glare antireflection layer which gave the shape of the fine unevenness | corrugation to the uppermost layer surface of such an antireflection film by application | coating is also mentioned.

[Granting antifouling properties]
For the purpose of imparting properties such as antifouling properties, water resistance, chemical resistance, and slipperiness, a known silicone-based or fluorine-based antifouling agent, slipping agent, etc., may be appropriately added to a cellulose acetate-based resin film. You can also. When these additives are added, it is preferably added in the range of 0.01 to 20% by mass, more preferably in the range of 0.05 to 10% by mass of the total solid content of the low n layer. Particularly preferably 0.1 to 5% by mass.

[Addition of dustproof / antistatic layer]
For the purpose of imparting dustproof and antistatic properties, a known antistatic agent such as a cationic surfactant or a polyoxyalkylene compound, an antistatic agent, or the like can be appropriately added to a resin film such as cellulose acetate. . These dustproofing agent and antistatic agent may contain the structural unit as a part of the function in the above-mentioned silicone compound or fluorine compound. When these are added as additives, it is preferably added in the range of 0.01 to 20% by mass, more preferably in the range of 0.05 to 10% by mass of the total solid content of the low n layer. Particularly preferably 0.1 to 5% by mass.

(4) Adhesive layer (not shown)
The polarizing film 21 and the protective film 25 are usually bonded via an adhesive layer. The adhesive that forms the adhesive layer provided on both surfaces of the polarizing film 21 may be the same or different.

  As the adhesive, an adhesive having an epoxy resin, urethane resin, cyanoacrylate resin, acrylamide resin, or the like as an adhesive component can be used. One of the adhesives preferably used is a solventless type adhesive. Solventless adhesives do not contain a significant amount of solvent, and are curable compounds (monomers or oligomers) that are reactively cured by heating or irradiation with active energy rays (for example, ultraviolet rays, visible light, electron beams, X-rays, etc.) The adhesive layer is formed by curing of the curable compound, and typically includes a curable compound that is reactively cured by heating or irradiation with active energy rays, and a polymerization initiator. In particular, when the protective film 25 is made of a polypropylene resin, the polypropylene resin film has low moisture permeability, so that when water-based adhesive is used, water drainage is poor, and the polarizing film 21 is damaged or polarized by moisture of the adhesive. It may cause deterioration of the product. Therefore, when bonding such a resin film with low moisture permeability, a solventless adhesive is preferable.

  From the viewpoint of rapid curing and productivity improvement of the polarizing plate 20 associated therewith, as an example of a preferable adhesive for forming the adhesive layer, an active energy ray-curable adhesive that is cured by irradiation with active energy rays can be mentioned. it can. As an example of such an active energy ray-curable adhesive, for example, a photo-curable adhesive that is cured by light energy such as ultraviolet light and visible light can be cited. The photocurable adhesive is preferably one that is cured by cationic polymerization from the viewpoint of reactivity. In particular, the solventless epoxy adhesive that uses an epoxy compound as a curable compound includes the polarizing film 21 and the protective film 25. It is more preferable because of its excellent adhesiveness.

  Although it does not restrict | limit especially as an epoxy compound which is a sclerosing | hardenable compound contained in the said solventless type epoxy adhesive, The thing hardened | cured by cationic polymerization is preferable. In particular, from the viewpoint of weather resistance and refractive index, it is more preferable to use an epoxy compound that does not contain an aromatic ring in the molecule. Examples of such epoxy compounds that do not contain an aromatic ring in the molecule include hydrides of aromatic epoxy compounds, alicyclic epoxy compounds, and aliphatic epoxy compounds. In addition, the epoxy compound that is a curable compound usually has two or more epoxy groups in the molecule.

  After bonding the protective film 25 to the polarizing film 21 through an adhesive layer made of an uncured epoxy adhesive, the adhesive layer is cured by irradiating active energy rays or heating, A protective film 25 is fixed on the polarizing film 21. In the case of curing by irradiation with active energy rays, ultraviolet rays are preferably used. Specific examples of the ultraviolet light source include a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, a black light lamp, and a metal halide lamp. The irradiation intensity and irradiation amount of active energy rays such as ultraviolet rays are appropriately selected so as to sufficiently activate the cationic polymerization initiator and not adversely affect the cured adhesive layer, the polarizing film 21 and the like. . In addition, when cured by heating, it can be heated by a generally known method, and the temperature and time at that time can sufficiently activate the cationic polymerization initiator, and the cured adhesive layer or It is appropriately selected so as not to adversely affect the film such as the polarizing film 21.

  The thickness of the adhesive layer comprising the cured epoxy adhesive obtained as described above is usually 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less, and usually 1 μm or more.

  Further, from the viewpoint of thinning the adhesive layer, an aqueous adhesive, that is, an adhesive in which an adhesive component is dissolved in water or an adhesive component is dispersed in water can also be used as the adhesive. Examples of the water-based adhesive include a water-based composition using a crosslinkable epoxy resin or a urethane resin as a main component.

  As the crosslinkable epoxy resin, for example, a polyamide epoxy obtained by reacting a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine with a polycarboxylic acid such as adipic acid and epichlorohydrin. Resins can be mentioned. Examples of such commercially available polyamide epoxy resins include “Smileys Resin 650” and “Smileys Resin 675” sold by Sumika Chemtex Co., Ltd.

  When a water-soluble epoxy resin is used as the adhesive component, it is preferable to mix other water-soluble resins such as a polyvinyl alcohol-based resin in order to further improve coatability and adhesiveness. Polyvinyl alcohol resins are modified such as partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, as well as carboxyl group-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, and amino group-modified polyvinyl alcohol. Polyvinyl alcohol resin may be used. Among them, a saponified product of a copolymer of vinyl acetate and unsaturated carboxylic acid or a salt thereof, that is, carboxyl group-modified polyvinyl alcohol is preferably used. Here, the “carboxyl group” is a concept including “—COOH” and a salt thereof.

  Examples of suitable commercially available carboxyl group-modified polyvinyl alcohol include Kuraray Poval KL-506, Kuraray Poval KL-318 and Kuraray Poval KL-118, which are sold by Kuraray Co., Ltd. From Goseinal (registered trademark) T-330 and Gosenal (registered trademark) T-350, and DR-0415 sold from Denki Kagaku Kogyo Co., Ltd. Examples include AF-17, AT-17, and AP-17 sold on the market.

  When an adhesive containing a water-soluble epoxy resin is used, the epoxy resin and other water-soluble resins such as a polyvinyl alcohol-based resin added as necessary are dissolved in water to constitute an adhesive solution. In this case, the water-soluble epoxy resin preferably has a concentration in the range of about 0.2 to 2 parts by weight per 100 parts by weight of water. Moreover, when mix | blending polyvinyl alcohol-type resin, the quantity is about 1-10 weight part per 100 weight part of water, Furthermore, it is preferable to set it as about 1-5 weight part.

  On the other hand, when a water-based adhesive containing a urethane resin is used, examples of suitable urethane resins include ionomer-type urethane resins, particularly polyester-based ionomer-type urethane resins. Here, the ionomer type is obtained by introducing a small amount of an ionic component (hydrophilic component) into the urethane resin constituting the skeleton. The polyester ionomer type urethane resin is a urethane resin having a polyester skeleton, into which a small amount of an ionic component (hydrophilic component) is introduced. Such an ionomer type urethane resin is suitable as a water-based adhesive because it is emulsified directly in water without using an emulsifier and becomes an emulsion. Examples of commercially available polyester ionomer-type urethane resins include “Hydran (registered trademark) AP-20” and “Hydran (registered trademark) APX-101H” sold by DCI Co., Ltd., both of which are emulsions. It can be obtained in the form of

  When an ionomer type urethane resin is used as an adhesive component, it is usually preferable to add an isocyanate-based crosslinking agent. The isocyanate-based crosslinking agent is a compound having at least two isocyanato groups (—NCO) in the molecule. Examples thereof include 2,4-tolylene diisocyanate, phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1, In addition to polyisocyanate monomers such as 6-hexamethylene diisocyanate and isophorone diisocyanate, adducts in which a plurality of these molecules are added to a polyhydric alcohol such as trimethylolpropane, and three molecules of diisocyanate are each of the isocyanate groups at one end. There are trifunctional isocyanurate forms in which isocyanurate rings are formed at the part, and polyisocyanate modified forms such as burettes formed by hydration and decarboxylation of the three diisocyanate molecules at the respective one-end isocyanato groups. . Examples of commercially available isocyanate-based crosslinking agents that can be suitably used include "Hydran (registered trademark) Assister C-1" sold by DCI Corporation.

  When an aqueous adhesive containing an ionomer type urethane resin is used, the concentration of the urethane resin is about 10 to 70% by weight, more preferably 20% by weight or more, and 50% by weight or less from the viewpoint of viscosity and adhesiveness. Thus, those dispersed in water are preferred. When the isocyanate crosslinking agent is blended, the blending amount may be appropriately selected so that the isocyanate crosslinking agent is about 5 to 100 parts by weight with respect to 100 parts by weight of the urethane resin.

  As a method for bonding the protective film 25 to the surface of the polarizing film 21 using an adhesive, a conventionally known method can be used. For example, the polarizing film 21 and / or the film to be bonded to it by the casting method, Meyer bar coating method, gravure coating method, comma coater method, doctor blade method, die coating method, dip coating method, spraying method, etc. The method of apply | coating an adhesive agent to a surface and superimposing both is mentioned. The casting method is a method of spreading and spreading an adhesive on the surface of a film to be coated while moving the film in a substantially vertical direction, a substantially horizontal direction, or an oblique direction between the two.

  In order to improve the adhesiveness, the polarizing film 21 and / or the adhesive surface of the film bonded thereto are subjected to surface treatment such as plasma treatment, corona treatment, ultraviolet irradiation treatment, flame (flame) treatment, saponification treatment, etc. You may give suitably. Examples of the saponification treatment include a method of immersing in an aqueous alkali solution such as sodium hydroxide or potassium hydroxide.

  The laminated body joined through the water-based adhesive is usually subjected to a drying treatment, and the adhesive layer is dried and cured. The drying process can be performed, for example, by blowing hot air. A drying temperature is normally selected from the range of about 40-100 degreeC, Preferably it is 60-100 degreeC. The drying time is, for example, about 20 to 1,200 seconds. The thickness of the adhesive layer after drying is usually about 0.001 to 5 μm, preferably 0.01 μm or more, preferably 2 μm or less, more preferably 1 μm or less. If the thickness of the adhesive layer becomes too large, the appearance of the polarizing plate 20 tends to be poor.

(Lamination of polarizing film 21, retardation film 23 and protective film 25)
Next, the bonding method of the polarizing film 21, the retardation film 23, and the protective film 25 is demonstrated. First, a method for bonding the polarizing film 21 and the retardation film 23 will be described. The polarizing plate 20 can be manufactured by a known method such as sheet-to-sheet bonding, sheet-to-roll bonding (also referred to as roll-to-sheet bonding), roll-to-roll bonding method, and the like. it can. The sheet-to-sheet bonding method is a method in which both the polarizing film 21 and the retardation film 23 are chip-cut and bonded to a sheet. In addition, the sheet-to-roll bonding method is such that one of the polarizing film 21 and the retardation film 23 is a roll-shaped film, and the other film is chip-cut into a sheet to be bonded to the roll-shaped film. It is a method. The roll-to-roll bonding method is a method of bonding the roll-shaped polarizing film 21 and the roll-shaped retardation film 23. The same applies to the case where the polarizing film and the protective film 25 are bonded.

  When the polarizing film 21 and the retardation film 23 are bonded together, the surface of the polarizing film 21 that is bonded to the retardation film 23 is subjected to a corona discharge treatment, and the polarizing film 21 is bonded to the retardation film 23 via this processed surface. It is preferable to match. By performing the surface treatment in this way, the adhesion between the polarizing film 21 and the retardation film 23 is improved. The same applies to the case where the polarizing film and the protective film 25 are bonded.

(Liquid crystal display device 1)
Next, a liquid crystal display device provided with the polarizing plate 20 of the present invention will be described. In the following example, a liquid crystal display device including the polarizing plate 20 illustrated in FIG. FIG. 4 is a schematic cross-sectional view showing an example of a basic layer configuration of the liquid crystal display device 1. As shown in FIG. 1, the liquid crystal display device 1 includes a liquid crystal panel 2, a backlight 10, and a light diffusion plate 50. The liquid crystal panel 2 includes a liquid crystal cell 40, a polarizing plate 20 bonded to the back side of the liquid crystal cell 40, and a polarizing plate 30 bonded to the viewing side of the liquid crystal cell 40. The polarizing plate 20 of this embodiment has a layer configuration in which a protective film 25, a polarizing film 21, a retardation film 23, and an adhesive layer 27 are laminated in this order.

  The polarizing plate 20 is bonded to the liquid crystal cell 40 so that the retardation film 23 is disposed on the liquid crystal cell 40 side and the protective film 25 is disposed on the opposite side (the farthest side from the liquid crystal cell 40). The polarizing plate 30 also has a similar layer configuration. In addition, although this embodiment demonstrated the structure by which the optical film F was provided in the polarizing plate 20 of the back side, it cannot be overemphasized that the optical film of this invention may be used as a protective film of the polarizing plate 30 of a visual recognition side. is there. Furthermore, the optical film of the present invention may be used as a protective film on both the viewing side and the back side polarizing plates. In these cases, since the protective film on the viewing side is in a position facing the observer, damage and wear are likely to occur, and thus the functions such as antireflection, low reflection, antifouling, and antistatic described above are imparted to the protective film. It is preferable.

  The liquid crystal cell 40 is an element that displays an image by electrically controlling a cell in which a liquid crystal material is sealed between glass substrates. More specifically, the liquid crystal cell 40 has a back surface polarized by the polarizing plate 20 disposed on the back side of the liquid crystal cell 40 by changing the molecular orientation of the liquid crystal material by electrical control from a display control unit (not shown). An image is displayed by changing the polarization state of the light of the light 10 and controlling the amount of light transmitted through the polarizing plate 30 disposed on the viewing side of the liquid crystal cell 40. The mode of the liquid crystal cell 40 is not particularly limited. For example, a VA mode, an IPS mode, a TN mode, an STN mode, an OCB mode, an ASM mode, or the like can be used.

  The liquid crystal panel 2 and the liquid crystal display device 1 can be manufactured by a known method. As a manufacturing method of the liquid crystal panel 2, the long polarizing plate 20 and the polarizing plate 30 wound in a roll shape can be cut into pieces and bonded to the liquid crystal cell 40.

  Usually, when the liquid crystal panel 2 is formed using the TN mode liquid crystal cell 40, the absorption axes of the polarizing plate 20 and the polarizing plate 30 are orthogonal to each other (crossed Nicols), and these absorption axes are rectangular. The liquid crystal cell 40 is disposed so as to be parallel to the long side direction or the short side direction.

  The backlight 10 is a device for illuminating the liquid crystal cell 40. Examples of the type of the backlight 10 include an edge light type and a direct type. The edge-light type backlight 10 irradiates light to the liquid crystal cell 40 through a light guide plate from a light source such as a cold cathode tube arranged on a side surface. In the direct type backlight 10, a light source is disposed on the back side of the liquid crystal cell 40 to irradiate the liquid crystal cell 40 with light. As the type of the backlight 10, a backlight according to the application of the liquid crystal display device 1 can be appropriately adopted.

  The light diffusing plate 50 is an optical member having a function of diffusing light from the backlight 10, for example, a material in which particles as a light diffusing agent are dispersed in a thermoplastic resin to impart light diffusibility, thermoplasticity The surface of the resin film may be uneven to provide light diffusibility, or the resin film may be provided with a coating layer of a resin composition in which particles are dispersed on the surface of the thermoplastic resin film. . The thickness of the light diffusion plate 50 can be about 0.1 to 5 mm.

  Between the light diffusing plate 50 and the liquid crystal panel 2, a sheet or film exhibiting other optical functionality such as a brightness enhancement sheet (a reflective polarizing film (such as “DBEF”)) or a light diffusing sheet is disposed. You can also Two or more sheets or films exhibiting other optical functionalities can be arranged as needed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited by these examples. In the following examples, the part representing the amount used is based on weight unless otherwise specified.

[Measurement of crystallinity]
X-ray diffraction measurement was performed with the following apparatus and conditions. As a measurement sample, a size of 10 cm × 10 cm was cut out from the film and used. Irradiation was performed by changing the irradiation angle for each of the following steps, and a diffraction pattern of X-ray diffraction intensity in the following scanning range was obtained. The degree of crystallinity was calculated by the method described in this specification.
Apparatus: Spectris Co., Ltd. X'Pert PRO MPD
Radiation source: Cu 40 mA, 45 kV
Detector: IP (imaging plate)
Scanning range: 2θ = 3-60 °
Step: 2θ = 0.01671 °

[Measurement of phase difference value]
The in-plane retardation value _Ro and the thickness direction retardation value _Rth of the sample film were measured with the following apparatus and conditions. The measurement method is such that light of the above wavelength is incident from a direction inclined in 10 ° steps up to an angle of 50 ° on one side with respect to the normal direction of the film, all six points are measured, and the measured retardation value and average refractive index are measured. Based on the process value and the input film thickness value, the KOBRA WPR software was used.
Measuring apparatus: KOBRA-WPR, manufactured by Oji Scientific Instruments Co., Ltd. Measuring conditions: Rotating analyzer method using monochromatic light with a wavelength of 590 nm

[Example 1: Unstretched film]
Polypropylene resin (propylene-ethylene random copolymer, parameter (A) obtained in resin selection test = 0.011, Tm = 138 ° C., MFR = 8 g / 10 min, ethylene content = 4.6% by weight, CXS = 4%, manufactured by Sumitomo Chemical Co., Ltd., trade name: Nobrene W151) was introduced into a 65 mmφ extruder with a cylinder temperature of 200 ° C., melted and kneaded, and attached to the extruder at an extrusion rate of 65 kg / h. Extruded from the resulting 1200 mm wide T-die.

  The extruded molten polypropylene resin is sandwiched between a 400 mmφ casting roll adjusted to 12 ° C., an outer cylinder made of a metal sleeve adjusted to 12 ° C., and an elastic roll inside the outer cylinder. And cooled to obtain a polypropylene resin film having a thickness of 90 μm. The air gap was 115 mm, and the distance in which the molten polypropylene resin was sandwiched between the casting roll and the touch roll was 20 mm.

  The diffraction pattern of the optical film obtained as described above is shown in FIG. From this diffraction pattern, the crystallinity and the retardation value were calculated by the methods described in “[Measurement of crystallinity]” and “Measurement of retardation value”. The results are shown in Table 1.

[Example 2: Biaxially stretched film]
A polypropylene resin (manufactured by Sumitomo Chemical Co., Ltd., trade name: Nobrene W151) was melt kneaded and extruded under the same conditions as in Example 1 to obtain an unstretched film. Next, the obtained polypropylene-based resin film was introduced into a long span longitudinal stretching machine having two nip roll pairs and an air floating type oven between the two nip roll pairs, and longitudinal stretching was performed. The oven can be divided into a first zone on the inlet side of the polypropylene resin film, a second zone in the middle, and a third zone on the outlet side. The length of each zone is 2.5 m (overall length of the oven: 7 0.5 m). In the longitudinal stretching, the temperature of the first zone is 70 ° C., the temperature of the second zone is 90 ° C., the temperature of the third zone is 110 ° C., the speed of the polypropylene resin film at the oven inlet is 5 m / min, and the longitudinal stretching ratio is 1. The test was performed at 8 times. The obtained film was slit at a width of 900 mm and then wound up by a winder. The raw material thus obtained was stored for 14 days under conditions of a temperature of 23 ° C. and a humidity of 50%.

  Further, the longitudinally stretched film was stretched laterally by a tenter method to obtain a biaxially stretched film. The conditions for transverse stretching were as follows: preheating zone temperature = 141 ° C., stretching zone temperature = 130 ° C., heat setting zone temperature = 130 ° C., stretching ratio = 3.4 times. The diffraction pattern of the optical film obtained by the above is shown in FIG. From this diffraction pattern, the crystallinity and the retardation value were calculated by the methods described in “[Measurement of crystallinity]” and “Measurement of retardation value”. The results are shown in Table 1.

[Comparative Example 1]
An olefin resin having a low crystallinity (trade name: Vistamaxx, manufactured by ExxonMobil) was used as the polypropylene resin material. Since this olefin resin material has a low degree of crystallinity and the self-supporting force of the resin molded product is small and fragile, it is difficult to form a melt-extruded film as in Examples 1 and 2. Therefore, the olefin-based resin material is formed into a sheet by hot pressing at a temperature of 230 ° C., a preheating time of 5 minutes, a pressurization time of 5 minutes, a cooling temperature of 5 minutes, and a pressure of 5 MPa during pressurization. On the other hand, X-ray crystal diffraction measurement was performed under the same conditions as in Examples 1 and 2. The obtained diffraction pattern is shown in FIG. From this diffraction pattern, the crystallinity was calculated by the method described in “[Measurement of crystallinity]”. The results are shown in Table 1. In addition, as shown in this table | surface, the thickness of the obtained sample is as thick as 500 micrometers, and it turns out that it is not suitable for an optical use. Further, since it is not suitable for optical use, the phase difference values R ₀ and R _th could not be measured.

[Comparative Example 2]
A sheet-like sample was prepared under the same conditions as in Comparative Example 1, except that the olefin resin material having a low crystallinity was changed to Mitsui Chemicals, Inc., trade name: NOTIO. X-ray crystal diffraction measurement was performed on the sheet-like sample under the same conditions as in Examples 1 and 2. The obtained diffraction pattern is shown in FIG. From this diffraction pattern, the crystallinity was calculated by the method described in “[Measurement of crystallinity]”. The results are shown in Table 1. As shown in this table, the thickness of the obtained sample is as thick as 500 μm as in Comparative Example 1, indicating that it is not suitable for optical use. Further, since it is not suitable for optical use, the phase difference values R ₀ and R _th could not be measured.

  From Table 1, in Example 1 (unstretched film) and Example 2 (biaxially stretched film), the crystallinity is 35% or more, the retardation value is within an appropriate range, and the film thickness is small. Therefore, it can be seen that it is suitable for optical use. In particular, the biaxially stretched film of Example 2 has a very small film thickness of 16 μm, which proves very advantageous in reducing the thickness. Further, from the diffraction patterns (FIGS. 5 and 6), the crystal of Example 1 (unstretched film) is mainly a smectic crystal (smectic crystal), and in Example 2 (biaxially stretched film), α It is considered that crystals are the main crystal structure.

  On the other hand, since both Comparative Examples 1 and 2 have a low crystallinity, the self-supporting force of the resin molded product is small. For this reason, in these comparative examples, it is difficult to form into a small film thickness suitable for an optical film, and even if it can be processed into a sheet shape, it is found that the film thickness is large and unsuitable for optical applications.

F optical film, 1 liquid crystal display device, 2 liquid crystal panel, 10 backlight, 20 polarizing plate, 21 polarizing film, 23 retardation film, 25 protective film (optical film), 27 adhesive layer, 30 polarizing plate, 40 liquid crystal cell , 50 Light diffusing plate

Claims (10)

  An optical film for a polarizing plate made of an olefin resin, wherein the crystallinity is 35% or more.   The optical film according to claim 1, wherein the crystallinity is 45% or more. Plane retardation value _{R o} in the 590nm as defined by the following formula is in the range of 0～400Nm, the thickness direction retardation _{R th} in the 590nm is 0～400Nm, optical film according to claim 1 or 2 .
_{R o = (n x -n y} ) × d
_Rth = (( _nx + _ny ) / 2- _nz ) * d
_(Wherein, n _x, n y, _{n z} is the main axis x of the respective refractive index ellipsoid, y, represents the refractive index in the z-direction, and _n x, is _{n y} a refractive index of the optical film plane direction, ( _nz represents the refractive index in the thickness direction of the optical film, and d represents the thickness (nm) of the film.)   The optical film according to claim 1, wherein the optical film is a non-oriented film or a biaxially stretched film.   The optical film according to claim 4, wherein the optical film is a biaxially stretched film and has a thickness in the range of 5 to 40 μm.   The optical film according to claim 1, wherein the olefin resin is a polypropylene resin.   A polarizing plate comprising the optical film according to claim 1 and a polarizing film bonded to the optical film.   The polarizing plate according to claim 7, wherein the optical film is a protective film made of a non-oriented film.   The polarizing plate according to claim 7, wherein the optical film is a retardation film made of a biaxially stretched film.   A liquid crystal display device comprising: the polarizing plate according to claim 7; and a liquid crystal cell to which the polarizing plate is bonded.

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