JP6907904B2 - Optical film and its manufacturing method, polarizing plate and liquid crystal display device - Google Patents

Description

The present invention relates to an optical film, a method for producing the same, a polarizing plate, and a liquid crystal display device.

Liquid crystal display devices are widely used as display devices for televisions, notebook computers, smartphones, and the like. A liquid crystal display device usually includes a liquid crystal cell and a pair of polarizing plates that sandwich the liquid crystal cell; the polarizing plate includes a polarizing element and a pair of protective films that sandwich the polarizing element.

As the protective film, a cycloolefin resin film having good moisture resistance is used. In addition, the protective film usually contains inorganic fine particles such as silica particles for enhancing slipperiness. Patent Document 1 discloses a cycloolefin-based resin film containing silica fine particles. This cycloolefin-based resin film comprises 1) a step of dissolving a cycloolefin-based resin and silica particles in a mixed solvent of methylene chloride and methanol to prepare a dope; and 2) a support for the obtained dope. It is produced through a step of casting and drying it on top to obtain a film-like substance; and 3) a step of uniaxially stretching the obtained film-like substance in the width direction while further drying it.

Japanese Unexamined Patent Publication No. 2007-112967

However, the cycloolefin-based resin film obtained by the method of Patent Document 1 has a problem that adhesion failure with a polarizer and display unevenness in a liquid crystal display device are likely to occur.

Although the cause of this is not clear, it is presumed as follows. That is, in the step 3), when the film-like material containing the silica particles is uniaxially stretched, the stretching tension is likely to be applied in only one direction around the silica particles. Further, since the solvent contained in the film-like substance is only a low boiling point solvent such as methylene chloride or methanol, the solvent tends to be non-uniformly volatilized in the film-like substance around the silica particles in the step 3). , Stretch tension tends to be applied non-uniformly. As a result, in the obtained cycloolefin-based resin film, highly anisotropic voids are likely to be formed around the silica particles, and the residual stress is likely to vary. As a result, it is considered that the permeation of the adhesive varies, resulting in poor adhesion or uneven display.

The present invention has been made in view of the above circumstances, and provides an optical film containing a cycloolefin resin, which can suppress poor adhesion to a polarizer and display unevenness in a liquid crystal display device. With the goal.

[1] An optical film containing a cycloolefin resin, organic fine particles, and a high boiling point solvent having a boiling point of 90 ° C. or higher, which is heated at 10 ° C./min from 23 ° C. to 180 ° C. in thermomechanical analysis measurement. Then, when the optical film is held at 180 ° C. for 10 minutes, the amount of elongation of the optical film in the first direction in which the shrinkage rate of the optical film is maximized is S1 (μm), and the amount of elongation in the second direction orthogonal to the first direction is said. An optical film satisfying the following formulas (1) and (2) when the elongation amount of the optical film is S2 (μm).
Equation (1): S1 <0 <S2
Equation (2): | S1 / S2 | <3.0
[2] The optical film according to [1], wherein the average particle size of the organic fine particles is 0.04 to 2 μm.
[3] The optical film according to [1] or [2], wherein the organic fine particles contain a polymer containing a structural unit derived from a (meth) acrylic monomer and a structural unit derived from a styrene monomer. ..
[4] The optical film according to any one of [1] to [3], wherein the content of the high boiling point solvent is 0.01 to 1% by mass with respect to the total mass of the optical film.

[5] A polarizing plate including a polarizing element and an optical film according to any one of [1] to [4] arranged on at least one surface of the polarizing element.
[6] The first polarizing plate includes a liquid crystal cell, a first polarizing plate arranged on one surface of the liquid crystal cell, and a second polarizing plate arranged on the other surface of the liquid crystal cell. The first polarizer, the protective film F1 arranged on the surface of the first polarizing element opposite to the liquid crystal cell, and the protective film F2 arranged on the surface of the first polarizing element on the liquid crystal cell side. The second polarizing plate includes a second polarizing element, a protective film F3 arranged on the surface of the second polarizer on the liquid crystal cell side, and a side of the second polarizing element opposite to the liquid crystal cell. A liquid crystal display device including the protective film F4 arranged on the surface of the liquid crystal display device, wherein at least one of the protective films F1, F2, F3 and F4 is the optical film according to any one of [1] to [4]. ..
[7] The liquid crystal display device according to [6], wherein the liquid crystal cell is a VA mode liquid crystal cell.

[8] A step of obtaining a dope containing a cycloolefin resin, organic fine particles, and a solvent containing a high boiling point solvent having a boiling point of 90 ° C. or higher, and the obtained dope is cast on a metal support, dried, and dried. A method for producing an optical film, which comprises a step of peeling to obtain a film-like substance and a step of stretching the obtained film-like substance in two directions orthogonal to each other.

According to the present invention, it is possible to provide an optical film capable of suppressing poor adhesion to a polarizer and display unevenness in a liquid crystal display device.

It is a graph which shows an example of the thermomechanical analysis measurement result. It is a schematic diagram which shows an example of the structure of the liquid crystal display device of this invention.

The present inventors have found that an optical film containing organic fine particles and a high boiling point solvent and satisfying the formulas (1) and (2) in thermomechanical analysis measurement has good adhesiveness to a polarizer. It has been found that display unevenness of the display device can be suppressed.
Equation (1): S1 <0 <S2
Equation (2): | S1 / S2 | <3.0
S1: Elongation amount (μm) of the optical film in the first direction where the shrinkage rate is maximized.
S2: Elongation amount (μm) of the optical film in the second direction orthogonal to the first direction.

In order to satisfy the formulas (1) and (2), for example, the optical film is preferably stretched in two directions orthogonal to each other and the stretching ratio is appropriately adjusted, as will be described later.

The reason for this is not clear, but it is speculated as follows. First, the optical film is a biaxially stretched film-like material containing a cycloolefin resin, organic fine particles, and a high boiling point solvent. First, since the organic fine particles have higher flexibility than the inorganic fine particles, they can easily follow the stretching. Further, by biaxially stretching the film-like material, the stretching tension applied to the periphery of the organic fine particles can be made isotropic. Furthermore, since the film-like substance contains a high boiling point solvent, the solvent tends to volatilize uniformly around the organic fine particles, so that the variation in the amount of residual solvent is reduced and the variation in the stretching tension applied to the periphery of the organic fine particles is reduced. sell. As a result, it is considered that isotropic voids can be uniformly formed around the organic fine particles and the variation in residual stress can be reduced. It is considered that the isotropic voids can be formed around the organic fine particles in this way, so that the adhesive easily permeates into the voids and the adhesiveness with the polarizer is improved. Further, it is considered that display unevenness is suppressed by improving the adhesiveness with the polarizer and reducing the variation in the residual stress of the optical film. The present invention has been made based on such findings.

1. 1. Optical Film The optical film of the present invention contains a cycloolefin resin, organic fine particles, and a high boiling point solvent.

1-1. Cycloolefin-based resin The cycloolefin-based resin is preferably a homopolymer or copolymer of a cycloolefin monomer represented by the following general formula (A-1) or (A-2).

The cycloolefin monomer represented by the general formula (A-1) will be described.

^{R 1 to} R ⁴ of the general formula (A-1) represent a hydrogen atom, a halogen atom, a substituted or unsubstituted hydrocarbon group having 1 to 30 carbon atoms, or a polar group, respectively. However, ^{except when all of R 1 to} R ⁴ are hydrogen atoms, it is assumed that R ¹ and R ² are not hydrogen atoms at the same time, or R ³ and R ⁴ are hydrogen atoms at the same time.

The halogen atom is a fluorine atom, a chlorine atom, a bromine atom or an iodine atom. Examples of hydrocarbon groups having 1 to 30 carbon atoms include alkyl groups having 1 to 30 carbon atoms. Examples of polar groups include a carboxy group, a hydroxy group, an alkoxycarbonyl group, an allyloxycarbonyl group, an amino group, an amide group, a cyano group, a group in which these groups are bonded via a linking group such as a methylene group, and a carbonyl group. , A hydrocarbon group to which a polar divalent organic group such as an ether group, a silyl ether group, a thioether group and an imino group is bonded as a linking group is included. Among these, a carboxy group, a hydroxy group, an alkoxycarbonyl group or an allyloxycarbonyl group is preferable, and an alkoxycarbonyl group or an allyloxycarbonyl group is particularly preferable from the viewpoint of ensuring solubility during solution film formation.

At ^{least one of R 1 to} R ⁴ is preferably a polar group from the viewpoint of ensuring the solubility of the cycloolefin resin during solution film formation.

P in the general formula (A-1) represents an integer of 0 to 2. From the viewpoint of increasing the heat resistance of the optical film, p is preferably 1 to 2. This is because when p is 1 to 2, the obtained resin becomes bulky and the glass transition temperature tends to improve.

Next, the cycloolefin monomer represented by the general formula (A-2) will be described.

^{R 5} of the general formula (A-2) represents a hydrogen atom, a hydrocarbon group having 1 to 5 carbon atoms, or an alkylsilyl group having an alkyl group having 1 to 5 carbon atoms. Among them, R ⁵ is preferably a hydrocarbon group having 1 to 3 carbon atoms.

^{R 6} of the general formula (A-2) represents a polar group or a halogen atom. The polar group is preferably a carboxy group, a hydroxy group, an alkoxycarbonyl group, an allyloxycarbonyl group, an amino group, an amide group, or a cyano group. The halogen atom is a fluorine atom, a chlorine atom, a bromine atom or an iodine atom. Among them, R ⁶ is preferably a polar group, preferably a carboxy group, a hydroxy group, an alkoxycarbonyl group or an allyloxycarbonyl group, and particularly preferably an alkoxycarbonyl group or an allyloxycarbonyl group at the time of solution film formation. It is also preferable from the viewpoint of ensuring solubility.

By using a cycloolefin monomer represented by the general formula (A-2), the symmetry of the molecule is lowered, and the diffusion motion of the resin at the time of solvent volatilization is easily promoted.

P in the general formula (A-2) represents an integer of 0 to 2.

Specific examples of the structures of the general formulas (A-1) and (A-2) are shown below.

An example of a copolymerizable monomer copolymerizable with the cycloolefin monomer represented by the formula (A-1) or the formula (A-2) is represented by the formula (A-1) or the formula (A-2). A copolymerizable monomer capable of ring-opening copolymerization with the cycloolefin monomer, and a copolymerizable monomer additionally copolymerizable with the cycloolefin monomer represented by the formula (A-1) or the formula (A-2) are included.

Examples of copolymerizable monomers ring-open copolymerizable with the cycloolefin monomer represented by the formula (A-1) or the formula (A-2) include cyclobutene, cyclopentene, cycloheptene, cyclooctene, and dicyclopentadiene. Other cycloolefin monomers are included.

Examples of copolymerizable monomers that can be additionally copolymerized with the cycloolefin monomer represented by the formula (A-1) or the formula (A-2) include unsaturated double bond-containing compounds and vinyl-based cyclic hydrocarbon compounds. Contains (meth) acrylates. Examples of unsaturated double bond-containing compounds are olefin compounds having 2 to 12 (preferably 2 to 8) carbon atoms, and examples thereof include ethylene, propylene, and butene. Examples of vinyl-based cyclic hydrocarbon compounds include vinyl cyclopentene-based monomers such as 4-vinylcyclopentene and 2-methyl-4-isopropenylcyclopentene. Examples of (meth) acrylates include alkyl (meth) acrylates having 1 to 20 carbon atoms such as methyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and cyclohexyl (meth) acrylate.

The content of the structural units derived from the cycloolefin monomer represented by the formula (A-1) or the formula (A-2) is 50 to 100 mol% with respect to the total of the structural units constituting the cycloolefin resin. It can be preferably 60 to 100 mol%, more preferably 70 to 100 mol%.

The cycloolefin-based resin is a polymer obtained by homopolymerizing or copolymerizing a cycloolefin monomer represented by the general formula (A-1) or (A-2), and examples thereof include the following. (1) to (3) and (5) are preferable, and (3) and (5) are more preferable.
(1) Ring-opening copolymer of cycloolefin monomer represented by the general formula (A-1) or (A-2) (2) Cycloolefin represented by the general formula (A-1) or (A-2) Ring-opening copolymer of monomer and copolymerizable monomer (3) Hydrogenated (co) polymer of ring-opening (co) polymer of (1) or (2) above (4) (1) or (2) above ) Is cyclized by the Friedelcraft reaction, and then hydrogenated (co) polymer. (5) Cycloolefin represented by the general formula (A-1) or (A-2). Copolymer of monomer and unsaturated double bond-containing compound (6) Copolymer of cycloolefin monomer represented by general formula (A-1) or (A-2) and hydrogenation thereof (copolymer) Co) Copolymer (7) Alternating copolymer of cycloolefin monomer represented by the general formula (A-1) or (A-2) and methacrylate or acrylate

Examples of the cycloolefin resin include those having at least one of a structural unit represented by the following general formula (B-1) and a structural unit represented by the general formula (B-2). Above all, from the viewpoint that the glass transition temperature of the obtained cycloolefin resin is high and an optical film having high transmittance can be easily obtained, a polymer containing a structural unit represented by the general formula (B-2) or a general formula. A copolymer having a structural unit represented by (B-1) and a structural unit represented by the general formula (B-2) is preferable.

X in the general formula (B-1) is a group represented by −CH = CH− or a group represented by −CH ₂ CH ₂₋ . R ¹ to R ⁴ and p are each identical to ^R 1 to R ⁴ and p of the general formula (A-1).

X in the general formula (B-2) is a group represented by −CH = CH− or a group represented by −CH ₂ CH ₂₋ . ^R 5, ^{R 6} and p in the general formula (B-2) are respectively identical to ^R 5, ^{R 6} and p in the general formula (A-2).

The cycloolefin-based resin may be used alone or in combination of two or more.

The intrinsic viscosity [η] inh of the cycloolefin resin is, for example, 0.2 to ⁵ cm 3 / g, preferably 0.3 to ³ cm 3 / g, and more preferably 0.4 to 1.5 cm ³ / g. The number average molecular weight (Mn) of the cycloolefin resin is, for example, 8000 to 10000, preferably 1000 to 80000, more preferably 12000 to 50000, and the weight average molecular weight (Mw) is, for example, 20000 to 30000, more preferably 30000. It is ~ 250,000, more preferably 40,000 ~ 200,000. The number average molecular weight (Mn) and the weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC) in terms of polystyrene.

When the intrinsic viscosity [η] inh, the number average molecular weight and the weight average molecular weight are within the above ranges, the heat resistance, water resistance, chemical resistance, mechanical properties of the cycloolefin resin and the molding processability as a film are good. Become.

The glass transition temperature (Tg) of the cycloolefin resin is usually 110 ° C. or higher, preferably 110 to 350 ° C., more preferably 120 to 250 ° C., and particularly preferably 120 to 220 ° C. A case where the Tg is 110 ° C. or higher is preferable because deformation is unlikely to occur due to use under high temperature conditions or secondary processing such as coating and printing. On the other hand, when the Tg is 350 ° C. or lower, it is possible to avoid the case where the molding process becomes difficult and suppress the possibility that the resin is deteriorated by the heat during the molding process.

Commercially available products can be preferably used as the cycloolefin-based resin, and examples of the commercially available products are trade names from JSR Corporation, ARTON (registered trademark) G, Arton F, Arton R, and Arton RX. It is on sale at, and you can use these.

1-2. Organic fine particles Organic fine particles have a function of imparting slipperiness to an optical film. Examples of resins constituting organic fine particles include (meth) acrylic acid esters, itaconic acid diesters, maleic acid diesters, vinyl esters, olefins, styrenes, (meth) acrylamides, allyl compounds, and vinyl ethers. , Vinyl ketones, vinyl heterocyclic compounds, unsaturated nitriles, unsaturated monomers, and unsaturated carboxylic acids. Polymers containing structural units derived from one or more selected from the group, silicone resins, fluorine-based polymers. Includes resins, polyphenylene sulfides, etc. The (meth) acrylic means acrylic or methacryl.

Examples of (meth) acrylates constituting the polymer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and ethylene glycol di (meth). ) Acrylate, trimethylolpropane tri (meth) acrylate and the like are included. Examples of itaconic acid diesters include dimethyl itaconic acid, diethyl itaconic acid, dipropyl itaconic acid and the like. Examples of maleic acid diesters include dimethyl maleate, diethyl maleate, dipropyl maleate and the like. Examples of vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl chloroacetate, vinyl methoxy acetate, vinyl phenyl acetate, vinyl benzoate, vinyl salicylate and the like. included. Examples of olefins include dicyclopentadiene, ethylene, propylene, 1-butene, 1-pentene, vinyl chloride, vinylidene chloride, isoprene, chloroprene, butadiene, 2,3-dimethylbutadiene and the like. Examples of styrenes include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, isopropyl styrene, chloromethyl styrene, methoxy styrene, acetoxy styrene, chloro styrene, dichloro styrene, brom styrene, trifluoromethyl styrene and vinyl. Includes benzoic acid methyl ester, divinylbenzene, etc. Examples of (meth) acrylamides include (meth) acrylamide, methyl (meth) acrylamide, ethyl (meth) acrylamide, propyl (meth) acrylamide, butyl (meth) acrylamide, tert-butyl (meth) acrylamide, and phenyl (meth) acrylamide. ) Acrylamide, dimethyl (meth) acrylamide, methylenebisacrylamide, etc. are included. Examples of allyl compounds include allyl acetate, allyl caproate, allyl laurate, allyl benzoate and the like. Examples of vinyl ethers include methyl vinyl ether, butyl vinyl ether, hexyl vinyl ether, methoxyethyl vinyl ether, dimethylaminoethyl vinyl ether and the like. Examples of vinyl ketones include methyl vinyl ketone, phenyl vinyl ketone, methoxyethyl vinyl ketone and the like. Examples of vinyl heterocyclic compounds include vinylpyridine, N-vinylimidazole, N-vinyloxazolidone, N-vinyltriazole, N-vinylpyrrolidone and the like. Examples of unsaturated nitriles include acrylonitrile, methacrylonitrile and the like. Examples of unsaturated carboxylic acids include (meth) acrylic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester and the like.

Among them, (meth) acrylic acid has a high affinity with cycloolefin resins, is flexible against stress, and is unlikely to generate eccentric voids, that is, it is easy to improve the adhesiveness with a polymer. Polymers containing structural units derived from one or more selected from the group consisting of esters, vinyl esters, styrenes, and olefins are preferable, and polymers containing structural units derived from (meth) acrylic acid esters, styrene. Polymers containing structural units derived from the like, copolymers containing structural units derived from (meth) acrylic acid esters and structural units derived from styrenes are more preferable, and are derived from (meth) acrylic acid esters. A copolymer containing a structural unit and a structural unit derived from styrenes is more preferable.

Particles made of such a polymer (polymer particles) can be produced by any method, for example, a method such as emulsion polymerization, suspension polymerization, dispersion polymerization, or seed polymerization. Of these, seed polymerization and emulsion polymerization under an aqueous medium are preferable from the viewpoint that polymer particles having the same particle size can be easily obtained.

As a method for producing polymer particles, for example,
A one-stage polymerization method in which the monomer mixture is dispersed in an aqueous medium and then polymerized.
-A two-stage polymerization method in which seed particles are obtained by polymerizing a monomer in an aqueous medium, and then the monomer mixture is absorbed by the seed particles and then polymerized.
-A multi-stage polymerization method in which the process of producing seed particles of the two-stage polymerization method is repeated can be mentioned. These polymerization methods can be appropriately selected according to the desired average particle size of the polymer particles. The monomer for producing the seed particles is not particularly limited, and any monomer for polymer particles can be used.

The organic fine particles may be particles having a core-shell structure. Examples of such organic fine particles include core-shell particles having a low Tg core layer containing a homopolymer or copolymer of a (meth) acrylic acid ester and a high Tg shell layer.

The absolute value Δn of the difference in refractive index between the organic fine particles and the cycloolefin resin is preferably 0.1 or less, and more preferably 0.085 or less, from the viewpoint of highly suppressing the haze increase of the optical film. It is preferably 0.065 or less, and more preferably 0.065 or less.

The average particle size of the organic fine particles is preferably 0.04 to 2 μm, more preferably 0.08 to 1 μm. When the average particle size of the organic fine particles is 0.04 μm or more, not only is it easy to impart sufficient slipperiness to the optical film, but also it is easy to appropriately increase the gap between the organic fine particles and the cycloolefin resin. As a result, the adhesive easily permeates into the voids, and the adhesiveness with the polarizer tends to be improved. When the average particle size of the organic fine particles is 2 μm or less, it is easy to suppress an increase in haze.

The average particle size of the organic fine particles is specified as an average value of the equivalent circle diameters of 100 particles obtained by SEM or TEM photography of the film surface and sections. The equivalent circle diameter can be obtained by converting the projected area of the particles obtained by photographing into the diameter of a circle having the same area. At this time, the organic fine particles observed by SEM observation and / or TEM observation at a magnification of 5000 times are used for calculating the average particle size. The average particle size of the organic fine particles in the dispersion can be measured by a zeta potential / particle size measurement system (ELSZ-1000Z manufactured by Otsuka Electronics Co., Ltd.).

The average particle size of the organic fine particles means the average size of the aggregates (average secondary particle size) in the case of cohesive particles, and the average measured size of one particle in the case of non-aggregate particles. Means a value.

The content of the organic fine particles is preferably 0.03 to 1.0% by mass, more preferably 0.05 to 0.6% by mass, and 0.08 to 0.08 to the total mass of the optical film. It is more preferably 0.4% by mass. When the content of the organic fine particles is 0.03% by mass or more, it is easy to impart sufficient slipperiness to the optical film, and when it is 1.0% by mass or less, it is easy to suppress an increase in haze.

1-3. High boiling point solvent The high boiling point solvent is derived from the solvent contained in the dope used in the manufacturing process of the optical film by the solution film forming method. A small amount of the high boiling point solvent remains on the optical film.

The boiling point of the high boiling point solvent is preferably 90 ° C. or higher, more preferably 100 ° C. or higher. Examples of high boiling solvents include toluene, xylene, cresol, phenol, methyl methacrylate, heptane, n-octane, acetophenone, acetylacetone, aniline, benzyl alcohol, cyclohexanone, N, N-dimethylformamide, N, N-dimethylacetamide. , Dimethylsulfoxide, 1,4-dioxane, tetrachloroethylene, ethylene glycol, diethylene glycol, n-butyl ether, 1-butanol, 2-butanol, 2-ethyl-1-hexanol, ethyl propionate, frill alcohol, 1-hexanol, 2 -Includes methoxyethanol, 2-methyl-2-butanol, 3-methyl-1-butanol, 1-octanol, 2-octanol, 1-pentanol, 3-pentanol, 1-propanol, n-propyl acetate and the like. .. Of these, toluene is preferable because the cycloolefin resin has high solubility.

The content of the high boiling point solvent is preferably 0.001 to 1% by mass, more preferably 0.01 to 1% by mass, and 0.1 to 1% by mass with respect to the total mass of the optical film. Is more preferable. Such an optical film can be obtained by a solution film forming method using a dope in which a cycloolefin resin is dissolved in a solvent containing a high boiling point solvent. When the content of the high boiling point solvent is more than a certain level, the solvent tends to be uniformly volatilized from the film-like substance obtained from the dope, and isotropic voids are easily formed around the organic fine particles, so that the adhesive is uniform. It is easy to soak into the solvent and improve the adhesiveness with the polarizer. Further, when the content of the high boiling point solvent is a certain level or more, the solvent is likely to be uniformly volatilized around the organic fine particles, so that it is easy to suppress the variation in the residual stress. As a result, display unevenness can be further suppressed. When the content of the high boiling point solvent is below a certain level, it is possible to prevent the drying rate of the film-like substance from being excessively lowered. The content of the high boiling point solvent can be adjusted by the content of the high boiling point solvent in the dope and the drying conditions in the manufacturing process of the optical film described later.

The content of the high boiling point solvent in the optical film can be measured by headspace gas chromatography. In the headspace gas chromatography method, a sample is sealed in a container, heated, and the gas in the container is promptly injected into a gas chromatograph with the container filled with volatile components, and mass spectrometry is performed to identify the compound. The volatile components are quantified while doing so. In the headspace method, it is possible to observe all peaks of volatile components by gas chromatography, and by using an analytical method that utilizes electromagnetic interaction, volatile substances and monomers can be quantified with high accuracy. Can also be done at the same time. The measurement conditions of the headspace gas chromatography method may be the same as in the examples described later.

1-4. Other Components The optical film may further contain other components as long as the effects of the present invention are not impaired. Examples of other components include UV absorbers, antioxidants and the like.

The optical film may be composed of one layer (single layer) or a plurality of layers, but it should be a single layer because there is little display unevenness and it is possible to reduce the thickness. Is preferable.

1-5. Physical characteristics (thermomechanical analysis)
In the thermomechanical analysis measurement, the optical film has an elongation amount of S1 (μm) in the first direction in which the shrinkage ratio of the optical film is maximized, and an elongation amount of the optical film in the second direction orthogonal to the first direction. When S2 (μm) is set, it is preferable to satisfy the following formulas (1) and (2).
Equation (1): S1 <0 <S2
Equation (2): | S1 / S2 | <3.0

In thermomechanical analysis, the amount of elongation of the optical film when heated is measured with a constant load applied in the measurement direction. If the amount of elongation is negative, it indicates that it is contracting, and if the amount of elongation is positive, it indicates that it is expanding. Therefore, if the optical film has no residual stress (eg, residual stress due to stretching), usually only expansion due to load occurs; if the optical film has residual stress, expansion due to load and contraction due to residual stress Occurs at the same time.

1A to 1C are graphs showing an example of thermomechanical analysis measurement results. Of these, FIG. 1A is a measurement result of a conventional unstretched optical film, FIG. 1B is a measurement result of a conventional uniaxially stretched optical film, and FIG. 1C is a biaxially stretched optical film of the present invention. It is a measurement result of. In the figure, the horizontal axis is the heating temperature (° C.), and the vertical axis is the elongation amount (μm) of the optical film.

In FIG. 1A, the elongation amounts S1 and S2 near 180 ° C. are both positive. That is, it is shown that the optical film expands with a load because there is no residual stress in either the first direction or the second direction. That is, FIG. 1A does not satisfy the equation (1).

In FIG. 1B, the elongation amount S1 near 180 ° C. is negative, and the elongation amount S2 is positive. That is, since there is residual stress in the first direction, the contraction occurs as a result of the contraction due to the residual stress exceeding the expansion due to the load; the second direction has no residual stress, so that it is the same as in FIG. 1A. Shows that it expands with the load. That is, FIG. 1B satisfies the equation (1), but does not satisfy the equation (2) because the absolute value of S2 is much larger than the absolute value of S1.

In FIG. 1C, the elongation amount S1 near 180 ° C. is negative, the elongation amount S2 is positive, and the absolute values of the elongation amounts S1 and S2 are about the same. That is, since there is residual stress (smaller than the first direction) not only in the first direction but also in the second direction, it is shown that the expansion due to the load in the second direction is reduced as compared with FIG. 1B. ing. That is, FIG. 1C satisfies the equations (1) and (2) at the same time.

As described above, in order to satisfy the equations (1) and (2) at the same time, for example, the residual stress of the optical film can be adjusted; the residual stress of the optical film can be adjusted, for example, according to the stretching conditions. Specifically, in order to satisfy the equations (1) and (2), the optical film has a residual stress due to stretching in both the first direction and the second direction, and the residual stress due to stretching in the second direction. However, it is preferably smaller than the residual stress due to stretching in the first direction. That is, it is preferable that the optical film is stretched in two directions orthogonal to each other and the ratio of the stretching ratios thereof is adjusted within a predetermined range. The optical film preferably satisfies the formula (2'): | S1 / S2 | <2.0.

The direction in which the shrinkage rate is maximum (first direction) is obtained by measuring the shrinkage rate in any plurality of in-plane directions of the optical film while holding the optical film at 180 ° C., and the shrinkage rate is the maximum. Is the first direction.

The optical film of the present invention contains organic fine particles and a high boiling point solvent, and by satisfying the formulas (1) and (2) at the same time, the adhesiveness to the polarizer and the display unevenness of the display device can be suppressed. ..

The reason for this is not clear, but it is speculated as follows. First, the optical film is a biaxially stretched film-like material containing a cycloolefin resin, organic fine particles, and a high boiling point solvent. First, since the organic fine particles have higher flexibility than the inorganic fine particles, they can easily follow the stretching. Further, by biaxially stretching the film-like material, the stretching tension applied to the periphery of the organic fine particles can be made isotropic. Furthermore, since the film-like substance contains a high boiling point solvent, the solvent tends to volatilize uniformly around the organic fine particles, so that the variation in the amount of residual solvent is reduced and the variation in the stretching tension applied to the periphery of the organic fine particles is reduced. sell. As a result, it is considered that isotropic voids can be uniformly formed around the organic fine particles and the variation in residual stress can be reduced. It is considered that the isotropic voids can be formed around the organic fine particles in this way, so that the adhesive easily permeates into the voids and the adhesiveness with the polarizer is improved. Further, it is considered that display unevenness is suppressed by improving the adhesiveness with the polarizer and reducing the variation in the residual stress of the optical film.

(Haze)
The haze of the optical film is preferably 4.0% or less, more preferably 2.0% or less, and even more preferably 1.0% or less. The haze can be measured by measuring a sample of 40 mm × 80 nm at 25 ° C. and 60% RH with a haze meter (HGM-2DP, Suga Test Instruments Co., Ltd.) according to JIS K-6714.

(Phase difference Ro and Rt)
When the optical film is used, for example, as a retardation film for VA mode, the in-plane retardation Ro measured in an environment with a measurement wavelength of 550 nm and 23 ° C. and 55% RH is preferably 20 to 120 nm. , 30-100 nm, more preferably. The phase difference Rt in the thickness direction of the optical film is preferably 70 to 350 nm, more preferably 100 to 320 nm.

Ro and Rt of the optical film are defined by the following formulas, respectively.
Equation (2a): Ro = (nx-ny) × d
Equation (2b): Rt = ((nx + ny) /2-nz) × d
(During the ceremony,
nx represents the refractive index in the in-plane slow-phase axial direction (the direction in which the refractive index is maximized) of the optical film.
ny represents the refractive index in the direction orthogonal to the in-plane slow-phase axis of the optical film.
nz represents the refractive index in the thickness direction of the optical film.
d represents the thickness (nm) of the optical film. )

The in-plane slow-phase axis of the optical film means the axis having the maximum refractive index on the film surface. The in-plane slow-phase axis of the optical film can be confirmed by an automatic birefringence meter Axoscan (Axo Scan Mueller Matrix Polarimeter: manufactured by Axometrics).

The Ro and Rt of the optical film can be measured by the following method.
1) The optical film is humidity-controlled for 24 hours in an environment of 23 ° C. and 55% RH. The average refractive index of this optical film is measured with an Abbe refractometer, and the thickness d is measured with a commercially available micrometer.
2) The retardation Ro and Rt of the optical film after humidity control at a measurement wavelength of 550 nm were measured at 23 ° C. and 55% RH using an automatic birefringence meter Axoscan (Axo Scan Mueller Matrix Polarimeter). Measure in the environment of.

The phase difference Ro and Rt of the optical film can be adjusted mainly by the draw ratio. In order to increase the phase difference Ro and Rt of the optical film, it is preferable to increase the draw ratio.

(Thickness)
The thickness of the optical film can be, for example, 5 to 100 μm, preferably 5 to 40 μm.

2. Method for Producing Optical Film The optical film of the present invention is preferably produced by a solution film forming method (casting method).

That is, in the optical film of the present invention, 1) a step of obtaining a dope containing at least the above-mentioned cycloolefin resin, organic fine particles, and a solvent containing a high boiling point solvent, and 2) the obtained dope is placed on a metal support. It can be produced through a step of casting, drying and peeling to obtain a film-like substance, and 3) a step of stretching the obtained film-like substance in two directions orthogonal to each other.

About step 1) Cycloolefin resin and organic fine particles are dissolved in a solvent to prepare a dope.

The solvent used for doping includes at least an organic solvent (good solvent) capable of dissolving the cycloolefin resin and a high boiling point solvent.

Examples of good solvents include chlorine-based organic solvents such as methylene chloride; non-chlorine-based organic solvents such as methyl acetate, ethyl acetate, acetone and tetrahydrofuran. Of these, methylene chloride is preferable.

As the high boiling point solvent, the above-mentioned high boiling point solvent can be used. The content of the high boiling point solvent in the solvent used for doping may be adjusted so that the content of the high boiling point solvent remaining in the optical film is within the above range. For example, 0. It is preferably 01 to 1.5% by mass, more preferably 0.05 to 1.0% by mass.

The solvent used for doping may further contain a poor solvent. Examples of poor solvents include straight-chain or branched-chain aliphatic alcohols having 1 to 4 carbon atoms. When the ratio of alcohol in the dope is high, the film-like substance tends to gel and peels off from the metal support easily. Examples of the linear or branched aliphatic alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Of these, ethanol is preferable because of its stability of doping, relatively low boiling point, and good drying property.

The method of adding the organic fine particles is not particularly limited, and the organic fine particles may be added directly to the solvent, or an aggregate of the organic fine particles may be prepared and then added to the solvent. In particular, when the organic fine particles are the above-mentioned polymer particles, an aggregate of the polymer particles can be added to the solvent. As the aggregate of the polymer particles, the aggregate of the polymer particles can be obtained by spray-drying the slurry containing the polymer particles, the surfactant, the inorganic powder, and the aqueous medium. The aggregate of polymer particles can be prepared by the method described in JP-A-2010-138365. The aggregate of polymer particles is composed of a plurality of polymer particles in which mutual connection (fusion) is suppressed. Therefore, it is excellent in handleability, and if the aggregate is dispersed in a cycloolefin resin or a solvent, it is easily separated into polymer particles, so that the dispersibility of the polymer particles can be improved.

The dope obtained in step 2) is cast on a metal support. Doping casting can be performed by discharging from a casting die.

The solvent in the dope cast on the metal support is then evaporated and dried. The dried dope is stripped from the metal support to give a film. The residual solvent amount of the doping at the time of peeling from the metal support (residual solvent amount at the time of peeling) is 10 to 150% by mass in terms of facilitating the reduction of the phase difference Ro and Rt of the obtained optical film. It is preferably 20 to 40% by mass, more preferably 20 to 40% by mass. When the amount of the residual solvent at the time of peeling is 10% by mass or more, the cycloolefin resin easily flows during drying or stretching and tends to be non-oriented, so that Ro and Rt of the obtained optical film can be easily reduced. When the amount of the residual solvent at the time of peeling is 150% by mass or less, the force required for peeling the dope is unlikely to be excessively large, so that the breakage of the dope is easily suppressed.

The amount of residual solvent in the doping is defined by the following formula. The same applies to the following.
Residual solvent amount of dope (mass%) = (mass before heat treatment of dope-mass after heat treatment of dope) / mass after heat treatment of dope × 100
The heat treatment for measuring the amount of residual solvent means a heat treatment at 120 ° C. for 60 minutes.

The film-like material obtained in the step 3) is stretched (biaxially stretched) in at least two directions orthogonal to each other. The stretching direction is preferably the width direction (TD direction) of the film-like material and the transport direction (MD direction) orthogonal to the width direction.

The stretching ratio may be set so as to satisfy the above formulas (1) and (2), but in order to satisfy the formula (2), the stretching ratio in the TD direction / the stretching ratio in the MD direction is set to, for example, 1. It is preferably 0 to 3.0. The draw ratios in the TD direction and the MD direction can be 1.01 to 3.5 times, respectively, from the viewpoint of making the optical film function as a retardation film for VA, for example, functioning as a retardation film for IPS. From the viewpoint of making the film 1.01 to 1.3 times, respectively. The higher the draw ratio, the larger the residual stress of the obtained optical film. The stretch ratio is defined as (size of the film after stretching in the stretching direction) / (size of the film before stretching in the stretching direction).

The in-plane slow-phase axial direction of the optical film (the direction in which the refractive index is maximized in the plane) is usually the direction in which the stretching ratio is maximized, and the first direction in which the shrinkage rate of the optical film is maximized. Match.

The stretching temperature is preferably (Tg-65) ° C. to (Tg + 60) ° C., preferably (Tg-50) ° C. to (Tg + 50) ° C., where Tg is the glass transition temperature of the cycloolefin resin. More preferably, it is (Tg-30) ° C. to (Tg + 50) ° C. When the stretching temperature is (Tg-30) ° C. or higher, not only is it easy to soften the film-like material suitable for stretching, but also the tension applied to the film-like material during stretching does not become too large, so that the obtained optical film can be obtained. Excessive residual stress is unlikely to remain, and Ro and Rt are unlikely to increase excessively. When the stretching temperature is (Tg + 60) ° C. or lower, an appropriate residual stress tends to remain in the optical film after stretching, and the generation of bubbles due to the vaporization of the solvent in the film-like material is also likely to be highly suppressed. Specifically, the stretching temperature can be 100 to 220 ° C.

The amount of residual solvent in the film-like material at the start of stretching is preferably 2 to 50% by mass. When the amount of the residual solvent at the start of stretching is 2% by mass or more, the substantial Tg of the film-like substance at the time of stretching is lowered due to the plasticizing effect of the residual solvent, so that Ro and Rt of the optical film are unlikely to increase. .. When the amount of residual solvent at the start of stretching is 50% by mass or less, the generation of bubbles due to the vaporization of the solvent in the film-like material can be highly suppressed.

Stretching of the film-like material in the MD direction can be performed, for example, by a method (roll method) in which a plurality of rolls are provided with a peripheral speed difference and the roll peripheral speed difference is used between them. Stretching of the film-like object in the TD direction can be performed, for example, by fixing both ends of the film-like object with clips or pins and widening the distance between the clips or pins in the traveling direction (tenter method).

3. 3. Polarizing Plate The polarizing plate of the present invention includes a polarizing element and an optical film of the present invention. The optical film of the present invention is preferably arranged on at least one surface of the polarizer (at least the surface facing the liquid crystal cell). The polarizer and the optical film are adhered to each other via an adhesive layer.

3-1. Polarizer A polarizing element is an element that allows only light on a plane of polarization in a certain direction to pass through, and is a polyvinyl alcohol-based polarizing film. The polyvinyl alcohol-based polarizing film includes a polyvinyl alcohol-based film dyed with iodine and a film obtained by dyeing a dichroic dye.

The polyvinyl alcohol-based polarizing film may be a film obtained by uniaxially stretching a polyvinyl alcohol-based film and then dyeing it with iodine or a bicolor dye (preferably a film further subjected to a durability treatment with a boron compound); polyvinyl. An alcohol-based film may be a film that has been dyed with iodine or a bicolor dye and then uniaxially stretched (preferably a film that has been further subjected to a durability treatment with a boron compound). The absorption axis of the polarizer is usually parallel to the maximum stretching direction.

For example, the ethylene unit content described in JP-A-2003-248123, JP-A-2003-342322, etc. has a content of 1 to 4 mol%, a degree of polymerization of 2000 to 4000, and a degree of saponification of 99.0 to 99.99 mol%. Ethylene-modified polyvinyl alcohol is used.

The thickness of the polarizer is preferably 5 to 30 μm, and more preferably 5 to 20 μm in order to reduce the thickness of the polarizing plate.

3-2. Other Optical Films When the optical film of the present invention is arranged on only one surface of the polarizer, another optical film may be arranged on the other surface of the polarizer. Examples of other optical films include commercially available cellulose ester films (eg, Konica Minolta Tuck KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR, KC4KR, KC8UY, KC6UY, KC4UY, KC6UY, KC4UY KC8UY-HA, KC2UA, KC4UA, KC6UAKC, 2UAH, KC4UAH, KC6UAH, manufactured by Konica Minolta Co., Ltd. Includes (manufactured by Film Co., Ltd.).

The thickness of the other protective film is not particularly limited, but is preferably 10 to 100 μm, more preferably 10 to 60 μm, and particularly preferably 20 to 60 μm.

3-3. Method for manufacturing a polarizing plate The polarizing plate of the present invention can be obtained by bonding a polarizing element and an optical film of the present invention via an adhesive. The adhesive may be a fully saponified polyvinyl alcohol aqueous solution (water glue) or an active energy ray-curable adhesive.

Above all, it is preferable that the optical film of the present invention and the polarizer are bonded with an active energy ray-curable adhesive from the viewpoint that a polarizing plate having high strength and excellent flatness can be easily obtained even with a thin film.

The active energy ray-curable adhesive is a photoradical polymerization type composition using photoradical polymerization, a photocationic polymerization type composition using photocationic polymerization, and a hybrid type composition using photoradical polymerization and photocationic polymerization in combination. It may be any of.

The photoradical polymerization type composition contains a radically polymerizable compound containing a polar group such as a hydroxy group or a carboxy group described in JP-A-2008-09329 and a radically polymerizable compound not containing a polar group in a specific ratio. Compositions and the like are known. In particular, the radically polymerizable compound is preferably a compound having a radically polymerizable ethylenically unsaturated bond. Preferred examples of compounds having a radically polymerizable ethylenically unsaturated bond include compounds having a (meth) acryloyl group. Examples of compounds having a (meth) acryloyl group include N-substituted (meth) acrylamide-based compounds, (meth) acrylate-based compounds, and the like. (Meta) acrylamide means acrylamide or methacrylamide.

Examples of the photocationic polymerization type composition include (α) a cationically polymerizable compound, (β) a photocationic polymerization initiator, and (γ) light having a wavelength longer than 380 nm, as disclosed in Japanese Patent Application Laid-Open No. 2011-028234. Examples thereof include a composition containing each component of a photosensitizer exhibiting maximum absorption and a (δ) naphthalene-based photosensitizer.

The method for producing a polarizing plate using an active energy ray-curable adhesive is as follows: 1) a step of applying an active energy ray-curable adhesive to at least one of the adhesive surfaces between the polarizer and the optical film, and 2) obtained. Step of bonding the polarizer and the optical film via the adhesive layer 3) With the polarizing element and the optical film bonded via the adhesive layer, irradiate active energy rays to form the adhesive layer. The present invention includes a step of curing the obtained polarizing plate to obtain a polarizing plate, and 4) a step of punching (cutting) the obtained polarizing plate into a predetermined shape. Before the step 1), if necessary, a step of 4) an easy-adhesion treatment (corona treatment, plasma treatment, etc.) on the surface to which the polarizer of the optical film is bonded may be carried out.

In the step 1), the active energy ray-curable adhesive is preferably applied so that the thickness of the adhesive layer after curing is, for example, 0.01 to 10 μm, preferably 0.5 to 5 μm.

In the step 3), visible light, ultraviolet rays, X-rays, electron beams and the like can be used as the active energy rays to be irradiated. Generally, it is preferable to use ultraviolet rays because it is easy to handle and the curing speed is sufficient. The ultraviolet irradiation conditions may be any conditions that can cure the adhesive. For example, the irradiation amount of ultraviolet rays is preferably from 50~1500mJ / cm ² in accumulated light quantity, it is more preferably 100 to 500 mJ / cm ^2.

4. Liquid crystal display device The liquid crystal display device of the present invention includes a liquid crystal cell, a first polarizing plate arranged on one surface of the liquid crystal cell, and a second polarizing plate arranged on the other surface of the liquid crystal cell. One or both of the first and second polarizing plates are the polarizing plates of the present invention.

FIG. 2 is a schematic view showing an example of a basic configuration of a liquid crystal display device. As shown in FIG. 2, the liquid crystal display device 10 of the present invention is arranged on the liquid crystal cell 30, the first polarizing plate 50 arranged on one surface of the liquid crystal cell 30, and the other surface of the liquid crystal cell 30. The second polarizing plate 70 and the backlight 90 are included.

The display mode of the liquid crystal cell 30 may be, for example, STN, TN, OCB, HAN, VA (MVA, PVA), IPS, OCB, or the like. Of these, the VA (MVA, PVA) mode and the IPS mode are preferable.

The first polarizing plate 50 has a first polarizing element 51 arranged on one surface (viewing side surface) of the liquid crystal cell 30 and a surface of the first polarizing element 51 opposite to the liquid crystal cell 30 (viewing side surface). The protective film 53 (F1) arranged on the surface) and the protective film 55 (F2) arranged on the surface of the first polarizing element 51 on the liquid crystal cell 30 side are included.

The second polarizing plate 70 has a second polarizing element 71 arranged on the other surface of the liquid crystal cell 30 (the surface on the backlight 90 side) and a protection arranged on the surface of the second polarizing element 71 on the liquid crystal cell 30 side. A film 73 (F3) and a protective film 75 (F4) arranged on a surface (the surface on the backlight 90 side) opposite to the liquid crystal cell 30 of the second polarizing element 71 are included.

It is preferable that the absorption axis of the first polarizer 51 and the absorption axis of the second polarizer 71 are orthogonal to each other (cross Nicol).

At least one of the protective films 53 (F1), 55 (F2), 73 (F3) and 75 (F4) can be the optical film of the present invention. Among them, the optical film of the present invention is preferably used as the protective film 55 (F2) or 73 (F3). The liquid crystal display device including the optical film of the present invention as the protective film 55 (F2) or 73 (F3) has good front contrast and reduced display unevenness.

By using the polarizing plate of the present invention, it is possible to obtain a liquid crystal display device having excellent visibility such as display unevenness and front contrast, even if the screen is a large-screen liquid crystal display device having a size of 30 inches or more.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

1. 1. Optical film material 1-1. Cycloolefin resin ARTON-G7810 (manufactured by JSR Corporation): Cycloolefin resin (polymer of monomer represented by formula (A-2) and other monomer (polymer of (5) above) ), Weight average molecular weight = 140000)

1-2. Fine particles Fine particles 1: Polymer particles produced in Production Example 1 below [Production Example 1]
(Manufacturing of seed particles)
1000 g of deionized water was placed in a polymer equipped with a stirrer and a thermometer, 200 g of methyl methacrylate and 6 g of t-dodecyl mercaptan were charged therein, and the mixture was heated to 70 ° C. while substituting nitrogen under stirring. The internal temperature was kept at 70 ° C., 20 g of deionized water in which 1 g of potassium persulfate was dissolved was added as a polymerization initiator, and then polymerization was carried out for 10 hours. The average particle size of the polymer particles in the obtained emulsion was 0.44 μm.

(Manufacturing of polymer particles)
800 g of deionized water in which 3 g of polyoxyethylene tridecyl ether ammonium sulfate was dissolved was placed in a polymer equipped with a stirrer and a thermometer, and 144 g of methyl acrylate, 22 g of styrene and 34 g of ethylene glycol dimethacrylate were added thereto as a monomer mixture. , A mixed solution with 1 g of azobisisobutyronitrile was added as a polymerization initiator. Then, the mixed solution was added to T.I. The dispersion was obtained by stirring with a K homomixer (manufactured by Tokushu Kagaku Kogyo Co., Ltd.).

Further, 60 g of the above emulsion containing seed particles was added to the dispersion liquid, and the mixture was stirred at 30 ° C. for 1 hour to allow the seed particles to absorb the monomer mixture. Next, the absorbed monomer mixture was polymerized by heating at 50 ° C. for 5 hours under a nitrogen stream, and then cooled to room temperature (about 25 ° C.) to obtain a slurry containing polymer particles. The average particle size of the obtained polymer particles (organic fine particles) was 0.3 μm.

(Manufacturing of aggregates of polymer particles)
After cooling, 50 g of Snowtex O-40 (manufactured by Nissan Chemical Industries, Ltd .: colloidal silica (inorganic powder) having a solid content of 40% and a particle size of 0.02-0.03 μm) was added to the obtained slurry, and T.I. The mixture was stirred with a K homomixer (manufactured by Tokushu Kagaku Kogyo Co., Ltd.) for 10 minutes. This slurry was spray-dried under the following conditions with a spray dryer (model: atomizer take-up method, model number: TRS-3WK) manufactured by Sakamoto Giken Co., Ltd. as a spray dryer to obtain a polymer particle aggregate. The average particle size of the polymer particle aggregate was 30 μm.
Supply rate: 25 ml / min
Atomizer rotation speed: 11000 rpm
Air volume: 2m ³ / min
Slurry inlet temperature of spray dryer: 130 ° C
Polymer particle aggregate outlet temperature: 70 ° C

Fine particles 2-5: Polymer particles produced in Production Examples 2 to 5 below [Production Examples 2 to 5]
The polymer particles and their aggregates were produced in the same manner as in the organic fine particles 1 except that the polymerization conditions were adjusted so that the average particle size of the polymer particles was as shown in Table 1.

Fine particles 6: Core shell particles (Aica Kogyo Staphyroid)
Fine particles 7: Polyphenylene sulfide particles (Toray Industries, Inc. Trepearl PPS)
Fine particles 8: Silica particles (SiO ₂ manufactured by CIK Nanotech)

The average particle size of the obtained fine particles was measured by the following method.

(Average particle size)
The dispersed particle size of the fine particles in the obtained dispersion was measured by a zeta potential / particle size measuring system (ELSZ-1000Z manufactured by Otsuka Electronics Co., Ltd.). The average particle size of the organic fine particles measured using the zeta potential / particle size measurement system (ELSZ-1000Z manufactured by Otsuka Electronics Co., Ltd.) is almost the same as the average particle size of the fine particles measured by TEM observation of the optical film. To do.

The average particle size of the fine particles 1 to 8 is shown in Table 1.

1-3. Solvent Toluene (boiling point: 110 ° C)
Methyl methacrylate (boiling point: 104 ° C)
Methanol (boiling point: 64 ° C)
Methylene chloride (boiling point: 40 ° C)

2. Manufacture of optical film <Manufacture of optical film 101>
(Preparation of fine particle dispersion liquid 1)
1.0 part by mass of fine particles 1 and 100 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes and then dispersed with mantongoline to obtain a fine particle dispersion liquid 1.

(Preparation of doping)
Then, the main dope 1 having the following composition was prepared. First, methylene chloride, ethanol and toluene were added to the pressurized dissolution tank. Next, ARTON-G7810 was charged into the pressure dissolution tank as a cycloolefin resin with stirring. Next, the above-prepared fine particle dispersion 1 was added, and the mixture was heated to 60 ° C. and completely dissolved while stirring. The heating temperature was raised from room temperature at 5 ° C./min, dissolved in 30 minutes, and then lowered at 3 ° C./min.
The viscosity of the obtained solution was 7000 cp and the water content was 0.50%. This was converted, using SHP150 manufactured by (Corporation) Rokitekuno, filtered flow rate 300L ^{/ m} 2 · h, and filtered through a filtration pressure 1.0 × ¹⁰ 6 Pa, to obtain a primary dope 1.

(Composition of main dope 1)
Cycloolefin resin ARTON-G7810: 100 parts by mass Methylene chloride: 270 parts by mass Ethanol: 20 parts by mass Toluene (high boiling point solvent): 0.01 parts by mass Fine particle dispersion liquid 1:30 parts by mass

(Film formation)
Then, using an endless belt casting device, the main dope 1 was uniformly cast on the stainless belt support at a temperature of 31 ° C. and a width of 1800 mm. The temperature of the stainless steel belt was controlled to 28 ° C. The transport speed of the stainless steel belt was 20 m / min.

On the stainless belt support, the solvent was evaporated until the amount of residual solvent in the cast film was 30%. Then, it was peeled from the stainless belt support at a peeling tension of 128 N / m. While transporting the peeled film with a large number of rollers, the film was stretched 1.2 times in the transport direction at 120 ° C. (Tg-45 ° C.). The residual solvent at the start of stretching was 10% by mass. Then, the film-like material was stretched 1.5 times in the width direction under the condition of 150 ° C. (Tg-15 ° C.) with a tenter. Then, the end portion sandwiched between the tenter clips was slit with a laser cutter, and then wound up to obtain an optical film 101 having a film thickness of 40 μm.

<Manufacturing of optical films 102 to 103>
Optical films 102 to 103 were obtained in the same manner as the optical film 101 except that the drying conditions were changed so that the amount of the residual solvent was the value shown in Table 2.

<Manufacturing of optical films 104 to 109>
Optical films 104 to 109 were obtained in the same manner as the optical films 101 except that the organic fine particles 1 were changed to those shown in Table 2.

<Manufacturing of optical film 110>
An optical film 110 was obtained in the same manner as the optical film 101 except that the solvent composition of the main dope 1 was changed from 0.01 parts by mass of toluene to 0.02 parts by mass of methyl methacrylate (boiling point 101 ° C.).

<Manufacturing of optical film 111>
The solvent composition of the main dope 1 was the same as that of the optical film 101 except that toluene was not added, to obtain an optical film 111.

<Manufacturing of optical film 112>
An optical film 112 was obtained in the same manner as the optical film 101 except that the solvent composition of the main dope 1 was changed from 0.01 parts by mass of toluene to 0.02 parts by mass of methanol (boiling point 64 ° C.).

<Manufacturing of optical film 113>
An optical film 113 was obtained in the same manner as the optical film 101 except that no organic fine particles were added.

<Manufacturing of optical film 114>
An optical film 114 was obtained in the same manner as the optical film 106 except that the film was not stretched.

<Manufacturing of optical film 115>
An optical film 115 was obtained in the same manner as the optical film 106 except that the film was stretched 1.5 times only in the width direction.

<Manufacturing of optical film 116>
An optical film 116 was obtained in the same manner as the optical film 101 except that the organic fine particles 1 and the high boiling point solvent were not added.

<Manufacturing of optical film 117>
An optical film 117 was obtained in the same manner as the optical film 105 except that the organic fine particles 1 were changed to fine particles 8.

The residual solvent amount and thermomechanical measurement of the obtained optical films 101 to 117 were measured by the following methods.

(Content of high boiling point solvent)
The solvent content in the optical film was quantified by headspace gas chromatography. Headspace gas chromatography measurement was performed under the following conditions.
(conditions)
Headspace device: HP7694 Head Space Sampler (manufactured by Hewlett-Packard)
Temperature conditions: Transfer line 200 ° C, loop temperature 200 ° C
Sample volume: 0.8 g / 20 ml vial GC: HP5890 (manufactured by Hewlett-Packard)
MS: HP5791 (manufactured by Hewlett-Packard)
Column: HP-624 (30 m x inner diameter 0.25 mm)
Oven temperature: Initial temperature 40 ° C (holding time 3 minutes), heating rate 10 ° C / min, reaching temperature 200 ° C (holding time 5 minutes)
Then, the composition of the solvent (residual solvent) remaining on the optical film was analyzed. Then, among the solvents constituting the residual solvent, the types and contents of the high boiling point solvents having a boiling point of 90 ° C. or higher were specified and shown in Table 2.

(Thermal mechanical measurement)
The thermomechanical measurement of the optical film was performed using TMA7100 manufactured by Hitachi High-Tech Science Corporation.
Specifically, the optical film was cut into a size of 1.0 mm × 10.0 mm to prepare a sample piece. Then, the sample piece was set in TMA7100 manufactured by Hitachi High-Tech Science Corporation, and the temperature was raised from 23 ° C. to 150 ° C. at 10 ° C./min with a constant tensile load applied in the measurement direction of the variable length. After holding for a minute, the temperature was lowered from 150 ° C. to 23 ° C. at 20 ° C./min (First Scan). Then, after holding at 23 ° C. for 10 minutes, the temperature was raised to 180 ° C. at 10 ° C./min, and the state at 180 ° C. was held for 10 minutes (Second Scan).
Then, based on the data of Second Scan, the fluctuation length (elongation amount) in the direction in which the shrinkage rate is maximized (first direction) in the sample piece is set to S1 (μm) while being held at 180 ° C., and shrinkage is performed. The fluctuation length (elongation amount) in the direction (second direction) orthogonal to the direction in which the rate is maximized (first direction) was defined as S2 (μm).
As for the direction in which the shrinkage rate is maximum in the sample piece (first direction), the shrinkage rate of the prepared sample piece is measured separately in any plurality of in-plane directions while being held at 180 ° C. However, the direction in which the shrinkage rate is maximized is set as the first direction. The measurement conditions (heating rate, holding time, holding temperature) in the measurement in the direction in which the shrinkage rate was maximized (first direction) were the same as the measurement conditions in the measurement of S1 and S2.

(Phase difference measurement)
Ro and Rt of the optical film of Example 1 were measured by the following methods.
1) The optical film was humidity-controlled for 24 hours in an environment of 23 ° C. and 55% RH. The average refractive index of this optical film was measured with an Abbe refractometer, and the thickness d was measured with a commercially available micrometer.
2) The retardation Ro and Rt of the optical film after humidity control at a measurement wavelength of 550 nm were measured at 23 ° C. and 55% RH using an automatic birefringence meter Axoscan (Axo Scan Mueller Matrix Polarimeter). It was measured in the environment of.

Next, a polarizing plate and a liquid crystal display device were produced using the optical films 101 to 117, and the adhesiveness and display unevenness were evaluated.

3. 3. Manufacture of polarizing plate <Manufacture of polarizer>
A 70 μm-thick polyvinyl alcohol film was swollen with water at 35 ° C. The obtained film was immersed in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and further immersed in an aqueous solution of 45 ° C. consisting of 3 g of potassium iodide, 7.5 g of boric acid and 100 g of water. .. The obtained film was uniaxially stretched under the conditions of a stretching temperature of 55 ° C. and a stretching ratio of 5 times. This uniaxially stretched film was washed with water and then dried to obtain a polarizer having a thickness of 20 μm.

<Preparation of polarizing plate 201>
(Preparation of active energy ray-curable adhesive)
After mixing each of the following components, defoaming was performed to prepare an active energy ray-curable adhesive. The triarylsulfonium hexafluorophosphate was blended as a 50% propylene carbonate solution, and the solid content of the triarylsulfonium hexafluorophosphate is shown below.
3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate: 45 parts by mass Epolide GT-301 (alicyclic epoxy resin manufactured by Daicel): 40 parts by mass 1,4-butanediol diglycidyl ether: 15 Parts by mass Triarylsulfonium hexafluorophosphate: 2.3 parts by mass 9,10-dibutoxyanthracene: 0.1 parts by mass 1,4-diethoxynaphthalene: 2.0 parts by mass

The optical film 101 produced above was prepared, and its surface was subjected to a corona discharge treatment. The conditions for the corona discharge treatment were a corona output strength of 2.0 kW and a line speed of 18 m / min. Next, the active energy ray-curable adhesive was applied to the corona discharge-treated surface of the optical film with a bar coater so that the film thickness after curing was about 3 μm. One surface of the above-prepared polarizer was attached to the obtained adhesive layer.

On the other hand, as another optical film, a cellulose triacetate film (KC4UA, manufactured by Konica Minolta Co., Ltd., film thickness 40 μm) was prepared, and the surface thereof was subjected to corona treatment in the same manner as described above. Next, the active energy ray-curable adhesive was applied to the corona discharge-treated surface of KC4UA with a bar coater so that the film thickness after curing was about 3 μm. The other surface of the polarizer with the optical film 101 produced above was bonded to the obtained adhesive layer to obtain a laminate.

Next, from both sides of the laminated laminate, an ultraviolet irradiation device with a belt conveyor (the lamp uses a D bulb manufactured by Fusion UV Systems) is used to emit ultraviolet rays so ^{that the integrated light intensity is 750 mJ / cm 2.} The polarizing plate 201 was produced by irradiating and curing the adhesive layer.

<Preparation of polarizing plates 202 to 217>
Polarizing plates 202 to 217 were produced in the same manner as the polarizing plates 201 except that the optical films 101 were changed to optical films 102 to 117.

The adhesiveness of the obtained polarizing plates 2001 to 217 was evaluated by the following method.

[Adhesiveness]
At the end of the polarizing plate, the cutting edge of the cutter was inserted between the polarizer and the optical film. At the insertion portion, the polarizer and the optical film were grasped and pulled in opposite directions.
⊚: The polarizer or the optical film is broken and cannot be peeled off, and the adhesiveness is very good. ○: Partially peels off between the polarizer and the optical film, but the adhesiveness is good. Partially peeled off between the two, but the adhesiveness is slightly poor, but there is no problem in practical use. ×: All peeled off between the polarizer and the optical film, and the adhesiveness is poor, which is a problem in practical use. If so, it was judged to be good.

4. Manufacture of liquid crystal display device <Manufacture of liquid crystal display device 301>
In order to evaluate the characteristics of the produced polarizing plate, it is attached to the observer side surface (front surface) and the light source side surface (back surface) of the liquid crystal cell of Sony's 40-inch liquid crystal display (BRAVIA X1) in VA mode. Each of the polarizing plates was peeled off. Then, the above-mentioned prepared polarizing plates are attached to the light source side surface (back surface) and the observation side surface (front surface) of the obtained liquid crystal cell, respectively, using an acrylic transparent adhesive to form a liquid crystal display device 301. Made. The polarizing plates were bonded so that the transmission axis of the polarizing plate after bonding coincided with the transmission axis of the polarizing plate that was originally bonded. The polarizing plate was attached so that the optical film of the present invention was in contact with the liquid crystal cell (so that it was F2 or F3).

<Manufacturing of liquid crystal display devices 302 to 317>
Liquid crystal display devices 302 to 317 were produced in the same manner as the liquid crystal display devices 301 except that the polarizing plate 201 was changed to the polarizing plates 202 to 217.

The display unevenness of the obtained liquid crystal display devices 301 to 317 was evaluated by the following method.

[Display unevenness]
After turning on the backlight of each liquid crystal display device continuously for one week in an environment of 23 ° C. and 55% RH, the display screen is displayed in white and black on the liquid crystal display device using EZ-Contrast 160D manufactured by ELDIM. The brightness from the normal direction of was measured, and the ratio was taken as the front contrast. That is,
Front contrast (%) = {(Brightness of white display measured from the normal direction of the display device)
/ (Brightness of black display measured from the normal direction of the display device)} x 100
Is. Then, the front contrast of any five points of the liquid crystal display device was measured, and the unevenness of the front contrast was evaluated as the display unevenness based on the following criteria.
⊚: The front contrast varies from 0% to less than 3%, the unevenness is small, and there is no problem in practical use.
◯: The front contrast varies from 3% to less than 5%, the unevenness is small, and there is no problem in practical use.
Δ: The front contrast varies from 5% to less than 10%, and there is some unevenness, but there is no problem in practical use.
X: The front contrast varies by 10% or more, the unevenness is large, and there is a problem in practical use.
If it is Δ or more, it is judged to be good.

Table 2 shows the evaluation results of the adhesiveness of the polarizing plates 201 to 217 and the display unevenness of the liquid crystal display devices 301 to 217 using the optical films 101 to 117.
In Table 2, the notation of the polarizing plates 2001 to 217 and the liquid crystal display devices 301 to 217 is omitted.

As shown in Table 2, it can be seen that the optical films 101 to 110 have good adhesiveness to the polarizer and do not cause display unevenness. It is considered that this is because the anisotropy of the voids formed around the organic fine particles is low and the variation in the residual stress is small. The in-plane retardation Ro of the optical film 101 was 52 nm, and the thickness direction retardation Rt was 135 nm.

In particular, it can be seen that the adhesiveness with the polarizer is improved by setting the content of the high boiling point solvent to a certain level or higher (contrast with the optical films 101 to 103).

Further, it can be seen that when the composition of the organic fine particles is an acrylic / styrene copolymer, the adhesiveness to the polarizer is further improved as compared with the acrylic particles and the polyphenylene sulfide particles having a core-shell structure (optical film 102). , 108 and 109). It is considered that this is because the acrylic / styrene copolymer has a high affinity with the cycloolefin resin, has flexibility against stress, and is less likely to generate anisotropic voids.

Further, it can be seen that the adhesiveness with the polarizer is improved by setting the average particle size of the organic fine particles to 0.04 to 2 μm (contrast with the optical films 104 to 107).

On the other hand, it can be seen that the optical films 111 and 112, which do not contain a high boiling point solvent having a boiling point of 90 ° C. or higher, have low adhesiveness to the polarizer and display unevenness occurs. Further, in the thermomechanical measurement, the optical film 114 that does not satisfy the formula (1) and the optical film 115 that satisfies the formula (1) but does not satisfy the formula (2) both have low adhesiveness and may cause display unevenness. Understand. Further, it can be seen that the optical film 117 containing silica particles instead of organic fine particles also has low adhesiveness to the polarizer and causes display unevenness. It is considered that all of these are due to the formation of highly anisotropy voids around the organic fine particles. The optical films 113 and 116 were not sufficiently impregnated with the adhesive, and could not be adhered to the polarizer, and subsequent evaluation was also impossible. It is considered that this is because the optical films 113 and 116 do not contain fine particles, so that the voids to be impregnated with the adhesive are not formed.

According to the present invention, it is possible to provide an optical film capable of suppressing poor adhesion to a polarizer and display unevenness in a liquid crystal display device.

10 Liquid crystal display device 30 Liquid crystal cell 50 1st polarizing plate 51 1st polarizing element 53 Protective film (F1)
55 Protective film (F2)
70 Second polarizing plate 71 Second polarizing element 73 Protective film (F3)
75 Protective film (F4)
90 backlight

Claims (8)

An optical film containing a cycloolefin resin, organic fine particles, and a high boiling point solvent having a boiling point of 90 ° C. or higher.
In thermomechanical analysis measurement, the elongation of the optical film in the first direction in which the shrinkage rate of the optical film is maximized when the temperature is raised from 23 ° C. to 180 ° C. at 10 ° C./min and held at 180 ° C. for 10 minutes. An optical film satisfying the following formulas (1) and (2), where S1 (μm) is the amount and the elongation amount of the optical film in the second direction orthogonal to the first direction is S2 (μm).
Equation (1): S1 <0 <S2
Equation (2): | S1 / S2 | <3.0 The optical film according to claim 1, wherein the average particle size of the organic fine particles is 0.04 to 2 μm. The optical film according to claim 1 or 2, wherein the organic fine particles contain a polymer containing a structural unit derived from a (meth) acrylic monomer and a structural unit derived from a styrene monomer. The optical film according to any one of claims 1 to 3, wherein the content of the high boiling point solvent is 0.01 to 1% by mass with respect to the total mass of the optical film. A polarizing plate comprising a polarizing element and an optical film according to any one of claims 1 to 4 arranged on at least one surface of the polarizing element. A liquid crystal cell, a first polarizing plate arranged on one surface of the liquid crystal cell, and a second polarizing plate arranged on the other surface of the liquid crystal cell are included.
The first polarizing plate is formed on a first polarizing element, a protective film F1 arranged on a surface of the first polarizing element on a surface opposite to the liquid crystal cell, and a surface of the first polarizing element on the liquid crystal cell side. Including the arranged protective film F2
The second polarizing plate is formed on a surface of the second polarizing element opposite to the liquid crystal cell, a protective film F3 arranged on the surface of the second polarizing element on the liquid crystal cell side, and a surface of the second polarizing element on the surface opposite to the liquid crystal cell. Including the arranged protective film F4
A liquid crystal display device in which at least one of the protective films F1, F2, F3 and F4 is the optical film according to any one of claims 1 to 4. The liquid crystal display device according to claim 6, wherein the liquid crystal cell is a liquid crystal cell in VA mode. A step of obtaining a dope containing a cycloolefin resin, organic fine particles, and a solvent containing a high boiling point solvent having a boiling point of 90 ° C. or higher.
The steps of casting the obtained dope on a metal support, drying and peeling to obtain a film-like material, and
A step of stretching the obtained film-like material in two directions orthogonal to each other,
A method for manufacturing an optical film, including.

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