JP2018054640A - Optical film, production method of optical film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film with high productivity, which suppresses display unevenness and to provide a production method of an optical film for producing the above optical film, and a polarizing plate and a liquid crystal display device including the optical film.SOLUTION: The optical film of the present invention is an optical film having a slow axis in a direction inclined with respect to the longitudinal direction and essentially comprising a cycloolefin resin. The film has a film thickness of 30 μm or less, an in-plane retardation value Ro of 80 to 180 nm, and a film thickness deviation in a width direction of 2.0 μm or less.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical film, an optical film manufacturing method, a polarizing plate, and a liquid crystal display device. More specifically, the present invention relates to an optical film containing a cycloolefin resin.

  Transparent resin films containing cellulose ester, polycarbonate, cycloolefin and the like are used for optical films, mainly optical compensation films for liquid crystal display devices. Among them, cycloolefin resins are widely used because of their excellent transparency and moldability. In particular, when a cycloolefin resin is used for a λ / 4 retardation film, it is preferably used because of a good yield when it is attached to a polarizing plate.

However, since the retardation value is proportional to the film thickness, the thinner the film, the higher the retardation value per unit film thickness, and even a slight film thickness deviation has a greater effect on the retardation value. It was difficult to satisfy the demand for thinning.
In addition, in the oblique stretching performed when producing a λ / 4 retardation film, stretching or shrinkage that is asymmetrical on the left and right sides occurs. Therefore, compared with conventional longitudinal stretching or lateral stretching, casting is performed from a film thickness profile after stretching. It is difficult to accurately feed back to the die gap control.
Specifically, after the film thickness profile before stretching is uniformly adjusted, a two-stage operation of adjusting the stretching conditions without unevenness is necessary, which has a problem of poor productivity.

In addition, as a method of stretching an optical film without unevenness, for example, a technique of stretching by adjusting the residual solvent of the optical film to 5% by mass or more is known (see, for example, Patent Documents 1 and 2). .
However, in the case of oblique stretching, there is a problem that when the residual solvent of the optical film is adjusted to 5% by mass or more, the in-plane retardation value Ro is not sufficiently developed and the retardation is insufficient.

JP 2003-207772 A JP 2002-196138 A

  This invention is made | formed in view of the said problem and the situation, The solution subject is providing the optical film with high productivity which suppresses display nonuniformity, and its manufacturing method. Moreover, it is providing the polarizing plate and liquid crystal display device which comprise the said optical film.

In order to solve the above problems, the present inventor, in the process of examining the cause of the above problems, the film thickness is 30 μm or less, the in-plane retardation value Ro is in the range of 80 to 180 nm, the width It has been found that when the film thickness deviation in the hand direction is 2.0 μm or less, a highly productive optical film for suppressing display unevenness and a method for producing the optical film for producing the optical film can be provided, and the present invention has been achieved. It was.
The above-mentioned problem according to the present invention is solved by the following means.

1. An optical film having a slow axis in a direction inclined with respect to the longitudinal direction and having a cycloolefin resin as a main component,
The film thickness is 30 μm or less,
The in-plane retardation value Ro is in the range of 80 to 180 nm,
An optical film having a thickness direction deviation in the width direction of 2.0 μm or less.

2. The film thickness is 25 μm or less,
2. The optical film according to item 1, comprising an ultraviolet absorber and a retardation increasing agent.

3. An optical film manufacturing method for manufacturing the optical film according to item 1 or 2,
The residual solvent amount when obliquely stretching is in the range of 0.1 to 3.0% by mass,
An optical film characterized by being stretched 1.1 times or more in an oblique direction at a temperature in the range of (Tg-20) to (Tg + 30) ° C. with respect to the glass transition temperature (Tg) of the film dried after the oblique stretching. Manufacturing method.

  4). 4. The method for producing an optical film according to item 3, wherein the amount of residual solvent in the oblique stretching is in the range of 0.1 to 1.0% by mass.

  5. A polarizing plate comprising the optical film according to item 1 or 2.

  6). A liquid crystal display device comprising the optical film according to item 1 or 2.

  By the means of the present invention, an optical film with high productivity that suppresses display unevenness can be provided. Moreover, the manufacturing method of the optical film which manufactures the said optical film can be provided. In addition, a polarizing plate and a liquid crystal display device including the optical film can be provided.

The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.
The thicker the film, the slower the internal diffusion of the solvent, so it is considered that the solvent remains selectively in the thickened part of the film. It is considered that the thicker part becomes softer than the thin part even if it is heated to the same temperature, and is easily stretched when it is obliquely stretched so that the film thickness becomes uniform.

Schematic diagram of diagonally stretched tenter Schematic showing the track (rail pattern) of the tenter rail Schematic diagram showing the configuration of the polarizing plate of the present invention

  The optical film of the present invention is an optical film mainly composed of a cycloolefin resin having a slow axis in a direction inclined with respect to the longitudinal direction, having a film thickness of 30 μm or less, and an in-plane retardation value Ro. Is within the range of 80 to 180 nm, and the thickness deviation in the width direction is 2.0 μm or less. This feature is a technical feature common to the inventions according to claims 1 to 6.

  As an embodiment of the present invention, from the viewpoint of manifesting the effects of the present invention, the film thickness is 25 μm or less, and containing an ultraviolet absorber and a retardation increasing agent can reduce the amount of residual solvent and reduce the thickness. Therefore, it is preferable.

  Moreover, as a manufacturing method of the optical film which manufactures the optical film of this invention, the residual solvent amount at the time of diagonally stretching is in the range of 0.1-3 mass%, and the glass transition of the film dried after diagonally stretching It is preferable that the film is stretched 1.1 times or more in an oblique direction at a temperature within the range of (Tg−20) to (Tg + 30) ° C. with respect to the temperature (Tg) from the viewpoint of manifesting the effect of the present invention.

  Furthermore, it is preferable that the amount of residual solvent in the oblique stretching is in the range of 0.1 to 1.0% by mass because the film thickness becomes more uniform.

The optical film of the present invention can be suitably included in a polarizing plate.
Moreover, the optical film of the present invention can be suitably included in a liquid crystal display device.

  Hereinafter, the present invention will be described in detail. In addition, in this application, "-" is used in the meaning which includes the numerical value described before and behind that as a lower limit and an upper limit. Moreover, in this invention, unless it deviates from a claim and its equivalent range, a preferable aspect can be changed arbitrarily and implemented. In the present specification, “gradient” represents the gradient of a numerical value obtained based on the difference between the characteristic value at one end of the film and the characteristic value at the other end of the film, and the distance between both ends. Shall.

<Optical film>
The optical film of the present invention contains a cycloolefin resin as a main component, has a film thickness of 30 μm or less, has an in-plane retardation value Ro in the range of 80 to 180 nm, and has a film thickness deviation of 2 in the width direction. 0.0 μm or less. The optical film of the present invention can be used as a λ / 4 retardation film.
Furthermore, the film thickness is preferably 25 μm or less, and preferably contains an ultraviolet absorber and a retardation increasing agent.

In the present specification, Ro and Rt respectively represent an in-plane retardation value at the optical wavelength λ and a retardation value in the thickness direction. Ro is measured by making light having a wavelength of λ nm incident in the normal direction of the film in AXOSCAN-AFM-2000 × 500H (manufactured by Axometrics). Rt is incident on light having a wavelength of λ nm from a direction inclined by + 40 ° with respect to the normal direction of the film with the slow axis in the plane (determined by AXOSCAN-AFM-2000x500H) as the tilt axis (rotation axis). The phase difference (retardation) value measured and the in-plane slow axis as the tilt axis (rotation axis) was measured by making light of wavelength λ nm incident from a direction inclined by −40 ° with respect to the film normal direction. AXOSCAN-AFM-2000x500H is calculated based on the phase difference (retardation) values measured in a total of three directions. Here, as the assumed value of the average refractive index, values in the polymer handbook (John Wiley & Sons, Inc.) and catalogs of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. By inputting the assumed average refractive index values and thicknesses, the phase difference based on AXOSCAN-AFM-2000x500H calculates the _{n x, n y, n z} formula (i) and (ii) (Retardation ) Calculate the value.

Formula _{(i): Ro = (n} x -n y) × d (nm)
Formula (ii): Rt = {(n _x + n _y ) / 2−n _z } × d (nm)
In the formula, Ro represents an in-plane retardation (retardation) value in the film, and Rt represents a thickness direction retardation (retardation) value in the film. D represents the thickness (nm) of the optical film. n _x represents the maximum refractive index in the plane of the film, also referred to as a slow axis direction of the refractive index. n _y represents a refractive index of the direction perpendicular to the slow axis in the film plane. _nz represents the refractive index of the film in the thickness direction.
The in-plane retardation value Ro of the optical film of the present invention is in the range of 80 to 180 nm.

In addition, the optical film of the present invention is characterized in that the film thickness deviation in the width direction is 2.0 μm or less. The film thickness deviation in the width direction is cut at both ends of the stretched optical film, cut into a strip shape from a film sample with a width of 1400 mm, for example, a film width using a dimatic thickness gauge (manufactured by Mitutoyo Corporation). The film thickness is measured at intervals of 50 mm in the direction, the average of all the measured points is taken as the film thickness, and the difference between the maximum value and the minimum value is the thickness unevenness.
When the film thickness deviation (unevenness) after stretching is 2.0 μm or less, the unevenness is small and the occurrence of display unevenness can be suppressed.

The optical film of the present invention is preferably highly transparent from the viewpoint of improving contrast and improving luminance. The total light transmittance measured after humidity adjustment in an environment of 23 ° C. and 55% RH is 80% or more, preferably 85% or more, more preferably 90% or more, and particularly preferably 95% or more.
The total light transmittance can be measured according to JIS K 7375-2008 “Plastics—Determination of total light transmittance and total light reflectance”.

  In the optical film of the present invention, the equilibrium water content at 25 ° C. and 60% relative humidity is preferably 3% or less, and more preferably 1% or less from the viewpoint of phase difference fluctuation and flexibility. By setting the equilibrium moisture content to 3% or less, it is preferable to easily cope with a change in humidity and to hardly change the optical characteristics and dimensions.

  Equilibrium moisture content was determined by leaving the sample film in a room conditioned at 23 ° C and 20% relative humidity for 4 hours or more, then leaving it in a room conditioned at 23 ° C and 80% RH for 24 hours. It can be quantified by the Karl Fischer method after moisture is dried and vaporized at a temperature of 150 ° C. using a moisture meter (for example, CA-20 model manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

(Cycloolefin resin)
Examples of the cycloolefin resin according to the present invention include the following (co) polymers.

式中、Ｒ^１〜Ｒ^４は、それぞれ独立に、水素原子、炭化水素基、ハロゲン原子、ヒドロキシ基、エステル基、アルコキシ基、シアノ基、アミド基、イミド基、シリル基又は極性基（すなわち、ハロゲン原子、ヒドロキシ基、エステル基、アルコキシ基、シアノ基、アミド基、イミド基、又はシリル基）で置換された炭化水素基である。
ただし、Ｒ^１〜Ｒ^４は、二つ以上が互いに結合して、不飽和結合、単環又は多環を形成していてもよく、この単環又は多環は、二重結合を有していても、芳香環を形成してもよい。Ｒ^１とＲ^２とで、又はＲ^３とＲ^４とで、アルキリデン基を形成していてもよい。ｐ及びｍは０以上の整数である。

In the formula, each of R ^{1 to} R ⁴ independently represents a hydrogen atom, a hydrocarbon group, a halogen atom, a hydroxy group, an ester group, an alkoxy group, a cyano group, an amide group, an imide group, a silyl group, or a polar group (that is, A hydrocarbon group substituted by a halogen atom, a hydroxy group, an ester group, an alkoxy group, a cyano group, an amide group, an imide group, or a silyl group.
However, two or more of R ^{1 to} R ⁴ may be bonded to each other to form an unsaturated bond, a monocycle or a polycycle, and this monocycle or polycycle has a double bond. Alternatively, an aromatic ring may be formed. R ¹ and R ² , or R ³ and R ⁴ may form an alkylidene group. p and m are integers of 0 or more.

In the general formula (1), the hydrocarbon group represented by R ¹ and R ³ is preferably a hydrocarbon group having 1 to 10 carbon atoms, more preferably 1 to 4, particularly preferably 1 to 2.
R ² and R ⁴ are each a hydrogen atom or a monovalent organic group, and at least one of R ² and R ⁴ preferably represents a polar group having a polarity other than a hydrogen atom and a hydrocarbon group, and m is 0 An integer of ˜3, p is an integer of 0 to 3, more preferably m + p = 0 to 4, more preferably 0 to 2, particularly preferably m = 1 and p = 0.
The specific monomer with m = 1 and p = 0 is preferable in that the resulting cycloolefin resin has a high glass transition temperature and excellent mechanical strength.
The glass transition temperature here is a value obtained by a method based on JIS K 7121-2012 using DSC (Differential Scanning Colorimetry).

Examples of the polar group of the specific monomer include a carboxy group, a hydroxy group, an alkoxycarbonyl group, an allyloxycarbonyl group, an amino group, an amide group, and a cyano group. These polar groups have a linking group such as a methylene group. It may be bonded via.
In addition, a hydrocarbon group in which a divalent organic group having a polarity such as a carbonyl group, an ether group, a silyl ether group, a thioether group, or an imino group is bonded as a linking group can also be exemplified.
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.

Furthermore, a monomer in which at least one of R ² and R ⁴ is a polar group represented by the formula — (CH ₂ ) _n COOR is obtained by using a cycloolefin resin having a high glass transition temperature, a low hygroscopic property, and various materials. It is preferable in that it has excellent adhesion.
In the formula relating to the specific polar group, R is a hydrocarbon group having 1 to 12 carbon atoms, more preferably 1 to 4, particularly preferably 1 to 2, and preferably an alkyl group.

Specific examples of the copolymerizable monomer include cycloolefin resins such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, and dicyclopentadiene.
The number of carbon atoms of the cycloolefin is preferably 4-20, and more preferably 5-12.

In this invention, cycloolefin resin can be used individually by 1 type or in combination of 2 or more types.
The preferred molecular weight of the cycloolefin resin according to the present invention is 0.2 to 5 dl / g, more preferably 0.3 to 3 dl / g, particularly preferably 0.4 to 1.5 dl / g in terms of intrinsic viscosity [η] inh. The number average molecular weight (Mn) in terms of polystyrene measured by gel permeation chromatography (GPC) is 8000 to 100,000, more preferably 10,000 to 80,000, particularly preferably 12,000 to 50,000, and the weight average molecular weight (Mw). Is preferably in the range of 20000 to 300,000, more preferably 30000 to 250,000, particularly preferably 40000 to 200000.

  Inherent viscosity [η] inh, number average molecular weight and weight average molecular weight are within the above ranges, so that the heat resistance, water resistance, chemical resistance, mechanical properties of the cycloolefin resin, and molding as the optical film of the present invention Property is improved.

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

  For the cycloolefin resin, a specific hydrocarbon resin or a known thermoplastic resin described in, for example, JP-A-9-221577 and JP-A-10-287732, as long as the effects of the present invention are not impaired. Resins, thermoplastic elastomers, rubbery polymers, organic fine particles, inorganic fine particles, etc. may be blended. Specific wavelength dispersants, sugar ester compounds, antioxidants, release accelerators, rubber particles, plasticizers, UV absorption An additive such as an agent may be included.

  In addition, as the cycloolefin resin, a commercially available product can be preferably used, and examples of commercially available products include trade names of Arton (registered trademark) G, Arton F, Arton R, and Arton RX from JSR Corporation. ZEONOR (registered trademark) ZF14, ZF16, ZEONEX (registered trademark) 250, or ZEONEX 280 are commercially available from ZEON CORPORATION and can be used. .

(Additive)
The optical film of the present invention may contain other optional components as long as the effects of the present invention are not impaired.
As an arbitrary component, it is preferable from a viewpoint of improving light resistance to contain a ultraviolet absorber. The ultraviolet absorber is intended to improve light resistance by absorbing ultraviolet rays of 400 nm or less, and the transmittance at a wavelength of 380 nm is preferably in the range of 15% or less, more preferably 10%. Hereinafter, it is more preferably 5% or less.

  The ultraviolet absorber preferably used in the present invention is a benzotriazole ultraviolet absorber, a benzophenone ultraviolet absorber, or a triazine ultraviolet absorber, and particularly preferably a benzotriazole ultraviolet absorber or a benzophenone ultraviolet absorber.

  For example, 5-chloro-2- (3,5-di-sec-butyl-2-hydroxylphenyl) -2H-benzotriazole, (2-2H-benzotriazol-2-yl) -6- (linear and side Chain dodecyl) -4-methylphenol, 2-hydroxy-4-benzyloxybenzophenone, 2,4-benzyloxybenzophenone, etc., and tinuvin 109, tinuvin 171, tinuvin 234, tinuvin 326, tinuvin 327, tinuvin 328, There are tinuvins such as tinuvin 928, and these are all commercial products manufactured by BASF Japan Ltd. and can be preferably used. Of these, halogen-free ones are preferred. You may contain multiple types of ultraviolet absorbers.

  The method of adding the UV absorber is to add the UV absorber to the dope after dissolving the UV absorber in an alcohol such as methanol, ethanol or butanol, an organic solvent such as dichloromethane, methyl acetate, acetone or dioxolane, or a mixed solvent thereof, or You may add directly in dope composition. Moreover, what does not melt | dissolve in an organic solvent like an inorganic powder should just add to a dope, after using a dissolver and a sand mill in an organic solvent and acetylcellulose, disperse | distributing.

As the UV absorber, a polymer UV absorber can also be preferably used, and in particular, a polymer type UV absorber described in JP-A-6-148430 is preferably used. Moreover, it is preferable that the ultraviolet absorber does not have a halogen group.
The amount of UV absorber used is not uniform depending on the type of UV absorber, usage conditions, etc. When the dry film thickness of the optical film is 15-50 μm, 100 parts by mass of cycloolefin resin contained in the optical film Is preferably 0.5 parts by mass or more, particularly preferably in the range of 0.5 to 10% by mass, and more preferably in the range of 0.6 to 3.0% by mass.

<Hard coat layer>
The optical film of the present invention preferably has a hard coat layer. By having a hard coat layer, the impact resistance and ease of handling of the optical film can be improved.
The material for forming the hard coat layer is not particularly limited as long as it shows a hardness of “HB” or higher in the pencil hardness test specified in JIS K 5600-2014. The actinic radiation-curable compound is preferably a component containing a monomer having an ethylenically unsaturated double bond. Examples of the actinic radiation curable compound include an ultraviolet curable compound and an electron beam curable compound, and a compound that is cured by ultraviolet irradiation is preferable from the viewpoint of excellent mechanical film strength (abrasion resistance, pencil hardness).

  Examples thereof include organic hard coat materials such as organic silicone, melamine, epoxy, acrylate, and polyfunctional (meth) acrylic compounds; inorganic hard coat materials such as silicon dioxide; and the like. Among these, from the viewpoint of good adhesion and excellent productivity, it is preferable to use a hard coat forming material of a (meth) acrylate-based or polyfunctional (meth) acrylic-based compound. Here, (meth) acryl means acryl and methacryl.

  (Meth) acrylates have one polymerizable unsaturated group in the molecule, two have, two or more, (meth) acrylate oligomers containing three or more polymerizable unsaturated groups in the molecule Can be mentioned. (Meth) acrylates may be used alone or in combination of two or more.

  In addition, various additives can be further blended into the hard coat layer as necessary within a range that does not impair the effects of the present invention. For example, an antioxidant, an ultraviolet stabilizer, an ultraviolet absorber, a surfactant, a leveling agent, an antistatic agent and the like can be used. In addition, the hard coat layer of the present invention may be provided with antiglare properties by containing particles having an average particle size of 0.2 to 10 μm, and contains high refractive index fine particles in a dispersed manner to provide a refractive index. May be.

  The leveling agent is particularly effective in reducing surface irregularities when a hard coat layer is applied. As the leveling agent, for example, a dimethylpolysiloxane-polyoxyalkylene copolymer is suitable as a silicone leveling agent.

As particles having an average particle size of 0.2 to 10 μm, inorganic particles are preferable. Examples of inorganic particles include silica, zinc oxide, ITO (indium oxide / tin oxide), ATO (antimony oxide / tin oxide), Examples thereof include at least one selected from the group consisting of tin oxide, indium oxide, tungsten oxide, composite tungsten oxide, and antimony oxide. Among these, silica fine particles are preferred because the effect of improving the surface hardness can be particularly increased and the strength can be particularly increased.
In addition, from the viewpoint of adding ultraviolet absorption performance to the hard coat layer and suppressing deterioration with time of the hard coat layer, it is preferable to use ITO, ATO, tungsten oxide, or composite tungsten oxide.

  As the ultraviolet stabilizer, for example, a hindered amine ultraviolet stabilizer having high stability against ultraviolet rays is preferably used. When the hard coat layer contains an ultraviolet stabilizer, radicals, active oxygen and the like generated by ultraviolet rays are inactivated, and ultraviolet stability, weather resistance, and the like can be improved.

Examples of the UV absorber include salicylic acid UV absorbers, benzophenone UV absorbers, benzotriazole UV absorbers, cyanoacrylate UV absorbers, triazine UV absorbers, and benzoxazinone UV absorbers. 1 type or 2 types or more selected from these groups can be used.
Among these, from the viewpoint of dispersibility, triazine-based UV absorbers and benzoxazinone-based UV absorbers are preferable. Moreover, as the ultraviolet absorber, a polymer having an ultraviolet absorbing group in the molecular chain is also preferably used. By using a polymer having an ultraviolet absorbing group in such a molecular chain, it is possible to prevent deterioration of the ultraviolet absorbing function due to bleeding out of the ultraviolet absorbent. Examples of the ultraviolet absorbing group include a benzotriazole group, a benzophenone group, a cyanoacrylate group, a triazine group, a salicylate group, and a benzylidene malonate group. Among these, a benzotriazole group, a benzophenone group, and a triazine group are particularly preferable.

  The method of forming the hard coat layer is not particularly limited, and the coating liquid of the hard coat forming material is a dipping method, a spray method, a slide coat method, a bar coat method, a roll coater method, a die coater method, a gravure coater method, screen printing. After coating the optical film containing the alicyclic structure-containing polymer by a known method such as the method, and removing the organic solvent by drying in an atmosphere such as air or nitrogen, an acrylic hard coat material is applied. It is carried out by crosslinking and curing with ultraviolet rays or electron beams, or by applying a silicone, melamine or epoxy hard coat material and thermally curing.

Since unevenness of the coating film thickness is likely to occur during drying, it is preferable to control the intake and exhaust air so as not to impair the appearance of the coating film so that the entire coating film surface is uniform. In the case of using a material that is cured by ultraviolet rays, the irradiation time for curing the hard coat forming material after coating by ultraviolet irradiation is usually in the range of 0.01 to 10 seconds, and the irradiation amount of the energy beam source is an ultraviolet wavelength of 365 nm. of accumulative exposure in a range of usually 40 mJ / cm ² of 1000 mJ / cm ^2. Further, the irradiation of ultraviolet rays may be performed in an inert gas such as nitrogen and argon, or may be performed in the air.
The dry thickness of the hard coat layer is an average layer thickness of 0.01 to 20 μm, preferably 0.5 to 10 μm. More preferably, it is the range of 0.5-5.0 micrometers.

<Polarizing plate protective film>
As a polarizing plate protective film used for this invention, it may produce similarly to the said (lambda) / 4 phase difference film, and a commercially available triacetyl cellulose film can also be used.
For example, Konica Minolta Konica Minolta KC2CT1 is preferably used.

(Optical film molding method)
The optical film of the present invention has a residual solvent amount in the range of 0.1 to 3.0% by mass when obliquely stretched, and (Tg−) with respect to the glass transition temperature (Tg) of the film dried after stretching. 20) to (Tg + 30) ° C. at a temperature in the range of 1.1 times or more in an oblique direction. Furthermore, it is more preferable that the residual solvent amount in the oblique stretching is in the range of 0.1 to 1.0% by mass.
The glass transition temperature here is a value obtained by a method based on JIS K 7121-2012 using DSC (Differential Scanning Colorimetry).
Below, the shaping | molding method and diagonal stretch process of the optical film of this invention are demonstrated.
Examples of the method for molding the optical film of the present invention include known methods such as a melt extrusion method, a solution casting method (solution casting method), a calendar method, and a compression molding method.

  Examples of the solvent used in the solution casting method include chlorinated solvents such as chloroform and dichloromethane, aromatic solvents such as toluene, xylene, benzene, and mixed solvents thereof, methanol, ethanol, isopropanol, n-butanol, Examples include alcohol solvents such as 2-butanol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, dimethylformamide, dimethyl sulfoxide, dioxane, cyclohexanone, tetrahydrofuran, acetone, methyl ethyl ketone (MEK), ethyl acetate, and diethyl ether. These solvents may be used alone or in combination of two or more.

  In the solution casting method, it is preferable that the concentration of the cycloolefin resin in the dope is high because the drying load after casting on the metal support can be reduced. The load increases, and the filtration accuracy deteriorates. The concentration for achieving both of these is preferably 10 to 35% by mass, and more preferably 15 to 25% by mass. The metal support in the casting (casting) step preferably has a mirror-finished surface, and a stainless steel belt or a drum whose surface is plated with a casting is preferably used as the metal support.

  The cast width can be 1 to 4 m. The surface temperature of the metal support in the casting step is set to −50 ° C. or higher and is set to a temperature not boiling and foaming. A higher temperature is preferable because the web drying speed can be increased, and by setting the temperature below the temperature at which foaming does not occur, foaming of the web and deterioration of flatness can be suppressed.

  A preferable support temperature is appropriately determined at 0 to 100 ° C, and more preferably 5 to 30 ° C. It is also a preferable method that the web is gelled by cooling and peeled from the drum in a state containing a large amount of residual solvent. The method for controlling the temperature of the metal support is not particularly limited, and there are a method of blowing warm air or cold air, and a method of contacting hot water with the back side of the metal support. It is preferable to use warm water because heat transfer is performed efficiently, so that the time until the temperature of the metal support becomes constant is short.

When using hot air, considering the temperature drop of the web due to the latent heat of vaporization of the solvent, hot air above the boiling point of the solvent may be used, and air at a temperature higher than the target temperature may be used while preventing foaming. .
In particular, it is preferable to perform drying efficiently by changing the temperature of the support and the temperature of the drying air during the period from casting to peeling.

  In order for the optical film to exhibit good flatness, the amount of residual solvent when peeling the web from the metal support is preferably in the range of 10 to 150% by mass, more preferably 20 to 40% by mass or 60 to 130%. It is in the range of mass%, and particularly preferably in the range of 20-30 mass% or 70-120 mass%.

The amount of residual solvent is defined by the following formula.
Residual solvent amount (% by mass) = {(MN) / N} × 100
Note that M represents the mass of a sample collected at any time during or after production of the web or film, and N represents the mass after heating at 115 ° C. for 1 hour.

  In the optical film drying step, the amount of residual solvent when the web is peeled from the metal support, further dried and obliquely stretched is preferably in the range of 0.1 to 3.0% by mass. More preferably, it is in the range of 0.1 to 1.0% by mass.

  In the film drying process, a roller drying method (a method in which webs are alternately passed through a plurality of rollers arranged above and below) and a method of drying while transporting the web by a tenter method are adopted.

<Diagonally stretched film>
The optical film of the present invention has a residual solvent amount in the range of 0.1 to 3.0% by mass, preferably 0.1 to 1.0% by mass, in order to exhibit good flatness. %, And the film is stretched 1.1 times or more in an oblique direction.
The optical film of the present invention is a stretched film in which an in-plane slow axis is given at an arbitrary angle with respect to the longitudinal direction of the film by obliquely stretching a film mainly composed of a long cycloolefin resin. . The film before oblique stretching is referred to as “unstretched film”.
Here, the “long” means a film having a length of at least about 5 times the width of the film, preferably a length of 10 times or more, and specifically wound in a roll shape. And a length (film roll) that can be stored or transported. In the manufacturing method of a long film, a film can be manufactured to desired arbitrary length by manufacturing a film continuously.

  The stretched film production method may be such that the film is wound once on the core after film formation and then supplied to the oblique stretching process after forming the wound body, or the film is formed without winding the film after film formation. You may supply to the diagonal stretch process continuously from the process. It is preferable to continuously perform the film forming step and the oblique stretching step because a desired stretched film can be obtained by feeding back the stretched film thickness and optical value results to change the film forming conditions.

  The polarizing plate of the present invention is sandwiched between a λ / 4 retardation film having a slow axis inclined at an angle within a range of 45 ± 10 ° with respect to the absorption axis of the polarizer, and a polarizing plate protective film. It is preferable that Here, the angle with respect to the extending direction of the film is an angle in the film plane. Since the slow axis is usually expressed in the stretching direction or a direction perpendicular to the stretching direction, in the production method of the present invention, by stretching at an angle within a range of 45 ± 10 ° with respect to the extending direction of the film, A stretched film having such a slow axis can be produced. That is, the angle (orientation angle θ) formed by the film extension direction and the slow axis is an angle in the range of 45 ± 10 °.

The unstretched film can be obtained by a known method such as a solution cast molding method, an extrusion molding method, an inflation molding method and the like. Among these, the solution cast molding method is excellent in flatness and transparency of the film, and the extrusion molding method makes it easy to reduce the retardation value Rt in the thickness direction after oblique stretching, and the amount of residual volatile components is small. It is preferable because it is excellent in dimensional stability.
This unstretched film may be a single layer or a laminated film of two or more layers. The laminated film can be obtained by a known method such as a coextrusion molding method, a co-casting molding method, a film lamination method, or a coating method. Of these, the coextrusion molding method and the co-casting molding method are preferable.

In the present invention, the thickness unevenness σm in the flow direction of a long unstretched film that is subjected to stretching maintains a constant film take-up tension at an obliquely stretched tenter inlet described later, and the Martens hardness in the film width direction. Is preferably less than 0.30 μm, more preferably less than 0.25 μm, and particularly preferably less than 0.20 μm.
Moreover, when thickness unevenness (sigma) m is less than 0.30 micrometer, degradation of the Martens hardness of the film width direction of a diagonally stretched film can be suppressed.

In order to make the thickness unevenness σm in the flow direction of a long unstretched film within the above range, in the case of an extrusion molding method, it is brought into close contact with a cooling drum as described in JP-A-2004-233604. It can be achieved by a method of keeping the cycloolefin resin in a molten state in a stable state.
Specifically, 1) A method in which a sheet-like cycloolefin resin extruded from a die is brought into close contact with a cooling drum under a pressure of 50 kPa or less when an unstretched film is produced by melt extrusion, and 2) melting When an unstretched film is produced by an extrusion method, the enclosure member covers from the die opening to the cooling drum that first adheres, and the distance from the enclosure member to the die opening or the first cooling drum that adheres first is 100 mm or less. Method 3) When producing an unstretched film by the melt extrusion method, the method satisfies the relationship and the method of heating the temperature of the atmosphere within 10 mm from the sheet-like cycloolefin resin extruded from the die opening to a specific temperature. The sheet-like cycloolefin resin extruded from the die is taken into close contact with the cooling drum under a pressure of 50 kPa or less, 4 When producing an unstretched film by the melt extrusion method, a speed difference of 0.2 m / s or less from the take-up speed of the cooling drum that first adheres to the sheet-like cycloolefin resin extruded from the die opening. The method of spraying is mentioned.

  Moreover, the film which has the thickness gradient of the width direction may be supplied as an unstretched film. The thickness gradient of the unstretched film so that the film thickness at the position where stretching has been completed is the most uniform is empirically determined by stretching films with various thickness gradients experimentally. Can be sought. The gradient of the thickness of the unstretched film is adjusted so that, for example, the thickness of the end portion on the thick side is about 0.5 to 3.0% thicker than the end portion on the thin side. be able to.

  Although the width | variety of an unstretched film is not specifically limited, 500-4000 mm, Preferably it can be in the range of 1000-2000 mm. The total thickness of the film is not particularly limited, but is preferably in the range of 20 to 400 μm, more preferably 20 to 200 μm.

  The preferable elastic modulus at the stretching temperature at the time of oblique stretching of the unstretched film is 0.01 MPa or more and 5000 MPa or less, more preferably 0.1 MPa or more and 500 MPa or less, expressed as Young's modulus. When the elastic modulus is 0.01 MPa or more, it is possible to suppress the reduction of shrinkage rate and wrinkle generation during stretching and after stretching, and to moderately suppress the tension applied during stretching by setting it to 5000 MPa or less. it can.

<Stretching with an oblique stretching tenter>
In the present invention, an oblique stretching apparatus (obliquely stretched tenter) is used in order to impart orientation to a long unstretched film subjected to stretching. The obliquely stretched tenter used in the present invention can freely set the orientation angle of the film by changing the rail pattern in various ways. A film stretching apparatus that can be oriented and can control the film thickness and retardation with high accuracy is preferable.

FIG. 1 is a schematic diagram of a tenter capable of oblique stretching used in the present invention. However, this is an example, and the present invention is not limited to this.
The unstretched film 1 whose direction is controlled by the guide roll 8-1 on the tenter entrance side is held at the position of the film holding start point 2-1 on the right side and the film holding start point 2-2 on the left side. The film is conveyed and stretched by the tenter 4 in the oblique direction indicated by the locus 3-1 of the right film holding means and the locus 3-2 of the left film holding means, and the right film holding end point 5 -1, the film holding end point 5-2 on the left side is released, and the conveyance is controlled by the guide roll 8-2 on the tenter outlet side, so that the obliquely stretched film 6 is formed. In the figure, the unstretched film is obliquely stretched at an angle (orientation angle θ) in the film stretching direction 9 with respect to the film feeding direction 7-1.

In the present invention, the distances X ₁ and X ₂ between the main shaft position of the guide roll 8-1 closest to the inlet portion of the obliquely stretched tenter and the gripping tool at the inlet portion of the obliquely stretched tenter are in the range of 20 to 100 cm. It is preferable to maintain the distance, so that the plane of the film can be maintained when the film is grasped, and the optical characteristics such as the longitudinal orientation angle θ and the retardation value can be stabilized. Preferably it is 20-60 cm, More preferably, it exists in the range of 20-40 cm.
Wherein, X ₁ is the distance of the main shaft position of the guide roll 8-1 and the right film holding start point 2-1 gripper in (clip gripping portion), X ₂ is a guide roll 8-1 spindle It is the distance between the position and the gripping tool (clip gripping portion) at the film holding start point 2-2 on the left side.

X ₁ and X ₂ may be either X ₁ = X ₂ or X ₁ ≠ X ₂ , but preferably X ₁ = X ₂ . In the present invention, both X ₁ and X ₂ are preferably in the range of 20 to 100 cm.
The uniformity of the Martens hardness of the obliquely stretched film is maintained because the distance between the main shaft position of the guide roll 8-1 closest to the entrance of the obliquely stretched tenter and the gripping tool at the entrance of the obliquely stretched tenter is 100 cm or less. can do.

  In order to set the distance between the main shaft position of the guide roll 8-1 closest to the entrance of the obliquely stretched tenter and the gripping tool of the obliquely stretched tenter to the above range, a mechanism capable of adjusting the position of the guide roll and the clip gripping part; The length of the gripping tool in the conveying direction is 1 to 5 inches (1 inch is 2.54 cm), and the diameter of the guide roll 8-1 closest to the entrance portion of the obliquely stretched tenter is 1 to 20 cm. And a mechanism that can further install a roll in the vicinity of the entrance of the obliquely stretched tenter.

  In the present invention, it is preferable to produce an obliquely stretched film using the above-described obliquely stretchable tenter. However, this tenter can be used to produce a long film in an advancing environment (in the film width direction) in an oven heating environment. It is a device that widens in an oblique direction with respect to the point movement direction. The tenter includes an oven, a pair of rails on the left and right on which a gripping tool for transporting the film travels, and a number of gripping tools that travel on the rails. Both ends of the film fed from the film roll and sequentially supplied to the inlet portion of the tenter are gripped by a gripping tool, the film is guided into the oven, and the film is released from the gripping tool at the outlet portion of the tenter. The film released from the gripping tool is wound around the core. Each of the pair of rails has an endless continuous track, and the gripping tool that has released the grip of the film at the exit portion of the tenter travels outside and is sequentially returned to the entrance portion.

  The rail shape of the tenter is asymmetrical on the left and right according to the orientation angle θ, the draw ratio, etc. given to the stretched film to be manufactured, and can be finely adjusted manually or automatically. In the present invention, a long cycloolefin resin film is stretched, and the orientation angle θ can be set to an arbitrary angle within a range of preferably 10 to 80 ° with respect to the winding direction after stretching. Yes. In the present invention, the gripping tool of the tenter is configured to travel at a constant speed with a certain distance from the front and rear gripping tools.

  The traveling speed of the gripping tool can be selected as appropriate, but is usually in the range of 10 to 100 m / min. The difference in travel speed between the pair of left and right grippers is usually 1% or less, preferably 0.5% or less, more preferably 0.1% or less of the travel speed. This is because if there is a difference in the traveling speed between the left and right sides of the film at the exit of the stretching process, wrinkles and shifts will occur at the exit of the stretching process. Because. In general tenter devices, etc., there are speed irregularities that occur in the order of seconds or less depending on the period of the sprocket teeth that drive the chain, the frequency of the drive motor, etc. This does not correspond to the speed difference described in the invention.

Moreover, in the diagonally stretched tenter used in the present invention, it is preferable that the positions of the rail portions and the rail connecting portions can be freely set. Therefore, when an arbitrary entrance width and exit width are set, the stretch ratio corresponding to this is set. be able to. 2 is an example of a connecting part.
In the obliquely stretched tenter used in the present invention, a large bending rate is often required for the rail that regulates the locus of the gripping tool. For the purpose of avoiding interference between gripping tools due to sudden bending or local stress concentration, it is desirable that the trajectory of the gripping tool draws an arc at the bent portion.

  FIG. 2 shows a track (rail pattern) of a rail of a tenter used in the present invention. The traveling direction DR1 at the tenter inlet of the unstretched film is different from the traveling direction DR2 at the tenter outlet side of the stretched film, and thus, even in a stretched film having a relatively large orientation angle θ, it is wide and uniform. Optical characteristics can be obtained. The feeding angle θi is an angle formed by the traveling direction D1 at the tenter entrance and the traveling direction DR2 on the tenter exit side of the stretched film. In the present invention, in order to produce a film having an orientation angle θ of preferably 10 to 80 ° as described above, the feeding angle θi is 10 ° <θi <60 °, preferably 15 ° <θi <50 °. Is set. By setting the feeding angle θi in the above range, the variation in optical characteristics in the width direction of the obtained film becomes good (smaller).

  The long film is sequentially gripped by the right and left grippers at the tenter entrance (position 10), and travels as the grippers travel. The left and right grips CL and CR facing the direction substantially perpendicular to the film traveling direction (DR1) at the tenter entrance (position 10) run on the left and right asymmetric rails, preheating zone, stretching Pass through an oven with zones and cooling zones. Here, “substantially perpendicular” indicates that the angle formed by the straight line connecting the aforementioned gripping tools CL and CR and the film feeding direction DR1 is within 90 ± 1 °.

  As described above, in the film after stretching of the obliquely stretched film of the present invention, in order to make the Martens hardness in the width direction within the above range, the film temperature during the oblique stretching in the stretching zone has a gradient in the width direction. It is preferable to take a method of adjusting the temperature so that the preheating temperature in the preheating zone or the holding temperature in the holding zone and the cooling temperature in the cooling zone have a gradient in the width direction.

  The preheating zone refers to a section in which the vehicle travels while maintaining a constant interval between the gripping tools gripping both ends at the oven entrance. The stretching zone refers to an interval until the gap between the gripping tools gripping both ends starts to become constant again. The holding zone refers to a section in which the temperature in the zone is set to be equal to or higher than the glass transition temperature Tg ° C. of the cycloolefin resin constituting the film in a period in which the interval between the gripping tools after the stretching zone becomes constant again. In addition, the cooling zone refers to a section in which the temperature in the zone is set to be equal to or lower than the glass transition temperature Tg ° C. of the cycloolefin resin constituting the film in a period in which the interval between the gripping tools after the stretching zone becomes constant again. .

  The temperature of each zone (preheat zone, stretching zone and holding zone) is set to a temperature within the range of (Tg-20) to (Tg + 30) ° C. with respect to the glass transition temperature (Tg) of the dried film after stretching, The temperature of the cooling zone is preferably set to (Tg-30) to Tg ° C.

  In order to make the film temperature have a gradient in the width direction, the opening degree of the nozzle that sends warm air into the temperature-controlled room in the preheating zone, the stretching zone, the holding zone, or the cooling zone is differentiated in the width direction. A known method such as a method of adjusting the temperature and controlling the heating by arranging the heaters in the width direction can be used.

The gradient in the width direction of the film temperature during oblique stretching in the stretching zone is preferably 0.5 to 10.0 ° C, more preferably 1.0 to 5.0 ° C, and most preferably 1.5 to 3. 0 ° C. By making it 0.5 degreeC or more, the effect of a temperature gradient is large and the effect of making the Martens hardness of a film width direction uniform is acquired. Moreover, uniform Ro can be obtained in a film width direction by setting it as 10.0 degrees C or less.
The preheating temperature in the preheating zone, the holding temperature in the holding zone, and the gradient in the width direction of the cooling temperature in the cooling zone are preferably 0.5 to 10.0 ° C, more preferably 1.0 to 5.0 ° C, most preferably Preferably it is 1.5-3.0 degreeC. When the temperature is lower than 0.5 ° C, the effect of the temperature gradient is small, and the effect of uniforming the Martens hardness in the film width direction cannot be obtained. When the temperature is higher than 10.0 ° C, Ro is uniform in the film width direction. Cannot be obtained.

  Moreover, in order to obtain the effect of making the Martens hardness uniform, when performing another stretching (for example, the width direction) before the oblique stretching according to the present invention, the residual solvent in the film is inclined in the width direction. It is preferable to employ a method of adjusting the stretching temperature or a method of adjusting the stretching temperature so as to have a gradient in the width direction.

  The gradient of the residual solvent in the film in the width direction is preferably 0.5 to 20.0% by mass, more preferably 2.0 to 15.0% by mass, and most preferably 4.0 to 12.0%. The difference is in the mass% range. By setting it as 0.5 mass% or more, the effect of the gradient of a residual solvent is large and the effect of making the Martens hardness of a film width direction uniform is acquired. By being 20.0 mass% or less, Ro uniform in the film width direction cannot be obtained.

  The gradient of the stretching temperature in the width direction is preferably in the range of 0.5 to 10.0 ° C, more preferably 1.0 to 5.0 ° C, most preferably 1.5 to 3.0 ° C. Is to provide a difference. When the temperature is 0.5 ° C. or higher, the effect of the temperature gradient is small, and the effect of making the Martens hardness in the film width direction uniform cannot be obtained. Ro cannot be obtained.

The thickness of the finished optical film used in the present invention (after drying) varies depending on the purpose of use, but is usually in the range of 5 to 500 μm, preferably in the range of 10 to 150 μm, and for liquid crystal display devices, 20 to 110 μm. It is preferable that the thickness be 40 μm or less in view of recent thinning.
In order to reduce the thickness of the optical film to 40 μm or less, it is generally necessary to increase the content of the additive in order to maintain the performance of the optical film, and the bleeding out of the additive becomes a problem. By having the cycloolefin resin as a main component, it has an effect of suppressing precipitation of the additive contained in the optical film, which is preferable in that the adhesion between the optical film and the hard coat layer can be improved.

  The thickness of the optical film is adjusted so that the desired thickness and thickness distribution in the present invention are obtained, the solid content concentration contained in the dope, the slit gap of the die base, the extrusion pressure from the die, the metal support speed. Etc. may be adjusted. The width of the optical film obtained as described above is preferably in the range of 0.5 to 4.0 m, more preferably in the range of 0.6 to 3.0 m, and still more preferably in the range of 0.8 to 2.5 m. It is. The length is preferably wound in the range of 100 to 10000 m per roll, more preferably in the range of 500 to 9000 m, and still more preferably in the range of 1000 to 8000 m.

The optical film of the present invention can realize desired optical characteristics by appropriately adjusting the process conditions such as the polymer structure to be used, the type and amount of additives, the draw ratio, the residual volatile content at the time of peeling.
In general, the larger the amount of residual solvent at the time of peeling, the smaller Rt, and the smaller the amount of residual solvent at the time of peeling, the larger Rt. For example, by shortening the drying time on a metal endless support and increasing the amount of residual solvent at the time of peeling, the surface orientation can be relaxed and Rt can be freely lowered, and by adjusting the process conditions It is possible to express various retardations according to various uses.

≪Polarizing plate≫
The polarizing plate of the present invention comprises the optical film of the present invention.
Specifically, as shown in FIG. 3, the polarizing plate A of the present invention bonds an optical film on both surfaces of the polarizer A2. For example, the optical film attached to one surface functions as the λ / 4 retardation film A1, and the optical film attached to the other surface functions as the polarizing plate protective film A3. The absorption axis a of the λ / 4 retardation film and the slow axis b of the polarizing plate protective film have an orientation angle in the range of 45 ± 10 °.

≪Application of optical film≫
The optical film of the present invention can be used for a liquid crystal display device. Moreover, it is preferable that it is a functional film used for various display apparatuses, such as a plasma display and an organic electroluminescent display, and a touch panel.
Specifically, the optical film of the present invention is a polarizing plate protective film for liquid crystal display devices, a retardation film, an antireflection film, a brightness enhancement film, a hard coat film, an antiglare film, an antistatic film, an enlarged viewing angle, etc. Or an optical compensation film. Typically, the optical film of the present invention is a polarizing plate protective film, a retardation film, or an optical compensation film. The optical film of the present invention can serve as both a retardation film and a polarizing plate protective film.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "mass part" or "mass%" is represented. Moreover, the glass transition temperature was calculated | required by the method based on JISK7121-2012 using DSC (Differential Scanning Colorimetry: Differential scanning calorimetry).

<< Production of Optical Film 101 >>
<Preparation of hard coat layer coating solution>
A hard coat layer coating solution having the following composition was prepared. After mixing the ultraviolet curable resin, the surfactant, and propylene glycol monomethyl ether, the mixed solution was stirred for 30 minutes to prepare a hard coat layer coating solution.
(Composition of hard coat layer coating solution)
UV curable resin (Opstar Z7527, manufactured by JSR) 100 parts by mass Surfactant (Surflon S-651, manufactured by AGC Seimi Chemical Co., Ltd.) 0.1 parts by mass Methyl ethyl ketone 30 parts by mass

<Preparation of fine particle dispersion>
11.3 parts by mass of fine particles (Aerosil R972V, manufactured by Nippon Aerosil Co., Ltd.) and 84 parts by mass of ethanol were stirred and mixed with a dissolver for 50 minutes, and then dispersed with Manton Gorin.
To a well-stirred dichloromethane (100 parts by mass) in a dissolution tank, 5 parts by mass of the fine particle dispersion was slowly added. Further, the particles were dispersed by an attritor so that the secondary particles had a predetermined particle size. This was filtered with Finemet NF manufactured by Nippon Seisen Co., Ltd. to prepare a fine particle additive solution.

<Preparation of main dope>
A main dope having the following composition was prepared. First, dichloromethane and ethanol were added to the pressure dissolution tank. A cycloolefin resin, an ultraviolet absorber, and a fine particle additive solution were charged into a pressure dissolution tank containing a mixed solution of dichloromethane and ethanol with stirring. This was completely dissolved with heating and stirring. This was designated as Azumi Filter Paper No. The main dope was prepared by filtration using 244. As the cycloolefin resin, ARTON G7810 manufactured by JSR Corporation was used. The cycloolefin resin is a resin having an alkoxycarbonyl group having a glass transition temperature of 178 ° C.
(Main dope composition)
Cycloolefin resin (ARTON G7810, manufactured by JSR Corporation) 100 parts by mass Dichloromethane (SP value: 20) 200 parts by mass Ethanol (SP value: 26) 10 parts by mass Ultraviolet absorber (Tinuvin 928, manufactured by BASF Japan Ltd.) 2.5 parts by mass Retardation raising agent 1 3 parts by mass Particulate additive solution 3 parts by mass

  The above components were put into a closed container and dissolved with stirring to prepare a main dope. Next, using an endless belt casting apparatus, the dope was cast uniformly on a stainless steel belt support at a temperature of 31 ° C. and a width of 1800 mm. The temperature of the stainless steel belt was controlled at 28 ° C.

Next, using an endless belt casting apparatus, the dope was cast on a stainless belt support at a temperature of 33 ° C. and a width of 1500 mm. The temperature of the stainless steel belt was controlled at 30 ° C.
On the stainless steel belt support, the solvent was evaporated until the amount of residual solvent in the cast (cast) film reached 40% by mass, and then peeled off from the stainless steel belt support with a peeling tension of 110 N / m. The peeled film was stretched 5% in the width direction using a tenter while applying heat at 120 ° C. The residual solvent amount at the start of stretching was 15% by mass.

  Next, drying was terminated while transporting the drying zone with a number of rolls, and the ends sandwiched between tenter clips were slit with a laser cutter, and then wound. The drying temperature was 130 ° C. and the transport tension was 100 N / m.

The roll-shaped film 1 was set in a slidable feeding device shown in FIG. 2 and supplied to an obliquely stretched tenter in which a rail pattern was set so that the angle θi = 47 °.
In addition, as a combination of the zones of the oblique stretching tenter at this time, a combination including a preheating zone, a lateral stretching zone, an oblique stretching zone, a holding zone, and a cooling zone was used.
At that time, the distance between the main axis of the guide roll closest to the entrance portion of the obliquely stretched tenter and the gripping tool (clip gripping portion) of the obliquely stretched tenter was 80 cm.
A clip with a length of 2 inches in the conveying direction was used, and a guide roll with a diameter of 10 cm was used.
In the oblique stretching tenter, the temperature of the preheating zone was 160 ° C., the temperature of the transverse stretching zone was 160 ° C., the temperature of the oblique stretching zone was 160 ° C., and the temperature of the cooling zone was 110 ° C. The take-up tension at the tenter outlet was 200 N / m.

  The stretching ratio at this time was stretched in an oblique direction so as to be 1.05 times. The stretched film was controlled by feedback control in which the variation in tension measured with the first roll on the outlet side of the obliquely stretched tenter was reflected in the number of revolutions of the take-up motor, and the change in take-up tension was controlled to be less than 3%. Thereafter, both ends of the film are trimmed, the conveyance direction is changed by a conveyance direction changing device composed of an air flow roll, the film is wound by a slidable winding device, the film width is 1200 mm, and the dried film thickness is 25 μm. Got.

  A hard coat layer coating solution was applied to one side of the obtained optical film using a micro gravure so that the dry film thickness was 5 μm and dried.

Next, using a high-pressure mercury lamp, the coating film was cured by irradiating the coating film with ultraviolet rays at a light amount of 270 mJ / cm ² in the atmosphere to form a hard coat layer on the optical film.

<< Production of optical films 102-119 >>
The optical films 102 to 119 were produced in the same manner as the optical film 101 according to the conditions shown in Table 1.

<Measurement method of residual solvent amount>
The optical films 101 to 119 immediately before being introduced into the oblique stretching machine were sampled and cut into 100 mm squares. The cut out optical film was heated in an electric furnace adjusted to 140 ° C. for 1 hour, cooled to room temperature, and mass was measured again. The amount of residual solvent was calculated | required by the following formula (I).
Formula (I):
Residual solvent amount [% by mass] = (optical film before heating−optical film after heating) / mass of optical film after heating × 100

<Method for measuring thickness deviation in the width direction>
Cut both ends of the optical film after stretching, cut it into a strip shape from a film sample with a width of 1400 mm, and measure the film thickness at intervals of 50 mm in the film width direction using a Digimatic Thickness Gauge (manufactured by Mitutoyo Corporation). The average of all measured points was taken as the film thickness, and the difference between the maximum value and the minimum value was evaluated as thickness unevenness.

<In-plane retardation value (Ro)>
The in-plane retardation value of the optical film obtained above is an in-plane retardation value (Ro) defined by the following formula (i) at a wavelength of 550 nm in an environment of a temperature of 23 ° C. and a relative humidity of 55%. It measured using Axoscan by Axometrics.
Specifically, lambda / 4 phase difference film in an environment of 23 ℃ · 55% RH, subjected to refractive index measurement of three-dimensional at a wavelength of 550 nm, the refractive indices _{n x,} n y, the average value of _{n z} After the determination, the in-plane retardation value Ro was calculated according to the following formula.
Formula _{(i): Ro = (n} x -n y) × d (nm)
Formula (ii): Rt = {(n _x + n _y ) / 2−n _z } × d (nm)
In the formula, Ro represents an in-plane retardation value in the λ / 4 retardation film, and Rt represents a thickness direction retardation value in the λ / 4 retardation film. D represents the thickness (nm) of the λ / 4 retardation film. n _x represents the maximum refractive index in the plane of the lambda / 4 phase difference film, also referred to as a slow axis direction of the refractive index. n _y represents a direction perpendicular refractive index to the slow axis in lambda / 4 phase difference film plane. _nz represents the refractive index of the λ / 4 retardation film in the thickness direction.

<< Polarization Production 201 >>
A 120 μm-thick polyvinyl alcohol film was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times).
This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water for 60 seconds, and then immersed in an aqueous solution of 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid and 100 g of water. This was washed with water and dried to obtain a 7 μm polarizer.

  Next, in accordance with the following steps 1 to 5, the optical film 101 provided with a polarizer and a hard coat layer and the Konica Minolta Tack KC2CT1 (Konica Minolta Co., Ltd. cellulose ester film, thickness 20 μm) are bonded to the back side for polarization. A plate 201 is produced.

Step 1: The polarizer, the optical film 101 saponified on the side to be bonded, and Konica Minolta Tack KC2CT1 were immersed in a 2 mol / L sodium hydroxide solution at 60 ° C. for 90 seconds, then washed with water and dried.
Process 2: The said polarizer was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.
Step 3: Excess adhesive adhered to the polarizer in Step 2 was gently wiped off and placed on the optical film 101 processed in Step 1.
Step 4: the optical film 101 and the polarizer and the back side Konica Minolta tack KC2CT1 pressure 20-30 N / cm ² were laminated in step 3, the conveying speed was pasted at approximately 2m / min.
Step 5: A sample in which the polarizer prepared in Step 4 was bonded to the optical film 101 and Konica Minoltack KC2CT1 in a drier at 80 ° C. was dried for 2 minutes to prepare a polarizing plate 201.

<< Production of Polarizing Plates 202 to 219 >>
The polarizing plates 202 to 219 were prepared by providing a hard coat layer in the same manner as the polarizing plate 201 (the polarizing plates corresponding to the optical films 101 to 119 are referred to as polarizing plates 201 to 219).

≪Evaluation of production volume≫
For the optical films 101 to 119, the case where only the roll of 1000 m or less could be produced due to the breaking of the optical film being stretched or conveyed, the case where the roll of 1000 m or more could be produced, and the roll of 4000 m was wound without any problem. The case was evaluated as ○.

≪Production of liquid crystal display device and evaluation of display unevenness≫
Using iPad (registered trademark) 2 (a liquid crystal display device in IPS mode) manufactured by Apple, the polarizing plates on both sides bonded in advance are peeled off, and the produced polarizing plates 201 to 219 are respectively attached to the glass surfaces of the liquid crystal cells. Pasted. Each of the prepared polarizing plates is such that the λ / 4 retardation film is on the outside of the glass surface of the liquid crystal cell, and the absorption axis of the polarizer is oriented in the same direction as the polarizing plate previously bonded. The liquid crystal display device was produced by pasting.
Display unevenness when this liquid crystal display device was observed while wearing a change glass was evaluated.
×: Partial brightness is clearly visible △: Partial brightness is slightly visible ○: Partial brightness is not visible

≪Evaluation of color unevenness of liquid crystal display device≫
A liquid crystal display device was manufactured by the same manufacturing procedure as that of the liquid crystal display device on which display unevenness was evaluated.
Color unevenness when this liquid crystal display device was observed while wearing polarizing glass was evaluated.
×: The color of the liquid crystal display changes with or without polarized sunglasses. ○: The color of the liquid crystal display does not change with or without polarized sunglasses.

  From the above results, it was found that the liquid crystal display device of the present invention is excellent in productivity, has no display unevenness and color unevenness, and has excellent visibility.

A Polarizing plate A1 λ / 4 retardation film (optical film)
A2 Polarizer A3 Polarizing plate protective film (optical film)
a Absorption axis b Slow axis 1 Unstretched film 2-1 Right film holding start point 2-2 Left film holding start point 3-1 Right film holding means locus 3-2 Left film holding means locus 4 Tenter 5-1 Right film holding end point 5-2 Left film holding end point 6 Diagonally stretched film 7-1 Film feed direction 8-1 Tenter inlet side guide roll 8-2 Tenter outlet side guide roll 9 Film Stretching direction 10 Tenter inlet DR1 Feeding direction DR2 Winding direction θi Feeding angle (angle formed between feeding direction and winding direction)
CR, CL Gripping device Wo Film width before stretching W Film width after stretching

Claims (6)

An optical film having a slow axis in a direction inclined with respect to the longitudinal direction and having a cycloolefin resin as a main component,
The film thickness is 30 μm or less,
The in-plane retardation value Ro is in the range of 80 to 180 nm,
An optical film having a thickness direction deviation in the width direction of 2.0 μm or less. The film thickness is 25 μm or less,
The optical film according to claim 1, comprising an ultraviolet absorber and a retardation increasing agent. An optical film manufacturing method for manufacturing the optical film according to claim 1 or 2,
The residual solvent amount when obliquely stretching is in the range of 0.1 to 3.0% by mass,
An optical film characterized by being stretched 1.1 times or more in an oblique direction at a temperature in the range of (Tg-20) to (Tg + 30) ° C. with respect to the glass transition temperature (Tg) of the film dried after the oblique stretching. Manufacturing method.   The method for producing an optical film according to claim 3, wherein a residual solvent amount in the oblique stretching is in a range of 0.1 to 1.0 mass%.   A polarizing plate comprising the optical film according to claim 1.   A liquid crystal display device comprising the optical film according to claim 1.

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