JP2017009883A - Method for producing optical film, optical film, circularly polarizing plate and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical film which has improved curling of a film when having been obliquely stretched, and has reduced display unevenness under high temperature and high humidity environment when provided on a display device.SOLUTION: There is provided a method for producing an optical film which includes a step of preparing a dope containing a resin and a solvent with a solution flow-cast film forming method, a step of flow-casting the dope onto a support body to form a flow-cast film, a step of peeling the flow-cast film from the support body in a state where a residual solvent is contained, a step of stretching the peeled flow-cast film in a direction oblique to a width direction, and a step of heating and drying the flow-cast film stretched in the oblique direction, evaporating a residual solvent, and winding the flow-cast film as an optical film, where the flow-cast film is dried on conditions that an amount of a residual solvent of the flow-cast film when stretching in the oblique direction starts is in a range of 2-20 mass%, a heating and drying temperature after having been stretched in the oblique direction is in a range of 100-140°C, and a heating and drying time is in a range of 5-50 minutes.SELECTED DRAWING: None

Description

  The present invention relates to an optical film manufacturing method, an optical film, a circularly polarizing plate, and a display device. More specifically, the present invention relates to an optical film manufacturing method, an optical film, a circularly polarizing plate, and a display device in which curling of the film when obliquely stretched is improved and display unevenness in a high-temperature and high-humidity environment when the display device is provided is reduced. .

  With the spread of smartphones and tablets in recent years, the demand for obliquely stretched optical films has increased. By sticking with a long polarizer having a absorption axis in the longitudinal direction and a roll-to-roll by obliquely stretching the long optical film and providing a slow axis in the film plane in the 45 ° direction. Thus, it becomes possible to easily produce a long circularly polarizing plate.

  When pasting with the long polarizer, it is necessary for the optical film to have no curl or the like in order to improve the yield of the polarizing plate.

  For example, in Patent Document 1, a saponification of a cyclic polyolefin resin layer formed by containing a cyclic polyolefin resin having an ester group in the side chain, followed by providing a layer containing a water-soluble resin on the layer. It is described that curling of the polarizing plate can be suppressed by using the characteristic cyclic polyolefin film.

  However, an obliquely stretched film tends to curl in an oblique direction with respect to the transport direction due to shrinkage in a direction orthogonal to the stretching direction (slow axis direction). This oblique curl not only deteriorates the yield during processing of the polarizing plate, but also when exposed to a harsh environment such as a high temperature and high humidity environment when the polarizing plate is provided in a display device. A phenomenon was observed in which unevenness occurred only at a pair of corners of the display device. This unevenness impairs the contrast and color of the display image of the part.

  Therefore, there is a demand for an elongated optical film that is obliquely stretched and has a slow axis in the oblique direction with respect to the conveyance direction without causing oblique curling even when obliquely stretched.

JP 2007-90613 A

  The present invention has been made in view of the above-mentioned problems and situations, and the problem to be solved is display unevenness in a high-temperature and high-humidity environment when the curling of the film when obliquely stretched is improved and the display device is provided. It is providing the manufacturing method of an optical film, optical film, a circularly-polarizing plate, and a display apparatus with reduced.

  In order to solve the above-mentioned problems, the present inventor, in the process of examining the cause of the above-mentioned problems, stretches the casting film in a specific residual solvent amount when stretching the casting film in an oblique direction, and then performs a specific drying temperature and drying. By producing an optical film by drying over time, the curl of the film when obliquely stretched is improved, and a method for producing an optical film that reduces display unevenness in a high-temperature and high-humidity environment when equipped in a display device It was found that it can be obtained.

  That is, the said subject which concerns on this invention is solved by the following means.

1. A method for producing an optical film by a solution casting method,
Preparing a dope containing a resin and a solvent;
Casting the dope on a traveling support to form a casting film;
Peeling the cast film from the support in a state containing the solvent;
While holding both ends in the width direction of the separated casting film with a pair of gripping tools, one of the gripping tools is relatively advanced, and the other gripping tool is relatively delayed so that the casting film is A step of stretching the cast film in an oblique direction with respect to the width direction by conveying, and thermally drying the cast film stretched in the oblique direction to volatilize the residual solvent, thereby forming an optical film. A winding process,
The residual solvent amount of the cast film when starting stretching in the oblique direction is in the range of 2 to 20% by mass,
The method for producing an optical film is characterized in that the film is dried within a range of 100 to 140 ° C. after drying in the oblique direction and within a range of 5 to 50 minutes.

2. The method for producing an optical film according to item 1, wherein the amount of residual solvent in the cast film is in the range of 5 to 20% by mass.
3. 3. The method for producing an optical film according to item 1 or 2, wherein a temperature difference within a range of 3 to 15 ° C. is provided in the width direction during the stretching.

  4). Any one of the items 1 to 3 is characterized in that a film thickness difference within a range of 2.5 to 7.5% in the width direction is given to the film thickness of the finished film before stretching. The manufacturing method of the optical film of description.

  5. The method for producing an optical film according to any one of Items 1 to 4, wherein a tension of the film at the time of the thermal drying is set in a range of 50 to 150 N / m.

  6). A circularly polarizing plate comprising an optical film produced by the method for producing an optical film according to any one of items 1 to 5.

  7). A display device comprising an optical film produced by the method for producing an optical film according to any one of items 1 to 5.

  By the above-mentioned means of the present invention, the curl of the film when obliquely stretched is improved, and the optical film manufacturing method, optical film, and circularly polarizing plate with reduced display unevenness in a high temperature and high humidity environment when equipped in a display device In addition, a display device can be provided.

  The expression mechanism or action mechanism of the effect of the present invention is not clear, but is presumed as follows.

  In the process of improving the curl of the film when obliquely stretched, the present inventor obliquely stretched with a specific residual solvent amount at the time of stretching, and was thermally stretched at a specific temperature and time after the stretching, thereby being diagonally stretched. It has been found that curling is eliminated by relaxing the shrinkage stress in the direction perpendicular to the stretching direction of the film.

  That is, when the residual solvent within a specific range is in the film at the time of stretching, it becomes possible to orient the resin in an oblique direction without applying excessive stress to the resin. It is presumed that the heat-drying and volatilization over time can sufficiently relieve the shrinkage stress remaining in the film and improve the curling.

  As a result, when an optical film that can improve the occurrence of curling is provided in a display device, it is presumed that curling resistance under a high-temperature and high-humidity environment is improved and display unevenness can be further reduced.

The figure which showed typically an example of the dope preparation process, casting process, and drying process of the solution casting film forming method preferable for this invention The schematic plan view explaining the whole structure of an example of the extending | stretching apparatus used for the manufacturing method of this invention The schematic diagram explaining one embodiment of the diagonal stretch which concerns on this invention The graph which shows the relationship between each zone of the extending | stretching apparatus in the case of the diagonal stretch shown in FIG. 3, and a clip pitch Sectional view along the width direction before and after oblique stretching of a cast film having a constant film thickness in the width direction 4 is a cross-sectional view along the width direction before and after oblique stretching of a cast film having a film thickness distribution symmetrical to the film thickness distribution in FIG. Explanatory drawing showing temperature distribution during heat treatment along with film thickness distribution of cast film Schematic sectional view showing an example of the configuration of the display device of the present invention

  The method for producing an optical film of the present invention is a method for producing an optical film by a solution casting film forming method, comprising preparing a dope containing a resin and a solvent, and casting the dope on a support. A film is formed, and when the cast film is stretched in an oblique direction, the film is stretched with a specific residual solvent amount, and then dried at a specific drying temperature and drying time to produce an optical film. This feature is a technical feature common to the inventions according to claims 1 to 7.

As an embodiment of the present invention, the residual solvent amount of the cast film is preferably in the range of 5 to 20% by mass from the viewpoint of manifesting the effects of the present invention. The curling suppression effect is achieved by being in the range of 2 to 20% by mass, but if it is in the range of 5 to 20% by mass, the effect of sufficiently suppressing curling is manifested and more preferable.
Also, by attaching a temperature difference in the range of 3 to 15 ° C. in the width direction at the time of stretching, the leading side of the gripping tool is more easily stretched than the delay side when stretching diagonally, so The influence of the stretching stress difference can be canceled, and this is preferable in order to produce a film having a uniform retardation with the width of the film.

  In addition, a difference in the film thickness within a range of 2.5 to 7.5% with respect to the finished film thickness before stretching can be applied in the width direction. In order to cancel the influence of the difference in the stretching temperature of the width, and to maintain the uniformity of the thickness of the width of the resulting film, this is a preferred embodiment.

  Furthermore, the tension of the film at the time of the thermal drying is set within the range of 50 to 150 N / m, and the film is stretched by being conveyed while moderately reducing the shrinkage stress in the direction orthogonal to the slow axis. This is a preferred embodiment from the viewpoint of maintaining the uniformity of the width orientation angle.

  The optical film manufactured by the method for manufacturing an optical film of the present invention is suitably included in a circularly polarizing plate and a display device. Thereby, the effect that a polarizing plate with a high yield and a display device with reduced display unevenness can be obtained.

  Hereinafter, the present invention, its components, and modes and modes for carrying out 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.

<< Outline of Manufacturing Method of Optical Film of the Present Invention >>
A method for producing an optical film by a solution casting method,
A dope preparation step of preparing a dope containing a resin and an organic solvent;
Casting the dope on a traveling support to form a casting film;
Peeling the cast film from the support in a state containing the solvent;
While holding both ends in the width direction of the separated casting film with a pair of gripping tools, one of the gripping tools is relatively advanced, and the other gripping tool is relatively delayed so that the casting film is A step of stretching the cast film in an oblique direction with respect to the width direction by conveying, and thermally drying the cast film stretched in the oblique direction to volatilize the residual solvent, thereby forming an optical film. A winding process,
The residual solvent amount of the cast film when starting stretching in the oblique direction is in the range of 2 to 20% by mass,
The heat drying temperature after stretching in the oblique direction is within a range of 100 to 140 ° C., and the heat drying time is within a range of 5 to 50 minutes.
[1] Method for Producing Optical Film The method for producing an optical film of the present invention is a method for producing an optical film by a solution casting film forming method, and includes a step of preparing a dope, a step of forming a casting film, and a casting film. In the step of stretching in the diagonal direction in the step of stretching in the diagonal direction, the residual solvent amount of the casting film when the film is stretched in the diagonal direction is 2 The heat drying temperature after stretching in the oblique direction is within a range of 100 to 140 ° C., and the heat drying time is within a range of 5 to 50 minutes. .

  The above process will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing an example of a dope preparation step, a casting step, a drying step, and a winding step of a solution casting film forming method preferable for the present invention.

  When the matting agent is used for the optical film, the fine particle dispersion in which the solvent and the matting agent are dispersed by the disperser passes from the charging vessel 41 through the filter 44 and is stocked in the stock vessel 42. On the other hand, the resin which is the main dope is dissolved in the dissolving pot 1 together with the solvent, and the matting agent stored in the stock pot 42 is added and mixed as appropriate to form the main dope. The obtained main dope is filtered from the filter 3 and the stock kettle 4 by the filter 6, the additive is added by the merge pipe 20, mixed by the mixer 21, and fed to the pressure die 30.

  On the other hand, an additive (for example, an ultraviolet absorber, a phase difference increasing agent, etc.) is dissolved in a solvent, and is passed from the additive charging vessel 10 through the filter 12 and stocked in the stock vessel 13. After that, the main dope is mixed by the merge pipe 20 and the mixer 21 through the conduit 15 through the filter 15.

  The main dope fed to the pressure die 30 is cast on a metal belt-like support 31 to form a cast film (also referred to as a web) 32 and is peeled off at a predetermined peeling position 33 after drying. Get a film. The peeled casting film 32 is dried until it reaches a predetermined residual solvent amount while passing through a number of conveying rollers in the first drying device 34, and then obliquely with respect to the longitudinal direction by an oblique stretching device 35 described later. Stretched. After the stretching, the film is dried while being conveyed by the conveying roller 37 until it reaches a predetermined residual solvent amount by the second drying device 36, and is wound into a roll by the winding device 38.

  Hereinafter, each step will be described. In the following description, the cycloolefin resin preferable for the present invention is described as “resin” according to the present invention, and the solvent according to the present invention is described as “organic solvent”.

(1) Dope preparation step First, the resin according to the present invention will be described. The resin is not particularly limited. For example, cellulose diacetate, cellulose acetate butyrate, cellulose acetate phthalate, cellulose triacetate, cellulose nitrate, cellulose acetate propionate, cellulose derivatives such as cellulose ether, polyester, polyethylene , Polypropylene, cellophane, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, ethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, cycloolefin resin, polyether ketone, polyether sulfone, polysulfone, Polyetherketoneimide, polyamide, fluororesin, nylon, polymethyl Methacrylate, polyether sulfone, alicyclic polyimide, acrylic resin or polyarylate resin. You may mix and use these resin.

  Among them, since the resin is a cycloolefin resin, it is excellent in optical properties such as handleability and retardation, physical properties such as mechanical strength and water permeability of the film, and is a hydrophobic resin. This is particularly preferable from the viewpoint of reducing display unevenness due to curling in a certain high temperature and high humidity environment. Hereinafter, the cycloolefin resin will be described.

  Examples of the cycloolefin resin used in 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、ｍは０以上の整数である。〕
上記一般式（１）中、Ｒ^１及びＲ^３が水素原子又は炭素数１〜１０、さらに好ましくは１〜４、特に好ましくは１〜２の炭化水素基であり、Ｒ^２及びＲ^４が水素原子又は１価の有機基であって、Ｒ^２及びＲ^４の少なくとも一つは水素原子及び炭化水素基以外の極性を有する極性基を示し、ｍは０〜３の整数、ｐは０〜３の整数であり、より好ましくはｍ＋ｐ＝０〜４、さらに好ましくは０〜２、特に好ましくはｍ＝１、ｐ＝０であるものである。ｍ＝１、ｐ＝０である特定単量体は、得られるシクロオレフィン樹脂のガラス転移温度が高くかつ機械的強度も優れたものとなる点で好ましい。

[Wherein R ^{1 to} R ⁴ each 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, it is a hydrocarbon group substituted with 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), R ¹ and R ³ are a hydrogen atom or a hydrocarbon group having 1 to 10, more preferably 1 to 4, particularly preferably 1 to ^2, and R ² and R ⁴ are hydrogen. An atom or a monovalent organic group, wherein at least one of R ² and R ⁴ represents a polar group having a polarity other than a hydrogen atom and a hydrocarbon group, m is an integer of 0 to 3, and p is 0 to 3 More preferably, m + p = 0-4, more preferably 0-2, particularly preferably m = 1, 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.

  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 ) nCOOR is obtained by using a cycloolefin resin having a high glass transition temperature, a low hygroscopic property, and various materials. It is preferable at the point which has the outstanding adhesiveness. 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 cycloolefins 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 cm ³ / g, more preferably 0.3 to ³ cm ³ / g, particularly preferably 0.4 to 1.5 cm in terms of intrinsic viscosity [η] inh. ³ / g, and the polystyrene-equivalent number average molecular weight (Mn) measured by gel permeation chromatography (GPC) is 8000 to 100,000, more preferably 10,000 to 80000, and 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 in the above ranges, so that heat resistance, water resistance, chemical resistance, mechanical properties of cycloolefin resin and cycloolefin which is the optical film of the present invention Formability as a film 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. When Tg is less than 110 ° C., it is not preferable because it is deformed by use under a high temperature condition or by secondary processing such as coating or printing. On the other hand, when Tg exceeds 350 ° C., the molding process becomes difficult, and the possibility that the resin deteriorates due to heat during the molding process increases.

  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, and the like may be blended, and additives such as plasticizers, ultraviolet absorbers, antioxidants, and retardation adjusting agents may be included.

  Commercially available products can be preferably used as the cycloolefin resin described above. Examples of commercially available products are released under the trade names of ARTON G, ARTON F, ARTON R, and ARTON RX by JSR Corporation. Moreover, ZEONOR ZF14, ZF16, ZEONEX 250, or ZEONEX 280 is commercially available from Nippon Zeon Co., Ltd., and these can be used.

  In the organic solvent mainly comprising a good solvent for the cycloolefin resin, the cycloolefin resin, in some cases, the other compound is dissolved while stirring in a dissolving kettle to prepare a dope, or the cycloolefin resin solution, The dope which is a main solution is prepared by mixing the compound solution.

  When the optical film of the present invention is produced by a solution casting method, an organic solvent useful for forming a dope can be used without limitation as long as it can simultaneously dissolve a cycloolefin resin and other compounds.

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

  The organic solvent used in the present invention is preferably a mixed solvent of a good solvent and a poor solvent. Examples of the good solvent include dichloromethane as a chlorine-based organic solvent, methyl acetate as a non-chlorine-based organic solvent, Ethyl acetate, amyl acetate, acetone, methyl ethyl ketone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol, 2,2,3,3-hexafluoro- 1-propanol, 1,3-difluoro-2-propanol, 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol, 1,1,1,3,3,3-hexa Fluoro-2-propanol, 2,2,3,3,3-pentafluoro-1-propanol, nitroethane, methanol, ethanol, - propanol, iso- propanol, n- butanol, sec- butanol, tert- butanol and the like, that among them is dichloromethane preferred. The good solvent is preferably used in an amount of 55% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more based on the total amount of the solvent.

  The poor solvent is preferably an alcohol solvent, and the alcohol solvent is preferably selected from methanol, ethanol and butanol from the viewpoint of improving peelability and enabling high-speed casting. Of these, methanol or ethanol is preferably used. When the proportion of alcohol in the dope increases, the cast membrane gels, and peeling from the metal support becomes easy. When the proportion of alcohol is small, cycloolefin resins and other solvents in non-chlorine organic solvent systems There is also a role of promoting dissolution of the compound. In film formation of the optical film of the present invention, it is preferable to form a film using a dope having an alcohol concentration in the range of 0.5 to 15.0% by mass from the viewpoint of improving the flatness of the obtained optical film. .

  For dissolving the cycloolefin resin and other compounds, a method carried out at normal pressure, a method carried out below the boiling point of the main solvent, a method carried out under pressure above the boiling point of the main solvent, JP-A-9-95544 and JP-A-9 Various dissolution methods such as a method of performing a cooling dissolution method as described in JP-A-95557 or JP-A-9-95538 and a method of performing at a high pressure described in JP-A-11-21379 can be used. However, a method in which pressure is applied above the boiling point of the main solvent is particularly preferable.

  The concentration of the cycloolefin resin in the dope is preferably in the range of 10 to 40% by mass. After the compound is added to the dope during or after dissolution and dissolved and dispersed, it is filtered through a filter medium, defoamed, and sent to the next step with a liquid feed pump.

  For dope filtration, it is preferable to filter the dope with a filter medium having a collection particle diameter of 90%, for example, 10 to 100 times the average particle diameter of the fine particles, preferably with a main filter 3 having a leaf disk filter. .

  In the present invention, the filter medium used for filtration preferably has a small absolute filtration accuracy. However, if the absolute filtration accuracy is too small, the filter medium is likely to be clogged, and the filter medium must be frequently replaced. There is a problem of lowering productivity.

  For this reason, in the present invention, the filter medium used for the dope in which the cycloolefin resin is dissolved preferably has an absolute filtration accuracy of 0.008 mm or less, more preferably in the range of 0.001 to 0.008 mm, and 0.003 to 0.003. A filter medium in the range of 0.006 mm is more preferable.

  There are no particular restrictions on the material of the filter medium, and normal filter media can be used. However, plastic fiber filter media such as polypropylene and Teflon (registered trademark), and metal filter media such as stainless steel fibers are used to remove fibers. This is preferable.

In the present invention, the dope flow rate during filtration is preferably 10 to 80 kg / (h · m ² ), more preferably 20 to 60 kg / (h · m ² ). Here, if the flow rate of the dope at the time of filtration is 10 kg / (h · m ² ) or more, it becomes efficient productivity, and the flow rate of the dope at the time of filtration is within 80 kg / (h · m ² ). If so, the pressure applied to the filter medium is appropriate, and the filter medium is not damaged, which is preferable.

  The filtration pressure is preferably 3500 kPa or less, more preferably 3000 kPa or less, and even more preferably 2500 kPa or less. The filtration pressure can be controlled by appropriately selecting the filtration flow rate and the filtration area.

  In many cases, the main dope may contain about 10 to 50% by mass of the recycled material.

  The return material is, for example, a product obtained by finely pulverizing the optical film of the present invention, which is generated when the optical film is formed, and has exceeded the specified value of the film due to a product obtained by cutting off both side portions of the film or scratches. An optical film stock is used.

  Moreover, as a raw material of resin used for dope preparation, what pelletized cycloolefin resin and another compound previously can be used preferably.

(2) Casting step (2-1) Casting of dope An endless metal support 31 that feeds the dope to the pressurizing die 30 through a feed pump (for example, a pressurization type metering gear pump) and transfers it infinitely, For example, the dope is cast from a pressure die slit at a casting position on a metal support such as a stainless steel belt or a rotating metal drum.

  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 in the range of 1-4 m, preferably in the range of 1.3-3 m, more preferably in the range of 1.5-2.8 m. The surface temperature of the metal support in the casting step is set in the range of −50 ° C. to a temperature at which the solvent boils and does not foam, more preferably in the range of −30 to 0 ° C. A higher temperature is preferable because the drying speed of the cast film (the dope is cast on the support for casting and the formed dope film is also called a cast film or web) can be increased, but it is too high. The cast film may foam or the flatness may deteriorate. A preferable support temperature is appropriately determined at 0 to 100 ° C, and more preferably 5 to 30 ° C. Alternatively, it is also preferable to peel the film from the drum in a state in which the cast film is gelled by cooling and contains 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 casting film due to the latent heat of vaporization of the solvent, use hot air that is higher than the target temperature while using hot air above the boiling point of the solvent and preventing foaming. There is. 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.

  The die is preferably a pressure die that can adjust the slit shape of the die portion of the die and easily make the film thickness uniform. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. The surface of the metal support is a mirror surface. In order to increase the film forming speed, two or more pressure dies may be provided on the metal support, and the dope amount may be divided and laminated.

(2-2) Solvent evaporation process It is the process of heating a casting film on the support body for casting, and evaporating a solvent.

  In order to evaporate the solvent, there are a method of blowing air from the casting membrane side, a method of transferring heat from the back surface of the support by a liquid, a method of transferring heat from the front and back by radiant heat, and the like. The drying efficiency is good and preferable. A method of combining them is also preferably used. The cast film on the support after casting is preferably dried on the support in an atmosphere of 30 to 100 ° C. In order to maintain the atmosphere at 30 to 100 ° C., it is preferable to apply hot air of this temperature to the upper surface of the casting film or to heat by means such as infrared rays.

  From the viewpoint of surface quality, moisture permeability, and peelability, it is preferable to peel the cast film from the support within 30 to 180 seconds.

(2-3) Peeling Step This is a step of peeling the cast film from which the solvent has evaporated on the metal support at the peeling position. The peeled cast film is sent to the next process as a film.

  The temperature at the peeling position on the metal support is preferably in the range of 10 to 40 ° C, more preferably in the range of 11 to 30 ° C.

  In the present invention, the solvent in the casting film is evaporated in the solvent evaporation step, but the residual solvent amount of the casting film on the metal support at the time of peeling is in the range of 15 to 100% by mass. It is preferable. The residual solvent amount is preferably controlled by the drying temperature and drying time in the solvent evaporation step.

  If the amount of the residual solvent is 15% by mass or more, the additive, for example, a matting agent or the like is not distributed in the thickness direction and is uniformly dispersed in the film in the drying process on the support, which is preferable. .

  Further, if the amount of the residual solvent is within 100% by mass, the film has self-supporting property, can avoid poor film peeling, and can maintain the mechanical strength of the cast film, thereby improving the flatness at the time of peeling. In addition, it is possible to suppress occurrence of slippage and vertical stripes due to peeling tension.

  The residual solvent amount of the cast film or film is defined by the following formula (Z).

Formula (Z)
Residual solvent amount (%) = (mass before heat treatment of casting film or film−mass after heat treatment of casting film or film) / (mass after heat treatment of casting film or film) × 100
Note that the heat treatment for measuring the residual solvent amount represents performing heat treatment at 115 ° C. for 1 hour.

  The peel tension when peeling the cast film from the metal support to form a film is usually in the range of 196 to 245 N / m. However, when peeling easily occurs, the tension is 190 N / m or less. It is preferable to peel off.

  In the present invention, the temperature at the peeling position on the metal support is preferably in the range of −50 to 40 ° C., more preferably in the range of 10 to 40 ° C., and in the range of 15 to 30 ° C. Is most preferred.

(3) Drying and stretching step The drying step can be divided into a preliminary drying step (first drying step) and a main drying step (second drying step).

(3-1) Pre-drying step The film obtained by peeling the cast film from the metal support is pre-dried by the first drying device 34. Preliminary drying of the film may be performed while the film is being transported by a number of rollers arranged above and below, or may be dried while being transported by fixing both ends of the film with clips like a tenter dryer. Good.

  The means for drying the cast film is not particularly limited, and can generally be performed with hot air, infrared rays, a heating roller, microwave, or the like, but it is preferably performed with hot air in terms of simplicity.

  The drying temperature in the pre-drying step of the cast film is preferably a glass transition point of the film of −5 ° C. or lower, and it is effective to perform heat treatment at a temperature of 30 ° C. or higher for 1 minute or longer and 30 minutes or shorter. Drying is carried out at a drying temperature in the range of 40 to 150 ° C, more preferably in the range of 50 to 100 ° C.

  In this invention, it is preferable to adjust the amount of residual solvents in the film at the time of extending | stretching mentioned later in this drying process. Although the residual solvent amount may be performed at the initial stage of the stretching step, the residual solvent amount is preferably controlled by the drying temperature and the drying time in the preliminary drying step.

(3-2) Stretching Step The optical film of the present invention can reduce the occurrence of curling caused by stretching in the oblique direction by stretching under a specific residual solvent amount with the stretching device 35. By controlling the orientation of the molecules in the film, target retardation values Ro and Rt can be obtained.

  The method for producing an optical film of the present invention is characterized in that, in the step of stretching the film in an oblique direction, the residual solvent amount at the start of stretching is in the range of 2 to 20% by mass. Preferably the effect which suppresses curl more fully expresses in the range of 5-20 mass%.

  If the amount of residual solvent at the start of stretching is less than 2% by mass, residual stress is excessively applied to the stretched film, so that the occurrence of curling at the time of oblique stretching increases, which is not preferable. Moreover, when it is going to reduce the residual solvent of a film by high temperature extending | stretching, a desired phase difference cannot be obtained.

  On the other hand, if the amount of residual solvent exceeds 20% by mass, it becomes difficult to apply stress during stretching, and thus it becomes difficult to control the phase difference, or foaming occurs in the stretching machine, resulting in unevenness due to bubbles on the film surface, resulting in flatness. to degrade.

(3-2-1) Diagonal Stretching In the stretching step according to the present invention, one gripping tool is relatively advanced while gripping both ends of the separated cast film in the width direction with a pair of gripping tools. This is a step of stretching the casting film in an oblique direction with respect to the width direction by transporting the casting film with a relative delay of the other gripping tool.

  As described above, the optical film of the present invention is formed by the solution casting film forming method using the dope, and then the casting film is preferably in a direction within a range of 45 ± 30 ° with respect to the width direction. More preferably, the film is obliquely stretched in the direction of 45 ± 10 °, and the slow axis is given in the direction of 45 ± 30 °, more preferably 45 ± 10 °, particularly preferably 45 ± 5 ° with respect to the width direction. It is a process.

  JP, 2005-321543, JP, 2013-120208, and JP, 2014-194484, A can be referred to for the method and apparatus for extending in the slanting direction.

[Diagonal stretching method and apparatus]
As described above, the oblique stretching step according to the present invention, as described above, relatively grips one gripping tool while gripping both ends in the width direction of the cast film with a pair of gripping tools. The tool is relatively delayed to convey the cast film and stretched in an oblique direction with respect to the width direction.

  More specifically, it is preferable to employ the following steps. Here, the carrier is described as a clip.

  In the oblique stretching step according to the present invention, the left and right end portions of the cast film are each gripped by variable pitch type left and right clips whose longitudinal clip pitches change (A: gripping step); Pre-heating (B: pre-heating step); increasing the distance between the left and right clips while increasing the clip pitch of one clip and decreasing the clip pitch of the other clip to stretch the film diagonally (C: first oblique stretching step); maintaining or reducing the clip pitch of the one clip so that the clip pitch of the left and right clips becomes equal while increasing the distance between the left and right clips; and , Increasing the clip pitch of the other clip and obliquely stretching the film (D: second oblique stretching step); and gripping the film Releasing the lip (E: releasing step); including.

A. 2. Grasping process First, with reference to FIG. 2, the extending | stretching apparatus which can be used for the manufacturing method of this invention including this process is demonstrated. FIG. 2 is a schematic plan view illustrating the overall configuration of an example of a stretching apparatus that can be used in the manufacturing method of the present invention. The stretching device 50 has an endless loop 60L having a large number of clips 80 for gripping films and an endless loop 60R symmetrically on the left and right sides in a plan view. In this specification, the left endless loop as viewed from the film entrance side is referred to as the left endless loop 60L, and the right endless loop is referred to as the right endless loop 60R. The clips 80 of the left and right endless loops 60L and 60R are guided by the reference rail 70 and move around in a loop. The left endless loop 60R moves in a counterclockwise direction, and the right endless loop 60R moves in a clockwise direction. In the stretching apparatus, a gripping zone A, a preheating zone B, a first oblique stretching zone C, a second oblique stretching zone D, and a release zone E are provided in this order from the entrance side to the exit side of the sheet. . Each of these zones means a zone in which the film to be stretched is substantially gripped, preheated, first obliquely stretched, second obliquely stretched and released, and mechanically and structurally independent. It does not mean a parcel. Further, the ratio of the lengths of the respective zones in the stretching apparatus of FIG. 2 is appropriately determined.

  In the gripping zone A and the preheating zone B, the left and right endless loops 60R and 60L are configured to be substantially parallel to each other at a separation distance corresponding to the initial width of the film to be stretched. In the first oblique stretching zone C and the second oblique stretching zone D, the separation distance of the left and right endless loops 60R and 60L corresponds to the width after stretching of the film as it goes from the preheating zone B side to the release zone E. It is configured to gradually expand until. In the release zone E, the left and right endless loops 60R and 60L are configured to be substantially parallel to each other at a separation distance corresponding to the width of the film after stretching.

  The clip of the left endless loop 60L (left clip) 80 and the clip of the right endless loop 60R (right clip) 80 can each independently move around. For example, the driving rollers 51, 52, 53 of the left endless loop 60L are rotationally driven counterclockwise by an electric motor (not shown), and the driving rollers 51, 52, 53 of the right endless loop 60R are clocked by the electric motor. It is driven to rotate around. As a result, a running force is applied to the clip carrying member engaged with the drive rollers 51, 52, 53. As a result, the left endless loop 60L cyclically moves in the counterclockwise direction, and the right endless loop 60R cyclically moves in the clockwise direction. By driving the left electric motor and the right electric motor independently of each other, the left endless loop 60L and the right endless loop 60R can be independently cyclically moved.

  Furthermore, the clip (left clip) 80 of the left endless loop 60L and the clip (right clip) 80 of the right endless loop 60R are each of a variable pitch type. That is, the clip pitches (distance between clips) in the vertical direction (MD) can be changed as the left and right clips 80 are independently moved by the clip variable mechanism 90 attached to the reference rail 70.

  By performing oblique stretching of the film using the stretching apparatus as described above, a retardation film having a slow axis in an oblique direction (for example, a direction of 45 ° with respect to the width direction or the longitudinal direction) can be produced. . First, in the gripping zone A (the entrance of the film take-in of the stretching device 50), the left and right endless loops 60R and 60L are gripped by the clips 80 on both sides of the film to be stretched at a constant clip pitch. The film is sent to the preheating zone B by the movement of the endless loops 60R and 60L (substantially, the movement of each clip guided by the reference rail 70).

B. Preheating process In the preheating zone (preheating process) B, the left and right endless loops 60R and 60L are configured to be substantially parallel to each other at a separation distance corresponding to the initial width of the cast film to be stretched as described above. Therefore, basically, neither the horizontal stretching nor the longitudinal stretching is performed, and the cast film is heated. However, the distance between the left and right clips (the distance in the width direction) may be slightly increased in order to avoid problems such as the casting film bending due to preheating and contact with the nozzles in the oven.

  In the preheating step, the film is heated to a temperature T1 (° C.). It is preferable that temperature T1 is more than the glass transition temperature (Tg) of a film, More preferably, it is Tg + 2 degreeC or more, More preferably, it is Tg + 5 degreeC or more. On the other hand, the heating temperature T1 is preferably Tg + 40 ° C. or lower, more preferably Tg + 30 ° C. or lower. Although it changes with resin to be used, temperature T1 is 70-190 degreeC, for example, Preferably it is 80-180 degreeC.

  The temperature raising time to the temperature T1 and the holding time at the temperature T1 can be appropriately set according to the constituent material of the film and the manufacturing conditions (for example, the film conveyance speed). These temperature raising time and holding time can be controlled by adjusting the moving speed of the clip 20, the length of the preheating zone, the temperature of the preheating zone, and the like.

C. First oblique stretching step In the first oblique stretching zone (first oblique stretching step) C, the distance between the left and right clips (more specifically, the distance between the left and right endless loops 60R and 60L) is increased. The film is stretched diagonally while increasing the clip pitch of one clip and decreasing or holding the clip pitch of the other clip. By changing the clip pitch in this way, the left and right clips are moved at different speeds, thereby extending one side edge of the film in the longitudinal direction and contracting the other side edge in the longitudinal direction. The oblique stretching can be performed. As a result, it is possible to develop a slow axis with high uniaxiality and in-plane orientation in a desired direction (for example, a direction of 45 ° with respect to the longitudinal direction or the width direction).

  Hereinafter, one embodiment of the first oblique stretching will be specifically described with reference to FIGS. 3 and 4. First, in the preheating zone B, the left and right clip pitches are both P1. P1 is the clip pitch when gripping the film. Next, as soon as the film enters the first oblique stretching zone C, the clip pitch of one (right side in the illustrated example) starts to increase, and the clip pitch of the other (left side in the illustrated example) Start decreasing. In the first oblique stretching zone C, the clip pitch of the right clip is increased to P2, and the clip pitch of the left clip is decreased to P3. Therefore, at the end portion of the first oblique stretching zone C (the start portion of the second oblique stretching zone D), the left clip moves at the clip pitch P3 and the right clip moves at the clip pitch P2. . The clip pitch ratio can generally correspond to the clip moving speed ratio. Therefore, the ratio of the clip pitch of the left and right clips can generally correspond to the ratio of the stretching ratio in the MD direction between the right side edge and the left side edge of the film.

  3 and 4, both the position where the clip pitch of the right clip begins to increase and the position where the clip pitch of the left clip begins to decrease are used as the start portion of the first oblique extension zone C, but unlike the illustrated example, The clip pitch of the left clip may begin to decrease after the clip pitch of the right clip begins to increase, and the clip pitch of the right clip may begin to increase after the clip pitch of the left clip begins to decrease. In one preferred embodiment, after the clip pitch of the clip on one side begins to increase, the clip pitch of the clip on the other side begins to decrease. According to such an embodiment, since the film has already been stretched in the width direction to a certain extent (preferably about 1.2 to 2.0 times), the wrinkle is reduced even if the clip pitch on the other side is greatly reduced. Is unlikely to occur. Therefore, a more acute oblique stretching is possible, and a retardation film having high uniaxiality and high in-plane orientation can be suitably obtained.

  Similarly, in FIG. 3 and FIG. 4, the clip pitch of the right clip continues to increase and the clip pitch of the left clip continues to the end of the first oblique stretching zone C (the start of the second oblique stretching zone D). However, unlike the illustrated example, either the increase or decrease of the clip pitch ends before the end of the first oblique stretching zone C and the clip is clipped to the end of the first oblique stretching zone C. The pitch may be maintained as it is.

  The increasing clip pitch change rate (P2 / P1) is preferably 1.25 to 1.75, more preferably 1.30 to 1.70, and still more preferably 1.35 to 1.65. Moreover, the decreasing rate (P3 / P1) of the clip pitch to be decreased is, for example, 0.50 or more and less than 1, preferably 0.50 to 0.95, more preferably 0.55 to 0.90, and still more preferably 0.8. 55 to 0.85. If the change rate of the clip pitch is within such a range, the slow axis can be expressed with high uniaxiality and in-plane orientation in a direction of approximately 45 degrees with respect to the longitudinal direction of the film.

  As described above, the clip pitch can be adjusted by positioning the slider by adjusting the distance between the pitch setting rail of the stretching device and the reference rail.

  The draw ratio (W2 / W1) in the width direction of the film in the first oblique stretching step is preferably 1.1 to 3.0 times, more preferably 1.2 to 2.5 times, and still more preferably 1.25. ~ 2.0 times. When the draw ratio is 1.1 times or more, it is possible to avoid a case where tin-like wrinkles are generated at the side edge portion on the contracted side. Moreover, if the said draw ratio is less than 3.0 times, the biaxiality of the obtained retardation film will not become high, and a viewing angle characteristic will not fall when it applies to a circularly-polarizing plate etc.

  In one embodiment, the first oblique stretching has a product of the rate of change of the clip pitch of one clip and the rate of change of the clip pitch of the other clip, preferably 0.7 to 1.5, more preferably It is carried out so as to be 0.8 to 1.45, more preferably 0.85 to 1.40. If the product of the rate of change is within such a range, a retardation film having high uniaxiality and in-plane orientation can be obtained.

  The first oblique stretching can typically be performed at a temperature T2. The temperature T2 is preferably Tg-20 ° C to Tg + 30 ° C, more preferably Tg-10 ° C to Tg + 20 ° C, and particularly preferably about Tg with respect to the glass transition temperature (Tg) of the resin film. Although it changes with resin films to be used, the temperature T2 is, for example, 70 ° C to 180 ° C, and preferably 80 ° C to 170 ° C. The difference (T1-T2) between the temperature T1 and the temperature T2 is preferably ± 2 ° C. or more, more preferably ± 5 ° C. or more. In one embodiment, T1> T2, and thus the film heated to temperature T1 in the preheating step can be cooled to temperature T2.

D. Second oblique stretching step In the second oblique stretching zone (second oblique stretching step) D, the distance between the left and right clips (more specifically, the distance between the left and right endless loops 60R and 60L) is increased. The film is stretched obliquely while maintaining or decreasing the clip pitch of the clip on one side and increasing the clip pitch of the clip on the other side so that the clip pitches of the left and right clips are equal. In this way, by stretching diagonally while reducing the difference between the left and right clip pitches, it is possible to sufficiently stretch in the diagonal direction while relaxing excess stress. In addition, since the film can be used in the release process with the left and right clips moving at the same speed, variations in the film transport speed and the like hardly occur when the left and right clips are released, and subsequent film winding is preferable. Can be done.

  Hereinafter, one embodiment of the second oblique stretching will be specifically described with reference to FIG. First, as soon as the film enters the second oblique stretching zone D, the clip pitch of the left clip starts to increase. In the second oblique stretching zone D, the clip pitch of the left clip is increased to P2. On the other hand, the clip pitch of the right clip is maintained at P2 in the second oblique stretching zone D. Therefore, both the left clip and the right clip move at the clip pitch P2 at the end portion of the second oblique stretching zone D (the start portion of the release zone E).

The increasing rate (P2 / P3) of the increasing clip pitch in the above embodiment is not limited as long as the effects of the present invention are not impaired. The rate of change (P2 / P3) is, for example, 1.3 to 4.0, preferably 1.5 to 3.0.
The draw ratio (W3 / W2) in the width direction of the film in the second oblique stretching step is preferably 1.1 to 3.0 times, more preferably 1.2 to 2.5 times, and still more preferably 1.25. ~ 2.0 times. When the draw ratio is 1.1 times or more, it is possible to avoid a case where tin-like wrinkles are generated at the side edge portion on the contracted side. Moreover, if the said draw ratio is less than 3.0 times, the biaxiality of the obtained retardation film will not become high, and a viewing angle characteristic will not fall when it applies to a circularly-polarizing plate etc. Moreover, the draw ratio (W3 / W1) in the width direction in the first oblique stretching step and the second oblique stretching step is preferably 1.2 to 4.0 times, more preferably from the same viewpoint as described above. Is 1.4 to 3.0 times.

  The second oblique stretching can typically be performed at a temperature T3. The temperature T3 may be equivalent to the temperature T2.

E. Release process Finally, the clip which grasps a cast film is released, and a phase contrast film is obtained. If necessary, the cast film is heat-treated to fix the stretched state, and after cooling, the clip is released, and the cast film obliquely stretched is transported to the next step.

(3-2-2) Adjustment of film thickness distribution and temperature distribution In addition, the cast film before oblique stretching has a film thickness deviation that occurs in the oblique stretch cast film after oblique stretching at each position in the width direction. It is preferable to increase the film thickness from the reference film thickness in advance by an amount that compensates for the film thickness so as to have an asymmetric film thickness distribution in the width direction, and 2.5 to 7.5% of the film thickness that is finished in the width direction. It is preferable to give a film thickness difference (film thickness distribution) within the range of.

  The film thickness distribution (film thickness profile) will be described.

  FIG. 5 is a cross-sectional view along the width direction before and after oblique stretching of the casting film S0 having a constant film thickness in the width direction (referred to as a reference film thickness T). As described above, when the stretched portion is obliquely stretched with respect to the casting film S0 having a constant film thickness T in the width direction, the film thickness is reduced by stretching. At this time, in the oblique stretching, the moving distance of the gripping tool is different between the one end side and the other end side of the casting film S0 in the width direction, and the stretching ratio is different. It differs between one end side and the other end side. As a result, in the long obliquely stretched cast film f after oblique stretching, a film thickness distribution that is asymmetrical with respect to the center in the width direction is generated. Note that in the cast film f after oblique stretching, the amount of decrease in film thickness from a desired film thickness (required film thickness) t, that is, the difference between the maximum value and the minimum value of the film thickness, here, Called thickness deviation t0.

  Therefore, in the present embodiment, as shown in FIG. 6, oblique stretching is performed using a casting film S <b> 1 having a film thickness distribution substantially symmetrical in the thickness direction with the film thickness distribution after oblique stretching in FIG. 5. More specifically, a film that is asymmetric in the width direction, in which the film thickness is increased in advance from the reference film thickness T at each position in the width direction by an amount t1 that compensates for the film thickness deviation t0 that occurs after oblique stretching. Diagonal stretching is performed using a cast film S1 having a thickness distribution. The material and width of the casting film S1 are the same as the material and width of the casting film S0.

  By obliquely stretching such a casting film S1, the amount of reduction from the desired film thickness t (<reference film thickness T) (= t0) of the film thickness reduced by the oblique stretching at all positions in the width direction. ) Can be supplemented without excess or deficiency by the amount of increase in film thickness before oblique stretching (= t1). Thereby, the film thickness of the long diagonally stretched film F after diagonal stretching can be made sufficiently uniform in the width direction (the film thickness in the width direction can be reliably aligned with the desired film thickness t). . As a result, variation in the width direction of the in-plane retardation (retardation value Ro) in the cast film F after oblique stretching is sufficiently reduced.

  Here, when performing the oblique stretching, the casting film S1 previously formed with the film thickness distribution as described above may be used for the oblique stretching, or the casting film S0 having a constant thickness may be obliquely formed. The film thickness distribution at the time of stretching may be obtained, the casting film S1 may be formed by adjusting the conditions at the time of casting based on the film thickness distribution, and then the casting film S1 may be stretched obliquely.

  Furthermore, the oblique stretching according to the present invention includes a heat treatment step (B. Preheating step to D. Second stretching step) for performing a heat treatment on the cast film before and after the oblique stretching, and in the heat treatment step, the oblique stretching is performed. Within the range of 3 to 15 ° C. in the width direction so that a temperature distribution according to the film thickness distribution of the cast film before the oblique stretching is obtained in the width direction with respect to the front and rear oblique stretching films. It is preferable to perform a heat treatment that gives a temperature difference of. More preferably, it is a temperature difference within the range of 5-10 degreeC.

  FIG. 7 shows the temperature distribution during heat treatment of the cast film together with the film thickness distribution of the long film S1 of FIG. As shown in the figure, the film thickness distribution in the width direction of the cast film S1 before oblique stretching has only one film thickness maximum in the width direction, and the maximum is the width of the cast film S1. The distribution is generated between the center in the hand direction and the end on the delay side.

In the present embodiment, in the heat treatment step, the heating section for heating the flow after oblique stretching so that a temperature distribution according to the film thickness distribution in the width direction of the casting film S1 before oblique stretching is obtained. The spread film F is heated. Here, as shown in FIG. 7, the temperature distribution corresponding to the film thickness distribution has only one temperature maximum in the width direction, and the maximum position of the temperature is a long oblique stretched film F. In FIG. 4, the distribution is the same as the position in the width direction where the film thickness is maximum before oblique stretching (corresponding to the maximum position of the film thickness of the long film S1 before oblique stretching).
As described above, the film F after the oblique stretching is subjected to the heat treatment so as to obtain a temperature distribution according to the film thickness distribution in the width direction of the cast film S1 before the oblique stretching. The stress remaining in the subsequent casting film F (residual stress having a magnitude corresponding to the film thickness before oblique stretching) is appropriately relaxed for each position in the width direction to reduce the variation of the residual stress, and the residual The stress can be made uniform in the width direction. As a result, variations in the retardation value Ro in the width direction of the cast film F after oblique stretching can be reduced.

(3-3) Main drying step In the main drying step, the stretched film is heated and dried by the second drying device 36. When the film is heated with hot air or the like, a means for preventing the mixing of used hot air by installing a nozzle that can exhaust used hot air (air containing solvent or wet air) is also preferably used. The hot air temperature is adjusted in consideration of the residual solvent amount, the expansion / contraction rate in conveyance, and the like so that the thermal drying temperature of the optical film is in the range of 100 to 140 ° C. Further, the heat drying time needs to be within a range of 5 to 50 minutes, and more preferably within a range of 20 to 40 minutes.

  If the heat drying temperature is not 100 ° C. or higher, the relaxation cannot be sufficiently performed and curling cannot be suppressed. Moreover, since drying property is also bad, it is necessary to set it as 100 degreeC or more.

  If the heat drying temperature is within 140 ° C., it is possible to suppress the elongation of the film during drying while transporting the cycloolefin resin containing the solvent, and to prevent generation of wrinkles in the transport direction.

  If the heat drying time is 5 minutes or less, the curl-inhibiting effect is not sufficient, and the solvent cannot be sufficiently dried.

  It is not preferable that the thermal drying time is 50 minutes or more from the viewpoint of productivity (production speed, production cost).

  Further, the heat drying means is not limited to hot air, and for example, infrared rays, heating rollers, microwaves, and the like can be used. From the viewpoint of simplicity, it is preferable to dry with hot air or the like while transporting the film with the transport rollers 37 arranged in a staggered manner.

  Further, the tension at the time of transporting the film during the heat drying can be transported while moderately reducing the shrinkage stress in the direction perpendicular to the slow axis, being in the range of 50 to 150 N / m. From the viewpoint of maintaining the uniformity of the width orientation angle after stretching. More preferably, it is in the range of 60 to 120 N / m.

  In the drying step, it is preferable to dry the film until the residual solvent amount is 1000 ppm or less.

(4) Winding step (4-1) Knurling processing It is preferable to provide a slitter after the predetermined heat treatment or cooling treatment and cut off the end portion before winding to obtain a good winding shape. Furthermore, it is preferable to knurling both ends of the width.

  The knurling process can be formed by pressing a heated embossing roller against the film width end. Fine embossing is formed on the embossing roller, and by pressing the embossing roller, unevenness can be formed on the film and the end can be made bulky.

  The height of the knurling at both ends of the width of the optical film according to the present invention is preferably 4 to 20 μm and a width of 5 to 20 mm.

  In the present invention, the knurling process is preferably provided after the drying in the film forming step and before the winding.

(4-2) Winding step This is a step of winding the film as a film after the residual solvent amount in the film is 2% by mass or less, and the dimensional stability is preferably set to 0.4% by mass or less. Can be obtained.

  As a winding method, a generally used method may be used, and there are a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress, and the like.

  According to the method for producing an optical film of the present invention, it is possible to apply an appropriate stress to the film at the time of stretching by controlling the residual solvent amount at the time of stretching to a specific range. It is possible to form a concavo-convex structure uniformly distributed on the surface, and a stable winding shape can be achieved by ensuring uniform slip.

[2] Additives The optical film of the present invention may contain a plasticizer, an ultraviolet absorber, an antioxidant, a matting agent, a retardation increasing agent, an antistatic agent, a release agent, and the like. Details.

[Plasticizer]
In the present invention, a polyester resin can be further used as a plasticizer. The polyester resin is obtained by polymerizing a dicarboxylic acid and a diol, and 70% or more of the dicarboxylic acid structural unit (the structural unit derived from the dicarboxylic acid) is derived from the aromatic dicarboxylic acid, and the diol structural unit (derived from the diol). 70% or more of the structural unit is derived from an aliphatic diol.

  The proportion of the structural unit derived from the aromatic dicarboxylic acid is 70% or more, preferably 80% or more, more preferably 90% or more.

  The proportion of the structural unit derived from the aliphatic diol is 70% or more, preferably 80% or more, and more preferably 90% or more. Two or more polyester resins may be used in combination.

  Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, naphthalenedicarboxylic acid such as 2,7-naphthalenedicarboxylic acid, and 4,4′-biphenyldicarboxylic acid. 3,4'-biphenyldicarboxylic acid and the like and ester-forming derivatives thereof.

  As the polyester resin, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid, and monocarboxylic acids such as benzoic acid, propionic acid, and butyric acid can be used without departing from the object of the present invention.

  Examples of the aliphatic diol include ethylene glycol, 1,3-propylene diol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, and the like, and ester-forming derivatives thereof.

As the polyester resin, monoalcohols such as butyl alcohol, hexyl alcohol, and octyl alcohol, and polyhydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol can be used as long as the object of the present invention is not impaired.

A known esterification method or transesterification method can be applied to the production of the polyester resin. Examples of the polycondensation catalyst used in the production of the polyester resin include known antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds such as germanium oxide, titanium compounds such as titanium acetate, and aluminum compounds such as aluminum chloride. Although it can, it is not limited to these.

  Preferred polyester resins include polyethylene terephthalate resin, polyethylene terephthalate-isophthalate copolymer resin, polyethylene-1,4-cyclohexanedimethylene-terephthalate copolymer resin, polyethylene-2,6-naphthalene dicarboxylate resin, polyethylene-2, 6-naphthalene dicarboxylate-terephthalate copolymer resin, polyethylene-terephthalate-4,4'-biphenyldicarboxylate resin, poly-1,3-propylene-terephthalate resin, polybutylene terephthalate resin, polybutylene-2,6-naphthalene There are dicarboxylate resins and the like.

  More preferable polyester resins include polyethylene terephthalate resin, polyethylene terephthalate-isophthalate copolymer resin, polyethylene-1,4-cyclohexanedimethylene-terephthalate copolymer resin, polybutylene terephthalate resin, and polyethylene-2,6-naphthalene dicarboxylate. Resin.

The intrinsic viscosity of the polyester resin (phenol / 1,1,2,2-tetrachloroethane = value measured at 25 ° C. in a 60/40 mass ratio mixed solvent) is in the range of 0.7 to 2.0 cm ³ / g. Is more preferable, and it is in the range of 0.8 to 1.5 cm ³ / g. Since the molecular weight of the polyester resin is sufficiently high when the intrinsic viscosity is 0.7 cm ³ / g or more, a molded product comprising the polyester resin composition obtained by using the polyester resin has mechanical properties necessary as a molded product. At the same time, transparency is improved. When the intrinsic viscosity is 2.0 cm ³ / g or less, the moldability is good. As other plasticizers, compounds described in the general formulas (PEI) and (PEII) in paragraphs 0056 to 0080 of JP2013-97279A may be used.

[Ultraviolet absorber]
The optical film of the present invention preferably contains an ultraviolet absorber in order to shield unnecessary ultraviolet rays irradiated to the polarizing plate and the liquid crystal display device.

  Examples of ultraviolet absorbers include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like, but less benzotriazole compounds. Compounds are preferred. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

  When the optical film of the present invention is used as a protective film for a polarizing plate in addition to a retardation film, the ultraviolet absorber is excellent in the ability to absorb ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing the deterioration of a polarizer and liquid crystal. In addition, from the viewpoint of the display properties of the liquid crystal, it is preferable that the liquid crystal display device has a characteristic that absorbs less visible light having a wavelength of 400 nm or more.

  The addition amount of the ultraviolet absorber is preferably in the range of 0.1 to 5.0% by mass and more preferably in the range of 0.5 to 5.0% by mass with respect to the polymer composition. preferable.

  Benzotriazole-based UV absorbers useful in the present invention include, for example, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-t -Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-t-butyl Phenyl) -5-chlorobenzotriazole, 2- [2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl] benzotriazole, 2,2 -Methylenebis [4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol], 2- (2'-hydroxy-3) -T-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol, octyl-3 -[3-t-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-t-butyl-4-hydroxy-5- ( A mixture of 5-chloro-2H-benzotriazol-2-yl) phenyl] propionate can be mentioned, but is not limited thereto.

  Further, as a commercial product, “TINUVIN 109”, “TINUVIN 171”, “TINUVIN 326”, “TINUVIN 328” (above, trade name, manufactured by BASF Japan Ltd.) are preferable. Can be used.

[Antioxidant]
Antioxidant has a role of delaying or preventing the base film from being decomposed by, for example, halogen of a residual solvent in the base film or phosphoric acid of a phosphoric acid plasticizer. It is preferable to make it.

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like.

  In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di- A phosphorus processing stabilizer such as t-butylphenyl) phosphite may be used in combination.

[Matting agent]
The optical film of the present invention contains a matting agent for imparting irregularities to the film surface during film formation, ensuring slipperiness, and achieving a stable winding shape.

  In addition, the matting agent can function in order to prevent the produced film from being scratched or having deteriorated transportability when handled.

  Examples of the matting agent include fine particles of an inorganic compound and fine particles of a resin. Examples of fine particles of inorganic compounds include silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, calcium carbonate, calcium carbonate, talc, clay, calcined kaolin, calcined calcium silicate, hydrated calcium silicate, aluminum silicate, silicic acid Examples thereof include magnesium and calcium phosphate. Fine particles containing silicon are preferable in terms of low turbidity, and silicon dioxide is particularly preferable.

  The average primary particle size of the fine particles is preferably in the range of 5 to 400 nm, and more preferably in the range of 10 to 300 nm. These may be mainly contained as secondary aggregates having a particle size in the range of 0.05 to 0.3 μm. If the particles have an average particle size in the range of 80 to 400 nm, the primary particles are not aggregated. It is also preferable that it is contained.

  The content of these fine particles in the film is preferably in the range of 0.01 to 1% by mass, and particularly preferably in the range of 0.05 to 0.5% by mass.

  Well, in the case of a multilayer structure by the co-casting method, it is preferable to contain fine particles of this addition amount on the surface.

  Silicon dioxide fine particles are commercially available under the trade names of, for example, Aerosil R972, R972V, R974, R812, 200, 200V, 300, R202, OX50, TT600 (manufactured by Nippon Aerosil Co., Ltd.). .

  Zirconium oxide fine particles are commercially available, for example, under the names of Aerosil R976 and R811 (manufactured by Nippon Aerosil Co., Ltd.) and can be used.

  Examples of resin fine particles include silicone resin, fluororesin, and acrylic resin. Silicone resins are preferable, and those having a three-dimensional network structure are particularly preferable. For example, Tospearl 103, 105, 108, 120, 145, 3120, and 240 (manufactured by Toshiba Silicone Co., Ltd.) Are commercially available and can be used.

  Among these, Aerosil 200V, Aerosil R972V, and Aerosil R812 are particularly preferably used because they have a large effect of reducing the friction coefficient while keeping the haze of the base film low.

  In the optical film which concerns on this invention, it is preferable that the dynamic friction coefficient of at least one surface is in the range of 0.2-1.0.

[Phase difference increasing agent]
The retardation increasing agent as used herein refers to an optical film in which the retardation value Rt (measured at a light wavelength of 590 nm) in the thickness direction of an optical film containing 3 parts by mass of the compound with respect to 100 parts by mass of a cycloolefin resin is not added. The compound which has a function which shows a value 1.1 times or more compared with a film.

  The retardation increasing agent according to the present invention is not particularly limited, and for example, a conventionally known disk-like shape having an aromatic ring described in JP-A-2006-113239, paragraphs [0143] to [0179]. Compounds (1,3,5-triazine compounds, etc.), rod-like compounds described in paragraphs [0106] to [0112] of JP-A-2006-113239, paragraphs [0118] to [0133] of JP-A-2012-214682 The pyrimidine-type compound etc. of this can be used.

  Properties required for the retardation increasing agent according to the present invention include excellent compatibility with cycloolefin resins, excellent retardation development when film-thinned, excellent precipitation resistance, high humidity Below, it is mentioned that it is excellent in the retardation value fluctuation | variation tolerance accompanying the in / out of a water | moisture content, However, It is preferable to select a phase difference raising agent from such a viewpoint.

  The addition amount of the retardation increasing agent in the optical film is preferably in the range of 0.1 to 10 parts by mass and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the cycloolefin resin. preferable.

[3] Physical properties of optical film Although the thickness of the optical film of the present invention varies depending on the purpose of use, it is usually in the range of 5 to 200 μm, preferably in the range of 5 to 100 μm, and 5 to 50 μm for liquid crystal display devices. It is preferable that the thickness is 35 μm or less in consideration of recent thinning.

  The thickness of the film may be adjusted by adjusting 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, and the like. The width of the optical film obtained as described above is preferably in the range of 0.5 to 4 m, more preferably in the range of 0.6 to 3 m, and still more preferably in the range of 0.8 to 2.5 m. 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.

  In the optical film of the present invention, the process conditions such as the polymer structure to be used, the kind and addition amount of additives, the residual solvent amount during stretching, the stretching direction, the stretching temperature, the stretching ratio, and the residual solvent amount during drying are appropriately adjusted. Thus, desired optical characteristics can be realized.

  In the present specification, Ro and Rt respectively represent an in-plane retardation value and a retardation value in the thickness direction at an optical wavelength of 550 nm in an environment of 23 ° C. and 55% RH.

Ro is measured by making light having a wavelength of 550 nm incident in the normal direction of the film in an AxoScan manufactured by AXOMETRICS. Rt was measured by making light having a wavelength of 550 nm incident from the direction inclined + 40 ° with respect to the normal direction of the film, with the Ro, in-plane slow axis (determined by AxoScan) as the tilt axis (rotation axis). The retardation value and the retardation value measured by making light of wavelength λ nm incident from a direction inclined −40 ° with respect to the film normal direction with the in-plane slow axis as the tilt axis (rotation axis). AxoScan is calculated based on the retardation value measured in the direction. 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, AxoScan calculates the retardation value on the basis of the following equation to calculate the _{n x, n y, n z} (i) and (ii).

Formula _{(i): Ro = (n} x -n y) × d (nm)
Formula (ii): Rt = {(n _x + n _y ) / 2−n _z } × d (nm)
(Wherein, Ro represents a plane retardation value of the film, Rt represents the thickness direction of the retardation value in the film. Further, d, .n _x representing a thickness of the optical film (nm) represents the maximum refractive index in the plane of the film, .n _y referred to as a refractive index in a slow axis direction, .n _z representing the refractive index of the direction perpendicular to the slow axis in the film plane, the thickness Represents the refractive index of the film in the vertical direction.)
The slow axis in the in-plane direction of the optical film of the present invention is inclined within a range of 45 ± 10 ° with respect to the longitudinal direction.

  The retardation value of the optical film of the present invention is not particularly limited, but in order to function as a λ / 4 plate in the visible light region, Ro is in the range of 100 to 180 nm, and Rt is in the range of 50 to 200 nm. When it is, it can be preferably used for a display device provided with a circularly polarizing plate.

  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 7375: 2008 “Plastics—How to determine total light transmittance and total light reflectance”.

  In the optical film of the present invention, the equilibrium water content at 25 ° C. and 60% RH is preferably 3% or less, and more preferably 1% or less from the viewpoint of retardation fluctuation and bending. 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.

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

[4] Application of optical film The optical film of the present invention is preferably a functional film used for various display devices such as liquid crystal displays, plasma displays, and organic EL displays, and touch panels. 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.

(4-1) Circularly polarizing plate A circularly polarizing plate can be produced using the optical film of the present invention. The circularly polarizing plate cuts a long roll having a long protective film, a long polarizer and a long optical film of the present invention (an optical film having a λ / 4 retardation) in this order. It is preferable to be manufactured.

  Since the circularly polarizing plate of the present invention is produced using the optical film of the present invention, and particularly preferably produced using a film having a λ / 4 retardation, an organic electroluminescent display device (organic EL) described later is used. When applied to a display device, etc., the effect of shielding the specular reflection of the metal electrode of the organic EL element can be exhibited at all wavelengths of visible light. As a result, reflection during observation can be prevented and black expression can be improved.

  The circularly polarizing plate preferably has an ultraviolet absorbing function.

  It is preferable that the protective film on the viewing side has an ultraviolet absorbing function from the viewpoint that both the polarizer and the organic EL element can exhibit a protective effect against ultraviolet rays.

  Furthermore, when the retardation film on the light emitter side also has an ultraviolet absorbing function, when used in a display device including an organic EL element, deterioration of the organic EL element can be further suppressed.

  The circularly polarizing plate uses, as a retardation film, the optical film of the present invention in which the angle of the slow axis (that is, the orientation angle θ) is adjusted to be within a range of 45 ± 10 ° with respect to the longitudinal direction. Thus, the polarizer having the absorption axis in the longitudinal direction and the roll-to-roll method can form the adhesive layer and bond the polarizer and the retardation film together by a consistent production line.

  Specifically, after finishing the process of producing a polarizer having an absorption axis in the longitudinal direction by stretching the polarizing film in the longitudinal direction, the polarizer and the retardation film during or after the subsequent drying process The process of pasting can be incorporated. Each can be continuously supplied, and can be connected in a production line that is consistent with the next process by winding in a roll state after bonding.

  In addition, when bonding a polarizer and retardation film, a protective film can also be simultaneously supplied in a roll state and can also be bonded continuously. From the viewpoint of performance and production efficiency, it is preferable to simultaneously bond a retardation film and a protective film to a polarizer. That is, after finishing the step of producing a polarizer by stretching the polarizing film, during the subsequent drying step or after the drying step, the protective film and the retardation film are respectively bonded to both sides with an adhesive, It is also possible to obtain a rolled circularly polarizing plate.

  Although the said circularly-polarizing plate can be comprised in a liquid crystal display device and an organic EL display device, the effect which shields the specular reflection of the metal electrode of an organic EL light-emitting body is expressed by applying to an organic EL display device.

(Protective film)
In the circularly polarizing plate, the polarizer is preferably sandwiched between the optical film of the present invention and the protective film.

  As such a protective film, other cellulose ester-containing films are suitably used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC5UX, KC4UX, KC8UCR3, KC4SR, KC4BR, KC4CR, KC4DR, KC4FR , KC4KR, KC8UY, KC6UY, KC4UY, KC4UE, KC8UE, KC8UY-HA, KC2UA, KC4UA, KC6UAKC, 2UAH, KC4UAH, KC6UAH, Z TD60UL, Fujitac TD40UL, Fujitac R02, Fujitac R06, Fujifilm Corporation) Used properly.

  Although the thickness in particular of a protective film is not restrict | limited, It can be set as about 10-200 micrometers, Preferably it exists in the range of 10-100 micrometers, More preferably, it exists in the range of 10-70 micrometers.

(Polarizer)
A polarizer is an element that passes only light having a plane of polarization in a certain direction. Examples thereof include a polyvinyl alcohol polarizing film.

  The polyvinyl alcohol polarizing film includes those obtained by dyeing iodine on a polyvinyl alcohol film and those obtained by dyeing a dichroic dye.

  The polarizer can be obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing or dyeing the polyvinyl alcohol film, and then uniaxially stretching, and preferably by further performing a durability treatment with a boron compound.

  The film thickness of the polarizer is preferably in the range of 5 to 30 μm, and more preferably in the range of 5 to 15 μm.

  Examples of the polyvinyl alcohol film include ethylene unit content of 1 to 4 mol%, polymerization degree of 2000 to 4000, and saponification degree of 99.0 to 99 described in JP2003-248123A, JP2003-342322A, and the like. 99 mol% ethylene-modified polyvinyl alcohol is preferably used. Moreover, it is preferable to produce a polarizing plate by the method of Unexamined-Japanese-Patent No. 2011-1000016, patent 4691205, and patent 4804589, and sticking it with the optical film of this invention.

(adhesive)
The bonding of the optical film of the present invention and the polarizer is not particularly limited, but can be performed using a completely saponified polyvinyl alcohol adhesive after saponifying the optical film.

  It can also be bonded using an actinic ray curable adhesive or the like, but from the point that the elastic modulus of the obtained adhesive layer is high and the deformation of the polarizing plate is easily suppressed, the bonding using the photocurable adhesive is performed. It is preferable to be a combination.

  Preferred examples of the photocurable adhesive include (α) a cationic polymerizable compound, (β) a photo cationic polymerization initiator, and (γ) a wavelength longer than 380 nm, as disclosed in JP2011-08234A. And a photo-curable adhesive composition containing each component of a photosensitizer exhibiting maximum absorption in the light of (δ) and a naphthalene-based photosensitization aid. However, other photocurable adhesives may be used.

[Production method of polarizing plate]
Hereinafter, an example of the manufacturing method of the polarizing plate using a photocurable adhesive agent is demonstrated.

  The polarizing plate includes (1) a pretreatment step for easily adhering the surface of the optical film to which the polarizer is bonded, and (2) at least one of the adhesive surfaces of the polarizer and the optical film. (3) a bonding step of bonding the polarizer and the optical film through the obtained adhesive layer, and (4) a polarizer and the optical film through the adhesive layer. It can manufacture by the manufacturing method including the hardening process which hardens an adhesive bond layer in the bonded state. What is necessary is just to implement the pre-processing process of (1) as needed.

<Pretreatment process>
In the pretreatment step, an easy adhesion treatment is performed on the adhesive surface of the optical film with the polarizer.

  When bonding an optical film to both surfaces of a polarizer, easy adhesion processing is performed on the bonding surface of each optical film with the polarizer. Examples of the easy adhesion treatment include corona treatment and plasma treatment.

<Adhesive application process>
In the adhesive application step, the photocurable adhesive is applied to at least one of the adhesive surfaces of the polarizer and the optical film.

  When the photocurable adhesive is directly applied to the surface of the polarizer or the optical film, the application method is not particularly limited. For example, various coating methods such as a doctor blade, a wire bar, a die coater, a comma coater, and a gravure coater can be used.

  Moreover, after casting a photocurable adhesive between a polarizer and an optical film, the method of pressurizing with a roller etc. and spreading uniformly can also be utilized.

<Bonding process>
Thus, after apply | coating a photocurable adhesive agent, it uses for a bonding process.

  In this bonding step, for example, when a photocurable adhesive is applied to the surface of the polarizer in the previous application step, an optical film is superimposed thereon. When a photocurable adhesive is applied to the surface of the optical film in the previous application step, a polarizer is superimposed thereon.

  In addition, when a photocurable adhesive is cast between the polarizer and the optical film, the polarizer and the optical film are superposed in that state. In the case where the optical film is bonded to both surfaces of the polarizer, and the photocurable adhesive is used on both surfaces, the optical film is superimposed on the both surfaces of the polarizer via the photocurable adhesive. Usually, in this state, both sides (if the optical film is superimposed on one side of the polarizer, the polarizer side and the optical film side, and if the optical film is superimposed on both sides of the polarizer, The pressure is sandwiched between rolls from the optical film side).

  As the material of the roll, metal, rubber or the like can be used. The rollers arranged on both sides may be made of the same material or different materials.

<Curing process>
In the curing step, the active energy ray is irradiated to the uncured photocurable adhesive to cure the adhesive layer containing the epoxy compound or the oxetane compound. Thereby, the overlapped polarizer and the optical film are bonded via the photocurable adhesive.

  When bonding an optical film to the single side | surface of a polarizer, you may irradiate an active energy ray from either a polarizer side or an optical film side.

  Moreover, when bonding an optical film on both surfaces of a polarizer, an active energy ray is applied from either one of the optical films in a state where the optical film is superimposed on both surfaces of the polarizer via a photocurable adhesive. It is advantageous to irradiate and simultaneously cure the photocurable adhesive on both sides.

  As the active energy ray, visible light, ultraviolet ray, X-ray, electron beam or the like can be used, and since it is easy to handle and has a sufficient curing speed, generally, an electron beam or ultraviolet ray is preferably used.

  Any appropriate condition can be adopted as the electron beam irradiation condition as long as the adhesive can be cured. For example, in the electron beam irradiation, the acceleration voltage is preferably in the range of 5 to 300 kV, more preferably in the range of 10 to 250 kV. If the acceleration voltage is within the above range, the electron beam reaches the adhesive and can be cured reliably, and the penetrating power through the sample is too strong and the electron beam rebounds, damaging the transparent optical film and the polarizer. There is no risk of giving.

  The irradiation dose is in the range of 5 to 100 kGy, more preferably in the range of 10 to 75 kGy. If the irradiation dose is within the above range, the adhesive is sufficiently cured, and the mechanical properties are prevented from lowering or yellowing without damaging the transparent optical film or the polarizer, and the predetermined optical characteristics are obtained. Can be obtained.

Arbitrary appropriate conditions can be employ | adopted for the irradiation conditions of an ultraviolet-ray, if it is the conditions which can harden the said adhesive agent. The dose of ultraviolet rays is preferably in the range of 50~1500mJ / cm ² in accumulated light quantity, and even more preferably in the range of 100 to 500 mJ / cm ^2.

  In the polarizing plate obtained as described above, the thickness of the adhesive layer is not particularly limited, but is usually in the range of 0.01 to 10 μm, and preferably in the range of 0.5 to 5 μm.

(4-2) Display Device The display device of the present invention is manufactured by including the optical film of the present invention.

  Moreover, it is preferable that the display apparatus of this invention is equipped with the circularly-polarizing plate using the optical film of this invention, and an organic EL element. By using the optical film of the present invention, reflection during observation can be prevented, and an organic EL display device with improved black expression can be obtained.

  The screen size of the display device is not particularly limited, and can be 20 inches or more.

  FIG. 8 is a schematic explanatory diagram of a configuration when the display device of the present invention includes an organic EL element. The configuration of the display device of the present invention is not limited to that shown in FIG.

  As shown in FIG. 8, on a transparent substrate 101 using glass, polyimide, or the like, a metal electrode 102, a TFT 103, an organic light emitting layer 104, a transparent electrode (ITO) 105, an insulating layer 106, a sealing layer 107, On the organic EL element B having the film 108 (which can be omitted), a long circular polarizing plate C in which the polarizer 110 is sandwiched between the optical film of the present invention and the protective film 111 is provided. The display device A is configured.

  It is preferable that a cured layer 112 is laminated on the protective film 111.

  The hardened layer 112 not only prevents the surface of the display device from being scratched but also has an effect of preventing warpage due to the long circularly polarizing plate.

  Further, an antireflection layer 113 may be provided on the cured layer.

  The thickness of the organic EL element itself is about 1 μm.

  In general, a display device including an organic EL element forms a light emitting element (organic EL element) by sequentially laminating a metal electrode, an organic light emitting layer, and a transparent electrode on a transparent substrate.

  Here, the organic light emitting layer is a laminate of various organic thin films, for example, a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light emitting layer made of a fluorescent organic solid such as anthracene, There are known configurations having various combinations such as a stacked body of an electron injection layer composed of such a light emitting layer and a perylene derivative, and a stacked body of these hole injection layer, light emitting layer, and electron injection layer. Yes.

  In the display device, holes and electrons are injected into the organic light-emitting layer by applying a voltage to the transparent electrode and the metal electrode, and the energy generated by the recombination of these holes and electrons excites the fluorescent material. The phosphor emits light on the principle that it emits light when it returns to the ground state. The mechanism of recombination in the middle is the same as that of a general diode, and as can be predicted from this, the current and the emission intensity show strong nonlinearity with rectification with respect to the applied voltage.

  In a display device, in order to extract light emitted from the organic light emitting layer, at least one of the electrodes needs to be transparent. Usually, a transparent electrode formed of a transparent conductor such as indium tin oxide (ITO) is used as an anode. It is preferable to use as.

  On the other hand, in order to facilitate electron injection and increase luminous efficiency, it is important to use a material having a small work function for the cathode, and usually metal electrodes such as Mg—Ag and Al—Li are used.

  The circularly polarizing plate having the retardation film described above can be applied to a display device having a large screen having a screen size of 20 inches or more, that is, a diagonal distance of 50.8 cm or more.

  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.

Example 1
[Cycloolefin resin]
The following cycloolefin resins 1 and 2 were used as cycloolefin resins used in the examples.

Cycloolefin resin 1 (COP1): ARTON G7810 (manufactured by JSR)
Cycloolefin resin 2 (COP2): ARTON R5000 (manufactured by JSR)
[Production of optical film 101: melt casting]
[Resin composition]
Cycloolefin resin 1 (COP1) 100 parts by mass Tinuvin 928 (manufactured by BASF Ciba Japan) 1.1 parts by mass GSY-P101 (manufactured by Sakai Chemical Industry) 0.25 parts by mass Irganox 1010 (manufactured by BASF Japan) ) 0.5 parts by mass Sumizer GS (manufactured by Sumitomo Chemical Co., Ltd.) 0.24 parts by mass R972V (manufactured by Nippon Aerosil Co., Ltd.) 0.15 parts by mass The obtained resin composition was obtained at 230 ° C. with a biaxial extruder. The mixture was melt kneaded and extruded into a strand shape. The resin composition extruded in a strand form was cooled with water and then cut to obtain pellets.

  The obtained pellets were dried by circulating dehumidified air at a temperature of 70 ° C. for 5 hours or more, and then put into a single screw extruder while maintaining a temperature of 100 ° C. The amount of moisture in the pellets charged into the single screw extruder was 120 ppm.

  The obtained pellets were melt-kneaded at 230 ° C. with a single screw extruder, and then extruded from a T-die onto a first cooling roller having a surface temperature of 90 ° C. And after pressing the resin extruded on the 1st cooling roller with the elastic touch roller whose surface metal layer thickness is 2 mm, it further cooled with the 2nd cooling roller and the 3rd cooling roller, and thickness A 50 μm web was obtained.

  After the cooled and solidified web was peeled off by a peeling roller, it was stretched at a stretch ratio of 1.4 times in the direction of 45 ° with respect to the longitudinal direction of the web by the oblique stretching machine shown in FIGS. In the main drying step, the obtained film is dried while being conveyed between a large number of rollers at a heat drying temperature of 120 ° C. and a heat drying time of 30 minutes, and then cooled until the film temperature reaches 30 ° C. Both end portions in the direction were cut off to produce an optical film 101 having a film thickness of 35 μm and a winding length of 4000 m.

[Production of optical film 102: solution casting]
<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 was added to the pressure dissolution tank. The cycloolefin resin and the fine particle addition liquid were added to a pressure dissolution tank containing dichloromethane with stirring. This is completely dissolved with heating and stirring. This was designated as Azumi Filter Paper No. The main dope was prepared by filtration using 244.

Cycloolefin resin 1 (COP1) 100 parts by mass Dichloromethane 200 parts by mass Ethanol 10 parts by mass Particulate additive solution 3 parts by mass Next, using an endless belt casting apparatus, the main dope was placed on a stainless steel belt support at a temperature of 31 ° C. and a width of 1800 mm. Cast uniformly. The temperature of the stainless steel belt was controlled at 28 ° C.

  On the stainless steel belt support, the solvent was evaporated until the amount of residual solvent in the cast film was 0.1%. Subsequently, it peeled from the stainless steel belt support body with the peeling tension of 128 N / m. The peeled film was stretched obliquely by 1.2 times in the direction in which the θi was 45 ° with respect to the longitudinal direction using the apparatus of FIG. The residual solvent at the start of stretching was 1% by mass. Next, drying was completed while transporting the drying zone with a number of rollers, and the end portion sandwiched between tenter clips was slit with a laser cutter, and then wound up to obtain an optical film 101 having a film thickness of 20 μm and a winding length of 4000 m. .

[Preparation of Optical Films 103 to 117: Solution Casting]
In the production of the optical film 102, except that the type of cycloolefin resin, the amount of residual solvent at the time of peeling, the thermal drying temperature and the thermal drying time were changed to the conditions described in Table 1, respectively, 117 was produced.

≪Evaluation≫
(1) Measurement of retardation value Ro Retardation value Ro represents an in-plane retardation value at an optical wavelength of 550 nm in an environment of 23 ° C. and 55% RH.

Ro was measured by making light having a wavelength of 550 nm incident in the normal direction of the film in an AxoScan manufactured by AXOMETRIC. The average refractive index value was measured with an Abbe refractometer. By inputting the assumed average refractive index values and thicknesses, AxoScan is _{n x,} was calculated retardation value Ro based on n y, the following equation to calculate the _{n z} (i).

Formula _{(i): Ro = (n} x -n y) × d (nm)
(Wherein, d represents maximum refractive index in the plane of .n _x is film represents the thickness of the optical film (nm) (the slow axis), n _y is perpendicular to the slow axis in the film plane Refractive index in any direction.
(2) Curl (Durability test) Each roll-shaped optical film wrapped in aluminum was stored for 30 days under the conditions of 85 ° C. and 80% RH, and was subjected to wet heat treatment.

  3 m was cut out from each roll of the roll-shaped optical film, and the cut-out optical film was conditioned for 2 hours under the conditions of a temperature of 23 ° C. and 55% RH, and then evaluated for the following curls.

  The curl of each optical film after the durability test was measured using the curl measurement template of Method A in “Method for Measuring Curl of Photo Film” of JIS K 7619-1988. Further, the curl is expressed by the following formula A.

(Formula A) Curl = 1 / R (R is radius of curvature (m))
The ranking was as follows according to the curl amount of the measurement result.

○ (Excellent): Within plus 10
× (somewhat inferior, there is a problem in practical use): more than plus 10 to less than plus 15
XX (Inferior): Plus 15 or more (3) Display unevenness (Production of circularly polarizing plate by roll-to-roll)
The above-obtained obliquely stretched optical film, a long polarizer and a protective film ((Konica Minolta Tack KC4UY, thickness 40 μm, manufactured by Konica Minolta Co., Ltd.) are bonded by a roll-to-roll, and the obliquely stretched optical film. A long circular polarizing plate having a three-layer structure of / polarizer / protective film was produced.

(Visibility with polarized sunglasses: display unevenness)
The circularly polarizing plate obtained above was cut into a predetermined size, and after peeling off the polarizing plate previously bonded to a commercially available smartphone (product name “iPhone 6”, manufactured by APPLE), the cut circular polarizing plate was Pasted together. The bonding was performed through an acrylic pressure-sensitive adhesive applied to the obliquely stretched optical film surface of the circularly polarizing plate. The smartphone with the circularly polarizing plate was exposed to an environment of high temperature and high humidity of 85 ° C. and 85% for 300 hours to output an image, and the appearance of the image was visually confirmed with commercially available polarized sunglasses.

  Judgment criteria are as follows.

○: Display unevenness is not visible at all △: Locations with slightly different color tone can be confirmed only at a pair of corners of the display device, but there is no practical problem ×: Locations where the color tone is clearly different only at a pair of corners of the display device (4) Foaming evaluation Cut out 3 m from each roll of the roll-shaped optical film, and confirm that there is no foaming failure in the stretching machine. Fluorescent lamp (40W fluorescent lamp ("FLR40S-" manufactured by Panasonic Corporation) EX-D / M ")) and confirmed visually.

○: Failure cannot be confirmed visually. ×: Circular failure due to foaming can be visually confirmed.

(5) Evaluation of wrinkles in conveyance direction 3 m was cut out from each roll of the roll-shaped optical film, and the strength of wrinkles in the conveyance direction was visually confirmed. A sample having a width of 90 cm and a length of 100 cm was cut out from the manufactured optical film and placed on a table. Five fluorescent lamps of 40 W (Panasonic “FLR40S-EX-D / M”) are arranged, and 1.5 m from the table so that light is irradiated from a 45 ° angle to the sample on the table. Fixed to height. The fluorescent lamp was turned on to illuminate the sample, and the surface of the sample was visually observed and evaluated according to the following criteria.

○: All five fluorescent lights look straight
X: The fluorescent lamp appears to bend even a little as a whole. (6) Residual solvent amount The residual amount of the solvent component was put into a 20 ml sealed glass container and processed at 120 ° C. for 20 min. Then, after maintaining the GC temperature rising condition at 40 ° C. for 5 minutes by gas chromatography (equipment: HP 5890SERIES II, column: J & W DB-WAX (inner diameter 0.32 mm, length 30 m), detection: FID)) It calculated | required as temperature rising to 100 degreeC at 80 degreeC / min.

  The solvent component is preferably 1000 ppm or less from the viewpoint of customer use, and is marked as ◯. When a solvent component exceeded 1000 ppm, it was a problem on the customer's use, and was set as x.

(7) Productivity The production rate (m / min) is preferably 20 m / min or more, more preferably 40 m / min or more, and particularly preferably 90 m / min or more.

  The manufacturing conditions of the optical film and the evaluation results are shown in Table 1 below.

  The optical films 103 to 106, 109 to 111, and 114 to 116 of the present invention are controlled in the range of the residual solvent amount, the thermal drying temperature, and the thermal drying time during stretching according to the present invention. On the other hand, it can be seen that the curl, display unevenness, foaming, wrinkles in the conveying direction, and residual solvent have excellent performance and high production speed.

  In addition, the optical film of the present invention is stretched in an oblique 45 ° direction, whereby the retardation value Ro exhibits a λ / 4 value, and a circularly polarizing plate can be easily produced.

  Moreover, it was found from a comparison between the optical films 105 and 115 that the effect was reproduced regardless of the type of the cycloolefin resin (COP1 and COP2).

Example 2
[Production of optical films 201-213: solution casting]
In the production of the optical film 105 of Example 1, in addition to the conditions of the residual solvent at the time of stretching, the heat drying temperature, and the heat drying time, the width temperature difference (see FIG. 7) and the width film thickness difference (FIG. 7). The optical films 201 to 213 were prepared in the same manner except that the tension during thermal drying was changed as shown in Table 2, and the following evaluation was performed in addition to the evaluation of Example 1.

≪Evaluation≫
(8) Wide retardation value Ro difference, wide orientation angle difference About the optical films 201 to 213 produced above, in order to evaluate the optical properties of the film, an in-plane retardation value in the width direction. Ro and the orientation angle (θ) were measured at a wavelength of 550 nm under an environment of 23 ° C. and 55% RH using an AxoScan manufactured by AXOMETRICS. The in-plane retardation value Ro of 20 points of the optical film obtained here was measured, the average value (Ro _ave ) was calculated, and the difference between the minimum value (Ro _min ) and the maximum value (Ro _max ) was retarded The variation of the foundation value (ΔRo) was calculated and evaluated.

The orientation angle (θ) was also evaluated by calculating Δθ (°) for the minimum value (θ _min ), the maximum value (θ _max ), and the difference between them.

  The retardation value difference ((ΔRo)) in the width direction of the obtained optical film is preferably 15 nm or less, more preferably 10 nm or less, and particularly preferably 5 nm or less.

  Moreover, the orientation angle difference (Δθ) in the width direction of the obtained optical film is preferably 1.0 ° or less, and more preferably 0.8 ° or less.

(9) Wide film thickness deviation With a contact-type film thickness meter manufactured by Mitutoyo Corporation, 20 to 200 film thicknesses of the optical film were measured in the width direction, and the difference between the measured value and the overall average value ( The ratio of the deviation) to the average value (average film thickness) was determined as the width film thickness deviation. The width difference of the thickness of the obtained optical film is preferably 2.5 μm or less, more preferably 2 μm or less, and particularly preferably 1.5 μm or less.

  The manufacturing conditions of the optical film and the evaluation results are shown in Table 2 below.

  From the results of Table 2, in the production of the optical film of the present invention, a temperature difference in the range of 3 to 15 ° C. is applied in the width direction during stretching, and the finished film thickness in the width direction before stretching is 2. By achieving a film thickness difference within the range of 5 to 7.5% and by setting the film tension during thermal drying within the range of 50 to 150 N / m, the object of the present invention is achieved and the width direction It was found that an optical film having uniform optical characteristics (retardation value and orientation angle) and a uniform film thickness can be obtained.

DESCRIPTION OF SYMBOLS 1 Melting pot 3, 6, 12, 15 Filter 4, 13 Stock pot 2, 5, 11, 14 Liquid feed pump 8, 16 Conduit 10 Additive charging pot 20 Merge pipe 21 Mixer 30 Pressure die 31 Metal belt 32 Casting film 33 Peeling position 34 First drying device 35 Stretching device 36 Second drying device 37 Conveying roller 38 Winding device 41 Feeding kettle 42 Stock kettle 43 Pump 44 Filter 50 Stretching device 60L Endless loop 60R Endless loop 70 Reference rail 80 Clip (supporting part)
90 Pitch setting rail A Display device B Organic EL element C Circular polarizing plate 101 Transparent substrate 102 Metal electrode 103 TFT
DESCRIPTION OF SYMBOLS 104 Organic light emitting layer 105 Transparent electrode 106 Insulating layer 107 Sealing layer 108 Film 109 (lambda) / 4 phase difference film 110 Polarizer 111 Protective film 112 Hardened layer 113 Antireflection layer

Claims (7)

A method for producing an optical film by a solution casting method,
Preparing a dope containing a resin and a solvent;
Casting the dope on a traveling support to form a casting film;
Peeling the cast film from the support in a state containing the solvent;
While holding both ends in the width direction of the separated casting film with a pair of gripping tools, one of the gripping tools is relatively advanced, and the other gripping tool is relatively delayed so that the casting film is A step of stretching the cast film in an oblique direction with respect to the width direction by conveying, and thermally drying the cast film stretched in the oblique direction to volatilize the residual solvent, thereby forming an optical film. A winding process,
The residual solvent amount of the cast film when starting stretching in the oblique direction is in the range of 2 to 20% by mass,
The method for producing an optical film is characterized in that the film is dried within a range of 100 to 140 ° C. after drying in the oblique direction and within a range of 5 to 50 minutes.   The method for producing an optical film according to claim 1, wherein a residual solvent amount of the cast film is in a range of 5 to 20% by mass.   The method for producing an optical film according to claim 1, wherein a temperature difference in a range of 3 to 15 ° C. is provided in the width direction during the stretching.   4. The film thickness difference in a range of 2.5 to 7.5% in the width direction is given to the film thickness of the finished film before the stretching. 5. The manufacturing method of the optical film of description.   The method for producing an optical film according to any one of claims 1 to 4, wherein a tension of the film at the time of the thermal drying is set in a range of 50 to 150 N / m.   A circularly polarizing plate comprising an optical film produced by the method for producing an optical film according to any one of claims 1 to 5.   A display device comprising an optical film manufactured by the method for manufacturing an optical film according to any one of claims 1 to 5.

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