Optical film, optical laminate, method for producing same, and polarizing plate

Abstract

This optical film has a main surface S1 having a thickness of 4 μm or less and an arithmetic mean height Sa of 50 nm or less, and satisfies expression (1).　(1): X ≥ Y. In formula (1), X is a standard deviation average value (μm) obtained by dividing a square region with a side length of 225 mm included in the optical film into 9 sections each being a square with a side length of 75 mm, measuring the thicknesses of a plurality of portions in each of the nine sections, calculating the respective standard deviations of the nine sections, and calculating the arithmetic mean of the calculated nine standard deviations, and Y is represented by expression (2). In expression (2), Haze represents the haze value (%) of the optical film.　(2): Y = -0.0159×Haze+0.0392

Description

Optical film, optical laminate and manufacturing method thereof, and polarizing plate

[0001] The present invention relates to an optical film, an optical laminate and a method for producing the same, and a polarizing plate.

[0002] Display devices may include optical elements such as polarizers. Resin films may be used as protective films for protecting these optical elements. Furthermore, in recent years, terminal devices such as smartphones have become smaller and thinner, increasing the demand for thinner display devices included in such terminal devices. Thinner optical elements included in display devices are also being sought. Accordingly, thinner protective films for protecting the optical elements are also being sought. To achieve a thin protective film, a method is known in which a resin film is formed on a support and then transferred to a polarizer (see, for example, Patent Document 1). Another method is known in which a hard coat layer formed on a support is further transferred to a laminate including a polarizer (see, for example, Patent Document 2).

[0003] Patent Document 1: JP 2014-130298 A, International Publication No. 2019 / 087806 (Corresponding Foreign Publication: U.S. Patent Application Publication No. 2021 / 0109268 Specification)

[0004] When an optical film is thinned and combined with other optical elements to form a laminate, display unevenness due to thin-film interference (hereinafter also referred to as thin-film interference unevenness) may be visible. Conventionally, when an optical film is combined with other optical elements to form a laminate, whether thin-film interference unevenness occurs has been evaluated by having an evaluator actually form the optical film into a laminate and observe the laminate. However, this evaluation method requires the time and effort of preparing an evaluation laminate from the optical film each time an evaluation is performed. Furthermore, from the perspective of quality control of optical films, it would be preferable if thin-film interference unevenness could be evaluated based on more objective numerical values, regardless of the evaluator's evaluation experience. It is necessary to identify optical films that are less likely to cause thin-film interference unevenness based on the properties of the optical film.

[0005] Therefore, there is a demand for an optical film that is less likely to cause thin film interference unevenness when formed into a laminate; an optical laminate including such an optical film; a method for producing an optical laminate; and a polarizing plate including such an optical film.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, the present inventors have found that when the average value X of the standard deviations described below has a certain relationship with the haze value of the optical film, thin film interference unevenness is unlikely to occur in a laminate including the optical film, and have completed the present invention. That is, the present invention provides the following.

[0007] <1> An optical film having a thickness of 4 μm or less, having a main surface S1 with an arithmetic mean height Sa of 50 nm or less, and satisfying the following formula (1): X≧Y (1) In formula (1), X represents the average value (μm) of standard deviations obtained by dividing a square region of the optical film with sides of 225 mm into nine square sections with sides of 75 mm, measuring the thickness at a plurality of locations in each of the nine sections, calculating the standard deviation for each of the nine sections, and calculating the arithmetic mean of the nine calculated standard deviations, and Y is represented by the following formula (2), in which Haze represents the haze value (%) of the optical film: Y=−0.0159×Haze+0.0392 (2) <2> A water vapor transmission rate per 100 μm of thickness is 4.0 g / (m ２ <3> The optical film according to <1>, wherein the photoelastic constant is 10×10 or less. －１３ cm ２ / dyn or less. <4> The optical film according to any one of <1> to <3>, having an in-plane retardation Re of 0 nm or more and 2 nm or less, and a thickness direction retardation Rth of −5 nm or more and 5 nm or less, measured at a wavelength of 550 nm. <5> The optical film according to any one of <1> to <4>, comprising a polymer containing an alicyclic structure. <6> An optical laminate comprising the optical film according to any one of <1> to <5>, and a base film provided directly on the main surface S1 of the optical film. <7> The optical laminate according to <6>, wherein the main surface S2 of the base film, which is directly connected to the main surface S1 of the optical film, has an arithmetic mean height Sa of 50 nm or less, and the optical film and the base film contain the same solvent. <8> A polarizing plate comprising the optical film according to any one of <1> to <5>, and a polarizer. <9> The polarizing plate according to <8>, further comprising an optically anisotropic layer, wherein the optically anisotropic layer, the optical film, and the polarizer are arranged in this order when viewed from the thickness direction. <10> The polarizing plate according to <9>, wherein the optically anisotropic layer comprises a first retardation layer, wherein the first retardation layer has Re1(550) of 100 nm or more and 150 nm or less, and Re1(450) / Re1(550) of 0.80 or more and 1.30 or less, wherein Re1(550) represents an in-plane retardation of the first retardation layer at a wavelength of 550 nm, and Re1(450) represents an in-plane retardation of the first retardation layer at a wavelength of 450 nm. <11> The polarizing plate according to <10>, wherein the optically anisotropic layer further comprises a second retardation layer, and the second retardation layer has a thickness direction retardation Rth2(550) at a wavelength of 550 nm of −140 nm or more and −10 nm or less.<12> The polarizing plate according to <9>, wherein the optically anisotropic layer includes a third retardation layer and a fourth retardation layer, wherein the third retardation layer has Re3(550) of 100 nm or more and 150 nm or less and Re3(450) / Re3(550) of 0.80 or more and 1.30 or less, and the fourth retardation layer has Re4(550) of 200 nm or more and 290 nm or less, wherein Re3(550) represents an in-plane retardation of the third retardation layer at a wavelength of 550 nm, Re3(450) represents an in-plane retardation of the third retardation layer at a wavelength of 450 nm, and Re4(550) represents an in-plane retardation of the fourth retardation layer at a wavelength of 550 nm. <13> The polarizing plate according to <12>, wherein the optically anisotropic layer further comprises a second retardation layer, and the second retardation layer has a thickness direction retardation Rth2(550) of −140 nm or more and −10 nm or less at a wavelength of 550 nm. <14> The method for producing the optical laminate according to <6> or <7>, comprising: (1) preparing a substrate film having a main surface S2 with an arithmetic mean height Sa of 50 nm or less; (2) applying a resin liquid containing a polymer and a solvent onto the main surface S2 of the substrate film to form a resin liquid layer; and (3) drying the resin liquid layer to form an optical film on the main surface S2 of the substrate film. <15> The method for producing an optical laminate according to <14>, wherein the step (3) includes a step (3-1) of drying the resin liquid layer at a drying temperature T1 and a step (3-2) of drying the resin liquid layer at a drying temperature T2, wherein T1<T2, T1 is equal to or greater than Sbp and equal to or less than Sbp+20°C, wherein Sbp represents the boiling point (°C) of a solvent contained in the resin liquid. <16> The method for producing an optical laminate according to <15>, wherein the step (3-1) satisfies the following conditional formula: 4≧B≧−0.25A+6.25, wherein A represents the drying time (seconds) in the step (3-1), and B represents the thickness (μm) of the optical film.

[0008] According to the present invention, it is possible to provide an optical film that is less likely to cause thin film interference unevenness when formed into a laminate; an optical laminate including such an optical film; a method for producing an optical laminate; and a polarizing plate including such an optical film.

[0009] FIG. 1 is a graph showing the relationship between the drying time A (seconds) under the first drying conditions (T1=90° C.) and the film thickness B (μm) of the optical film in Examples 1 to 7 and Comparative Examples 1 to 4.

[0010] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents. The components of the embodiments shown below can be combined as appropriate.

[0011] In the following description, a "long" film refers to a film having a length that is 5 times or more its width, preferably 10 times or more its width, and specifically refers to a film having a length that can be wound into a roll for storage or transportation. There is no particular upper limit to the length of the film, and it can be, for example, 100,000 times or less its width.

[0012] In the following description, unless otherwise specified, the term "plate" is not limited to a rigid member, but also includes a flexible member such as a resin film.

[0013] In the following description, unless otherwise specified, the front direction of a film means the normal direction of the main surface of the film, and specifically refers to the direction of the polar angle of 0° and the azimuthal angle of 0° of the main surface.

[0014] In the following description, unless otherwise specified, the tilt direction of a film means a direction that is neither parallel nor perpendicular to the main surface of the film, and specifically refers to a direction in which the polar angle of the main surface is in the range of greater than 0° and less than 90°.

[0015] In the following description, the term "(meth)acrylic" encompasses "acrylic", "methacrylic", and combinations thereof.

[0016] In the following description, unless otherwise specified, the in-plane retardation Re of a layer is a value expressed by Re = (nx - ny) x d. Furthermore, unless otherwise specified, the retardation Rth in the thickness direction of a layer is a value expressed by Rth = [{(nx + ny) / 2} - nz] x d. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the layer (in-plane direction) that gives the maximum refractive index. ny represents the refractive index in the in-plane direction of the layer that is perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer. The measurement wavelength is 550 nm unless otherwise specified.

[0017] In the following description, unless otherwise specified, the directions of elements as "parallel," "vertical," and "orthogonal" may include an error within a range that does not impair the effects of the present invention, for example, within a range of ±3°, ±2°, or ±1°.

[0018] In the following description, unless otherwise specified, the width direction of a long film refers to the in-plane direction of the film that is perpendicular to the longitudinal direction of the film. Usually, the longitudinal direction of a long film coincides with the film transport direction.

[0019] In the following description, unless otherwise specified, the term "adhesive" includes not only adhesives in the narrow sense (adhesives having a shear storage modulus of 1 MPa to 500 MPa at 23° C. after energy ray irradiation or heat treatment) but also pressure-sensitive adhesives having a shear storage modulus of less than 1 MPa at 23° C. Therefore, the term "adhesive layer" includes not only adhesive layers in the narrow sense but also pressure-sensitive adhesive layers.

[0020] In the following description, unless otherwise specified, the solvent includes a dispersion medium.

[0021] <1. Optical Film> <1.1. Overview of Optical Film> An optical film according to one embodiment of the present invention has a thickness of 4 μm or less, a main surface S1 having an arithmetic mean height Sa of 50 nm or less, and satisfies the following formula (1): X≧Y (1)

[0022] In formula (1), X represents the average value (μm) of standard deviations obtained by dividing a square region of the optical film with sides of 225 mm into nine square sections with sides of 75 mm, measuring the thickness at multiple locations in each of the nine sections, calculating the standard deviation for each of the nine sections, and calculating the arithmetic mean of the nine calculated standard deviations, and Y is represented by the following formula (2), in which Haze represents the haze value (%) of the optical film: Y=−0.0159×Haze+0.0392 (2)

[0023] By providing the optical film with the above-described configuration, when the optical film is laminated with other optical elements (e.g., polarizers), thin-film interference unevenness is unlikely to occur. Therefore, before the optical film is actually laminated with other optical elements, it can be easily determined whether the optical film is a film that is unlikely to cause thin-film interference unevenness.

[0024] The square region having a side length of 225 mm may be set at any position on the optical film. For example, when the optical film is a long film, the region may be set at the center in the width direction, at an end in the width direction, at the center in the longitudinal direction, or at an end in the longitudinal direction. The square region having a side length of 225 mm may be set so that the side direction of the square is parallel to the width direction or the longitudinal direction of the optical film, for example.

[0025] A square region with sides of approximately 225 mm is the range that can be seen by a person evaluating a typical optical film or a laminate containing an optical film without moving their head, and the presence or absence of typical thin-film interference unevenness can be efficiently evaluated within this range. Therefore, by calculating the average value X of the standard deviations in a square region with sides of 225 mm and determining the relationship with the Y value expressed by formula (2), it is possible to perform an evaluation equivalent to the evaluation of the presence or absence of thin-film interference unevenness performed by a person.

[0026] If a square area with sides of 225 mm is not divided into nine sections, but the thicknesses of multiple locations in the square area are measured and compared with the standard deviation (referred to as X') obtained from those thicknesses, the average value X obtained by dividing the square area into nine sections and calculating the arithmetic mean of the standard deviations as described above will usually be larger. Therefore, the strength of thin-film interference unevenness in the optical film can be sensitively determined. By dividing a square area with sides of 225 mm into nine sections, local unevenness can be detected.

[0027] The thickness measurement points in each of the nine sections may be located such that the distance between adjacent measurement points is, for example, 0.8 mm or more, for example, 0.9 mm or more, and for example, 1.2 mm or less, for example, 1.1 mm or less, for example, 1.0 mm. The number of thickness measurement points in each of the nine sections may be, for example, 4032 or more, for example, 4785 or more, and for example, 8977 or less, for example, 7111 or less, for example, 5776 or less, for example, 5776.

[0028] <1.2. Equation (1) and Equation (2)> X≧Y (1) Y=−0.0159×Haze+0.0392 (2) The present inventors have found that the degree of thin-film interference unevenness in an optical film correlates with the average standard deviation X (μm) related to the thickness unevenness of the optical film and the haze value Haze (%) of the optical film. Equation (1) indicates that even if the haze of the optical film is the same, when X related to the thickness unevenness of the optical film is large, thin-film interference unevenness in the optical film is less likely to occur. Equation (2) indicates that even if the average value X related to the thickness unevenness of the optical film is the same, the larger the haze value of the optical film, the less likely thin-film interference unevenness in the optical film is to occur.

[0029] The thickness unevenness of the optical film can be adjusted by adjusting the drying speed of the resin liquid layer when producing the optical film from the resin liquid. The drying speed of the resin liquid layer can be adjusted, for example, by selecting the type of solvent contained in the resin liquid according to its boiling point, or by adjusting the concentration of the non-volatile components of the resin liquid, the drying temperature, the temperature profile, the air velocity in the drying oven, the solvent gas concentration in the drying oven, the intake and exhaust volume of the drying oven, etc.

[0030] (Haze of Optical Film) The haze of the optical film is preferably 0.2% or more, more preferably 0.4% or more, and preferably 3% or less, more preferably 2% or less. The haze of the optical film can be measured using a haze meter in accordance with JIS-K-7361. Of the nine sections of the optical film for which the standard deviation was determined, the haze is measured in any three sections, and the average value of the haze values ​​obtained at the three locations can be used as the haze of the optical film. When the haze of the optical film is within the above range, thin film interference unevenness can be more effectively reduced.

[0031] <1.3. Thickness of Optical Film> The thickness of the optical film is usually 4 μm or less, preferably 3.8 μm or less, more preferably 3.5 μm or less, and may usually be greater than 0 μm and greater than 0.5 μm. The thickness of the optical film can be measured at a total of five locations: both ends and the center in the width direction of the optical film, and the midpoint between the ends and the center in the width direction. The average value is calculated from the obtained thickness data, and this average value can be used as the thickness of the optical film. The thickness of the optical film can be measured, for example, using an optical interferometry film thickness measuring instrument. If the thickness of the layers constituting a certain laminate is small, thin film interference unevenness is likely to occur in the laminate. However, with the optical film of this embodiment, thin film interference unevenness is unlikely to occur even when the thickness is 4 μm or less.

[0032] <1.4. Arithmetic Mean Height of Optical Film> The arithmetic mean height Sa of the main surface S1 of the optical film is usually greater than 0 nm, preferably greater than 4 nm, more preferably 5 nm or more, and even more preferably 6 nm or more, and is usually 50 nm or less, preferably 30 nm or less, and more preferably 10 nm or less.

[0033] When the arithmetic mean height Sa of the main surface S1 of the optical film is equal to or less than the upper limit, a display device incorporating the optical film can achieve a high-definition display with little blurring.

[0034] The arithmetic mean height Sa can be measured using a surface roughness measuring device in accordance with ISO 25178.

[0035] The arithmetic mean height Sa of the optical film on the main surface S1 can be adjusted by adjusting the arithmetic mean height Sa of the base film on the main surface S2 in the manufacturing method including the step (A) described below. The method for adjusting the arithmetic mean height Sa of the base film on the main surface S2 will be described later.

[0036] 1.5. Materials for Optical Film The optical film preferably contains a resin, and more preferably consists of only a resin. The resin is preferably a thermoplastic resin, and the resin usually contains a polymer and optional components that are included as needed.

[0037] From the viewpoint of significantly achieving the advantages of the present invention, it is preferable that the optical film is composed only of a resin and that the resin does not contain particles. From the viewpoint of significantly achieving the advantages of the present invention, the weight ratio of particles in the optical film, based on the weight of the optical film being 100% by weight, is preferably 0.5% by weight or less, more preferably 0.3% by weight or less, even more preferably 0.1% by weight or less, even more preferably 0.05% by weight or less, and even more preferably 0.01% by weight or less. It is usually 0.00% or more than 0.00%, and may even be 0.00%. Generally, when a resin film is formed by a coating method using a particle-free resin liquid, the surface of the resin film obtained by the coating method tends to be smooth, and thin film interference unevenness tends to occur in a laminate including the resin film. However, in the optical film of this embodiment, even when the weight ratio of particles is within the above range, thin film interference unevenness is unlikely to occur in a laminate including the optical film.

[0038] (Polymer) Examples of polymers contained in the optical film include polyesters, acrylic polymers, and polymers containing an alicyclic structure. These polymers may be used alone or in combination of two or more. Among them, from the viewpoint of reducing the water vapor transmission rate of the optical film, polymers containing an alicyclic structure, such as cyclic olefin polymers, are preferred. The cyclic olefin polymer refers to a polymer having a structural unit obtained by polymerizing a cyclic olefin, or a hydrogenated product thereof.

[0039] A polymer containing an alicyclic structure has a repeating unit containing an alicyclic structure. A polymer containing an alicyclic structure usually has a low water vapor permeability. Therefore, when an optical film is formed using a resin containing a polymer containing an alicyclic structure, an optical film with a low water vapor permeability can be obtained.

[0040] The polymer containing an alicyclic structure may contain the alicyclic structure in the main chain, may contain the alicyclic structure in the side chain, or may contain the alicyclic structure in both the main chain and the side chain. Among these, from the viewpoints of mechanical strength and heat resistance, a polymer containing an alicyclic structure at least in the main chain is preferred.

[0041] Examples of the alicyclic structure include saturated alicyclic hydrocarbon (cycloalkane) structures, unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structures, etc. Among these, from the viewpoints of mechanical strength and heat resistance, cycloalkane structures and cycloalkene structures are preferred, and cycloalkane structures are particularly preferred.

[0042] The number of carbon atoms constituting each alicyclic structure is preferably 4 or more, more preferably 5 or more, and is preferably 30 or less, more preferably 20 or less, particularly preferably 15 or less. When the number of carbon atoms constituting each alicyclic structure is within this range, the mechanical strength, heat resistance, and formability of the optical film are well balanced.

[0043] In the polymer containing an alicyclic structure, the proportion of the repeating unit containing an alicyclic structure can be appropriately selected depending on the intended use. The proportion of the repeating unit containing an alicyclic structure in the polymer containing an alicyclic structure is preferably 55% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of the repeating unit containing an alicyclic structure in the polymer containing an alicyclic structure is within this range, the transparency and heat resistance of the resin are good.

[0044] Examples of polymers containing an alicyclic structure include norbornene polymers, monocyclic olefin polymers, cyclic conjugated diene polymers, vinyl alicyclic hydrocarbon polymers, and hydrogenated products thereof. Among these, norbornene polymers and hydrogenated products thereof have good transparency and moldability.

[0045] Examples of norbornene polymers and their hydrogenated products include ring-opening polymers of monomers having a norbornene structure and their hydrogenated products; and addition polymers of monomers having a norbornene structure and their hydrogenated products. Examples of ring-opening polymers of monomers having a norbornene structure include ring-opening homopolymers of one type of monomer having a norbornene structure, ring-opening copolymers of two or more types of monomers having a norbornene structure, and ring-opening copolymers of a monomer having a norbornene structure and any monomer copolymerizable therewith. Examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one type of monomer having a norbornene structure, addition copolymers of two or more types of monomers having a norbornene structure, and addition copolymers of a monomer having a norbornene structure and any monomer copolymerizable therewith. Examples of these polymers include the polymers disclosed in, for example, JP 2002-321302 A.

[0046] Specific examples of norbornene polymers and hydrogenated products thereof include "ZEONOR" manufactured by Nippon Zeon Co., Ltd.; "ARTON" manufactured by JSR Corporation; and "TOPAS" manufactured by TOPAS ADVANCED POLYMERS.

[0047] The weight-average molecular weight Mw of the polymer contained in the optical film is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, and is preferably 100,000 or less, more preferably 80,000 or less, particularly preferably 50,000 or less. When the weight-average molecular weight is within this range, the mechanical strength and moldability of the resin forming the optical film are well balanced.

[0048] The molecular weight distribution (Mw / Mn) of the polymer contained in the optical film is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, and preferably 3.5 or less, more preferably 3.0 or less, particularly preferably 2.7 or less. Here, Mn represents the number average molecular weight. When the molecular weight distribution is equal to or greater than the lower limit of the above range, the productivity of the polymer can be increased and the production cost can be reduced. Furthermore, when the molecular weight distribution is equal to or less than the upper limit of the above range, the amount of low-molecular-weight components is reduced, thereby suppressing relaxation during exposure to high temperatures and improving the stability of the optical film.

[0049] The weight average molecular weight (Mw) and number average molecular weight (Mn) can be measured using gel permeation chromatography (GPC). Examples of solvents used in GPC include cyclohexane, toluene, and tetrahydrofuran. When using GPC, the weight average molecular weight can be measured as a relative molecular weight, for example, in terms of polyisoprene or polystyrene.

[0050] The glass transition temperature of the polymer contained in the optical film is preferably 100°C or higher, more preferably 110°C or higher, even more preferably 120°C or higher, and preferably 170°C or lower, more preferably 160°C or lower, and even more preferably 150°C or lower. When the glass transition temperature of the polymer is within the above range, the durability of the optical film in a high-temperature environment can be improved. The glass transition temperature can be measured using a differential scanning calorimeter (DSC) by increasing the temperature at a rate of 10°C / min.

[0051] The polymer content in the optical film is preferably within a specific range, based on 100% by weight of the optical film, and the specific range of the polymer content is preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and is preferably 99.99% by weight or less, more preferably 99.9% by weight or less, even more preferably 99% by weight or less, and particularly preferably 96% by weight or less.

[0052] (Solvent) The resin contained in the optical film may contain a solvent in addition to the polymer. The solvent that may be contained in the resin contained in the optical film is usually a part of the solvent used in producing the optical film that remains without being removed from the optical film. As the solvent, an organic solvent is preferred, and an organic solvent that can dissolve the polymer that may be contained in the optical film is particularly preferred. Examples of the solvent include hydrocarbon solvents such as cyclohexane, alkylcyclohexane (methylcyclohexane, ethylcyclohexane, etc.), and toluene; cyclic ether solvents such as tetrahydrofuran; and the like. One type of solvent may be used alone, or two or more types may be used in combination.

[0053] When the optical film contains a solvent, the content of the solvent contained in the optical film is preferably 0.01 wt % or more and preferably 10 wt % or less, where the unit weight of the optical film is 100 wt %. Here, when the optical film contains multiple types of solvents, the content of the solvent is the total content of the multiple types of solvents.

[0054] When the solvent content in the optical film is equal to or less than the upper limit, deterioration of resin components included in a display device incorporating the optical film due to volatilization of the solvent remaining in the optical film can be reduced. Furthermore, the mechanical strength of the optical film can be increased. When the solvent content in the optical film is equal to or greater than the lower limit, the optical film can be easily manufactured by a coating method using a resin liquid. Furthermore, the peel strength between the optical film and the substrate film described below can be adjusted to a more appropriate range.

[0055] The solvent content in the optical film can be measured using a gas chromatograph mass spectrometer. A specific measurement method may be the method described in the examples.

[0056] The content of the solvent in the optical film can be adjusted, for example, by adjusting the drying temperature and drying time of the resin liquid when forming the optical film.

[0057] (Other Optional Components) In addition to the polymer and optional solvent, the optical film may further contain optional components. Examples of the optional components include stabilizers such as antioxidants, UV absorbers, and light stabilizers; resin modifiers such as lubricants and plasticizers; and antistatic agents.

[0058] <1.6. Other Properties of Optical Film> (Water Vapor Transmission Rate) The optical film preferably has a low water vapor transmission rate. Specifically, the water vapor transmission rate per 100 μm of the optical film thickness is preferably 4.0 g / (m ２ ·day) or less, more preferably 3.0 g / (m ２ ·day) or less, particularly preferably 2.0 g / (m ２ ·day) or less. The lower limit is ideally 0 g / (m ２ · day), and is usually 0 g / (m ２ · day) or more, and 0.1 g / (m ２ ・day) or more. When the optical film has a small water vapor transmission rate as described above, the optical film can stably protect the polarizer. Therefore, deterioration of the polarizer due to moisture can be effectively suppressed, and therefore a decrease in the polarization degree of the polarizer can be suppressed. Furthermore, since it is possible to suppress the bleeding out of iodine in the polarizer due to moisture that has penetrated the polarizer, it is possible to effectively suppress the corrosion of metal parts such as electrodes in a display device by the iodine.

[0059] The water vapor transmission rate per 100 μm of thickness of the optical film can be measured by the following method. The water vapor transmission rate of the optical film is measured using a water vapor transmission rate measuring device ("PERMATRAN-W" manufactured by MOCON Corporation) in accordance with JIS K7129 Method B under conditions of a temperature of 40°C and a humidity of 90% RH. This measured water vapor transmission rate is multiplied by "100 (μm) / thickness of optical film (μm)" to convert it to a value per 100 μm of thickness, thereby obtaining the water vapor transmission rate per 100 μm of thickness of the optical film.

[0060] (Photoelastic Coefficient) The photoelastic constant of the optical film is preferably within a specific range. Specifically, the smaller the photoelastic constant of the optical film, the more preferable it is, and preferably 10×10 －１３ cm ２ / dyn or less, more preferably 5 × 10 －１３ cm ２ / dyn or less, particularly preferably 2 × 10 －１３ cm ２ / dyn or less. The lower limit is usually 0.0 × 10 －１３ cm ２ / dyn or more. When the photoelastic constant of the optical film is within the above range, the change in retardation due to the stress of expansion or contraction can be reduced, so that the display uniformity of the display device can be maintained. The photoelastic constant of the optical film can be calculated from the birefringence that occurs when stress is applied to the optical film. The specific measurement method can be the method described in the examples.

[0061] (Retardation) The optical film preferably has small optical anisotropy in both the in-plane direction and the thickness direction, and more preferably has optical isotropy.When the optical film has small optical anisotropy, the change in the polarization state of polarized light due to transmission through the optical film can usually be reduced, and preferably eliminated.Therefore, when the optical film is bonded to a polarizer, the change in the polarization state due to the optical film can be suppressed, and therefore, the control of the polarization state of polarized light transmitted through a polarizing plate including the optical film and the polarizer can be simplified.

[0062] Therefore, it is preferable that the in-plane retardation of the optical film is small. Specifically, the in-plane retardation of the optical film at a measurement wavelength of 550 nm is preferably 2 nm or less, usually 0 nm or more, and may be 0 nm. Furthermore, it is preferable that the retardation in the thickness direction of the optical film is zero or close to zero. Specifically, the retardation in the thickness direction of the optical film at a measurement wavelength of 550 nm is preferably −5 nm or more, more preferably −4 nm or more, even more preferably −3 nm or more, particularly preferably −2 nm or more, and is preferably 5 nm or less, more preferably 4 nm or less, even more preferably 3 nm or less, and particularly preferably 2 nm or less.

[0063] An optical film with small optical anisotropy can be formed by a method for forming an optical film that can reduce the stress applied to the optical film, such as the coating method described below.

[0064] (Dimensions of Optical Film) The dimensions of the optical film are such that a square area of ​​typically 225 mm can be defined, and typically the longitudinal direction is 225 mm or more and the width direction is 225 mm or more. The optical film may be long or in the form of a sheet. When the optical film is long, the optical film can be efficiently bonded to other members. The width of the optical film is not particularly limited. The width of the optical film is, for example, 1340 mm or more, for example, 1540 mm or more, and for example, 3000 mm or less, for example, 2800 mm or less.

[0065] (Total Light Transmittance) The higher the total light transmittance of the optical film, the better. The total light transmittance of the optical film is preferably 89% or more, more preferably 90% or more, and is usually 100% or less. The total light transmittance of the optical film can be measured using a haze meter in accordance with JIS-K-7361.

[0066] <1.7. Uses of Optical Film> The optical film is thin and yet does not easily cause display unevenness due to thin-film interference (thin-film interference unevenness). Therefore, the optical film can be suitably used as a component of a display device. For example, the optical film can be suitably used as a protective film for an optical element (e.g., a polarizer) that may be provided on the viewing side of the display device. Examples of display devices incorporating the optical film are not particularly limited, and include liquid crystal display devices and organic electroluminescence display devices.

[0067] <2. Manufacturing Method of Optical Film> (Outline of Manufacturing Method of Optical Film) The optical film can be manufactured by any method. For example, the optical film can be manufactured by a manufacturing method including a step (A) of manufacturing an optical laminate including an optical film and a base film provided directly on the main surface S1 of the optical film, and a step (B) of peeling the base film from the optical laminate to obtain the optical film. Hereinafter, a method including the steps (A) and (B) will be described as a preferred manufacturing method of the optical film.

[0068] (Step (A): Step of Producing an Optical Laminate) In step (A), an optical laminate is produced. The optical laminate includes the optical film and a base film provided directly on the main surface S1 of the optical film. The main surface S2 of the base film is directly connected to the main surface S1 of the optical film. The main surface S1 of the optical film and the main surface S2 of the base film being directly connected to each other means that no layer is interposed between the main surface S1 of the optical film and the main surface S2 of the base film.

[0069] The substrate film may be a stretched film, or an unstretched film, but is preferably a stretched film, since this makes it easier to adjust the arithmetic mean height Sa of the substrate film surface.

[0070] The substrate film may have a single-layer structure or a multi-layer structure. A film consisting of only a thermoplastic resin layer may be used as the substrate film. Alternatively, a release film including a thermoplastic resin layer and a release layer formed on the thermoplastic resin layer may be used. When the substrate film includes a release layer, the release layer is provided on the outermost side of the substrate film, and the main surface S2 of the substrate film corresponds to the surface of the release layer.

[0071] When the substrate film includes a thermoplastic resin layer, examples of polymers that can be included in the thermoplastic resin layer include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; α-olefin polymers such as polyethylene, polypropylene, and polymethylpentene; vinyl chloride polymers such as polyvinyl chloride and polyvinylidene chloride; polyvinyl alcohol; ethylene-vinyl acetate copolymers; polystyrene; polycarbonate; polysulfone; polyether ether ketone; polyethersulfone; polyphenylene sulfide; polyetherimide; polyimide; fluorine-containing polymers; polyamide; acrylic polymers; and cyclic olefin polymers such as norbornene-based polymers. The polymer that can be included in the thermoplastic resin layer may be a homopolymer or a copolymer. These may be used alone or in combination of two or more types in any ratio.

[0072] Among these, from the viewpoints of cost, mechanical strength, and ease of stretching, the thermoplastic resin layer preferably contains polyester, and more preferably contains polyethylene terephthalate.

[0073] The content of the polymer in the thermoplastic resin layer is preferably 80% by weight to 100% by weight, more preferably 90% by weight to 100% by weight, and even more preferably 95% by weight to 100% by weight.

[0074] The thermoplastic resin layer may contain optional components, if necessary, in addition to the polymer. Examples of the optional components include the same examples as those of the optional components that may be contained in the optical film. One type of optional component may be used alone, or two or more types may be used in combination.

[0075] When the base film includes a release layer, examples of resins that can be included in the release layer include alkyd resins; polyolefin resins; fluorine-containing resins; silicone resins; urethane resins; and acrylic resins.

[0076] The lower the elastic modulus of the release layer, the softer the resin from which it is formed. When a laminate of a thermoplastic resin layer and a release layer is stretched, the more easily the release layer follows the deformation caused by the stretching of the thermoplastic resin layer, making it less likely for the release layer to rupture. As a result, the arithmetic mean height Sa of the release layer surface can be reduced. On the other hand, the higher the elastic modulus of the release layer, the harder the resin from which it is formed, when a laminate of a thermoplastic resin layer and a release layer is stretched, the more difficult it is for the release layer to follow the deformation caused by the stretching of the thermoplastic resin layer, making it more likely for the release layer to rupture. As a result, the arithmetic mean height Sa of the release layer surface can be increased. The elastic modulus of the release layer can be adjusted by selecting the type of resin constituting the release layer; adjusting the weight-average molecular weight of the polymer contained in the resin, the blending ratio of the polymer contained in the resin, and / or the weight proportion of the structural unit in the copolymer contained in the resin. For example, the elastic modulus of the release layer tends to increase by increasing the weight-average molecular weight of the polymer contained in the resin constituting the release layer.

[0077] Furthermore, the smaller the stretching ratio when stretching the laminate of the thermoplastic resin layer and the release layer, the less likely the release layer is to break, and the smaller the arithmetic mean height Sa of the release layer surface can be made.

[0078] A commercially available product may be used as the base film. Examples of commercially available products include the "Uni-Peel Series" manufactured by Unitika Ltd. The commercially available base film may be further stretched to adjust the arithmetic mean height Sa of the main surface S2.

[0079] The arithmetic mean height Sa of the main surface S2 of the base film is preferably a value corresponding to the arithmetic mean height Sa of the main surface S1 of the desired optical film. Specifically, it is preferably the same value as the arithmetic mean height Sa of the main surface S1 of the desired optical film. The arithmetic mean height Sa of the main surface S2 of the base film is usually greater than 0 nm, preferably greater than 4 nm, more preferably 5 nm or more, even more preferably 6 nm or more, and is preferably 50 nm or less, more preferably 30 nm or less, even more preferably 10 nm or less.

[0080] Furthermore, the base film and the optical film preferably contain a common solvent, more preferably the same solvent, which improves the affinity between the base film and the optical film and allows the peel strength between the base film and the optical film to be adjusted.

[0081] For example, by forming an optical film on a substrate film by a coating method using a solvent, the type of solvent remaining in the substrate film and the optical film can be the same or the same.

[0082] When the solvent used to form the optical film is a mixed solvent of multiple types, the solvent that can be contained in the optical film and the solvent that can be contained in the base film may be multiple types. The weight composition of the solvent that can be contained in the optical film and the weight composition of the solvent that can be contained in the base film may be the same or different.

[0083] Step (A) of producing an optical laminate preferably includes the following steps (1), (2), and (3) in this order, and may further include any optional steps. In step (1), a substrate film having a main surface S2 with an arithmetic mean height Sa of 50 nm or less is prepared. In step (2), a resin liquid containing a polymer and a solvent is applied to the main surface S2 of the substrate film to form a resin liquid layer. In step (3), the resin liquid layer is dried to form an optical film on the main surface S2 of the substrate film.

[0084] In step (2), the resin liquid contains a polymer and a solvent that can be typically contained in an optical film, and further contains optional components other than the polymer that can be contained in the optical film. Examples of solvents that can be contained in the resin liquid include the examples listed as solvents that can be contained in the optical film. Here, part or all of the non-volatile components, such as the polymer and optional components, contained in the resin liquid may be dissolved in the solvent. Alternatively, part or all of the non-volatile components may be dispersed in the solvent.

[0085] In order to significantly exhibit the advantages of the present invention, the resin liquid preferably does not contain particles. In order to significantly exhibit the advantages of the present invention, the weight ratio of particles in the resin liquid is preferably 0.5 wt % or less, more preferably 0.3 wt % or less, even more preferably 0.1 wt % or less, even more preferably 0.05 wt % or less, and even more preferably 0.01 wt % or less, based on 100 wt % of the non-volatile components of the resin liquid. Usually, it may be 0.00% or more than 0.00%, and may even be 0.00%. According to a manufacturing method including steps (1), (2), and (3) in this order, even if the optical film does not contain particles, thin film interference unevenness in a laminate including the optical film can be effectively suppressed.

[0086] The solvent may be used alone or in combination of two or more.

[0087] The boiling point of the solvent under normal pressure is, for example, 60°C or higher and, for example, 150°C or lower.

[0088] The concentration of the nonvolatile components in the resin liquid can be set arbitrarily within a range that provides a viscosity suitable for application. A specific concentration range is preferably 5% by weight or more, more preferably 8% by weight or more, and particularly preferably 10% by weight or more, and is preferably 30% by weight or less, more preferably 20% by weight or less, and particularly preferably 15% by weight or less.

[0089] Examples of methods for applying a resin liquid to a substrate film include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, gravure coating, die coating, and gap coating.

[0090] In step (2), a layer of resin liquid is formed on the main surface S2 of the substrate film.

[0091] In step (3), the resin liquid layer is dried to form an optical film on the main surface S2 of the substrate film. Drying conditions for the resin liquid layer can be adjusted as appropriate. For example, drying conditions such as the drying temperature, drying temperature profile, air velocity in the drying oven, solvent gas concentration in the drying oven, and intake / exhaust volume of the drying oven can be adjusted. By adjusting the drying conditions, even if the optical film does not contain particles, thin film interference unevenness in a laminate including the optical film can be particularly effectively suppressed.

[0092] In one embodiment, the drying temperature in step (3) is preferably 90°C or higher, more preferably 100°C or higher, particularly preferably 110°C or higher, and preferably 140°C or lower, more preferably 135°C or lower, particularly preferably 130°C or lower.

[0093] In one embodiment, the drying time in step (3) is preferably 30 seconds or more, more preferably 60 seconds or more, particularly preferably 90 seconds or more, and preferably 5 minutes or less, more preferably 4 minutes or less, particularly preferably 3 minutes or less.

[0094] It is preferable to change the drying temperature of the resin liquid layer in a step (3) in a stepwise manner. In particular, it is preferable to change the drying temperature of the resin liquid layer in a stepwise manner immediately after forming the resin liquid layer. The drying temperature profile immediately after forming the resin liquid layer can particularly affect the surface shape of the optical film obtained by drying the resin liquid layer. The drying temperature of the resin liquid layer can be changed in a stepwise manner by passing the resin liquid layer through multiple sections set at different temperatures. It is preferable to dry the formed resin liquid layer by first passing it through a first drying section in which it is dried under first drying conditions, and then through a second drying section in which it is dried under second drying conditions. Here, the drying temperature T1 in the first drying section is preferably in the range of Sbp or higher to Sbp + 20°C or lower. Here, Sbp represents the boiling point (under normal pressure) of the solvent contained in the resin liquid. If the resin liquid contains multiple solvents, it represents the lowest boiling point of those solvents. Furthermore, the drying temperature T2 in the second drying section is preferably higher than the drying temperature T1 in the first drying section, with T1<T2. The lower T1, the more likely blushing occurs, resulting in greater haze. The higher T1, the more likely thin-film interference unevenness occurs. T2 is not particularly limited, but when a polyethylene terephthalate (PET) film is used as the substrate film, it can be 105°C or higher and 130°C or lower. The lower T2, the slower the solvent drying speed, and the more solvent remains in the optical film. If T2 is too high, the adhesion between the optical film and the substrate film may become too strong, or the optical film may peel off from the substrate film due to the difference in thermal expansion coefficients between the optical film and the substrate film.

[0095] Step (3) includes step (3-1) of drying the resin liquid layer at a drying temperature T1, followed by step (3-2) of drying the resin liquid layer at a drying temperature T2, where T1<T2 and T1 is preferably equal to or greater than Sbp and equal to or less than Sbp+20°C.

[0096] After the second drying section, the material may be passed through a drying section having different drying conditions, such as temperature setting, from those of the second drying section.

[0097] Here, it is preferable to set the drying time A and the thickness B of the optical film so that the conditional expression: 4≧B≧−0.25A+6.25 is satisfied, where A is the drying time in the first drying section (in step (3-1)) and B is the thickness of the optical film obtained by drying the resin liquid layer (μm). When this conditional expression is satisfied, thin film interference unevenness can be effectively reduced. Furthermore, it is particularly preferable that the conditional expression be satisfied when the drying temperature T1 in the first drying section is 90°C.

[0098] The main surface of the optical film formed on the main surface S2 of the base film has irregularities corresponding to the irregularities of the main surface S2 of the base film. Therefore, the main surface S1 of the optical film opposite the main surface S2 of the base film has an arithmetic mean height Sa corresponding to the arithmetic mean height Sa of the main surface S2 of the base film. The arithmetic mean height Sa of the main surface S1 of the optical film opposite the main surface S2 of the base film is usually greater than 0 nm, preferably greater than 4 nm, more preferably 5 nm or more, and even more preferably 6 nm or more, and is usually 50 nm or less, preferably 30 nm or less, and more preferably 10 nm or less.

[0099] By the method including the above steps (1) to (3), an optical laminate including an optical film and a substrate film can be obtained.

[0100] Examples of optional steps that may be included in step (A) include, but are not particularly limited to, a step of trimming the optical laminate and a step of winding up the optical laminate.

[0101] (Step (B)) In step (B), the substrate film is peeled from the optical laminate to obtain an optical film. When the optical laminate is long, peeling is usually performed continuously. In step (B), the optical film included in the optical laminate may be attached to an optical element such as a polarizer while facing each other, and the substrate film is peeled off, thereby transferring the optical film to the optical element. For the attachment, an appropriate adhesive or adhesive layer may be used. By peeling off the substrate film, a laminate including the optical film and an optical element such as a polarizer can be obtained.

[0102] <3. Polarizing Plate> <3.1. Overview of Polarizing Plate> A polarizing plate according to one embodiment of the present invention includes the optical film and a polarizer. When incorporated into a display device, the polarizing plate of this embodiment can achieve a display with less unevenness. The polarizer is preferably provided so as to be in contact with the main surface (main surface S3) of the optical film opposite the main surface S1. Here, the term "in contact" encompasses both direct and indirect contact, unless otherwise specified. That is, the polarizer may be provided so as to be directly in contact with the main surface (preferably main surface S3) of the optical film, or so as to be indirectly in contact with the main surface (preferably main surface S3) of the optical film. Here, "the polarizer is provided so as to be directly in contact with the main surface of the optical film" means that no layer is interposed between the polarizer and the main surface of the optical film. Furthermore, "the polarizer is provided so as to be indirectly in contact with the main surface of the optical film" means that any layer may be interposed between the polarizer and the main surface of the optical film.

[0103] As a polarizer, a film can be used that can transmit one of two linearly polarized light beams whose vibration directions intersect at right angles and absorb or reflect the other. Here, the vibration direction of linearly polarized light refers to the vibration direction of the electric field of the linearly polarized light. Such a film usually has a polarization transmission axis, and can transmit linearly polarized light beams whose vibration direction is parallel to the polarization transmission axis, and can absorb or reflect linearly polarized light beams whose vibration direction is perpendicular to the polarization transmission axis.

[0104] Examples of polarizers include films of polyvinyl alcohol resins containing vinyl alcohol-based polymers such as polyvinyl alcohol and partially formalized polyvinyl alcohol, which have been subjected to appropriate treatments, such as dyeing with a dichroic substance such as iodine, stretching, and crosslinking, in an appropriate order and by an appropriate method. The polarizer preferably contains a polyvinyl alcohol resin.

[0105] The thickness of the polarizer is preferably greater than 1 μm, more preferably 2 μm or greater, particularly preferably 3 μm or greater, and preferably 19 μm or less, more preferably 18 μm or less. When the thickness of the polarizer is greater than the lower limit, the optical performance of the polarizing plate can be sufficiently improved. When the thickness of the polarizer is equal to or less than the upper limit, warping of a display including the polarizing plate can be reduced, and the bending recovery of the polarizing plate can be effectively improved.

[0106] A polarizing plate can be produced by laminating an optical film and a polarizer with an appropriate adhesive. A polarizing plate containing an optical film and a polarizer may be obtained by laminating an optical laminate containing the optical film and a substrate film with a polarizer and then peeling off the substrate film. Alternatively, without peeling off the substrate film, a laminate containing the substrate film, optical film, and polarizer may be formed, and the laminate may be subjected to operations such as laminating with other optical elements, winding, storing, and transporting. Furthermore, a polarizing plate may be produced as a film containing the optical laminate, the polarizer, and the optical laminate in this order, and stored and transported as such. Since this film contains the substrate film, optical film, polarizer, optical film, and substrate film in this order, the optical film and polarizer can be protected by the substrate film. In this case, the substrate film is peeled off immediately before use to obtain a multilayer film, which can be used for applications such as attachment to a display device.

[0107] Examples of adhesives for bonding the optical film and the polarizer include acrylic adhesives, epoxy adhesives, urethane adhesives, polyester adhesives, polyvinyl alcohol adhesives, modified polyvinyl alcohol adhesives, polyolefin adhesives, modified polyolefin adhesives, polyvinyl alkyl ether adhesives, rubber adhesives, vinyl chloride-vinyl acetate adhesives, SEBS (styrene-ethylene-butylene-styrene copolymer) adhesives, ethylene adhesives such as ethylene-styrene copolymers, acrylic ester adhesives such as ethylene-methyl (meth)acrylate copolymers and ethylene-ethyl (meth)acrylate copolymers, etc. As the adhesive, from the viewpoint of curing the adhesive in a short time, ultraviolet-curable adhesives are preferred, but from the viewpoint of making the adhesive layer thinner, aqueous adhesives such as polyvinyl alcohol and modified polyvinyl alcohol may also be used.

[0108] The polarizing plate may include an optional layer in addition to the optical film and the polarizer. Examples of the optional layer include an optically isotropic layer having optical isotropy and an optically anisotropic layer having optical anisotropy. The in-plane retardation Re of the optically isotropic layer having optical isotropy is preferably 20 nm or less, more preferably 10 nm or less, even more preferably 5 nm or less, and usually 0 nm or more, and may be 0 nm. The absolute value of the retardation Rth in the thickness direction of the optically isotropic layer is preferably 20 nm or less, more preferably 10 nm or less, even more preferably 5 nm or less, and usually 0 nm or more, and may be 0 nm.

[0109] The polarizing plate may include an optically anisotropic layer in addition to an optical film and a polarizer, and the optically anisotropic layer, the optical film, and the polarizer may be arranged in this order when viewed from the thickness direction. Hereinafter, a polarizing plate according to an embodiment including an optically anisotropic layer, an optical film, and a polarizer will be described.

[0110] 3.2. Polarizing Plate Embodiment 1 The polarizing plate according to embodiment 1 includes an optically anisotropic layer, the optical film, and the polarizer arranged in this order when viewed from the thickness direction, and the optically anisotropic layer includes a first retardation layer. The first retardation layer has an in-plane retardation Re1(550) at a wavelength of 550 nm of preferably 100 nm or more, more preferably 110 nm or more, and preferably 150 nm or less, more preferably 145 nm or less. The first retardation layer having an in-plane retardation Re1(550) within the above range can function as a quarter-wave plate.

[0111] The first retardation layer has an Re1(450) / Re1(550) of preferably 0.80 or more, more preferably 0.83 or more, even more preferably 0.85 or more, and preferably 1.30 or less, more preferably 1.10 or less. Here, Re1(450) represents the in-plane retardation of the first retardation layer at a wavelength of 450 nm. When Re1(450) / Re1(550) is within the above range, the first retardation layer can function as a quarter-wave plate in a wide wavelength range.

[0112] The optically anisotropic layer may further include a second retardation layer in addition to the first retardation layer. The retardation Rth2(550) in the thickness direction at a wavelength of 550 nm of the second retardation layer is preferably −140 nm or more, more preferably −100 nm or more, and preferably −10 nm or less, more preferably −40 nm or less. By further including a second retardation layer, the optically anisotropic layer can be made to have the function of imparting retardation even in the tilt direction. The retardation Re2(550) in the in-plane direction at a wavelength of 550 nm of the second retardation layer is preferably 30 nm or less, more preferably 10 nm or less, and usually 0 nm or more.

[0113] When the optically anisotropic layer includes a first retardation layer and a second retardation layer, the first retardation layer and the second retardation layer may be arranged in any order in the thickness direction. For example, they may be arranged in the order of the first retardation layer, the second retardation layer, the optical film, and the polarizer, or they may be arranged in the order of the second retardation layer, the first retardation layer, the optical film, and the polarizer.

[0114] 3.3. Polarizing Plate Embodiment 2 A polarizing plate according to embodiment 2 includes an optically anisotropic layer, the optical film, and the polarizer arranged in this order when viewed from the thickness direction, and the optically anisotropic layer includes a third retardation layer and a fourth retardation layer. The third retardation layer has an in-plane retardation Re3(550) at a wavelength of 550 nm of preferably 100 nm or more, more preferably 110 nm or more, and preferably 150 nm or less, more preferably 145 nm or less. A third retardation layer having an in-plane retardation Re3(550) within the above range can function as a quarter-wave plate.

[0115] The third retardation layer has an Re3(450) / Re3(550) of preferably 0.80 or more, more preferably 0.83 or more, even more preferably 0.85 or more, and preferably 1.30 or less, more preferably 1.10 or less. Here, Re3(450) represents the in-plane retardation of the third retardation layer at a wavelength of 450 nm. When Re3(450) / Re3(550) is within the above range, the third retardation layer can function as a quarter-wave plate in a wide wavelength range.

[0116] The fourth retardation layer has an in-plane retardation Re4(550) of preferably 200 nm or more, more preferably 210 nm or more, and preferably 290 nm or less, more preferably 280 nm or less at a wavelength of 550 nm. The fourth retardation layer having an in-plane retardation Re4(550) within the above range can function as a half-wave plate.

[0117] When the optically anisotropic layer includes a third retardation layer and a fourth retardation layer, the third retardation layer, the fourth retardation layer, the optical film, and the polarizer are preferably arranged in this order.

[0118] The optically anisotropic layer may further include a second retardation layer in addition to the third and fourth retardation layers. The preferred ranges of the thickness direction retardation Rth2(550) and in-plane retardation Re2(550) of the second retardation layer may be the same as those described above.

[0119] When the optically anisotropic layer includes a third retardation layer, a fourth retardation layer, and a second retardation layer, the second retardation layer may be disposed in any position in the thickness direction. Furthermore, the optically anisotropic layer may include a plurality of second retardation layers.

[0120] 4. Method for Evaluating Optical Films The method for evaluating optical films includes the following steps: (1) dividing a square area of ​​an optical film with sides of 225 mm into nine square sections with sides of 75 mm and obtaining thickness data at multiple locations in each of the nine sections; (2) calculating the standard deviation of the thickness data measured at multiple locations in each of the nine sections and calculating the arithmetic mean of the nine calculated standard deviations to obtain an average standard deviation X (μm); (3) comparing the average X with the Y value and determining whether X≧Y; and (4) evaluating a laminate including the optical film as being unlikely to produce thin film interference unevenness if X≧Y, where the Y value is a value calculated by the formula (2).

[0121] The optical film evaluation method can be realized by a processing device including a film thickness meter and a control device such as a personal computer connected to the film thickness meter so as to be able to communicate with the film thickness meter.

[0122] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and can be practiced with any modifications within the scope of the claims of the present invention and their equivalents.

[0123] In the following description, the "%" and "parts" that represent amounts are by weight unless otherwise specified. Furthermore, the operations described below were carried out at room temperature (20°C ± 15°C) and atmospheric pressure (1 atm) unless otherwise specified.

[0124] <Evaluation Method> (Thickness) The thickness of the film or layer was measured using a film thickness measurement system "F20" manufactured by Filmetrics, Inc. Measurements were taken at five locations in total, namely, both ends and the center in the width direction of the film or layer, and the midpoint between the ends and the center in the width direction, and an average value was calculated from the obtained thickness data, and this average value was defined as the thickness of the film or layer.

[0125] (Arithmetic surface height Sa) The optical film was peeled off from the transfer laminate. The arithmetic mean height Sa of the surface (main surface S1) of the peeled optical film that had been in contact with the base film was measured in accordance with ISO 25178 using a surface roughness measuring device (Surfcorder SE800, manufactured by Koike Laboratory Co., Ltd.).

[0126] (Total Light Transmittance and Haze) The total light transmittance and haze of the optical film were measured in accordance with JIS-K-7361 using a haze meter (NDH 7000, manufactured by Nippon Denshoku Industries Co., Ltd.). Of the nine sections of the optical film for which the standard deviation was determined, the haze was measured in any three sections, and the average value of the haze values ​​obtained at the three locations was taken as the haze of the optical film. Similarly, the average value of the total light transmittance at the three locations was taken as the total light transmittance of the optical film.

[0127] (Retardation) The optical film was peeled off from the transfer laminate, and the in-plane retardation Re and the retardation Rth in the thickness direction of the optical film were measured at a measurement wavelength of 550 nm using a phase difference meter ("Axo Scan" manufactured by AXOMETRICS).

[0128] (Water Vapor Transmission Rate) The optical film was peeled off from the transfer laminate. The water vapor transmission rate of this optical film was measured using a water vapor transmission rate measuring device ("PERMATRAN-W" manufactured by MOCON) in accordance with JIS K7129 Method B under conditions of a temperature of 40°C and a humidity of 90% RH. The measured value of the water vapor transmission rate thus obtained was converted to a value per 100 μm of thickness to obtain the water vapor transmission rate per 100 μm of thickness of the optical film. Specifically, the measured value was multiplied by "100 (μm) / thickness (μm) of the optical film" to obtain the water vapor transmission rate per 100 μm of thickness.

[0129] (Photoelastic Constant) The optical film was peeled from the transfer laminate. This optical film was cut to prepare multiple film pieces with a width of 1 cm. Weights weighing 50 g, 100 g, 150 g, and 200 g were suspended from these film pieces, and the in-plane retardation was measured at a measurement wavelength of 550 nm. The in-plane retardation was measured using a phase difference meter (AXOMETRICS "Axo Scan"). The measured in-plane retardation was divided by the thickness of the optical film to determine the birefringence. The obtained birefringence and the magnitude of the force per unit cross-sectional area applied to the optical film by the weight corresponding to that birefringence were plotted on a coordinate system with the magnitude of the force on the horizontal axis and the birefringence on the vertical axis. An approximation line was obtained from the obtained plot by the least squares method. The photoelastic constant of the optical film was determined as the slope of this approximation line.

[0130] (Method for measuring solvent content) The optical film was peeled off from the transfer laminate. The peeled optical film was cut to 40 mm x 200 mm, weighed, and placed in a vial. The optical film was heated at 150°C for 30 minutes to vaporize the solvent in the optical film, and the amount of vaporized solvent was measured using a gas chromatograph mass spectrometer (Shimadzu Corporation "GC-2010 Plus / Trubomatrix 40"; column: Agilent Technologies "DB-5ms"). The specific amount of solvent was determined based on a calibration curve prepared in advance. The solvent content was calculated from the determined amount of solvent.

[0131] (Average Standard Deviation X and Y Values) For the inner 225 mm x 225 mm square area of ​​the transfer laminate cut into a 300 mm x 300 mm square, an interference film thickness meter (Optical NanoGauge manufactured by Hamamatsu Photonics) was used to measure the film thickness at a scanning speed of 0.5 mm / sec in both the conveying direction and the width direction at 1 mm intervals. Then, for nine square sections divided into 75 mm x 75 mm, the standard deviation of the film thickness measurements within each section was calculated, and then averaged to obtain the average standard deviation X. Then, the Y value for judgment was calculated using the calculation formula (2) above.

[0132] (Visual evaluation of thin film interference unevenness) A black adhesive tape for light blocking and appearance inspection (manufactured by Tomoegawa Paper Co., Ltd.) was attached to the surface of the base film of the transfer laminate, and thin film interference unevenness was visually evaluated under a three-wavelength fluorescent lamp. The degree of thin film interference unevenness was evaluated according to the following evaluation criteria: 0: Not visible at all. 1: Slightly visible, but at a level that does not pose a problem to display quality. 2: Clearly visible, and there is a concern that it may degrade display quality depending on the application. 3: Very strongly visible, and display quality is degraded.

[0133] Example 1 A norbornene polymer hydride (ZEONOR manufactured by Zeon Corporation; glass transition temperature: 132°C) was mixed with a mixed solvent obtained by mixing cyclohexane and ethylcyclohexane in a weight ratio of 2:1 to obtain a resin solution with a norbornene polymer concentration of 11 wt%. The boiling point of cyclohexane under normal pressure is 81°C, and the boiling point of ethylcyclohexane under normal pressure is 132°C.

[0134] (1-1. Preparation of Substrate Film) A long polyethylene terephthalate film ("Uni-Peel High Smooth Product" manufactured by Unitika Ltd., arithmetic mean height Sa=5 nm) having a release layer containing a polyolefin resin was prepared as the substrate film.

[0135] (1-2. Formation of Resin Solution Layer) The resin solution was applied to the release layer of the substrate film to form a layer of the resin solution. The thickness of the resin solution layer formed was set to a thickness that would result in an optical film having a thickness of 4 μm.

[0136] (1-3. Formation of Optical Film) The resin solution layer was then heated in an oven at 90°C for 10 seconds as a first drying condition, and then heated at 110°C for 1 minute 50 seconds as a second drying condition to dry the resin solution layer and form an optical film with a thickness of 4 µm on the substrate film. By the above operations, a transfer laminate (optical laminate) including the substrate film and the optical film formed on this substrate film was obtained.

[0137] Using the obtained transfer laminate, the arithmetic mean height Sa, solvent content of the optical film, haze, transmittance, in-plane retardation, retardation in the thickness direction, water vapor permeability, photoelastic constant, and thin film interference unevenness were evaluated using the methods described above.

[0138] Example 6 The operation in (1-3) above was changed as follows. In Example 6, the resin solution layer was heated at 90°C for 11 seconds as the first drying condition, and then heated at 110°C for 1 minute 49 seconds as the second drying condition. Except for the above operations, the same operations as in Example 1 were carried out to form an optical film having a thickness of 4 μm on a substrate film, and a transfer laminate (optical laminate) including the substrate film and the optical film formed on this substrate film was obtained, and evaluated in the same manner as in Example 1.

[0139] <Examples 2 to 5, 7, Comparative Examples 1 to 4> In (1-2) above, the thickness of the resin solution layer applied to the substrate film was changed so as to obtain an optical film with a thickness of 3 μm. In (1-3) above, the drying conditions in the oven were changed as follows. Example 2: After heating at 90°C for 17 seconds, the film was heated at 110°C for 1 minute 43 seconds. Example 3: After heating at 90°C for 16 seconds, the film was heated at 110°C for 1 minute 44 seconds. Example 4: After heating at 90°C for 15 seconds, the film was heated at 110°C for 1 minute 45 seconds. Example 5: After heating at 90°C for 14 seconds, the film was heated at 110°C for 1 minute 46 seconds. Example 7: After heating at 90°C for 13 seconds, the film was heated at 110°C for 1 minute 47 seconds. Comparative Example 1: After heating at 90°C for 12 seconds, the film was heated at 110°C for 1 minute 48 seconds. Comparative Example 2: After heating at 90°C for 10 seconds, the film was heated at 110°C for 1 minute 50 seconds. Comparative Example 3: After heating at 90°C for 11 seconds, the film was heated at 110°C for 1 minute 49 seconds. Comparative Example 4: After heating at 120°C for 2 minutes. Except for the above operations, the same procedures as in Example 1 were carried out to form an optical film having a thickness of 3 μm on the substrate film, and a transfer laminate (optical laminate) comprising the substrate film and the optical film formed on this substrate film was obtained, and evaluated in the same manner as in Example 1.

[0140] <Results> The results are shown in Tables 1 and 2. In Tables 1 and 2, the abbreviations have the following meanings: "Film thickness": thickness of the optical film "Sa": arithmetic mean height Sa of the main surface S1 of the optical film "Haze": haze of the optical film "Transmittance": total light transmittance "Residual solvent amount": solvent content in the optical film "X' value": standard deviation calculated for all thickness measurements "X value": average value of nine standard deviations of thickness calculated for each of the nine sections "Y value": Y value calculated by formula (2)

[0141]

[0142]

[0143] The above results show that the optical films according to Examples 1 to 7, in which the X value is equal to or greater than the Y value, have a small degree of thin-film interference unevenness. On the other hand, the optical films according to Comparative Examples 1 to 4, in which the X value is smaller than the Y value, have a large degree of thin-film interference unevenness.

[0144] Fig. 1 is a graph showing the relationship between the drying time A (seconds) under the first drying condition (T1 = 90°C) and the film thickness B (µm) of the optical film in Examples 1 to 7 and Comparative Examples 1 to 4. In the graph in Fig. 1, the horizontal axis represents the drying time A (seconds) at 90°C, and the vertical axis represents the film thickness B (µm). As shown in Fig. 1, in Examples 1 to 7, the relationship 4 ≥ B ≥ -0.25A + 6.25 is satisfied, and the evaluation of interference unevenness is 0 or 1, indicating that good results are obtained.

Claims

1. The thickness is 4 μm or less, It has a main surface S1 with an arithmetic mean height Sa of 50 nm or less, An optical film that satisfies the following formula (1): X ≧ Y (1) In formula (1), X is the average value (μm) of standard deviations obtained by dividing a square region of the optical film with sides of 225 mm into nine square sections with sides of 75 mm, measuring the thickness at a plurality of locations in each of the nine sections, calculating the standard deviation for each of the nine sections, and calculating the arithmetic mean of the nine calculated standard deviations, Y is expressed by the following formula (2), in which Haze represents the haze value (%) of the optical film. Y=-0.0159×Haze+0.0392 (2)

2. The water vapor permeability per 100 μm of thickness is 4.0 g / (m ２ 2. The optical film according to claim 1, wherein the optical film has a wavelength of 1000 nm or less.

3. The photoelastic constant is 10 × 10 －１３ cm ２ The optical film according to claim 1 , wherein the axial length is 1 / dyn or less.

4. 2. The optical film according to claim 1, wherein the in-plane retardation Re is 0 nm or more and 2 nm or less, and the retardation Rth in the thickness direction is −5 nm or more and 5 nm or less, measured at a wavelength of 550 nm.

5. The optical film of claim 1 , comprising a polymer containing an alicyclic structure.

6. An optical laminate comprising the optical film according to any one of claims 1 to 5 and a substrate film provided directly on the main surface S1 of the optical film.

7. 7. The optical laminate according to claim 6, wherein a main surface S2 of the base film that is directly adjacent to the main surface S1 of the optical film has an arithmetic mean height Sa of 50 nm or less, and the optical film and the base film contain the same solvent.

8. A polarizing plate comprising the optical film according to any one of claims 1 to 5 and a polarizer.

9. The polarizing plate according to claim 8 , further comprising an optically anisotropic layer, wherein the optically anisotropic layer, the optical film, and the polarizer are arranged in this order when viewed in the thickness direction.

10. The method for producing the optical laminate according to claim 6, A step (1) of preparing a substrate film having a main surface S2 with an arithmetic mean height Sa of 50 nm or less; A step (2) of applying a resin liquid containing a polymer and a solvent onto the main surface S2 of the base film to form a resin liquid layer; and A method for producing an optical laminate, comprising: a step (3) of drying the resin liquid layer to form an optical film on the main surface S2 of the base film.