Multilayer film, optical film, and manufacturing method

Abstract

This multilayer film comprises: a pA layer composed of a crystalline resin (a) having a positive intrinsic birefringence; and a pB layer composed of a material (b) having a negative intrinsic birefringence, wherein the pA layer and the pB layer satisfy specific optical requirements. An optical film is a uniaxial co-stretched product of the multilayer film and comprises: an A layer composed of a crystalline resin (a) having a positive intrinsic birefringence; and a B layer composed of a material (b) having a negative intrinsic birefringence. A manufacturing method comprises a step for applying a specific liquid composition onto a film oA composed of a crystalline resin (a).

Description

Technical Field

[0001] The present invention relates to an optical film, a multilayer film that can be usefully used as a member for manufacturing the same, and a method for manufacturing them.

Background Art

[0002] Conventionally, resin films having specific optical properties have been used for optical applications. For example, a film satisfying 0 < Nz < 1 is called a three-dimensional retardation film. It is known that when a three-dimensional retardation film is provided in a display device such as a liquid crystal display device, it can exhibit an effect of reducing the coloration of the display surface viewed from an inclined direction. In particular, a three-dimensional retardation film in which the relationship between retardation and wavelength is so-called inverse wavelength dispersion can obtain a desired optical effect in a wide wavelength range. Also, due to the demand for thinning of display devices, a three-dimensional retardation film is also required to be thin.

[0003] A three-dimensional retardation film has a larger retardation in the z-axis direction (i.e., the thickness direction) than the retardation in the y-axis direction (i.e., the in-plane direction orthogonal to the in-plane slow axis direction). Therefore, it cannot be manufactured by the usual method for manufacturing a retardation film, such as simply stretching a resin for an optical film having a normal positive intrinsic birefringence. Therefore, it has been proposed so far to manufacture a three-dimensional retardation film or a film similar thereto by combining a resin having a positive intrinsic birefringence and a resin having a negative intrinsic birefringence (for example, Patent Documents 1 to 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Previously proposed methods for manufacturing three-dimensional phase difference films by combining resins with positive and negative intrinsic birefringence have had problems such as requiring complex stretching processes, lamination processes after stretching, and significant effort in positioning. In particular, it is difficult to easily manufacture films with reverse wavelength dispersion. Furthermore, in such combinations, it is necessary to have a sufficiently large proportion of resin with negative intrinsic birefringence, but since resins with negative intrinsic birefringence generally have low mechanical strength, increasing the proportion of such resin can lead to problems with mechanical strength. Low mechanical strength can be particularly problematic when making thin films. In addition, haze may occur during resin stretching, which can impair the display quality of display devices.

[0006] Therefore, the object of the present invention is to provide a film that can exhibit good effects as a three-dimensional phase difference film over a wide wavelength range, has high mechanical strength, is thin, can improve the display quality of a display device, and can be easily manufactured, as well as a manufacturing method that can easily produce such a film. [Means for solving the problem]

[0007] The inventors conducted studies to solve the aforementioned problems. As a result, the inventors found that when a specific material is used as one of the layers in a multilayer film combining a layer of material with positive intrinsic birefringence and a layer of material with negative intrinsic birefringence, it is possible to construct a multilayer film that exhibits good effects as a three-dimensional phase difference film over a wide wavelength range and can be easily manufactured. Based on this finding, the inventors completed the present invention. In other words, the present invention includes the following:

[0008] [1] A multilayer film comprising a pA layer made of a crystalline resin (a) having a positive intrinsic birefringence and a pB layer made of a material (b) having a negative intrinsic birefringence, A multilayer film in which the pA layer satisfies the following equations (1) to (2), and the pB layer satisfies the following equations (3) to (4): nz(pA)>nx(pA)≧ny(pA) ···(1) nx(pA)-ny(pA)≦0.0003 ···(2) nz(pB)>nx(pB)≧ny(pB) ···(3) nx(pB)-ny(pB)≦0.0003 ···(4) however, nx(pA), ny(pA), and nz(pA) are the main refractive indices of the pA layer, nx(pB), ny(pB), and nz(pB) are the main refractive indices of the pB layer. [2] A long film, the multilayer film described in [1]. [3] The multilayer film according to [1] or [2], wherein the pA layer and the pB layer are in direct contact. [4] A multilayer film according to any one of items [1] to [3], wherein the thickness of the pB layer is 20 μm or less. [5] An optical film comprising a uniaxially co-stretched multilayer film according to any one of items [1] to [4], the A layer being made of a crystalline resin (a) having a positive intrinsic birefringence, and the B layer being made of a material (b) having a negative intrinsic birefringence, An optical film that satisfies the following equations (5) and (6). Re(450) <Re(550)<Re(650) ···(5) Nz<1 ···(6) however, Re(450), Re(550), and Re(650) are the in-plane retardation of the optical film at a wavelength of 450 nm, the in-plane retardation of the optical film at a wavelength of 550 nm, and the in-plane retardation of the optical film at a wavelength of 650 nm, respectively. Nz is the Nz coefficient of the optical film. [6] The optical film described in [5], which is a long film. [7] The optical film according to [5] or [6], wherein the uniaxial co-stretching is longitudinal uniaxial co-stretching, transverse uniaxial co-stretching, or diagonal uniaxial co-stretching. [8] An optical film according to any one of items [5] to [7], wherein the thickness of the B layer is 20 μm or less. [9] An optical film according to any one of [5] to [8], comprising one A layer and two B layers formed on both sides thereof.

[10] A method for manufacturing a multilayer film as described in any one of items [1] to [4], Step (I) involves preparing a film oA made of crystalline resin (a), A manufacturing method comprising the steps (II) of applying a liquid composition containing a solvent and a material (b) having negative intrinsic birefringence dissolved in the solvent to one or both sides of the film oA to form a pB layer and change the birefringence in the thickness direction of the film oA to form a pA layer, thereby obtaining a multilayer film comprising the pA layer and the pB layer.

[11] A method for manufacturing an optical film as described in any one of items [5] to [9], Step (I) involves preparing a film oA made of crystalline resin (a), Step (II) is to apply a liquid composition containing a solvent and a material (b) having negative intrinsic birefringence dissolved in the solvent to one or both sides of the film oA, thereby forming a pB layer and changing the birefringence in the thickness direction of the film oA to form a pA layer, thereby obtaining a multilayer film comprising the pA layer and the pB layer. A manufacturing method comprising the step (III) of uniaxially co-stretching the multilayer film. [Effects of the Invention]

[0009] The present invention provides an optical film that can exhibit good effects as a three-dimensional phase difference film over a wide wavelength range, has high mechanical strength, is thin, can improve the display quality of a display device, and can be easily manufactured; a multilayer film that can be usefully used as a component for manufacturing such an optical film; and a manufacturing method that can easily produce such a multilayer film and an optical film.

Best Mode for Carrying Out the Invention

[0010] In the following description, unless otherwise specified, the in-plane retardation Re of a structure having a film-like shape (such as a film and a layer constituting a part of a film composed of multiple layers) is a value represented by Re = (nx - ny) × d. Unless otherwise specified, the retardation Rth in the thickness direction of a film-like structure is a value represented by Rth = [{(nx + ny) / 2} - nz] × d. Unless otherwise specified, the NZ coefficient of a film-like structure is a value represented by (nx - nz) / (nx - ny).

[0011] Unless otherwise specified, nx, ny, and nz are the principal refractive indices of a film-like structure. The principal refractive indices nx, ny, and nz are the refractive indices in three orthogonal directions with the nx direction as the slow axis direction and the nz direction as the thickness direction. That is, nx represents the refractive index in the direction perpendicular to the thickness direction (in-plane direction) of a film-like structure and giving the maximum refractive index. ny represents the refractive index in the in-plane direction of a film-like structure and perpendicular to the direction of nx. nz represents the refractive index in the thickness direction of a film-like structure. d represents the thickness of a film-like structure. Unless otherwise specified, the measurement wavelength is 590 nm.

[0012] In the present application, the optical properties of a structure with a certain symbol are represented by a combination of a symbol representing the optical property (such as nx, ny, nz, Re, Rth, NZ, etc.) and the symbol of the structure. According to this notation, for example, the principal refractive indices nx, ny, and nz of layer A can be represented as nx(A), ny(A), and nz(A), respectively. Also, the principal refractive indices nx, ny, and nz of layer pA can be represented as nx(pA), ny(pA), and nz(pA), respectively.

[0013] In the following explanation, unless otherwise specified, a material with positive intrinsic birefringence means a material whose refractive index in the stretching direction is greater than its refractive index in the direction perpendicular to it. Similarly, unless otherwise specified, a material with negative intrinsic birefringence means a material whose refractive index in the stretching direction is less than its refractive index in the direction perpendicular to it. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

[0014] In the following description, "long film" refers to a film having a length of five times or more its width, preferably 10 times or more its width, and specifically a film long enough to be rolled up for storage or transport. There is no particular upper limit on the length, but it is usually 100,000 times or less its width.

[0015] In the following explanation, the phase-lagging axis of a film-like structure refers to the in-plane phase-lagging axis unless otherwise specified.

[0016] [Multilayer film: Optical properties] The multilayer film of the present invention comprises a pA layer made of a crystalline resin (a) having a positive intrinsic birefringence and a pB layer made of a material (b) having a negative intrinsic birefringence.

[0017] The pA layer satisfies equations (1) to (2) below, and the pB layer satisfies equations (3) to (4) below. nz(pA)>nx(pA)≧ny(pA) ···(1) nx(pA)-ny(pA)≦0.0003 ···(2) nz(pB)>nx(pB)≧ny(pB) ···(3) nx(pB)-ny(pB)≦0.0003 ···(4) nx(pA), ny(pA), and nz(pA) are the principal refractive indices of the pA layer, and nx(pB), ny(pB), and nz(pB) are the principal refractive indices of the pB layer.

[0018] A pA layer satisfying equations (1) to (2), and a pB layer satisfying equations (3) to (4) are called positive C plates. With respect to equation (1), the ratio of nz(pA) to nx(pA), i.e., nz(pA) / nx(pA), is greater than 1, preferably 1.0002 or more. The upper limit of this ratio can be, for example, 2 or less. With respect to equation (2), the ratio of nz(pB) to nx(pB), i.e., nz(pB) / nx(pB), is greater than 1, preferably 1.0002 or more. The upper limit of this ratio can be, for example, 2 or less.

[0019] As described above, the multilayer film of the present invention is a positive C plate comprising both a layer with positive intrinsic birefringence and a layer with negative intrinsic birefringence, both of which have high nz values. Therefore, a three-dimensional phase difference film having inverse wavelength dispersion can be easily manufactured by a simple method such as uniaxial stretching.

[0020] The slow axis direction of the pA layer and the pB layer can be adjusted as appropriate so that the optical properties of the multilayer film and the optical film prepared using it are at the desired values. However, since nx and ny are exactly the same or nearly the same for both the pA layer and the pB layer, the direction of the slow axis can be arbitrary.

[0021] [Multilayer film: Other features] The multilayer film of the present invention can be a long film. A "long film" refers to a film having a length of five times or more its width, preferably 10 times or more its width, and specifically a film long enough to be wound into a roll for storage or transportation. There is no particular upper limit on the length, but it is usually 100,000 times or less its width. The fact that the multilayer film is a long film makes it possible to achieve efficient optical film manufacturing.

[0022] The multilayer film of the present invention may comprise one pA layer and one pB layer. The multilayer film of the present invention may also comprise two or more pA layers and two or more pB layers. In one embodiment, from the viewpoint of efficiently carrying out the manufacturing method of the multilayer film of the present invention described later, it is preferable that the multilayer film of the present invention comprises one pA layer and one pB layer. In another embodiment, the multilayer film of the present invention preferably has one pA layer and two pB layers formed on both sides thereof. That is, the multilayer film of the present invention may be a film having a layer configuration of (pB layer) / (pA layer) / (pB layer). In the method for manufacturing the multilayer film of the present invention described later, it is possible to form pB layers on both sides of the film for forming the pA layer, so a film having a layer configuration of (pB layer) / (pA layer) / (pB layer) can be easily manufactured. When such a layer configuration is present, it is preferable that a multilayer film having the desired optical properties can be easily obtained even if the thickness of each pB layer is thin.

[0023] When multiple pA layers are present, the optical properties of a layer stacked in the same planar positional relationship as those in a multilayer film can be considered the optical properties of the pA layer described above. Similarly, when multiple pB layers are present, the optical properties of a layer stacked in the same planar positional relationship as those in a multilayer film can be considered the optical properties of the pB layer described above.

[0024] The multilayer film of the present invention may include any layer other than the pA layer and the pB layer. For example, an adhesive layer may be provided between the pA layer and the pB layer. However, in the multilayer film of the present invention, it is preferable that the pA layer and the pB layer are in direct contact. By having a multilayer film in which the pA layer and the pB layer are in direct contact, it is possible to make the resulting optical film thin while simultaneously imparting good optical properties to the optical film. Such a multilayer film can be easily manufactured by the method for manufacturing the multilayer film of the present invention, which will be described later.

[0025] Optical films used in devices such as display devices generally require a certain thickness to exhibit optical properties, while at the same time, they are required to be thin due to the demand for thinner devices. The thickness of the multilayer film of the present invention is not particularly limited, but by satisfying the requirements of the present invention, it is possible to form an optical film that satisfies desired optical properties even with a thin thickness. Specifically, the thickness of the multilayer film of the present invention is preferably 150 μm or less, and more preferably 100 μm or less. The lower limit of the thickness of the multilayer film is not particularly limited, but can be, for example, 10 μm or more.

[0026] The thicknesses of the pA layer and the pB layer can be adjusted as appropriate to obtain the desired optical properties. The thickness of the pA layer is preferably 10 μm or more, more preferably 30 μm or more, while preferably 100 μm or less, and more preferably 80 μm or less. The thickness of the pB layer is preferably 1 μm or more, more preferably 5 μm or more, while preferably 20 μm or less, and more preferably 15 μm or less. If the multilayer film comprises multiple pA layers, their total thickness can be adjusted to the above preferred range. Similarly, if the multilayer film comprises multiple pB layers, their total thickness can be adjusted to the above preferred range.

[0027] [Materials that make up the pA layer] The crystalline resin (a) constituting the pA layer may be a resin containing a crystalline polymer. A "crystalline polymer" refers to a polymer having a melting point Tm. That is, a "crystalline polymer" refers to a polymer whose melting point can be observed using a differential scanning calorimeter (DSC). In the following description, a crystalline polymer may be referred to as a "crystalline polymer." The crystalline resin is preferably a thermoplastic resin.

[0028] Crystalline polymers have positive intrinsic birefringence. By using crystalline polymers with positive intrinsic birefringence, optical films with desired optical properties can be easily manufactured in combination with material (b).

[0029] Crystalline polymers may include, for example, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefins such as polyethylene (PE) and polypropylene (PP); and are not particularly limited, but it is preferable that they contain an alicyclic structure. By using a crystalline polymer containing an alicyclic structure, the mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability, and lightweight properties of the optical film can be improved. A polymer containing an alicyclic structure refers to a polymer that has an alicyclic structure within its molecule. Such a polymer containing an alicyclic structure may be, for example, a polymer or its hydride obtained by a polymerization reaction using a cyclic olefin as a monomer.

[0030] Examples of alicyclic structures include cycloalkane and cycloalkene structures. Among these, cycloalkane structures are preferred because they easily yield phase difference films with excellent properties such as thermal stability. The number of carbon atoms in a single alicyclic structure is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. By having the number of carbon atoms in a single alicyclic structure within the above range, mechanical strength, heat resistance, and moldability are highly balanced.

[0031] In a crystalline polymer containing an alicyclic structure, the proportion of structural units having an alicyclic structure to all structural units is preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 70% by weight or more. By increasing the proportion of structural units having an alicyclic structure as described above, heat resistance can be improved. The proportion of structural units having an alicyclic structure to all structural units may be 100% by weight or less. Furthermore, in a crystalline polymer containing an alicyclic structure, the remainder other than structural units having an alicyclic structure is not particularly limited and can be appropriately selected according to the intended use.

[0032] Examples of crystalline polymers containing an alicyclic structure include polymers (α) to (δ) listed below. Among these, polymer (β) is preferred because it is easier to obtain a phase difference film with excellent heat resistance. Polymer (α): A ring-opening polymer of a cyclic olefin monomer that is crystalline. Polymer (β): A hydride of polymer (α) that is crystalline. Polymer (γ): An addition polymer of cyclic olefin monomers that is crystalline. Polymer (δ): A hydride of polymer (γ) that is crystalline.

[0033] Specifically, as crystalline polymers containing an alicyclic structure, ring-opened polymers of dicyclopentadiene that are crystalline, and hydrides of ring-opened polymers of dicyclopentadiene that are crystalline are more preferred. Among these, hydrides of ring-opened polymers of dicyclopentadiene that are crystalline are particularly preferred. Here, a ring-opened polymer of dicyclopentadiene refers to a polymer in which the proportion of structural units derived from dicyclopentadiene to the total structural units is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more, and even more preferably 100% by weight.

[0034] The hydride of a ring-opening polymer of dicyclopentadiene preferably has a high proportion of racemo-dyads. Specifically, the proportion of racemo-dyads in the repeating units of the hydride of a ring-opening polymer of dicyclopentadiene is preferably 51% or more, more preferably 70% or more, and particularly preferably 85% or more. A high proportion of racemo-dyads indicates high syndiotactic stereoregularity. Therefore, the higher the proportion of racemo-dyads, the higher the melting point of the hydride of the ring-opening polymer of dicyclopentadiene tends to be. The proportion of the racemo dyad is described in the examples below. 13 It can be determined by analyzing the 1C-NMR spectrum.

[0035] As the polymers (α) to polymers (δ) mentioned above, polymers obtained by the manufacturing method disclosed in International Publication No. 2018 / 062067 may be used.

[0036] The melting point Tm of the crystalline polymer is preferably 200°C or higher, more preferably 230°C or higher, and preferably 290°C or lower. By using a crystalline polymer having such a melting point Tm, a multilayer film with an even better balance of moldability and heat resistance can be obtained.

[0037] Typically, crystalline polymers have a glass transition temperature (Tg). While the specific glass transition temperature (Tg) of a crystalline polymer is not particularly limited, it is usually between 85°C and 170°C.

[0038] The glass transition temperature (Tg) and melting point (Tm) of a polymer can be measured by the following method. First, the polymer is melted by heating, and the molten polymer is rapidly cooled with dry ice. Then, using this polymer as a test specimen, the glass transition temperature (Tg) and melting point (Tm) of the polymer can be measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min (heating mode).

[0039] The weight-average molecular weight (Mw) of the crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, preferably 1,000,000 or less, and more preferably 500,000 or less. Crystalline polymers having such a weight-average molecular weight offer an excellent balance between moldability and heat resistance.

[0040] The molecular weight distribution (Mw / Mn) of the crystalline polymer is preferably 1.0 or higher, more preferably 1.5 or higher, preferably 4.0 or lower, and more preferably 3.5 or lower. Here, Mn represents the number-average molecular weight. Crystalline polymers having such a molecular weight distribution exhibit excellent moldability.

[0041] The weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of a polymer can be measured as polystyrene equivalent values ​​by gel permeation chromatography (GPC) using tetrahydrofuran as the developing solvent.

[0042] There are no particular restrictions on the degree of crystallinity of the crystalline polymer contained in the phase difference film, but it is usually above a certain level. The specific range of crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The degree of crystallinity of crystalline polymers can be measured by X-ray diffraction.

[0043] Crystalline polymers may be used individually or in combination of two or more types in any ratio.

[0044] The proportion of crystalline polymer in the crystalline resin (a) is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of crystalline polymer is above the lower limit, the birefringence and heat resistance of the phase difference film can be improved. The upper limit of the proportion of crystalline polymer may be 100% by weight or less.

[0045] Crystalline resin (a) may contain any components in addition to the crystalline polymer. These optional components include, for example, antioxidants such as phenolic antioxidants, phosphorus antioxidants, and sulfuric antioxidants; light stabilizers such as hindered amine light stabilizers; waxes such as petroleum waxes, Fischer-Tropsch waxes, and polyalkylene waxes; nucleating agents such as sorbitol compounds, metal salts of organic phosphoric acids, metal salts of organic carboxylic acids, kaolin, and talc; diaminostilbene derivatives, coumarin derivatives, and azole derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, benzimi). Examples include fluorescent whitening agents such as dazole derivatives and benzothiasol derivatives, carbazole derivatives, pyridine derivatives, naphthalic acid derivatives, and imidazolon derivatives; ultraviolet absorbers such as benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers; inorganic fillers such as talc, silica, calcium carbonate, and glass fibers; colorants; flame retardants; flame retardant additives; antistatic agents; plasticizers; near-infrared absorbers; lubricants; fillers; and any polymer other than crystalline polymers, such as soft polymers. Any component may be used alone or in combination of two or more in any ratio.

[0046] [Organic solvents contained in crystalline resin (a)] The crystalline resin (a) constituting the pA layer may contain an organic solvent. This organic solvent is typically incorporated into the film during step (II) of the manufacturing method of the present invention.

[0047] In step (II), all or part of the organic solvent incorporated into the film may penetrate into the polymer. Therefore, even if drying is performed at a temperature above the boiling point of the organic solvent, it is difficult to completely remove the solvent. Thus, the pA layer typically contains the organic solvent.

[0048] The organic solvent can be one that does not dissolve the crystalline polymer in the manufacturing process of the present invention, as described later. Preferred organic solvents include, for example, hydrocarbon solvents such as toluene, limonene, and decalin; ketones such as methyl ethyl ketone; and carbon disulfide. There may be one or more types of organic solvents.

[0049] The ratio of organic solvent contained in the crystalline resin (a) to 100% by weight (solvent content) is preferably 10% by weight or less, more preferably 5% by weight or less, and particularly preferably 0.1% by weight or less.

[0050] [Materials that make up the pB layer] The material (b) constituting the pB layer has negative intrinsic birefringence. By using a resin having negative intrinsic birefringence as material (b) and combining it with a crystalline resin (a) having positive intrinsic birefringence, a multilayer film that satisfies the requirements of the present invention can be manufactured particularly easily.

[0051] Resins with negative birefringence are typically thermoplastic resins and include polymers with negative birefringence. Examples of polymers with negative birefringence include polystyrene polymers, including homopolymers and copolymers of styrene or styrene derivatives, and copolymers of styrene or styrene derivatives with any monomer; polyacrylonitrile polymers; polymethyl methacrylate polymers; or multi-component copolymers thereof; and cellulose compounds such as cellulose esters. Preferred monomers that can be copolymerized with styrene or styrene derivatives include, for example, acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene. Among these, polystyrene polymers and cellulose compounds are preferred. These polymers may be used individually or in combination of two or more in any ratio.

[0052] The proportion of polymer in a resin with negative intrinsic birefringence is preferably 50% to 100% by weight, more preferably 70% to 100% by weight, and particularly preferably 90% to 100% by weight. When the proportion of polymer is within the above range, the desired optical properties can be easily imparted to the pB layer.

[0053] Material (b) preferably contains a plasticizer. By using a plasticizer, the glass transition temperature of material (b) can be appropriately adjusted. Examples of plasticizers include phthalate esters, fatty acid esters, phosphate esters, and epoxy derivatives. A specific example of a plasticizer is the one described in Japanese Patent Application Publication No. 2007-233114. Furthermore, one type of plasticizer may be used alone, or two or more types may be used in any ratio.

[0054] Among plasticizers, phosphate esters are preferred because they are readily available and inexpensive. Examples of phosphate esters include trialkyl phosphates such as triethyl phosphate, tributyl phosphate, and trioctyl phosphate; halogen-containing trialkyl phosphates such as trichloroethyl phosphate; triaryl phosphates such as triphenyl phosphate, tricresyl phosphate, tris(isopropylphenyl) phosphate, and cresyldiphenyl phosphate; alkyl-diaryl phosphates such as octyldiphenyl phosphate; and tri(alkoxyalkyl) phosphates such as tri(butoxyethyl) phosphate.

[0055] If material (b) contains a plasticizer, the amount is preferably 0.001% by weight or more, more preferably 0.005% by weight or more, particularly preferably 0.1% by weight or more, preferably 20% by weight or less, more preferably 18% by weight or less, and particularly preferably 15% by weight or less, based on 100% by weight of material (b). When the amount of plasticizer is within the above range, the glass transition temperature of material (b) can be appropriately adjusted, so that the desired optical properties can be easily imparted to the pB layer.

[0056] Material (b) may contain, in combination with the polymer and plasticizer, any other components besides the polymer and plasticizer. Examples of these optional components are the same as those that may be included in crystalline resin (a). These optional components may be used individually or in combination of two or more components in any ratio.

[0057] The glass transition temperature of material (b) is preferably 80°C or higher, more preferably 90°C or higher, even more preferably 100°C or higher, most preferably 110°C or higher, and especially preferably 120°C or higher. When the glass transition temperature of material (b) is this high, the desired optical properties can be easily imparted to the pB layer. There is no particular upper limit to the glass transition temperature of material (b), but it is usually 200°C or lower.

[0058] [Optical film] The optical film of the present invention is a uniaxially co-stretched product of the multilayer film of the present invention. That is, the film of the present invention is obtained by co-stretching the pA layer and the pB layer by stretching the multilayer film of the present invention. Through such co-stretching, all layers contained in the multilayer film are stretched at the same stretching ratio and stretching direction, and the polymer molecules contained in these layers are oriented in a direction corresponding to the stretching direction. Since the multilayer film has the specific requirements defined by formulas (1) to (4), it is possible to easily obtain an optical film with optical properties that are difficult to obtain by conventional methods of manufacturing phase difference films, such as simply stretching a resin for optical films.

[0059] The optical film of the present invention comprises an A layer made of a crystalline resin (a) having a positive intrinsic birefringence, and a B layer made of a material (b) having a negative intrinsic birefringence. The A layer may be a layer obtained as a result of stretching the pA layer. The B layer may be a layer obtained as a result of stretching the pB layer. Therefore, specific examples of the materials constituting the A layer and the B layer may be the same as those examples for the pA layer and the pB layer.

[0060] The optical film of the present invention satisfies the following formulas (5) and (6). Re(450) <Re(550)<Re(650) ···(5) Nz<1 ···(6)

[0061] In a preferred embodiment, the optical film of the present invention satisfies the following formula (7) or the following formula (8). Nz<0 ···(7) 0 <Nz<1 ···(8)

[0062] Re(450), Re(550), and Re(650) are the in-plane retardation of the optical film at a wavelength of 450 nm, 550 nm, and 650 nm, respectively, and Nz is the Nz coefficient of the optical film.

[0063] A film that satisfies formula (5) is called an inverse wavelength dispersive film. A film that satisfies formula (5) can obtain the desired optical effect over a wide wavelength range. A film that satisfies formula (8) is called a three-dimensional phase difference film. When a film that satisfies formula (8) is installed in a display device, it can exhibit effects such as reducing the coloration of the display surface when viewed from an inclined direction. In the prior art, a film that satisfies both formulas (5) and (8) had to be manufactured through a complicated process, but the optical film of the present invention can be easily manufactured by uniaxial stretching, as it utilizes the multilayer film of the present invention having a specific configuration in its manufacture. Furthermore, if the optical film of the present invention is a film that satisfies formulas (5) and (7), it can be easily converted into a film that satisfies both formulas (5) and (8) by further uniaxial stretching.

[0064] In relation to formula (1), there is no limit to the lower limit of Re(450) / Re(550), but it is preferably 0.60 or higher, more preferably 0.70 or higher, and particularly preferably 0.75 or higher.

[0065] The values ​​of Re(450), Re(550), and Re(650) can be adjusted to values ​​suitable for the application of the optical film. When the optical film can be used as a λ / 4 wave plate, Re(550) is preferably 80 nm or more, more preferably 100 nm or more, particularly preferably 120 nm or more, preferably 180 nm or less, more preferably 160 nm or less, and particularly preferably 150 nm or less. When an optical film can be used as a λ / 2 wave plate, the preferred range for Re(550) is 275 nm or a value close to it, specifically preferably 260 to 290 nm, and more preferably 265 to 285 nm.

[0066] In relation to equation (8), Nz is greater than 0 and less than 1. The NZ coefficient of the phase difference film is preferably 0.2 or greater, more preferably 0.4 or greater, preferably 0.8 or less, and more preferably 0.6 or less.

[0067] Uniaxial co-stretching to obtain a uniaxially co-stretched product can be longitudinal uniaxial co-stretching, transverse uniaxial co-stretching, or oblique uniaxial co-stretching. Longitudinal uniaxial stretching is stretching along the longitudinal direction of the film, transverse uniaxial stretching is stretching along the width direction of the film, and oblique uniaxial stretching is stretching along the oblique direction of the film, where the oblique direction is a direction perpendicular to the thickness direction and the angle it makes with the width direction is neither 0° nor 90° (i.e., a direction where the angle it makes with the width direction is greater than 0° and less than 90°). Since the optical film of the present invention is a stretched product of the above-mentioned specific multilayer film, it is possible to obtain a film that satisfies formulas (5) and (6), more preferably formulas (5) and (8), without performing complex stretching such as biaxial stretching.

[0068] The optical film of the present invention can be made into a long film. Because the optical film is a long film, efficient production of optical films can be achieved.

[0069] The optical film of the present invention may comprise one A layer and one B layer. The multilayer film of the present invention may also comprise two or more A layers and two or more B layers. In one embodiment, from the viewpoint of efficiently manufacturing the optical film, it is preferable that the optical film of the present invention comprises one A layer and one B layer. In another embodiment, it is preferable that the optical film of the present invention has one A layer and two B layers formed on both sides thereof. That is, the optical film of the present invention may be a film having a layer configuration of (B layer) / (A layer) / (B layer). When such a layer configuration is present, it is preferable because it is possible to easily obtain an optical film with desired optical properties even if the thickness of each B layer is thin.

[0070] When multiple A layers are present, the optical properties of a layer stacked in the same planar positional relationship as those in the optical film can be considered the optical properties of A layers as described above. Similarly, when multiple B layers are present, the optical properties of a layer stacked in the same planar positional relationship as those in the optical film can be considered the optical properties of B layers as described above.

[0071] The optical film of the present invention may include any layer other than layer A and layer B. For example, an adhesive layer may be provided between layer A and layer B. However, in the optical film of the present invention, it is preferable that layer A and layer B are in direct contact with each other from the viewpoint of reducing the thickness and obtaining good optical properties.

[0072] The thickness of the optical film of the present invention is not particularly limited, but it is possible to obtain an optical film that satisfies desired optical properties even with a thin thickness. Specifically, the thickness of the optical film of the present invention is preferably 100 μm or less, and more preferably 80 μm or less. The lower limit of the thickness of the optical film is not particularly limited, but can be, for example, 10 μm or more.

[0073] The thicknesses of layers A and B can be adjusted as appropriate to obtain the desired optical properties. The thickness of layer A is preferably 10 μm or more, more preferably 20 μm or more, while preferably 100 μm or less, and more preferably 80 μm or less. The thickness of layer B is preferably 1 μm or more, more preferably 5 μm or more, while preferably 20 μm or less, and more preferably 15 μm or less. If the optical film comprises multiple layers A, their total thickness can be adjusted to the above preferred range. Similarly, if the optical film comprises multiple layers B, their total thickness can be adjusted to the above preferred range.

[0074] [Method for manufacturing multilayer films, and method for manufacturing optical films] The multilayer film of the present invention can be manufactured by a manufacturing method comprising the following steps (I) to (II). Furthermore, the optical film of the present invention can be manufactured by a manufacturing method comprising the following steps (I) to (II) in addition to the following step (III). Step (I): A step to prepare a film oA made of crystalline resin (a). Step (II): A step of applying a liquid composition containing a solvent and a material (b) having negative intrinsic birefringence dissolved in the solvent to one or both sides of film oA to form a pB layer and change the birefringence in the thickness direction of film oA to form a pA layer, thereby obtaining a multilayer film comprising a pA layer and a pB layer. Process (III): A process for uniaxial co-stretching of a multilayer film. In the following, such manufacturing methods will be described as the method for manufacturing the multilayer film of the present invention and the method for manufacturing the optical film of the present invention.

[0075] [Process (I)] Step (I) can be carried out by forming the crystalline resin (a) into a film. Step (I) may also be carried out simply by obtaining a commercially available film. Any molding method can be used to form the crystalline resin (a) into a film. From the viewpoint of manufacturing efficiency, melt extrusion molding is preferred. The thickness of film oA can be adjusted as appropriate so that the thickness of the pA layer in the multilayer film product and the A layer in the optical film are of the desired thickness.

[0076] [Step (II): Liquid Composition] In step (II), a liquid composition containing a solvent and material (b) is used. Examples of solvents are the same as those listed above as examples of organic solvents that may exist in the crystalline resin (a) constituting the pA layer. More specifically, examples include hydrocarbon solvents such as toluene, limonene, and decalin; ketones such as methyl ethyl ketone; and carbon disulfide. From the viewpoint of exhibiting an effect that changes the film oA and dissolving polymers with negative birefringence well, ketones such as methyl ethyl ketone, or mixed solvents of ketones and other solvents are particularly preferred. The liquid composition may contain one type of solvent or two or more types.

[0077] The same examples as those described above can be given as examples of material (b). That is, the liquid composition may contain, as its components, the same polymers with negative inherent birefringence that constitute material (b) and other optional components that material (b) may contain, as described above.

[0078] The ratio of the solvent to material (b) in the liquid composition can be adjusted as appropriate so that a B layer of the desired thickness can be formed and the degree of change in film oA can be kept within the desired range. Specifically, the ratio of the polymer with negative intrinsic birefringence constituting material (b) to the total of the solvent and material (b) can be adjusted to a ratio of 1 to 50% by weight.

[0079] [Process (II): Coating] In step (II), the liquid composition is applied to one or both sides of film oA. The specific application procedure is not particularly limited, but from the viewpoint of forming a uniform B layer of the desired thickness, it is preferable that the application thickness can be precisely controlled. Specifically, application by a coater such as a die coater is preferred.

[0080] As a result of the coating, the solvent, which is a component of the liquid composition, comes into contact with the surface of the oA layer. The inventors have found that when a crystalline resin (a) film is used as the film oA, the birefringence in the thickness direction of the film oA can be changed by contact between the film oA and the solvent. As a result, in the resulting pA layer, optical properties such as nz(pA)>nx(pA)≧ny(pA), which are difficult to obtain in films formed by conventional processes such as film formation and stretching of resins with normal intrinsic birefringence, can be easily obtained. In step (II), the pB layer is formed on the surface of the film oA, and at the same time, this change in the film oA can be achieved. As a result, a multilayer film that is normally difficult to obtain can be easily manufactured, which has both a layer of material with a positive intrinsic birefringence and a layer of material with a negative intrinsic birefringence, and both layers have the optical properties of a positive C plate.

[0081] [Step (III)] In step (III), the multilayer film obtained in step (II) is uniaxially co-stretched. This co-stretching orients the polymer molecules contained in the pA and pB layers of the multilayer film in a direction corresponding to the stretching direction. Because the multilayer film has gone through step (II), as a result of step (III), an optical film with optical properties that are difficult to obtain by conventional phase difference film manufacturing methods, such as simply stretching the resin for optical films, can be easily obtained. There are no restrictions on the stretching direction in step (III), and examples include the longitudinal direction, the width direction, and the oblique direction.

[0082] When attempting to manufacture a film having optical properties equivalent to those of the optical film of the present invention using a manufacturing method that does not involve step (II), multiple complex stretching steps are usually required. Since the conditions for stretching must be strictly controlled when optical properties are achieved through stretching, having many stretching steps is a significant disadvantage from the standpoint of manufacturing efficiency. In contrast, the manufacturing method of the present invention allows the optical film of the present invention to be obtained by uniaxial stretching alone, which is advantageous from the standpoint of manufacturing efficiency.

[0083] The stretching ratio is preferably 1.1 times or more, more preferably 1.2 times or more, preferably 20.0 times or less, more preferably 10.0 times or less, even more preferably 5.0 times or less, and particularly preferably 2.0 times or less. It is desirable to set the specific stretching ratio appropriately according to factors such as the optical properties, thickness, and strength of the optical film product. When the stretching ratio is above the lower limit, the birefringence can be greatly changed by stretching. Also, when the stretching ratio is below the upper limit, the direction of the slow axis can be easily controlled and film breakage can be effectively suppressed.

[0084] The stretching temperature is preferably "Tg + 5°C" or higher, more preferably "Tg + 10°C" or higher, preferably "Tg + 100°C" or lower, and more preferably "Tg + 90°C" or lower. Here, "Tg" represents the glass transition temperature of the crystalline polymer. When the stretching temperature is above the lower limit, the film can be sufficiently softened and stretched uniformly. When the stretching temperature is below the upper limit, the hardening of the film due to the progression of crystallization of the crystalline polymer can be suppressed, allowing for smooth stretching and enabling the expression of large birefringence through stretching. Furthermore, it is usually possible to reduce the haze of the resulting multilayer film and improve its transparency.

[0085] Since the birefringence can be changed by process (III), the Nz coefficient can be adjusted. Therefore, by stretching in process (III), a film that satisfies the requirements of equation (7) or equation (8) described above can be obtained. The obtained film can be used as is as the optical film of the present invention. Alternatively, the obtained film can be subjected to further arbitrary processing to become the optical film of the present invention. Examples of arbitrary processes include adjusting the birefringence by heat treatment while maintaining the stretched dimensions or by relaxation treatment by shrinking the stretched dimensions.

[0086] [Other processes] The method for manufacturing a multilayer film and the method for manufacturing an optical film of the present invention may include any additional steps in combination with the steps described above. For example, after step (II), a step of drying the solvent in the liquid composition may be included.

[0087] The method for manufacturing an optical film of the present invention may include a preheating step before step (III) to bring the temperature of the multilayer film to the stretching temperature or a temperature close thereto. Usually, the preheating temperature and the stretching temperature are the same, but they may be different. The preheating temperature is preferably T1-10°C or more, more preferably T1-5°C or more, preferably T1+5°C or less, and more preferably T1+2°C or less, relative to the stretching temperature T1. The preheating time is arbitrary, preferably 1 second or more, more preferably 5 seconds or more, and also preferably 60 seconds or less, more preferably 30 seconds or less.

[0088] The long optical film obtained in process (III) can be wound into a roll as needed to form a film roll. It can also be cut into desired shapes, such as rectangles, as needed.

[0089] [Applications of optical films] The optical film of the present invention can be processed into a desired shape, such as a rectangle, as needed, and used as a component of an optical device such as a display device. When the optical film of the present invention is used as a component of a display device, the display quality, such as the viewing angle, contrast, and image quality of the image displayed on the display device, can be improved. [Examples]

[0090] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples shown below, and can be modified and implemented as appropriate without departing from the scope of the claims and equivalents of the present invention. In the following explanation, "%" and "parts" refer to weight unless otherwise specified. Furthermore, the operations described below were performed under normal temperature and pressure conditions unless otherwise specified.

[0091] In the following description, free-end uniaxial stretching of a film refers to uniaxial stretching performed in a manner that allows shrinkage in a direction perpendicular to the stretching direction within the in-plane direction. In contrast, uniaxial stretching performed in a manner that fixes the dimensions in a direction perpendicular to the stretching direction and does not allow shrinkage in that direction is called fixed-end uniaxial stretching. In the uniaxial stretching of long films described below, uniaxial stretching other than free-end uniaxial stretching in the longitudinal direction is fixed-end uniaxial stretching unless otherwise specified.

[0092] [Evaluation Method] (Method for measuring the weight-average molecular weight Mw and number-average molecular weight Mn of polymers) The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the polymer were measured as polystyrene equivalents using a gel permeation chromatography (GPC) system (Tosoh Corporation, "HLC-8320"). An H-type column (Tosoh Corporation) was used as the column, and tetrahydrofuran was used as the solvent. The measurement temperature was 40°C.

[0093] (Method for measuring the hydrogenation rate of polymers) The hydrogenation rate of the polymer is orthodichlorobenzene-d 4 Using as a solvent, at 145°C, 1 The measurement was performed by 1H-NMR.

[0094] (Method for measuring glass transition temperature Tg and melting point Tm) The glass transition temperature (Tg) and melting point (Tm) of the polymer were measured as follows. First, the polymer was melted by heating, and the molten polymer was rapidly cooled with dry ice. Subsequently, using this polymer as a test specimen, the glass transition temperature (Tg) and melting point (Tm) of the polymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min (heating mode).

[0095] (Method for measuring the ratio of racemo-dyad in polymers) The ratio of racemo-dyads in the polymer was measured as follows: orthodichlorobenzene-d 4Using [the solvent], the polymer was subjected to an inverse-gated decoupling method at 200°C. 13 ¹¹NMR measurements were performed. 13 In the results of the 1C NMR measurement, orthodichlorobenzene-d 4 Using the 127.5 ppm peak as the reference shift, we identified a 43.35 ppm signal from the meso-dyad and a 43.43 ppm signal from the racemo-dyad. Based on the intensity ratio of these signals, we determined the proportion of racemo-dyad in the polymer.

[0096] (Method for measuring the optical properties of film) The optical properties of the film (in-plane retardation Re, thickness retardation Rth, and NZ coefficient, etc.) were measured using a phase difference meter (Axometrics "AxoScan"). Unless otherwise specified, measurements were taken at a wavelength of 590 nm. The procedure for separating the layers of a film comprising layer A (or pA) and layer B (or pB) was as follows: The B layer (or pB layer) side of the film was bonded to a glass plate via an adhesive layer. Then, an incision was made in the edge of the plate using a cutter to separate layer A (or pA) and layer B (or pB). The optical properties of the separated A layer (or pA layer) and layer B (or pB layer) on the glass plate were measured separately.

[0097] (Method for measuring film thickness) The thickness of the film was measured at multiple points in the width direction of the film at 5 cm intervals using a snap gauge (Mitutoyo ID-C112BS). The average thickness of the film was determined by calculating the average of these measurements.

[0098] (Degree of crystallinity) The degree of crystallinity (%) of the crystalline polymer was measured by X-ray diffraction.

[0099] (Bending durability) A planar, unloaded U-shaped stretch test was performed on the film sample using a benchtop durability tester (Yuasa System Equipment Co., Ltd. "DLDMLH-FS"). In this test, the film was repeatedly folded under the conditions of a width of 50 mm, a bending radius of 1 mm, and a stretching speed of 80 times / minute. After 1000 folds, the device was stopped, the film was visually inspected, and evaluated according to the evaluation criteria below. "Good": No film fragment breakage, cracking, or whitening was observed. "Defective": Any of the following was observed: film fragment breakage, cracking, or whitening.

[0100] (Hayes) A piece of film was cut from the center of the film's width to obtain a 50mm x 50mm square sample. The haze of this sample was measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0101] (Effect of improving display quality) A long linear polarizing film with an absorption axis in the longitudinal direction was prepared. This linear polarizing film was laminated to the optical film to be evaluated. During lamination, the angle was adjusted so that the absorption axis of the linear polarizing film and the absorption axis of the optical film formed a 45° angle. This lamination was performed using an adhesive (Nitto Denko Corporation's "CS-9621"). As a result, a circular polarizing film was obtained. The polarizing plate from an image display device (Apple Watch®) was removed, and the display surface of the image display device and the optical film side of the circular polarizing film to be evaluated were bonded together via an adhesive layer (Nitto Denko CS9621). The display surface was set to a black display state (the entire screen was black), and the display surface was observed from all directions at extreme angles θ=0° (front direction) and extreme angles θ=60° (tilt direction). A lower brightness and coloration due to reflection of ambient light indicates a better result. The observation results were evaluated according to the following criteria. "A": Lacks visible brightness and color. "B": Brightness and coloration occur at a level that is visible. "C": Severe brightness and color distortion occur.

[0102] [Production Example 1: Hydrogenated ring-opening polymer of dicyclopentadiene] A metal pressure reactor was thoroughly dried and then purged with nitrogen. To this metal pressure reactor, 154.5 parts of cyclohexane, 42.8 parts of a 70% cyclohexane solution of dicyclopentadiene (endo-isomer content of 99% or more) (30 parts of dicyclopentadiene), and 1.8 parts of 1-hexene were added, and the mixture was heated to 53°C.

[0103] A solution was prepared by dissolving 0.014 parts of tetrachlorotungstenphenylimide (tetrahydrofuran) complex in 0.70 parts of toluene. To this solution, 0.061 parts of a 19% diethylaluminum ethoxide / n-hexane solution was added and the mixture was stirred for 10 minutes to prepare a catalyst solution. This catalyst solution was added to the mixture in the pressure reactor to initiate the ring-opening polymerization reaction. The reaction was then carried out for 4 hours while maintaining a temperature of 53°C to obtain a solution of the ring-opened polymer of dicyclopentadiene. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the obtained ring-opened dicyclopentadiene polymers were 8,830 and 29,800, respectively, and the molecular weight distribution (Mw / Mn) calculated from these values ​​was 3.37.

[0104] To 200 parts of the solution of the obtained ring-opened polymer of dicyclopentadiene, 0.037 parts of 1,2-ethanediol were added as a stopping agent, and the mixture was heated to 60°C and stirred for 1 hour to stop the polymerization reaction. To this, 1 part of a hydrotalcite-like compound (Kyowa Chemical Industry Co., Ltd. "Kyoword® 2000") was added, and the mixture was heated to 60°C and stirred for 1 hour. Subsequently, 0.4 parts of a filtration aid (Showa Chemical Industry Co., Ltd. "Radiolite® #1500") was added, and the adsorbent and solution were filtered off using a PP pleated cartridge filter (ADVANTEC Toyo Co., Ltd. "TCP-HX").

[0105] To 200 parts (30 parts polymer) of a filtered solution of the ring-opened polymer of dicyclopentadiene, 100 parts of cyclohexane were added, and 0.0043 parts of chlorohydridecarbonyltris(triphenylphosphine)ruthenium were added. A hydrogenation reaction was carried out at a hydrogen pressure of 6 MPa and 180°C for 4 hours. This yielded a reaction solution containing the hydride of the ring-opened polymer of dicyclopentadiene. The hydride precipitated from this reaction solution, forming a slurry solution.

[0106] The hydride and solution contained in the reaction mixture were separated using a centrifuge and dried under reduced pressure at 60°C for 24 hours to obtain 28.5 parts of a crystalline ring-opening polymer hydride. The hydrogenation rate of this hydride was over 99%, the glass transition temperature (Tg) was 97°C, the melting point (Tm) was 266°C, and the racemo-dyad ratio was 89%.

[0107] [Manufacturing Example 2: Pellets of crystalline resin (a)] To obtain crystalline resin (a), 1.1 parts of an antioxidant (tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane; "Irganox® 1010" manufactured by BASF Japan) were mixed with 100 parts of the hydride of the ring-opened polymer of dicyclopentadiene obtained in Production Example 1.

[0108] The obtained crystalline resin (a) was fed into a twin-screw extruder (Toshiba Machine Co., Ltd. "TEM-37B") equipped with four die holes with an inner diameter of 3 mmΦ. The resin was hot-melt extruded using the twin-screw extruder to form a strand-shaped molded body. This molded body was shredded with a strand cutter to obtain pellets of crystalline resin (a). The operating conditions of the twin-screw extruder are shown below. Barrel temperature setting: 270℃~280℃ Die setting temperature: 250℃ • Screw rotation speed: 145 rpm • Feeder rotation speed: 50 rpm

[0109] [Example 1] (1-1. Process (I): Film oA) The pellets of crystalline resin (a) obtained in Production Example 2 were dried at 100°C for 5 hours. The dried pellets were supplied to a film molding machine. The film molding machine is equipped with an extruder, polymer pipe, polymer filter, and T-die in that order in the resin flow path. The pellets fed into the extruder are melted and extruded through the flow path into a film shape from the T-die. The operating conditions for the film molding machine were set to a barrel temperature of 280°C to 290°C, a die temperature of 270°C, and a screw rotation speed of 30 rpm. Using this film molding machine, the molten crystalline resin (a) was extruded onto a rotating cast roll into a film with a width of 500 mm. The rotation speed of the cast roll at this time was set to 6 m / min. Subsequently, the crystalline resin (a) was cooled on the roll and formed into a long film. This obtained a film oA made of crystalline resin (a). The thickness of the obtained film oA was 68 μm. The obtained film oA was wound onto a core and recovered to form a film roll.

[0110] The in-plane retardation Re(oA) of film oA at a wavelength of 590 nm was 5 nm, the thickness-direction retardation Rth(oA) was 5 nm, and the slow-phase axis direction was in the width direction relative to the longitudinal direction.

[0111] (1-2. Process (II): Multilayer film) A resin containing a styrene-maleic anhydride copolymer (Nova Chemicals "Daylark D332", glass transition temperature 130°C) as a material with negative intrinsic birefringence was dissolved in methyl ethyl ketone to prepare a liquid composition. The concentration of the styrene-maleic anhydride copolymer in the liquid composition was 10% by weight.

[0112] The film oA obtained in (1-1) was pulled out from the film roll, and a liquid composition was applied onto one of its surfaces. Then, the liquid composition was dried. As a result, a layer of a styrene-maleic anhydride copolymer (thickness 10 μm) as the pB layer was formed, and the refractive index in the thickness direction of the film oA changed to become the pA layer (thickness 68 μm), and a multilayer film comprising the pA layer and the pB layer was obtained. The obtained multilayer film was wound around a core and recovered as a film roll.

[0113] The pA layer and the pB layer of the multilayer film were peeled off, and their respective optical properties were measured to determine the Re, Rth, and Nz coefficients. The in-plane retardation Re(pA) of the pA layer was 8 nm, the thickness-direction retardation Rth(pA) was -42 nm, the birefringence in the thickness direction Rth(pA) / d was -0.6×10 -3 and the Nz coefficient NZ(pA) was -4.53. The in-plane retardation Re(pB) of the pB layer was 1 nm, the thickness-direction retardation Rth(pB) was -59 nm, the birefringence in the thickness direction Rth(pA) / d was -5.9×10 -3 and the Nz coefficient NZ(pA) was 2.50.

[0114] (1-3. Step (III): Optical Film) The multilayer film obtained in (1-2) was pulled out from the film roll and continuously supplied to a tenter stretching machine. Then, co-stretching of the multilayer film was performed by the tenter stretching machine. The stretching direction was the film width direction. The stretching temperature was 145 °C and the stretching ratio was 1.15 times. As a result, an optical film comprising an A layer made of a crystalline resin (a) with positive intrinsic birefringence and a B layer made of a material (b) with negative intrinsic birefringence was obtained.

[0115] The Re(450), Re(550), and Re(650) of the optical film were measured to evaluate whether it had inverse wavelength dispersion. Also, the Nz coefficient of the optical film at a wavelength of 590 nm was measured. Furthermore, the bending durability, haze, and display quality improvement effect of the optical film were evaluated.

[0116] Furthermore, the A and B layers of the optical film were separated, and their respective thicknesses and optical properties were measured to determine the Re, Rth, and Nz coefficients. The degree of crystallinity of the A layer was also measured.

[0117] [Example 2] Except for the changes described below, the same procedure as in Example 1 was used to obtain and evaluate the multilayer film and optical film. • In the co-stretching of the multilayer film described in (1-3), the film was stretched using free-end uniaxial stretching along the longitudinal direction, with a stretching temperature of 140°C and a stretching ratio of 1.20.

[0118] [Comparative Example 1] (C1-1. Film) A 68 μm thick film made of amorphous resin was obtained by the same procedure as in (1-1) of Example 1, except that a thermoplastic resin pellet containing norbornene polymer, a type of alicyclic structure-containing polymer (ZEONOR1420, manufactured by Zeon Corporation, with a glass transition temperature of 137°C), was used instead of crystalline resin pellets (a). The in-plane retardation Re of this film at a wavelength of 590 nm was 3 nm, the thickness-direction retardation Rth was 10 nm, and the slow phase axis direction was in the width direction relative to the longitudinal direction.

[0119] (C1-2. Multilayer films and optical films) Except for using the film obtained in (C1-1) instead of the film oA obtained in (1-1), multilayer films and optical films were obtained and evaluated by the same procedure as in (1-2) to (1-3) of Example 1. However, the stretching temperature was 135°C and the stretching ratio was 1.20 times. In Comparative Example 1, after the completion of step (II) and before proceeding to step (III), the pA and pB layers delaminated in many areas, resulting in portions unsuitable for optical applications. Although an effective thin film was not formed, stretching was still possible. The optical film was evaluated only in the areas where delamination did not occur.

[0120] Tables 1 and 2 show summaries and results of the examples and comparative examples. In each item in the tables below, the measurement target is indicated in parentheses; for example, the measurement results for the pA layer, pB layer, A layer, and B layer are shown as (pA), (pB), (A), and (B), respectively. For optical properties, the measurement wavelength is indicated in parentheses; for example, the measurement result at 590 nm is shown as (590 nm). In addition, the units are also indicated in parentheses.

[0121] [Table 1]

[0122] [Table 2]

[0123] As is clear from the results of the examples and comparative examples, the optical film of the present invention, manufactured using the multilayer film obtained by the manufacturing method of the present invention, can exhibit good effects as a three-dimensional phase difference film over a wide wavelength range, has high mechanical strength, can be made into a thin film, can improve the display quality of display devices, and can be easily manufactured by uniaxial co-stretching.

Claims

1. A multilayer film comprising a pA layer made of a crystalline resin (a) with positive intrinsic birefringence and a pB layer made of a material (b) with negative intrinsic birefringence, A multilayer film in which the pA layer satisfies the following formulas (1) to (2), and the pB layer satisfies the following formulas (3) to (4): nz(pA)>nx(pA)≧ny(pA)...(1) nx(pA)-ny(pA)≦0.0003...(2) nz(pB)>nx(pB)≧ny(pB)...(3) nx(pB)-ny(pB)≦0.0003...(4) however, nx(pA), ny(pA), and nz(pA) are the main refractive indices of the pA layer, nx(pB), ny(pB), and nz(pB) are the main refractive indices of the pB layer.

2. A multilayer film according to claim 1, which is a long film.

3. The multilayer film according to claim 1 or 2, wherein the pA layer and the pB layer are in direct contact.

4. A multilayer film according to any one of claims 1 to 3, wherein the thickness of the pB layer is 20 μm or less.

5. An optical film comprising a uniaxially co-stretched multilayer film according to any one of claims 1 to 4, the A layer being made of a crystalline resin (a) having a positive intrinsic birefringence, and the B layer being made of a material (b) having a negative intrinsic birefringence, An optical film that satisfies the following equations (5) and (6). Re(450)<Re(550)<Re(650)...(5) Nz<1...(6) however, Re(450), Re(550), and Re(650) are the in-plane retardation of the optical film at a wavelength of 450 nm, the in-plane retardation of the optical film at a wavelength of 550 nm, and the in-plane retardation of the optical film at a wavelength of 650 nm, respectively. Nz is the Nz coefficient of the optical film.

6. The optical film according to claim 5, which is a long film.

7. The optical film according to claim 5 or 6, wherein the uniaxially co-stretched material is a longitudinally uniaxially co-stretched material, a transversely uniaxially co-stretched material, or a diagonally uniaxially co-stretched material.

8. The optical film according to any one of claims 5 to 7, wherein the thickness of layer B is 20 μm or less.

9. The optical film according to any one of claims 5 to 8, comprising one A layer and two B layers formed on both sides thereof.

10. A method for manufacturing a multilayer film according to any one of claims 1 to 4, Step (I) involves preparing a film oA made of crystalline resin (a), A manufacturing method comprising the steps (II) of applying a liquid composition containing a solvent and a material (b) having negative intrinsic birefringence dissolved in the solvent to one or both sides of the film oA to form a pB layer and change the birefringence in the thickness direction of the film oA to form a pA layer, thereby obtaining a multilayer film comprising the pA layer and the pB layer.

11. A method for manufacturing an optical film according to any one of claims 5 to 9, Step (I) involves preparing a film oA made of crystalline resin (a), Step (II) of applying a liquid composition containing a solvent and a material (b) having negative intrinsic birefringence dissolved in the solvent to one or both sides of the film oA to form a pB layer and change the birefringence in the thickness direction of the film oA to form a pA layer, thereby obtaining a multilayer film comprising the pA layer and the pB layer, A manufacturing method comprising the step (III) of uniaxially co-stretching the multilayer film.

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