Resin composition and film using same

Abstract

By using a resin composition having excellent retardation properties and transparency, a film having excellent adhesion to a substrate is provided. [Solution] A resin composition containing 80.0 to 99.9 wt % of a fumaric acid ester-based polymer containing a fumaric acid diester residue and 0.1 to 20.0 wt % of an aromatic hydrocarbon resin having a weight-average molecular weight of 5,000 or less and containing a residue unit represented by the following general formula (2): JPEG2026043089000008.jpg4769 (wherein, each R3 independently represents hydrogen or an alkyl group having 1 to 12 carbon atoms, and R4 represents hydrogen or a methyl group).

Description

[Technical Field]

[0001] The present invention relates to a resin composition suitable as an optical material. [Background technology]

[0002] Liquid crystal displays (LCDs) are the most important display devices in our multimedia society, and are widely used in everything from mobile phones and computer monitors to laptops and televisions. Many optical films are used as polarizers in LCDs to improve display characteristics such as contrast when viewed from the front or at an angle, and color compensation.

[0003] A typical example of an optical film related to polarizing plates is retardation film, which is used as an anti-reflection layer in liquid crystal displays, touch panels, and organic electroluminescence (EL) displays.

[0004] Conventional retardation films are made of polycarbonate or cyclic polyolefin, both of which have positive birefringence. Here, the positive and negative birefringence are defined as follows:

[0005] The optical anisotropy of a polymer film that has been molecularly oriented by stretching or casting using a coater can be expressed by an index ellipsoid, where nx is the refractive index in the fast axis direction (the direction with the smallest refractive index) within the film plane, ny is the refractive index in the direction perpendicular to that in the film plane (the slow axis), and nz is the refractive index in the thickness direction of the film (the perpendicular direction outside the film plane).

[0006] In other words, when a polymer with negative birefringence is uniaxially stretched, the refractive index in the direction of the stretching axis (fast axis: stretching direction) is small, and when a polymer with positive birefringence is uniaxially stretched, the refractive index in the direction perpendicular to the stretching axis is small (fast axis: direction perpendicular to the stretching direction).

[0007] Many polymers have positive birefringence. Polymers with negative birefringence include acrylic resin and polystyrene, but acrylic resin exhibits little retardation and does not have sufficient properties as a retardation film. Polystyrene is not currently used due to optical property issues such as a high wavelength dependency of retardation, practical issues such as low heat resistance, and retardation stability issues such as a large photoelastic coefficient at room temperature that causes the retardation to change with even slight stress.

[0008] There is a strong market demand for such a retardation film exhibiting negative birefringence, and various retardation films exhibiting negative birefringence have been developed to meet the above-mentioned required characteristics.

[0009] Patent Documents 1 and 2 propose fumaric acid ester resins as optical films that exhibit negative birefringence and have a high refractive index in the thickness direction.

[0010] Furthermore, Patent Document 3 proposes a resin composition containing a fumaric acid ester polymer and a vinyl aromatic polymer. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-064817 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-107281 [Patent Document 3] Patent Publication No. 2021-075615 Summary of the Invention [Problem to be solved by the invention]

[0012] The retardation films obtained in Patent Documents 1 and 2 have excellent optical properties such as retardation characteristics and wavelength dependency, but have low adhesion to the film-forming substrate due to their non-polar structure.

[0013] The vinyl aromatic polymer specifically exemplified in Patent Document 3 has a weight-average molecular weight of more than 5,000. When the resin composition is formed into a film, the vinyl aromatic polymers exhibit strong cohesive force, making it difficult for them to mix with the fumaric acid ester polymer, and resulting in low transparency.

[0014] The present invention has been made in view of the above problems, and an object of the present invention is to provide a resin composition which, when used as a film, has excellent retardation properties, transparency, and adhesion to a film-forming substrate. [Means for solving the problem]

[0015] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that a resin composition containing a specific fumaric acid ester polymer and a specific aromatic hydrocarbon resin solves the above-mentioned problems, and have thus completed the present invention.

[0016] That is, the present disclosure has the following gist. [1] A resin composition containing 80.0 to 99.9% by weight of a fumarate polymer containing a fumarate diester residue represented by the following general formula (1), and 0.1 to 20.0% by weight of an aromatic hydrocarbon resin having a weight-average molecular weight of 5,000 or less and containing a residue unit represented by the following general formula (2).

[0017] [ka]

[0018] (wherein R1 and R2 each independently represent one of the group consisting of a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms).

[0019] [ka]

[0020] (wherein, each R3 independently represents hydrogen or an alkyl group having 1 to 12 carbon atoms, and R4 represents hydrogen or a methyl group). [2] The resin composition according to the above [1], wherein the fumaric acid diester residue represented by the general formula (1) is at least one fumaric acid diester residue selected from the group consisting of dimethyl fumarate residue, diethyl fumarate residue, diisopropyl fumarate residue, di-tert-butyl fumarate residue, di-n-butyl fumarate residue, di-sec-butyl fumarate residue, isobutyl fumarate residue, dipentyl fumarate residue, diisopentyl fumarate residue, di-sec-pentyl fumarate residue, di-tert-pentyl fumarate residue, di-sec-hexyl fumarate residue, di-tert-hexyl fumarate residue, di-sec-isoamyl fumarate residue, dineopentyl fumarate residue, di-tert-pentyl fumarate residue, di-2-ethylhexyl fumarate residue, dicyclopropyl fumarate residue, dicyclobutyl fumarate residue, dicyclopentyl fumarate residue, and dicyclohexyl fumarate residue. [3] The resin composition according to the above [1] or [2], wherein the residue unit represented by the general formula (2) is one of the group consisting of a styrene residue, an α-methylstyrene residue, and an isopropenyltoluene residue. [4] The resin composition according to any one of the above [1] to [3], wherein the aromatic hydrocarbon resin contains 90 mol % or more of a residue represented by the general formula (2). [5] A film comprising the resin composition according to any one of the above [1] to [4], wherein the out-of-plane retardation (Rth) represented by the following formula (a) is −700 to 0 nm.

[0021] Rth=[(nx+ny) / 2-nz]×d (a) (where nx represents the refractive index in the fast axis direction in the film plane, and ny represents the refractive index in the slow axis direction in the film plane.) nz indicates the refractive index outside the film plane, and d indicates the film thickness.) [6] The film according to [5] above, characterized in that the haze is 1.0% or less. [7] A laminated film characterized in that the film according to [5] or [6] above is adjacent to a film-forming substrate. [8] A laminated film characterized in that the film-forming substrate described in [7] above is one selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyacrylic acid ester, polymethacrylic acid ester, cellulose acetate, cellulose ether, polyimide, aliphatic cyclic polyolefin, and polynorbornene. [9] The laminated film according to the above [7] or [8], wherein the peel strength between the film and the film-forming substrate is 0.02 N or more. [Effects of the Invention]

[0022] According to the present disclosure, it is possible to provide a novel resin composition having excellent retardation properties, transparency, and adhesion to a film-forming substrate, and a film containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0023] <Resin composition> The resin composition according to one embodiment of the present disclosure is described in detail below. The resin composition according to the present disclosure comprises 80.0 to 99.9% of a fumaric acid ester polymer containing a fumaric acid diester residue represented by the general formula (1) and 0.1 to 20.0% by weight of an aromatic hydrocarbon resin having a weight-average molecular weight of 5,000 or less and containing a residue unit represented by the general formula (2).

[0024] The fumarate polymer contained in the resin composition of the present disclosure contains a fumarate diester residue represented by the following general formula (1).

[0025] [ka]

[0026] (wherein R1 and R2 each independently represent one of the group consisting of a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms). Here, R1 and R2, which are ester substituents of the fumaric acid diester residue unit in general formula (1), are each independently a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms. Examples include an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a sec-pentyl group, a tert-pentyl group, a sec-hexyl group, a tert-hexyl group, a cyclopropyl group, a cyclopentyl group, and a cyclohexyl group. Among these, when the resin composition is formed into a film, the film will have excellent heat resistance and mechanical properties, so that an ethyl group, an isopropyl group, a sec-butyl group, a tert-butyl group, a cyclopentyl group, and a cyclohexyl group are preferred, and an isopropyl group is particularly more preferred.

[0027] The fumarate ester polymer in the present disclosure may be a copolymer containing residue units other than the residue units represented by general formula (1), or may be a polymer having only residue units represented by general formula (1). Preferably, the fumarate ester polymer is a polymer having only residue units represented by general formula (1).

[0028] Specific examples of the fumaric acid diester residue unit represented by general formula (1) include dimethyl fumarate residue, diethyl fumarate residue, diisopropyl fumarate residue, di-sec-butyl fumarate residue, di-tert-butyl fumarate residue, di-n-butyl fumarate residue, isobutyl fumarate residue, dipentyl fumarate residue, diisopentyl fumarate residue, di-sec-pentyl fumarate residue, di-tert-pentyl fumarate residue, di-sec-hexyl fumarate residue, di- -tert-hexyl residue, di-sec-isoamyl fumarate residue, dineopentyl fumarate residue, di-tert-pentyl fumarate residue, di-2-ethylhexyl fumarate residue, dicyclopropyl fumarate residue, dicyclobutyl fumarate residue, dicyclopentyl fumarate residue, dicyclohexyl fumarate residue, and residues in which R1 or R2 is replaced in these residues (e.g., ethyl isopropyl fumarate residue, ethyl-sec-butyl fumarate residue, etc.). Among these, diethyl fumarate residue, diisopropyl fumarate residue, di-sec-butyl fumarate residue, di-tert-butyl fumarate residue, dicyclopentyl fumarate residue, and dicyclohexyl fumarate residue are preferred, and diethyl fumarate residue, diisopropyl fumarate residue, di-sec-butyl fumarate residue, di-tert-butyl fumarate residue, dicyclopentyl fumarate residue, and dicyclohexyl fumarate residue are particularly preferred, with diethyl fumarate residue and diisopropyl fumarate residue being more preferred. These may be used alone or in combination of two or more.

[0029] When the fumarate polymer used in the present disclosure is a copolymer, the proportion of fumarate residues represented by general formula (1) is preferably 30 mol% or more, and more preferably 50 mol% or more, more preferably 70 mol% or more, and particularly preferably 80 mol% or more, since the resulting film has excellent heat resistance and mechanical properties. Furthermore, the proportion of fumarate residues represented by general formula (1) is preferably 100 mol% or less.

[0030] Furthermore, the fumarate ester polymer constituting the resin composition of the present disclosure may contain other monomer residues as long as the residue does not deviate from the objectives of the present disclosure. Examples of the other monomer residues include one or more of: styrene residues such as styrene residue and α-methylstyrene residue; acrylic acid residues; acrylic acid ester residues such as methyl acrylate residue, ethyl acrylate residue, and butyl acrylate residue; methacrylic acid residues; methacrylic acid ester residues such as methyl methacrylate residue, ethyl methacrylate residue, and butyl methacrylate residue; vinyl ester residues such as vinyl acetate residue and vinyl propionate residue; acrylonitrile residues; methacrylonitrile residues; and olefin residues such as ethylene residue and propylene residue.

[0031] Fumarate ester polymers have particularly excellent mechanical properties and excellent processability during film formation. Therefore, they are suitable for use in polymers with a number average molecular weight (Mn) of 1×10 in terms of standard polystyrene obtained from the elution curve measured by gel permeation chromatography (GPC). 3 ~5×10 6 Preferably, it is 5×10 4 ~5×10 5 Even more preferably, 8×10 4 ~5×10 5 is.

[0032] The method for producing the fumaric acid ester-based polymer constituting the resin composition of the present disclosure is not particularly limited as long as it can produce a fumaric acid ester-based polymer, and can be produced, for example, by radical polymerization of fumaric acid esters (monomers).

[0033] The radical polymerization method used can be any known polymerization method, such as bulk polymerization, solution polymerization, suspension polymerization, precipitation polymerization, emulsion polymerization, or the like.

[0034] Examples of polymerization initiators used in radical polymerization include organic peroxides such as benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, t-butyl peroxyacetate, t-butyl peroxybenzoate, and t-butyl peroxypivalate; and azo initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-butyronitrile), 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, and 1,1'-azobis(cyclohexane-1-carbonitrile).

[0035] Solvents that can be used in the solution polymerization method, suspension polymerization method, precipitation polymerization method, and emulsion polymerization method are not particularly limited, and examples thereof include aromatic solvents such as benzene, toluene, and xylene; alcoholic solvents such as methanol, ethanol, propyl alcohol, and butyl alcohol; cyclohexane; dioxane; tetrahydrofuran (THF); acetone; methyl ethyl ketone; dimethylformamide; isopropyl acetate; water; and mixed solvents thereof.

[0036] The polymerization temperature during radical polymerization can be appropriately set depending on the decomposition temperature of the polymerization initiator, and is generally preferably in the range of 40°C or higher and 150°C or lower.

[0037] The suspension polymerization method in the present disclosure may be a known radical suspension polymerization method, and is not particularly limited as long as an aqueous medium is used. The aqueous medium is also not particularly limited, and examples thereof include water, industrial water, ion-exchanged water, and distilled water.

[0038] Dispersants that are commonly used in the suspension polymerization reaction of the present disclosure can be used, and there are no particular limitations on the dispersant, and known dispersants can be used. Examples include polyvinyl alcohol-based dispersants such as polyvinyl alcohol; cellulose-based dispersants such as methyl cellulose, ethyl cellulose, propyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, and carboxyethyl cellulose; and inorganic compounds such as calcium phosphate. Among these, cellulose-based dispersants are preferred because they provide more stable suspension polymerization, and hydroxypropyl methyl cellulose is more preferred.

[0039] The blending ratios of the aqueous medium, monomer, dispersant, and polymerization initiator in the method for producing a fumarate ester polymer of the present disclosure can be appropriately selected depending on the desired quality of the fumarate ester polymer. Among these, it is preferable to use 50 to 150 parts by weight of the monomer, 0.01 to 20 parts by weight of the dispersant, and 0.001 to 5 parts by weight of the polymerization initiator per 100 parts by weight of the aqueous medium, as this method for producing a fumarate ester polymer has better production efficiency.

[0040] The suspension polymerization reaction apparatus in the present disclosure is not particularly limited, and known apparatuses can be used, such as glass-lined (GL) or stainless steel (SUS) reaction vessels equipped with stirring blades, temperature control devices, etc. Examples of stirring blades include paddle blades, four-blade paddle blades, anchor blades, three-blade swept blades, six-blade turbine blades, and blue margin blades.

[0041] The resin composition according to the present disclosure is characterized in that, when the resin composition is formed into a film and used, it has excellent adhesion to a film-forming substrate due to the inclusion of an aromatic hydrocarbon resin containing a residue unit represented by the following general formula (2): The fumarate ester polymer used in the present disclosure has low polarity and therefore low adhesion to a film-forming substrate because it has hydrogen or an alkyl group having 1 to 12 carbon atoms in its side chain, but the inclusion of a highly polar aromatic hydrocarbon resin improves adhesion to a film-forming substrate.

[0042] [ka]

[0043] (wherein, each R3 independently represents hydrogen or an alkyl group having 1 to 12 carbon atoms, and R4 represents hydrogen or a methyl group). The fumarate ester polymer used in the present disclosure has hydrogen or an alkyl group having 1 to 12 carbon atoms in its side chain. Therefore, the aromatic hydrocarbon residue represented by general formula (2) also has hydrogen or an alkyl group having 1 to 12 carbon atoms. This improves the affinity between the fumarate ester polymer and the aromatic hydrocarbon resin, and the resin composition is mixed uniformly, making it possible to produce a film with excellent transparency.

[0044] Here, R3 in the residue unit represented by general formula (2) is hydrogen or an alkyl group having 1 to 12 carbon atoms, and examples of the alkyl group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, an s-butyl group, a t-butyl group, an isobutyl group, and an ethylhexyl group. R3 is preferably hydrogen or an alkyl group having 1 to 4 carbon atoms, and more preferably hydrogen, a methyl group, an ethyl group, an isopropyl group, or an n-propyl group, and particularly preferably hydrogen or a methyl group, because these groups provide excellent transparency and adhesion to a film-forming substrate when the resin composition is formed into a film.

[0045] R4 is hydrogen or a methyl group, and is particularly preferably a methyl group because it provides excellent transparency and adhesion to the film-forming substrate.

[0046] Specific examples of the residue unit represented by general formula (2) include a styrene residue, an α-methylstyrene residue, a vinyltoluene residue, an isopropenyltoluene residue, etc. Among these, the styrene residue, the α-methylstyrene residue, and the isopropenyltoluene residue are preferred, and the α-methylstyrene residue and the isopropenyltoluene residue are particularly preferred, as they are excellent in transparency and heat resistance and also in adhesion to the film-forming substrate.

[0047] When the aromatic hydrocarbon resin used in the present disclosure is a copolymer, the proportion of residues represented by general formula (2) is preferably 30 mol% or more, and more preferably 50 mol% or more, more preferably 90 mol% or more, and particularly preferably 100 mol% because the resulting film is excellent in transparency and heat resistance and also in adhesion to the film-forming substrate.

[0048] In addition to the residue unit represented by general formula (2), other monomer residues may be contained within the scope of the present disclosure. Examples of such other monomer residues include aromatic residues such as indene, and aliphatic residues such as isoprene and piperylene.

[0049] Examples of aromatic hydrocarbon resins include styrene homopolymer, α-methylstyrene homopolymer, vinyltoluene homopolymer, isopropenyltoluene homopolymer, styrene / α-methylstyrene copolymer, styrene / vinyltoluene copolymer, styrene / isopropenyltoluene copolymer, α-methylstyrene / vinyltoluene copolymer, α-methylstyrene / isopropenyltoluene copolymer, vinyltoluene / isopropenyltoluene copolymer, etc. Among these, styrene homopolymer, α-methylstyrene homopolymer, isopropenyltoluene homopolymer, and styrene / α-methylstyrene copolymer are preferred because of their excellent transparency and heat resistance and excellent adhesion to the film-forming substrate, and α-methylstyrene homopolymer and isopropenyltoluene homopolymer are particularly preferred.

[0050] The aromatic hydrocarbon resin has excellent adhesion to the film-forming substrate and transparency, and therefore has a weight-average molecular weight (Mw) of 5,000 or less, preferably 500 to 3,000, more preferably 800 to 2,500, and particularly preferably 900 to 2,000, in terms of standard polystyrene, obtained from an elution curve measured by gel permeation chromatography (GPC).

[0051] The resin composition of the present disclosure preferably comprises 80.0 to 99.9 wt% fumarate ester polymer and 0.1 to 20.0 wt% aromatic hydrocarbon resin, more preferably 90.0 to 99.8 wt% fumarate ester polymer and 0.2 to 10.0 wt% aromatic hydrocarbon resin, still more preferably 91.5 to 99.5 wt% fumarate ester polymer and 0.5 to 8.5 wt% aromatic hydrocarbon resin, and particularly preferably 94.5 to 99.5 wt% fumarate ester polymer and 0.5 to 5.0 wt% aromatic hydrocarbon resin, in order to achieve excellent retardation properties, transparency, and adhesion to the film-forming substrate.

[0052] These aromatic hydrocarbon resins may be used alone or in combination of two or more.

[0053] The resin composition may contain an antioxidant to improve thermal stability, such as a hindered phenol-based antioxidant, a phosphorus-based antioxidant, a sulfur-based antioxidant, a lactone-based antioxidant, an amine-based antioxidant, a hydroxylamine-based antioxidant, a vitamin E-based antioxidant, or other antioxidants, and these antioxidants may be used alone or in combination of two or more.

[0054] The resin composition may contain a hindered amine light stabilizer or an ultraviolet absorber to enhance weather resistance, such as benzotriazole, benzophenone, triazine, or benzoate.

[0055] The resin composition may contain other polymers, surfactants, polymer electrolytes, conductive complexes, pigments, dyes, antistatic agents, antiblocking agents, lubricants, etc., within the scope of the invention.

[0056] The resin composition of the present disclosure can be produced by mixing the fumaric acid ester polymer and the aromatic hydrocarbon resin. <Film> The film, which is one embodiment of the present disclosure, will be described in detail below.

[0057] The resin composition of the present disclosure can be suitably used as a film for optical components. In particular, when the resin composition of the present disclosure contains an aromatic hydrocarbon resin and is used as a laminated film in which the film and the film-forming substrate are adjacent to each other, the film has excellent adhesion to the film-forming substrate, and can be transported at high speed with the film attached to the film-forming substrate.

[0058] In the film of the present disclosure, the out-of-plane retardation (Rth) measured at a wavelength of 589 nm and represented by the following formula (a) is −700 to 0 nm, preferably −240 to −20 nm, and particularly preferably −160 to −60 nm, in order to provide a film with excellent viewing angle characteristics. In this specification, the out-of-plane retardation of the film is a value measured by the measurement method in the examples described later.

[0059] Rth = [(nx + ny) / 2 - nz] × d (a) (In the formula, nx is the refractive index in the fast axis direction in the film plane, ny is the refractive index in the slow axis direction in the film plane, nz is the refractive index in the perpendicular direction outside the film plane, and d is the film thickness.) In terms of adaptability to thinner optical members, the thickness of the film is preferably 80.0 μm or less, more preferably 0.1 to 50.0 μm, and particularly preferably 0.1 to 35.0 μm.

[0060] The resin composition of the present disclosure uses an aromatic hydrocarbon resin having a specific weight average molecular weight and a specific residue unit for the fumaric acid ester polymer used in the present disclosure, By uniformly mixing the resin composition, a film with excellent transparency and low haze can be obtained.

[0061] The haze of the film is preferably 1.0% or less, more preferably less than 0.5%, more preferably 0.4% or less, even more preferably 0.3% or less, and particularly preferably 0.2% or less. By controlling the haze within the above range, a high-contrast image can be obtained when the film is incorporated into a display device. In this specification, the haze is a value measured by the measurement method in the Examples described below.

[0062] The method for producing the film is not particularly limited, and for example, the film can be produced by forming a raw material fumaric acid ester polymer into a long film by a method such as solution casting.

[0063] Here, the solution casting method is a method in which a fumaric acid ester polymer solution (resin solution) is cast onto a supporting substrate, and then the solvent is evaporated by heating and drying, and the film is peeled off from the substrate to obtain a film.

[0064] Examples of the film-forming substrate include polymer substrates made of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polycarbonates, polystyrene, polyethylene, polypropylene, polyacrylic acid esters, polymethacrylic acid esters, polyvinyl chloride and polyvinylidene chloride, cellulose acetate, cellulose ethers, and other celluloses, polyvinyl alcohol, polyamides, polyimides, polyarylates, polysulfones, polyethersulfones, polyetherketones, phenolic resins, epoxy resins, alicyclic polyolefins, and thermoplastic transparent resins such as polynorbornene; glass substrates such as glass plates and quartz substrates; metal substrates such as aluminum, stainless steel, and ferrotypes; and inorganic substrates such as ceramic substrates. Preferred substrates include polyethylene terephthalate, polyethylene naphthalate, polycarbonates, polyacrylic acid esters, polymethacrylic acid esters, cellulose acetate, cellulose ethers, polyimides, alicyclic polyolefins, and polynorbornene. More preferred are polyethylene terephthalate, polyethylene naphthalate, polyimides, polyacrylic acid esters, polymethacrylic acid esters, and alicyclic polyolefins. Particularly preferred are polyethylene terephthalate, polyacrylic acid ester, polymethacrylic acid ester, polyimide, and aliphatic cyclic polyolefin.

[0065] For a laminated film in which a film made of the resin composition of the present disclosure and a film-forming substrate are adjacent to each other, high adhesion between the film and the film-forming substrate allows for high-speed transport. Therefore, the peel strength between the film and the film-forming substrate is preferably 0.020 N or more, more preferably 0.022 N or more and 1.0 N or less, and particularly preferably 0.24 N or more and 0.5 N or less.

[0066] In this specification, the peel strength is a value measured by the measurement method in the examples described later.

[0067] The solvent used for the resin solution in the solution casting method may be any solvent that can dissolve the fumaric acid ester polymer, etc., and the boiling point of the solvent is preferably 200°C or lower, more preferably 170°C or lower, so that residual solvent is less likely to remain when the film is obtained.

[0068] Examples of the solvent include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, and dichlorobenzene; phenols such as phenol and chlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, mesitylene, and dimethoxybenzene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone, 2-pyrrolidone, and N-methyl-2-pyrrolidone; and esters such as ethyl acetate and butyl acetate. alcohol-based solvents such as t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, and 2-methyl-2,4-pentanediol; amide-based solvents such as dimethylformamide and dimethylacetamide; nitrile-based solvents such as acetonitrile and butyronitrile; ether-based solvents such as diethyl ether, dibutyl ether, and tetrahydrofuran; and solvents obtained by using carbon disulfide, ethyl cellosolve, butyl cellosolve, and the like, either alone or in combination.

[0069] The viscosity of the resin solution can be adjusted by the molecular weight and concentration of each component and the type of solvent. There are no particular restrictions on the viscosity of the resin solution, but to facilitate film casting, it is preferably 100 to 30,000 cps, more preferably 300 to 20,000 cps, and particularly preferably 300 to 15,000 cps.

[0070] In the present disclosure, the concentration of the fumaric acid ester polymer in the resin solution is not particularly limited as long as dissolution and film formation are possible. The dissolution may be carried out so that the desired concentration is achieved during dissolution, or a low-concentration solution may be prepared in advance and then adjusted to a desired high-concentration solution by a concentration process. Furthermore, a high-concentration resin solution may be prepared in advance, and then various additives may be added to obtain a desired low-concentration resin solution.

[0071] The casting method is not particularly limited, and a common method can be used, such as a T-die method, a doctor blade method, a bar coater method, a slot die method, a lip coater method, a reverse gravure coating method, a microgravure coating method, a spin coating method, a brush coating method, a roll coating method, or a flexographic printing method.

[0072] The drying method in the drying step is not particularly limited, and any ordinary heating means can be used, such as a hot air blower, a heating roll, or a far-infrared heater.

[0073] The drying temperature is preferably 30 to 200° C., and particularly preferably 40 to 160° C. The drying temperature may be a single-stage condition, or in order to maintain the appearance or shorten the drying time, multi-stage drying may be used in which the first stage is dried at a low temperature and the second and subsequent stages are dried at a high temperature.

[0074] The film peeling speed in the substrate peeling step is preferably in the range of 0.1 to 30 m / min, for example, and more preferably in the range of 1 to 30 m / min, in view of productivity, mechanical precision, stability, etc.

[0075] The film of the present disclosure can also be a stretched film. By stretching the film of the present disclosure, it is possible to control the retardation.

[0076] The in-plane retardation (Re) of the stretched film measured at 589 nm and represented by the following formula (b) is preferably 0 to 400 nm, more preferably 5 to 350 nm, even more preferably 30 to 300 nm, and particularly preferably 60 to 230 nm, since the film has excellent viewing angle characteristics such as low black brightness and high contrast. In this specification, the in-plane retardation of the film is a value measured, for example, by the measurement method in the examples described later.

[0077] Re=(ny-nx)×d (b) (In the formula, nx represents the refractive index in the fast axis direction in the film plane, ny represents the refractive index in the slow axis direction in the film plane, and d represents the thickness of the film.) In terms of suitability for thin optical components, the thickness of the stretched film is preferably 80.0 μm or less, more preferably 0.1 to 50.0 μm, even more preferably 0.1 to 40.0 μm, and particularly preferably 0.1 to 25.0 μm.

[0078] The stretching method can be, for example, a uniaxial stretching method or a biaxial stretching method, since it allows for phase difference control. Examples of the uniaxial stretching method include a longitudinal uniaxial stretching method in which stretching is performed between rolls and a transverse axial stretching method in which stretching is performed using a tenter. Examples of the biaxial stretching method include a method in which stretching is performed using a tenter and a method in which the film is expanded into a tubular shape and stretched.

[0079] The temperature during stretching is preferably 90 to 300°C, particularly preferably 105 to 250°C, since this makes it difficult for thickness unevenness to occur and results in a film with excellent mechanical and optical properties.

[0080] The stretching ratio of the film (hereinafter referred to as "stretching ratio") is preferably 1.05 to 4.0 times, more preferably 1.05 to 3.5 times, and particularly preferably 1.1 to 3.0 times, so that the resulting film is thin and exhibits good retardation properties.

[0081] The thickness of the film to be subjected to the stretching step is preferably 5 to 200 μm, more preferably 5 to 150 μm, and particularly preferably 5 to 100 μm, from the viewpoint of ease of stretching treatment and suitability for thinning the film.

[0082] In this way, by adjusting the stretching temperature and stretching ratio, the in-plane retardation of the resulting film can be controlled.

[0083] The film transport speed in the stretching step is preferably in the range of 0.5 to 30 m / min, for example, from the viewpoint of mechanical precision, stability, etc., and more preferably in the range of 1 to 20 m / min.

[0084] In the present disclosure, a shrinking step may be performed after the stretching to shrink the obtained film. Specifically, the stretched film is shrunk in the direction opposite to the stretching direction. This can relieve residual stress accumulated in the stretched film, and the obtained film will still exhibit a high retardation even after a long period of time has passed.

[0085] The film can be further laminated with a film containing other resins as needed. Examples of other resins include polyethersulfone, polyarylate, polyethylene terephthalate, polynaphthalene terephthalate, polycarbonate, cyclic polyolefin, maleimide resin, fluorine-based resin, polyimide, etc. It is also possible to laminate a liquid crystal layer, a hard coat layer, a gas barrier layer, or a layer with a controlled refractive index (low reflection layer).

[0086] The film of the present disclosure has excellent heat resistance and optical properties, and is suitable for use as a retardation film in applications such as liquid crystal displays and organic EL displays.

[0087] Furthermore, by disposing the film of the present disclosure on at least one surface of a polarizer, a polarizing plate with excellent heat resistance and optical properties can be obtained, and the polarizing plate is suitably used as a polarizing plate for liquid crystal displays or an anti-reflection polarizing plate. [Example]

[0088] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the reagents used were commercially available products.

[0089] The physical properties shown in the examples were measured by the following methods.

[0090] <Measurement of number average molecular weight and weight average molecular weight> A gel permeation chromatography (GPC) system (Tosoh Corporation, product name: HLC-8320GPC) was used, and the column was a Tosoh Corporation TSKgel Super HM- Two columns of H were used, the column temperature was set at 40°C, and measurements were carried out at 40°C using tetrahydrofuran as a solvent, and the values ​​were calculated in terms of standard polystyrene.

[0091] <Analysis of fumaric acid ester polymers> The structure of the fumarate ester polymer was analyzed using a nuclear magnetic resonance spectrometer (manufactured by JEOL Ltd., product name: JNM-ECZ400 / L1) and proton nuclear magnetic resonance spectroscopy ( 1 The values ​​were determined by H-NMR spectroscopy.

[0092] <Haze measurement> The haze of the prepared film was measured using a spectroscopic haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., trade name: SH7000) in accordance with JIS-K 7136 (2000 edition). <Measurement of phase difference characteristics (Rth)> The out-of-plane retardation Rth shown in formula (a) was measured at a wavelength of 589 nm using a polarized retardation measurement system (manufactured by Axometrics, trade name: AxoScan). <Thickness measurement> The film thickness was measured using a high-resolution linear gauge sensor (manufactured by Ono Sokki, product name: GS-3813B). <Peel strength measurement> A film (resin composition) formed on a 50 μm polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray) was cut into a rectangular shape measuring 25 mm wide and 250 mm long, along with the substrate, using a cutter to create a test specimen. The cut test specimen was gripped 50 mm from the edge of the film in the longitudinal direction and peeled away from the substrate by hand, taking care not to scratch the surface. Using a Tensilon universal material testing machine (manufactured by Orientec, product name: RTG-1210), the substrate side of the end of the test specimen from which the film was peeled was clamped between the lower chuck and the film side between the upper chuck, and the peel strength was measured using a T-peel test. The ambient temperature was set at 23°C and the peel rate was set at 100 mm / min. The peel strength was measured when the initial 50 mm length of film that had not peeled from the substrate was peeled away, and the average peel strength was calculated.

[0093] Synthesis Example 1 A 1-liter reactor equipped with a stirrer, condenser, nitrogen inlet, and thermometer was charged with 600 g of distilled water, 3.4 g of hydroxypropyl methylcellulose (Shin-Etsu Chemical Co., Ltd., trade name: Metrose 60SH-50) as a dispersant, 350.9 g of diisopropyl fumarate, 49.1 g of diethyl fumarate (14.0 parts by weight per 100 parts by weight of diisopropyl fumarate), and 8.3 g of polymerization initiator t-butyl peroxypivalate. After nitrogen bubbling for 1 hour, the mixture was stirred at 400 rpm and maintained at 50°C for 28 hours to carry out radical suspension polymerization. After completion of the polymerization reaction, the contents were recovered from the reactor, and the polymer was filtered, washed twice with distilled water and twice with methanol, and then dried under reduced pressure at 80°C (yield: 75%).

[0094] The number average molecular weight of the resulting fumaric acid ester polymer was 138,000. 1 H-NMR analysis confirmed that the fumarate polymer was a copolymer of diisopropyl fumarate and diethyl fumarate with a molar ratio of diisopropyl fumarate residues to diethyl fumarate residues of 86.7 / 13.3.

[0095] Example 1 9.9 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.1 g of isopropenyl toluene homopolymer (Mw = 1035) were dissolved in a methyl ethyl ketone-toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0096] Example 2 9.7 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.3 g of isopropenyl toluene homopolymer (Mw = 1035) were dissolved in a methyl ethyl ketone-toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0097] Example 3 9.6 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.4 g of isopropenyl toluene homopolymer (Mw = 1035) were dissolved in a methyl ethyl ketone-toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0098] Example 4 9.2 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.8 g of isopropenyl toluene homopolymer (Mw = 1035) were dissolved in a methyl ethyl ketone-toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0099] Example 5 9.7 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.3 g of isopropenyl toluene homopolymer (Mw = 1671) were dissolved in a methyl ethyl ketone-toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0100] Example 6 9.9 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.1 g of α-methylstyrene homopolymer (Mw=1406) were dissolved in a methyl ethyl ketone / toluene mixed solution (methyl ethyl ketone / toluene=60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0101] Example 7 9.7 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.3 g of α-methylstyrene homopolymer (Mw = 1966) were dissolved in a methyl ethyl ketone / toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0102] Example 8 9.7 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.3 g of a styrene homopolymer (Mw=1010) were dissolved in a methyl ethyl ketone / toluene mixed solution (methyl ethyl ketone / toluene=60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0103] Example 9 9.7 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.3 g of a styrene homopolymer (Mw = 2420) were dissolved in a methyl ethyl ketone-toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film exhibited excellent adhesion to the substrate and was suitable as an optical film.

[0104] Comparative Example 1 10.0 g of the fumarate ester polymer obtained in Synthesis Example 1 was dissolved in a methyl ethyl ketone / toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The peel strength of the film formed on the polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) was evaluated. Furthermore, a fumarate ester resin film formed in the same manner was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. Because the obtained film did not contain an aromatic hydrocarbon resin, it had low peel strength and did not have the desired adhesion to the substrate.

[0105] Comparative Example 2 9.7 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.3 g of a styrene homopolymer (Mw = 5390) were dissolved in a methyl ethyl ketone-toluene mixed solution (methyl ethyl ketone / toluene = 60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The formed fumarate ester resin film was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The resulting film had a high haze due to the high Mw of the styrene homopolymer, and did not have the desired optical properties.

[0106] Comparative Example 3 9.7 g of the fumarate ester polymer obtained in Synthesis Example 1 and 0.3 g of p-hydroxystyrene homopolymer (Mw=11,000) were dissolved in a methyl ethyl ketone / toluene mixed solution (methyl ethyl ketone / toluene=60 wt% / 40 wt%) to prepare an 18 wt% resin solution. The solution was applied to a polyethylene terephthalate substrate (Lumirror T60, manufactured by Toray Industries, Inc.) using a coater and dried in three stages at temperatures of 50°C, 80°C, and 140°C to form a film. The formed fumarate ester resin film was peeled from the substrate, and the film thickness, retardation properties, and haze of the film alone were measured. The results are also shown in Table 1. The obtained film had a high haze due to the use of p-hydroxystyrene homopolymer, and did not have the desired optical properties.

[0107] [Table 1]

Claims

1. A resin composition comprising 80.0 to 99.9% by weight of a fumarate polymer containing a fumarate diester residue represented by the following general formula (1), and 0.1 to 20.0% by weight of an aromatic hydrocarbon resin having a weight-average molecular weight of 5,000 or less and containing a residue unit represented by the following general formula (2): 【Chemistry 1】 (In the formula, R １ and R ２ each independently represents one of the group consisting of a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms. 【Chemistry 2】 (In the formula, R ３ each independently represents hydrogen or an alkyl group having 1 to 12 carbon atoms; R ４ indicates hydrogen or a methyl group)

2. The fumaric acid diester residue represented by the general formula (1) is a dimethyl fumarate residue, a diethyl fumarate residue, a diisopropyl fumarate residue, a di-tert-butyl fumarate residue, a di-n-butyl fumarate residue, a di-sec-butyl fumarate residue, an isobutyl fumarate residue, a dipentyl fumarate residue, a diisopentyl fumarate residue, a di-sec-pentyl fumarate residue, a di-tert-pentyl fumarate residue, a di-sec-hexyl fumarate residue, The resin composition according to claim 1, characterized in that the fumarate diester residue is at least one selected from the group consisting of di-tert-hexyl fumarate residue, di-sec-isoamyl fumarate residue, dineopentyl fumarate residue, di-tert-pentyl fumarate residue, di-2-ethylhexyl fumarate residue, dicyclopropyl fumarate residue, dicyclobutyl fumarate residue, dicyclopentyl fumarate residue, and dicyclohexyl fumarate residue.

3. 2. The resin composition according to claim 1, wherein the residue unit represented by the general formula (2) is one of the group consisting of a styrene residue, an α-methylstyrene residue, and an isopropenyltoluene residue.

4. 2. The resin composition according to claim 1, wherein the aromatic hydrocarbon resin contains 90 mol % or more of the residue unit represented by the general formula (2).

5. A film comprising the resin composition according to any one of claims 1 to 4, having an out-of-plane retardation (Rth) represented by the following formula (a) of -700 to 0 nm: Rth=[(nx+ny) / 2-nz]×d (a) (wherein nx represents the refractive index in the fast axis direction in the film plane, and ny represents the refractive index in the slow axis direction in the film plane) direction, nz indicates the refractive index outside the film plane, and d indicates the film thickness.

6. 6. The film of claim 5, having a haze of 1.0% or less.

7. A laminated film, comprising the film according to claim 6 and a film-forming substrate adjacent to each other.

8. 8. A laminated film characterized in that the film-forming substrate according to claim 7 is one of the group consisting of polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyacrylic acid ester, polymethacrylic acid ester, cellulose acetate, cellulose ether, polyimide, aliphatic cyclic polyolefin, and polynorbornene.

9. 9. The laminated film according to claim 8, wherein the peel strength between the film and the film-forming substrate is 0.02 N or more.

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