Resin film for optical film and method for producing resin film for optical film

Abstract

Disclosed is a resin film for an optical film, the resin film containing a (meth)acrylate ester polymer and a carboxylic acid amide compound having an aromatic ring. The carboxylic acid amide compound is contained in an amount of 1,000 ppm to 11,000 ppm inclusive with respect to the (meth)acrylate ester polymer, the carboxylic acid amide compound is contained as a crystal, and the crystal has a negative birefringence. Also disclosed is a method for producing a resin film for an optical film, the method comprising: a step in which a (meth)acrylate ester polymer and a carboxylic acid amide compound having an aromatic ring, the carboxylic acid amide compound being in an amount of 1,000 ppm to 11,000 ppm inclusive with respect to the (meth)acrylate ester polymer, are mixed and heated to a temperature equal to or higher than the softening temperature of the (meth)acrylate ester polymer and equal to or lower than the decomposition temperature of the (meth)acrylate ester polymer so as to be molded; and a step in which a film is formed by cooling.

Description

Resin film for optical film and method for producing resin film for optical film

[0001] The present invention relates to a resin film for optical films and a method for manufacturing a resin film for optical films. This application claims priority to Japanese Patent Application No. 2023-130926, filed on August 10, 2023, and the entire contents of said Japanese Patent Application are incorporated by reference.

[0002] Acrylic acid-based resin films having characteristic optical properties are known. For example, Patent Document 1 discloses a resin film for optical films, which is composed of a methacrylic acid ester-based polymer and a diacetal compound having a specific structure. The resin film disclosed in Patent Document 1 is characterized by no dispersion defects and small birefringence.

[0003] Patent Document 2 discloses a substrate for a surface protective film for protecting the surface of an image display device. The substrate for a surface protective film disclosed in Patent Document 2 is characterized by having a retardation property within a specific range. It is disclosed that the specific composition of this film substrate includes at least one resin selected from polycarbonate, polyester, cycloolefin resin, acrylic resin, and cellulose resin. It is also disclosed that the film substrate may include a resin having an alicyclic structure or an aromatic ring structure exhibiting negative intrinsic birefringence.

[0004] JP 2010-254370 A

[0005] An object of the present invention is to provide an optical film that exhibits negative birefringence and has high transparency, and a method for producing the same.

[0006] The resin film for optical film according to the present disclosure contains a (meth)acrylic acid ester-based polymer and a carboxylic acid amide compound having an aromatic ring. The carboxylic acid amide compound is contained in an amount of 1,000 ppm to 11,000 ppm relative to the (meth)acrylic acid ester-based polymer. The carboxylic acid amide compound is contained as crystals, and the crystals exhibit negative birefringence.

[0007] According to the resin film according to the present disclosure, an optical film that exhibits negative birefringence and has high transparency is provided.

[0008] FIG. 1 is a polarizing microscope photograph showing crystals of an optical adjuster contained in a resin film according to the present disclosure.

[0009] [Outline of the embodiment] First, embodiments of the resin film for optical film and the manufacturing method thereof according to the present disclosure will be listed and described. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less."

[0010] The resin film for optical film according to the present disclosure contains a (meth)acrylic acid ester-based polymer and a carboxylic acid amide compound having an aromatic ring. The carboxylic acid amide compound is contained in an amount of 1,000 ppm to 11,000 ppm relative to the (meth)acrylic acid ester-based polymer. The carboxylic acid amide compound is contained as crystals, and the crystals exhibit negative birefringence.

[0011] Many proposals have been made for resin films with adjusted optical properties. For example, Patent Document 1 proposes a resin film for optical film containing a specific acetal compound and having low birefringence. Also, Patent Document 2 proposes a film in which a chemical structure that is thought to exhibit negative birefringence is incorporated into the side chain of the resin constituting the film.

[0012] The resin film for optical film according to the present disclosure contains a (meth)acrylic acid ester polymer containing a carboxylic acid amide compound having a specific structure. The carboxylic acid amide compound exists as crystals in the film, and the crystals exhibit negative birefringence. The resin film for optical film according to the present disclosure can be formed into a film containing an optical adjuster at any content within a wide range of 1,000 ppm to 11,000 ppm relative to the base resin constituting the film, and this film exhibits remarkable optical properties. At the same time, the resin film for optical film according to the present disclosure is a film with sufficient transparency and has characteristic functions as a resin film for optical film.

[0013] In the resin film for optical films, the carboxylic acid amide compound may be contained in an amount of 2000 ppm to 10000 ppm relative to the (meth)acrylic acid ester-based polymer. When the content of the carboxylic acid amide compound is in this range, the effects of the resin film for optical films according to the present disclosure become more pronounced.

[0014] The resin film for optical films according to the present disclosure may have a haze value of 7.0 or less when the film is 0.1 mm thick. Even when the film is as thick as 0.1 mm and has sufficient strength, the film maintains its transparency and exhibits negative birefringence due to the precipitation of crystals in the film.

[0015] In the resin film for optical films, the carboxylic acid amide compound may be a carboxylic acid amide compound having an aromatic ring and an aliphatic ring, which exhibits negative birefringence and precipitates as crystals in a film produced by a general method.

[0016] In the resin film for optical film, the carboxylic acid amide compound may be a carboxylic acid amide compound having a structure in which a polycarboxylic acid having either a benzene ring or a naphthalene ring is condensed with an amide compound having an aliphatic ring. It has been found in the present disclosure that the carboxylic acid amide compound having such a structure exhibits negative birefringence and functions as an optical adjuster, and precipitates as crystals in a (meth)acrylic acid ester-based resin film.

[0017] The method for producing a resin film for an optical film according to the present disclosure includes the steps of: mixing a (meth)acrylic acid ester polymer with a carboxylic acid amide compound having an aromatic ring in an amount of 1,000 ppm to 11,000 ppm relative to the (meth)acrylic acid ester polymer; heating the mixture to a temperature above the softening temperature of the (meth)acrylic acid ester polymer and below its decomposition temperature; and cooling the mixture to form a film. This production method allows for the production of a resin film containing a high content of an optical adjuster, in which the optical adjuster precipitates as crystals in the film, exhibiting negative birefringence, using a commonly used method.

[0018] In the method for producing a resin film for an optical film, the carboxylic acid amide compound may be a carboxylic acid amide compound having a structure in which a polycarboxylic acid having either a benzene ring or a naphthalene ring is condensed with an amide compound having an aliphatic ring. By using a resin film containing such a carboxylic acid amide compound, the effects of the present disclosure can be more reliably obtained.

[0019] The resin film according to the present disclosure will be described in more detail below. In this specification, the term "(meth)acrylic acid ester" collectively refers to both acrylic acid ester and methacrylic acid ester.

[0020] (Resin) The resin film according to the present disclosure contains, as a base resin constituting the film, a (meth)acrylic acid ester-based polymer, that is, at least one selected from an acrylic acid ester-based polymer and a methacrylic acid ester-based polymer.

[0021] When the resin that forms the base of the resin film is a methacrylic acid ester polymer, i.e., a methacrylic acid ester resin, a suitable methacrylic acid ester resin is a polymer containing methacrylic acid ester as the main component. Here, "containing methacrylic acid ester as the main component" as used herein means that the content of methacrylic acid ester in the raw material monomers of the methacrylic acid ester polymer is 50% by mass or more. From the viewpoint of improving the heat resistance and transparency of the methacrylic acid ester polymer, the content of methacrylic acid ester in the raw material monomers of the methacrylic acid ester polymer is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more.

[0022] Representative examples of polymers containing methacrylic acid ester as a main component include methacrylic acid ester homopolymers and methacrylic acid ester copolymers which contain methacrylic acid ester and other monomers and are obtained by polymerizing raw material monomers containing methacrylic acid ester as a main component.

[0023] Methacrylic acid ester monomers suitable for constituting polymers containing methacrylic acid esters as the main component, from the viewpoint of improving fluidity and thermal decomposition resistance during heat melting, include, for example, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, tridecyl methacrylate, stearyl methacrylate, and other methacrylic acid alkyl esters in which the alkyl group in the ester moiety has 1 to 18 carbon atoms; cyclohexyl methacrylate, phenyl methacrylate, and the like. These may be used alone or in combination of two or more. These methacrylic acid esters have excellent fluidity and thermal decomposition resistance during heat melting.

[0024] Among the methacrylic acid esters, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, tridecyl methacrylate, and stearyl methacrylate are preferred because of their easy availability. Furthermore, from the viewpoint of heat resistance, methacrylic acid alkyl esters in which the alkyl group in the ester moiety has 1 to 4 carbon atoms are more preferred, and methyl methacrylate is even more preferred.

[0025] In the case of a methacrylic acid ester homopolymer, one of the above methacrylic acid esters is used as a raw material monomer. When two or more methacrylic acid esters are used as raw material monomers, the methacrylic acid ester-based polymer becomes a methacrylic acid ester copolymer.

[0026] Examples of methacrylic acid ester copolymers obtained by polymerizing a raw material monomer containing a methacrylic acid ester and another monomer and having a methacrylic acid ester as the main component include copolymers obtained by polymerizing a raw material monomer containing one or more of the above methacrylic acid esters and another monomer and having a methacrylic acid ester as the main component. The methacrylic acid ester copolymer may be a random copolymer or a block copolymer. The methacrylic acid ester copolymer obtained by polymerizing a raw material monomer having a methacrylic acid ester as the main component is usually a random copolymer, and this random copolymer is easily available commercially.

[0027] Examples of the other monomers include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, dodecyl acrylate, and stearyl acrylate; hydroxyl group-containing alkyl acrylates such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate; other acrylic esters such as cyclohexyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, trifluoromethyl acrylate, trifluoroethyl acrylate, pentafluoroethyl acrylate, glycidyl acrylate, allyl acrylate, phenyl acrylate, toluyl acrylate, benzyl acrylate, isobornyl acrylate, and 3-dimethylaminoethyl acrylate; unsaturated monocarboxylic acids such as methacrylic acid and acrylic acid; acrylic acid; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; aromatic vinyl compounds such as styrene, α-methylstyrene, p-methylstyrene, p-methoxystyrene, divinylbenzene and vinylnaphthalene; unsaturated dicarboxylic acid compounds or derivatives thereof such as maleic anhydride, maleic acid, maleic acid monoesters, maleic acid diesters, fumaric acid, fumaric acid monoesters and fumaric acid diesters; maleimide compounds such as maleimide, methylmaleimide, ethylmaleimide, propylmaleimide, butylmaleimide, hexylmaleimide, octylmaleimide, dodecylmaleimide, stearylmaleimide, phenylmaleimide and cyclohexylmaleimide; conjugated diene compounds such as butadiene and isoprene; halogen-containing unsaturated compounds such as vinyl chloride, vinylidene chloride, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride and chloroprene; silicon-containing unsaturated compounds such as vinyltrimethoxysilane and vinyltriethoxysilane, but are not limited to these. These other monomers can be used alone or in combination of two or more.

[0028] Among the other monomers, from the viewpoint of heat resistance, alkyl acrylates and vinyl cyanide compounds are preferred, and alkyl acrylates in which the alkyl group in the ester moiety has 1 to 4 carbon atoms, acrylonitrile, and methacrylonitrile are more preferred.

[0029] The content of the other monomers in the raw material monomers of the methacrylic acid ester polymer is 50% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of improving the heat resistance and transparency of the methacrylic acid ester copolymer.

[0030] In the resin film for optical film according to the present disclosure, it is preferable to use a methacrylic acid ester polymer containing methyl methacrylate as the main component as the raw material monomer, from the viewpoint of heat resistance and transparency.

[0031] When the resin used as the base of the resin film is an acrylic acid ester polymer, i.e., an acrylic acid ester resin, suitable acrylic acid ester resins include polymers containing acrylic acid ester as the main component, such as isobutyl acrylate polymers, 2-ethylhexyl acrylate polymers, isodecyl acrylate polymers, nonyl acrylate polymers, and dodecyl acrylate polymers.

[0032] The (meth)acrylic acid ester polymer serving as the substrate of the resin film according to the present disclosure may be a copolymer of an acrylic acid ester monomer and a methacrylic acid ester monomer. Examples of such copolymers include methyl methacrylate-(meth)acrylic acid copolymer, methyl methacrylate-(meth)acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymer, and methyl (meth)acrylate-styrene copolymer. These polymers may be modified to introduce glutarimide structural units or lactone ring structural units.

[0033] The melt flow rate (230°C, 37.3N) of the (meth)acrylic acid ester polymer used in the resin film for optical film according to the present disclosure is not particularly limited, but is preferably 0.5 g / 10 min or more, more preferably 1.5 g / 10 min or more, from the viewpoint of increasing the fluidity of the (meth)acrylic acid ester polymer when heated and melted. From the viewpoint of increasing the mechanical strength of the methacrylic acid ester polymer, it is preferably 30 g / 10 min or less, more preferably 25 g / 10 min or less.

[0034] The weight-average molecular weight (Mw) of the (meth)acrylic acid ester polymer used in the resin film for optical film according to the present disclosure is preferably 40,000 to 200,000, more preferably 50,000 to 180,000, and even more preferably 55,000 to 160,000. An Mw of 40,000 or more improves the strength and toughness of the resin film. An Mw of 200,000 or less improves the fluidity of the (meth)acrylic acid ester polymer, improving moldability. The weight-average molecular weight (Mw) is a value calculated by converting a chromatogram measured by gel permeation chromatography (GPC) into the molecular weight of standard polystyrene.

[0035] The acid value of the (meth)acrylic ester polymer used in the resin film according to the present disclosure is preferably 0.01 to 0.30 mmol / g, more preferably 0.05 to 0.28 mmol / g. The acid value is a value proportional to the content of carboxylic acid units and carboxylic anhydride units in the (meth)acrylic ester polymer. The acid value can be measured, for example, by dissolving the resin to be measured in a mixed solvent of xylene and 2-propanol, followed by titration with a 0.1 mol / L potassium hydroxide-ethanol solution by potentiometric titration, with the inflection point on the titration curve being the endpoint. When the acid value is within the above range, an excellent balance between fluidity and film formability is achieved.

[0036] The resin film according to the present disclosure may contain, as the resin constituting the film substrate, one or more polymers other than the (meth)acrylic acid ester polymer, in addition to the (meth)acrylic acid ester polymer described above, within a range that does not impair the object of the present invention. Examples of other polymers include polyolefin resins such as polyethylene and polypropylene, cycloolefin resins, styrene resins such as polystyrene and styrene-acrylonitrile copolymers, thermoplastic resins such as polyamide, polyphenylene sulfide resin, polyether ether ketone resin, polyester resin, polycarbonate resin, polysulfone, polyphenylene oxide, polyimide, polyetherimide, and polyacetal, and thermosetting resins such as phenolic resin, melamine resin, silicone resin, and epoxy resin.

[0037] The resin constituting the film substrate in the resin film according to the present disclosure may have a mass ratio of (meth)acrylic acid ester polymer to the entire resin of 50% or more, preferably 60% or more, and more preferably 100%. That is, the resin constituting the film substrate in the resin film according to the present disclosure is preferably composed of a (meth)acrylic acid ester polymer.

[0038] (Optical Adjusting Agent) The resin film for optical film according to the present disclosure is characterized by containing a carboxylic acid amide compound having an aromatic ring. This carboxylic acid amide compound functions as an optical adjusting agent that adjusts the optical properties of the film. According to the present disclosure, by containing a carboxylic acid amide compound with a specific structure, crystals exhibiting negative birefringence are precipitated in the film, and a transparent (meth)acrylic acid ester-based resin film is obtained.

[0039] The carboxylic acid amide compound having an aromatic ring is typically a compound obtained by condensation of a polycarboxylic acid having an aromatic ring with an amine, and may be a carboxylic acid amide compound having a benzene ring or a naphthalene ring. The optical adjuster used in the present disclosure has negative intrinsic birefringence and exists as a crystal in the resin film, thereby exhibiting negative birefringence.

[0040] The aromatic ring of the carboxylic acid amide compound having an aromatic ring may be monocyclic or polycyclic, and examples thereof include a benzene ring, a naphthalene ring, a biphenyl ring, an anthracene ring, and a pyrene ring. Examples of carboxylic acids having an aromatic ring include dicarboxylic acids having either a benzene ring or a naphthalene ring, and tricarboxylic acids having either a benzene ring or a naphthalene ring. Typical examples of carboxylic acid amide compounds include condensates of polycarboxylic acids having either a benzene ring or a naphthalene ring and amides having an aliphatic ring. The carboxylic acid amide compound may be a condensate of dicarboxylic acid or tricarboxylic acid having a benzene ring and amides having an aliphatic ring, or a condensate of dicarboxylic acid or tricarboxylic acid having a naphthalene ring and amides having an aliphatic ring.

[0041] Specific examples of carboxylic acids that serve as raw materials for the carboxylic acid amide compounds used in the resin films according to the present disclosure include phthalic acid, isophthalic acid, 5-tert-butylisophthalic acid, terephthalic acid, pyromellitic acid, trimellitic acid, p-phenylenediacetic acid, 4,4'-biphenyldicarboxylic acid, 2,2'-biphenyldicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, trimesic acid, etc. Of these, 2,6-naphthalenedicarboxylic acid and trimesic acid are preferred.

[0042] The amine used as a raw material for the carboxylic acid amide compound used in the resin film according to the present disclosure is preferably an amine having an aliphatic ring. The aliphatic ring may be a saturated aliphatic ring or an unsaturated aliphatic ring, and is preferably a saturated aliphatic ring. Examples of groups containing a saturated aliphatic ring include cycloalkyl groups such as cyclohexyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl, and amines having these cycloalkyl groups can be used. Examples of groups containing an unsaturated aliphatic ring include cycloalkenyl groups such as cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, cyclooctenyl, and cyclopentadienyl, and amines having these cycloalkenyl groups can be used. Specific examples of amines that can be used as raw materials for optical adjusters include cyclohexylamine, cyclopentylamine, 2-methylcyclohexylamine, 3-methylcyclohexylamine, 4-methylcyclohexylamine, 2,3-dimethylcyclohexylamine, 2,6-dimethylcyclohexylamine, 2-ethylcyclohexylamine, 3,3,5-trimethylcyclohexylamine, cyclooctylamine, cyclododecylamine, etc. Of these, cyclohexylamine is preferred.

[0043] Specific examples of carboxylic acid amide compounds used as optical adjusters include N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide and N,N',N''-tricyclohexyltrimesic acid amide. These compounds have conventionally been used as crystal nucleating agents in crystalline resins, but have not been used as optical adjusters in (meth)acrylic acid ester resins. These carboxylic acid amide compounds are available, for example, from New Japan Chemical Co., Ltd. under the trade names NJESTAR NU-100 (N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide) and NJESTAR TF-1 (N,N',N''-tricyclohexyltrimesic acid amide), but are not limited to these compounds. The carboxylic acid amide compounds may be used alone or in combination of two or more.

[0044] It has been known that some compounds having a benzene ring or a naphthalene ring have negative intrinsic birefringence. It has been discovered that in the resin film according to the present disclosure, when a compound having a specific structure among compounds exhibiting negative birefringence is used, it precipitates as crystals in the (meth)acrylic acid film and exhibits negative birefringence. Without being bound by any particular theory, it is believed that in the resin film according to the present disclosure, the optical adjuster is a carboxylic acid amide, and further, the carboxylic acid amide has at least an aromatic ring and preferably an aliphatic ring, thereby achieving both precipitation and dispersibility in the film and the development of negative intrinsic birefringence.

[0045] (Resin film) In the resin film according to the present disclosure, the mass ratio of the optical adjuster to the (meth)acrylic acid ester polymer is 1000 ppm or more, preferably 2000 ppm or more, from the viewpoint of precipitating the optical adjuster as crystals and improving the dispersibility of the crystals, and is 11000 ppm or less, preferably 10000 ppm or less, from the viewpoint of maintaining transparency and dispersibility. The crystalline form of the optical adjuster contained in the film according to the present disclosure is not particularly limited, but examples thereof include crystals with a high aspect ratio such as fibrous crystals, needle-like crystals, columnar crystals, and plate-like crystals, and the crystalline form is typically needle-like. The aspect ratio of the crystals is preferably 2:1 or more.

[0046] The transparency of the resin film according to the present disclosure is measured using a haze meter. The resin film according to the present disclosure preferably has a haze value of 7.0 or less when the resin film is 0.1 mm thick, and more preferably has a haze value of 4.0 or less when the resin film is 0.1 mm thick. When the haze value is within this range, the resin film can be evaluated as transparent, and the resin film according to the present disclosure can be used in applications where transparency is required.

[0047] The thickness of the resin film according to the present disclosure can be appropriately selected depending on the application and is not particularly limited, but may be, for example, about 5 to 500 μm, and preferably about 10 to 200 μm. The resin film according to the present disclosure has high transparency even in a relatively thick film of about 100 μm (0.1 mm).

[0048] The resin film according to the present disclosure may contain, in addition to the (meth)acrylic acid ester-based polymer and the optical adjuster, additives such as a stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a foaming agent, a lubricant, a filler, a colorant, and a plasticizer, as needed, as long as the effects according to the present disclosure are exhibited.

[0049] The resin film of the present invention exhibits negative birefringence and has transparency, and therefore can be suitably used as an optical film such as a polarizing plate protective film or a retardation film used in a liquid crystal display.

[0050] (Method for producing resin film) The resin film according to the present disclosure can be obtained by mixing a (meth)acrylic acid ester polymer and an optical adjuster, heating the mixture to a temperature equal to or higher than the softening temperature of the (meth)acrylic acid ester polymer and equal to or lower than the decomposition temperature of the (meth)acrylic acid ester polymer, and molding the mixture obtained by mixing.

[0051] In the mixing and molding step, the (meth)acrylic acid ester polymer and the optical adjuster may be mixed and then heated to a temperature equal to or higher than the softening temperature of the (meth)acrylic acid ester polymer and equal to or lower than the decomposition temperature of the (meth)acrylic acid ester polymer. Alternatively, the (meth)acrylic acid ester polymer may be heated to the aforementioned temperature range, and then the optical adjuster may be added and mixed thereto. The latter method is preferred from the viewpoint of precipitating crystals in the resin film and obtaining a uniform film.

[0052] A mixture of a (meth)acrylic acid ester polymer and an optical adjuster is heated to a temperature equal to or higher than the softening temperature of the (meth)acrylic acid ester polymer in order to dissolve the optical adjuster in the molten (meth)acrylic acid ester polymer. The softened (meth)acrylic acid ester polymer functions as a solvent for the optical adjuster. That is, in the molten state, the optical adjuster is believed to be dissolved in the (meth)acrylic acid ester polymer. The molten mixture is preferably stirred, kneaded, or other known means to uniformly disperse the optical adjuster in the (meth)acrylic acid ester polymer.

[0053] Next, the resulting mixture is molded, for example, by extrusion, and cooled to obtain a resin film. It is believed that when the mixture is cooled in this manner, the optical adjuster dissolved in the (meth)acrylic acid ester polymer crystallizes and precipitates. This process results in the optical adjuster being uniformly dispersed in the (meth)acrylic acid ester resin, resulting in a resin film that exhibits negative birefringence and transparency. The cooling temperature is preferably 60°C or lower, more preferably around room temperature, from the viewpoint of increasing the transparency of the resin film.

[0054] The resin film according to the present disclosure can be produced by any method for producing a composite material made of a general thermoplastic resin, and is not particularly limited. Examples of production equipment that can be used include a single-screw extruder, a twin-screw extruder, a Banbury mixer, a roll mixer, and a solvent mixer.

[0055] The film molding method for producing the resin film according to the present disclosure is not limited as long as the effects according to the present disclosure can be obtained. Examples include, but are not limited to, extrusion molding, solution casting, T-die molding, inflation molding, compression molding, and calendar molding. Among these molding methods, T-die molding and compression molding are preferred because they do not use solvents and are therefore environmentally friendly and can accurately control the film thickness.

[0056] When the resin film according to the present disclosure is produced by a melt extrusion molding method such as a T-die molding method or an inflation molding method, the (meth)acrylic acid ester polymer and the optical adjuster are mixed, the resulting mixture is heated to a temperature not lower than the softening temperature and not higher than the decomposition temperature of the resin to melt-knead, and the resulting kneaded product is molded into a predetermined shape using an extrusion molding machine and then cooled, thereby obtaining the resin film according to the present disclosure.

[0057] Next, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0058] Example 1 50 g of methacrylic resin (Mitsubishi Chemical Corporation, ACRYPET VH001) was slowly added over 4 minutes to a kneading extruder (Toyo Seiki Seisaku-sho, Ltd., Labo Plastomill (Model 10S100)) set at a temperature of 220°C and a rotation speed of 5 rpm. Subsequently, 0.2 g (4000 ppm relative to the amount of resin) of N,N',N''-tricyclohexyl trimesic acid amide (New Japan Chemical Co., Ltd., NJSTAR TF-1) was added as an optical modifier over 1 minute. Subsequently, the rotation speed was changed from 5 rpm to 30 rpm, and the resin and optical modifier were mixed for 5 minutes to obtain a mixture.

[0059] Using a press device (manual hydraulic heating and cooling press (model IMC-481E) manufactured by Imoto Machinery Co., Ltd.), 1.0 g of the mixture was heated at 290°C under a pressure of 10 MPa for 2 minutes, and then cooled for 3 minutes to obtain a film with a thickness of 0.1 mm.

[0060] Example 2 A film was obtained in the same manner as in Example 1, except that the amount of N,N',N''-tricyclohexyltrimesic acid amide added as an optical adjuster was 0.5 g (10,000 ppm based on the amount of resin).

[0061] Example 3 A film was obtained in the same manner as in Example 1, except that 0.2 g (4000 ppm based on the amount of resin) of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide (NJester NU-100, manufactured by New Japan Chemical Co., Ltd.) was added as an optical adjuster.

[0062] Comparative Example 1 A film was obtained in the same manner as in Example 1, except that no optical adjuster was used.

[0063] Comparative Example 2 A film was obtained in the same manner as in Example 1, except that the amount of N,N',N''-tricyclohexyltrimesic acid amide added as an optical adjuster was 1.0 g (20,000 ppm based on the amount of resin).

[0064] Comparative Example 3 A film was obtained in the same manner as in Example 1, except that the amount of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide added as an optical adjuster was changed to 0.6 g (12,000 ppm based on the amount of resin).

[0065] Comparative Example 4 A film was obtained in the same manner as in Example 1, except that N,N",N'"-tris(2-methylcyclohexyl)-1,2,3-propanetricarboxyamide (Rikaclear PC-1, manufactured by New Japan Chemical Co., Ltd.) was used as the optical adjuster in an amount of 0.5 g (10,000 ppm relative to the resin amount).

[0066] <Confirmation of Film Properties> The haze values ​​were measured, the film appearances were observed, and the refraction properties were confirmed for the films obtained in Examples 1 to 3 and Comparative Examples 1 to 4. The confirmation methods were as follows. The confirmation results are summarized in Table 1.

[0067] <Measurement of Haze Value> The haze value of the prepared film was measured using a haze meter (HazeMater (Model NDH7000SPII) manufactured by Nippon Denshoku Industries Co., Ltd.). Total light transmittance was measured according to the method of JIS-K-7136. The measurement was performed on three sheets of film, and the average of the actual measured values ​​obtained in these measurements was used as the measured value.

[0068] <Observation of Film Appearance> The appearance of the prepared film was visually observed to confirm its transparency.

[0069] <Confirmation of Optical Properties> A portion of the prepared film was sandwiched between a glass slide and a cover glass and then placed on a hot stage device (Mettler Toledo K.K., hot stage (product number FP82HT Hot Stage)). The entire hot stage was placed on the stage of a polarizing microscope (Nikon Solutions Corporation, polarizing microscope (product number Nikon ECLIPSE LV100POL)). The hot stage was initially set to 290°C, cooled from 290°C to 100°C at a temperature decrease rate of 3°C / min, and maintained at 100°C for 30 minutes. The sample was then cooled from 100°C to 25°C at a temperature decrease rate of 5°C / min over 15 minutes. The sample cooled to 25°C was observed under a polarizing microscope with a sensitive color plate inserted to determine whether crystals were observed and the color of the crystals when their long axes were oriented parallel to the fast axis of the sensitive color plate. It is known that when the elongation direction of a crystal is parallel to X', it exhibits a negative crystal (blue color), and when it is Z', it becomes a positive crystal (yellow color) [Reference: Journal of the Crystallographic Society of Japan 42, 401-412 (2000)]. When the long axis of the crystal is oriented in a direction parallel to the fast axis of the sensitive color plate and the crystal color is blue, it is determined to have negative birefringence.

[0070]

[0071] As shown in Table 1, the resin films of Examples 1 to 3 had low haze values ​​and were confirmed to be transparent when visually observed. In particular, the resin films of Examples 1 and 3 exhibited haze values ​​equivalent to that of the resin film of Comparative Example 1, which did not contain an optical adjuster, and were highly transparent. Furthermore, in crystal color observation, blue crystals were observed in the fast phase direction of the sensitive color plate, confirming that a film in which crystals having negative birefringence were dispersed was obtained.

[0072] A polarizing microscope photograph of the film obtained in Example 3 is shown in Figure 1. Crystals precipitated in the film were observed to be blue in the direction parallel to the fast axis of the sensitive color plate. In the photograph shown in Figure 1, the length of the scale bar shown in the image is 500 μm. In the film of Example 3, the optical adjuster was confirmed to have precipitated as needle-like crystals with a diameter of approximately 1000 μm.

[0073] No crystals were observed in the resin film of Comparative Example 1, which did not contain any optical adjuster. Comparative Example 2, in which 20,000 ppm of optical adjuster (N,N',N''-tricyclohexyl trimesic acid amide) was added to the resin, had a haze value of 7.5, and the film was cloudy. Comparative Example 3, in which 12,000 ppm of optical adjuster (N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide) was added to the resin, had a haze value of 64.9, and the film was cloudy. Comparative Example 4, in which N,N'',N'''-tris(2-methylcyclohexyl)-1,2,3-propanetricarboxamide was used as the optical adjuster, was confirmed to be a transparent film. However, no crystals were observed in the resin film of Comparative Example 4. It was thought that crystals must precipitate in the film to impart optical properties.

[0074] The present invention is intended to cover a wide range of applications, including those related to the present invention, including those related to the present invention.

Claims

1. A resin film for optical films comprising: a (meth)acrylic acid ester polymer; and a carboxylic acid amide compound having an aromatic ring, the carboxylic acid amide compound being contained in an amount of 1,000 ppm or more and 11,000 ppm or less relative to the (meth)acrylic acid ester polymer, the carboxylic acid amide compound being contained as crystals, the crystals exhibiting negative birefringence.

2. The resin film for optical films according to claim 1, wherein the carboxylic acid amide compound is contained in an amount of 2,000 ppm or more and 10,000 ppm or less based on the (meth)acrylic acid ester polymer.

3. The resin film for optical films according to claim 1 or 2, wherein the haze value of a film having a thickness of 0.1 mm is 7.0 or less.

4. The resin film for optical films according to claim 1 or 2, wherein the carboxylic acid amide compound is a carboxylic acid amide compound having an aromatic ring and an aliphatic ring.

5. The resin film for optical films according to claim 1 or 2, wherein the carboxylic acid amide compound is a carboxylic acid amide compound having a structure in which a polyvalent carboxylic acid having either a benzene ring or a naphthalene ring is condensed with an amide compound having an aliphatic ring.

6. A method for producing a resin film for optical films, comprising the steps of: mixing a (meth)acrylic acid ester polymer with a carboxylic acid amide compound having an aromatic ring in an amount of 1,000 ppm or more and 11,000 ppm or less relative to the (meth)acrylic acid ester polymer; heating the mixture to a temperature not lower than the softening temperature of the (meth)acrylic acid ester polymer and not higher than the decomposition temperature of the (meth)acrylic acid ester polymer; and forming the mixture into a film by cooling.

7. The method for producing a resin film for optical films according to claim 6, wherein the carboxylic acid amide compound is a carboxylic acid amide compound having a structure in which a polyvalent carboxylic acid having either a benzene ring or a naphthalene ring is condensed with an amide compound having an aliphatic ring.

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