Resin film for optical films and method for manufacturing a resin film for optical films

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

Technical Field

[0001] The present invention relates to a resin film for an optical film and a method for producing the resin film for an optical film. This application claims priority based on Japanese Patent Application No. 2023-130926 filed on August 10, 2023, and incorporates all the descriptions set forth in the Japanese patent application.

Background Art

[0002] Acrylic resin films having characteristics in optical properties are known. For example, Patent Document 1 discloses a resin film for an optical film comprising a methacrylic acid ester polymer and a diacetal compound having a specific structure. The resin film disclosed in Patent Document 1 is disclosed to have the characteristics that no dispersion failure occurs and birefringence is small.

[0003] Patent Document 2 discloses a base material for a surface protection film for protecting the surface of an image display device. The base material for the surface protection film disclosed in Patent Document 2 is characterized by having retardation characteristics within a specific range. As a specific composition of this base material for a film, it is disclosed to contain at least one resin selected from polycarbonate, polyester, cycloolefin resin, acrylic resin, and cellulose resin. Further, it is disclosed that the base material for a film may contain a resin having an alicyclic structure or an aromatic ring structure showing negative intrinsic birefringence.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The object of this invention is to provide an optical film that exhibits negative birefringence and high transparency, and a method for manufacturing the same. [Means for solving the problem]

[0006] The resin film for optical films according to this disclosure contains a (meth)acrylic acid 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 relative to the (meth)acrylic acid ester polymer. The carboxylic acid amide compound is contained as crystals, and these crystals exhibit negative birefringence. [Effects of the Invention]

[0007] The resin film according to this disclosure provides an optical film that exhibits negative birefringence and has high transparency. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a polarized light microscope image showing the crystals of the optical modifier contained in the resin film according to this disclosure. [Modes for carrying out the invention]

[0009] [Summary of the Embodiment] First, embodiments of the resin film for optical films and the method for manufacturing the same according to this disclosure will be listed and described. In this specification, unless otherwise specified, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B".

[0010] The resin film for optical films according to this disclosure contains a (meth)acrylic acid 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 relative to the (meth)acrylic acid ester polymer. The carboxylic acid amide compound is contained as crystals, and these crystals exhibit negative birefringence.

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

[0012] The resin film for optical films according to this disclosure contains a carboxylic acid amide compound having a specific structure in a (meth)acrylic acid ester polymer. The carboxylic acid amide compound exists as crystals in the film, and these crystals exhibit negative birefringence. The resin film for optical films according to this disclosure can be constructed by containing the optical modifier at any concentration 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 films according to this disclosure is a film with sufficient transparency and has characteristic functions as a resin film for optical films.

[0013] In the aforementioned resin film for optical films, the carboxylic acid amide compound may be contained in an amount of 2,000 ppm to 10,000 ppm relative to the (meth)acrylic acid ester polymer. When the content of the carboxylic acid amide compound is within this range, the effects of the resin film for optical films according to this disclosure become clearer.

[0014] In the aforementioned resin film for optical films, the haze value of a 0.1 mm thick film may be 7.0 or less. According to the resin film for optical films of this disclosure, even when the film is thick at 0.1 mm and has sufficient strength, transparency is maintained and the characteristic of exhibiting negative birefringence due to crystal precipitation in the film is achieved.

[0015] In the aforementioned 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. Compounds having this structure exhibit negative birefringence and precipitate as crystals in films produced by general methods.

[0016] In the aforementioned resin film for optical films, 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 this disclosure that a carboxylic acid amide compound having such a structure exhibits negative birefringence and functions as an optical modifier, and that it precipitates as crystals in a (meth)acrylic acid ester resin film.

[0017] A method for producing a resin film for optical films according to this disclosure involves mixing a (meth)acrylic acid ester polymer with a carboxylic acid amide compound having an aromatic ring in a proportion of 1000 ppm to 11000 ppm relative to the (meth)acrylic acid ester polymer. The manufacturing method includes a step of heating the (meth)acrylic acid ester polymer to a temperature above its softening temperature and below its decomposition temperature, and molding it, and a step of forming a film by cooling. According to this manufacturing method, a resin film containing an optical modifier at a high concentration and in which the optical modifier precipitated as crystals in the film exhibits negative birefringence can be obtained using a general method.

[0018] In the method for producing the resin film for optical films, 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. The effects described in this disclosure can be obtained more reliably with a resin film containing such a carboxylic acid amide compound.

[0019] Hereinafter, the resin film according to the present disclosure will be described in more detail. In this specification, the term “(meth)acrylate” collectively represents both acrylate and methacrylate.

[0020] (Resin) The resin film according to the present disclosure contains, as the resin serving as the substrate constituting the film, at least any one selected from (meth)acrylate polymers, that is, acrylate polymers and methacrylate polymers.

[0021] When the resin serving as the substrate of the resin film is a methacrylate polymer, that is, a methacrylate resin, a polymer mainly composed of methacrylate can be mentioned as a suitable methacrylate resin. Here, “mainly composed of methacrylate” as used in this specification means that the content of methacrylate in the raw material monomers of the methacrylate polymer is 50% by mass or more. From the viewpoint of enhancing the heat resistance and transparency of the methacrylate polymer, the content ratio of methacrylate in the raw material monomers of the methacrylate polymer is preferably 80% by mass or more, more preferably 85% by mass or more, and still more preferably 90% by mass or more.

[0022] Typical examples of the polymer mainly composed of methacrylate include a methacrylate homopolymer and a methacrylate copolymer obtained by polymerizing a raw material monomer containing methacrylate and other monomers and mainly composed of methacrylate.

[0023] Suitable methacrylate monomers for forming polymers mainly composed of methacrylate esters include, from the viewpoint of improving fluidity and heat decomposition resistance during heating and melting, alkyl methacrylates in which the alkyl group in the ester portion has 1 to 18 carbon atoms, such as 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, and stearyl methacrylate; cyclohexyl methacrylate and phenyl methacrylate. These can be used individually or in combination of two or more. These methacrylate esters exhibit excellent fluidity and heat decomposition resistance during heating and melting.

[0024] Among the methacrylate esters mentioned above, 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 due to their availability. Furthermore, from the viewpoint of heat resistance, alkyl methacrylate esters in which the alkyl group in the ester portion 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 aforementioned methacrylic acid esters is used as the raw material monomer. When two or more methacrylic acid esters are used as raw material monomers, the methacrylic acid ester polymer becomes a methacrylic acid ester copolymer.

[0026] A methacrylic acid ester copolymer obtained by polymerizing a raw material monomer mainly composed of methacrylic acid ester, containing methacrylic acid ester and other monomers, is an example of a copolymer obtained by polymerizing a raw material monomer mainly composed of methacrylic acid ester, containing one or more of the aforementioned methacrylic acid esters and other monomers. 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 mainly composed of methacrylic acid ester is usually a random copolymer, and this random copolymer is readily available commercially.

[0027] Other monomers include, for example, 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 acid esters such as cyclohexyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, trifluoromethyl acrylate, trifluoroethyl acrylate, pentafluoroethyl acrylate, glycidyl acrylate, allyl acrylate, phenyl acrylate, tolyl acrylate, benzyl acrylate, isobornyl acrylate, and 3-dimethylaminoethyl acrylate; unsaturated monocarboxylic acids such as methacrylic acid and acrylic acid; acrylic acid Examples include, but are not limited to, vinyl cyanide compounds such as nitrile and methacrylonitrile; aromatic vinyl compounds such as styrene, α-methylstyrene, p-methylstyrene, p-methoxystyrene, divinylbenzene, and vinylnaphthalene; unsaturated dicarboxylic acid compounds or derivatives such as maleic anhydride, maleic acid, maleic acid monoester, maleic acid diester, fumaric acid, fumaric acid monoester, and fumaric acid diester; maleimide compounds such as maleimide, methyl maleimide, ethyl maleimide, propyl maleimide, butyl maleimide, hexyl maleimide, octyl maleimide, dodecyl maleimide, stearyl maleimide, phenyl maleimide, and cyclohexyl maleimide; conjugated diene compounds such as butadiene and isoprene; halogen-containing unsaturated compounds such as vinyl chloride, vinylidene chloride, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, and chloroprene; and silicon-containing unsaturated compounds such as vinyltrimethoxysilane and vinyltriethoxysilane. These other monomers can be used individually or in combination of two or more.

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

[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 films according to this disclosure, it is preferable to use a methacrylate ester polymer mainly composed of methyl methacrylate as the raw material monomer, from the viewpoint of heat resistance and transparency.

[0031] When the resin that forms 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 mainly composed of acrylic acid esters. Examples of polymers mainly composed of acrylic acid esters include isobutyl acrylate polymer, 2-ethylhexyl acrylate polymer, isodecyl acrylate polymer, nonyl acrylate polymer, and dodecyl acrylate polymer.

[0032] The (meth)acrylic acid ester polymer that forms the base of the resin film according to this 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 have glutarimide structural units or lactone ring structural units introduced into them by modification.

[0033] The melt flow rate (230°C, 37.3N) of the (meth)acrylic acid ester polymer used in the resin film for optical films according to this disclosure is not particularly limited, but from the viewpoint of increasing the fluidity of the (meth)acrylic acid ester polymer when heated and melted, it is preferably 0.5 g / 10 min or more, more preferably 1.5 g / 10 min or more. 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 films according to this disclosure is preferably 40,000 to 200,000, more preferably 50,000 to 180,000, and even more preferably 55,000 to 160,000. When Mw is 40,000 or higher, the strength and toughness of the resin film are improved. When Mw is 200,000 or lower, the fluidity of the (meth)acrylic acid ester polymer is improved, and the moldability is improved. The weight-average molecular weight (Mw) is a value calculated by converting the chromatogram measured by gel permeation chromatography (GPC) to the molecular weight of standard polystyrene.

[0035] The acid value of the (meth)acrylic ester polymer used in the resin film according to this disclosure is preferably 0.01 to 0.30 mmol / g, more preferably 0.05 to 0.28 mmol / g. The acid value is proportional to the content of carboxylic acid units and carboxylic acid 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, and then titrating it with a 0.1 mol / L potassium hydroxide-ethanol solution by potentiometric titration, with the inflection point on the titration curve as the endpoint. When the acid value is within the above range, an excellent balance between fluidity and moldability of the film is obtained.

[0036] The resin film according to this disclosure may, in addition to the (meth)acrylic acid ester polymer described above, contain one or more other polymers other than the (meth)acrylic acid ester polymer as the resin constituting the film substrate, within a range that does not hinder the objectives 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, polyetheretherketone 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] In the resin film according to this disclosure, the resin constituting the film substrate may have a mass ratio of (meth)acrylic acid ester polymer to the total 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 this disclosure is preferably composed of a (meth)acrylic acid ester polymer.

[0038] (Optical correcting agent) The resin film for optical films according to this disclosure is characterized by containing a carboxylic acid amide compound having an aromatic ring. This carboxylic acid amide compound functions as an optical modifier to adjust the optical properties of the film. According to this disclosure, by containing a carboxylic acid amide compound of a specific structure, crystals exhibiting negative birefringence precipitate in the film, and a transparent (meth)acrylic acid ester resin film can be obtained.

[0039] Carboxylate amide compounds having an aromatic ring are typically compounds obtained by the condensation of a polycarboxylic acid having an aromatic ring with an amine, and may be carboxylic acid amide compounds having a benzene ring or a naphthalene ring. The optical modifiers used in this disclosure have negative intrinsic birefringence and exhibit negative birefringence when existing as crystals in the resin film.

[0040] The aromatic ring in a carboxylic acid amide compound having an aromatic ring may be monocyclic or polycyclic, and examples include benzene rings, naphthalene rings, biphenyl rings, anthracene rings, and pyrene rings. 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 an amide having an aliphatic ring. The carboxylic acid amide compound may be a condensate of a dicarboxylic acid or tricarboxylic acid having a benzene ring and an amide having an aliphatic ring, or a condensate of a dicarboxylic acid or tricarboxylic acid having a naphthalene ring and an amide having an aliphatic ring.

[0041] Examples of carboxylic acids used as raw materials for the carboxylic acid amide compounds used in the resin films according to this disclosure include, specifically, 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, and the like. 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 in the resin film according to this disclosure is preferably an amine having an aliphatic ring. The aliphatic ring may be a saturated aliphatic ring or an unsaturated aliphatic ring, but a saturated aliphatic ring is preferred. Examples of groups containing a saturated aliphatic ring include cycloalkyl groups such as cyclohexyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, and cyclodecyl group, and amines having these cycloalkyl groups can be used. Examples of groups containing an unsaturated aliphatic ring include cyclopropenyl group, cyclobutenyl group, cyclopentenyl group, cyclohexenyl group, cycloheptenyl group, cyclooctenyl group, and cyclopentadienyl group, and amines having these cycloalkenyl groups can be used. Examples of amines used as raw materials for optical modifiers include cyclohexylamine, cyclopentylamine, 2-methylcyclohexylamine, 3-methylcyclohexylamine, 4-methylcyclohexylamine, 2,3-dimethylcyclohexylamine, 2,6-dimethylcyclohexylamine, 2-ethylcyclohexylamine, 3,3,5-trimethylcyclohexylamine, cyclooctylamine, and cyclododecylamine. Of these, cyclohexylamine is preferred.

[0043] Examples of carboxylic acid amide compounds used as optical modifiers include N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide and N,N',N''-tricyclohexyltrimesinamide. These compounds have traditionally been used as nucleating agents in crystalline resins and have never been used as optical modifiers in (meth)acrylic acid ester resins. These carboxylic acid amide compounds are available, for example, from Shin Nippon Rika Co., Ltd., under the trade names NJester NU-100 (N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide) and NJester TF-1 (N,N',N''-tricyclohexyltrimesinamide), but are not limited to these compounds. Carboxylic acid amide compounds may be used individually or in combination of two or more.

[0044] It was known that some compounds containing benzene or naphthalene rings exhibit negative intrinsic birefringence. In the resin film according to this disclosure, it has been found that when a compound exhibiting negative birefringence with a specific structure is used, it precipitates as crystals in the (meth)acrylic acid film and exhibits negative birefringence. Although not bound by any particular theory, it is believed that in the resin film according to this disclosure, the optical modifier is a carboxylic acid amide, and furthermore, the carboxylic acid amide contains at least an aromatic ring, preferably an aliphatic ring, which allows for both precipitation and dispersibility in the film and the manifestation of negative intrinsic birefringence.

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

[0046] The transparency of the resin film according to this disclosure is measured by a haze meter. Preferably, the haze value of the resin film according to this disclosure is 7.0 or less for a resin film with a thickness of 0.1 mm, and more preferably, the haze value of the resin film with a thickness of 0.1 mm is 4.0 or less. When the haze value is within this range, the resin film can be evaluated as transparent, and the resin film according to this disclosure can be applied to applications where transparency is required.

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

[0048] The resin film relating to this disclosure may, insofar as it exhibits the effects relating to this disclosure, contain additives such as stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, foaming agents, lubricants, fillers, colorants, and plasticizers as needed, in addition to (meth)acrylic acid ester polymers and optical modifiers.

[0049] Since the resin film of the present invention exhibits negative birefringence and transparency, it can be suitably used as an optical film, such as a polarizing plate protective film or a phase difference film used in liquid crystal displays.

[0050] (Method of manufacturing resin film) The resin film according to this disclosure is obtained by mixing a (meth)acrylic acid ester polymer and an optical modifier, heating the mixture to a temperature above the softening temperature of the (meth)acrylic acid ester polymer and below the decomposition temperature of the (meth)acrylic acid ester polymer, and then molding the resulting mixture.

[0051] The mixing and molding process may involve mixing the (meth)acrylic acid ester polymer and the optical modifier, followed by heating to a temperature above the softening temperature of the (meth)acrylic acid ester polymer and below its decomposition temperature. Alternatively, the (meth)acrylic acid ester polymer may be heated to the aforementioned temperature range, and then the optical modifier may be added and mixed. The latter method is preferred from the viewpoint of precipitating crystals in the resin film and obtaining a uniform film.

[0052] A mixture of (meth)acrylic acid ester polymer and an optical modifier is heated to a temperature above the softening temperature of the (meth)acrylic acid ester polymer in order to dissolve the optical modifier in the molten (meth)acrylic acid ester polymer. The softened (meth)acrylic acid ester polymer then functions as a solvent for the optical modifier. That is, in the molten state, the optical modifier is considered to be dissolved in the (meth)acrylic acid ester polymer. It is preferable to uniformly disperse the optical modifier in the (meth)acrylic acid ester polymer using known means such as stirring and kneading.

[0053] Next, the obtained mixture is molded, for example, by extrusion and cooled to obtain a resin film. When the mixture is cooled in this way, it is thought that the optical modifier dissolved in the (meth)acrylic acid ester polymer precipitates as crystals. Through this process, the optical modifier is uniformly dispersed in the (meth)acrylic acid ester resin, and a resin film exhibiting negative birefringence and transparency is obtained. From the viewpoint of enhancing the transparency of the resin film, the cooling temperature is preferably 60°C or lower, more preferably around room temperature.

[0054] The resin film according to this disclosure can be manufactured by a general method for manufacturing composite materials made of thermoplastic resins, and is not particularly limited. Examples of manufacturing equipment include a single-screw extruder, a twin-screw extruder, a Banbury mixer, a roll kneader, and a solvent mixer.

[0055] The method for molding the resin film according to this disclosure is not limited as long as the effects described herein are obtained. Examples include, but are not limited to, extrusion molding, solution casting, T-die molding, inflation molding, compression molding, and calendering. Among these molding methods, T-die molding and compression molding are preferred because they are environmentally friendly as they do not use solvents and allow for precise control of the film thickness.

[0056] When the resin film according to this disclosure is manufactured by a melt extrusion molding method such as a T-die molding method or an inflation molding method, the resin film according to this disclosure can be obtained by mixing a (meth)acrylic acid ester polymer and an optical modifier, heating the resulting mixture to a temperature above the resin softening temperature and below the decomposition temperature and melt kneading it, molding the resulting kneaded material into a predetermined shape using an extruder, and then cooling it. [Examples]

[0057] Next, the present invention will be described in more detail based on examples, but the present invention is not limited to such 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 Seisakusho Co., Ltd., Laboplast Mill (model 10S100)) set to a temperature of 220°C and a rotation speed of 5 rpm. Then, 0.2 g of N,N',N''-tricyclohexyltrimesinamide (Shin Nippon Rika Co., Ltd., NJester TF-1) (4000 ppm relative to the amount of resin) was added over 1 minute as an optical modifier. After that, the rotation speed was changed from 5 rpm to 30 rpm, and the resin and optical modifier were mixed for 5 minutes to obtain the mixture.

[0059] Using a press (manufactured by Imoto Seisakusho Co., Ltd., manual hydraulic heating and cooling press (model IMC-481E)), 1.0 g of the mixture was heated at 290°C and 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] The same procedure as in Example 1 was followed to obtain a film, except that the amount of N,N',N''-tricyclohexyltrimesinamide added as an optical modifier was 0.5 g (10,000 ppm relative to the amount of resin).

[0061] [Example 3] A film was obtained by performing the same procedure as in Example 1, except that 0.2 g of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide (NJester NU-100, manufactured by Shin-Nippon Rika Co., Ltd.) was added as an optical modifier (4000 ppm relative to the amount of resin).

[0062] [Comparative Example 1] In Example 1, the same procedure was followed, except that no optical modifier was used, to obtain a film.

[0063] [Comparative Example 2] The same procedure as in Example 1 was followed to obtain a film, except that the amount of N,N',N''-tricyclohexyltrimesinamide added as an optical modifier was 1.0 g (20,000 ppm relative to the amount of resin).

[0064] [Comparative Example 3] The same procedure as in Example 1 was followed to obtain a film, except that the amount of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide added as an optical modifier was 0.6 g (12,000 ppm relative to the amount of resin).

[0065] [Comparative Example 4] A film was obtained by performing the same procedure as in Example 1, except that N,N'',N'''-tris(2-methylcyclohexyl)-1,2,3-propanetricarboxamide (manufactured by Shin Nippon Rika Co., Ltd., Ricaclear PC-1) was used as an optical modifier, with an addition amount of 0.5 g (10,000 ppm relative to the amount of resin).

[0066] <Checking the characteristics of the film> For the films obtained in Examples 1-3 and Comparative Examples 1-4, the haze value was measured, the film appearance was observed, and the refractive properties were confirmed. The confirmation methods were as follows. The confirmation results are summarized in Table 1.

[0067] <Haze value measurement> The haze value of the fabricated film was measured using a haze meter (HazeMater (Model NDH7000SPII) manufactured by Nippon Denshoku Industries Co., Ltd.). The total light transmittance was measured according to the method of JIS-K-7136. Measurements were performed on three films, and the average of the measured values ​​obtained was used as the measured value.

[0068] <Film appearance observation> The appearance of the prepared film was visually inspected to confirm its transparency.

[0069] <Verification of optical properties> A portion of the prepared film was sandwiched between a glass slide and a cover slip, and then placed on a hot stage (Mettler Toledo Co., Ltd., Hot Stage (Model No. FP82HT Hot Stage)). The entire hot stage was then placed on the stage of a polarizing microscope (Nikon Solutions Co., Ltd., Polarizing Microscope (Model No. Nikon ECLIPSE LV100POL)). The hot stage was initially set to 290°C, and the sample was cooled from 290°C to 100°C at a cooling rate of 3°C / min, maintaining the temperature at 100°C for 30 minutes. Then, it was cooled from 100°C to 25°C over 15 minutes at a cooling rate of 5°C / min. The sample cooled to 25°C was observed using a polarizing microscope with a color-sensitive plate inserted to check for crystal formation and to confirm the crystal color when the long axis of the crystal was oriented parallel to the phase-advancing axis of the color-sensitive plate. It is known that crystals exhibit negative birefringence (blue) when the elongation direction is parallel to X', and positive birefringence (yellow) when it is parallel to Z' [Reference: Journal of the Crystallographic Society of Japan 42, 401-412 (2000)]. When the crystal color was blue when the long axis of the crystal was oriented parallel to the phase-advancing axis of the color-sensitive plate, it was determined that the crystal possessed negative birefringence.

[0070] [Table 1]

[0071] As shown in Table 1, the resin films of Examples 1 to 3 had low haze values ​​and were confirmed to be transparent upon visual inspection of the films. In particular, the resin films of Examples 1 and 3 showed haze values ​​equivalent to those of the resin film of Comparative Example 1, which did not contain an optical modifier, and exhibited high transparency. Furthermore, in crystal color observation, crystals exhibiting blue coloration in the phase advancement direction of the sensitive color plate were observed, confirming that films with dispersed crystals having negative birefringence were obtained.

[0072] Figure 1 shows a polarized light microscope image of the film obtained in Example 3. The crystals precipitated in the film were observed to be blue in a direction parallel to the phase advancement axis of the sensitive color plate. In the image 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 modifier was confirmed to have precipitated as needle-shaped crystals with a diameter of approximately 1000 μm.

[0073] In Comparative Example 1, which did not contain an optical modifier, no crystals were observed in the resin film. In Comparative Example 2, where 20,000 ppm of the optical modifier (N,N',N''-tricyclohexyltrimesinamide) was added to the resin, the haze value was 7.5 and the film was cloudy. In Comparative Example 3, where 12,000 ppm of the optical modifier (N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide) was added to the resin, the haze value was 64.9 and the film was cloudy. In Comparative Example 4, which used N,N'',N'''-tris(2-methylcyclohexyl)-1,2,3-propanetricarboxamide as the optical modifier, it was confirmed to be a transparent film. However, no crystals were observed in the resin film of Comparative Example 4. It was considered that crystal precipitation in the film is necessary to impart optical properties.

[0074] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the present invention is defined by the claims and is intended to include all modifications in the sense and scope equivalent to the claims.

Claims

1. (Meth)acrylic acid ester polymers, Carboxylic acid amide compounds having an aromatic ring, It contains, 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 polymer. The carboxylic acid amide compound is contained in crystalline form, and the crystal exhibits negative birefringence. Resin film for optical films.

2. The carboxylic acid amide compound is contained in an amount of 2,000 ppm to 10,000 ppm relative to the (meth)acrylic acid ester polymer. A resin film for optical films according to claim 1.

3. The haze value of a 0.1 mm thick film is 7.0 or less. A resin film for optical films according to claim 1 or claim 2.

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

5. The carboxylic acid amide compound is It is 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 amine having an aliphatic ring. A resin film for optical films according to claim 1 or claim 2.

6. A (meth)acrylic acid ester polymer and a carboxylic acid amide compound having an aromatic ring in a proportion of 1,000 ppm to 11,000 ppm relative to the (meth)acrylic acid ester polymer are mixed. A process of heating the polymer to a temperature above the softening temperature of the (meth)acrylic acid ester polymer and below the decomposition temperature of the (meth)acrylic acid ester polymer, and then molding it. The process includes forming a film by cooling, A method for manufacturing resin films for optical films.

7. The carboxylic acid amide compound is It is 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 amine having an aliphatic ring. A method for manufacturing a resin film for optical films according to claim 6.

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