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

Abstract

A resin film for an optical film, the resin film containing a (meth) acrylate polymer and a carboxylic acid amide compound having an aromatic ring, the carboxylic acid amide compound being contained in an amount of 1000 ppm or more and 11000 ppm or less with respect to the (meth) acrylate polymer, the carboxylic acid amide compound being contained therein in the form of a crystal, and the (meth) acrylate polymer being a polymer having an aromatic ring. The crystal exhibits negative birefringence. Furthermore, a method for producing a resin film for an optical film, said method comprising a step for mixing a (meth) acrylate polymer and a carboxylic acid amide compound having an aromatic ring at a ratio of 1000 ppm to 11000 ppm (inclusive) with respect to the (meth) acrylate polymer; heating to a temperature not less than the softening temperature of the (meth) acrylate polymer and not more than the decomposition temperature of the (meth) acrylate polymer, and molding; and forming a thin film by cooling.

Description

Technical Field

[0001] This invention relates to resin films for optical thin films and methods for manufacturing resin films for optical thin films. This application claims priority based on Japanese Patent Application No. 2023-130926, filed on August 10, 2023, and invokes all the contents described in the aforementioned Japanese patent application. Background Technology

[0002] Acrylic resin films known to possess optical properties are present. For example, Patent Document 1 discloses a resin film for optical films, which is composed of a methacrylate polymer and a diacetal compound having a specific structure. The resin film disclosed in Patent Document 1 has the following characteristics: it does not exhibit poor dispersion and has low birefringence.

[0003] Patent Document 2 discloses a substrate for a surface protective film used to protect the surface of an image display device. The surface protective film substrate disclosed in Patent Document 2 is characterized by having a specific range of phase difference characteristics. It also discloses that the substrate comprises at least one resin selected from polycarbonate, polyester, cyclic olefin resin, acrylic resin, and cellulose resin. Furthermore, it discloses that the substrate may contain a resin having an alicyclic structure or an aromatic ring structure exhibiting negative intrinsic birefringence.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-254370

[0007] Patent Document 2: WO2020 / 054135 Summary of the Invention

[0008] The objective of this invention is to provide an optical thin film exhibiting negative birefringence and high transparency, and a method for manufacturing the same.

[0009] The optical thin film of the present invention comprises: a (meth)acrylate polymer and a carboxylate compound having an aromatic ring. The carboxylate compound is present in an amount of 1000 ppm to 11000 ppm relative to the (meth)acrylate polymer. The carboxylate compound is contained therein in crystalline form, and the crystals exhibit negative birefringence.

[0010] Invention Effects

[0011] According to the resin film of the present invention, an optical film exhibiting negative birefringence and high transparency is provided. Attached Figure Description

[0012] Figure 1 This is a polarizing microscope photograph showing the crystallization of the optical modifier contained in the resin film involved in the present invention. Detailed Implementation

[0013] [Summary of Implementation Methods]

[0014] First, embodiments of the resin film for optical thin films and the manufacturing method thereof according to the present invention will be listed and described. It should be noted that, unless otherwise specified, "A to B" in this specification refers to "A or more and B or less" when indicating a numerical range.

[0015] The optical thin film of the present invention comprises: a (meth)acrylate polymer and a carboxylate compound having an aromatic ring. The carboxylate compound is present in an amount of 1000 ppm to 11000 ppm relative to the (meth)acrylate polymer. The carboxylate compound is contained therein in crystalline form, and the crystals exhibit negative birefringence.

[0016] Previously, many solutions have been proposed for resin films with adjusted optical properties. For example, Patent Document 1 proposes a resin film for optical films containing a specific acetal compound with low birefringence. Patent Document 2 proposes that the side chains of the resin constituting the film contain a chemical structure believed to exhibit negative birefringence.

[0017] The optical thin film according to this invention contains a carboxylic amide compound with a specific structure relative to (meth)acrylate polymers. This carboxylic amide compound exists in crystalline form within the film, exhibiting negative birefringence. The optical thin film according to this invention can be configured to contain an optical modifier at any content within a wide range of 1000 ppm to 11000 ppm relative to the matrix resin constituting the film, resulting in films exhibiting significant optical properties. Furthermore, the optical thin film according to this invention is a film with sufficient transparency, possessing characteristic functions as an optical thin film resin.

[0018] The resin film for optical thin films may contain 2000 ppm to 10000 ppm of the carboxylic acid amide compound relative to the (meth)acrylate polymer. When the content of the carboxylic acid amide compound is within this range, the effect of the resin film for optical thin films according to the present invention is more pronounced.

[0019] In the aforementioned resin film for optical thin films, the haze value of a 0.1 mm thick film can be 7.0 or less. According to the resin film for optical thin films of the present invention, even when the film thickness reaches 0.1 mm and the film has sufficient strength, it exhibits the characteristics of maintaining transparency and crystallizing within the film to exhibit negative birefringence.

[0020] In the resin film for optical thin films, the carboxylic acid amide compound can be a carboxylic acid amide compound having aromatic and aliphatic rings. Compounds with this structure exhibit negative birefringence and precipitate in crystalline form in thin films fabricated using common methods.

[0021] In the resin film for optical thin films, the carboxylic acid amide compound can be a carboxylic acid amide compound having a structure obtained by condensing a polycarboxylic acid having either a benzene ring or a naphthalene ring with an amide compound having an aliphatic ring. In this invention, it has been found that the carboxylic acid amide compound with this structure exhibits negative birefringence, functions as an optical modulator, and precipitates crystallinely in (meth)acrylate resin films.

[0022] The method for manufacturing the resin film for optical thin films according to the present invention includes the following steps: mixing a (meth)acrylate polymer with a carboxylic acid amide compound having an aromatic ring in a proportion of 1000 ppm or more and 11000 ppm or less relative to the (meth)acrylate polymer; heating to a temperature above the softening temperature and below the decomposition temperature of the (meth)acrylate polymer; and molding; and forming a thin film by cooling. According to this manufacturing method, a resin film containing a high content of optical modifiers and exhibiting negative birefringence due to the crystalline precipitation of optical modifiers in the film can be obtained using a common method.

[0023] In the method for manufacturing the resin film for optical thin films, the carboxylic acid amide compound can be a carboxylic acid amide compound having a structure obtained by condensing a polycarboxylic acid having either a benzene ring or a naphthalene ring with an amide compound having an aliphatic ring. The effects of the present invention can be obtained more reliably based on the resin film containing this carboxylic acid amide compound.

[0024] The resin film involved in this invention will now be described in more detail. It should be noted that in this specification, the term "(meth)acrylate" refers to both acrylate and methacrylate.

[0025] (Resin)

[0026] In the resin film of the present invention, the resin serving as the matrix constituting the film contains at least a (meth)acrylate polymer, that is, any one selected from acrylate polymers and methacrylate polymers.

[0027] When the resin that forms the matrix of the resin film is a methacrylate-based polymer, i.e., a methacrylate-based resin, polymers with methacrylate as the main component are preferred examples. Here, "with methacrylate as the main component" as used in this specification means that the content of methacrylate in the monomer of the methacrylate-based polymer is 50% by mass or more. The preferred content of methacrylate in the monomer of the methacrylate-based polymer is 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of improving the heat resistance and transparency of the methacrylate-based polymer.

[0028] Representative examples of polymers with methacrylate as the main component include: methacrylate homopolymers and methacrylate copolymers obtained by polymerizing raw material monomers containing methacrylate and other monomers, with methacrylate as the main component.

[0029] Preferred methacrylate monomers for polymers primarily composed of methacrylates, from the viewpoint of improving melt flowability and resistance to thermal decomposition, 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, etc., where the alkyl group of the ester portion has 1 to 18 carbon atoms; cyclohexyl methacrylate, phenyl methacrylate, etc. These can be used individually or in mixtures of two or more. These methacrylates exhibit excellent melt flowability and resistance to thermal decomposition.

[0030] From the perspective of ease of acquisition, 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 among the methacrylates. Furthermore, from the viewpoint of heat resistance, alkyl methacrylates in which the alkyl group of the ester moiety has 1 to 4 carbon atoms are more preferred, and methyl methacrylate is even more preferred.

[0031] It should be noted that in methacrylate homopolymers, only one of the methacrylates is used as a raw material monomer. When two or more methacrylates are used as raw material monomers, the methacrylate-based polymer becomes a methacrylate copolymer.

[0032] Examples of methacrylate-based copolymers obtained by polymerizing raw material monomers containing methacrylates and other monomers, with methacrylates as the main component, include copolymers obtained by polymerizing raw material monomers containing one or more of the aforementioned methacrylates and other monomers, with methacrylates as the main component. Methacrylate-based copolymers can be random copolymers or block copolymers. Methacrylate-based copolymers obtained by polymerizing raw material monomers with methacrylates as the main component are typically random copolymers, which are commercially readily available.

[0033] Other monomers mentioned include, for example: 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, stearyl acrylate, and other alkyl acrylates; 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, and other hydroxyl-containing alkyl acrylates; cyclohexyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, trifluoromethyl acrylate, trifluoroethyl acrylate, pentafluoroethyl acrylate, glycidyl acrylate, allyl acrylate, phenyl acrylate, toluene acrylate, benzyl acrylate, isobornyl acrylate, 3-dimethylaminoethyl acrylate, and other acrylates; unsaturated monocarboxylic acids such as methacrylic acid and acrylic acid; and ethylene cyanide 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 their 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, methylmaleimide, ethylmaleimide, propylmaleimide, butylmaleimide, hexylmaleimide, octylmaleimide, dodecylmaleimide, stearylmaleimide, phenylmaleimide, and cyclohexylmaleimide; conjugated diene compounds such as butadiene and isoprene; halogenated unsaturated compounds such as vinyl chloride, vinylidene chloride, tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, and chloroprene; and silicon-containing unsaturated compounds such as vinyltrimethoxysilane and vinyltriethoxysilane, but not limited to these monomers. These other monomers can be used in combination, one or more.

[0034] From the viewpoint of heat resistance, the other monomers are preferably alkyl acrylates and vinyl cyanide compounds, and more preferably alkyl acrylates, acrylonitrile and methacrylonitrile in which the alkyl group of the ester moiety has 1 to 4 carbon atoms.

[0035] From the viewpoint of improving the heat resistance and transparency of methacrylate copolymers, the content of the other monomers in the raw material monomers of the methacrylate copolymer 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.

[0036] In the optical thin film resin film involved in this invention, from the viewpoint of heat resistance and transparency, it is preferable to use a methyl methacrylate-based polymer as the raw material monomer.

[0037] When the resin that forms the matrix of the resin film is an acrylate polymer, i.e., an acrylate-based resin, polymers with acrylate as the main component are preferred. Examples of polymers with acrylate as the main component include: isobutyl acrylate polymers, 2-ethylhexyl acrylate polymers, isodecyl acrylate polymers, nonyl acrylate polymers, and dodecyl acrylate polymers.

[0038] The (meth)acrylate polymer that forms the matrix of the resin film according to the present invention can be a copolymer of acrylate monomers and methacrylate monomers. Examples of such copolymers include methyl methacrylate-(meth)acrylate copolymers, methyl methacrylate-(meth)acrylate copolymers, methyl methacrylate-acrylate-(meth)acrylate copolymers, and methyl methacrylate-styrene copolymers. In these polymers, glutarimide structural units or lactone ring structural units can be introduced through modification.

[0039] The melt flow rate (230°C, 37.3N) of the (meth)acrylate polymer used in the optical thin film according to the present invention is not particularly limited, but from the viewpoint of improving the fluidity of the (meth)acrylate polymer during heating and melting, it is preferably 0.5 g / 10 min or more, more preferably 1.5 g / 10 min or more. From the viewpoint of improving the mechanical strength of the methacrylate polymer, it is preferably 30 g / 10 min or less, more preferably 25 g / 10 min or less.

[0040] The weight-average molecular weight (Mw) of the (meth)acrylate polymer used in the optical thin film resin film according to the present invention is preferably 40,000 to 200,000, more preferably 50,000 to 180,000, and even more preferably 55,000 to 160,000. If Mw is 40,000 or higher, the strength and toughness of the resin film are improved. If Mw is 200,000 or lower, the flowability and molding processability of the (meth)acrylate polymer are improved. It should be noted that the weight-average molecular weight (Mw) is a value calculated by converting the chromatogram determined by gel permeation chromatography (GPC) into the molecular weight of standard polystyrene.

[0041] The acid value of the (meth)acrylate polymer used in the resin film of the present invention 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)acrylate polymer. The acid value can be determined as follows: for example, the resin to be tested is dissolved in a mixed solvent of xylene and 2-propanol, and then titrated with a 0.1 mol / L potassium hydroxide·ethanol solution using potentiometric titration, with the inflection point on the titration curve as the endpoint, thereby determining the acid value. If the acid value is within the above range, the balance between flowability and film formability is excellent.

[0042] Regarding the resin film involved in this invention, the resin constituting the film matrix may include, in addition to the (meth)acrylate polymers described above, one or more other polymers besides (meth)acrylate polymers, without hindering the purpose of this invention. Examples of other polymers include: polyolefin resins such as polyethylene and polypropylene; styrene resins such as cycloolefin resins, polystyrene, and styrene-acrylonitrile copolymers; thermoplastic resins such as polyamide, polyphenylene sulfide resin, polyetheretherketone resin, polyester resin, polycarbonate resin, polysulfone, polyphenylene ether, polyimide, polyetherimide, and polyacetal; and thermosetting resins such as phenolic resin, melamine resin, silicone resin, and epoxy resin.

[0043] Regarding the resin constituting the film matrix of the resin film according to the present invention, the (meth)acrylate polymer accounts for 50% or more, preferably 60% or more, and more preferably 100% of the total resin mass. That is, the resin constituting the film matrix of the resin film according to the present invention is preferably composed of a (meth)acrylate polymer.

[0044] (Optical conditioning agent)

[0045] The resin film for optical thin films according to the present invention is characterized by containing a carboxylic acid amide compound having an aromatic ring. This carboxylic acid amide compound functions as an optical modulator to adjust the optical properties of the film. According to the present invention, by using a carboxylic acid amide compound containing a specific structure, a transparent (meth)acrylate resin film exhibiting negative birefringence can be obtained.

[0046] Aromatic carboxylate compounds are typically compounds obtained by the condensation of a polycarboxylic acid with an aromatic ring and an amine, and can be carboxylate compounds with a benzene ring or a naphthalene ring. The optical modulator used in this invention has negative intrinsic birefringence and exhibits negative birefringence when it exists in crystalline form in the resin film.

[0047] The aromatic ring of a carboxylic acid amide compound can be monocyclic or polycyclic, and examples include benzene rings, naphthalene rings, biphenyl rings, anthracene rings, and pyrene rings. Examples of carboxylic acids with aromatic rings include dicarboxylic acids having either a benzene ring or a naphthalene ring, and tricarboxylic acids having either a benzene ring or a naphthalene ring. Typically, carboxylic acid amide compounds are condensations of polycarboxylic acids having either a benzene ring or a naphthalene ring and an amide having an aliphatic ring. Carboxylic acid amide compounds can be condensations of dicarboxylic acids or tricarboxylic acids having a benzene ring and an amide having an aliphatic ring, or condensations of dicarboxylic acids or tricarboxylic acids having a naphthalene ring and an amide having an aliphatic ring.

[0048] Carboxylic acids used as raw materials for the carboxylic acid amide compounds used in the resin films according to the present invention include, for example, phthalic acid, isophthalic acid, 5-tert-butylisophthalic acid, terephthalic acid, pyromellitic acid, trimellitic acid, terephthalic acid, 4,4'-biphenyl dicarboxylic acid, 2,2'-biphenyl dicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and pyromellitic acid. Among these, 2,6-naphthalenedicarboxylic acid and pyromellitic acid are preferred.

[0049] The amine used as a raw material for the carboxylic acid amide compound used in the resin film according to the present invention is preferably an amine having an aliphatic ring. The aliphatic ring can be a saturated aliphatic ring or an unsaturated aliphatic ring, but a saturated aliphatic ring is preferred. Examples of cycloalkyl groups containing a saturated aliphatic ring include cyclohexyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl, and amines having these cycloalkyl groups can be used. Examples of cycloalkenyl groups containing an unsaturated aliphatic ring include cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, cyclooctenyl, and cyclopentadienyl, and amines having these cycloalkenyl groups can be used. Amines used as raw materials for optical modulators include, specifically, cyclohexylamine, cyclopentylamine, 2-methylcyclohexylamine, 3-methylcyclohexylamine, 4-methylcyclohexylamine, 2,3-dimethylcyclohexylamine, 2,6-dimethylcyclohexylamine, 2-ethylcyclohexylamine, 3,3,5-trimethylcyclohexylamine, cyclooctylamine, and cyclododecylamine. Cyclohexylamine is preferred among these.

[0050] Carboxylic acid amide compounds used as optical modifiers include, specifically, N,N'-dicyclohexyl-2,6-naphthalenediamide and N,N',N''-tricyclohexylpyromellitic acid trimellitamide. These compounds have historically been used as nucleating agents in crystalline resins and have never been used as optical modifiers in (meth)acrylate resins. These carboxylic acid amide compounds are available, for example, under trade names such as NJSTAR NU-100 (N,N'-dicyclohexyl-2,6-naphthalenediamide) and NJSTAR TF-1 (N,N',N''-tricyclohexylpyromellitic acid trimellitamide) manufactured by Shin Nippon Rikka Co., Ltd., but are not limited to these compounds. One carboxylic acid amide compound may be used alone, or two or more may be used in combination.

[0051] It is known that some compounds containing benzene or naphthalene rings exhibit negative intrinsic birefringence. In the resin films of this invention, it has been found that when using compounds with specific structures exhibiting negative birefringence, (meth)acrylic acid films precipitate in crystalline form, thus exhibiting negative birefringence. While not adhering to a specific theory, it is believed that in the resin films of this invention, by using carboxylic amides as optical modifiers, and further considering that the carboxylic amides contain at least an aromatic ring, preferably also an aliphatic ring, precipitation, dispersion, and the presentation of negative intrinsic birefringence in the film can be simultaneously achieved.

[0052] (Resin film)

[0053] In the resin film of the present invention, the mass ratio of the optical modifier to the (meth)acrylate polymer is 1000 ppm or more, preferably 2000 ppm or more, from the viewpoint of causing the optical modifier to precipitate in crystalline form and improving the dispersibility of the crystals. From the viewpoint of maintaining transparency and dispersibility, it is 11000 ppm or less, preferably 10000 ppm or less. The morphology of the optical modifier crystals contained in the film of the present invention is not particularly limited. Examples include fibrous crystals, needle-like crystals, columnar crystals, and plate-like crystals with high aspect ratios, typically needle-like crystals. Specifically, the aspect ratio of the crystals is preferably 2:1 or more.

[0054] The transparency of the resin film involved in this invention is measured using a haze meter. Regarding the resin film involved in this invention, a haze value of 7.0 or less is preferred for a resin film with a thickness of 0.1 mm, and a haze value of 4.0 or less is more preferred for a resin film with a thickness of 0.1 mm. When the haze value is within this range, the resin film can be evaluated as transparent, and the resin film involved in this invention can be applied to applications requiring transparency.

[0055] The thickness of the resin film involved in this invention can be appropriately selected according to the application and is not particularly limited. As an example, it can be about 5 to 500 μm, preferably about 10 to 200 μm. Even a relatively thick film of about 100 μm (0.1 mm) has high transparency.

[0056] The resin film involved in this invention can contain additives such as stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, foaming agents, lubricants, fillers, colorants, and plasticizers, as needed, in addition to (meth)acrylate polymers and optical modifiers, as long as the effects of this invention are achieved.

[0057] The resin film of the present invention exhibits negative birefringence and transparency, and therefore can be preferably used as an optical film such as a polarizer protective film or a phase difference film used in liquid crystal displays.

[0058] (Method for manufacturing resin film)

[0059] The resin film involved in this invention is obtained as follows: a (meth)acrylate polymer and an optical modifier are mixed, heated to a temperature above the softening temperature of the (meth)acrylate polymer and below the decomposition temperature of the (meth)acrylate polymer, and the mixture is molded to obtain a resin film.

[0060] Regarding the mixing and molding process, after mixing the (meth)acrylate polymer and the optical modifier, the mixture can be heated to a temperature above the softening temperature of the (meth)acrylate polymer and below its decomposition temperature. Alternatively, the (meth)acrylate polymer can be heated to the aforementioned temperature range, and then the optical modifier can be added and mixed. From the viewpoint of causing crystallization in the resin film and obtaining a uniform film, the latter is preferred.

[0061] The mixture of the (meth)acrylate polymer and the optical modifier is heated to a temperature above the softening temperature of the (meth)acrylate polymer, so that the optical modifier dissolves in the molten (meth)acrylate polymer. The softened (meth)acrylate polymer acts as a solvent relative to the optical modifier. That is, it is considered that the optical modifier is molten in the (meth)acrylate polymer in the molten state. Regarding this molten mixture, it is preferable to uniformly disperse the optical modifier in the (meth)acrylate polymer by known means such as stirring or kneading.

[0062] Next, the resulting mixture is shaped by, for example, extrusion and then cooled to obtain a resin film. It is believed that when the mixture is cooled in this way, the optical modifier dissolved in the (meth)acrylate polymer crystallizes and precipitates. Through this process, the optical modifier is uniformly dispersed in the (meth)acrylate resin, resulting in a resin film exhibiting negative birefringence and transparency. From the viewpoint of improving the transparency of the resin film, the cooling temperature is preferably below 60°C, and more preferably around room temperature.

[0063] The resin film involved in this invention can be manufactured by a method for manufacturing composite materials composed of conventional thermoplastic resins, without particular limitation. Manufacturing apparatus may include, for example, a single-spindle extruder, a twin-spindle extruder, a closed-loop mixer, a roller mixer, or a solvent mixer.

[0064] Regarding the molding method for the resin film involved in this invention, any method that achieves the effects of this invention is acceptable and is not limited. Examples include: extrusion molding, solution injection molding, T-die molding, expansion molding, compression molding, calendering, etc., but the method is not limited to these. Among these molding methods, T-die molding and compression molding do not use solvents, are environmentally friendly, and can precisely control the film thickness, therefore they are preferred.

[0065] When manufacturing the resin film involved in this invention using melt extrusion molding methods such as T-die molding or expansion molding, a (meth)acrylate polymer and an optical modifier are mixed, and the resulting mixture is heated to a temperature above the resin's softening temperature and below its decomposition temperature for melt mixing. The resulting mixture is then formed into a specified shape using an extrusion molding machine and cooled, thereby obtaining the resin film involved in this invention.

[0066] Example

[0067] The present invention will now be described in further detail based on embodiments; however, the present invention is not limited to these embodiments.

[0068] [Example 1]

[0069] 50g of methacrylic resin (ACRYPET VH001, manufactured by Mitsubishi Chemical Corporation) was slowly added over 4 minutes to a mixing extrusion apparatus (LaboPlastomill (model 10S100), manufactured by Toyo Seiki Co., Ltd.) set to a temperature of 220°C and a rotation speed of 5 rpm. Then, 0.2g (4000ppm relative to the resin amount) of N,N',N''-tricyclohexylpyromellitic methyl methacrylate (NJSTAR TF-1, manufactured by Shin Nippon Rikka Co., Ltd.) as an optical modifier was added over 1 minute. The rotation speed was then increased from 5 rpm to 30 rpm, and the resin and optical modifier were mixed for 5 minutes to obtain a mixture.

[0070] Using a pressing device (a manual hydraulic heating and cooling pressing device (model IMC-481E) manufactured by Imoto Manufacturing Co., Ltd.), a pressure of 10 MPa was applied to 1.0 g of the mixture and heated to 290°C for 2 minutes. After that, it was cooled for 3 minutes to obtain a film with a thickness of 0.1 mm.

[0071] [Example 2]

[0072] The amount of N,N',N''-tricyclohexylpyromellitic methyl methacrylate, which serves as an optical modifier, was set to 0.5 g (10,000 ppm relative to the amount of resin). Otherwise, the same procedure as in Example 1 was performed to obtain a film.

[0073] [Example 3]

[0074] As an optical modifier, 0.2 g of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide (NJSTAR NU-100 manufactured by Shin Nippon Rikka Co., Ltd.) was added (4000 ppm relative to the amount of resin), and otherwise the same operation as in Example 1 was performed to obtain a film.

[0075] [Comparative Example 1]

[0076] In Example 1, no optical modifier was used; otherwise, the same operation as in Example 1 was performed to obtain a thin film.

[0077] [Comparative Example 2]

[0078] The amount of N,N',N''-tricyclohexylpyromellitic methyl methacrylate, which serves as an optical modifier, was set to 1.0 g (20,000 ppm relative to the amount of resin). Otherwise, the same procedure as in Example 1 was performed to obtain a film.

[0079] [Comparative Example 3]

[0080] The amount of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide added as an optical modifier was set to 0.6 g (12,000 ppm relative to the amount of resin). Otherwise, the same operation as in Example 1 was performed to obtain a film.

[0081] [Comparative Example 4]

[0082] As an optical modifier, N,N'',N'''-tris(2-methylcyclohexyl)-1,2,3-propanetriformamide (Rikaclear PC-1 manufactured by Shin Nippon Rikka Co., Ltd.) was used, and the addition amount was set to 0.5 g (10,000 ppm relative to the amount of resin). Otherwise, the same operation as in Example 1 was performed to obtain a film.

[0083] <Confirmation of Thin Film Properties>

[0084] For the films obtained in Examples 1-3 and Comparative Examples 1-4, haze values ​​were measured, film appearance was observed, and refractive properties were confirmed. The confirmation methods are as follows. The confirmation results are summarized in Table 1.

[0085] <Determination of Haze Value>

[0086] The haze value of the fabricated film was measured using a haze meter (HazeMater (model NDH7000SPII) manufactured by Nippon Denshoku Kogyo Co., Ltd.). The total light transmittance was measured according to JIS-K-7136. Measurements were performed on three films, and the average of the measured values ​​was taken as the final value.

[0087] <Film Appearance Observation>

[0088] The appearance of the prepared film is observed with the naked eye to confirm its transparency.

[0089] <Confirmation of optical properties>

[0090] A portion of the fabricated film is held between a sliding glass and a cover glass and placed on a hot stage (a hot stage manufactured by METTLERTOLEDO Co., Ltd. (product number: FP82HT Hot Stage)). The entire hot stage is then placed on the stage of a polarizing microscope (a polarizing microscope manufactured by NIKON SOLUTIONS Co., Ltd. (product number: Nikon ECLIPSE LV100POL)).

[0091] The initial setting of the hot stage was 290°C. The temperature was reduced from 290°C to 100°C at a rate of 3°C / min, and held at 100°C for 30 minutes. Then, the temperature was reduced from 100°C to 25°C over 15 minutes at a rate of 5°C / min. The sample cooled to 25°C was observed using a polarizing microscope with a sensitive color plate inserted to confirm whether crystallization was observed. Additionally, the color of the crystal was determined when its long axis was aligned parallel to the phase-advance axis of the sensitive color plate. It is known that according to crystallization, if the elongation direction is parallel to X', it exhibits negative crystallization (blue), and at Z', it becomes positive crystallization (yellow) [Reference: Journal of the Japanese Society for Crystallography 42, 401-412 (2000)]. When the long axis of the crystal is aligned parallel to the phase-advance axis of the sensitive color plate, and the crystal color is blue, it is determined to have negative birefringence.

[0092] Table 1

[0093]

[0094] As shown in Table 1, regarding the resin films of Examples 1-3, it was confirmed that the haze values ​​were low and the films were transparent to the naked eye. In particular, the resin films of Examples 1 and 3 exhibited haze values ​​equivalent to those of the resin film of Comparative Example 1, which did not contain optical modifiers, and had high transparency. Furthermore, in the observation of crystal color, it was confirmed that blue crystals were observed in the advancing direction of the sharp color plate, and it was confirmed that a film with dispersed crystals exhibiting negative birefringence was obtained.

[0095] A polarizing microscope image of the thin film obtained in Example 3 is shown below. Figure 1 The crystals precipitated in the thin film appear blue in a direction parallel to the phase advancement axis of the sharp color plate. Figure 1 In the photograph shown, the scale bar in the image is 500 μm in length. In the film of Example 3, an optical modifier was confirmed to precipitate in the form of needle-like crystals with a diameter of approximately 1000 μm.

[0096] No crystallization was observed in the resin film of Comparative Example 1, which did not contain the optical modifier. Comparative Example 2, with an optical modifier (N,N',N''-tricyclohexylpyromellitic amide) added at 20,000 ppm relative to the resin, had a haze value of 7.5, and the film appeared cloudy. Comparative Example 3, with an optical modifier (N,N'-dicyclohexyl-2,6-naphthalenediamide) added at 12,000 ppm relative to the resin, had a haze value of 64.9, and the film appeared cloudy. Comparative Example 4, which used N,N'',N'''-tris(2-methylcyclohexyl)-1,2,3-propanetriformamide as the optical modifier, was confirmed to be a transparent film. However, no crystallization was observed in the resin film of Comparative Example 4. It is believed that crystallization is necessary for the film to impart optical properties.

[0097] The embodiments disclosed herein should be understood as illustrative in all respects and are not intended to limit the scope of the invention in any way. The scope of the invention is intended to be defined by the claims, including all modifications within the meaning and scope of the claims.

Claims

1. A resin film for optical thin films, wherein, Contains: (meth)acrylate polymers, carboxylic acid amide compounds with aromatic rings, The carboxylic acid amide compound contains 1000 ppm or more and 11000 ppm or less of the aforementioned carboxylic acid amide compound relative to the (meth)acrylate polymer. The carboxylic acid amide compound is contained therein in crystalline form, which exhibits negative birefringence.

2. The resin film for optical thin films according to claim 1, wherein, The (meth)acrylate polymer contains 2,000 ppm or more and 10,000 ppm or less of the carboxylic acid amide compound.

3. The resin film for optical thin films according to claim 1 or 2, wherein, A film with a thickness of 0.1 mm has a haze value of 7.0 or less.

4. The resin film for optical thin 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 thin films according to claim 1 or 2, wherein, The carboxylic acid amide compound is a carboxylic acid amide compound having the following structure. This structure is obtained by condensing a polycarboxylic acid having either a benzene ring or a naphthalene ring with an amide compound having an aliphatic ring.

6. A method for manufacturing a resin film for optical thin films, comprising the following steps: A (meth)acrylate polymer is mixed with a carboxylic acid amide compound having an aromatic ring in a proportion of more than 1,000 ppm and less than 11,000 ppm relative to the (meth)acrylate polymer. Molding is performed at a temperature above the softening temperature of the (meth)acrylate polymer and below its decomposition temperature; and A thin film is formed by cooling.

7. The method for manufacturing a resin film for optical thin films according to claim 6, wherein, The carboxylic acid amide compound is a carboxylic acid amide compound having the following structure. This structure is obtained by condensing a polycarboxylic acid having either a benzene ring or a naphthalene ring with an amide compound having an aliphatic ring.

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