Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics

Definitions

• 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 based on Japanese Patent Application No. 2023-130926, filed on August 10, 2023, and incorporates all of the contents of said Japanese Patent Application by reference.
• Patent Document 1 discloses a resin film for optical films, which is composed of a methacrylic acid ester-based polymer and a diacetal compound with a specific structure. It is disclosed that the resin film disclosed in Patent Document 1 has the characteristics of having no dispersion defects and small birefringence.
• 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 phase difference characteristic within a specific range. It is disclosed that the specific composition of this substrate for film contains at least one resin selected from polycarbonate, polyester, cycloolefin resin, acrylic resin, and cellulose resin. It is also disclosed that the substrate for film may contain a resin having an alicyclic structure or an aromatic ring structure that exhibits negative intrinsic birefringence.
• the objective of the present invention is to provide an optical film that exhibits negative birefringence and is highly transparent, and a method for producing the same.
• the resin film for optical films according to the present 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 1000 ppm or more and 11000 ppm or less relative to the (meth)acrylic acid ester polymer.
• the carboxylic acid amide compound is contained as crystals, and the crystals exhibit negative birefringence.
• the resin film disclosed herein provides an optical film that exhibits negative birefringence and is highly transparent.
• FIG. 1 is a polarizing microscope photograph showing crystals of an optical adjuster contained in a resin film according to the present disclosure.
• the resin film for optical films according to the present 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 1000 ppm or more and 11000 ppm or less relative to the (meth)acrylic acid ester polymer.
• the carboxylic acid amide compound is contained as crystals, and the crystals exhibit negative birefringence.
• Patent Document 1 proposes a resin film for optical films that contains a specific acetal compound and has low birefringence.
• Patent Document 2 also proposes a film in which a chemical structure that is thought to exhibit negative birefringence is incorporated into the side chains of the resin that constitutes the film.
• the resin film for optical films according to the present 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 the crystals exhibit negative birefringence.
• the resin film for optical films according to the present disclosure can be formed into a film containing an optical adjuster at any content within a wide range of 1000 ppm to 11000 ppm relative to the base resin constituting the film, and this film exhibits remarkable optical properties.
• the resin film for optical films according to the present disclosure is a film with sufficient transparency and has characteristic functions as a resin film for optical films.
• the carboxylic acid amide compound may be contained in an amount of 2000 ppm or more and 10000 ppm or less relative to the (meth)acrylic acid ester polymer.
• the content of the carboxylic acid amide compound is within this range, the effect of the resin film for optical films according to the present disclosure becomes clearer.
• the resin film for optical films may have a haze value of 7.0 or less when the film is 0.1 mm thick. According to the resin film for optical films of the present disclosure, even when the film is as thick as 0.1 mm and has sufficient strength, the film maintains transparency and exhibits the property of crystals precipitating in the film and exhibiting negative birefringence.
• 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 a general-purpose method.
• 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 a carboxylic acid amide compound having such a structure exhibits negative birefringence and functions as an optical adjuster, and that it precipitates as crystals in a (meth)acrylic acid ester resin film.
• the method for producing a resin film for an optical film includes mixing a (meth)acrylic acid ester-based polymer and 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-based polymer,
• the method includes a step of heating the (meth)acrylic acid ester polymer to a temperature equal to or higher than the softening temperature and equal to or lower than the decomposition temperature of the (meth)acrylic acid ester polymer, and forming the polymer into a film, and a step of cooling the film to form the film.
• a resin film containing a high content of an optical adjuster and in which the optical adjuster precipitated as crystals in the film exhibits negative birefringence can be obtained using a general-purpose method.
• the carboxylic acid amide compound may be 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.
• (meth)acrylic acid ester collectively refers to both acrylic acid ester and methacrylic acid ester.
• 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.
• a suitable methacrylic acid ester resin is a polymer that contains methacrylic acid ester as the main component.
• "containing methacrylic acid ester as the main component" as used in this specification means that the content of methacrylic acid ester in the raw material monomer of the methacrylic acid ester polymer is 50% by mass or more.
• the content of methacrylic acid ester in the raw material monomer 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.
• polymers containing methacrylic acid esters as the main component include methacrylic acid ester homopolymers and methacrylic acid ester copolymers, which contain methacrylic acid esters and other monomers and are obtained by polymerizing raw material monomers containing methacrylic acid esters as the main component.
• Methacrylic acid ester monomers suitable for forming polymers mainly composed of methacrylic acid esters 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 portion has 1 to 18 carbon atoms; cyclohexyl methacrylate
• 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 due to their ease of availability. Furthermore, from the viewpoint of heat resistance, methacrylic acid alkyl 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.
• methacrylic acid ester homopolymer In the case of a methacrylic acid ester homopolymer, one of the above methacrylic acid esters is used as the raw material monomer. When two or more types of methacrylic acid esters are used as raw material monomers, the methacrylic acid ester polymer becomes a methacrylic acid ester copolymer.
• Methacrylic acid ester copolymers obtained by polymerizing a raw material monomer containing a methacrylic acid ester and other monomers 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 other monomers 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 containing a methacrylic acid ester as the main component is usually a random copolymer, and this random copolymer is easily available commercially.
• 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 acrylates such as cyclohexyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, trifluoromethyl acrylate, trifluoroethyl acrylate, pentafluoroethyl acrylate, gly
• vinyl cyanide compounds examples include acrylonitrile and methacrylonitrile; aromatic vinyl compounds such as styrene, ⁇ -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;
• alkyl acrylates and vinyl cyanide compounds are preferred, and alkyl acrylates in which the alkyl group in the ester portion has 1 to 4 carbon atoms, acrylonitrile and methacrylonitrile are more preferred.
• 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 increasing the heat resistance and transparency of the methacrylic acid ester copolymer.
• the resin film for optical film 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.
• suitable acrylic acid ester resins include polymers that have acrylic acid ester as the main component.
• polymers that have acrylic acid ester as the main component include isobutyl acrylate polymer, 2-ethylhexyl acrylate polymer, isodecyl acrylate polymer, nonyl acrylate polymer, and dodecyl acrylate polymer.
• the (meth)acrylic acid ester polymer that serves 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.
• copolymers include methyl methacrylate-(meth)acrylic acid copolymer, methyl methacrylate-(meth)acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymer, methyl (meth)acrylate-styrene copolymer, etc. These polymers may be modified to introduce glutarimide structural units or lactone ring structural units.
• 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.
• 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.
• Mw is 40,000 or more
• the strength and toughness of the resin film are improved.
• Mw is 200,000 or less
• 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 a chromatogram measured by gel permeation chromatography (GPC) into the molecular weight of standard polystyrene.
• 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, and then titrating with a 0.1 mol/L potassium hydroxide-ethanol solution by potentiometric titration, with the inflection point on the titration curve being the endpoint.
• the acid value is within the above range, the balance between fluidity and film formability is excellent.
• the resin film according to the present disclosure may contain, as the resin constituting the film base, one or more types of polymers other than the (meth)acrylic acid ester polymers, in addition to the above-mentioned (meth)acrylic acid ester polymers, within the scope of not impairing the object of the present invention.
• polystyrene 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, polyacetal, and thermosetting resins such as phenol resin, melamine resin, silicone resin, and epoxy resin.
• the resin constituting the film base 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%.
• the resin constituting the film base in the resin film according to the present disclosure is preferably made of a (meth)acrylic acid ester polymer.
• 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 adjuster that adjusts the optical properties of the film.
• by containing a carboxylic acid amide compound having a specific structure crystals exhibiting negative birefringence are precipitated in the film, and a transparent (meth)acrylic acid ester-based resin film is obtained.
• 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 a negative intrinsic birefringence, and exists as a crystal in the resin film to exhibit negative birefringence.
• the aromatic ring of the carboxylic acid amide compound having an aromatic ring may be a single ring or multiple rings, 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 a dicarboxylic acid having either a benzene ring or a naphthalene ring, and a tricarboxylic acid having either a benzene ring or a naphthalene ring.
• carboxylic acid amide compounds include a condensation product of a polycarboxylic acid having either a benzene ring or a naphthalene ring and an amide having an aliphatic ring.
• the carboxylic acid amide compound may be a condensation product of a dicarboxylic acid or tricarboxylic acid having a benzene ring and an amide having an aliphatic ring, or a condensation product of a dicarboxylic acid or tricarboxylic acid having a naphthalene ring and an amide having an aliphatic ring.
• the amine used as the raw material of 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.
• 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.
• 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.
• 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 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.
• NJSTAR NU-100 N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide
• NJSTAR TF-1 N,N',N''-tricyclohexyltrimesic acid amide
• Only one type of carboxylic acid amide compound may be used, or two or more types may be used in combination.
• 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 appearance of negative intrinsic birefringence.
• the mass ratio of the optical regulator to the (meth)acrylic acid ester polymer is 1000 ppm or more, preferably 2000 ppm or more, from the viewpoint of precipitating the optical regulator as crystals and increasing 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 regulator contained in the film according to the present disclosure is not particularly limited, but examples thereof include crystals with high aspect ratios such as fibrous crystals, needle crystals, columnar crystals, and plate crystals, and is typically in the form of needle crystals.
• the aspect ratio of the crystals is preferably 2:1 or more.
• the transparency of the resin film according to the present disclosure is measured by 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 being transparent, and the resin film according to the present disclosure can be applied to applications where transparency is required.
• 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 as an example, it may be about 5 to 500 ⁇ m, and preferably about 10 to 200 ⁇ m.
• the resin film according to the present disclosure has high transparency even in a relatively thick film of about 100 ⁇ m (0.1 mm).
• the resin film according to the present disclosure may contain, in addition to the (meth)acrylic acid ester polymer and optical adjuster, additives such as stabilizers, antioxidants, UV absorbers, antistatic agents, foaming agents, lubricants, fillers, colorants, and plasticizers as necessary, so long as the effects according to the present disclosure are exhibited.
• additives such as stabilizers, antioxidants, UV absorbers, antistatic agents, foaming agents, lubricants, fillers, colorants, and plasticizers as necessary, so long as the effects according to the present disclosure are exhibited.
• the resin film of the present invention exhibits negative birefringence and is transparent, and therefore can be suitably used as an optical film, such as a polarizing plate protective film or a retardation film, for use in liquid crystal displays.
• the resin film according to the present disclosure can be obtained by mixing a (meth)acrylic acid ester-based 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-based polymer and equal to or lower than the decomposition temperature of the (meth)acrylic acid ester-based polymer, and molding the mixture obtained by mixing.
• 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.
• the (meth)acrylic acid ester polymer may be heated to the aforementioned temperature range, and then the optical adjuster may be added and mixed therein. The latter is preferred from the viewpoint of precipitating crystals in the resin film and obtaining a uniform film.
• the mixture of the (meth)acrylic acid ester polymer and the 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 considered to be dissolved in the (meth)acrylic acid ester polymer. It is preferable to uniformly disperse the optical adjuster in the (meth)acrylic acid ester polymer by known means such as stirring or kneading this molten mixture.
• the resulting mixture is molded, for example by extrusion, and cooled to obtain a resin film.
• the optical adjuster dissolved in the (meth)acrylic acid ester polymer crystallizes and precipitates.
• the cooling temperature is preferably 60°C or lower, and more preferably around room temperature, from the viewpoint of increasing the transparency of the resin film.
• the resin film disclosed herein can be manufactured by any method for manufacturing a composite material made of a general thermoplastic resin, and is not particularly limited.
• a single-screw extruder, twin-screw extruder, Banbury mixer, roll kneader, solvent mixer, etc. can be used as the manufacturing device.
• the film molding method used in the production of 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. Of these molding methods, the 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.
• the (meth)acrylic acid ester polymer and the optical adjuster are mixed, the resulting mixture is heated to a temperature above the softening temperature and below the decomposition temperature of the resin and melt-kneaded, and the resulting kneaded product is molded into a predetermined shape using an extrusion molding machine and then cooled to obtain the resin film according to the present disclosure.
• Example 1 50 g of methacrylic resin (Mitsubishi Chemical Corporation, ACRYPET VH001) was slowly added over 4 minutes to a kneading extrusion device (Toyo Seiki Seisakusho Co., Ltd., Labo Plastomill (Model 10S100)) set at a temperature of 220° C. and a rotation speed of 5 rpm. Then, 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 adjuster over 1 minute. Then, the rotation speed was changed from 5 rpm to 30 rpm, and the resin and optical adjuster were mixed for 5 minutes to obtain a mixture.
• a kneading extrusion device Toyo Seiki Seisakusho Co., Ltd., Labo Plastomill (Model 10S100)
• a press device manufactured by Imoto Manufacturing Co., Ltd.
• 1.0 g of the mixture was heated at 290°C and 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.
• 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).
• Example 3 A film was obtained by carrying out the same operations as in Example 1, except that 0.2 g (4000 ppm based on the amount of resin) of N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide (manufactured by New Japan Chemical Co., Ltd., NJSTAR NU-100) was added as an optical adjuster.
• Example 1 A film was obtained by the same procedure as in Example 1, except that no optical adjuster was used.
• 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).
• 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 0.6 g (12,000 ppm based on the amount of resin).
• ⁇ 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 value of the actual measured values obtained in these measurements was taken as the measured value.
• Hot stage product number FP82HT Hot Stage
• polarizing microscope product number Nikon ECLIPSE LV100POL
• the initial setting of the hot stage was set to 290°C, and the sample was cooled from 290°C to 100°C at a rate of 3°C/min, and the temperature was maintained at 100°C for 30 minutes. The sample was then cooled from 100°C to 25°C over 15 minutes at a rate of 5°C/min.
• the sample cooled to 25°C was observed under a polarizing microscope with a sensitive color plate inserted to check whether crystals were observed and the color of the crystals when the long axis of the crystals was oriented in a direction parallel to the fast axis of the sensitive color plate. It is known that if the elongation direction of the crystals is parallel to X', they show negative crystals (blue color), and when it is Z', they show positive crystals (yellow color) [Reference: Journal of the Crystallographic Society of Japan 42, 401-412 (2000)]. When the long axis of the crystals is oriented in a direction parallel to the fast axis of the sensitive color plate and the crystal color is blue, it was determined that the sample had negative birefringence.
• the resin films of Examples 1 to 3 had low haze values, and were confirmed to be transparent when visually observed.
• the resin films of Examples 1 and 3 showed a haze value equivalent to that of the resin film of Comparative Example 1, which did not contain an optical adjuster, and were highly transparent.
• crystal color observation crystals in which blue color was observed in the leading phase direction of the sensitive color plate were confirmed, and it was confirmed that a film in which crystals with negative birefringence were dispersed was obtained.
• a polarizing microscope photograph of the film obtained in Example 3 is shown in Figure 1.
• the crystals precipitated in the film were observed to be blue in the direction parallel to the fast axis of the sensitive color plate.
• the length of the scale bar shown in the image is 500 ⁇ m.
• the optical adjuster was confirmed to have precipitated as needle-shaped crystals with a diameter of approximately 1000 ⁇ m.
• Comparative Example 1 No crystals were observed in the resin film of Comparative Example 1, which did not contain an optical adjuster.
• Comparative Example 2 in which the amount of optical adjuster (N,N',N''-tricyclohexyl trimesic acid amide) added to the resin was 20,000 ppm, had a haze value of 7.5 and the film was cloudy.
• Comparative Example 3 in which the amount of optical adjuster (N,N'-dicyclohexyl-2,6-naphthalenedicarboxyamide) added to the resin was 12,000 ppm, 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-propanetricarboxyamide 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.

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