polyester film

Abstract

To provide a polyester film excellent in flexibility and visibility.SOLUTION: In a polyester film containing polybutylene naphthalate, b* value is 2.0 or less, and a mean value of a hysteresis loss ratio is 56% or less, when performing a tensile cycle test up to 5% tensile strain in respective directions of a longer direction (MD) and width direction (TD).SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a polyester film. [Background technology]

[0002] Polyester film is highly versatile due to its excellent properties such as heat resistance, weather resistance, mechanical strength, transparency, chemical resistance, and gas barrier properties, as well as its affordability and availability. It is used in a variety of applications, including packaging materials and optical applications.

[0003] On the other hand, in recent years, with the miniaturization and weight reduction of electronic devices, there has been a growing trend towards the use of flexible substrates and flexible printed circuits. Following this trend, the demand for flexibility in display applications has also increased, creating a strong need for films with excellent resilience and resistance to repeated bending (flexibility).

[0004] Flexible displays include types such as foldable displays that can be folded, bendable displays that can be folded and bent, rollable displays that can be rolled up, and stretchable displays that can be extended and retracted. A typical example of a flexible display includes a substrate film made from a synthetic resin such as polyimide, and elements such as thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) supported on the substrate film. In addition to the substrate film, optical films with excellent flexibility are also used as components such as the front panel of the flexible display, the base film for touch sensors, and the film that protects the substrate film.

[0005] For example, Patent Document 1 discloses a foldable display that is excellent in mass production and does not cause distortion of the image displayed at the folded part after folding, and a polyester film for a foldable display that does not cause creases or cracks at the folded part, in order to provide a portable terminal device equipped with such a foldable display.

[0006] Furthermore, Patent Documents 2 and 3 disclose a polyester film containing polycyclohexylene dimethylene terephthalate and polyarylate as a display film with excellent folding resistance and heat resistance. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2021 / 182191 [Patent Document 2] Japanese Patent Publication No. 2020-50872 [Patent Document 3] Japanese Patent Publication No. 2020-56016 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, the polyester film disclosed in Patent Document 1 had a low level of flexibility and did not meet market requirements.

[0009] Furthermore, the polyester films described in Patent Documents 2 and 3 may have impaired visibility because the polyarylate yellows when exposed to ultraviolet light.

[0010] Furthermore, in addition to the examples in Patent Documents 1-3, depending on the type of polyester selected, the film may take on a yellowish tint, which can lead to visibility problems such as deterioration of image quality and discoloration.

[0011] The problem that this invention aims to solve is to provide a polyester film that has excellent flexibility and visibility, while resolving the above-mentioned problems. [Means for solving the problem]

[0012] As a result of diligent research, the inventors have found that the above problems can be solved by having the following configuration. The present invention has the following aspects.

[0013] [1] Contains polybutylene naphthalate, b * A polyester film having a value of 2.0 or less, and an average hysteresis loss rate of 56% or less when subjected to tensile cycle testing up to 5% tensile strain in both the longitudinal (MD) and widthwise (TD) directions. [2] The polyester film described in [1] above, wherein the yellowness (YI) is less than 0.00. [3] The polyester film according to [1] or [2] above, containing 5 to 70% by mass of polybutylene naphthalate. [4] A polyester film according to any of [1] to [3] above, further comprising a crystalline polyester. [5] The polyester film according to [4] above, wherein the crystalline polyester is polyethylene naphthalate. [6] A polyester film according to any of [1] to [5] above, further comprising a blue coloring agent. [7] The polyester film according to [6] above, wherein the content of the blue coloring agent is 0.01 to 1% by mass relative to the entire polyester film. [8] The polyester film according to [6] or [7] above, wherein the blue coloring agent is an anthraquinone-based blue dye. [9] A polyester film as described in any of [1] to [8] above, for use in flexible displays.

[10] A laminated polyester film having a cured resin layer on at least one surface layer of the polyester film described in any of [1] to [9] above, wherein the cured resin layer is formed from a resin composition containing a crosslinking agent in an amount of 70% by mass or more relative to the nonvolatile component.

[11] The laminated polyester film described in

[10] above, for use in flexible displays. [Effects of the Invention]

[0014] The polyester film of the present invention has excellent flexibility and visibility. Therefore, the polyester film of the present invention can be suitably used for displays, particularly for flexible displays. [Brief explanation of the drawing]

[0015] [Figure 1] This is a stress-strain curve profile. [Modes for carrying out the invention]

[0016] Next, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiment described below.

[0017] <<Polyester film>> The polyester film of the present invention (hereinafter also referred to as "this film") contains polybutylene naphthalate (hereinafter also referred to as "PBN"), b * The value is 2.0 or less, and the average hysteresis loss rate when performing tensile cycle tests up to 5% tensile strain in both the longitudinal (MD) and widthwise (TD) directions is 56% or less.

[0018] The longitudinal direction (MD) of the film refers to the direction in which the film progresses during the film manufacturing process, i.e., the winding direction of the film roll. The width direction (TD) of the film refers to the direction parallel to the film surface and perpendicular to the longitudinal direction, that is, the direction parallel to the central axis of the roll when the film is in a roll form.

[0019] <Polybutylene naphthalate> As described above, this film contains PBN. The mechanism by which this film possesses excellent flexibility due to the inclusion of PBN is not entirely clear, but it is presumed that the rigidity and symmetry of the naphthalene ring, which is a condensed polycyclic aromatic structure, improves its impact resistance. For example, polyethylene terephthalate and polybutylene terephthalate use terephthalic acid with one benzene ring, while polyethylene naphthalate and polybutylene naphthalate use naphthalene rings with two linked benzene rings, thus improving rigidity while maintaining symmetry.

[0020] Furthermore, PBN contains 1,4-butanediol as its diol component, and it is presumed to have superior impact resistance because it undergoes a structural transition between α-crystals and β-crystals due to the conformation of its alkyl chain. Therefore, from the viewpoint of improving flexibility by enhancing impact resistance, it is preferable to contain 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid rather than terephthalic acid, and it is preferable to contain 1,4-butanediol as the diol component rather than ethylene glycol.

[0021] The PBN constituting this film is a polyester containing 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (a-1) and 1,4-butanediol as the diol component (a-2), preferably with 2,6-naphthalenedicarboxylic acid and 1,4-butanediol as the main components. Specifically, it is preferable that the film contains 50 mol% or more of 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (a-1) and 50 mol% or more of 1,4-butanediol as the diol component (a-2). In particular, the PBN used in the present invention more preferably contains 90 mol% or more of 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (a-1) and 90 mol% or more of 1,4-butanediol as the diol component (a-2).

[0022] The dicarboxylic acid component (a-1) constituting the PBN includes 2,6-naphthalenedicarboxylic acid, and of the dicarboxylic acid component (a-1), it is more preferable that 2,6-naphthalenedicarboxylic acid is 92 mol% or more, even more preferable that it is 94 mol% or more, particularly preferable that it is 96 mol% or more, especially preferable that it is 98 mol% or more, and most preferably that all (100 mol%) of the dicarboxylic acid component (a-1) is 2,6-naphthalenedicarboxylic acid. By using 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (a-1) at a concentration of 90 mol% or more, the glass transition temperature and crystallinity of PBN are improved, and consequently, the heat resistance and mechanical properties of the film are enhanced. Furthermore, by using 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (a-1) at a concentration of 90 mol% or more, the naphthalene skeleton content increases, improving impact resistance. As a result, flexural resistance is also improved.

[0023] The aforementioned PBN may be copolymerized with acid components other than 2,6-naphthalenedicarboxylic acid for the purpose of improving moldability and heat resistance. Specifically, examples include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-frandicarboxylic acid, 2,4-frandicarboxylic acid, 3,4-frandicarboxylic acid, benzophenone dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 3,3'-diphenyldicarboxylic acid, and 4,4'-diphenyl ether dicarboxylic acid; and aliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. These acid components can be used individually or in combination of two or more. Among these, isophthalic acid, 2,5-franglicarboxylic acid, 2,4-franglicarboxylic acid, and 3,4-franglicarboxylic acid are preferred from the viewpoint of moldability. Furthermore, from the viewpoint of flexibility, acid components having a rigid and highly symmetrical naphthalene skeleton are preferred among these. For example, acid components having a benzene skeleton, such as terephthalic acid and isophthalic acid, are preferably present in amounts of 5 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less. Furthermore, it is preferable that the content of acid components other than 2,6-naphthalenedicarboxylic acid be 10 mol% or less of the total acid components including 2,6-naphthalenedicarboxylic acid.

[0024] The diol component (a-2) constituting the PBN contains 1,4-butanediol, and of the diol component (a-2), it is more preferable that 1,4-butanediol accounts for 92 mol% or more, even more preferably 94 mol% or more, particularly preferably 96 mol% or more, and especially preferably 98 mol% or more, with the most preferable being that all (100 mol%) of the diol component (a-2) is 1,4-butanediol. By setting the diol component (a-2) to 90 mol% or more of 1,4-butanediol, the compatibility with the mixed polyester is improved, further improving the glass transition temperature and crystallinity of the PBN, and consequently improving the heat resistance and mechanical properties of the film.

[0025] The aforementioned PBN may be copolymerized with diol components other than 1,4-butanediol for the purpose of improving moldability and heat resistance. Specifically, examples include 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, ethylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, hydroquinone, bisphenol, spiroglycol, 2,2,4,4-tetramethylcyclobutane-1,3-diol, isosorbide, and the like. These diol components can be used individually or in combination of two or more. Among these, from the viewpoint of moldability, ethylene glycol, diethylene glycol, 1,3-propanediol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol are preferable. In addition, the content of the diol component other than the 1,4-butanediol is preferably 10 mol% or less in all the diol components including the 1,4-butanediol.

[0026] The content of the PBN is preferably 5 to 70% by mass when the film is 100% by mass. If the content is 5% by mass or more, the excellent flex resistance of the PBN is exhibited. Further, if the content is 70% by mass or less, an appropriate amount of the content of at least one kind of polyester other than the PBN described later can be ensured, and while improving the extrusion moldability and stretching processability during film forming, the flex resistance can be made good.

[0027] Among them, from the viewpoint of making the flex resistance more excellent, the content of the PBN is preferably 35 to 70% by mass, more preferably 40 to 65% by mass, still more preferably 45 to 62% by mass, and particularly preferably 50 to 60% by mass.

[0028] <At least one kind of polyester other than PBN> As described above, this film contains PBN as an essential component, but preferably contains two or more kinds of polyesters, and in addition to PBN, it is preferable to contain at least one kind of polyester other than PBN (hereinafter, also referred to as "polyester other than PBN"). By including the polyester other than PBN, the crystallization rate can be controlled, and it also becomes excellent in extrusion molding and stretching processes that are difficult with PBN alone. The polyester other than PBN can be used alone or in combination of two or more kinds.

[0029] The polyester other than the PBN is not particularly limited, and examples include those composed of the following dicarboxylic acid components and diol components. Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, orthophthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfisoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, monopotassium salt of trimellitic acid, and their ester-forming derivatives.

[0030] Examples of diol components include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, potassium dimethylolpropionate, and the like. From the above compounds, one or more can be appropriately selected, and polyesters can be synthesized by conventional polycondensation reactions. In addition, depending on the combination of the dicarboxylic acid component and the diol component, a polyester equivalent to the above-mentioned PBN may be included; however, in the present invention, a polyester different from the above-mentioned PBN is used.

[0031] The polyester other than PBN is preferably a crystalline polyester, and more preferably the crystalline polyester has a higher glass transition temperature than PBN. By mixing the crystalline polyester with PBN, the crystallization rate of PBN can be controlled, thereby improving its extrusion and stretchability. Furthermore, because the crystalline polyester has a higher glass transition temperature than PBN, a resin composition with a higher glass transition temperature than PBN alone can be obtained, resulting in good heat resistance.

[0032] The crystalline polyester can be polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, or the like, and it is more preferable to include polyethylene naphthalate (hereinafter also referred to as "PEN") from the viewpoint of improving the balance of flexibility, heat resistance, and moldability. Furthermore, if PEN is used, it can be expected to have a high degree of crystallinity without mutual inhibition of crystallization, as it forms a cocrystal with PBN. In addition, because PEN has a high structural similarity to PBN, it is expected to have good compatibility and be easy to transesterify.

[0033] (Polyethylene naphthalate) The PEN may be a homopolyester or a copolymerized polyester, but it is preferable that the acid component having a benzene skeleton as a copolymer component other than 2,6-naphthalenedicarboxylic acid is 5 mol% or less of the total dicarboxylic acid component. Alternatively, it may not contain any other copolymer components, and all of the dicarboxylic acid component (100 mol%) may be 2,6-naphthalenedicarboxylic acid. Among these, homopolyester is preferred from the viewpoint of maintaining high crystallinity. Furthermore, homopolyester is also preferred from the viewpoint of increasing rigidity and symmetry by increasing the naphthalene skeleton content, thereby making it easier to improve bending resistance. Furthermore, homopolyester and copolymerized polyester may be blended, but if homopolyester and one type of copolymerized polyester are blended, it shall be considered as if two types of crystalline polyester were used.

[0034] When PEN consists of a homopolyester, it is obtained by polycondensation of 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (b-1) and ethylene glycol as the diol component (b-2). Normally, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is produced as a by-product from ethylene glycol. In this specification, this diethylene glycol is referred to as by-product diethylene glycol. The amount of diethylene glycol produced as a by-product from ethylene glycol varies depending on the type of polycondensation, but it is approximately 5 mol% or less of the ethylene glycol. In the present invention, the by-product diethylene glycol of 5 mol% or less is also included in ethylene glycol. On the other hand, depending on the content of diethylene glycol, more specifically, if the content of diethylene glycol exceeds 5 mol%, then the diethylene glycol is distinguished from ethylene glycol.

[0035] On the other hand, when PEN consists of copolymerized polyester, 2,6-naphthalenedicarboxylic acid is an essential component as the dicarboxylic acid component (b-1), and other copolymerization components may be added as needed. Other copolymer components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,5-frandicarboxylic acid, 2,4-frandicarboxylic acid, 3,4-frandicarboxylic acid, benzophenone dicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 3,3'-diphenyldicarboxylic acid, and 4,4'-diphenyl ether dicarboxylic acid; aliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dimer acid; and oxycarboxylic acids such as p-oxybenzoic acid. Among these, isophthalic acid, 2,5-frandicarboxylic acid, 2,4-frandicarboxylic acid, and 3,4-frandicarboxylic acid are preferred from the viewpoint of moldability. Furthermore, among these, copolymer components having a naphthalene skeleton with high rigidity and symmetry are preferred from the viewpoint of flexural resistance. These copolymer components can be used individually or in combination of two or more.

[0036] Ethylene glycol is an essential component of the diol component (b-2), and other copolymer components may be used as needed, including 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, propylene glycol, polyalkylene glycol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, hydroquinone, spiroglycol, 2,2,4,4-tetramethylcyclobutane-1,3-diol, isosorbide, 1,4-cyclohexanedimethanol, polytetramethylene ether glycol, dimer diol, and bisphenols (bisphenol compounds such as bisphenol A, bisphenol F, or bisphenol S, or their derivatives, or their ethylene oxide adducts). Of these, 1,4-cyclohexanedimethanol, polytetramethylene ether glycol, dimer diol, and bisphenols are preferred. In particular, bisphenols are preferred from the viewpoint of maintaining strength. Furthermore, it is preferable to use bisphenol A-ethylene oxide adducts as the bisphenol compounds. These copolymer components can be used individually or in combination of two or more.

[0037] The copolymer polyester constituting PEN preferably contains 2,6-naphthalenedicarboxylic acid as the dicarboxylic acid component (b-1), and ethylene glycol and a bisphenol A-ethylene oxide adduct as the diol component (b-2).

[0038] The copolymerized polyester contains, preferably, 0 mol% to 10 mol%, more preferably 0 mol% to 8 mol%, even more preferably 0 mol% to 6 mol%, particularly preferably 0 mol% to 4 mol%, and especially preferably 0 mol% to 2 mol% of other copolymerized components in the dicarboxylic acid component. By keeping the content of other copolymer components in the dicarboxylic acid component within the above numerical range, the glass transition temperature and crystallinity of the copolymerized polyester are improved, and consequently, the heat resistance and mechanical properties of the film are improved. A particularly preferred configuration is, as described above, the use of a copolymer component having a naphthalene skeleton with high rigidity and symmetry as another copolymer component. For example, the acid component having a benzene skeleton, such as terephthalic acid or isophthalic acid, is preferably 5 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less.

[0039] The copolymerized polyester preferably contains 90 mol% or more, more preferably 92 mol% or more, even more preferably 94 mol% or more, particularly preferably 96 mol% or more, and especially preferably 98 mol% or more of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component, and all (100 mol%) of the dicarboxylic acid component may be 2,6-naphthalenedicarboxylic acid. By keeping the content of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component within the above numerical range, the glass transition temperature and crystallinity of the copolymerized polyester are improved, and consequently, the heat resistance and mechanical properties of the film are enhanced. Furthermore, by keeping the content of 2,6-naphthalenedicarboxylic acid in the dicarboxylic acid component within the above numerical range, the naphthalene skeleton content increases, improving impact resistance. As a result, flexural resistance is also improved.

[0040] The copolymerized polyester contains, preferably, 4 mol% to 70 mol%, more preferably 4.2 mol% to 60 mol%, even more preferably 4.4 mol% to 50 mol%, particularly preferably 4.6 mol% to 40 mol%, and especially preferably 4.8 mol% to 30 mol% of other copolymerized components in the diol component. By keeping the content of other copolymer components in the diol component within the above numerical range, the glass transition temperature of the copolymerized polyester is improved, and consequently, the heat resistance of the film is enhanced. Furthermore, because the crystallinity can be controlled, the crystallization rate can be slowed, improving the extrusion and stretchability of the film. In addition, if the content is 70 mol% or less, the melting point will not become too high. Therefore, there is no need to set a high molding temperature, and there is no concern about thermal decomposition.

[0041] The copolymerized polyester contains ethylene glycol in the diol component, preferably 30 mol% to 96 mol%, more preferably 40 mol% to 95.8 mol%, even more preferably 50 mol% to 95.6 mol%, particularly preferably 60 mol% to 95.4 mol%, and especially preferably 70 mol% to 95.2 mol%. By keeping the ethylene glycol content in the diol component within the above numerical range, the crystallinity of the copolymerized polyester is maintained, and consequently, the heat resistance of this film is improved.

[0042] From the viewpoint of improving the balance of flexibility, heat resistance, and moldability, the content of the crystalline polyester such as PEN is preferably 50 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of PBN, more preferably 55 parts by mass or more and 980 parts by mass or less, even more preferably 60 parts by mass or more and 950 parts by mass or less, and particularly preferably 65 parts by mass or more and 900 parts by mass or less. If the content of the crystalline polyester in this film is 50 parts by mass or more, the crystallization rate can be slowed down, thereby improving the extrusion and stretchability during film manufacturing. Furthermore, if the content is 50 parts by mass or more, the glass transition temperature can be improved, thereby improving the heat resistance of this film. On the other hand, if the content of the crystalline polyester is 1000 parts by mass or less, the excellent flexibility of PBN is not significantly impaired, and the resulting film has good flexibility.

[0043] In particular, from the viewpoint of achieving superior bending resistance, the content of the crystalline polyester such as PEN is preferably 50 parts by mass or more and 185 parts by mass or less per 100 parts by mass of PBN, more preferably 55 parts by mass or more and 150 parts by mass or less, even more preferably 60 parts by mass or more and 125 parts by mass or less, and especially preferably 65 parts by mass or more and 110 parts by mass or less.

[0044] For example, when PEN is used as the crystalline polyester, both PBN and PEN are polyesters having a naphthalene skeleton, but as mentioned above, having 1,4-butanediol as the diol component results in superior impact resistance. In other words, if this film contains the aforementioned PBN and PEN, it is believed that the flexibility improves as the PBN content increases.

[0045] <Other resins> This film may contain other resins other than the PBN and polyesters other than the PBN, as long as the effects of the present invention are not impaired. Other resins include polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polycarbonate resins, polyamide resins, polyacetal resins, acrylic resins, ethylene vinyl acetate copolymers, polymethylpentene resins, polyvinyl alcohol resins, cyclic olefin resins, polylactic acid resins, polybutylene succinate resins, polyacrylonitrile resins, polyethylene oxide resins, cellulose resins, polyimide resins, polyurethane resins, polyphenylene sulfide resins, polyphenylene ether resins, polyvinyl acetal resins, polybutadiene resins, polybutene resins, polyamide-imide resins, polyamide-bismaleimide resins, polyetherimide resins, polyetherether ketone resins, polyethersulfone resins, polyketone resins, polysulfone resins, aramid resins, and fluorine resins.

[0046] <Blue colorant> For the film, in order to improve visibility, it is preferable to contain a blue colorant as necessary. As described above, the film contains PBN. However, since PBN has a naphthalene skeleton, that is, more cyclic structures than polyethylene terephthalate, the resonance effect is enhanced, resulting in a tendency to be colored more yellow. Therefore, in order to suppress visibility problems such as image quality degradation and discoloration, it is preferable to contain a blue colorant for color tone adjustment.

[0047] Examples of the blue colorant include conventionally known blue dyes, blue pigments, etc. Among them, it is preferable to use a blue dye. Examples of the blue dye include anthraquinone-based, azo-based, phthalocyanine-based blue dyes, etc. From the viewpoints of dyeability and fastness, anthraquinone-based blue dyes are more preferable. In addition, the blue colorant is preferably halogen-free. When using a halogen-free colorant, when the polyester film is discarded, the adverse effect on the environment, that is, the environmental load, can be reduced. Therefore, as the blue colorant, it is particularly preferable to use a halogen-free blue dye, and most preferably to use a halogen-free anthraquinone-based blue dye.

[0048] The halogen-free anthraquinone-based blue dye used in the present invention is not particularly limited, and examples thereof include compounds represented by the following general formula (I).

[0049] [Chemical formula]

[0050] (In the formula, R 1 and R 4 each independently represent a substituted or unsubstituted amino group, and R 2 , R 3 , R 5 ~R 8 each independently represent a hydrogen atom or a substituent, and R 2 and R 3They may be bonded to each other, forming a ring.

[0051] R 1 and R 4Each of these independently represents a substituted or unsubstituted amino group. Substituents for substituted amino groups include substituted or unsubstituted alkyl groups having 1 to 20 carbon atoms, such as methyl, ethyl, propyl, butyl, octyl, 2-ethylhexyl, dodecyl, 2-hydroxyethyl, 2-methoxyethyl, 2-(2-methoxyethoxy)ethyl, benzyl, 2-phenethyl, and tetrahydrofurfuryl; alkenyl groups having 2 to 20 carbon atoms, such as vinyl, allyl, propenyl, butenyl, and pentenyl; and cyclopentyl and cyclo Cycloalkyl groups such as hexyl groups; substituted or unsubstituted aryl groups having linear or branched alkyl groups with 1 to 10 carbon atoms as substituents, linear or branched alkoxy groups with 1 to 10 carbon atoms, substituted alkyl groups such as hydroxyethyl groups and methoxyethyl groups, specifically phenyl groups, m-methylphenyl groups, p-methoxyphenyl groups, 2,4,6-trimethylphenyl groups, 2,6-diethyl-4-methylphenyl groups, p-cyanophenyl groups, p-carboxyphenyl groups, p-hydroxyphenyl groups, Substituted or unsubstituted aryl groups such as p-mercaptophenyl, p-(N,N-dimethylamino)phenyl, p-nitrophenyl, p-acetylphenyl, and 1-naphthyl; substituted or unsubstituted heterocyclic groups such as pyridyl, quinolyl, furyl, pyranyl, pyrrolyl, imidazolyl, oxazolyl, pyrazolyl, thienyl, thiazolyl, isothiazolyl, isoxazolyl, pyrimidyl, triazinyl, benzothiazolyl, and benzoxazolyl; formyl, acetyl, propionyl Substituted or unsubstituted acyl groups having 1 to 20 carbon atoms, such as yl group, butyryl group, octanoyl group, benzoyl group, p-methylbenzoyl group, 1-naphthoyl group, and thienoyl group; Substituted or unsubstituted alkylsulfonyl groups having 1 to 20 carbon atoms, such as methylsulfonyl group, ethylsulfonyl group, propylsulfonyl group, butylsulfonyl group, and 2-methoxyethylsulfonyl group; Substituted or unsubstituted arylsulfonyl groups having 1 to 20 carbon atoms, such as phenylsulfonyl group, p-methylphenylsulfonyl group, p-methoxyphenylsulfonyl group, and 1-naphthylsulfonyl group;Examples include substituted or unsubstituted alkoxycarbonyl groups such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, and benzyloxycarbonyl groups; substituted or unsubstituted aryloxycarbonyl groups such as phenyloxycarbonyl, p-methylphenyloxycarbonyl, and 1-naphthyloxycarbonyl groups; and cycloalkyloxycarbonyl groups such as cyclohexyloxycarbonyl and cyclopentyloxycarbonyl groups. Substitutive amino groups may have one or two of these substituents. Furthermore, the nitrogen atom of the amino group and the two substituents may form a five-membered or six-membered ring. Examples of such rings include morpholine rings, thiomorpholine rings, piperidine rings, piperazine rings, and rings represented by structures (II-a) to (II-d) below. These rings may also have substituents.

[0052] [ka]

[0053] (In the above structures (II-a) to (II-d), * indicates the bonding portion with the anthraquinone skeleton.)

[0054] R 2 , R 3 , R 5 ~R 8Each of these independently represents a hydrogen atom or a substituent, and the substituents are specifically: a nitro group, a hydroxyl group, a mercapto group, a carboxyl group, a cyano group, a thiocyano group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted amino group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted cycloalkyloxy group, a substituted or unsubstituted alkenyloxy group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted heterocyclic oxy group, a substituted or unsubstituted acyloxy group, a substituted or unsubstituted alkylsulfonyloxy group, a substituted or unsubstituted arylsulfonyloxy group, a substituted or unsubstituted alkoxycarbonyloxy group, a substituted or unsubstituted aryloxycarbonyloxy group, and a substituted or unsubstituted aryl R represents a coxycarbonyl group, a substituted or unsubstituted cycloalkyloxycarbonyl group, a substituted or unsubstituted alkenyloxycarbonyl group, a substituted or unsubstituted aryloxycarbonyl group, a substituted or unsubstituted heterocyclic oxycarbonyl group, a substituted or unsubstituted carbamoyl group, a substituted or unsubstituted sulfamoyl group, a substituted or unsubstituted acyl group, a substituted or unsubstituted alkylsulfonyl group, a substituted or unsubstituted arylsulfonyl group, a substituted or unsubstituted alkylthio group, a substituted or unsubstituted cycloalkylthio group, a substituted or unsubstituted arylthio group, a substituted or unsubstituted heterocyclic thio group, a substituted or unsubstituted alkoxysulfonyl group, a substituted or unsubstituted cycloalkyloxysulfonyl group, a substituted or unsubstituted alkenyloxysulfonyl group, a substituted or unsubstituted aryloxysulfonyl group, or a substituted or unsubstituted heterocyclic oxysulfonyl group. 2 and R 3 They may be bonded to each other, forming a ring.

[0055] Examples of unsubstituted alkyl groups include linear or branched alkyl groups having 1 to 20 carbon atoms, specifically methyl, ethyl, i-propyl, n-propyl, i-butyl, n-butyl, pentyl, hexyl, 2-ethylhexyl, n-octyl, n-decyl, and n-dodecyl groups.

[0056] Substituting alkyl groups include hydroxyl group-substituted alkyl groups such as 2-hydroxyethyl group and 3-hydroxyethyl group; carboxyl group-substituted alkyl groups such as carboxymethyl group and 2-carboxyethyl group; cyano group-substituted alkyl groups such as 2-cyanoethyl group; substituted or unsubstituted amino group-substituted alkyl groups such as 2-aminoethyl group, 2-(N-methylamino)ethyl group, and 2-(N,N-dimethylamino)ethyl group; substituted or unsubstituted carbamoyl group-substituted alkyl groups such as carbamoylmethyl group and N,N-dimethylcarbamoylethyl group; substituted or unsubstituted aryl group-substituted alkyl groups such as 2-phenylethyl group and 2-(p-methylphenyl)ethyl group; substituted or unsubstituted alkoxy group-substituted alkyl groups such as 2-methoxyethyl group and 3-methoxypropyl group; substituted or unsubstituted aryloxy group-substituted alkyl groups such as 2-phenoxyethyl group and 2-(p-methylphenoxy)ethyl group; substituted or unsubstituted acyloxy group-substituted alkyl groups such as 2-acetoxyethyl group; and cycloalkyl groups such as cyclohexyloxymethyl group. Examples include xyloid-substituted alkyl groups; alkylthio-substituted alkyl groups such as 2-methylthioethyl group and 3-ethylthiopropyl group; substituted or unsubstituted arylthio-substituted alkyl groups such as phenylthiomethyl group and 2-(p-methylphenylthio)ethyl group; cycloalkylthio-substituted alkyl groups such as cyclohexylthiomethyl group; heterocyclic thio-substituted alkyl groups such as 2-(2-mercaptobenzothiazolyl)ethyl group; substituted or unsubstituted alkoxycarbonyl-substituted alkyl groups such as methoxycarbonylmethyl group, 2-ethoxycarbonylethyl group, and 2-(2-methoxyethoxy)carbonylethyl group; substituted or unsubstituted aryloxycarbonyl-substituted alkyl groups such as 2-phenoxycarbonylethyl group and 2-(p-methoxyphenoxy)carbonylethyl group; cycloalkyloxycarbonyl-substituted alkyl groups such as 2-cyclohexyloxycarbonylethyl group; carboxyl-substituted alkyl groups such as 2-carboxyethyl group; and mercapto-substituted alkyl groups such as 2-mercaptoethyl group.

[0057] Examples of substituted or unsubstituted cycloalkyl groups include those with 4 to 7 carbon atoms, such as cyclopentyl, cyclohexyl, and cycloheptyl groups. Examples of substituted or unsubstituted alkenyl groups include linear or branched groups having 2 to 10 carbon atoms, such as vinyl groups, allyl groups, propenyl groups, butenyl groups, and pentenyl groups.

[0058] Examples of substituted or unsubstituted aryl groups include phenyl groups and naphthyl groups, and their substituents include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl groups and methoxyethyl groups.

[0059] Examples of substituted or unsubstituted heterocyclic groups include pyridyl, quinolyl, furyl, pyranyl, pyrrolyl, imidazolyl, oxazolyl, pyrazolyl, thienyl, thiazolyl, isothiazolyl, isoxazolyl, pyrimidyl, triazinyl, benzothiazolyl, and benzoxazolyl groups. Substituents for these groups include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl and methoxyethyl groups.

[0060] Substituents for substituted amino groups include substituted or unsubstituted C1-C20 alkyl groups such as methyl, ethyl, propyl, butyl, octyl, 2-ethylhexyl, dodecyl, 2-hydroxyethyl, 2-methoxyethyl, 2-(2-methoxyethoxy)ethyl, benzyl, 2-phenethyl, and tetrahydrofurfuryl; C2-C20 alkenyl groups such as vinyl, allyl, propenyl, butenyl, and pentenyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; and substituted or unsubstituted aryl groups with carbon as a substituent. These include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, substituted alkyl groups such as hydroxyethyl groups and methoxyethyl groups, specifically phenyl groups, m-methylphenyl groups, p-methoxyphenyl groups, 2,4,6-trimethylphenyl groups, 2,6-diethyl-4-methylphenyl groups, p-cyanophenyl groups, p-carboxyphenyl groups, p-hydroxyphenyl groups, p-mercaptophenyl groups, p-(N,N-dimethylamino)phenyl groups, p-nitrophenyl groups, and p-acetyl groups. Substituted or unsubstituted aryl groups such as phenyl group, 1-naphthyl group; substituted or unsubstituted heterocyclic groups such as pyridyl group, quinolyl group, furyl group, pyranyl group, pyrrolyl group, imidazolyl group, oxazolyl group, pyrazolyl group, thienyl group, thiazolyl group, isothiazolyl group, isoxazolyl group, pyrimidyl group, triazinyl group, benzothiazolyl group, benzoxazolyl group; substituted or unsubstituted C1-C20 groups such as formyl group, acetyl group, propionyl group, butyryl group, octanoyl group, benzoyl group, p-methylbenzoyl group, 1-naphthoyl group, thienol group, etc. Unsubstituted acyl groups; substituted or unsubstituted alkylsulfonyl groups having 1 to 20 carbon atoms, such as methylsulfonyl group, ethylsulfonyl group, propylsulfonyl group, butylsulfonyl group, and 2-methoxyethylsulfonyl group; substituted or unsubstituted arylsulfonyl groups, such as phenylsulfonyl group, p-methylphenylsulfonyl group, p-methoxyphenylsulfonyl group, and 1-naphthylsulfonyl group; substituted or unsubstituted alkoxycarbonyl groups, such as methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, butoxycarbonyl group, and benzyloxycarbonyl group;Examples include substituted or unsubstituted aryloxycarbonyl groups such as phenyloxycarbonyl groups, p-methylphenyloxycarbonyl groups, and 1-naphthyloxycarbonyl groups; and cycloalkyloxycarbonyl groups such as cyclohexyloxycarbonyl groups and cyclopentyloxycarbonyl groups. A substituted amino group may have one or two of these substituents. Furthermore, the nitrogen atom of the amino group and the two substituents may form a five-membered or six-membered ring. Examples of such rings include morpholine rings, thiomorpholine rings, piperidine rings, piperazine rings, and rings represented by structures (II-a) to (II-d) below. These rings may also have substituents.

[0061] [ka]

[0062] (In the above structures (II-a) to (II-d), * indicates the bonding portion with the anthraquinone skeleton.)

[0063] Examples of substituted or unsubstituted alkoxy groups include, for unsubstituted alkoxy groups, linear or branched alkoxy groups having 1 to 20 carbon atoms, specifically methoxy, ethoxy, i-propoxy, n-propoxy, i-butoxy, n-butoxy, pentyloxy, hexyloxy, 2-ethylhexyloxy, n-octyloxy, n-decyloxy, and n-dodecyloxy groups, while for substituted alkoxy groups, the total number of carbon atoms in the substituted alkoxy group is 1 to 20. Preferably, hydroxy-substituted alkoxy groups such as 2-hydroxyethoxy group, 2-hydroxypropoxy group, 3-hydroxypropoxy group, 4-hydroxybutoxy group; phenyl-substituted alkoxy groups such as benzyloxy group, 2-phenylethoxy group; 2-methoxyethoxy group, 2-ethoxyethoxy group, 2-(n)propoxyethoxy group, 2-(iso)propoxyethoxy group, 3-methoxypropoxy group, 4-methoxybutoxy group, 3-methoxybutoxy group, 2,3-dimethoxyp Alkoxy-substituted alkoxy groups such as ropoxy group and 2,2-dimethoxyethoxy group; alkoxy-substituted alkoxy groups such as 2-(2-methoxyethoxy)ethoxy group, 2-(2-ethoxyethoxy)ethoxy group, 2-(2-(n)propoxyethoxy)ethoxy group, 2-(2-(n)butoxyethoxy)ethoxy group, and 2-{2-(2-ethylhexyloxy)ethoxy}ethoxy group; aralkyloxy-substituted alkoxy groups such as 2-phenethyloxyethoxy group and 2-benzyloxyethoxy group. Examples include lucoxy groups; acyloxy-substituted alkoxy groups such as 2-acetyloxyethoxy group and 2-propionyloxyethoxy group; alkoxycarbonyl-substituted alkoxy groups such as 2-methoxycarbonylethoxy group and 2-ethoxycarbonylethoxy group; heterocyclic-substituted alkoxy groups such as furfuryloxy group and tetrahydrofurfuryloxy group; alkenyloxy-substituted alkoxy groups such as 2-allyloxyethoxy group; and aryloxy-substituted alkoxy groups such as 2-phenoxyethoxy group.

[0064] Examples of substituted or unsubstituted cycloalkyloxy groups include those with 4 to 7 carbon atoms, such as cyclopentyloxy, cyclohexyloxy, and cycloheptyloxy groups. Examples of substituted or unsubstituted alkenyloxy groups include linear or branched groups having 2 to 10 carbon atoms, such as vinyloxy groups, allyloxy groups, propenyloxy groups, butenyloxy groups, and pentenyloxy groups.

[0065] Examples of substituted or unsubstituted aryloxy groups include phenoxy and naphthoxy groups, and their substituents include nitro, hydroxyl, mercapto, carboxyl, cyano, thiocyano, linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl and methoxyethyl groups.

[0066] Examples of substituted or unsubstituted heterocyclic oxy groups include pyridyloxy, quinolyloxy, furyloxy, pyranyloxy, pyrrolyloxy, imidazolyloxy, oxazolyloxy, pyrazolyloxy, thienyloxy, thiazolyloxy, isothiazolyloxy, isoxazolyloxy, pyrimidyloxy, triazinyloxy, benzothiazolyloxy, and benzoxazolyloxy. Substituents for these include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl and methoxyethyl groups.

[0067] Examples of substituted or unsubstituted acyloxy groups include those with 1 to 20 carbon atoms, such as acetyloxy group, propionyloxy group, butyryloxy group, octanoyloxy group, benzoyloxy group, p-methylbenzoyloxy group, 1-naphthoyloxy group, and thienoyloxy group. Examples of substituted or unsubstituted alkylsulfonyloxy groups include methylsulfonyloxy, ethylsulfonyloxy, propylsulfonyloxy, butylsulfonyloxy, pentylsulfonyloxy, hexylsulfonyloxy, 2-ethylhexylsulfonyloxy, n-octylsulfonyloxy, n-decylsulfonyloxy, n-dodecylsulfonyloxy, and 2-methoxyethoxysulfonyloxy, which have 1 to 20 carbon atoms.

[0068] Examples of substituted or unsubstituted aryloxycarbonyloxy groups include phenoxycarbonyloxy group, p-methylphenoxycarbonyloxy group, p-methoxyphenoxycarbonyloxy group, and 1-naphthoxycarbonyloxy group. As substituted or unsubstituted alkoxycarbonyl groups, unsubstituted alkoxycarbonyl groups include linear or branched alkoxycarbonyl groups having 1 to 20 carbon atoms, specifically methoxycarbonyl group, ethoxycarbonyl group, i-propoxycarbonyl group, n-propoxycarbonyl group, i-butoxycarbonyl group, n-butoxycarbonyl group, pentyloxycarbonyl group, hexyloxycarbonyl group, 2-ethylhexyloxycarbonyl group, n-octyloxycarbonyl group, n-decyloxycarbonyl group Examples include nyl groups and n-dodecyloxycarbonyl groups. The substituted alkoxycarbonyl groups are preferably those with 1 to 20 carbon atoms in total, such as hydroxysubstituted alkoxycarbonyl groups like 2-hydroxyethoxycarbonyl, 2-hydroxypropoxycarbonyl, 3-hydroxypropoxycarbonyl, and 4-hydroxybutoxycarbonyl; phenylsubstituted alkoxycarbonyl groups like benzyloxycarbonyl and 2-phenylethoxycarbonyl; and 2-methoxyethoxycarbonyl groups. Alkoxy-substituted alkoxycarbonyl groups such as 2-ethoxyethoxycarbonyl group, 2-(n)propoxyethoxycarbonyl group, 2-(iso)propoxyethoxycarbonyl group, 3-methoxypropoxycarbonyl group, 4-methoxybutoxycarbonyl group, 3-methoxybutoxycarbonyl group, 2,3-dimethoxypropoxycarbonyl group, 2,2-dimethoxyethoxycarbonyl group, etc.; 2-(2-methoxyethoxy)ethoxycarbonyl group, 2-(2-ethoxyethoxy)ethoxycarbonyl group, 2-(2-(n) Alkoxy-alkoxy substituted alkoxycarbonyl groups such as ropoxyethoxy)ethoxycarbonyl group, 2-(2-(n)butoxyethoxy)ethoxycarbonyl group, and 2-{2-(2-ethylhexyloxy)ethoxy}ethoxycarbonyl group; aralkyloxy substituted alkoxycarbonyl groups such as 2-phenethyloxyethoxycarbonyl group and 2-benzyloxyethoxycarbonyl group; acyloxy substituted alkoxycarbonyl groups such as 2-acetyloxyethoxycarbonyl group and 2-propionyloxyethoxycarbonyl group;Examples include alkoxycarbonyl-substituted alkoxycarbonyl groups such as 2-methoxycarbonylethoxycarbonyl group and 2-ethoxycarbonylethoxycarbonyl group; heterocyclic-substituted alkoxycarbonyl groups such as furfuryloxycarbonyl group and tetrahydrofurfuryloxycarbonyl group; alkenyloxy-substituted alkoxycarbonyl groups such as 2-allyloxyethoxycarbonyl group; and aryloxy-substituted alkoxycarbonyl groups such as 2-phenoxyethoxycarbonyl group.

[0069] Examples of substituted or unsubstituted cycloalkyloxycarbonyl groups include those with 4 to 7 carbon atoms, such as cyclopentyloxycarbonyl group, cyclohexyloxycarbonyl group, and cycloheptyloxycarbonyl group. Examples of substituted or unsubstituted alkenyloxycarbonyl groups include linear or branched groups having 2 to 10 carbon atoms, such as vinyloxycarbonyl group, allyloxycarbonyl group, propenyloxycarbonyl group, butenyloxycarbonyl group, and pentenyloxycarbonyl group.

[0070] Examples of substituted or unsubstituted aryloxycarbonyl groups include phenoxycarbonyl groups and naphthoxycarbonyl groups, and their substituents include nitro groups, hydroxyl groups, mercapto groups, carboxyl groups, cyano groups, thiocyano groups, linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl groups and methoxyethyl groups.

[0071] Examples of substituted or unsubstituted heterocyclic oxycarbonyl groups include pyridyloxycarbonyl group, quinolyloxycarbonyl group, furyloxycarbonyl group, pyranyloxycarbonyl group, pyrrolyloxycarbonyl group, imidazolyloxycarbonyl group, oxazolyloxycarbonyl group, pyrazolyloxycarbonyl group, thienyloxycarbonyl group, thiazolyloxycarbonyl group, isothiazolyloxycarbonyl group, isoxazolyloxycarbonyl group, pyrimidyloxycarbonyl group, triazinyloxycarbonyl group, benzothiazolyloxycarbonyl group, and benzoxazolyloxycarbonyl group. Substituents for these groups include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl and methoxyethyl groups.

[0072] Substituents for substituted carbamoyl groups include substituted or unsubstituted alkyl groups with 1 to 20 carbon atoms such as methyl, ethyl, propyl, butyl, octyl, 2-ethylhexyl, dodecyl, 2-hydroxyethyl, 2-methoxyethyl, 2-(2-methoxyethoxy)ethyl, benzyl, 2-phenethyl, and tetrahydrofurfuryl; alkenyl groups with 2 to 20 carbon atoms such as vinyl, allyl, propenyl, butenyl, and pentenyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; and substituted or unsubstituted ali groups. These are alkyl groups having substituents such as linear or branched alkyl groups with 1 to 10 carbon atoms, linear or branched alkoxy groups with 1 to 10 carbon atoms, hydroxyethyl groups, methoxyethyl groups, and other substituted alkyl groups. Specifically, these include phenyl groups, m-methylphenyl groups, p-methoxyphenyl groups, p-cyanophenyl groups, p-carboxyphenyl groups, p-hydroxyphenyl groups, p-mercaptophenyl groups, p-(N,N-dimethylamino)phenyl groups, p-nitrophenyl groups, p-acetylphenyl groups, and 1-naphthyl groups. or unsubstituted aryl groups; substituted or unsubstituted heterocyclic groups such as pyridyl, quinolyl, furyl, pyranyl, pyrrolyl, imidazolyl, oxazolyl, pyrazolyl, thienyl, thiazolyl, isothiazolyl, isoxazolyl, pyrimidyl, triazinyl, benzothiazolyl, and benzoxazolyl groups; substituted or unsubstituted acyl groups with 1 to 20 carbon atoms such as formyl, acetyl, propionyl, butyryl, octanoyl, benzoyl, p-methylbenzoyl, 1-naphthoyl, and thienol groups; Substituted or unsubstituted alkylsulfonyl groups having 1 to 20 carbon atoms, such as ethylsulfonyl group, ethylsulfonyl group, propylsulfonyl group, butylsulfonyl group, and 2-methoxyethylsulfonyl group; Substituted or unsubstituted arylsulfonyl groups, such as phenylsulfonyl group, p-methylphenylsulfonyl group, p-methoxyphenylsulfonyl group, and 1-naphthylsulfonyl group; Substituted or unsubstituted alkoxycarbonyl groups, such as methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, butoxycarbonyl group, and benzyloxycarbonyl group;Examples include substituted or unsubstituted aryloxycarbonyl groups such as phenyloxycarbonyl groups, p-methylphenyloxycarbonyl groups, and 1-naphthyloxycarbonyl groups; and cycloalkyloxycarbonyl groups such as cyclohexyloxycarbonyl groups and cyclopentyloxycarbonyl groups. A substituted carbamoyl group may have one or two of these substituents. Furthermore, the nitrogen atom of the carbamoyl group and the two substituents may form a five-membered or six-membered ring. Examples of such rings include morpholine rings, thiomorpholine rings, piperidine rings, piperazine rings, and rings represented by structures (II-a) to (II-d) below. These rings may also have substituents.

[0073] [ka]

[0074] Substituents for substituted sulfamoyl groups include substituted or unsubstituted alkyl groups having 1 to 20 carbon atoms, such as methyl, ethyl, propyl, butyl, octyl, 2-ethylhexyl, dodecyl, 2-hydroxyethyl, 2-methoxyethyl, 2-(2-methoxyethoxy)ethyl, benzyl, 2-phenethyl, and tetrahydrofurfuryl; alkenyl groups having 2 to 20 carbon atoms, such as vinyl, allyl, propenyl, butenyl, and pentenyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; and substituted or unsubstituted ali groups. These are alkyl groups having substituents such as linear or branched alkyl groups with 1 to 10 carbon atoms, linear or branched alkoxy groups with 1 to 10 carbon atoms, hydroxyethyl groups, methoxyethyl groups, and other substituted alkyl groups. Specifically, these include phenyl groups, m-methylphenyl groups, p-methoxyphenyl groups, p-cyanophenyl groups, p-carboxyphenyl groups, p-hydroxyphenyl groups, p-mercaptophenyl groups, p-(N,N-dimethylamino)phenyl groups, p-nitrophenyl groups, p-acetylphenyl groups, and 1-naphthyl groups. or unsubstituted aryl groups; substituted or unsubstituted heterocyclic groups such as pyridyl, quinolyl, furyl, pyranyl, pyrrolyl, imidazolyl, oxazolyl, pyrazolyl, thienyl, thiazolyl, isothiazolyl, isoxazolyl, pyrimidyl, triazinyl, benzothiazolyl, and benzoxazolyl groups; substituted or unsubstituted acyl groups with 1 to 20 carbon atoms such as formyl, acetyl, propionyl, butyryl, octanoyl, benzoyl, p-methylbenzoyl, 1-naphthoyl, and thienol groups; Substituted or unsubstituted alkylsulfonyl groups having 1 to 20 carbon atoms, such as ethylsulfonyl group, ethylsulfonyl group, propylsulfonyl group, butylsulfonyl group, and 2-methoxyethylsulfonyl group; Substituted or unsubstituted arylsulfonyl groups, such as phenylsulfonyl group, p-methylphenylsulfonyl group, p-methoxyphenylsulfonyl group, and 1-naphthylsulfonyl group; Substituted or unsubstituted alkoxycarbonyl groups, such as methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, butoxycarbonyl group, and benzyloxycarbonyl group;Examples include substituted or unsubstituted aryloxycarbonyl groups such as phenyloxycarbonyl groups, p-methylphenyloxycarbonyl groups, and 1-naphthyloxycarbonyl groups; and cycloalkyloxycarbonyl groups such as cyclohexyloxycarbonyl groups and cyclopentyloxycarbonyl groups. A substituted sulfamoyl group may have one or two of these substituents. Furthermore, the nitrogen atom of the sulfamoyl group and the two substituents may form a five-membered or six-membered ring. Examples of such rings include morpholine rings, thiomorpholine rings, piperidine rings, piperazine rings, and rings represented by structures (II-a) to (II-d) below. These rings may also have substituents.

[0075] [ka]

[0076] Examples of substituted or unsubstituted acyl groups include substituted or unsubstituted acyl groups having 1 to 20 carbon atoms, such as formyl group, acetyl group, propionyl group, butyryl group, octanoyl group, benzoyl group, p-methylbenzoyl group, 1-naphthoyl group, and thienoyl group.

[0077] Examples of substituted or unsubstituted alkylsulfonyl groups include linear or branched alkylsulfonyl groups having 1 to 20 carbon atoms, specifically methylsulfonyl group, ethylsulfonyl group, i-propylsulfonyl group, n-propylsulfonyl group, i-butylsulfonyl group, n-butylsulfonyl group, pentylsulfonyl group, hexylsulfonyl group, 2-ethylhexylsulfonyl group, n-octylsulfonyl group, n-decylsulfonyl group, n-dodecylsulfonyl group, etc., which may have substituents such as hydroxyl groups or alkoxy groups.

[0078] Examples of substituted or unsubstituted arylsulfonyl groups include phenylsulfonyl groups and naphthylsulfonyl groups, and their substituents include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl groups and methoxyethyl groups.

[0079] Examples of substituted or unsubstituted alkylthio groups include linear or branched alkylthio groups having 1 to 20 carbon atoms, specifically methylthio group, ethylthio group, i-propylthio group, n-propylthio group, i-butylthio group, n-butylthio group, pentylthio group, hexylthio group, 2-ethylhexylthio group, n-octylthio group, n-decylthio group, n-dodecylthio group, etc., which may have substituents such as hydroxyl groups and alkoxy groups.

[0080] Examples of substituted or unsubstituted cycloalkylthio groups include those with 4 to 7 carbon atoms, such as cyclopentylthio, cyclohexylthio, and cycloheptylthio groups. Examples of substituted or unsubstituted arylthio groups include phenylthio groups and naphthylthio groups, and their substituents include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl groups and methoxyethyl groups.

[0081] Examples of substituted or unsubstituted heterocyclic thio groups include pyridylthio, quinolylthio, furylthio, pyranylthio, pyrlorylthio, imidazolylthio, oxazolylthio, pyrazolylthio, thienylthio, thiazolylthio, isothiazolylthio, isoxazolylthio, pyrimidylthio, triazinylthio, benzothiazolylthio, and benzoxazolylthio. Substituents for these include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl and methoxyethyl groups.

[0082] As substituted or unsubstituted alkoxysulfonyl groups, unsubstituted alkoxysulfonyl groups include linear or branched alkoxysulfonyl groups having 1 to 20 carbon atoms, specifically methoxysulfonyl group, ethoxysulfonyl group, i-propoxysulfonyl group, n-propoxysulfonyl group, i-butoxysulfonyl group, n-butoxysulfonyl group, pentyloxysulfonyl group, hexyloxysulfonyl group, 2-ethylhexyloxysulfonyl group, n-octyloxysulfonyl group, and n-decyloxysulfonyl group. Examples include nyl groups and n-dodecyloxysulfonyl groups. The substituted alkoxysulfonyl groups preferably have 1 to 20 carbon atoms in total, including hydroxysubstituted alkoxysulfonyl groups such as 2-hydroxyethoxysulfonyl, 2-hydroxypropoxysulfonyl, 3-hydroxypropoxysulfonyl, and 4-hydroxybutoxysulfonyl groups; phenylsubstituted alkoxysulfonyl groups such as benzyloxysulfonyl and 2-phenylethoxysulfonyl groups; and 2-methoxyethoxysulfonyl groups. Alkoxy-substituted alkoxysulfonyl groups such as 2-ethoxyethoxysulfonyl group, 2-(n)propoxyethoxysulfonyl group, 2-(iso)propoxyethoxysulfonyl group, 3-methoxypropoxysulfonyl group, 4-methoxybutoxysulfonyl group, 3-methoxybutoxysulfonyl group, 2,3-dimethoxypropoxysulfonyl group, 2,2-dimethoxyethoxysulfonyl group, etc.; 2-(2-methoxyethoxy)ethoxysulfonyl group, 2-(2-ethoxyethoxy)ethoxysulfonyl group, 2-(2-(n)propoxysulfonyl group, etc. Alkoxyalkoxy-substituted alkoxysulfonyl groups such as ropoxyethoxy)ethoxysulfonyl group, 2-(2-(n)butoxyethoxy)ethoxysulfonyl group, and 2-{2-(2-ethylhexyloxy)ethoxy}ethoxysulfonyl group; aralkyloxy-substituted alkoxysulfonyl groups such as 2-phenethyloxyethoxysulfonyl group and 2-benzyloxyethoxysulfonyl group; acyloxy-substituted alkoxysulfonyl groups such as 2-acetyloxyethoxysulfonyl group and 2-propionyloxyethoxysulfonyl group;Examples include alkoxycarbonyl-substituted alkoxysulfonyl groups such as 2-methoxycarbonylethoxysulfonyl group and 2-ethoxycarbonylethoxysulfonyl group; heterocyclic-substituted alkoxysulfonyl groups such as furfuryloxysulfonyl group and tetrahydrofurfuryloxysulfonyl group; alkenyloxy-substituted alkoxysulfonyl groups such as 2-allyloxyethoxysulfonyl group; and aryloxy-substituted alkoxysulfonyl groups such as 2-phenoxyethoxysulfonyl group.

[0083] Examples of substituted or unsubstituted cycloalkyloxysulfonyl groups include those with 4 to 7 carbon atoms, such as cyclopentyloxysulfonyl group, cyclohexyloxysulfonyl group, and cycloheptyloxysulfonyl group. Examples of substituted or unsubstituted alkenyloxysulfonyl groups include linear or branched groups having 2 to 10 carbon atoms, such as vinyloxysulfonyl group, allyloxysulfonyl group, propenyloxysulfonyl group, butenyloxysulfonyl group, and pentenyloxysulfonyl group.

[0084] Examples of substituted or unsubstituted aryloxysulfonyl groups include phenoxysulfonyl groups and naphthoxysulfonyl groups, and their substituents include nitro groups, hydroxyl groups, mercapto groups, carboxyl groups, cyano groups, thiocyano groups, linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl groups and methoxyethyl groups.

[0085] Examples of substituted or unsubstituted heterocyclic oxysulfonyl groups include pyridyloxysulfonyl group, quinolyloxysulfonyl group, furyloxysulfonyl group, pyranyloxysulfonyl group, pyrloryloxysulfonyl group, imidazolyloxysulfonyl group, oxazolyloxysulfonyl group, pyrazolyloxysulfonyl group, thienyloxysulfonyl group, thiazolyloxysulfonyl group, isothiazolyloxysulfonyl group, isoxazolyloxysulfonyl group, pyrimidyloxysulfonyl group, triazinyloxysulfonyl group, benzothiazolyloxysulfonyl group, and benzoxazolyloxysulfonyl group. Substituents for these groups include linear or branched alkyl groups having 1 to 10 carbon atoms, linear or branched alkoxy groups having 1 to 10 carbon atoms, and substituted alkyl groups such as hydroxyethyl and methoxyethyl groups.

[0086] R 2 , R 3 , R 5 ~R 8 Each of these is preferably a hydrogen atom, or R 5 ~R 8 Each represents a hydrogen atom, and R 2 and R 3 These are substituents, and it is preferable that they are bonded to each other to form a ring. Specific examples of substituents are as described above. Also, R 2 and R 3 Examples of compounds in which elements bond to each other to form a ring include those with a structure represented by the following general formula (III).

[0087] [ka]

[0088] (In the formula, X 1 and X 4 ~X 8 These are R in equation (I), respectively. 1 and R 4 ~R 8 It is synonymous with X 9 and X 10X represents an oxygen atom, a sulfur atom, or NH, 11 (This represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a phenyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted aralkyl group.)

[0089] X in equation (III) 11 For substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted alkyl groups, and substituted or unsubstituted aryl groups in R 1 ~R 8 As explained in [reference], examples of substituted or unsubstituted aralkyl groups include aralkyl groups having 7 to 20 carbon atoms. Groups that may be substituted for aralkyl groups include alkyl groups having 1 to 15 carbon atoms, alkoxy groups having 1 to 15 carbon atoms, hydroxyl groups, amino groups, dimethylamino groups, diethylamino groups, halogen atoms, sulfo groups, and carboxyl groups. Specific examples of aralkyl groups include benzyl groups, phenethyl groups, α-methylbenzyl groups, α-methylphenylethyl groups, β-methylphenylethyl groups, and fluorenyl groups.

[0090] Furthermore, among the compounds represented by the above general formula (III), the compound represented by the following general formula (III-a) is preferred.

[0091] [ka]

[0092] (In the formula, X 11 (As stated above.)

[0093] X 11 The carbon atoms preferably have 1 to 20 carbon atoms, more preferably 2 to 10 carbon atoms, and even more preferably 2 to 6 carbon atoms. In particular, X 11 It is preferably a C2-C6 alkyl group, and is either substituted or unsubstituted, and from the viewpoint of robustness, X 11It is more preferable that the group is an alkoxy-substituted alkyl group such as a 2-methoxyethyl group or a 3-methoxypropyl group.

[0094] The halogen-free anthraquinone-based blue dye used in the present invention may also be a compound represented by the following general formula (IV).

[0095] [ka]

[0096] (In the formula, X 21 ~X 24 Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a phenyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted aralkyl group.

[0097] X in general formula (IV) 21 ~X 24 For substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted alkyl groups, and substituted or unsubstituted aryl groups in R 1 ~R 8 As explained above, the substituted or unsubstituted aralkyl group is X 11 As explained in [the previous section]. In the above general formula (IV), X 21 ~X 24 In the case of atoms other than hydrogen atoms, each atom preferably has 1 to 20 carbon atoms, more preferably 6 to 15, and even more preferably 8 to 14 carbon atoms. Among the compounds represented by the general formula (IV) above, X 21 and X 23 Compounds represented by the following general formula (IV-a), in which is a hydrogen atom, are preferred, and among them, X 22 and X 24 Compounds selected from a phenyl group and a substituted or unsubstituted aryl group are more preferably X 22 and X 24It is even more preferable that each is selected from a 2,4,6-trimethylphenyl group and a 2,6-diethyl-4-methylphenyl group.

[0098] [ka]

[0099] (In the formula, X 22 and X 24 These are as described above.

[0100] Furthermore, the halogen-free anthraquinone-based blue dye used in the present invention is also preferably a compound represented by the following general formula (V).

[0101] [ka]

[0102] (In the formula, X 27 , X 28 Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a phenyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted aralkyl group. 1 and Y 2 (Either one is a hydroxyl group and the other is a nitro group (-NO2) or an amino group (-NH2), or both are hydrogen atoms.)

[0103] X in general formula (V) 27 , X 28 For substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted alkyl groups, and substituted or unsubstituted aryl groups in R 1 ~R 8 As explained above, the substituted or unsubstituted aralkyl group is X 11 As explained in [the previous section]. X 27 and X 28In the case of atoms other than hydrogen atoms, each atom preferably has 1 to 20 carbon atoms, more preferably 4 to 15, and even more preferably 6 to 14 carbon atoms.

[0104] Among the compounds represented by the above general formula (V), compounds represented by the following general formulas (Va) to (Vc) are more preferred.

[0105] [ka]

[0106] (In the formula, X 31 ~X 34 Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkoxy group, a phenyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted aralkyl group.

[0107] X in the general formula (Va)~(Vc) 31 ~X 34 For substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted alkyl groups, and substituted or unsubstituted aryl groups in R 2 , R 3 , R 5 ~R 8 As explained above, the substituted or unsubstituted aralkyl group is X 11 As explained in [the previous section]. In the above general formulas (Va) to (Vc), X 31 ~X 34 In the case of atoms other than hydrogen atoms, each atom preferably has 1 to 20 carbon atoms, more preferably 4 to 15, and even more preferably 6 to 14 carbon atoms. Among the compounds represented by the general formulas (Va) to (Vc), from the viewpoint of improving light resistance, the compound represented by general formula (Va) is X 31 is a 4-(2-ethoxyethoxy)phenyl group, X 32 A compound in which the atom is a hydrogen atom, X 31 is a 4-hydroxyphenoxy group, X 32A compound in which X is a hydrogen atom, or X 31 is a 4-methoxyphenoxy group, X 32 is a hydrogen atom is preferred. Also, in the compound represented by the general formula (V-b), X 33 is a 2-hydroxyethylphenyl group, or X 33 is a phenyl group is also preferred. Further, in the compound represented by the general formula (V-c), X 34 is a phenyl group is also preferred. However, in the present invention, as the halogen-free anthraquinone-based blue dye, compounds other than those represented by the general formula (I) and the general formula (V) can also be used.

[0108] Specific examples of the halogen-free anthraquinone-based blue dye include Disperse Blue 3, Disperse Blue 5, Disperse Blue 14, Disperse Blue 26, Disperse Blue 28, Disperse Blue 35, Disperse Blue 334, Disperse Blue 359, Disperse Blue 60, Disperse Blue 72, Disperse Blue 73, Disperse Blue 77, Disperse Blue 214, Disperse Blue 167, Disperse Blue 54, SolventBlue 101, Solvent Blue 102, Solvent Blue 104, Solvent Blue 122, Solvent Blue 35, Solvent Blue 36, Solvent Blue 59, Solvent Blue 63, Solvent Blue 68, Solvent Blue 78, Solvent Blue 97, and the like. Among these, preferred compounds include Disperse Blue 60, a dye containing the compound represented by the general formula (III-a) described above. Also, Solvent Blue 104 and Solvent Blue 97 are dyes containing the compound represented by the general formula (IV) described above. Furthermore, Disperse Blue 214, Disperse Blue 167, and Disperse Blue 54 are dyes containing the compound represented by the general formula (V) described above. The dyes mentioned above may be used individually or in combination of two or more.

[0109] As described later, when the blue coloring agent in the polyester is added to the polyester raw material for this film to form a masterbatch, the content of the blue coloring agent in the polyester raw material of the film is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 2 to 10% by mass. If the content is above the lower limit, the effect of the blue coloring agent is sufficiently obtained, and if it is below the upper limit, it is preferable in terms of the stability of the masterbatch. Furthermore, the content of the blue coloring agent is preferably 0.01 to 1% by mass relative to the total polyester film, more preferably 0.01 to 0.8% by mass, even more preferably 0.01 to 0.6% by mass, and particularly preferably 0.01 to 0.5% by mass. Within this range, the film can be manufactured without problems, and the b of the film * The values ​​and yellowness (YI) can be easily adjusted to the desired values, leading to improved visibility.

[0110] The method of adding the blue coloring agent is not particularly limited, but the blue coloring agent and the raw material of the film (e.g., polyester) may be prepared in advance as a masterbatch, or it may be added directly at the raw material input stage in the manufacturing process of the film.

[0111] <Other> There are no particular restrictions on the polymerization catalyst for polyester, and conventionally known compounds can be used, such as titanium compounds, germanium compounds, antimony compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds.

[0112] To suppress the precipitation of oligomer components, the film may be manufactured using polyester with a low oligomer content as the raw material. Various known methods can be used to manufacture polyester with a low oligomer content, such as a method of solid-phase polymerization after polyester production. Alternatively, polyester may be obtained by esterification or transesterification, followed by further increasing the reaction temperature and melt polycondensation under reduced pressure.

[0113] This film may be an unstretched film (sheet) or a stretched film. In particular, it is preferably a film that is stretched in at least one direction, specifically a uniaxial or biaxially oriented film, and more preferably a biaxially oriented film from the viewpoint of balance of mechanical properties, flatness, and thinness.

[0114] The intrinsic viscosity of the polyester is not particularly limited, but from the viewpoint of film-forming properties and productivity, it is preferably 0.45 to 1.3 dL / g, and more preferably 0.5 to 1.2 dL / g.

[0115] This film may also contain particles primarily for the purpose of providing slipperiness and preventing scratches during each process. The types of particles mentioned above are not particularly limited as long as they can impart slipperiness. Examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide; and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. Furthermore, during the polyester manufacturing process, precipitated particles obtained by precipitating and finely dispersing a portion of metal compounds such as catalysts can also be used.

[0116] There are no particular restrictions on the shape of the particles used; spherical, lumpy, rod-shaped, flattened, etc., may be used. Furthermore, there are no particular restrictions on their hardness, specific gravity, color, etc. These particles may be used individually or in combination of two or more types as needed.

[0117] The average particle size of the particles used is not particularly limited, but is usually 5 μm or less, preferably in the range of 0.01 to 3 μm. An average particle size of 5 μm or less is preferable because it ensures the transparency of the film and prevents the surface roughness of the film from becoming too rough. If the average particle size is 0.01 μm or more, effects such as providing slipperiness and preventing scratch formation can be ensured. Furthermore, if the particles are in powder form, the average particle size can be determined by using a centrifugal sedimentation particle size distribution analyzer (e.g., Shimadzu Corporation's "SA-CP3" model) to measure the particle size distribution at 50% of the cumulative volume fraction (d50). For particles in films, layers, or resins, the average particle size can be determined by observing 10 or more particles with a scanning electron microscope (SEM), measuring the diameter of each particle, and taking the average value. In the case of non-spherical particles, the average of the longest and shortest diameters can be used as the diameter of each particle.

[0118] The particle content in the layer containing the above-mentioned particles is not particularly limited, but is usually less than 5% by mass, preferably in the range of 0.0003 to 3% by mass. If no particles are present, or if the particle content is low, a film with excellent transparency is obtained. On the other hand, if particles are included within the above range, a film with sufficient slipperiness is obtained. Even if particles are present, sufficient transparency of the film can be ensured if the particle content is less than 5% by mass. When incorporating particles into this film, it is preferable to provide, for example, a surface layer and an intermediate layer, and to incorporate particles into at least one of the surface layers. If this film is a single layer, the layer containing particles is the entire film.

[0119] This film may be single-layer or multi-layer. In the case of a multi-layer film, examples include a two-layer structure consisting of a surface layer and an intermediate layer, or a three-layer structure in which the intermediate layer is sandwiched between two surface layers. In both single-layer and multi-layer cases, the resin composition of each layer may consist solely of PBN as described above, or it may consist of a mixture of PBN and at least one of polyesters other than PBN and other resins other than these polyesters. In the case of multi-layer cases, the content of each resin in each layer may also be as described above on a layer-by-layer basis. Furthermore, in a multilayer structure, the resin composition of each layer may be the same or different from one another.

[0120] The method for adding particles to this film is not particularly limited, and conventionally known methods can be employed. For example, they can be added at any stage in the production of the raw material polyester, but it is preferable to add them after the esterification or transesterification reaction is completed.

[0121] In addition to the particles mentioned above, conventionally known antioxidants, ultraviolet absorbers, antistatic agents, heat stabilizers, lubricants, and other colorants (dyes, pigments), etc., may be added to this film as needed.

[0122] The thickness of this film is preferably 4 to 300 μm, more preferably 20 to 250 μm, even more preferably 25 to 200 μm, and particularly preferably 30 to 150 μm. If the film thickness is 4 μm or more, the film strength is maintained within a practical range, making it suitable for use in displays. On the other hand, if the thickness is 300 μm or less, flexibility is easily achieved, making it particularly suitable for use in flexible displays. The thickness can be adjusted by the film formation and stretching conditions. The thickness of this film was determined by cutting a roughly square sample piece with sides of 40 mm from the film, measuring the thickness at five arbitrary points on the film surface using a dial gauge with a scale of 1 / 1000 mm, and calculating the average value.

[0123] <Method for manufacturing polyester film> The method for manufacturing this film will be described below. However, the following description is just one example of a method for manufacturing polyester film and is not limited to that method.

[0124] For example, when manufacturing a biaxially oriented film as a polyester film, the method described above, in which the polyester raw material is extruded from a die as a molten sheet using an extruder and then cooled and solidified in a rotating cooling drum (casting drum) to obtain an unstretched sheet, is preferred. In this case, in order to improve the flatness of the sheet, it is preferable to increase the adhesion between the sheet and the rotating cooling drum, and electrostatic application adhesion and / or liquid coating adhesion methods are preferably employed. An unstretched sheet is obtained in this way. The polyester raw material should be supplied to the extruder after being appropriately dried, such as in the form of pellets. Particles, UV absorbers, and other additives may also be blended into the pellets as appropriate.

[0125] Next, the obtained unstretched sheet is stretched in two axial directions. First, the unstretched sheet is stretched in one direction using a roll or tenter type stretcher. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Next, the material is stretched in a direction perpendicular to the first stretching direction. In this case, the stretching temperature is usually 70 to 170°C, and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times.

[0126] Then, the film is heat-treated at a temperature of 180-270°C under tension or under relaxation of 30% or less to obtain a biaxially oriented film. In the above stretching, a method of performing unidirectional stretching in two or more stages can also be employed. In that case, it is preferable to perform the stretching so that the final stretching ratios in both directions are within the above ranges.

[0127] In addition, the simultaneous biaxial stretching method can also be adopted in the production of the polyester film. The simultaneous biaxial stretching method is a method of simultaneously stretching and orienting the above-mentioned unstretched sheet in the longitudinal direction and the width direction while controlling the temperature at usually 70 to 120 °C, preferably 80 to 110 °C. The stretching ratio is 4 to 50 times, preferably 7 to 35 times, more preferably 10 to 25 times in terms of area ratio. Subsequently, heat treatment is carried out at a temperature of 170 to 250 °C under tension or under relaxation within 30% to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching device adopting the above stretching method, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be adopted.

[0128] <Physical properties of the polyester film> The b * value of this film is 2.0 or less. The b * value is a physical property indicating yellow - blue, and it is preferably near zero. b * If the b value is 2.0 or less, the film does not appear yellowed, and when applied to a display film, there are no problems such as image quality deterioration and discoloration, which is preferable. From this perspective, the b * value is preferably 1.5 or less, more preferably 1.0 or less, further preferably 0.5 or less, and particularly preferably 0.3 or less. On the other hand, the b * value is preferably -0.5 or more. If it is -0.5 or more, the film does not appear blue and does not give a dark impression, which is preferable. From this perspective, it is more preferably -0.3 or more, and further preferably -0.1 or more. In addition, the b * value can be adjusted by the polyester used in this film, the addition of a colorant, etc. The b * value defined in the present invention is the measured value when the film is 125 μm.

[0129] The yellowness index (YI) of this film is preferably less than 0.00. The yellowness index (YI) is related to the above-mentioned b *It is possible to capture the degree of color that cannot be fully captured by numerical values ​​alone. A yellowness index (YI) of less than 0.00 is preferable because it avoids problems such as image degradation or discoloration due to the yellowing of the film. From this viewpoint, it is more preferable to have a yellowness index (YI) of -0.03 or less, more preferably -0.05 or less, and even more preferably -0.10 or less. On the other hand, it is preferable that the yellowness index (YI) is -0.30 or higher. A value of -0.30 or higher is preferable because it prevents the film from appearing too blue and does not give a dark impression. From this viewpoint, it is more preferable to have a yellowness index (YI) of -0.20 or higher, and even more preferably -0.15 or higher. The degree of yellowness (YI) can be adjusted by the polyester used in this film, the addition of colorants, etc., and the degree of yellowness (YI) defined in this invention is the measured value when the film is 125 μm thick.

[0130] The average hysteresis loss rate when tensile cycle tests were performed on this film up to a 5% tensile strain in both the longitudinal (MD) and widthwise (TD) directions was 56% or less. There is no specific lower limit, but it is 0.1% or higher. The smaller the hysteresis loss rate, the greater the film's resilience and the easier it is to return to its original state, meaning it has excellent bending resistance. If the hysteresis loss rate of this film is 56% or less, the film's resilience increases, resulting in good bending resistance. From this viewpoint, the hysteresis loss rate is preferably 53% or less, and more preferably 50% or less. The hysteresis loss rate can be adjusted by the polyester used in this film, the film manufacturing and stretching conditions, etc., and the hysteresis loss rate specified in this invention is the measured value when the film is 125 μm thick.

[0131] The haze of this film is preferably 3.0% or less, more preferably 2.5% or less, even more preferably 2.0% or less, and particularly preferably 1.5% or less. The lower limit is not particularly limited, but is 0.1% or more. Within the range where haze is present, this film can be said to have good transparency and excellent visibility.

[0132] The thermal shrinkage rate of this film after heat treatment at 150°C for 30 minutes is preferably -5 to 5% in both the longitudinal direction (MD) and the width direction (TD), more preferably -3 to 3%, and even more preferably -2 to 2%. Within the range of thermal shrinkage, the film possesses sufficient flatness and heat resistance. In particular, it exhibits excellent dimensional stability at high temperatures and can be used without practical problems for display applications. The thermal shrinkage rate was measured by the method described in the examples, where a positive value represents the shrinkage rate and a negative value represents the expansion rate.

[0133] <<Laminated polyester film>> The laminated polyester film of the present invention (hereinafter also referred to as "this laminated film") may, if necessary, have a cured resin layer on at least one surface layer of the polyester film for the purpose of improving visibility, and it is preferable that the cured resin layer is formed from a resin composition containing a crosslinking agent at a concentration of 70% by mass or more relative to the non-volatile components. In particular, it is more preferable to provide cured resin layers on both surface layers of the polyester film. Here, a polyester film having a cured resin layer is referred to as a laminated polyester film and is distinguished from a polyester film. Furthermore, other layers may be present between the polyester film and the cured resin layer.

[0134] <Crosslinking agent> Various known crosslinking agents can be used as the aforementioned crosslinking agent, including, for example, oxazoline compounds, melamine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds, and the like. Among these, oxazoline compounds are preferably used, for example, when another layer is provided on top of a cured resin layer, from the viewpoint of improving durability and adhesion. Furthermore, melamine compounds are preferably used from the viewpoint of preventing oligomer precipitation on the film surface due to heating and improving the durability of the cured resin layer.

[0135] (Oxazoline compounds) Oxazoline compounds are compounds having an oxazoline group in their molecule, and polymers containing an oxazoline group are particularly preferred. These can be produced by polymerization of an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of addition-polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline. One or more of these can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is readily available industrially. Other monomers are not limited as long as they are copolymerizable with addition-polymerizable oxazoline group-containing monomers. Examples include alkyl (meth)acrylates, with alkyl groups including methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups. Unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid, and their salts are also included, with examples of salts including sodium salts, potassium salts, ammonium salts, and tertiary amine salts. Furthermore, examples include unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated amides such as (meth)acrylamide, N-alkyl(meth)acrylamide, and N,N-dialkyl(meth)acrylamide, with alkyl groups including methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups. Other examples include vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α,β-unsaturated monomers such as vinyl chloride and vinylidene chloride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene. One or more of these monomers can be used. From the viewpoint of improving the durability of the cured resin layer, the amount of oxazoline groups in the oxazoline compound is preferably in the range of 0.5 to 10 mmol / g, more preferably 3 to 9 mmol / g, and even more preferably 5 to 8 mmol / g.

[0136] (Melamine compound) Melamine compounds are compounds that have a melamine skeleton in the compound. For example, alkylolated melamine derivatives, compounds that have been partially or completely etherified by reacting alkylolated melamine derivatives with alcohol, and mixtures thereof can be used. Suitable alcohols for etherification include methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, and isobutanol. Furthermore, the melamine compound may be a monomer, a polymer of two or more commensals, or a mixture thereof. In addition, a compound in which urea or the like is co-condensed with a portion of the melamine can be used, and a catalyst can be used to increase the reactivity of the melamine compound.

[0137] (Epoxy compound) Epoxy compounds are compounds that have an epoxy group in their molecule. Examples include condensates of epichlorohydrin, ethylene glycol, polyethylene glycol, glycerin, polyglycerin, and bisphenol A with hydroxyl or amino groups, as well as polyepoxy compounds, diepoxy compounds, monoepoxy compounds, and glycidylamine compounds. Examples of polyepoxy compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris(2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether. Examples of diepoxy compounds include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polytetramethylene glycol diglycidyl ether. Examples of monoepoxy compounds include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether, while examples of glycidylamine compounds include N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylamino)cyclohexane.

[0138] (Isocyanate compounds) Isocyanate compounds are compounds having an isocyanate derivative structure, such as isocyanates or blocked isocyanates. Examples of isocyanates include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylenediphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic isocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic isocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylenebis(4-cyclohexyl isocyanate), and isopropylidene dicyclohexyl diisocyanate. Furthermore, polymers and derivatives of these isocyanates, such as biuretized, isocyanurateized, uretdioneized, and carbodiimide-modified compounds, can also be mentioned. These may be used individually or in combination. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferred than aromatic isocyanates in order to avoid yellowing due to ultraviolet light.

[0139] When used in the form of blocked isocyanates, examples of blocking agents include phenolic compounds such as bisulfites, phenol, cresol, and ethylphenol; alcoholic compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, and ethanol; active methylene compounds such as methyl isobutanoylacetate, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone; mercaptan compounds such as butyl mercaptan and dodecyl mercaptan; lactam compounds such as ε-caprolactam and δ-valerolactam; amine compounds such as diphenylaniline, aniline, and ethyleneimine; acid amide compounds such as acetanilide and acetic acid amide; and oxime compounds such as formaldehyde, acetaldehyde oxime, acetone oxime, methyl ethyl ketone oxime, and cyclohexanone oxime. These may be used individually or in combination of two or more.

[0140] Furthermore, isocyanate compounds may be used alone or as mixtures or binders with various polymers. It is preferable to use mixtures or binders with polyester resins or urethane resins to improve the dispersibility and crosslinking properties of the isocyanate compounds.

[0141] (Carbodiimide compounds) A carbodiimide compound is a compound having a carbodiimide structure, specifically a compound having one or more carbodiimide structures within its molecule. However, polycarbodiimide compounds having two or more carbodiimide structures within their molecule are more preferable for better adhesion and other properties.

[0142] Carbodiimide compounds can be synthesized using conventionally known techniques, and generally, condensation reactions of diisocyanate compounds are employed. The diisocyanate compounds are not particularly limited and can be either aromatic or aliphatic. Specifically, examples include tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane diisocyanate.

[0143] The amount of carbodiimide groups contained in a carbodiimide compound is typically in the range of 100 to 1000, preferably 250 to 700, and more preferably 300 to 500, in terms of carbodiimide equivalents (weight [g] of the carbodiimide compound required to give 1 mol of carbodiimide groups). Using a compound within this range improves the durability of the cured resin layer.

[0144] Furthermore, to the extent that it does not impair the spirit of the present invention, surfactants may be added, or hydrophilic monomers such as polyalkylene oxides, quaternary ammonium salts of dialkylamino alcohols, and hydroxyalkyl sulfonates may be added to improve the water solubility and water dispersibility of the polycarbodiimide compound.

[0145] (Silane coupling compounds) Silane coupling compounds are organosilicon compounds that contain both an organic functional group and a hydrolysis group such as an alkoxy group within a single molecule. For example, epoxy group-containing compounds such as 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; vinyl group-containing compounds such as vinyltrimethoxysilane and vinyltriethoxysilane; styryl group-containing compounds such as p-styryltrimethoxysilane and p-styryltriethoxysilane; (meth)acrylic group-containing compounds such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)- Examples include amino group-containing compounds such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane; isocyanurate group-containing compounds such as tris(trimethoxysilylpropyl)isocyanurate and tris(triethoxysilylpropyl)isocyanurate; and mercapto group-containing compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane.

[0146] These crosslinking agents may be used individually or in combination of two or more, but using two or more in combination can improve the ability to prevent oligomer precipitation after heating. Furthermore, using two or more crosslinking agents in combination can improve the adhesion between the cured resin layer and other layers, for example, when the laminated film has other layers on top of the cured resin layer. Among these, a combination of an oxazoline compound, which can improve the adhesion between the cured resin layer and other layers, and a melamine compound, which has good ability to prevent oligomer precipitation after heating, is particularly preferred.

[0147] Furthermore, when the laminated film has another layer on top of the cured resin layer, it is more preferable to combine three or more crosslinking agents to further improve the adhesion between the cured resin layer and the other layer. As for the combination of three or more crosslinking agents, it is preferable to select a melamine compound as one of the crosslinking agents, and as crosslinking agents to be combined with the melamine compound, oxazoline compounds and epoxy compounds, and carbodiimide compounds and epoxy compounds are even more preferable. In addition, from the viewpoint of obtaining excellent visibility by improving the prevention of oligomer precipitation after heating, a combination of melamine compounds, oxazoline compounds and epoxy compounds is particularly preferable.

[0148] When such a crosslinking agent is included, components that promote crosslinking, such as a crosslinking catalyst, can be used in combination.

[0149] The crosslinking agent is preferably present in an amount of 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total nonvolatile components in the resin composition forming the cured resin layer according to the present invention. If the amount is 70% by mass or more, not only is the ability to prevent oligomer precipitation after heating improved, but the adhesion to other layers that may be further provided on the cured resin layer can also be improved.

[0150] <Binder resin> The resin composition that forms the cured resin layer may also contain a binder resin, to the extent that it does not impair the spirit of the present invention, in order to improve the appearance of the cured resin layer or to improve adhesion with other layers that may be provided on the cured resin layer. While conventionally known binder resins can be used, it is preferable to use polyester resin, acrylic resin, or urethane resin from the viewpoint of improving adhesion with the layer provided on the cured resin layer.

[0151] <particle> Furthermore, the resin composition may also contain particles for the purpose of blocking and improving slipperiness. From the viewpoint of film transparency, the average particle size is preferably 1.0 μm or less, more preferably 0.5 μm or less, and even more preferably 0.2 μm or less. On the other hand, in order to more effectively improve slipperiness, it is preferably 0.01 μm or more, more preferably 0.03 μm or more, and particularly preferably in a range greater than the film thickness of the cured resin layer. Specific examples of particles include silica, alumina, kaolin, calcium carbonate, and organic particles.

[0152] <Other> Furthermore, to the extent that it does not impair the spirit of the present invention, the resin composition may optionally contain crosslinking catalysts, defoaming agents, coating properties improvers, thickeners, organic lubricants, antistatic agents, ultraviolet absorbers, antioxidants, foaming agents, dyes, pigments, and the like.

[0153] Furthermore, the analysis of various compounds (components) in the cured resin layer can be performed, for example, by TOF-SIMS, ESCA, or X-ray fluorescence.

[0154] The film thickness of the cured resin layer (after drying) is preferably 0.003 to 1.0 μm, more preferably 0.005 to 0.5 μm, and even more preferably 0.01 to 0.2 μm. If the film thickness is 1.0 μm or less, the appearance and blocking resistance of the cured resin layer are sufficient. On the other hand, if the film thickness is 0.003 μm or more, the amount of oligomer precipitated from the film is reduced, which can improve visibility.

[0155] <Method for forming a hardened resin layer> The following description will explain a method for forming a cured resin layer. However, this description is merely one example of a method for forming a cured resin layer and is not limited to this method.

[0156] The resin composition is generally preferably diluted with water, an organic solvent, or a mixture thereof. The cured resin layer is formed by coating the surface of the polyester film with the diluted resin composition as a coating solution and then drying it. Conventional coating methods can be used to apply the coating solution to the film, such as air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss roll coating, cast coating, spray coating, curtain coating, calender coating, and extrusion coating. Furthermore, in order to improve the applicability and adhesion of the coating agent (coating liquid) to the film, the film may be subjected to chemical treatment, corona discharge treatment, plasma treatment, etc., before coating.

[0157] Coating methods include in-line coating and off-line coating, but in-line coating is preferred. In-line coating is a method of coating within the manufacturing process of polyester film, and specifically, it is a method of coating at any stage from the melt extrusion of the raw material polyester to stretching, heat fixing, and winding. Usually, the coating is applied to an unstretched sheet obtained by melting and rapidly cooling, a stretched uniaxially oriented film, a biaxially oriented film before heat fixing, or a polyester film after heat fixing but before winding, but it is particularly preferred to coat a uniaxially oriented film stretched in the longitudinal direction (vertical direction) and then stretch it in the width direction (lateral direction). Furthermore, when a cured resin layer is provided by in-line coating, it is preferable to use a coating solution prepared by adjusting the solid content concentration to approximately 0.1 to 50% by mass using the above-mentioned series of compounds as an aqueous solution or aqueous dispersion. In addition, within the limits that do not impair the spirit of the present invention, the coating solution may contain a small amount of one or more organic solvents for the purpose of improving dispersibility in water, improving film-forming properties, etc.

[0158] The drying and curing conditions when forming a cured resin layer on a film are not particularly limited. For example, when providing a cured resin layer by offline coating, it is preferable to perform heat treatment at 80-200°C for 3-40 seconds, and more preferably at 100-180°C for 3-40 seconds. On the other hand, when a cured resin layer is provided by in-line coating, it is preferable to perform heat treatment at 70 to 280°C for approximately 3 to 200 seconds.

[0159] Furthermore, regardless of whether it is offline coating or in-line coating, heat treatment and active energy ray irradiation such as ultraviolet irradiation may be used in combination as needed.

[0160] <Physical properties of the cured resin layer> When this laminated film has a cured resin layer, it is effective in preventing oligomer precipitation on the film surface due to heating. By reducing oligomer precipitation, it is possible to suppress the decrease in visibility caused by whitening of the film's appearance due to oligomer precipitation and whitening. The amount of oligomer (ester cyclic trimer) precipitated on the surface of at least one cured resin layer in this laminated film is 0.40 mg / m². 2 Preferably, it is 0.35 mg / m² 2 It is more preferable that the following is the case: 0.30 mg / m² 2 It is even more preferable that the following is the case: 0.25 mg / m² 2 The following is particularly preferred: 0.20 mg / m² 2 The following is particularly preferable: Oligomer precipitation amount: 0.40 mg / m² 2The following is preferable, as it avoids reduced visibility due to whitening of the film's appearance caused by oligomer precipitation and crystallization on the surface, the occurrence of defects during post-processing, and contamination of the process and components. There is no particular lower limit, but 0.01 mg / m² is preferable. 2 That's all. The amount of oligomer precipitated is the value obtained by the method described in the examples.

[0161] <<Application>> Because this film and this laminated film have excellent flexibility and visibility, they can be suitably used for displays, especially flexible displays. Flexible displays include foldable displays that can be folded, bendable displays that can be folded and bent, rollable displays that can be rolled up, and stretchable displays that can be extended and retracted, among which foldable displays are preferred. Furthermore, "for flexible displays" refers to display components such as front panels, base films for touch sensors, and films that protect the back side of the display device. Because this film offers excellent visibility, it is particularly suitable for use as a front panel among these display components.

[0162] Furthermore, the display is suitable for use in mobile phones, smartphones, digital cameras, personal computers, etc. There are no particular restrictions on the type of display, but examples include liquid crystal displays, plasma displays, organic EL displays, etc., and touch panel displays are also acceptable.

[0163] <<Explanation of terms and phrases>> In this invention, the term "film" includes "sheets," and the term "sheet" includes "film." In this invention, when "X~Y" (where X and Y are any numbers) is written, unless otherwise specified, it means "X or greater and Y or less," and also includes the meaning of "preferably greater than X" or "preferably less than Y." Furthermore, when "X or greater" (where X is any number) is written, unless otherwise specified, it includes the meaning of "preferably greater than X," and when "Y or less" (where Y is any number) is written, unless otherwise specified, it also includes the meaning of "preferably less than Y." [Examples]

[0164] Next, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples described below.

[0165] <Evaluation Method> (1) Intrinsic viscosity of polyester 1 g of polyester was accurately weighed, dissolved in 100 ml of a phenol / tetrachloroethane mixed solvent (50 / 50 by mass ratio), and measured at 30°C.

[0166] (2) Average particle size The average particle size d50 was defined as the particle size at which the cumulative volume fraction of 50% of the equivalent spherical distribution was measured using a centrifugal sedimentation type particle size distribution analyzer (SA-CP3 model) manufactured by Shimadzu Corporation.

[0167] (3) Polyester film b * value Polyester film b * The values ​​were determined using a Konica Minolta Japan CM-3700d spectrophotometer as follows: Samples were taken by punching out a sample from a designated location with a round holder blade approximately 60 mm in diameter. The measurement conditions were transmission conditions. Note that b * The values ​​were measured in an environment of 23°C.

[0168] (4) Yellowness (YI) of polyester film The yellowness (YI) of polyester film was determined using a Konica Minolta Japan CM-3700d spectrophotometer as follows: Samples were taken by punching out a sample from a predetermined location using a round holder blade with a diameter of approximately 60 mm. The measurement conditions were transmission conditions, and the auxiliary illuminant C was used. The value obtained in the XYZ color system was calculated using the following formula (1). Yellowness index (YI)=100(1.2769X-1.0592Z) / Y...Equation (1) The yellowness (YI) was measured in an environment of 23°C.

[0169] (5) Hysteresis loss rate of polyester film In accordance with JIS K 7312:1996, the average value of the hysteresis loss rate at 23°C was determined by the following method. The measuring device used was a tensile testing machine (Autograph AG-I, manufactured by Shimadzu Corporation). The test specimens were rectangular pieces cut from any point on the polyester film to be measured, with a length of 100 mm and a width of 10 mm in the measurement direction. The test specimens were chucked at both ends in the longitudinal direction with a chuck distance of 50 mm, and the specimens were raised to a strain of 5% at a crosshead speed of 0.5 mm / min. A stress-strain curve was obtained from one cycle of tensile cycle testing, in which the specimens were lowered to the initial position at the same speed. The stress-strain curves took the profile shown in Figure 1, and the hysteresis loss rate was calculated from the obtained stress-strain curves using the area A1 (abcda) of the curve obtained during the raising motion and the area A2 (abcef), which is the difference between area A1 and the area of ​​the curve obtained during the lowering motion, using the following formula (2). The test was performed three times, and the average value was calculated. The above tensile cycle test was performed in the longitudinal direction (MD) and the axial direction (TD) of the film, and the average value was calculated. Hysteresis loss rate = A2 / A1 × 100 ... Equation (2)

[0170] (6) Flexural test of polyester film The obtained films were subjected to a bending test 1000 times at 23°C using a bending test machine (CL09-typeD01-FSC90) manufactured by Yuasa System Equipment Co., Ltd., under conditions of bending radius (R) = 5 mm and 3 mm. ◎ indicated no change in appearance, ○ indicated bending marks that were not problematic for practical use, △ indicated bending marks that could be problematic for practical use, and × indicated clear bending marks. (comprehensive evaluation) Based on the results of the bending test, the following evaluation was made. ○: With a radius of R=5 and a thickness of 3mm, there were no noticeable changes in appearance that would pose practical problems, indicating it is practical. ×: There is an appearance change that could be problematic in practical use, whether R=5 or 3mm, making it impractical.

[0171] (7) Polyester film haze Measurements were taken in accordance with JIS K 7136:2000, using a haze meter DH-2000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0172] (8) Heat shrinkage rate of polyester film A 1.5 cm x 15 cm sample film was heat-treated for 30 minutes in a hot-air oven maintained at a predetermined temperature (150°C) in a tension-free state. The length of the sample film was measured before and after the treatment, and the length was calculated using the following formula. Measurements were taken in both the longitudinal direction (MD) and the width direction (TD) of the film. Thermal shrinkage rate (%) = {(Sample length before heat treatment) - (Sample length after heat treatment)} ÷ (Sample length before heat treatment) × 100

[0173] (9) Amount of oligomer (ester cyclic trimer) precipitated on the surface of the cured resin layer due to heating For both cured resin layers of the laminated polyester film, sample sizes of 300 mm in length and 225 mm in width were heat-treated for 120 minutes in a hot-air oven maintained at a predetermined temperature (180°C). After heat treatment, a box-shaped specimen measuring 200 mm in length and 125 mm in width with an open top was fabricated, with the measurement surface facing inward. Next, 10 mL of DMF (dimethylformamide) was placed in the box-shaped container described above and left for 3 minutes. After the DMF was recovered, it was supplied to a liquid chromatograph (Shimadzu Corporation: LC-7A, mobile phase A: acetonitrile, mobile phase B: 2% aqueous acetic acid solution, column: Mitsubishi Chemical Corporation "MCI GEL ODS 1HU", column temperature: 40°C, flow rate: 1 mL / min, detection wavelength: 254 nm) to determine the amount of ester cyclic trimers in the DMF. This value was then divided by the film area in contact with the DMF to determine the amount of oligomers (ester cyclic trimers) on the surface of the cured resin layer (mg / m²). 2The ester cyclic trimers in DMF were determined from the peak area ratio of the standard sample peak area to the measured sample peak area (absolute calibration curve method). The standard sample was prepared by accurately weighing a pre-parate ester cyclic trimer and dissolving it in accurately weighed DMF.

[0174] (10) Thickness of polyester film The thickness of the polyester film was measured at five unspecified points within the surface using a 1 / 1000 mm dial gauge, and the average of these measurements was taken as the thickness.

[0175] (11) Thickness of the cured resin layer The surface of the cured resin layer was stained with RuO4 and embedded in epoxy resin. Subsequently, sections prepared by the ultrathin sectioning method were stained with RuO4, and the cross-section of the cured resin layer was measured using a transmission electron microscope (TEM) (Hitachi High-Technologies Corporation, H-7650, accelerating voltage 100kV).

[0176] <Materials used> [Polyester raw material] Raw material A: Homopolyethylene terephthalate (intrinsic viscosity = 0.64 dL / g)

[0177] Raw material B: A masterbatch containing 0.3% by mass of silica particles with an average particle size of 3 μm, made from homopolyethylene terephthalate (intrinsic viscosity = 0.61 dL / g).

[0178] Raw material C: Homopolybutylene naphthalate (intrinsic viscosity = 1.13 dL / g)

[0179] Raw material D: Homopolyethylene naphthalate (crystalline polyester)

[0180] Raw material E: A polyester obtained by melt - mixing homopolyethylene naphthalate and a blue colorant and then pelletizing. More specifically, it is a mixture of polyethylene naphthalate and a blue colorant at a ratio of 90:10 (mass ratio). The blue colorant is Solvent Blue 104, an anthraquinone - based blue colorant, and its structural formula is as follows.

[0181] [Chemical formula]

[0182] Raw material F: Polyarylate (dicarboxylic acid component: terephthalic acid / isophthalic acid (molar ratio) = 50 / 50, dihydric phenol component: bisphenol A 100 mol%)

[0183] [Cured resin layer] The following was used as the resin composition for forming the cured resin layer. (A1): Hexamethoxymethylmelamine (A2): Epocros (manufactured by Nippon Shokubai Co., Ltd.), an oxazoline compound; oxazoline group content 7.7 mmol / g (A3): Polyglycerol polyglycidyl ether (B1): Silica particles with an average particle size of 0.07 μm

[0184] Note that the compositions of the coating liquids used in the examples and comparative examples are as shown in Table 1. More specifically, a resin composition obtained by stirring and mixing with the composition shown in Table 1 below was diluted with water to prepare a coating liquid.

[0185] [Table 1]

[0186] (Example 1) Raw materials C and D were mixed at a mass ratio of 60:40, put into a twin - screw extruder, extruded at 280 °C, and cooled and solidified on a cooling roll set at 50 °C to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched 3.0 times in the longitudinal direction (MD) at 100°C using a roll stretcher. Furthermore, after preheating in a tenter at 100°C, it was stretched 4.5 times in the width direction (TD) at 110°C. Finally, it was heat-treated at 200°C (heat-fixing temperature) to obtain a biaxially oriented polyester film with a thickness of 125 μm. The properties of the obtained polyester film were evaluated using the method described above. The evaluation results are shown in Table 3.

[0187] In the production of the polyester film described above, after stretching in the longitudinal direction (MD) and before stretching in the width direction (TD), a coating solution of the resin composition that forms the cured resin layer described above was applied to both sides of the uniaxially oriented polyester film so that the film thickness (after drying) was 0.04 μm. Then, stretching in the width direction and heat treatment were performed under the conditions described above to obtain a laminated polyester film. The properties of the obtained laminated polyester film were evaluated using the method described above. The evaluation results are shown in Table 4.

[0188] (Example 2, Comparative Examples 1-2) A biaxially oriented polyester film was obtained in the same manner as in Example 1, except that the composition, thickness, and film-forming conditions were as described in Table 2 below. The evaluation results of the obtained polyester films are shown in Table 3.

[0189] Furthermore, in the process of forming the polyester film described above, a cured resin layer was provided on both sides of the polyester film of each example and comparative example in the same manner as in Example 1 to obtain a laminated polyester film. The evaluation results of the obtained laminated polyester film are shown in Table 4.

[0190] [Table 2]

[0191] [Table 3]

[0192]

Table 4

[0193] As shown in the above embodiments, by setting the average value of the hysteresis loss rate in the tensile cycle test up to 5% tensile strain in each of the longitudinal direction (MD) and the width direction (TD) to be less than a specific value, the restoring force of the film becomes large and it is easy to return to the original state, that is, it can be seen that the film has excellent flex resistance. On the other hand, for the polyester film of Comparative Example 2, since the average value of the hysteresis loss rate exceeded a specific value, the evaluation in the bending test was also inferior, and the flex resistance was not sufficient.

[0194] Also, as shown in the above embodiments, by setting the b * value to be less than a specific value, it can be expected that the occurrence of visibility problems such as image quality deterioration and discoloration can be suppressed. On the other hand, the polyester film of Comparative Example 1 is the same as the embodiment in that it contains PBN, but due to the selection of other compositions, the b * value becomes a film that exceeds a specific value and is not excellent in visibility.

[0195] Furthermore, it can be seen that the film of the embodiment has low haze and heat shrinkage rate, and is also excellent in transparency and heat resistance. Also, in the laminated polyester film of the present invention, by having a cured resin layer on the polyester film, the amount of oligomer precipitation on the surface of the cured resin layer can be reduced, so that the visibility can be improved. Therefore, the polyester film and the laminated polyester film of the present invention are very useful for displays, particularly for flexible displays.

Industrial Applicability

[0196] The polyester film of the present invention has excellent flexibility and visibility, making it suitable for use in displays, particularly flexible displays. Therefore, the embodiments of this disclosure are useful for flexible displays such as foldable displays, bendable displays, rollable displays, and stretchable displays, which take advantage of the benefits of flexible display panels that can be folded, folded back, or rolled up.

Claims

1. It contains polybutylene naphthalate and polyethylene naphthalate, b ＊ A polyester film having a value of 2.0 or less, and an average hysteresis loss rate of 56% or less when subjected to tensile cycle testing up to 5% tensile strain in both the longitudinal (MD) and widthwise (TD) directions.

2. The polyester film according to claim 1, wherein the degree of yellowness (YI) is less than 0.

00.

3. A polyester film according to claim 1 or 2, containing 5 to 70% by mass of polybutylene naphthalate.

4. The polyester film according to claim 1 or 2, further comprising crystalline polyester.

5. The polyester film according to claim 1 or 2, wherein the content ratio of polyethylene naphthalate is 50 parts by mass or more and 1000 parts by mass or less per 100 parts by mass of polybutylene naphthalate.

6. The polyester film according to claim 1 or 2, further comprising a blue coloring agent.

7. The polyester film according to claim 6, wherein the content of the blue coloring agent is 0.01 to 1% by mass relative to the entire polyester film.

8. The polyester film according to claim 6, wherein the blue coloring agent is an anthraquinone-based blue dye.

9. A polyester film according to claim 1 or 2, for use in flexible displays.

10. A laminated polyester film having a cured resin layer on at least one surface layer of the polyester film according to claim 1 or 2, wherein the cured resin layer is formed from a resin composition containing a crosslinking agent in an amount of 70% by mass or more relative to the nonvolatile component.

11. A laminated polyester film according to claim 10, for use in flexible displays.

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