JP7830871B2 - Optical polyester film, optical laminated film, display and display device - Google Patents

Description

This invention relates to an optical polyester film, an optical laminated film, a display, and a display device.

Polyester film possesses excellent mechanical properties, heat resistance, transparency, and chemical resistance, making it suitable for a wide range of applications, including packaging, electronic components, electrical insulation, metal lamination, and optics.

In recent years, in particular, there has been a growing demand for thinner, lighter, and higher-performance display devices such as liquid crystal displays and organic EL displays, leading to increased demand for various optical films.
As a means of improving the performance of display devices, the suppression of light degradation of various optical components that make up the display (hereinafter also referred to as "optical components") is being considered. As an example, an adhesive sheet containing an ultraviolet absorber is known to be used by placing it between the surface protection panel and the image display module.

For example, Patent Document 1 discloses an optical adhesive sheet having an acrylic adhesive layer, with b ^* being 0.42 or less, and a transmittance of 5% or less for light with a wavelength of 350 nm.
Furthermore, Patent Document 2 discloses an ultraviolet-curable acrylic adhesive layer that is placed between a cover glass or cover plastic and a polarizing film in a display device, having a transmittance of 40% or less at a wavelength of 380 nm and a transmittance of 30% or more at a wavelength of 400 nm.

On the other hand, focusing on the configuration of conventional displays, in liquid crystal displays, polarizing plates are used on the viewing side of the display to convert backlight light into linearly polarized light, and in organic EL displays, they are used to prevent reflection of ambient light. Polyvinyl alcohol (PVA) is used as the polarizer within these polarizing plates, but PVA is known to degrade due to ultraviolet light entering from the outside. Therefore, it is necessary to sandwich it between protective films such as triacetylcellulose (TAC) film to achieve UV protection.

As an alternative to the above-mentioned TAC film, for example, Patent Document 3 discloses a method for imparting ultraviolet-blocking properties to a polyester film.
Furthermore, Patent Document 4 discloses an optical film containing at least one ultraviolet absorber and/or a visible light absorbing dye, which has excellent ultraviolet blocking properties and steep wavelength blocking properties in the short wavelength region of visible light, for the purpose of suppressing the degradation of PVA, liquid crystals, light-emitting elements, etc.

Japanese Patent Publication No. 2019-214722 Japanese Patent Publication No. 2016-155981 Japanese Patent Publication No. 2013-210598 Japanese Patent Publication No. 2017-187619

However, the transparent adhesives for display devices with light-absorbing functions described in Patent Documents 1 and 2 complement the functions of conventional polarizing plates with protective films such as TAC, i.e., protective films containing ultraviolet absorbers. Therefore, in order to further reduce the thinness and weight of display devices, it is necessary to suppress the photodegradation of optical components without providing a protective film.

Furthermore, in the polyester films described in Patent Documents 3 and 4, achieving UV-blocking and wavelength-blocking properties in the short-wavelength region of visible light using only UV absorbers requires increasing the amount of UV absorber, which increases the risk of bleed-out. This problem is particularly pronounced in thin-film optical films, making it difficult to achieve the thinning and weight reduction required for display devices.
Furthermore, Patent Documents 3 and 4 do not mention suppressing the photodegradation of optical components without sandwiching the polarizer with a protective film containing an ultraviolet absorber.

Therefore, the present invention has been made in view of the above circumstances, and its objective is to provide an optical polyester film that can suppress the photodegradation of various optical components constituting a display, and that is compatible with thinning and weight reduction of display devices, while also exhibiting excellent ultraviolet cut properties and wavelength cut properties in the short-wavelength region of visible light.

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

[1] A polyester film containing an ultraviolet absorber, comprising either a triazine-based ultraviolet absorber (A) bonded to at least one, two, or three naphthalene rings, or a copolymer polyester (B) having a benzotriazole-based ultraviolet absorber, and satisfying both (1) and (2) below, for optical purposes.
(1) Average light transmittance of 30% or less at wavelengths of 300 to 430 nm (2) Thickness of 9 to 125 μm

[2] The optical polyester film described in [1] above, wherein the total light transmittance is 85% or more.

[3] The optical polyester film described in [1] or [2] above, wherein the haze content is 3.0% or less.

[4] An optical polyester film according to any one of [1] to [3] above, wherein the thermal shrinkage rate when heated at 120°C for 5 minutes is 5.0% or less in both the longitudinal direction (MD) and the width direction (TD).

[5] An optical polyester film according to any one of [1] to [4] above, wherein the total content of the ultraviolet absorber is 7% by mass or less relative to the entire polyester film.

[6] The optical polyester film according to any one of [1] to [5] above, wherein the polyester film comprises at least three layers, and the layers other than the outermost layer contain the ultraviolet absorber.

[7] The optical polyester film according to any one of [1] to [6] above, wherein the ultraviolet absorber comprises the triazine-based ultraviolet absorber (A) and the benzotriazole-based ultraviolet absorber (excluding the copolymer polyester (B) having the benzotriazole-based ultraviolet absorber).

[8] An optical polyester film according to any one of items [1] to [7] above, wherein the light transmittance at a wavelength of 380 nm is 10% or less.

[9] An optical polyester film according to any one of [1] to [8] above, wherein the light transmittance at a wavelength of 400 nm is 80% or less.

[10] An optical laminated film having a functional layer on at least one side of the optical polyester film described in any one of [1] to [9] above.

[11] The optical laminated film according to [10], wherein the functional layer is a hard coat layer.

[12] An optical laminated film as described in [11] above, for surface protection.

[13] An optical laminated film according to any one of [10] to [12] above, wherein an adhesive layer is provided on the side opposite to the side having the functional layer.

[14] A display comprising an optical polyester film as described in any one of [1] to [9] above, or an optical laminated film as described in any one of [10] to [13] above, and a coated polarizing element.

[15] A display comprising an optical polyester film as described in any one of [1] to [9] above, or an optical laminated film as described in any one of [10] to [13] above, and a color filter.

[16] A display device equipped with the display described in [14] or [15] above.

The optical polyester film according to the present invention exhibits excellent ultraviolet light blocking properties and wavelength blocking properties in the short wavelength region of visible light.
Therefore, since the photodegradation of optical components can be suppressed without sandwiching the polarizer with a protective film containing an ultraviolet absorber, as in conventional methods, it can also contribute to making display devices thinner and lighter.

This is a schematic cross-sectional view showing an example of the display of the present invention. This is a schematic cross-sectional view showing an example of the display of the present invention. This is a schematic cross-sectional view showing an example of the display of the present invention.

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.

[Polyester film for optical use]
The optical polyester film of the present invention (hereinafter also referred to as "this polyester film") contains either a triazine-based ultraviolet absorber (A) bonded to at least one, two, or three naphthalene rings, or a copolymer polyester (B) having a benzotriazole-based ultraviolet absorber, and simultaneously satisfies the following (1) and (2).
(1) Average light transmittance of 30% or less at wavelengths of 300 to 430 nm (2) Thickness of 9 to 125 μm

This polyester film may have a single-layer structure or a multi-layer structure (i.e., a laminated film). If the film has a multi-layer structure, it may have a two-layer structure, a three-layer structure, or more, and may have four or more layers, as long as it does not depart from the gist of the present invention; the number of layers is not particularly limited. In the case of a multi-layer structure of three or more layers, it has an outermost surface layer and intermediate layers other than the surface layer.
However, from the viewpoint of enabling thin-film production and reducing the number of manufacturing steps, a single-layer structure or a multilayer structure of three or fewer layers is preferable, and a three-layer structure is more preferable. In the case of a three-layer structure, it may be two types of three layers or three types of three layers.

Furthermore, this polyester film may be an unstretched polyester film (sheet) or a stretched film, but it is preferable that it be stretched in at least one direction, specifically a uniaxially or biaxially oriented polyester film. Among these, a biaxially oriented polyester film is more preferable from the viewpoint of balance of mechanical properties, flatness, and thin-film formation.

This polyester film preferably uses polyester as its main component resin.
Furthermore, if the polyester film has a multilayer structure, it is preferable that the main component resin of each layer is polyester.
The term "main component resin" refers to the resin with the highest content among the resins that make up each layer. For example, it refers to the resin that accounts for 50% or more by mass, especially 70% or more by mass, and among those, 80% or more by mass (including 100% by mass) of the resins that make up each layer.

This polyester film may contain resins other than polyester. Examples of resins other than polyester include polystyrene resins, polyvinyl chloride resins, polyvinylidene chloride resins, chlorinated polyethylene resins, polylactic acid resins, polybutylene succinate resins, polycarbonate resins, polyamide resins (including aramid resins), polyacetal resins, acrylic resins, ethylene-vinyl acetate copolymers, polymethylpentene resins, polyvinyl alcohol resins, cyclic olefin 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, polyetheretherketone resins, polyetherketone resins, polyethersulfone resins, polyketone resins, polysulfone resins, and fluorine resins. These resins other than polyester can be used individually or in combination of two or more.

<Polyester>
The polyester used in this polyester film is not particularly limited. Specifically, examples include polyesters obtained by polycondensation of a dicarboxylic acid component and a diol component.

Examples of dicarboxylic acid components include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,4-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, dimer acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, and succinic acid.
As the dicarboxylic acid component, tricarboxylic acids such as trimellitic acid and trimesic acid, as well as tetracarboxylic acids such as pyromellitic acid, can also be used.
Furthermore, ester-forming derivatives of dicarboxylic acids, such as acid anhydrides like phthalic anhydride and trimellitic anhydride, and carboxylate salts like monopotassium trimellitic acid, can also be used.

Examples of diol components include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 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 ether glycol, spiroglycol, isosorbide, and dimethylolpropionic acid, as well as potassium dimethylolpropionate. Trivalent or higher alcohols such as glycerin and trimethylolpropane can also be used as diol components.
From the above compounds, one or more can be appropriately selected, and polyesters can be synthesized by conventional polycondensation reactions.

Furthermore, in this invention, it is preferable to use a polyester containing 50 mol% or more of aromatic dicarboxylic acid or aliphatic dicarboxylic acid when the dicarboxylic acid component is considered to be 100 mol%.

The polyester mentioned above may be homopolyester or copolymer polyester.
When the product consists of a homopolyester, it is preferable to obtain it by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Among these, terephthalic acid and 2,6-naphthalenedicarboxylic acid are more preferred as aromatic dicarboxylic acids, and ethylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol are more preferred as aliphatic glycols.
Typical polyesters include polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), with PET being preferred from the standpoint of versatility.

On the other hand, in the case of copolymerized polyester, the copolymer includes a third component other than the main component of the dicarboxylic acid component and the main component of the diol component that constitute the polyester. For example, in PET, the third component is a component other than terephthalic acid and ethylene glycol. Specific examples of the main component and the third component, dicarboxylic acid and diol, are as described above. In the case of PET, isophthalic acid is preferred as the dicarboxylic acid component other than terephthalic acid, and 1,4-cyclohexanedimethanol is preferred as the diol component other than ethylene glycol.

This polyester film contains an ultraviolet absorber (UVA). As one embodiment of the ultraviolet absorber, a high molecular weight type ultraviolet absorber may be included. Examples of high molecular weight type ultraviolet absorbers include polymers having the ultraviolet absorber in their backbone. More specifically, considering compatibility with polyester as described later, the ultraviolet absorber may be included in the form of a copolymerized polyester (hereinafter also referred to as "UVA copolymerized polyester") in which the ultraviolet absorber is included in the main chain or side chains of the polymer backbone. In this case, the UVA copolymerized polyester is one form that imparts ultraviolet absorption ability to the polyester film and is different from the components that form the polyester film itself; therefore, in this invention, it is distinguished from the copolymerized polyester described above. The detailed form of the UVA copolymerized polyester is described below.

The polyester used in this polyester film may be homopolyester or copolymer polyester used alone, or homopolyester and copolymer polyester may be used in combination. Alternatively, homopolyester and UVA copolymer polyester, or copolymer polyester and UVA copolymer polyester may be used in combination. Or, homopolyester, copolymer polyester, and UVA copolymer polyester may be used in combination.
The polyester used in each layer may be the same or different, and the above-mentioned materials can be used.

In this polyester film, the copolymer content of 100 mol% of the total dicarboxylic acid components is preferably 30 mol% or less, more preferably 27 mol% or less, and even more preferably 25 mol% or less. Similarly, the copolymer content of 100 mol% of the total diol components in this polyester film is preferably 30 mol% or less, more preferably 27 mol% or less, and even more preferably 25 mol% or less. The lower limit of the copolymer content is 0 mol% (homo).
The copolymer content referred to here is the copolymer content with respect to the dicarboxylic acid component or diol component of copolymerized polyester (excluding UVA copolymerized polyester as described above), and is the ratio of the copolymer to the total amount of dicarboxylic acid component or diol component of all polyester (including UVA copolymerized polyester) constituting the polyester film. The copolymer is the total amount of copolymer components other than the main component that copolymerizes with the main component in the dicarboxylic acid component or diol component of the above-mentioned all polyester. The copolymer content should be within the above range with respect to at least one of the dicarboxylic acid component or diol component.
Furthermore, the main component, as mentioned above, is a type of dicarboxylic acid or diol component that has the highest content (mol% amount) in all the polyesters described above. More specifically, for example, with respect to the dicarboxylic acid component, if the main component is terephthalic acid, then isophthalic acid other than terephthalic acid that copolymerizes with terephthalic acid is the copolymer component. With respect to the diol component, if ethylene glycol is the main component, then 1,4-cyclohexanedimethanol other than ethylene glycol that copolymerizes with ethylene glycol is the copolymer component.
Furthermore, for example, if the diol components include ethylene glycol, 1,4-cyclohexanedimethanol, and two diols contained in UVA copolymer polyester, the main component will be ethylene glycol, the copolymer component will be 1,4-cyclohexanedimethanol, and the two diols contained in UVA copolymer polyester will not be included in the copolymer component. On the other hand, when calculating the content of copolymer components, the ratio of 1,4-cyclohexanedimethanol to the total amount of diol components of ethylene glycol, 1,4-cyclohexanedimethanol, and the two diols contained in UVA copolymer polyester is calculated.

Normally, when polyester is manufactured (polycondensed) using ethylene glycol as one of the raw materials, diethylene glycol is produced as a by-product from the 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 polycondensation method, but it is generally about 5 mol% or less of the ethylene glycol. In this invention, the by-product diethylene glycol of 5 mol% or less is included in ethylene glycol. On the other hand, depending on the diethylene glycol content, more specifically, if the diethylene glycol content exceeds 5 mol%, diethylene glycol is distinguished from ethylene glycol.

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

To suppress the precipitation of oligomer components, polyester with a low oligomer content may be used as the raw material. Various known methods can be used to produce polyester with a low oligomer content, such as a method of solid-phase polymerization after polyester production.
Furthermore, the polyester film may be constructed with three or more layers, and the outermost layer of the polyester film may be made of a polyester raw material with a low oligomer content to suppress the amount of oligomer component precipitated.
Alternatively, polyester may be obtained by esterification or transesterification, followed by further increasing the reaction temperature and melt polycondensation under reduced pressure.

<UV absorber>
Polarizing plates, which are components of displays, typically consist of a polyvinyl alcohol (PVA) film sandwiched between two protective films, such as a triacetylcellulose (TAC) film, with an adhesive applied or an adhesive sheet laminated on top. However, such polarizing plates are very brittle because they use a polarizer made from stretched PVA, and the need to sandwich them between two protective films limits the possibility of thinning them.
On the other hand, in recent years, with the trend towards thinner and lighter display devices, there is a demand for thinner optical anisotropic components such as polarizing plates that make up displays.

Therefore, coated polarizing elements are attracting attention as a means of thinning optical anisotropic components such as polarizers. Compared to conventional polarizing elements, coated polarizing elements, as described below, can be made thinner by forming a film through coating. Furthermore, by using coated polarizing elements, it is not always necessary to sandwich the polarizer with a protective film, thus enabling the creation of thin-film polarizers.
However, coated polarizing elements are susceptible to degradation by light, resulting in a problem where their polarization performance deteriorates over time due to ambient light (exposure).
Furthermore, various optical components, including not only polarizing elements but also iodine used in polarizing plates, dichroic organic dyes, liquid crystal panels used in displays, and light-emitting elements that make up organic EL devices, have problems with insufficient light resistance.

Furthermore, with the need for further thinning and weight reduction of display devices, color filter-integrated displays are also being considered. Color filter-integrated displays, particularly color filter-integrated organic EL displays, can reduce external light reflection through the integrated color filter and, if necessary, a black matrix or anti-reflective layer. This eliminates the need for polarizers and phase difference plates (circular polarizers) used in conventional displays (especially organic EL displays), contributing to further thinning and weight reduction of display devices.
Color filters are filters responsible for color display, such as those used in liquid crystal displays, and are patterned with RGB dyes, which are the three primary colors of light: red, green, and blue. Although the RGB dyes themselves have light resistance, as mentioned above, there are problems such as the insufficient light resistance of the light-emitting elements that make up liquid crystal panels and organic EL devices, and even when color filters are used, protection of the optical components may still be necessary.

As a solution to these challenges, by imparting ultraviolet absorption properties to this polyester film, it becomes possible to mount the polyester film in various display devices in combination with coated polarizing elements or color filters.

When using a polyester film for a display having a coated polarizing element or a color filter, as described above, it is preferable to impart ultraviolet absorption capabilities to the polyester film by incorporating an ultraviolet absorber in order to reduce the photodegradation of the coated polarizing element and to protect various optical components that do not have sufficient light resistance.
Furthermore, even when using polyester film for displays that do not have a coated polarizing element or color filter, it is possible to incorporate an ultraviolet absorber to complement the function of conventional polarizing plates with protective films, i.e., protective films containing ultraviolet absorbers.

This polyester film contains either a triazine-based ultraviolet absorber (A), which is a triazine compound bonded to at least one, two, or three naphthalene rings, or a copolymer polyester (B) having a benzotriazole-based ultraviolet absorber.
By including at least one of the above-mentioned triazine-based ultraviolet absorber (A) or copolymer polyester (B) having the above-mentioned benzotriazole-based ultraviolet absorber, it is possible to achieve not only excellent ultraviolet blocking properties but also excellent wavelength blocking properties in the short-wavelength region of visible light, thereby suppressing photodegradation of various optical components.
Furthermore, a copolymer polyester (B) containing a triazine-based UV absorber (A) and a benzotriazole-based UV absorber can also be used in combination.

(Triazine-based UV absorber (A))
The triazine-based ultraviolet absorber (A) is a triazine compound bonded to one, two, or three naphthalene rings. Due to the action of the naphthalene rings bonded to the triazine ring, the triazine-based ultraviolet absorber (A) can absorb light in the visible light short-wavelength region of approximately 400 to 420 nm, in addition to the ultraviolet region with wavelengths less than 400 nm.
Furthermore, since the triazine-based ultraviolet absorber (A) allows for absorption of the desired wavelength with a smaller amount of additive than conventional methods, it reduces the risk of ultraviolet absorber bleed-out in the polyester film and suppresses the decrease in transparency of the polyester film.

In the aforementioned triazine-based ultraviolet absorber (A), it is preferable that at least one naphthalene ring is directly bonded to the triazine ring without the need for a linking group. Furthermore, it is more preferable that at least one of the 1 to 3 naphthalene rings directly bonded to the triazine ring has a hydroxyl group at the 2-position.
The triazine-based ultraviolet absorber (A) is preferably a compound selected from the group consisting of the following general formulas (1), (2), and (3).

In general formulas (1) to (3), _R1b to _R1g , _R2a to _R2g , and _R3a to _R3g are, independently, a hydrogen atom, a hydroxyl group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a nitrile group, a nitro group, a sulfo group, _R7 , _Ar1 , or a group represented by the following general formulas (4-1) to (4-3).
_R7 is an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or an alkenyloxy group having 2 to 20 carbon atoms, and may have substituents such as a hydroxyl group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a nitrile group, a nitro group, a carboxyl group, or a sulfo group, and the carbon atoms of the alkyl group having 1 to 20 carbon atoms, the alkenyl group having 2 to 20 carbon atoms, the alkoxy group having 1 to 20 carbon atoms, or the alkenyloxy group having 2 to 20 carbon atoms may be linked by one or more -O-, -CO-, -COO-, -OCO-, -CONH-, or -NHCO-.
Ar ₁ is an aryl group having 6 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, or a biphenyl group, and may have substituents such as a hydroxyl group, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an alkenyloxy group having 2 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a nitrile group, a nitro group, a carboxyl group, or a sulfo group.
Furthermore, in general formulas (2) to (3), R ₄ , R ₅ , and R ₆ are each independently a hydroxyl group, R ₇ , or Ar ₁ .

In general formula (4-1), X ₁ is -CO-, -COO-, -OCO-, -CONH-, or -NHCO-. _{R 8} is a hydrogen atom, a hydroxyl group, R ₇ , or Ar _1. However, the asterisk (*) in general formula (4-1) represents the bonding site with the naphthalene ring in general formulas (1) to (3).

In general formula (4-2), _X2 and _X3 are independently -CO-, -COO-, -OCO-, -CONH-, or -NHCO-, respectively. _R9 is an arylene group having 6 to 20 carbon atoms. _R10 is _R7 or _Ar1 . However, the asterisk (*) in general formula (4-2) represents the bonding site with the naphthalene ring in general formulas (1) to (3).

In general formula (4-3), _X4 and _X5 are independently -CO-, -COO-, -OCO-, -CONH-, or -NHCO-, respectively. _R11 is a linear or branched alkylene group having 1 to 20 carbon atoms, or an arylene group having 6 to 20 carbon atoms. _R12 is _R7 or _Ar1 . n is 1 to 20. However, the asterisk (*) in general formula (4-3) represents the bonding site with the naphthalene ring in general formulas (1) to (3).

Furthermore, the group represented by general formula (4-1) is preferably the group represented by general formula (4).

In general formula (4), Y is -NH- or -O-. R ₁₃ is a hydrogen atom, a hydroxyl group, a C1-C20 alkyl group, a C2-C20 alkenyl group, a C6-C20 aryl group, a C1-C20 alkoxy group, a C2-C20 alkenyloxy group, a C6-C20 aryloxy group, or a C1-C20 alkyl group or C6-C20 aryl group having a fluorine atom, chlorine atom, bromine atom, iodine atom, nitrile group, nitro group, carboxyl group, or sulfo group as substituents. However, the asterisk (*) in general formula (4) represents the bonding site with the naphthalene ring in general formulas (1) to (3).

Among the compounds represented by general formulas (1) to (3), compounds represented by general formulas (1) and (3) are preferred, and in general formula (1), compounds in which both R _2a and R _3a are hydroxyl groups are preferred. Furthermore, in general formula (1), R _1b to R _1g are preferably hydrogen, and the compound represented by formula (8) described in the examples is particularly preferred. In addition, as for the compound represented by general formula (3), compounds in which R _1b to R _1g are hydrogen are preferred, and compounds in which R ₅ and R ₆ are each independently Ar ₁ are more preferred. As Ar ₁ , aryl groups having 6 to 20 carbon atoms are preferred, and in particular, compounds in which both R ₅ and R ₆ are phenyl groups are preferred.
Compounds represented by general formulas (1) to (3) include, for example, the compounds described in the examples.

The above triazine compounds can be synthesized using known synthesis methods for compounds having a triazine structure. For example, one method involves adding naphthol or a naphthol derivative to cyanuryl chloride using aluminum trichloride. Another method involves condensation cyclization of methyl 2-hydroxy-1-naphthoate and benzamidine hydrochloride using sodium methoxide. The naphthalene ring and substituents _R4 , _R5 , and _R6 , which are single-bonded to the triazine ring, may be introduced after the triazine structure is formed or before the triazine structure is formed.

(Copolymer polyester (B) containing a benzotriazole-based UV absorber)
Copolymer polyester (B) containing a benzotriazole-based ultraviolet absorber (corresponding to the aforementioned UVA copolymer polyester) incorporates the ultraviolet absorber into a polyester film as a high molecular weight type ultraviolet absorber, thereby imparting a high level of light resistance to this polyester film.
Furthermore, high molecular weight UV absorbers can provide superior light resistance with smaller amounts compared to using low molecular weight UV absorbers, thus significantly reducing the risk of bleed-out.
Furthermore, by using the UV absorber not simply as a mixture, but in the form of a copolymer polyester (B) containing the benzotriazole-based UV absorber, the copolymer polyester (B) containing the benzotriazole-based UV absorber exhibits high affinity to the film constituent resin, enabling uniform dispersion. Therefore, even with a larger surface area of this polyester film, stable light resistance can be achieved regardless of the location on the film.

There are no particular restrictions on the polyester constituting the copolymer polyester (B) having the benzotriazole-based UV absorber, but it is preferably a polycondensation polymer of a dicarboxylic acid and a diol. Aromatic dicarboxylic acids are preferred as the dicarboxylic acid, and a diol compound having a benzotriazole group (corresponding to the benzotriazole-based UV absorber) is an essential component of the diol, with other aliphatic diols also being used in combination.

Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, biphenyl dicarboxylic acid, diphenyl ether-dicarboxylic acid, diphenyl sulfone-dicarboxylic acid, diphenyl ketone-dicarboxylic acid, naphthalenedicarboxylic acid such as 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. Among these, terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-biphenyl dicarboxylic acid are preferred, with terephthalic acid being more preferred.

The diol must contain a diol compound having a benzotriazole group (benzotriazole-based UV absorber). An example of a diol compound having a benzotriazole group is 2,2'-methylenebis[6-(2H-benzotriazole-2-yl)-4-(2-hydroxyethyl)phenol], represented by the following formula (5). The content of the diol compound having a benzotriazole group is preferably 5 to 20 mol% relative to the total glycol components. If the content is 5 mol% or more, sufficient UV absorption capacity can be imparted to the film; if it is 20 mol% or less, the mechanical strength of the film will also be sufficient.

Examples of the aforementioned other aliphatic diols include linear or branched aliphatic diols such as ethylene glycol, 1,4-butanediol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentyl glycol, methylpentanediol, and diethylene glycol; and alicyclic diols such as cyclohexanedimethanol, isosorbide, spiroglycol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, norbornenedimethanol, and tricyclodecanedimethanol. These may be used individually or in combination of two or more as needed.

In this invention, as the copolymer polyester (B) having the benzotriazole-based ultraviolet absorber, it is preferable to use a copolymer polyester in which a benzotriazole group is added to a polybutylene terephthalate (PBT) skeleton, given its good compatibility with PET, its close glass transition temperature, and its good suitability for film molding.

The method for producing copolymer polyester (B) having a benzotriazole-based ultraviolet absorber is not particularly limited and can be produced by conventionally known methods.
Furthermore, the timing of adding benzotriazole-based UV absorbers is not particularly limited; they can be added at any stage during the polycondensation of dicarboxylic acid and diol.

Furthermore, when using copolymer polyester (B) (UVA copolymer polyester) containing a benzotriazole-based UV absorber, the UVA copolymer polyester content in the UVA copolymer polyester layer is preferably 1 to 25 parts by mass, more preferably 5 to 20 parts by mass, and even more preferably 10 to 15 parts by mass, based on 100 parts by mass of the total amount of polyester in the layer. Within this range, sufficient UV absorption capacity can be obtained without impairing the basic properties of the film.

(Other UV absorbers)
In the present invention, it is sufficient to include at least the triazine-based ultraviolet absorber (A) or the copolymer polyester (B) having the benzotriazole-based ultraviolet absorber, and other ultraviolet absorbers may also be used in combination.

Other UV absorbers are compounds that absorb ultraviolet light and are not particularly limited as long as they can withstand the heat added during the manufacturing process of polyester film.
UV absorbers include organic UV absorbers and inorganic UV absorbers, but organic UV absorbers are preferred from the viewpoint of transparency. Organic UV absorbers are not particularly limited, but examples include benzophenone-based UV absorbers, benzotriazole-based UV absorbers other than the copolymer polyester (B) having the benzotriazole-based UV absorber, triazine-based UV absorbers other than the triazine-based UV absorber (A), benzoxazine-based UV absorbers, salicylic acid-based UV absorbers, cyanoacrylate-based UV absorbers, and the like.
Furthermore, UV absorbers can be used individually or in combination of two or more types.

Examples of benzophenone-based UV absorbers include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2-hydroxy-4-methoxy-5-sulfoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfoxytrihydridebenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxy-5-sodium sulfoxybenzophenone, bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane, 2-hydroxy-4-n-dodecyloxybenzophenone, and 2-hydroxy-4-methoxy-2'-carboxybenzophenone.

Examples of benzotriazole-based UV absorbers include 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2-hydroxy-3,5-dicumylphenyl)phenylbenzotriazole, 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole, 2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazole-2-yl)phenol], 2,2'-methylenebis[6-(2H-benzotriazole-2-yl)-4-(2-hydroxyethyl)phenol], 2, Examples include 2'-methylenebis[6-(2H-benzotriazol-2-yl)-4-tert-octylphenol], 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-4-octoxyphenyl)benzotriazole, 2,2'-methylenebis(4-cumyl-6-benzotriazolphenyl), and 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimidomethyl)-5-methylphenyl]benzotriazole.

Examples of triazine-based UV absorbers include 2-(2-hydroxy-4-methoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-ethoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-propoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-butoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-hexyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, and 2-(2-hydroxy-4-octyloxyphenyl)-4,6-diphenyl Phenyl-1,3,5-triazine, 2-(2-hydroxy-4-dodecyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-benzyloxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2,4-bis(2-hydroxy-4-butoxyphenyl)-6-(2,4-dibutoxyphenyl)-1,3-5-triazine, 2,4,6-tris(2-hydroxy-4-hexyloxy-3-methylphenyl)-1,3,5-triazine, 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5 - Triazine, 2-[4-[(2-hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-tridecyloxypropyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-[(2-hydroxy-3-(2'-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4 Examples include -(3-octyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-nonyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, 2,4-bis(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-decyloxy-2-hydroxypropyloxy)-5-α-cumylphenyl]-s-triazine, and 2-(2-hydroxy-4-acryloyloxyethoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine.

Examples of benzoxazine-based ultraviolet absorbers include 2,2'-(p-phenylene)di-3,1-benzoxazin-4-one, 2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinon-4-one), 2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one, and 2-phenyl-3,1-benzoxazin-4-one.
Examples of salicylic acid-based UV absorbers include phenyl salicylate, p-tert-butylphenyl salicylate, and p-octylphenyl salicylate.
Examples of cyanoacrylate-based ultraviolet absorbers include 2-ethylhexyl-2-cyano-3,3'-diphenyl acrylate and ethyl-2-cyano-3,3'-diphenyl acrylate.

As for the other UV absorbers mentioned above, it is preferable to use a benzotriazole-based UV absorber (excluding copolymer polyester (B) having the benzotriazole-based UV absorber) in combination with the triazine-based UV absorber (A).

From the viewpoint of improving light resistance reliability, the total content of the ultraviolet absorber is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, relative to the total polyester film.
On the other hand, the upper limit of the total content of ultraviolet absorbers is preferably 7% by mass or less, more preferably 6% by mass or less, and even more preferably 5% by mass or less, relative to the entire polyester film, from the viewpoint of suppressing bleed-out and improving resistance to yellowing.
In this invention, when a copolymer polyester (B) having a benzotriazole-based UV absorber is used, the UV absorber refers to a benzotriazole-based UV absorber added to a part of the skeleton. In this case, it is preferable that the content of the copolymer polyester (B) having a benzotriazole-based UV absorber satisfies the above range, and the total content of the UV absorber satisfies the above range.

If the polyester film has a multilayer structure, the ultraviolet absorber should be included in at least one of the layers. In particular, it is preferable to include it in a layer other than the outermost layer. Specifically, if the polyester film has a surface layer and an intermediate layer as described in the preferred embodiment above, it is preferable to include the ultraviolet absorber in the intermediate layer. By including the ultraviolet absorber in the intermediate layer, it is possible to suppress the ultraviolet absorber from bleeding out to the surface of the film.
Furthermore, the layer containing the ultraviolet absorber is preferably an intermediate layer if the film has a multilayer structure, but if the film has a single-layer structure, it is the entire film.

<Particle>
This polyester film may also contain particles primarily for the purpose of providing slipperiness and preventing scratches during each process. The type of particles is not particularly limited as long as they can provide slipperiness. Specific 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, precipitated particles obtained by precipitating and finely dispersing a portion of metal compounds such as catalysts during the polyester manufacturing process can also be used.

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

Furthermore, considering the balance between film transparency and handling, the average particle size of the particles used is typically in the range of 0.05 to 5 μm, preferably 0.1 to 4 μm, and more preferably 0.3 to 4 μm. The average particle size is the particle size at which the cumulative volume fraction (d50) of the equivalent spherical distribution is 50%, measured using a centrifugal sedimentation particle size distribution analyzer.

This polyester film has a multilayer structure and, if it contains particles, it is preferable to include the particles in at least one of the layers, but it is preferable to include them in the outermost layer. Specifically, if this polyester film has a surface layer and an intermediate layer as described in the preferred embodiment above, it is preferable to include the particles in the surface layer. The particles may be included in one of the outermost layers, but it is preferable to include them in both outermost layers. By including the particles in the outermost layers, it is possible to effectively impart properties such as smoothness while reducing the overall particle content of the film.

The particle content in the particle-containing layer is typically in the range of 0.01 to 10% by mass, preferably 0.02 to 5% by mass. If there are no particles or only a small amount, the transparency of the film increases, resulting in a film with good transparency. On the other hand, including particles within the above range also improves the slipperiness.
Furthermore, if the film has a multilayer structure, the layer containing the particles is preferably the surface layer, but if the film has a single-layer structure, it is the entire film.

The method for adding particles to polyester is not particularly limited, and conventionally known methods can be employed. For example, the particles can be added at any stage in the production of the polyester constituting each layer, but it is preferable to add them after the esterification or transesterification reaction is completed.

<Other additives>
In addition to the UV absorber and particles mentioned above, conventionally known additives such as antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, and pigments may be added to this polyester film as needed. If the polyester film has a multilayer structure, each additive may be added to at least one of the multiple layers.

<Manufacturing method>
Next, we will explain a method for manufacturing a polyester film, using the case where the polyester film is a biaxially oriented polyester film as an example. When the polyester film is a biaxially oriented polyester film, it is preferable to first manufacture an unstretched sheet and then stretch it in two directions to obtain a biaxially oriented polyester film.

The unstretched sheet is preferably obtained by supplying the aforementioned polyester, a copolymer polyester (B) having a triazine-based ultraviolet absorber (A) and/or a benzotriazole-based ultraviolet absorber, along with particles, other ultraviolet absorbers, and other additives as needed, to an extruder, mixing them appropriately, extruding the resulting molten sheet from the die using the extruder, and cooling and solidifying it in a rotating cooling drum. In this case, it is preferable to improve the adhesion between the sheet and the rotating cooling drum in order to improve the flatness of the sheet, and electrostatic application adhesion and/or liquid coating adhesion methods are preferably employed.
Furthermore, if the polyester film has a multilayer structure, it is preferable to co-extrude multiple layers using a co-extrusion method to obtain an unstretched sheet with a multilayer structure.
Furthermore, the polyester raw material may 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.

The resulting unstretched sheet is then stretched uniaxially, and then biaxially.
Specifically, the unstretched sheet is first 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. Here, it is preferable that the stretching direction of the first stage is the longitudinal direction (MD), and the direction perpendicular to that direction is the width direction (TD), but the reverse is also acceptable.
Then, the film is heat-treated at a temperature of 180 to 270°C under tension or under relaxation of 30% or less to obtain a biaxially oriented polyester 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.

Alternatively, a simultaneous biaxial stretching method can be employed. The simultaneous biaxial stretching method is a method of simultaneously stretching and oriented the aforementioned unstretched sheet in the longitudinal and width directions while maintaining a temperature controlled to typically 70 to 120°C, preferably 80 to 110°C, with a stretching ratio of 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area.
Subsequently, heat treatment is performed at a temperature of 170 to 250°C under tension or under relaxation of 30% or less to obtain a stretched and oriented film. For the simultaneous biaxial stretching apparatus employing the above-described stretching method, conventionally known stretching methods such as screw type, pantograph type, and linear drive type can be used.

In this invention, 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.

The thickness of this polyester film is 9 to 125 μm. Beyond 125 μm, it becomes difficult to achieve the thinning and weight reduction requirements for display devices. On the other hand, if the thickness is less than 9 μm, the film strength becomes insufficient.
From this viewpoint, the thickness of the polyester film is preferably 12 to 100 μm, and more preferably 25 to 75 μm.

When the polyester film comprises at least two surface layers and an intermediate layer disposed between the two surface layers, the thickness of each surface layer is preferably 1 to 20% of the total thickness of the polyester film, more preferably 1 to 19%, and even more preferably 1 to 18%. By keeping the thickness of the surface layers within this range, if the surface layers contain particles, the particles can impart slipperiness without impairing transparency, and problems such as particle shedding are less likely to occur.
Furthermore, from a similar viewpoint, the thickness of each surface layer is preferably 0.2 to 10 μm, more preferably 0.4 to 9.5 μm, and even more preferably 0.6 to 9.0 μm.

The thickness of the intermediate layer is preferably 60 to 98% of the total thickness of the polyester film, more preferably 62 to 98%, and even more preferably 63 to 98%.
Furthermore, the thickness of the intermediate layer is preferably 7 to 100 μm, more preferably 12 to 74 μm, and even more preferably 15 to 70 μm. The intermediate layer is a layer in the polyester film other than the two surface layers.

<Physical Properties>
The average light transmittance of this polyester film at wavelengths of 300 to 430 nm is 30% or less. If the average light transmittance at wavelengths of 300 to 430 nm exceeds 30%, the ultraviolet absorption capacity and the light absorption capacity in the short-wavelength region of visible light become insufficient, and the photodegradation of various optical components cannot be adequately suppressed.
From this viewpoint, the average light transmittance at wavelengths of 300 to 430 nm is preferably 28% or less, more preferably 25% or less, and even more preferably 23% or less. There is no particular limit on the lower limit, and it may be 0%, but considering that it is not necessary to cut out more than necessary, it may be 1% or more.

This polyester film preferably has a light transmittance of 10% or less at a wavelength of 380 nm, more preferably 5% or less, even more preferably 2% or less, and particularly preferably 1% or less. Within this range, it exhibits good ultraviolet absorption capabilities and can suppress photodegradation of various optical components.

This polyester film preferably has a light transmittance of 80% or less at a wavelength of 400 nm, more preferably 70% or less, and even more preferably 60% or less. Within this range, it exhibits good ultraviolet absorption capabilities and can suppress photodegradation of various optical components.

The total light transmittance of this polyester film is preferably 85% or higher, more preferably 86% or higher, and even more preferably 87% or higher. A total light transmittance of 85% or higher ensures sufficient visibility. While a higher total light transmittance is generally preferable, from the standpoint of stable production, it may be 99% or lower, or even 95% or lower.

The haze of this polyester 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. Within this haze range, the transparency of the polyester film can be considered good. The lower limit is not particularly limited, but is approximately 0.01%.

The heat shrinkage rate of this polyester film when heated at 120°C for 5 minutes is preferably 5.0% or less in both the longitudinal direction (MD) and the width direction (TD), more preferably 4.5% or less, even more preferably 4.0% or less, and particularly preferably 3.0% or less. If the heat shrinkage rate is 5.0% or less, planar defects such as curling and waviness during the processing of functional layers, including the hard coat layer described later, can be suppressed. Furthermore, in order to accommodate the thinning and weight reduction of display devices, when the optical polyester film is also made into a thin film, it is possible to suppress variations in optical properties caused by planarness.
While a lower thermal shrinkage rate is generally preferable, it is preferably -1% or higher, and more preferably -0.5% or higher. The negative value here indicates expansion after heating, and a value of -1% or higher can suppress flatness defects.

[Laminated film for optical applications]
The optical laminated film of the present invention (hereinafter also referred to as "this laminated film") comprises the optical polyester film described above and a functional layer provided on at least one side of the polyester film. The presence of the functional layer provides this laminated film with various functions.
The functional layer may be at least one of the following: a hard coat layer, an antistatic layer, an anchor layer, a release layer, an easy-adhesion layer, an infrared absorption layer, a gas barrier layer, an adhesive layer, a protective layer, a bleeding prevention layer, or a planarizing layer. It is preferable that the functional layer be either an easy-adhesion layer or a hard coat layer, and it is more preferable that it includes at least a hard coat layer. It is also preferable that the functional layer be an adhesive layer. The functional layer may be used as a single layer or two layers may be laminated together.

A preferred form of this laminated film is one in which a hard coat layer is provided on one side of the optical polyester film described above, and an adhesive layer is provided on the side opposite to the side with the hard coat layer. In this case, the laminated film is formed by sequentially laminating the adhesive layer, the polyester film, and the hard coat layer.
Another preferred embodiment is one in which an easy-adhesion layer and a hard coat layer are sequentially provided on one side of a polyester film, and an adhesive layer is provided on the side opposite to the side with the hard coat layer. In this case, a laminated film is formed by sequentially laminating the adhesive layer, polyester film, easy-adhesion layer, and hard coat layer.

(Hard court layer)
The hard coat layer is a functional layer provided on the surface of the laminated film for the purpose of imparting hardness. More specifically, the hard coat layer is a functional layer provided on the display for the purpose of imparting hardness to prevent scratches during handling, and is preferably used as a surface protection film to protect the display by positioning it on the display surface. Therefore, it is preferable to position the hard coat layer on the display surface side of the polyester film.

The hard coat layer is formed by curing a curable resin composition. The resin used to form the hard coat layer is not particularly limited and includes acrylic, siloxane, inorganic hybrid, urethane acrylate, polyester acrylate, and epoxy resins. Furthermore, two or more materials may be used in combination, and particles such as inorganic or organic fillers may be added.

The thickness of the hard coat layer is preferably 1 to 10 μm, more preferably 1 to 8 μm, and even more preferably 1 to 6 μm. If the thickness is 1 μm or more, sufficient curing results in high pencil hardness, and the hard coat layer can adequately protect the polyester film. On the other hand, if the thickness is 10 μm or less, curling and thermal wrinkling due to hard coat curing shrinkage can be prevented, ensuring good flatness. Furthermore, it is suitable for thin-film applications in displays.

The hard coat layer preferably has a surface hardness of 2H or higher. A surface hardness of 2H or higher provides the laminated film with appropriate scratch resistance. Furthermore, if the display is a flexible display or the like, the surface hardness is preferably 8H or lower, more preferably 6H or lower, and even more preferably 4H or lower, from the viewpoint of providing the laminated film with appropriate bending characteristics.
The surface hardness is measured using the pencil hardness scale, in accordance with JIS K 5600-5-4, under a 750g load condition. A pencil hardness tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) can be used as the measuring device.

The hard coat layer is obtained by applying a curable resin composition to the surface of a polyester film, drying it to form a coating layer, and then curing the coating layer.
Methods for applying the curable resin composition can be appropriately selected according to viscosity and film thickness, such as air doctor coating, blade coating, rod coating, bar coating, knife coating, die 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.
The drying conditions are not particularly limited and may be carried out at or near room temperature or by heating, for example, around 25 to 120°C, preferably around 50 to 100°C. The drying time is also not particularly limited as long as the solvent has evaporated sufficiently, for example, around 10 seconds to 30 minutes, preferably around 15 seconds to 10 minutes.
The curing method can be appropriately selected according to the curing mechanism of the curable resin composition. For example, if the curable resin composition is a thermosetting resin composition, it can be cured by heating, and if it is a photocurable resin composition, it can be cured by irradiation with energy rays. In laminated films, the active energy rays that can be used to cure the curable resin composition include ultraviolet rays, electron beams, X-rays, infrared rays, and visible light. Of these active energy rays, curing by ultraviolet rays and electron beams is preferred from the viewpoint of curability and prevention of resin degradation.

(Easy adhesive layer)
The easy-adhesion layer is a functional layer provided to improve the adhesion between the polyester film and the hard coat layer, etc.
The easy-to-adhere layer is formed from an easy-to-adhere layer composition containing a binder resin and a crosslinking agent.

Examples of the binder resin include polyester resin, acrylic resin, urethane resin, polyvinyl resin such as polyvinyl alcohol, polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, and starches. From the viewpoint of improving adhesion to the hard coat layer, it is preferable to use at least one selected from polyester resin, acrylic resin, and urethane resin. Examples of the crosslinking agent include epoxy compounds, melamine compounds, oxazoline compounds, isocyanate compounds, carbodiimide compounds, and silane coupling compounds, and one or more may be used alone or in combination.

The aforementioned easy-adhesion layer composition may contain particles to improve the blocking resistance and slipperiness of the easy-adhesion layer. Examples of particles include inorganic particles such as silica, alumina, kaolin, and calcium carbonate, as well as organic particles. These particles may be used individually or in combination of two or more types.
In addition, other additives such as crosslinking catalysts, defoamers, coating properties improvers, thickeners, lubricants, antistatic agents, UV absorbers, antioxidants, foaming agents, dyes, and pigments can also be used in combination.

The easy-adhesion layer composition is generally preferably diluted with water, an organic solvent, or a mixture thereof. The easy-adhesion layer is formed by coating the surface of a polyester film with the diluted easy-adhesion layer composition as a coating solution and then drying it.
The coating can be applied by conventionally known methods, but it is preferable to apply it by in-line coating, which involves treating the film surface during the polyester film manufacturing process.
The thickness of the easy-adhesion layer is preferably 0.003 to 1 μm, more preferably 0.005 to 0.6 μm, and even more preferably 0.01 to 0.4 μm. If the thickness of the easy-adhesion layer is 0.003 μm or more, sufficient adhesion can be ensured. On the other hand, if it is 1 μm or less, deterioration of appearance and blocking can be less likely to occur.

(adhesive layer)
As adhesives for forming the adhesive layer, acrylic adhesives, urethane adhesives, synthetic rubber adhesives, natural rubber adhesives, silicone adhesives, polyester adhesives, vinyl alkyl ether adhesives, epoxy adhesives, etc., can be used, with acrylic adhesives, urethane adhesives, and silicone adhesives being preferred. In addition, as long as it does not cause any abnormalities in optical properties, two or more materials can be mixed and used, or two or more layers can be used.
Furthermore, the adhesive may be of emulsion type, solvent type, or solvent-free type, and may be of crosslinked type or non-crosslinked type.
Furthermore, particles such as fillers and additives can also be added.
When a functional layer is provided on one side, the adhesive layer is preferably provided on the opposite side. Therefore, it is preferable that the laminated film has a hard coat layer on one side of the polyester film and an adhesive layer on the opposite side.

Preferably, the (meth)acrylic resin (base polymer) constituting the acrylic adhesive is a polymer or copolymer using one or more (meth)acrylic acid esters as monomers, such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate.
The base polymer is preferably copolymerized with polar monomers. Examples of polar monomers include monomers having carboxyl groups, hydroxyl groups, amide groups, amino groups, epoxy groups, etc., such as (meth)acrylic acid, 2-hydroxypropyl (meth)acrylic acid, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate.

The adhesive composition may consist solely of the base polymer described above, but it usually contains a crosslinking agent. Examples of crosslinking agents include divalent or higher metal ions, polyamine compounds, polyepoxy compounds, and polyisocyanate compounds, with polyisocyanate compounds being particularly preferred.

Preferably, the urethane-based adhesive consists of a urethane-based polymer, which is an adhesive polymer obtained by reacting a polyol with a polyisocyanate compound.
Examples of polyols include polyether polyols, polyester polyols, polycarbonate polyols, and polycaprolactone polyols.
Examples of polyisocyanate compounds include diphenylmethane diisocyanate, tolylene diisocyanate, and hexamethylene diisocyanate.

Examples of silicone-based adhesives include adhesives obtained by blending or agglomerating silicone-based polymers, which are adhesive polymers.
Examples of the aforementioned silicone-based adhesives include addition-curing type silicone-based adhesives and peroxide-curing type silicone-based adhesives. However, addition-curing type silicone-based adhesives are preferred because they do not use peroxides and do not generate decomposition products.
Examples of curing reactions for the aforementioned addition-curing type silicone adhesive include curing a polyalkyl hydrogen siloxane composition, which is used to obtain a polyalkyl silicone adhesive, with a platinum catalyst.

The thickness of the adhesive layer is, for example, 10 to 175 μm, preferably 20 to 120 μm, more preferably 30 to 80 μm, and particularly good if it is 40 to 60 μm. If the adhesive layer thickness is 10 μm or more, it has sufficient adhesive strength, and if the display is a flexible display, it will not lift or peel off even when bent, protecting various optical components. On the other hand, if it is 175 μm or less, it can contribute to thinning the display.

The adhesive layer can be formed by applying the above-mentioned adhesive to a polyester film. Alternatively, the adhesive may be applied to a release sheet, and the adhesive layer formed on another substrate such as a release sheet (mold release film) may be transferred to the polyester film to form the adhesive layer on the polyester film. The method of applying the adhesive is not particularly limited and can be any method such as a comma coater, knife coater, die coater, gravure coater, or Meyer bar coater, and can be appropriately selected according to viscosity and film thickness.
Furthermore, the adhesive may be formed into a sheet and cured as needed to create an adhesive sheet. Various known methods can be used for forming the sheet, such as wet lamination, dry lamination, extrusion casting using a T-die, extrusion lamination, calendering, inflation, injection molding, and liquid curing.

Furthermore, when curing the adhesive layer, various curing methods can be selected as appropriate, including those using energy rays such as ultraviolet light or electron beams, or heat curing.

[Application]
The polyester film and laminated film of the present invention can be used for optical applications. Specifically, they are preferably used as display components such as surface protective films, substrates for display cells, and back-side protective members. Furthermore, when the laminated film has a hard coat layer as a functional layer, it is preferable to use it as a surface protective film.
Flexible displays are preferred as the display, and examples include foldable displays, bendable displays, rollable displays, stretchable displays, and the like.

(Self-luminous light source)
The display of the present invention is preferably a self-emissive display, and preferably has either the polyester or laminated film mentioned above and a self-emissive light source. A self-emissive display refers to one in which images or videos can be displayed by the light source (self-emissive light source) itself. Examples of self-emissive displays include plasma displays, micro-LEDs, and organic EL displays, but among these, organic EL displays are preferred. The display may also be a touch panel type display.

(Coated polarizing element)
The display of the present invention more preferably comprises either the polyester film or the laminated film described above, and a coated polarizing element. When laminating the coated polarizing element with either the polyester film or the laminated film, it is preferable to interpose an adhesive layer.
In other words, the laminated film is a surface-protective optical laminated film having at least a hard coat layer on one side of a polyester film and an adhesive layer on the side opposite to the side with the hard coat layer, and it is most preferable to laminate a coated polarizing element with the adhesive layer or other adhesive layer interposed between them.
Furthermore, since the polyester film or laminated film contains an ultraviolet absorber, it can reduce the photodegradation of various optical components, especially coated polarizing elements.

In this invention, "polarizing element" refers to an optical component possessing optical anisotropy, and "coated polarizing element" refers to a laminate including a film formed by coating an optically anisotropic composition containing a liquid crystal compound. Examples of liquid crystal compounds include polymerizable liquid crystal compounds, polymer liquid crystal compounds, and lyotropic liquid crystal compounds. For example, a cured product obtained by coating an optically anisotropic composition containing a polymerizable liquid crystal compound onto a substrate and curing it in an oriented state can be used as a polarizing element. In this case, the substrate may be omitted.

Methods for laminating coated polarizing elements include, for example, forming a polarizing element on a release-type substrate and then transferring the polarizing element to the surface of a polyester film or laminated film; directly forming a polyester film or laminated film on a coated polarizing element; or forming a coated polarizing element on a polyester film or laminated film as a substrate.

The coated polarizing element in this invention, as described above, is a laminate containing a film formed by coating an optically anisotropic composition containing a liquid crystal compound. This film is typically obtained by coating an optically anisotropic composition containing a liquid crystal compound onto an alignment film formed on a substrate, and then polymerizing it while the liquid crystal compound is oriented.

Examples of substrates include resin sheets (films) or glass primarily composed of one or more resins selected from the group consisting of polyolefin resins, cyclic polyolefin resins, polyester resins, poly(meth)acrylic acid ester resins, cellulose ester resins, polycarbonate resins, and polyimide resins. The substrate may have other layers, such as various functional layers, as needed.
Furthermore, as mentioned above, this polyester film or laminated film may be used as a base material, for example.

Methods for aligning liquid crystal compounds include using an alignment film provided on the substrate to restrict alignment, an external field such as an electric or magnetic field to restrict alignment, and/or a shear force during coating. In particular, the method using an alignment film is preferred from the viewpoint that the liquid crystal compound will be in a highly ordered oriented state, and a coated polarizing element exhibiting good optical performance can be obtained.
The alignment film provided on the substrate is a layer having an orientation-regulating force that orients the liquid crystal compound, described later, in a desired direction. Preferably, the alignment film has solvent resistance that prevents dissolution when applying the optically anisotropic composition solution, moderate solution affinity that does not repel the optically anisotropic composition solution, and heat resistance during heat treatment during solvent drying and liquid crystal orientation.
The alignment film may be subjected to orientation treatment for orientation control by known methods described on pages 226-239 of the "Liquid Crystal Handbook" (Maruzen Co., Ltd., published October 30, 2000), etc. (rubbing method, method of forming grooves (fine groove structures) on the surface of the alignment film, method using polarized ultraviolet light/polarized laser (photo-alignment method), orientation method by LB film formation, orientation method by oblique deposition of inorganic material, etc.). In particular, the rubbing method and the photo-alignment method are preferred from the viewpoint of easily obtaining a high degree of orientation.
The thickness of the alignment film is typically 10 nm to 1000 nm, preferably 50 nm to 800 nm. This range allows for both sufficient alignment control force for aligning the liquid crystal compound and thin film thickness.

The optically anisotropic composition may also contain various additives and solvents, such as polymerization initiators, polymerization inhibitors, polymerization aids, polymerizable non-liquid crystal compounds, non-polymerizable non-liquid crystal compounds, surfactants, leveling agents, coupling agents, pH adjusters, dispersants, antioxidants, organic and inorganic fillers, and metal oxides, in addition to liquid crystal compounds and photopolymerization initiators. The cured layer of this composition exhibits optical functionality as a polarizing element.
If the polarizing element is a polarizing film, it is preferable that the composition contains a dichroic dye. Examples of dichroic dyes include iodine and dichroic organic dyes, and one type of dichroic dye may be used, or a combination of multiple different dyes may be used.
The aforementioned dichroic organic dyes are not particularly limited and include azo dyes, quinone dyes (including naphthoquinone dyes, anthraquinone dyes, etc.), stilbene dyes, cyanine dyes, phthalocyanine dyes, indigo dyes, and condensed polycyclic dyes (including perylene dyes, oxazine dyes, acridine dyes, etc.). Among these dyes, azo dyes are preferred because they have a large ratio of molecular length to short axis and can exhibit good dichroism.

Polymerizable liquid crystal compounds are liquid crystal compounds that have polymerizable functional groups and possess both polymerizable monomer properties and liquid crystal properties. Therefore, when polymerized and cured in an oriented state, a cured product consisting of a polymer with fixed orientation, i.e., an optically anisotropic material, can be obtained.
Therefore, by applying an optically anisotropic composition containing a polymerizable liquid crystal compound to a substrate and curing it in an oriented state, an optically anisotropic polarizing film can be formed. The polymerizable liquid crystal compound used may be a single type, or a combination of multiple compounds with different structures may be used.
The polymerizable liquid crystal compound may be either a low-molecular-weight liquid crystal compound having polymerizable functional groups or a high-molecular-weight liquid crystal compound having polymerizable functional groups. Among these, low-molecular-weight liquid crystal compounds are preferred because polymerizable liquid crystal compounds tend to yield cured products with high orientation.
The liquid crystal phase exhibited by the polymerizable liquid crystal compound can be appropriately selected from nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal, discotic liquid crystal, etc., but from the viewpoint of ease of manufacturing and obtaining a highly ordered orientation state, it is preferable to exhibit nematic liquid crystal or smectic liquid crystal.
The polymerizable functional group is preferably a photopolymerizable group due to the ease of fixing the orientation structure. Specifically, examples include acryloyl group, methacryloyl group, acryloyloxy group, methacryloyloxy group, acryloylamino group, methacryloylamino group, vinyl group, vinyloxy group, ethynyl group, ethynyloxy group, 1,3-butadienyl group, 1,3-butadienyloxy group, oxyranyl group, oxetanyl group, glycidyl group, glycidyloxy group, styryl group, styryloxy group, etc. Among these, the (meth)acryloyl group is preferred.

As the polymerizable liquid crystal compound, any liquid crystal compound having polymerizable groups can be used without any particular limitation on its molecular structure. For example, an example of a polymerizable liquid crystal compound included in the optical anisotropic composition according to the present invention is a compound represented by the following general formula (a) (hereinafter sometimes referred to as "polymerizable liquid crystal compound (a)").

Q ¹ -R ¹ -A ¹¹ -Y ¹ -A ¹² -(Y ² -A ¹³ ) _k -R ² -Q ² ...(a)

(In formula (a),
^-Q1 represents a hydrogen atom or a polymerizable group;
^-Q2 represents a polymerizable group;
^-R1- and ^-R2- each independently represent a chain-like organic group;
^-A11- and ^-A13- each independently represent a substructure, divalent organic group, or single bond represented by the following general formula (b);
-A ^12- represents a substructure or divalent organic group represented by the following general formula (b);
^-Y1- and ^-Y2- independently represent a single bond, -C(=O)O-, -OC(=O)-, -C(=S)O-, -OC(=S)-, -C(=O)S-, -SC(=O)-, _-CH2CH2- , -CH=CH-, _-C≡C- , -C(=O)NH-, _-NHC (=O)-, _-CH2O- , -OCH2-, _-CH2S- , or _SCH2- ;
One of ^-A11- and ^-A13- is a substructure or divalent organic group represented by the following general formula (b);
k is either 1 or 2.
If k is 2, the two ^-Y2 - ^A13- may be identical or different.

-Cy-X ² -C≡C-X ¹ -...(b)

(In formula (b),
-Cy- represents a hydrocarbon ring group or a heterocyclic group;
-X ¹ - is -C(=O)O-, -OC(=O)-, -C(=S)O-, -OC(=S)-, -C(=O)S-, -SC(=O)-, -CH ₂ CH ₂ -, -CH=CH-, -C(=O)NH-, -NHC(=O)-, -CH ₂ O-, -OCH ₂ -, -CH ₂ S-, or -SCH ₂ -;
^-X²- represents a single bond, -C(=O)O-, -OC(=O)-, -C(=S)O-, -OC(=S)-, -C(=O)S-, -SC(=O)-, _-CH²CH²- , _-CH =CH-, -C(=O)NH-, -NHC(=O)-, _-CH²O- , _-OCH²- , _-CH²S- , or _-SCH²- .

Furthermore, if -A ^11- is a substructure represented by general formula (b), then general formula (a) may be the following general formula (a-1) or the following general formula (a-2).
Q ¹ -R ¹ -Cy-X ² -C≡C-X ¹ -Y ¹ -A ¹² -(Y ² -A ¹³ ) _k -R ² -Q ² ... (a-1)
Q ¹ -R ¹ -X ¹ -C≡C-X ² -Cy-Y ¹ -A ¹² -(Y ² -A ¹³ ) _k -R ² -Q ² ... (a-2)

Furthermore, if -A ^12- is a substructure represented by general formula (b), then general formula (a) may be the following general formula (a-3) or the following general formula (a-4).
Q ¹ -R ¹ -A ¹¹ -Y ¹ -Cy-X ² -C≡C-X ¹ -(Y ² -A ¹³ ) _k -R ² -Q ² ... (a-3)
Q ¹ -R ¹ -A ¹¹ -Y ¹ -X ¹ -C≡C-X ² -Cy-(Y ² -A ¹³ ) _k -R ² -Q ² ... (a-4)

Furthermore, if -A ^13- is a substructure represented by general formula (b), then general formula (a) may be the following general formula (a-5) or the following general formula (a-6).
Q ¹ -R ¹ -A ¹¹ -Y ¹ -A ¹² -(Y ² -Cy-X ² -C≡C-X ¹ ) _k -R ² -Q ² ... (a-5)
Q ¹ -R ¹ -A ¹¹ -Y ¹ -A ¹² -(Y ² -X ¹ -C≡C-X ² -Cy) _k -R ² -Q ² ... (a-6)

Similarly, if two or more of ^-A11- , ^-A12- , and ^-A13- are substructures represented by general formula (b), the orientation of each substructure represented by general formula (b) may be reversed independently.

Furthermore, as described above, ^-A11- , ^-A12- , and ^-A13- are each independently substructures or divalent organic groups represented by general formula (b), and in addition, ^-A11- and ^-A13- may be single bonds, but ^-A11- and ^-A13- cannot both be single bonds.

The polymerizable liquid crystal compound (a) is preferably a compound represented by the general formulas (a-1), (a-2), (a-5), or (a-6) because it tends to provide high orientation.

When photopolymerizing polymerizable liquid crystal compounds, it is preferable to include a photopolymerization initiator in the optically anisotropic composition. Any known photopolymerization initiator can be used as appropriate.

The thickness of the cured film of the optically anisotropic composition is preferably 100 nm or more, more preferably 300 nm or more, and even more preferably 1 μm or more, from the viewpoint of ensuring optical functionality.
Furthermore, the thickness of the cured film of the optically anisotropic composition is preferably 50 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less, from the viewpoint of contributing to the thinning of the image display device.
Other layers, such as the functional layer, may be formed on the cured film of the composition as needed.

Furthermore, it is more preferable that the display of the present invention has both the polyester film or the laminated film described above, as well as a self-emissive light source and a coated polarizing element.
Specific examples of displays having a self-emissive light source and a coated polarizing element include, for example, liquid crystal displays, organic EL displays, inorganic EL displays, electronic paper, plasma displays, and microelectromechanical systems (MEMS) displays, with organic EL displays being preferred among them.

(Color filter)
The display of the present invention preferably comprises either the polyester film or the laminated film described above, and a color filter. When laminating the color filter with either the polyester film or the laminated film, it is preferable to interpose an adhesive layer.
In other words, the laminated film is a surface protection laminated film having at least a hard coat layer on one side of a polyester film and an adhesive layer on the side opposite to the side with the hard coat layer, and it is most preferable to laminate a color filter with the adhesive layer or another adhesive layer interposed between them.
Furthermore, since this polyester film or laminated film contains an ultraviolet absorber, it can protect various optical components from photodegradation.

Furthermore, it is more preferable that the display of the present invention has both the polyester film or the laminated film described above, as well as a self-emissive light source and a color filter.
Specific examples of displays having a self-emissive light source and a color filter include liquid crystal displays, organic EL displays, inorganic EL displays, electronic paper, plasma displays, and microelectromechanical systems (MEMS) displays, with organic EL displays being preferred among them.
As mentioned above, organic EL displays with built-in color filters eliminate the need for circular polarizers used in conventional displays, thus contributing to further thinning of the display.
Furthermore, organic EL displays with built-in color filters dramatically improve the luminous efficiency and lifespan of the light-emitting elements that make up the organic EL device, because the circular polarizer eliminates the light-emitting loss caused by the absorption of light emitted from the light-emitting elements of the organic EL device.

An example of the display 1 of the present invention is the conventional display shown in Figure 1. As shown in Figure 1, a hard coat layer 11 is provided on one side of an optical polyester film 12, and an adhesive layer 13 is provided on the side opposite to the side with the hard coat layer 11. Furthermore, a PVA polarizer 14 and a self-emissive light source 15 are laminated on top of it.
Furthermore, an example of a preferred embodiment of the display 1 of the present invention is shown in Figure 2. In the display 1 of Figure 2, a coated polarizing element 16 is stacked in place of the PVA polarizer 14 of Figure 1.
Furthermore, another example of a preferred form is shown in Figure 3. In the display 1 of Figure 3, a color filter 17 is stacked in place of the PVA polarizer 14 of Figure 1 and the coated polarizing element 16 of Figure 2.
In this invention, as described above, the displays shown in Figures 2 and 3 are preferred, and because the polyester film 12 contains a specific ultraviolet absorber, photodegradation of various optical components can be suppressed, and the display device can be made thinner and lighter.

However, the configuration of the display according to the present invention is not limited to Figures 1, 2, and 3. As described above, a functional layer, including an easy-adhesion layer, may be laminated between the polyester film 12 and the hard coat layer 11, and a functional layer may also be present between the polyester film 12 and the adhesive layer 13.
Furthermore, other components may be interposed between the polyester film 12 and the PVA polarizer 14/coated polarizing element 16/color filter 17, and between the PVA polarizer 14/coated polarizing element 16/color filter 17 and the self-luminous light source 15. Examples of such other components include reflective sheets, anti-reflective films, light guide plates, phase difference plates, glass substrates, and resin sheets (films). In addition to these components, other layers such as antistatic layers, anchor layers, easy-adhesion layers, and protective layers may be interposed as needed, and there may also be another adhesive layer for laminating the above-mentioned other components.

The display can be used in devices equipped with a display (display devices). Examples of display devices include mobile phones, smartphones, various tablet displays, digital cameras, personal computers, televisions, and other electrical equipment. The display of the present invention is suitable for use in various types of electrical equipment.

<<Explanation of terms>>
In this invention, the term "film" includes "sheets," and the term "sheet" includes "film."
In this invention, when "X to Y" (where X and Y are arbitrary 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."

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the scope of its essence.

<Evaluation Method>
(1) Measurement of the intrinsic viscosity (dl/g) of polyester: When particles were included in the formulation, 1 g of polyester from which the particles had been removed was accurately weighed, and 100 ml of a mixed solvent of phenol/tetrachloroethane = 50/50 (mass ratio) was added to dissolve it, and the viscosity was measured at 30°C.

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

(3) Measurement of light transmittance Using a spectrophotometer (V-670, manufactured by JASCO Corporation), the light transmittance in the wavelength range of 300 to 800 nm was measured with the air layer as the standard, and the average light transmittance in the wavelength range of 300 to 430 nm was determined. The light transmittances at wavelengths of 380 nm, 400 nm, and 430 nm are also listed in the table.

(4) Total light transmittance and haze In accordance with JIS K 7136:2000, the total light transmittance and haze were measured using a haze meter NDH-2000 manufactured by Nippon Denshoku Industries Co., Ltd.

(5) Film Thickness The thickness of this 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.

(6) Heat shrinkage rate The polyester films (samples) obtained in the examples and comparative examples were treated in an oven maintained at 120°C for 5 minutes in a tension-free state, and the length of the samples before and after treatment was measured to calculate the heat shrinkage rate in the longitudinal direction (MD) and the width direction (TD) of the film using the following formula.
Thermal shrinkage rate (%) = {(L0 - L1) / L0} × 100
(In the above formula, L0 is the sample length before heat treatment, and L1 is the sample length after heat treatment.)
Five measurements were taken in the longitudinal direction (MD) and the width direction (TD) of the film, and the average value was calculated for each.

<Materials used>
[Polyester raw materials]
Table 1 shows the composition and intrinsic viscosity of each polyester raw material used in the present invention.
In Table 1, TPA is terephthalic acid, IPA is isophthalic acid, EG is ethylene glycol, BG is 1,4-butanediol, CHDM is 1,4-cyclohexanedimethanol, and T-33 is 2,2'-methylenebis[6-(2H-benzotriazole-2-yl)-4-(2-hydroxyethyl)phenol] (manufactured by Daiwa Chemical Industries, Ltd., DAINSORB T-33).
Furthermore, in raw materials A to I, 1 to 5 mol% of by-product diethylene glycol is also treated as ethylene glycol.
Furthermore, raw material C contains 0.55% by mass of silica particles with an average particle size of 3 μm.
Furthermore, raw material F is homopolyethylene terephthalate blended with 16% by mass of an ultraviolet absorber (corresponding to a triazine compound shown in formula (6) below (triazine-based ultraviolet absorber (A))) and 5% by mass of an ultraviolet absorber (benzotriazole compound shown in formula (7) below). Raw material G is homopolyethylene terephthalate blended with 3% by mass of a triazine compound represented by formula (8) below (corresponding to triazine-based ultraviolet absorber (A)) and 6% by mass of a benzotriazole compound represented by formula (7) below. Raw material H uses copolymerized polybutylene terephthalate (UVAPBT, manufactured by Daiwa Chemical Co., Ltd.) containing 30% by mass of units derived from the ultraviolet absorber 2,2'-methylenebis[6-(2H-benzotriazole-2-yl)-4-(2-hydroxyethyl)phenol] (manufactured by Daiwa Chemical Co., Ltd., DAINSORB T-33) (corresponding to copolymerized polyester (B) having a benzotriazole-based ultraviolet absorber). Raw material I is homopolyethylene terephthalate blended with 10% by mass of an ultraviolet absorber (Siasorb 3638F, manufactured by Sun Chemical Co., Ltd.).

(Example 1)
As shown in Table 2, raw materials A and C were mixed in a mass ratio of 94:6 as the raw material for the surface layer, and raw materials A and F were mixed in a mass ratio of 93:7 as the raw material for the intermediate layer.
The mixed raw materials for the surface layer and the intermediate layer were each fed into separate twin-screw extruders, co-extruded at 280°C, and then cooled and solidified on cooling rolls set to 25°C to obtain two types of three-layer (surface layer/intermediate layer/surface layer) unstretched films.
Next, the obtained unstretched film was stretched 3.3 times in the longitudinal direction (MD) at 86°C using a roll stretcher. Furthermore, after preheating in a tenter at 90°C, it was stretched 3.6 times in the width direction (TD) at 110°C. Finally, it was heat-treated at 200°C to obtain a polyester film with a thickness of 50 μm (each surface layer: 2.5 μm, intermediate layer: 45 μm).
The properties of the obtained polyester film were evaluated using the method described above. The evaluation results are shown in Table 3.

(Examples 2-5)
The procedure was the same as in Example 1, except that the composition and film formation conditions were as described in Table 2 below. The evaluation results are shown in Table 3.

(Comparative Examples 1-3)
The procedure was the same as in Example 1, except that the composition and film formation conditions were as described in Table 2 below. The evaluation results are shown in Table 3.

Tables 1-3 show that the polyester films of Examples 1 and 2 containing the triazine-based UV absorber (A), and the polyester films of Examples 3-5 containing the copolymer polyester (B) with the benzotriazole-based UV absorber, all exhibit excellent wavelength-cutting properties in the ultraviolet and short-wavelength visible light regions. On the other hand, the polyester films of Comparative Examples 1-3, which used UV absorbers other than those according to the present invention, exhibited inferior wavelength-cutting properties in the ultraviolet and short-wavelength visible light regions.

The optical polyester film and optical laminated film of the present invention have excellent ultraviolet light blocking properties and wavelength blocking properties in the short wavelength region of visible light.
Therefore, the embodiments of this disclosure are also useful for display devices that do not have protective films such as TAC, and that are designed for further thinning and weight reduction.
These displays and display devices can suppress the photodegradation of various optical components using the optical polyester film and optical laminated film described above.

1 Display 11 Hard coat layer 12 Polyester film 13 Adhesive layer 14 PVA polarizer 15 Self-emissive light source 16 Coated polarizing element 17 Color filter

Claims (16)

A polyester film containing an ultraviolet absorber,
It comprises a triazine-based ultraviolet absorber (A ) bonded to at least one, two, or three naphthalene rings,
The polyester film comprises at least two surface layers and an intermediate layer disposed between the two surface layers.
The thickness of the intermediate layer is 60 to 98% of the total thickness of the polyester film.
The intermediate layer contains the ultraviolet absorber,
The total light transmittance is 85% or higher.
An optical polyester film that satisfies both (1) and (2) below.
(1) Average light transmittance of 30% or less at wavelengths of 300 to 430 nm (2) Thickness of 9 to 125 μm A polyester film containing an ultraviolet absorber,
The UV absorber comprises a triazine-based UV absorber (A) bonded to one, two, or three naphthalene rings and a benzotriazole-based UV absorber (excluding a copolymer polyester (B) having a benzotriazole-based UV absorber),
The total light transmittance is 85% or higher.
An optical polyester film that satisfies both (1) and (2) below.
(1) Average light transmittance of 30% or less at wavelengths of 300 to 430 nm (2) Thickness of 9 to 125 μm An optical polyester film according to claim 1 or 2, comprising at least one of polyethylene terephthalate and polyethylene naphthalate. An optical polyester film according to any one of claims 1 to 3 , wherein the haze is 3.0% or less. An optical polyester film according to any one of claims 1 to 4 , wherein the thermal shrinkage rate when heated at 120°C for 5 minutes is 5.0% or less in both the longitudinal direction (MD) and the width direction (TD). The optical polyester film according to any one of claims 1 to 5 , wherein the total content of the ultraviolet absorber is 7% by mass or less relative to the entire polyester film. The polyester film comprises at least two surface layers and an intermediate layer disposed between the two surface layers.
The thickness of the intermediate layer is 60 to 98% of the total thickness of the polyester film.
The optical polyester film according to any one of claims 2 to 6 , wherein the intermediate layer contains the ultraviolet absorber. An optical polyester film according to any one of claims 1 to 7 , wherein the light transmittance at a wavelength of 380 nm is 10% or less. An optical polyester film according to any one of claims 1 to 8 , wherein the light transmittance at a wavelength of 400 nm is 80% or less. An optical laminated film having a functional layer on at least one side of an optical polyester film according to any one of claims 1 to 9 . The optical laminated film according to claim 10 , wherein the functional layer is a hard coat layer. An optical laminated film according to claim 10 or 11 , for surface protection. The optical laminated film according to any one of claims 10 to 12 , wherein an adhesive layer is provided on the side opposite to the side having the functional layer. A display comprising an optical polyester film according to any one of claims 1 to 9 , or an optical laminated film according to any one of claims 10 to 13 , and a coated polarizing element. A display having an optical polyester film according to any one of claims 1 to 9 , or an optical laminated film according to any one of claims 10 to 13 , and a color filter. A display device comprising the display according to claim 14 or 15 .