JP7505508B2 - Copolymer polyester film, laminated film and method of using same - Google Patents

Description

The present invention relates to a copolymer polyester film having a copolymer polyester layer containing a copolymer polyester, a laminate film having a copolymer polyester film, and a method for using the same.

Polyethylene terephthalate (PET) film, a typical polyester film, especially biaxially oriented PET film, has excellent transparency, mechanical strength, heat resistance, and flexibility, and is therefore used in a variety of fields, including industrial materials, optical materials, electronic component materials, and battery packaging materials.

Regarding this type of polyester film, for example, Patent Document 1 proposes a softened polyester film that exhibits flexibility not found in conventional polyester films and has excellent formability at relatively low temperatures and pressures, the softened polyester film having a film elastic modulus E' of 20 MPa or less at 120°C and 5 MPa or less at 180°C, a film haze of 1.0% or less, containing 29 to 32 mol% of 1,4-cyclohexanedimethanol units as a diol constituent, and containing no isophthalic acid units as a dicarboxylic acid constituent.

2. Description of the Related Art In recent years, due to the miniaturization and high performance of portable terminals, computers that are small enough to be worn on the body (wearable computers) have been attracting attention as image display devices.
Ideally, electronic devices used in wearable computers (wearable terminals) would be attached to objects around the human body, such as cards, bags, watches, clothes, and shoes (Patent Document 2).

In addition, flexible displays that can be bent freely are attracting attention as next-generation image display devices. Organic electroluminescence (organic EL) displays are mainly used for flexible displays.
Since flexible displays use thin glass substrates or plastic substrates, the polyester films used in these image display device components are required to have the optical properties and durability required for conventional flat display panels, as well as flexibility such that they do not break even when subjected to bending tests.

Furthermore, as one of the applications of softened polyester films, multilayer films with various functions using a so-called lamination and stretching technique, in which different materials are laminated and stretched, are attracting attention (Non-Patent Document 1).
For example, examples of combinations of different materials include EVA-based resin-PVC, EVA-polyester, EVA-low density polyethylene, PVA-PVC, PVA-polyester, PVA-low density polyethylene, etc. Examples of functions to be imparted include gas barrier properties, heat seal properties, scratch resistance, printability, moisture resistance, etc.

In recent years, as electronic devices such as smartphones and other communication devices and laptops have become more powerful, the electronic components they are fitted with are also required to be smaller and more powerful. For example, when it comes to ceramic multilayer capacitors, there is a trend for the green sheets used to become thinner, and it is necessary to stably manufacture thin green sheets of about 0.5 μm to 1 μm. In conventional coating methods, it is common to apply a relatively low-viscosity slurry diluted with a solvent onto a substrate film and dry it to form a sheet.

However, after coating and drying using a low-concentration slurry, pinholes were generated in the obtained green sheet, and the performance was not necessarily satisfactory. Therefore, as another method, as described in Patent Document 3, a method has been proposed in which a green sheet is obtained by stretching the base film and the slurry-coated layer together in a laminated state during the process of coating and drying the slurry on the base film.
When the above-mentioned different materials (e.g., materials constituting the slurry) are laminated on a base film and the laminate is subjected to a stretching process, there is an advantage that the occurrence of pinholes can be reduced by adjusting the slurry concentration (e.g., by increasing the concentration).

In addition to the use of manufacturing green sheets, it is also being considered to laminate different materials such as a resin layer onto a base film to create a multilayer body, and then stretch the multilayer body to stretch the resin layer provided on the base film.

JP 2014-169371 A JP 2002-174688 A Japanese Patent Application Laid-Open No. 10-250014

"Textiles and Industry" Biaxial Stretching Technology for Multilayer Films, by Mutsuo Kuga (Vol. 35, No. 7 (1979))

However, the stretching process when dissimilar materials are laminated on a base film is subject to processing conditions that are limited by the mechanical properties, especially the elongation rate, of the base film or the dissimilar materials that are provided on the base film. For example, when stretching a thin dissimilar material sheet from a comparatively thick dissimilar material layer in a laminated state of dissimilar materials before stretching, the base film is required to be capable of being stretched at a high stretch ratio. Conventionally used polyester films, such as copolymer polyester films using isophthalic acid, sometimes have insufficient elongation rate at room temperature, making stretching difficult.

Furthermore, when looking at materials that can be used for the base film and are expected to have high elongation at room temperature, examples include nylon, PVC, and PP (polypropylene) films. However, while these often have high elongation, they also have poor heat resistance. For example, after passing through a heat treatment process, the shrinkage rate of the film increases, making it difficult to use in applications that require dimensional precision.

Therefore, an object of the present invention is to provide a copolymer polyester film which is capable of satisfying the contradictory properties of excellent flexibility and high elongation at room temperature, while also having good heat resistance.
A more specific object of the present invention is to provide a copolymer polyester film, a laminate film, and a method for using the same, which are suitable for producing a thin functional sheet by stretching a functional layer laminated on a base film.

The present invention relates to the following.
[1] A copolymer polyester film having a copolymer polyester layer (A1) containing a copolymer polyester (a1),
The copolymer polyester (a1) is a copolymer containing terephthalic acid (X1), a dicarboxylic acid component (X2) having 4 to 10 carbon atoms, and an alcohol component (Y2) other than ethylene glycol (Y1),
A copolymer polyester film having a difference (ΔTcg) between its cold crystallization temperature (Tcc) and its glass transition temperature (Tg) of more than 60°C.
[2] A copolymer polyester film having a copolymer polyester layer (A1) containing a copolymer polyester (a1),
The copolymer polyester (a1) is a copolymer containing terephthalic acid (X1), a dicarboxylic acid component (X), and an alcohol component (Y2) other than ethylene glycol (Y1), and contains two or more types of the other alcohol component (Y2),
A copolymer polyester film having a difference (ΔTcg) between its cold crystallization temperature (Tcc) and its glass transition temperature (Tg) of more than 60°C.
[3] The copolymer polyester film according to the above [1] or [2], wherein the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in all the dicarboxylic acid components in the polyester (A) contained in the copolymer polyester layer (A1) is 3 to 50 mol %.
[4] The copolymer polyester film according to any one of the above [1] to [3], wherein the ratio of the other alcohol component (Y2) to the alcohol components in all the polyesters (A) contained in the copolymer polyester layer (A1) is 15 to 60 mol %.
[5] The copolymer polyester film according to any one of the above [1] to [4], having a tensile elongation at break at 25°C of 295% or more.
[6] The copolymer polyester film according to any one of the above [1] to [5], having a storage modulus at 25° C. of 2,500 MPa or less and a storage modulus at 120° C. of 10 MPa or more.
[7] The copolymer polyester film according to any one of the above [1] and [3] to [6], wherein the dicarboxylic acid component (X2) having 4 to 10 carbon atoms includes an aliphatic dicarboxylic acid.
[8] The copolymer polyester film according to the above [7], wherein the aliphatic dicarboxylic acid includes adipic acid.
[9] The copolymer polyester film according to any one of the above [1] to [8], wherein the other alcohol component (Y2) contains 1,4-butanediol.
[10] The copolymer polyester film according to any one of the above [1] to [9], wherein the other alcohol component (Y2) contains 1,4-butanediol and 1,6-hexanediol.
[11] The copolymer polyester film according to any one of the above items [1] to [10], wherein the copolymer polyester layer (A1) is a polyester other than the copolymer polyester (a1) and further contains a polyester (a2) containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as an alcohol component.
[12] The copolymer polyester film according to any one of the above [1] to [11], further comprising a polyester layer (B1) and a polyester layer (B2) on both sides of the copolymer polyester layer (A1).
[13] A laminate film comprising the copolymer polyester film according to any one of [1] to [12] above and a functional layer provided on at least one surface of the copolymer polyester film.
[14] The laminate film according to the above [13], wherein the functional layer is a resin layer containing a resin containing a vinyl alcohol structural unit.
[15] The laminate film according to the above [13] or [14], wherein the functional layer constitutes a green sheet.
[16] The laminate film according to the above [13] or [14], wherein the functional layer constitutes a polarizer.
[17] The laminate film described in [13] above, wherein the functional layer is an adhesive layer.
[18] The laminate film according to [17] above, wherein the adhesive layer contains a conductive material.
[19] The laminate film according to the above [13], wherein the functional layer is a conductive layer.
[20] A method for using a copolymer polyester film or a laminate film, comprising a step of stretching the copolymer polyester film or the laminate film according to any one of [1] to [12] above, or the laminate film according to any one of [13] to [19] above.
[21] The method for using the copolymer polyester film or laminate film according to the above [20], wherein the stretching is carried out in air or in water.
[22] A method for using the copolymer polyester film or laminate film according to the above [20] or [21], wherein the stretching is carried out at a stretching ratio of 2.0 to 6.0 times.
[23] The copolymer polyester film according to any one of [1] to [12] above, which is used for an adhesive tape, a surface protection film, or a dicing tape for a semiconductor.
[24] The laminate film according to any one of the above [13] to [19], which is used for an adhesive tape, a surface protection film, or a semiconductor dicing tape.
[25] The method for use according to the above [20] or [21], wherein the copolymer polyester film or laminate film is for use in any one of an adhesive tape, a surface protection film, and a semiconductor dicing tape.
[25] The copolymer polyester film according to any one of [1] to [12] above, which is used for a wearable terminal, a bioelectrode substrate, or a biosensor substrate.
[26] The laminate film according to any one of the above [13] to [19], which is used for a wearable terminal, a bioelectrode substrate, or a biosensor substrate.
[27] The method for use according to the above [20] or [21], wherein the copolymer polyester film or laminate film is for use in a wearable terminal, a bioelectrode substrate, or a biosensor substrate.
[28] The copolymer polyester film according to any one of [1] to [12] above, which is used for producing electronic parts.
[29] The laminate film according to any one of the above [13] to [19], which is used for manufacturing electronic parts.
[30] The method for using the copolymer polyester film or the laminated film according to the above [20] or [21], wherein the copolymer polyester film or the laminated film is used for producing electronic parts.
[31] The copolymer polyester film according to any one of the above [1] to [12], which is for producing an optical member.
[32] The laminate film according to any one of the above [13] to [19], which is for producing an optical component.
[33] The method for using the copolymer polyester film or laminate film according to the above [20] or [21], wherein the copolymer polyester film or laminate film is used for producing an optical member.

The copolymer polyester film of the present invention has excellent flexibility at room temperature, and is not only flexible but also has a large elongation rate, and at the same time, has a suitably low heat shrinkage rate, which is the contradictory property, and thus has heat resistance sufficient for practical use.
Furthermore, according to the present invention, it is possible to provide a copolymer polyester film, a laminate film, and a method for using the same that are suitable for producing a thin functional sheet, for example, by stretching a functional layer laminated on a base film.

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.

<The present copolymer polyester film>
A copolymer polyester film according to one embodiment of the present invention (referred to as "the present copolymer polyester film") is a single-layer or multilayer film having a copolymer polyester layer (A1) containing a copolymer polyester (a1).

The present copolymer polyester film is preferably a uniaxially or biaxially stretched film, and may be a uniaxially or biaxially stretched film. Among them, a biaxially stretched film is preferred from the viewpoints of excellent balance of mechanical properties and flatness.
When the copolymer polyester film is such a stretched film, it is easy to achieve a storage modulus at 120° C. of 10 MPa or more and a tensile elongation at break at 25° C. of 295% or more.

<Copolymer Polyester Layer (A1)>
The copolymer polyester layer (A1) is a layer containing a copolymer polyester (a1). The copolymer polyester layer (A1) preferably contains a polyester (a2) in addition to the copolymer polyester (a1). The copolymer polyester layer (A1) may contain a resin (a3) in addition to the copolymer polyester (a1) and the polyester (a2).

(Copolymer polyester (a1))
In one embodiment of the present invention, the copolymer polyester (a1) is a copolymer containing terephthalic acid (X1), a dicarboxylic acid component (X2) having 4 to 10 carbon atoms, and an alcohol component (Y2) other than ethylene glycol (Y1). The copolymer polyester (a1) may be crystalline or amorphous.
The dicarboxylic acid component (X2) having 4 to 10 carbon atoms means a dicarboxylic acid component having 4 to 10 carbon atoms excluding terephthalic acid (X1).
The copolymer polyester (a1) in this embodiment is a polycondensate of a dicarboxylic acid including terephthalic acid (X1) and a dicarboxylic acid component (X2) having 4 to 10 carbon atoms, and an alcohol component including an alcohol component (Y2) other than ethylene glycol (Y1). The alcohol component is generally a diol component.
In the present invention, by using a dicarboxylic acid component having 4 to 10 carbon atoms as the dicarboxylic acid, it becomes easier to ensure flexibility, elongation, and the like at low temperatures.

Examples of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, and polyfunctional acids. Among these, aliphatic dicarboxylic acids are preferred from the viewpoint of improving the storage modulus at room temperature and improving flexibility and elongation. The aliphatic dicarboxylic acid may be used alone as the dicarboxylic acid component (X2) having 4 to 10 carbon atoms, or may be used in combination with other dicarboxylic acid components having 4 to 10 carbon atoms.
Examples of the aliphatic dicarboxylic acid having 4 to 10 carbon atoms include saturated aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid, and among them, from the viewpoint of ease of reaction during polymerization, adipic acid and sebacic acid are more preferable, and adipic acid is even more preferable. Examples of the aromatic dicarboxylic acid include isophthalic acid.

In one embodiment, the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in the dicarboxylic acid components constituting the copolymerized polyester (a1) may be adjusted so that the proportion of (X2) in all of the polyesters (A) described below falls within a predetermined range, and is not particularly limited, for example, 5 to 35 mol %, preferably 8 to 25 mol %, and more preferably 10 to 20 mol %.
In one embodiment, the proportion of terephthalic acid (X1) in the dicarboxylic acid components constituting the copolymerized polyester (a1) is, for example, 65 to 95 mol %, preferably 75 to 92 mol %, and more preferably 80 to 90 mol %.

In one embodiment of the copolymer polyester (a1), the dicarboxylic acid component may be composed of terephthalic acid (X1) and a dicarboxylic acid component (X2) having 4 to 10 carbon atoms, or may contain a dicarboxylic acid component (another dicarboxylic acid component (X3)) other than terephthalic acid (X1) and the dicarboxylic acid component (X2) having 4 to 10 carbon atoms as a copolymer component within a range that does not depart from the gist of the present invention. Examples of such dicarboxylic acid components include dodecanedioic acid, eicosanoic acid, dimer acid, and derivatives thereof.
In the above embodiment, the ratio of the other dicarboxylic acid component (X3) to the dicarboxylic acid components constituting the copolymerized polyester (a1) is, for example, 10 mol % or less, preferably 5 mol % or less, more preferably 3 mol % or less, and most preferably 0 mol %.

Other examples of the alcohol component (Y2) include aliphatic diols such as 1,4-butanediol, 1,4-hexanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, pentamethylene glycol, octamethylene glycol, decamethylene glycol, neopentyl glycol, and 2-ethyl-2-butyl-1,3-propanediol; 1,2-cyclohexanediol, 1,1-cyclohexanedimethylol, 1,4-cyclohexanedimethanol, and 2,5-norbornane diol. Examples of such diols include alicyclic diols such as methylol, aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4'-hydroxyphenyl)propane, 2,2-bis(4'-β-hydroxyethoxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, and bis(4-β-hydroxyethoxyphenyl)sulfonic acid, as well as ethylene oxide or propylene oxide adducts of 2,2-bis(4'-hydroxyphenyl)propane, and dimer diol. These diols may be used alone or in combination.
Among the above, from the viewpoints of flexibility and crystallinity, aliphatic diols are preferred. The aliphatic diol is preferably an aliphatic diol having 4 to 8 carbon atoms, more preferably an aliphatic diol having 4 to 6 carbon atoms.
More specifically, the aliphatic diol is preferably at least one selected from diethylene glycol, 1,4-butanediol, 1,4-hexanediol, and 1,6-hexanediol. It is more preferable that the other alcohol component (Y2) contains at least 1,4-butanediol. It is also preferable to use two or more types of alcohol component (Y2). When two or more types are used, they may be appropriately selected from those described above. Among them, it is more preferable that the alcohol component in the copolymer polyester (a1) contains both 1,4-butanediol and 1,6-hexanediol. By using two or more types of other alcohol component (Y2), it has the advantage that it is easier to adjust the crystallinity in combination with the acid component than before.
The copolymer polyester (a1) may contain ethylene glycol (Y1) as an alcohol component (copolymer component). Any of the polyesters (A) constituting the copolymer polyester layer (A1) may contain ethylene glycol (Y1) as an alcohol component. Therefore, when the copolymer polyester (a1) does not contain ethylene glycol (Y1) as an alcohol component (copolymer component), for example, the polyester (a2) may contain ethylene glycol (Y1) as an alcohol component (copolymer component).

The proportion of the other alcohol component (Y2) in the alcohol components constituting the copolymerized polyester (a1) may be adjusted so that the proportion of (Y2) in all of the polyesters (A) described below is within a specified range, for example, 50 to 100 mol%, preferably 70 to 100 mol%, and more preferably 90 to 100 mol%.

In addition, since the copolymer polyester (a1) contains a certain amount or more of terephthalic acid, a dicarboxylic acid having 4 to 10 carbon atoms, and a polyester having one or both of 1,4-butanediol and 1,6-hexanediol as structural units, the copolymer polyester layer (A1) is flexible and has excellent elongation at low temperatures, and also has strength and heat resistance.

In another embodiment of the present invention, the copolymer polyester (a1) is a copolymer containing terephthalic acid (X1), a dicarboxylic acid component (X), and an alcohol component (Y2) other than ethylene glycol (Y1), and the other alcohol component (Y2) contains two or more types.
Therefore, the copolymerized polyester (a1) in another embodiment of the present invention is a polycondensate of a dicarboxylic acid including terephthalic acid (X1) and a dicarboxylic acid component (X), and an alcohol component including an alcohol component (Y2) other than ethylene glycol (Y1), and the other alcohol component (Y2) includes two or more kinds of alcohol components. The alcohol component is generally a diol component.
The dicarboxylic acid component (X) refers to a dicarboxylic acid component other than terephthalic acid (X1). However, in this specification, when the term "dicarboxylic acid" is used simply, the term also includes terephthalic acid (X1).
In another embodiment, the other alcohol component (Y2) is as described above, except that two or more kinds are used, and the details of the case where two or more kinds are used are also as described above.

In the present invention, the use of two or more types of alcohol component (Y2) has the advantage that the crystallinity can be adjusted more easily than before in combination with the acid component, and the difference between Tcc and Tg, which will be described later, can be easily adjusted. In particular, in the present invention, a remarkable effect is obtained in combination with a dicarboxylic acid component (X2) having 4 to 10 carbon atoms. Therefore, in another embodiment of the present invention, it is preferable that the dicarboxylic acid component (X) contains a dicarboxylic acid component (X1) having 4 to 10 carbon atoms, and in such a case, the details of the copolymer polyester (a1) are as described in the copolymer polyester (a1) of the above embodiment.
However, in another embodiment, the dicarboxylic acid used in the copolymer polyester (a1) may consist of terephthalic acid (X1) and another dicarboxylic acid component (X3), and in this case, the details of the other dicarboxylic acid component (X3) are as described above.
In each embodiment, the copolymer polyester (a1) may be used alone or in combination of two or more kinds.

(Intrinsic Viscosity (IV) of Copolymer Polyester (a1))
The intrinsic viscosity (IV) of the copolymer polyester (a1) (as a polyester mixture when two or more types of copolymer polyesters (a1) are used) is preferably 0.40 dL/g to 1.20 dL/g, more preferably 0.45 dL/g or more, even more preferably 0.48 dL/g or more, and more preferably 1.15 dL/g or less, even more preferably 1.10 dL/g or less.
When the intrinsic viscosity of the copolymer polyester (a1) is within this range, it is possible to obtain a polyester having excellent moldability without deteriorating productivity.
The intrinsic viscosity (IV) of the polyester was measured at 30° C. by precisely weighing 1 g of polyester from which components incompatible with the polyester had been removed and dissolving the 1 g of polyester in 100 ml of a mixed solvent of phenol/tetrachloroethane = 50/50 (weight ratio).

The content of the copolymer polyester (a1) may be a certain percentage or more of the resin components constituting the copolymer polyester layer (A1) so that the percentages of each component in all polyesters (A) described later are within a predetermined range. The copolymer polyester (a1) may account for, for example, 20% by mass or more, preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 50% by mass or more of the resin components constituting the copolymer polyester layer (A1), and may account for, for example, 80% by mass or more. The copolymer polyester (a1) may account for 100% by mass or less of the resin components constituting the copolymer polyester layer (A1), but may also account for, for example, 70% by mass or less, or 60% by mass or less.

(Polyester (a2))
The copolymer polyester layer (A1) may be composed of only the copolymer polyester (a1) as a resin, but preferably contains a polyester (a2) in addition to the copolymer polyester (a1).
Here, in each of the above-mentioned embodiments, the polyester (a2) is a polyester other than the copolymer polyester (a1) of each of the above-mentioned embodiments, and is a homopolyester or copolymer polyester containing terephthalic acid (X1) as a dicarboxylic acid component and ethylene glycol (Y1) as an alcohol component.

The homopolyester is a polyethylene terephthalate in which the dicarboxylic acid component is terephthalic acid (X1) and the alcohol component is ethylene glycol (Y1). It is preferable to use a homopolyester as the polyester (a2). However, when referring to a homopolyester, the alcohol component may contain diethylene glycol, which is inevitably mixed in. Specifically, in the polyethylene terephthalate (homopolyester), the ratio of diethylene glycol to the alcohol component may be, for example, 5 mol% or less, or 3 mol% or less. The same applies to the polyester (B) described later.
When polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, a part of the ethylene glycol is modified to become diethylene glycol, which is then introduced into the polyester skeleton.

When the polyester (a2) is a copolymer polyester, the copolymer polyester may be, for example, a copolymer of a dicarboxylic acid component consisting of terephthalic acid (X1) and a dicarboxylic acid component other than terephthalic acid (X1) and an alcohol component consisting of ethylene glycol. In this case, the alcohol component may contain diethylene glycol which is inevitably mixed in as described above, and the content ratio of diethylene glycol in this case is as described above. In this way, a copolymer polyester consisting of ethylene glycol and diethylene glycol which is inevitably mixed in is referred to as polyester (a2).
In addition, when the polyester (a2) is a copolymer polyester, the copolymer polyester may be, for example, a copolymer of terephthalic acid (X1) and an alcohol component including ethylene glycol and an alcohol component (Y2) other than ethylene glycol (Y1).
In each of the above-mentioned embodiments, the polyester (a2) may be any polyester other than the polyester (a1).

In the case where the polyester (a2) is a copolymer polyester, examples of the dicarboxylic acid component other than terephthalic acid (X1) include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, polyfunctional acids, etc. Examples of these dicarboxylic acid components include the same as those listed in the copolymer polyester (a1). Here, the dicarboxylic acid component other than terephthalic acid (X1) may be used alone or in combination of two or more. In addition, as the dicarboxylic acid component other than terephthalic acid (X1), a dicarboxylic acid component having 4 to 10 carbon atoms may be used, but other dicarboxylic acid components such as dimer acid may be used, or these may be used in combination. As the dicarboxylic acid component, an aromatic dicarboxylic acid is preferable, and among them, isophthalic acid is more preferable.
When the polyester (a2) is a copolymer polyester and the dicarboxylic acid component contains a dicarboxylic acid component other than terephthalic acid, the proportion of the dicarboxylic acid component other than terephthalic acid in the dicarboxylic acid component is preferably 1 to 30 mol %, more preferably 3 mol % or more, even more preferably 5 mol % or more, and more preferably 20 mol % or less, even more preferably 15 mol % or less.

When the polyester (a2) is a copolymer polyester, the alcohol component (Y2) other than ethylene glycol (Y1) can be appropriately selected from the compounds listed in the copolymer polyester (a1), and preferred examples thereof include 1,4-butanediol, 1,6-hexanediol, 1,4-hexanediol, diethylene glycol, trimethylene glycol, neopentyl glycol, and 1,4-cyclohexanedimethanol.
When the polyester (a2) is a copolymer polyester and the alcohol component contains an alcohol component (Y2) other than ethylene glycol (Y1), the proportion of the alcohol component (Y2) other than ethylene glycol in the alcohol component in the copolymer polyester is preferably 1 mol % or more and less than 100 mol %, more preferably 3 mol % or more, even more preferably 5 mol % or more, and even more preferably 90 mol % or less, even more preferably 50 mol % or less, even more preferably 30 mol % or less, and particularly preferably 10 mol % or less.

The intrinsic viscosity (IV) of the polyester (a2) (as a polyester mixture when two or more kinds of polyesters (a2) are used) is preferably 0.40 dL/g to 1.20 dL/g, more preferably 0.45 dL/g or more, even more preferably 0.48 dL/g or more, and more preferably 1.15 dL/g or less, even more preferably 1.10 dL/g or less.
When the intrinsic viscosity of the copolymer polyester (a2) is within this range, it is possible to obtain a polyester having excellent moldability without deteriorating productivity.

The polyester (a2) may be used alone or in combination of two or more kinds.
The content of polyester (a2) may be within the range of the proportion of each component in polyester (A) as described below, and is, for example, 80 mass% or less, preferably 70 mass% or less, more preferably 65 mass% or less, and even more preferably 50 mass% or less of the resin components constituting the copolymerized polyester layer (A1), and is preferably 30 mass% or more, and more preferably 40 mass% or more.

(Resin (a3))
The copolymer polyester layer (A1) may be a layer containing a resin (a3) other than the copolymer polyester (a1) and the polyester (a2). As the resin (a3), a resin compatible with the copolymer polyester (a1) may be used, and when the polyester (a2) is used, the resin may also be compatible with the polyester (a2).
When the copolymer polyester layer (A1) is a layer in which a sea-island structure is formed by the copolymer polyester (a1) or the copolymer polyester (a1) and the polyester (a2) and the resin (a3), shielding properties and heat resistance can be imparted by selecting, as the resin (a3), for example, a polyester such as polyolefin, polystyrene, an acrylic resin, a urethane resin, or polybutylene terephthalate (PBT).

In the copolymer polyester layer (A1), the mass ratio of the total amount of the copolymer polyester (a1) and the polyester (a2) to the resin (a3) ((a1+a2):a3) is preferably 98:2 to 50:50, more preferably 95:5 to 60:40, and even more preferably 90:10 to 65:35.

The resin (a3) is preferably a resin compatible with the copolymer polyester (a1) or the copolymer polyester (a1) and the polyester (a2), and has a melting point of 270° C. or less and a glass transition temperature of 30 to 120° C. By selecting such a resin (a3), the glass transition temperature of the copolymer polyester layer (A1) can be increased, and the heat resistance can be improved. An example of such a resin is polybutylene terephthalate (PBT), but is not limited to PBT.
The resin (a3) may be used alone or in combination of two or more kinds.

(Proportion of each ingredient)
In the present invention, the ratio of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms to the dicarboxylic acid components in all the polyesters (A) contained in the copolymer polyester layer (A1) is, for example, 3 to 50 mol %. Note that all the polyesters (A) referred to here means all the polyesters contained in the copolymer polyester layer (A1). Therefore, the above ratio means the ratio based on the dicarboxylic acid components constituting all the polyesters (A), and hereinafter, similar terms will be used with the same meaning.

Here, by setting the ratio of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms to 3 mol % or more, the effect of using the dicarboxylic acid component (X2) having 4 to 10 carbon atoms can be sufficiently obtained, and flexibility, elongation, etc. at low temperatures can be ensured. By setting the ratio to 50 mol % or less, the thermal shrinkage rate is reduced and heat resistance can be ensured.
From the viewpoint of ensuring heat resistance while improving flexibility, elongation, and the like at low temperatures, the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms is preferably 5 mol % or more, more preferably 7 mol % or more, and is preferably 45 mol % or less, more preferably 40 mol % or less, even more preferably 25 mol % or less, and still more preferably 12 mol % or less.

As described above, it is preferable to use adipic acid as the dicarboxylic acid component (X2) having 4 to 10 carbon atoms. When adipic acid is used, adipic acid may be used alone as the dicarboxylic acid component (X2) having 4 to 10 carbon atoms, or may be used in combination with a dicarboxylic acid having 4 to 10 carbon atoms other than adipic acid.
The proportion of adipic acid in the dicarboxylic acid components in all of the polyesters (A) is, for example, 3 to 50 mol%, but is preferably 4 mol% or more, more preferably 5 mol% or more, even more preferably 7 mol% or more, and is preferably 40 mol% or less, more preferably 25 mol% or less, even more preferably 12 mol% or less, and still more preferably 10 mol% or less.

In addition, the proportion of terephthalic acid (X1) in the dicarboxylic acid components in all polyesters (A) is, for example, 50 to 97 mol%, from the viewpoint of maintaining various performance properties such as heat resistance well, but is preferably 95 mol% or less, more preferably 93 mol% or less, and is preferably 60 mol% or more, more preferably 65 mol% or more, even more preferably 75 mol% or more, and even more preferably 88 mol% or more.

In addition, the ratio of the other dicarboxylic acid (X3) to the dicarboxylic acid components in all of the polyesters (A) is, for example, 10 mol% or less, preferably 5 mol% or less, more preferably 3 mol% or less, and most preferably 0 mol%. In other words, it is most preferable that the dicarboxylic acid components in the polyesters (A) do not contain the other dicarboxylic acids (X3).

The dicarboxylic acid component of the polyester (A) contained in the copolymer polyester layer (A1) can be quantified by measuring the 1H-NMR spectrum.

In the present invention, the ratio of the other alcohol component (Y2) to the alcohol components in all the polyesters (A) contained in the copolymer polyester layer (A1) is, for example, 15 to 60 mol%. If it is 15 mol% or more, it is easier to ensure flexibility, elongation, etc. at low temperatures. Also, if it is 60 mol% or less, the thermal shrinkage rate is low and it is easier to ensure heat resistance. From the viewpoint of ensuring heat resistance while improving flexibility and elongation at low temperatures, the ratio of the other alcohol component (Y2) is preferably 20 mol% or more, more preferably 25 mol% or more, even more preferably 30 mol% or more, and preferably 55 mol% or less.

From the viewpoint of ensuring flexibility and high elongation at low temperatures, the other alcohol component (Y2) preferably contains at least 1,4-butanediol, and as described above, preferably two or more types are used. Among them, it is more preferable to contain both 1,4-butanediol and 1,6-hexanediol. By using two or more types of other alcohol component (Y2), there is an advantage that it is easier to adjust the crystallinity in combination with the acid component than before. In particular, there is a remarkable effect in combination with the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in the present invention.
The proportion of 1,4-butanediol and 1,6-hexanediol in the alcohol components in all of the polyesters (A) is preferably 15 to 60 mol %, more preferably 20 mol % or more, even more preferably 25 mol % or more, even more preferably 30 mol % or more, and more preferably 55 mol % or less.
The proportion of 1,4-butanediol and 1,6-hexanediol means the proportion of 1,4-butanediol when only 1,4-butanediol is used, means the proportion of 1,4-hexanediol when only 1,6-hexanediol is used, and means the total proportion of these when both 1,4-butanediol and 1,6-hexanediol are used.
When 1,4-butanediol and 1,6-hexanediol are contained, the ratio of the molar amount of 1,6-hexanediol to the molar amount of 1,4-butanediol is, for example, 0.5 or more, preferably 0.7 or more, more preferably 0.8 or more, even more preferably 0.9 or more, or for example, 2.5 or less, preferably 2.0 or less, more preferably 1.6 or less, even more preferably 1.4 or less.

In all polyesters (A), the proportion of ethylene glycol (Y1) in the alcohol component is, for example, 40 to 85 mol%, preferably 45 mol% or more, and more preferably 80 mol% or less, more preferably 75 mol% or less, and even more preferably 70 mol% or less.

In addition, each alcohol component of the polyester (A) contained in the copolymer polyester layer (A1) can be quantified by measuring the 1H-NMR spectrum.

Among the above, a particularly preferred embodiment is one in which the copolymer polyester (a1) is a crystalline copolymer polyester (Aa) consisting of a copolymer of terephthalic acid and an aliphatic dicarboxylic acid having 4 to 10 carbon atoms with one or both of 1,4-butanediol and 1,6-hexanediol, in which the proportion of the aliphatic dicarboxylic acid having 4 to 10 carbon atoms in the dicarboxylic acid components in all of the polyesters (A) is 3 to 50 mol %, and the total proportion of 1,4-butanediol and 1,6-hexanediol in the alcohol components is 15 to 60 mol %.
Usually, when the ratio of copolymerization components is increased in a copolymer polyester to reduce the elastic modulus, the crystallinity is reduced and the polyester becomes amorphous. The copolymer polyester (Aa) has a high ratio of copolymerization components and can achieve a low elastic modulus, but maintains its crystallinity, so that it can be heat-set by heat treatment after stretching. As a result, the copolymer polyester (Aa) is flexible, yet has good elongation and strength, and can suppress heat shrinkage.

In addition, the copolymer polyester film has good solvent resistance by containing the copolymer polyester (a1), or the copolymer polyester (a1) and the polyester (a2). Therefore, as described later, when a resin layer is formed using an organic solvent, the copolymer polyester film can be prevented from being dissolved by the solvent.

(polyester blend)
The polyester (A) contained in the copolymer polyester layer (A1) may be one kind of polyester or a blend of two or more kinds of polyesters, as described above. When the polyester (A) is made of one kind of polyester, that is, when the copolymer polyester layer (A1) contains one kind of polyester as the copolymer polyester (a1), the polyester is preferably a copolymer polyester (a1) containing, as the dicarboxylic acid component, a dicarboxylic acid having 4 to 10 carbon atoms and terephthalic acid, and, as the alcohol component, ethylene glycol, and one or both of 1,4-butanediol and 1,6-hexanediol.

On the other hand, when the polyester (A) contained in the copolymer polyester layer (A1) is composed of two or more kinds of polyesters, that is, when the copolymer polyester layer (A1) contains a polyester blend composed of two or more kinds of polyesters as the polyester (A), it is preferable that the polyester blend contains, as the dicarboxylic acid component, a dicarboxylic acid having 4 to 10 carbon atoms and terephthalic acid, and, as the diol component, ethylene glycol, and one or both of 1,4-butanediol and 1,6-hexanediol.
In this case, it is sufficient for the polyester blend to have the above-mentioned structural units. For example, when the polyester blend is a mixed resin of a first polyester and a second polyester, each of the first polyester and the second polyester does not need to have all of the above-mentioned structural units.

In the copolymer polyester layer (A1), the polyester (A) is a main component resin. The "main component resin" means a resin that is contained in the largest proportion among the resin components constituting the copolymer polyester layer (A).
The content of the polyester (A) relative to the resin components contained in the copolymer polyester layer (A1) is, for example, 50% by mass or more, preferably 60% by mass or more, and more preferably 80% by mass or more, and is not particularly limited as long as it is 100% by mass or less.
The content of the polyester (A) refers to the total amount of all polyesters contained in the copolymer polyester layer (A1).

The copolymer polyester layer (A1) may contain particles. Specific examples of particles 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, phenol resin, epoxy resin, and benzoguanamine resin. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.
The particles may be used alone or in combination of two or more kinds.
The shape of the particles to be used is not particularly limited, and any of spherical, blocky, rod-like, flat, etc. may be used. There are also no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as necessary.

The average particle size of the particles used is preferably 5 μm or less, more preferably in the range of 0.1 to 4 μm. By using particles with an average particle size in the above range, an appropriate surface roughness can be imparted to the film, and good slipperiness and smoothness can be ensured.
The average particle size of the particles can be determined by measuring the diameters of 10 or more particles selected from the copolymer polyester layer (A1) using a scanning electron microscope (SEM) and averaging the diameters. In the case of non-spherical particles, the average value of the longest and shortest diameters ((short diameter+long diameter)/2) can be measured as the diameter of each particle.
The copolymer polyester layer (A1) may contain a combination of two or more types of particles having different particle sizes.
The content of particles in the copolymer polyester layer (A1) is preferably 5% by mass or less, more preferably in the range of 0.0003 to 3% by mass, and even more preferably in the range of 0.001 to 0.2% by mass. By setting the content of particles within the above range, it becomes easy to impart slipperiness to the substrate film while ensuring the transparency of the substrate film. In addition, by keeping the content of particles low, it becomes easy to increase the tensile elongation at break.

In addition to the particles described above, the copolymer polyester layer (A1) may contain, as an additive, at least one selected from the group consisting of a crystal nucleating agent, an antioxidant, a color inhibitor, a pigment, a dye, an ultraviolet absorber, a release agent, a lubricant, a flame retardant, an antistatic agent, etc., as necessary.

(Method for producing copolymer polyester (a1))
The method for producing the copolymerized polyester (a1) is not particularly limited, and a normal method can be applied. For example, first, a dicarboxylic acid component containing terephthalic acid or an ester-forming derivative thereof, and a dicarboxylic acid other than terephthalic acid such as a dicarboxylic acid having 4 to 10 carbon atoms or an ester-forming derivative thereof, and an alcohol component containing an alcohol component other than ethylene glycol are mixed under stirring in a predetermined ratio to prepare a raw material slurry (raw material slurry preparation step). Next, the raw material slurry is heated under normal pressure or pressure to cause an esterification reaction to obtain a polyester low polymer (hereinafter sometimes referred to as "oligomer") (oligomer preparation step). Thereafter, a dicarboxylic acid other than terephthalic acid such as a dicarboxylic acid having 4 to 10 carbon atoms or an ester-forming derivative thereof and the alcohol component are added to the obtained oligomer, and the mixture is gradually reduced in pressure and heated in the presence of an ester exchange catalyst or the like to cause a melt polycondensation reaction to obtain a polyester (polyester preparation step). The obtained polyester may be further subjected to a solid-phase polycondensation reaction as necessary (solid-phase polycondensation step).

However, the method for producing polyester (a1) is not limited to the above method, and dicarboxylic acids other than terephthalic acid, such as dicarboxylic acids having 4 to 10 carbon atoms, or ester-forming derivatives thereof do not need to be added to both the raw material slurry and the oligomer, and may be added only to the raw material slurry or only to the oligomer. Furthermore, terephthalic acid or an ester-forming derivative thereof may be added only to the raw material slurry, or may be added to the oligomer.
Similarly, the alcohol component may be added to both the raw material slurry and the oligomer, or may be added only to the raw material slurry.

Examples of the transesterification catalyst include antimony compounds such as diantimony trioxide; germanium compounds such as germanium dioxide and germanium tetroxide; titanium compounds such as titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate and tetrabutyl titanate, and titanium phenolates such as tetraphenyl titanate; dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, cyclohexahexylditin oxide, didodecyltin oxide, triethyltin hydroxide, triphenyltin hydroxide, triisobutyltin hydroxide, Examples of the suitable tin compounds include tin acetate, dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, tributyltin chloride, dibutyltin sulfide, butylhydroxytin oxide, methylstannoic acid, ethylstannoic acid, and butylstannoic acid; magnesium compounds such as magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, and magnesium hydrogen phosphate; and calcium compounds such as calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide, and calcium hydrogen phosphate.
These catalysts may be used alone or in combination of two or more.

In addition, during the production of polyester, it is preferable to use a stabilizer together with the transesterification catalyst. Examples of the stabilizer include orthophosphoric acid, polyphosphoric acid, pentavalent phosphorus compounds such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, tris(triethylene glycol) phosphate, ethyl diethyl phosphonoacetate, methyl acid phosphate, ethyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, monobutyl phosphate, dibutyl phosphate, dioctyl phosphate, and triethylene glycol acid phosphate, phosphorous acid, hypophosphorous acid, and trivalent phosphorus compounds such as diethyl phosphite, trisdodecyl phosphite, trisnonyldecyl phosphite, and triphenyl phosphite.
Among them, trivalent phosphorus compounds are generally more reducing than pentavalent phosphorus compounds, and there is a risk that the metal compound added as a polycondensation catalyst will be reduced and precipitated, which may cause the generation of foreign matter, and therefore pentavalent phosphorus compounds are preferred.

The reaction pressure in the melt polycondensation reaction is preferably 0.001 kPa to 1.33 kPa in terms of absolute pressure. The reaction temperature in the melt polycondensation reaction is preferably 220° C. to 280° C., and more preferably 230° C. or higher and 260° C. or lower.
The solid-phase polycondensation reaction may be carried out under reduced pressure or in an inert gas atmosphere, and the reaction temperature is preferably 180° C. to 220° C. The reaction time of the solid-phase polycondensation reaction is preferably 5 hours to 100 hours. By adopting the above melt polycondensation reaction conditions and solid-phase polycondensation reaction conditions, a polyester having a desired intrinsic viscosity can be obtained.

<In the case of a multi-layer structure>
As described above, the present copolymer polyester film may have a multilayer structure comprising the copolymer polyester layer (A1) and other layers.

In the case where the copolymer polyester film has a multilayer structure, it may have, for example, a copolymer polyester layer (A1) and a polyester layer (B1) and a polyester layer (B2) laminated on both sides of the copolymer polyester layer (A1). Each of the polyester layer (B1) and the polyester layer (B2) contains a polyester (B) as a main component resin.
Here, the term "main component resin" refers to the resin that is contained in the largest proportion of the resin components constituting each of the copolymer polyester layers (B1) and (B2). The main component resin may account for 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and may, for example, account for 100% by mass or less of the resin components constituting each of the polyester layers (B1) and (B2).

The polyester (B) contained in each of the polyester layers (B1) and (B2) is preferably a polyester having a melting point higher than that of the copolymer polyester (a1) when the copolymer polyester (a1) is crystalline, and the polyester (B) is preferably a polyester having a melting point higher than the glass transition point of the copolymer polyester (a1) when the copolymer polyester (a1) is amorphous.
In the case of a multilayer structure having a configuration in which polyester layers (B1) and (B2) containing polyester (B) as a main component resin are laminated, the raw material resin composition can be laminated by coextrusion or the like so as to have a polyester layer (B1)/copolymer polyester layer (A1)/polyester layer (B2), stretched, and then heat-set at a higher temperature than in the case of a single layer of copolymer polyester layer (A1). Therefore, it is possible to soften the film to a level that cannot be achieved with a single layer of copolymer polyester layer (A1), and to further prevent heat shrinkage.
Specifically, the storage modulus of the present copolymer polyester film at 25° C. can be set to 300 to 2500 MPa, preferably 500 MPa or more or 2000 MPa or less, and more preferably 800 MPa or more or 1500 MPa or less.

In the above multi-layer structure, the thickness of each of the polyester layers (B1) and (B2) is preferably 1 to 20% of the thickness of the copolymer polyester layer (A1).
When the thickness of each of the polyester layers (B1) and (B2) is 1% or more of the thickness of the copolymerized polyester layer (A1), film formation is possible without significantly impairing productivity, and when the thickness is 20% or less, the required flexibility can be sufficiently ensured, which is preferable.
From such a viewpoint, the thickness of each of the polyester layers (B1) and (B2) is preferably 3% or more and 15% or less of the thickness of the copolymer polyester layer (A1), and more preferably 5% or more and 12% or less.
The thickness of each of the polyester layers (B1) and (B2) present on both sides of the copolymer polyester layer (A1) may be different on the front and back sides or may be the same on the front and back sides.

When the copolymer polyester (a1) is crystalline, the polyester (B) is a polyester having a melting point that is preferably 10 to 100° C. higher than the melting point of the copolymer polyester (a1), more preferably 20° C. or higher, even more preferably 40° C. or higher, and more preferably 90° C. or lower, even more preferably 70° C. or lower.
On the other hand, when the copolymer polyester (a1) is amorphous, the polyester (B) is a polyester having a melting point that is preferably 120 to 260° C. higher than the glass transition point of the copolymer polyester (a1), more preferably 140° C. or higher, even more preferably 160° C. or higher, and more preferably 230° C. or lower, and even more preferably 200° C. or lower.
The polyester (B), which is the main component of each of the polyester layers (B1) and (B2) present on both the front and back sides of the copolymer polyester layer (A1), may be different or the same on the front and back sides. However, it is preferable that the melting points of the polyesters (B) on the front and back sides do not differ significantly.

As the polyester (B), for example, a homopolyester or copolymer polyester containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as an alcohol component can be suitably used. However, this is not limited thereto. The homopolyester is polyethylene terephthalate.

When the polyester (B) is a copolymer polyester, examples of the dicarboxylic acid component other than terephthalic acid include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, polyfunctional acids, etc. Examples of these dicarboxylic acid components include the same ones as those listed in the copolymer polyester (a1).
When the polyester (B) is a copolymer polyester, the ratio of dicarboxylic acid components other than terephthalic acid in the dicarboxylic acid components is preferably 1 to 30 mol %, more preferably 5 mol % or more, and among these, more preferably 10 mol % or more, and more preferably 25 mol % or less, and even more preferably 20 mol % or less.

When the polyester (B) is a copolymer polyester, examples of the alcohol component other than ethylene glycol include 1,4-butanediol, 1,6-hexanediol, ethylene glycol, diethylene glycol, trimethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, bisphenol, and derivatives thereof.
In the polyester (B), the proportion of alcohol components other than ethylene glycol in the alcohol components is preferably 1 mol % or more and less than 100 mol %, more preferably 5 mol % or more, even more preferably 10 mol % or more, and more preferably 95 mol % or less, even more preferably 90 mol % or less.

<Thickness of the Copolymer Polyester Film>
The thickness of the present copolymer polyester film is not particularly limited, and an appropriate thickness can be selected depending on the application.
In particular, from the viewpoint of fully exhibiting the characteristics of the present copolymerized polyester film, it is preferable that the total thickness of the film exceeds 5 μm.
The stiffness of a film is said to be proportional to the cube of its thickness. However, the present copolymer polyester film has the characteristic of being weak and flexible even when it has a thickness of more than 5 μm, and can further enjoy the benefits of the present invention.
From this viewpoint, the total thickness of the present copolymerized polyester film is preferably more than 5 μm, more preferably 12 μm or more, and even more preferably 30 μm or more.
The total thickness of the present copolymer polyester film is not particularly limited, but is, for example, 200 μm or less, preferably 150 μm or less, and more preferably 100 μm or less.

(Difference between Tcc and Tg (ΔTcg))
The copolymer polyester film of the present invention has a difference (ΔTcg) between the cold crystallization temperature (Tcc) and the glass transition temperature (Tg) exceeding 60° C. If the difference (ΔTcg) between Tcc and Tg is 60° C. or less, the heat resistance decreases, making it difficult to achieve both of the contradictory properties of excellent flexibility and high elongation at room temperature, on the one hand, and good heat resistance on the other.
From the viewpoint of improving heat resistance, the difference between Tcc and Tg (ΔTcg) is preferably 63° C. or more, and even more preferably 70° C. or more. The difference between Tcc and Tg (ΔTcg) is not particularly limited, but may be, for example, 150° C. or less, or may be 100° C. or less.
The cold crystallization temperature (Tcc) is higher than the glass transition temperature (Tg), and the difference between Tcc and Tg (ΔTcg) is defined as "Tcc-Tg".
The difference between Tcc and Tg can be adjusted by the type and amount of the dicarboxylic acid component (X2), the type and amount of the other alcohol component (Y2), the presence or absence of stretching, the stretching ratio, the stretching temperature, and the amount of the copolymerized polyester (a1).

The copolymer polyester film has a cold crystallization temperature (Tcc) of, but not limited to, 90 to 150°C, for example, and preferably 105 to 135°C. The copolymer polyester film has a glass transition temperature (Tg) of, but not limited to, 10 to 60°C, for example, and preferably 25 to 45°C.

(Tensile elongation at break)
The present copolymer polyester film preferably has a tensile elongation at break of 295% or more at 25° C. When the tensile elongation at break of 295% or more at 25° C. is 295% or more, the film tends to have a high elongation at room temperature, and the stretching process described below can be appropriately performed. In addition, the flexibility of the copolymer polyester film can be ensured.
In order to ensure excellent elongation while maintaining flexibility at room temperature, the tensile elongation at break of the present copolymer polyester film at 25° C. is more preferably 300% or more, and even more preferably 320% or more.
The tensile elongation at break is not particularly limited, but is, for example, 600% or less, preferably 500% or less, in order to easily impart a certain level of mechanical strength to the present copolymer polyester film.

(Tensile Breaking Strength)
The present copolymer polyester film preferably has a tensile breaking strength of 30 MPa or more at 25° C. By setting the tensile breaking strength to 30 MPa or more, it becomes easier to impart a certain level of mechanical strength to the present copolymer polyester film. From this viewpoint, the tensile breaking strength at 25° C. is more preferably 40 MPa or more, and further preferably 50 MPa or more.
The tensile breaking strength at 25° C. is, for example, 300 MPa or less, preferably 200 MPa or less, more preferably 150 MPa or less, and even more preferably 100 MPa or less, from the viewpoint of easily increasing the above-mentioned tensile breaking elongation.

In the present copolymer polyester film, the tensile elongation at break and the tensile strength at break can be adjusted to the above range by adjusting the type and content of the copolymer component of the copolymer polyester (a1). They can also be adjusted by the presence or absence of stretching, the stretching ratio, etc. They can also be adjusted by the stretching temperature.

When the MD and TD of the above-mentioned copolymer polyester film are known, the tensile breaking elongation is measured in these directions and the higher value is used. On the other hand, when the MD and TD are unknown, the tensile breaking elongation in the direction with the highest tensile breaking elongation is used. The tensile breaking strength is the value obtained by measuring in the direction in which the tensile breaking elongation is used.

(Storage modulus at 25° C.)
The polyester film preferably has a storage modulus of 2500 MPa or less at 25° C. By having a storage modulus of 2500 MPa or less at 25° C., i.e., at room temperature, the film can have sufficient flexibility and good curved surface conformability, and can sufficiently conform to the skin when a wearable device is worn, for example.
From this viewpoint, the storage modulus of the present polyester film at 25° C. is more preferably 2000 MPa or less, even more preferably 1800 MPa or less, and even more preferably 1600 MPa or less.

On the other hand, the storage modulus at 25° C. is preferably 500 MPa or more, more preferably 800 MPa or more, and even more preferably 1000 MPa or more, from the viewpoint of handling properties in each step.
The storage modulus at 25° C. and at 120° C., which will be described later, is a value obtained by the measurement method described in the examples, which will be described later.

In the present copolymerized polyester film, the storage modulus at 25°C can be adjusted to the above range by adjusting the type and content of the copolymerization component of the copolymerized polyester (a1). From this viewpoint, the copolymerization component of the copolymerized polyester (a1) preferably contains an aliphatic dicarboxylic acid having 4 to 10 carbon atoms and one or both of 1,4-butanediol and 1,6-hexanediol, and the proportions of these in the dicarboxylic acid component and the alcohol component in the polyester (A) are preferably 3 to 50 mol% and 15 to 60 mol%, respectively, as described above. More preferably, the aliphatic dicarboxylic acid having 4 to 10 carbon atoms is adipic acid.
Among these, the other alcohol component (Y2) is preferably 1,4-butanediol and 1,6-hexanediol, and in this case, the total amount (mol %) of the other alcohol component (Y2) is preferably 15 to 60 mol %.

In addition, the storage modulus at 25°C can also be easily adjusted to fall within the above range by laminating polyester layers (B1) and (B2) containing the polyester (B) as a main component resin on both sides of the copolymer polyester layer (A1) to form a multilayer structure.
Furthermore, the storage modulus at 25° C. can also be adjusted by the stretching conditions during production of the present copolymerized polyester film and the conditions for the subsequent heat setting.

(Storage modulus at 120° C.)
The present copolymer polyester film has a storage modulus at 120° C. of, for example, 10 MPa or more, preferably 20 MPa or more, more preferably 25 MPa or more, and even more preferably 30 MPa or more.
The storage modulus of 10 MPa or more, particularly 20 MPa or more at 120° C., i.e., near the processing temperature, is preferable in that the heat resistance is good. In addition, the good heat resistance makes it easier to suppress heat shrinkage and the like.
The storage modulus at 120° C. is not particularly limited, but from the viewpoint of flexibility, it is, for example, 400 MPa or less, preferably 200 MPa or less, and more preferably 150 MPa or less.

(Crystal melting enthalpy ΔHm)
In the present copolymer polyester film, when the polyester contained in the copolymer polyester layer (A1) is crystalline, the crystalline melting enthalpy ΔHm of the polyester (when there are two or more types of polyester, the polyester composition consisting of the two or more types of polyester) is preferably 15.0 J/g or more, more preferably 20.0 J/g or more, and even more preferably 25.0 J/g or more.
ΔHm is an index of the degree of crystallinity, and when it is 15.0 J/g or more, sufficient heat resistance is obtained, and the heat shrinkage of the copolymer polyester film can be suppressed in processing steps including a heat treatment step.
The crystalline melting enthalpy ΔHm is not particularly limited, but from the viewpoint of flexibility and the like, it is, for example, 50 J/g or less, preferably 40 J/g or less, and more preferably 32 J/g or less.

(Young's modulus)
The Young's modulus of the present copolymer polyester film is preferably 5.0 GPa or less, more preferably 4.0 GPa or less, and even more preferably 3.5 GPa or less. By making the Young's modulus equal to or less than the upper limit, appropriate flexibility can be ensured. The Young's modulus is not particularly limited, but is preferably 0.5 GPa or more, more preferably 0.8 GPa or more, from the viewpoint of ensuring a certain mechanical strength.
When the MD and TD of the present copolymerized polyester film are known, the Young's modulus in these directions is measured and the higher value is used, whereas when the MD and TD are unknown, the Young's modulus in the direction in which the Young's modulus is the highest is used.

<Method of producing the present copolymer polyester film>
As an example of the method for producing the present copolymer polyester film, a method for producing the present copolymer polyester film as a biaxially stretched film will be described below, although the present copolymer polyester film is not limited to the method described here.

First, using a known method, raw materials, such as polyester chips, are fed into a melt extrusion device and heated above the melting point of each polymer. The molten polymer is extruded through a die and cooled to a temperature below the glass transition point of the polymer on a rotating cooling drum to solidify the polymer, thereby obtaining an unoriented sheet in a substantially amorphous state.

Next, the unoriented sheet is stretched in one direction by a roll or tenter type stretching machine, at a stretching temperature of usually 25 to 120° C., preferably 35 to 100° C., and at a stretching ratio of usually 2.5 to 7 times, preferably 2.8 to 6 times.
Then, the film is stretched in a direction perpendicular to the first stretching direction at a temperature of usually 50 to 140° C. and a stretch ratio of usually 3.0 to 7 times, preferably 3.5 to 6 times.
In the above stretching, a method in which the stretching in one direction is carried out in two or more stages can also be adopted.

After the stretching, the film is subsequently heat-set under tension or relaxation of 30% or less at a temperature of 130 to 270° C. to obtain the present copolymerized polyester film as a biaxially oriented film. By subjecting the present copolymerized polyester film to heat-setting, the flexibility, heat resistance, etc. can be improved.
The heat setting treatment (also referred to as "heat treatment") is preferably carried out at a temperature 5 to 70°C lower than the melting point of the polyester for forming the copolymer polyester layer (A1) in the case of a single layer of the copolymer polyester layer (A1). In the case of a multi-layer structure, the heat setting treatment is preferably carried out at a temperature 5 to 70°C lower than the melting point of the polyester for forming the copolymer polyester layer (A1), and is also preferably carried out at a temperature 5 to 70°C lower than the melting point of the polyester for forming the polyester layer (B).

When the copolymer polyester film has a laminated structure of polyester layer (A1) and polyester layers (B1) and (B2), the polyester layer (A1) and the polyester layers (B1) and (B2) are co-extruded, and then the resulting integrated film is stretched and heat-set as described above.

<Laminated film>
The laminated film according to one embodiment of the present invention has the above-mentioned copolymerized polyester film and a functional layer provided on at least one surface of the copolymerized polyester film. The functional layer is not particularly limited, but may be a resin layer. It is preferable that the functional layer such as the resin layer is stretched together with the copolymerized polyester film in a state where it is laminated on the above-mentioned copolymerized polyester film. As a result, the functional layer becomes thinner and is formed into a functional sheet.
The copolymer polyester film is flexible and has a high elongation rate at room temperature, so it can be easily stretched and is suitable for forming into functional sheets by stretching. In addition, because it has good heat resistance, there is little thermal shrinkage even when the laminated film is heat-treated.

(Resin Layer)
The resin layer is a layer laminated on the copolymer polyester film. The type of the resin layer is not particularly limited, but a resin having stretchability can be suitably used. The resin layer is preferably one having an elongation rate of 295% or more. The resin layer having an elongation rate of 295% or more means that the resin layer will not break even if it is stretched at an elongation rate of 295%. In other words, the resin layer will not break even if it is stretched at least 295% (i.e., at least 3.0 times the stretch ratio) together with the copolymer polyester film in a state where it is laminated on the copolymer polyester film. The elongation rate of the resin layer is more preferably 300% or more, even more preferably 350% or more, and particularly preferably 400% or more. The elongation rate of the resin layer is not particularly limited, but is, for example, 800% or less, preferably 600% or less.
By satisfying the above range, it becomes possible to stably mold a thin resin sheet from a relatively thick state by performing stretch processing.

The resin layer may contain ceramic particles in addition to the resin. By using the ceramic particles, for example, the resin layer after stretching can be used as a green sheet. As the ceramic particles, known ceramic particles used for green sheets can be used. Specifically, barium titanate, Pb(Mg1 _/3 , Nb2 _/3 ) _O3 , Pb(Sm1 _/2 , Nb1 _/2 ) _O3 , Pb(Zn1 _/3 , Nb2 _/3 ) _O3 , _PbThO3 , _PbZrO3 , etc. can be mentioned, but the ceramic particles are not limited to these, and any ceramic particles that can obtain the dielectric properties required for a ceramic multilayer capacitor can be used.
When the resin layer contains ceramic particles, examples of the resin to be used include polyurethane resins, urea resins, melamine resins, aqueous polymer-isocyanate resins, epoxy resins, vinyl acetate resins, acrylic resins, etc. Also, resins containing vinyl alcohol structural units, which will be described later, may be used.
When ceramic particles are contained, the ceramic particles are preferably the main component of the resin layer (for example, 50 mass % or more of the resin layer), and the mass ratio of the ceramic particles to the resin (ceramic particles)/(resin) is preferably in the range of 70/30 to 95/5.
In addition to the resin and ceramic particles, the resin layer may contain additives such as a dispersant, a plasticizer, an antistatic agent, and an antifoaming agent.

When the resin layer contains ceramic particles in addition to the above resin, it can be formed by applying a slurry containing ceramic particles and resin, in which the ceramic particles are dispersed in any solvent such as water or an organic solvent, to a copolymer polyester film, and then heating and drying the slurry.

In addition, the resin layer preferably contains a resin as a main component. Here, "containing a resin as a main component" means that the content of the resin is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the resin layer.
When a resin is contained as a main component resin, it is preferable to use a resin containing a vinyl alcohol structural unit, which will be described later, and among these, a vinyl alcohol-based polymer is preferable.
When the resin layer contains a resin as a main component, the resin composition containing a resin as a main component can be formed by diluting the resin composition with an organic solvent, water, etc., as necessary, and then applying the diluted resin composition to the present copolymer polyester film, and then heating, drying, etc., as necessary. The resin composition may contain additives such as a crosslinking agent in addition to the resin.

(Resin containing vinyl alcohol structural unit)
In the present invention, the resin used in the resin layer is preferably a resin containing a vinyl alcohol structural unit. The vinyl alcohol structural unit is a structural unit consisting of —(CH ₂ CHOH)—. Specific examples include vinyl acetal polymers such as vinyl butyral polymers, vinyl alcohol polymers, and the like.
The vinyl alcohol polymer is obtained by polymerizing a vinyl ester monomer or by copolymerizing a vinyl ester monomer with a monomer having an ethylenic double bond other than the vinyl ester monomer, and then saponifying the polymer.
The vinyl alcohol polymer may be unmodified vinyl alcohol, but may be a modified vinyl alcohol polymer by using a copolymer with a monomer having an ethylenic double bond as described above. The vinyl acetal polymer may be introduced with a functional group by a post-reaction. The modified vinyl alcohol polymer is preferably an acetoacetyl group modified vinyl alcohol polymer.

The vinyl acetal polymer is obtained by acetalizing the vinyl alcohol polymer. The vinyl acetal polymer has a hydroxyl group that is not acetalized, and thus has a vinyl alcohol structural unit. In the case of the vinyl acetal polymer, the monomer having an ethylenic double bond preferably contains a polyfunctional monomer having two or more ethylenic double bonds (hereinafter, sometimes simply referred to as a polyfunctional monomer).
In order to obtain a vinyl acetal polymer by acetalizing a vinyl alcohol copolymer, it is preferable that the vinyl alcohol copolymer is water-soluble. Therefore, the vinyl acetal polymer can be obtained, for example, by acetalizing a vinyl alcohol copolymer that contains an ethylenic double bond in its side chain but is water-soluble. Here, the ethylenic double bond in the side chain refers to an unreacted ethylenic double bond in the multifunctional monomer copolymerized in the vinyl alcohol polymer.

When the resin layer contains ceramic particles as a main component, the resin containing the vinyl alcohol structural unit is preferably a vinyl acetal polymer, and more preferably a vinyl acetal polymer containing an ethylenic double bond in the side chain. By using a vinyl acetal polymer containing an ethylenic double bond in the side chain, the dispersibility of the ceramic particles in the slurry is excellent, and the storage stability of the slurry is also good.
In addition, when the resin layer is mainly composed of a resin, it is preferable to use a vinyl alcohol-based polymer as the resin containing a vinyl alcohol structural unit. By using a vinyl alcohol-based polymer, the resin sheet obtained after stretching can be suitably used as an optical member such as a polarizer.

Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate, and vinyl benzoate. Of these, vinyl acetate is preferred from the viewpoint of ease of production.

Examples of polyfunctional monomers include monomers containing a vinyl ether group, such as 1,4-butanediol divinyl ether and triethylene glycol divinyl ether; monomers containing an allyl group, such as 1,9-decadiene, polyethylene glycol diallyl ether and pentaerythritol diallyl ether; and monomers having multiple (meth)acrylates in one molecule, such as ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, glycerin tri(meth)acrylate and pentaerythritol tri(meth)acrylate.

The saponification degree of the vinyl alcohol copolymer is preferably 60 to 99.9 mol%. If the saponification degree is 60 mol% or more, the water solubility of the vinyl alcohol copolymer will be good. From this viewpoint, it is more preferable that the saponification degree is 65 mol% or more. On the other hand, if the saponification degree is 99.9 mol% or less, industrial production will be easy, and the viscosity stability of the vinyl alcohol copolymer aqueous solution will be good, making it easy to handle. From this viewpoint, it is more preferable that the saponification degree is 99.5 mol% or less.

The viscosity average degree of polymerization Pη of the vinyl alcohol-based copolymer is preferably 100 to 8000. By making the viscosity average degree of polymerization Pη 100 or more, the industrial production of the vinyl alcohol-based copolymer becomes easy. From this viewpoint, it is more preferable that the viscosity average degree of polymerization Pη is 200 or more. On the other hand, by making the viscosity average degree of polymerization Pη 8000 or less, the industrial production of the vinyl alcohol-based copolymer becomes easy. In addition, the viscosity of the aqueous solution of the vinyl alcohol-based copolymer is prevented from becoming too high, and the handling thereof becomes easy. From these viewpoints, it is more preferable that the viscosity average degree of polymerization Pη of the vinyl alcohol-based copolymer is 5000 or less, and even more preferable that it is 2500 or less.

The viscosity average degree of polymerization Pη can be measured according to JIS K6726. Specifically, the vinyl alcohol copolymer is resaponified to completely saponify the remaining carboxylic acid residues. The resaponified vinyl alcohol copolymer is purified and dried, and then 1 g of the dried sample is added to 100 ml of water, heated and dissolved, and cooled to 30°C. The resulting aqueous solution is weighed into a viscometer, and the intrinsic viscosity [η] (unit: L/g) in water at 30°C is measured, and the measured intrinsic viscosity [η] can be calculated using the following formula (1).

(Adhesive layer)
The functional layer may be an adhesive layer. When the functional layer is an adhesive layer, the laminated film becomes an adhesive tape. The adhesive layer is a layer having pressure-sensitive adhesive properties, and is formed of a known adhesive. The adhesive is not particularly limited as long as it is a material that can follow the present copolymerized polyester film even when it is stretched to the tensile breaking elongation, and conventionally known materials such as acrylic, silicone, urethane, and polyester can be used.

The adhesive layer may contain a conductive material therein. By containing the conductive material, the adhesive layer becomes a conductive adhesive layer (conductive layer) having conductivity. The conductive adhesive layer is preferably formed from an adhesive containing a conductive material.
Examples of the conductive material include conductive particles such as metal powder particles of gold, silver, copper, nickel, aluminum, etc., conductive carbon particles such as carbon black, graphite, etc., and particles having a metal coating on the surface of a core material such as resin, solid glass beads, hollow glass beads, etc. As the conductive material, conductive polymers can be used in addition to conductive particles.
A conductive polymer may be used as the conductive material. The conductive polymer is not particularly limited as long as it is an organic polymer whose main chain is composed of a π-conjugated system, and examples of the conductive polymer include polythiophenes, polypyrroles, polyacetylenes, polyphenylenes, polyphenylenevinylenes, polyanilines, polyacenes, polythiophenevinylenes, and copolymers thereof.
The conductive materials may be used alone or in combination of two or more.
Among the above-mentioned conductive materials, at least one selected from carbon black and polythiophenes is preferable.
Polythiophenes are polymers of unsubstituted or substituted thiophene, and a specific example of a substituted thiophene polymer is poly(3,4-ethylenedioxythiophene).
Furthermore, the conductive layer is not limited to a conductive adhesive layer, but may be a resin layer containing a conductive material.

<Applications of this copolymer polyester film>
As described above, the present copolymer polyester film has excellent flexibility at room temperature, and is not only flexible but also has a large elongation rate, and yet can exhibit sufficient heat resistance for practical use.
The copolymer polyester film has the above-mentioned properties and is therefore suitable for various stretch processing applications, and is particularly suitable for stretch molding applications in which various molded products are obtained by stretch processing.

In addition, the present copolymerized polyester film and laminate film are suitable for use in, for example, packaging materials for batteries, surface protection films, dicing tapes, adhesive tapes, image display components such as flexible displays, wearable terminals, substrates for bioelectrodes, substrates for biosensors, and other bio-related components, for the manufacture of electronic components, for example, for molding green sheets used in the manufacture of ceramic laminate components, and for the manufacture of optical components, for example, for the manufacture of polarizers that constitute polarizing plates.
Among these, it is more suitable for use in any of adhesive tapes, surface protection films, semiconductor dicing tapes, wearable terminals, bioelectrode substrates, biosensor substrates, electronic component manufacturing, and optical component manufacturing. In particular, in wearable terminals, bioelectrode substrates, and biosensor substrates, it is preferable to provide a conductive layer containing the conductive material on the copolymer polyester film of the present invention.

First, the use of the present copolymer polyester film for stretch processing will be described in more detail below.
The stretching process is not limited as long as it includes a step of stretching the copolymer polyester film (stretching process), but preferably includes a step of stretching the laminated film described above. By stretching the laminated film, the functional layer laminated on the copolymer polyester film is also stretched, so that the functional layer can also be stretched. As a result, the functional layer is formed into a functional sheet, for example by reducing the thickness. The functional sheet may be peeled off from the copolymer polyester film as needed.

In the above stretching step, the film may be stretched in a uniaxial or biaxial direction. The stretching ratio is preferably 2.0 to 6.0 times, and more preferably 3.0 to 5.5 times. By setting the stretching ratio within the above range, the thickness can be made sufficiently thin without causing defects or tears in the functional layer or copolymer polyester film, and appropriate stretching processing can be performed. Note that the stretching ratio means the stretching ratio per axis when stretching in a biaxial direction.

The stretching may be performed in a dry or wet manner. The dry stretching is performed in air at a temperature of, for example, 25 to 70° C., preferably 30 to 60° C.
The wet method is a method of stretching a copolymer polyester film or a laminated film immersed in a liquid such as water, and the liquid temperature is, for example, 25 to 70° C., preferably 30 to 60° C. The copolymer polyester film has a high elongation even at around room temperature, and can be appropriately stretched.

As described above, when the functional layer is formed into a functional sheet by stretching, the functional layer may be a resin layer and may be formed into various resin sheets by stretching. For example, when the resin layer contains resin and ceramic particles, the functional sheet (resin sheet) may be used as a green sheet. A ceramic multilayer capacitor can be obtained by laminating a plurality of green sheets.
Furthermore, when the resin layer contains a resin as a main component, the functional sheet may be used as an optical component, etc., and when the resin layer contains, for example, a vinyl alcohol-based polymer as a main component, the functional sheet may be used as a polarizer.

As described above, when the copolymer polyester film is stretched, it can be suitably used for the manufacture of electronic components, particularly for forming green sheets used in the manufacture of ceramic laminate components, and can also be suitably used for the manufacture of optical components, such as the manufacture of polarizers that make up polarizing plates.

In addition, when the functional layer is an adhesive layer, the laminated film may be used as an adhesive tape. The adhesive tape may be used for household adhesive tapes, industrial adhesive tapes, packaging adhesive tapes, adhesive tapes for electronic components, etc., but is preferably used for surface protection films, semiconductor dicing tapes, etc. The surface protection film is attached to an adherend such as an electronic component, an optical member, a semiconductor wafer, etc., and is used to protect the adherend.
The semiconductor dicing tape is attached to the back surface of the semiconductor wafer to support the semiconductor wafer during dicing. After dicing, the dicing tape is stretched so that the individual semiconductor chips are separated from each other and then picked up.
The copolymer polyester film has excellent flexibility at low temperatures and a large elongation rate, so that the adhesive tape can be attached to the adherend even if the adherend has a curved or uneven surface. Furthermore, when the adhesive tape is used as a dicing tape, it can be easily stretched when picking up semiconductor chips. In addition, since the film has high heat resistance and is not easily heat-shrinkable, the reliability of the adhesive tape is improved, and when the adhesive tape is used as a surface protection film, for example, the protective performance is good.

The copolymer polyester film may be used for a bioelectrode substrate, a biosensor substrate, or for a bio-related member such as a substrate for a wearable terminal. The copolymer polyester film has flexibility and a high elongation rate at low temperatures, and therefore can easily conform to the skin surface, making it suitable for use in a bio-related member.
The bioelectrode substrate or biosensor substrate is a substrate that supports an electrode or various sensors, and specifically, an electrode or a sensor element is provided on one surface of a substrate made of the present copolymer polyester film. The electrode may be composed of a conductive adhesive layer, and therefore an adhesive tape may be used.

Furthermore, the copolymer polyester film or laminate film may be used as a battery packaging material, such as the exterior material of a lithium-ion battery, or as an image display member such as a flexible display. Battery packaging materials and image display members are sometimes bent when used, but the present copolymer polyester film is flexible and has a high elongation rate at low temperatures, so it can be bent to conform to the shape of the battery or display when used. In these applications, the copolymer polyester film may be exposed to high temperatures, but because it has excellent heat resistance, it is possible to prevent thermal shrinkage.

<Explanation of terms, etc.>
In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film".
Furthermore, when the term "panel" is used, such as an image display panel or a protective panel, it encompasses a plate, a sheet, and a film.

In the present invention, when it is written "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as "preferably larger than X" or "preferably smaller than Y".

In addition, when it is stated that something is "X or more" (X is any number), it also means that it is "preferably greater than X" unless otherwise specified, and when it is stated that something is "Y or less" (Y is any number), it also means that it is "preferably smaller than Y" unless otherwise specified.

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

<Evaluation method>
In the following, the measurements and evaluations of various physical properties were carried out as follows.

(1) Tensile storage modulus E'
In accordance with JIS K 7244, a dynamic viscoelasticity measuring device DVA-200 manufactured by IT Measurement & Control Co., Ltd. was used to measure the width direction (TD) of the polyester films (samples) obtained in the Examples and Comparative Examples from -100°C to 200°C at a vibration frequency of 10 Hz, a strain of 0.1%, and a heating rate of 1°C/min. From the obtained data, the tensile storage moduli E' at 25°C and 120°C were obtained, which were defined as the storage moduli at 25°C and 120°C.

(2) Crystal melting enthalpy ΔHm
Based on JIS K7141-2 (2006), the measurement sample was subjected to differential scanning calorimetry (DSC) measurement. The temperature was raised from 30°C to 280°C at 10°C/min, held for 1 minute, then lowered from 280°C to 30°C at 10°C/min, held for 1 minute, and then reheated from 30°C to 280°C at 10°C/min. The crystal melting enthalpy (ΔHm) was calculated from the crystal melting peak area during the reheating process.
In the case of a single layer, the polyester film is used as the measurement sample, and in the case of a laminate structure, the copolymer polyester layer (A1) is used as the measurement sample.

(3) Young's modulus For the polyester films (samples) obtained in the Examples and Comparative Examples, a tensile tester (Intesco Model 2001, manufactured by Intesco Corporation) was used to tensile a polyester film (sample) having a length of 300 mm and a width of 20 mm at a strain rate of 10%/min in a room adjusted to a temperature of 23° C. and a humidity of 50% RH. Using the initial linear portion of the tensile stress-strain curve, the Young's modulus was calculated in each of the machine direction (MD) and the width direction (TD) of the film according to the following equation.
E = Δσ / Δε
(In the above formula, E is Young's modulus (GPa), Δσ is the stress difference (GPa) due to the original average cross-sectional area between two points of the line, and Δε is the strain difference between the same two points/initial length.)
Measurements were taken at five points each in the machine direction (MD) and the width direction (TD) of the film, and an average value was calculated for each.

(4) Tensile Breaking Strength For the polyester films (samples) obtained in the Examples and Comparative Examples, a tensile tester (Intesco Model 2001, manufactured by Intesco Corporation) was used to test a 15 mm wide polyester film (sample) in a room controlled at a temperature of 25° C. and a humidity of 50% RH, with the film set to a chuck distance of 50 mm and pulled at a strain rate of 200 mm/min. The tensile breaking strength in each of the longitudinal direction (MD) and transverse direction (TD) of the film was calculated according to the following formula:
Tensile breaking strength (MPa) = F/A
In the above formula, F is the load (N) at break, and A is the original cross-sectional area (mm ² ) of the test piece.
Measurements were taken at five points each in the machine direction (MD) and the width direction (TD) of the film, and an average value was calculated for each.

(5) Tensile Breaking Elongation The polyester films (samples) obtained in the Examples and Comparative Examples were subjected to the same test as for the tensile breaking strength described above, and the tensile breaking elongation in each of the machine direction (MD) and the width direction (TD) of the film was calculated according to the following formula.
Tensile elongation at break (%) = 100 × (L - L0) / L0
In the above formula, L is the gauge length (mm) at break, and L0 is the original gauge length (mm).
Measurements were taken at five points each in the machine direction (MD) and the width direction (TD) of the film, and an average value was calculated for each.

(6) Heat Shrinkage Rate The polyester films (samples) obtained in the Examples and Comparative Examples were treated in an oven maintained at 120° C. in an untensioned state for 5 minutes, and the lengths of the samples before and after treatment were measured to calculate the heat shrinkage rates of the film in both the machine direction (MD) and the width direction (TD) according to the following formula.
Heat shrinkage rate (%) = {(L0 - L1) / L0} x 100
(In the above formula, L0 is the sample length before heat treatment, and L1 is the sample length after heat treatment)
Measurements were taken at five points each in the machine direction (MD) and the width direction (TD) of the film, and an average value was calculated for each.

(7) Difference between cold crystallization temperature (Tcc) and glass transition temperature (Tg) (ΔTcg)
Using a differential scanning calorimeter (PerkinElmer DSC8500), the specific heat change due to the transition from the glass state to the rubber state was read under the condition of a temperature rise rate of 10°C/min, and Tg (glass transition temperature) was obtained. The exothermic peak temperature associated with crystallization was taken as the cold crystallization temperature (Tcc). The difference (ΔTcg (°C)) between the cold crystallization temperature (Tcc) and the glass transition temperature (Tg) was calculated by the following formula.
ΔTcg=Tcc−Tg
In the present invention, it is necessary that ΔTcg exceeds 60° C. The larger this value is, the higher the crystallinity is.
In the case of a single layer, the polyester film is used as the measurement sample, and in the case of a laminate structure, the copolymer polyester layer (A1) is used as the measurement sample.

(8) Solvent Resistance After immersing a sample film in each solvent for 24 hours, the condition was visually observed and judged according to the following criteria.
(Judgment criteria)
A: No change in appearance or flatness.
B: The film curls.
C: The solvent resistance is poor and the film dissolves.

(9) Lamination stretching followability A resin layer composition consisting of the following components was applied onto a sample film and dried at 80°C for 5 minutes to form a functional layer with a thickness of 3.6 μm, and a sample consisting of a laminated film was prepared. The film was then stretched in air at a temperature of 25°C and a stretching ratio of 3.5 times (corresponding to an elongation rate of 250%) using a tensile tester (AUTOGRAPH AG-I) manufactured by Shimadzu Corporation. The stretching followability of the obtained laminated film was judged according to the following criteria.
(Resin Layer Composition)
Mitsubishi Chemical Corporation's "Gosenex Z-200" 100 parts by weight Mitsubishi Chemical Corporation's "Safelink SPM-01" 5 parts by weight (criteria)
A: The stretchability is particularly good.
B: Good stretchability.
C: Poor stretchability.

(material)
The following raw materials were used in the examples and comparative examples.
(1) Copolymer polyester (a1-1)
A copolymer polyester (a1-1) (intrinsic viscosity (IV) 0.70 dl/g) was prepared, which contained terephthalic acid and adipic acid (having 6 carbon atoms) as dicarboxylic acid components, with the terephthalic acid content being 85 mol % and the adipic acid content being 15 mol %, and containing 45 mol % of 1,4-butanediol and 55 mol % of 1,6-hexanediol as alcohol components.

(2) Copolymer polyester (a1-2)
A copolymer polyester (a1-2) (intrinsic viscosity (IV) 0.70 dl/g) was prepared, which contained terephthalic acid and isophthalic acid as dicarboxylic acid components, the terephthalic acid content being 78 mol %, the isophthalic acid content being 22 mol %, and the alcohol components being 98 mol % ethylene glycol and 2 mol % diethylene glycol.

(3) Copolymer polyester (a1-3)
A copolymer polyester (a1-3) (intrinsic viscosity 0.64 dl/g) was prepared, which contained terephthalic acid, isophthalic acid, and a hydrogenated dimer acid having 36 carbon atoms as dicarboxylic acid components, with 88 mol % of terephthalic acid, 5 mol % of isophthalic acid, and 7 mol % of hydrogenated dimer acid as dicarboxylic acid components, and 95 mol % of ethylene glycol and 5 mol % of diethylene glycol as alcohol components.

(4) Copolymer polyester (a1-4)
A copolymer polyester (a1-3) (intrinsic viscosity 0.72 dl/g) was prepared, which contained terephthalic acid and hydrogenated dimer acid having 36 carbon atoms as dicarboxylic acid components, with 88 mol % of terephthalic acid and 12 mol % of hydrogenated dimer acid as dicarboxylic acid components, and 67 mol % of ethylene glycol and 33 mol % of 1,4-butanediol as alcohol components.

(5) Copolymer polyester (a1-5)
A copolymer polyester (a1-5) (intrinsic viscosity 1.6 dl/g) containing terephthalic acid as a dicarboxylic acid component and 1,4-butanediol as an alcohol component was prepared.

(6) Copolymer polyester (a1-6)
A copolymer polyester (a1-6) (intrinsic viscosity 0.69 dl/g) was prepared, which contained terephthalic acid, isophthalic acid, and sebacic acid as dicarboxylic acid components, with terephthalic acid being 56 mol%, isophthalic acid being 12 mol%, and sebacic acid being 32 mol%, and which contained ethylene glycol being 95 mol% and diethylene glycol being 5 mol% as alcohol components.

(5) Homopolyester (a2-1)
A homopolyester (a2-1) was prepared, which was a polyester having a dicarboxylic acid component of terephthalic acid and an alcohol component of 98 mol % of ethylene glycol and 2 mol % of diethylene glycol, and had an intrinsic viscosity (IV) of 0.64 dl/g.

(6) Homopolyester (a2-2)
A homopolyester (a2-2) was prepared, which was a polyester having a dicarboxylic acid component of terephthalic acid and an alcohol component of 98 mol % of ethylene glycol and 2 mol % of diethylene glycol, and had an intrinsic viscosity (IV) of 0.82 dl/g.

(7) Homopolyester (a2-3)
A particle-containing homopolyester (a2-3) (particle-containing homoPET) was prepared, which was a polyester having a dicarboxylic acid component of terephthalic acid and 98 mol % of ethylene glycol and 2 mol % of diethylene glycol as alcohol components, and had an intrinsic viscosity (IV) of 0.62 dl/g and contained 0.2 mass % of silica particles having an average particle size of 3 μm.

(8) Homopolyester (a2-4)
A particle-containing homopolyester (a2-4) (particle-containing homoPET) was prepared, which was a polyester having a dicarboxylic acid component of terephthalic acid and 98 mol % of ethylene glycol and 2 mol % of diethylene glycol as alcohol components, and had an intrinsic viscosity (IV) of 0.63 dl/g and contained 1.0 mass % of silica particles having an average particle size of 3 μm.

[Example 1]
Chips of a polyester composition containing 50% by mass of copolymer polyester (a1-1), 35% by mass of homopolyester (a2-1) and 15% by mass of homopolyester (a2-3) were fed into a main vented twin-screw extruder set at 270°C.
The extrusion was performed through a die, and the extrusion was rapidly cooled and solidified on a cooling roll having a surface temperature set at 25° C. using an electrostatic application adhesion method, to obtain an unstretched sheet.

The resulting unstretched sheet was then stretched 3.0 times in the longitudinal direction (MD) at 75°C, introduced into a tenter, and then stretched 4.5 times in the transverse direction (TD) at 95°C, after which it was heat-treated at 240°C for 10 seconds to obtain a copolymer polyester film (sample) with a thickness of 50 μm.

[Example 2]
Chips of a polyester composition containing 35% by mass of copolymer polyester (a1-1), 50% by mass of homopolyester (a2-1) and 15% by mass of homopolyester (a2-3) were fed into a main vented twin-screw extruder set at 270°C.
The extrusion was performed through a die, and the extrusion was rapidly cooled and solidified on a cooling roll having a surface temperature set at 25° C. using an electrostatic application adhesion method, to obtain an unstretched sheet.

The resulting unstretched sheet was then stretched 3.0 times in the longitudinal direction (MD) at 75°C, introduced into a tenter, and then stretched 4.3 times in the transverse direction (TD) at 95°C, after which it was heat-treated at 240°C for 10 seconds to obtain a copolymer polyester film (sample) with a thickness of 50 μm.

[Example 3]
Chips of a polyester composition containing 50% by mass of copolymer polyester (a1-1), 20% by mass of homopolyester (a2-2) and 30% by mass of homopolyester (a2-4) were fed into a main vented twin-screw extruder set at 270°C.
The extrusion was performed through a die, and the extrusion was rapidly cooled and solidified on a cooling roll having a surface temperature set at 25° C. using an electrostatic application adhesion method, to obtain an unstretched sheet.

The resulting unstretched sheet was then stretched 3.3 times in the longitudinal direction (MD) at 65°C, introduced into a tenter, and then stretched 4.7 times in the transverse direction (TD) at 90°C, after which it was heat-treated at 230°C for 10 seconds to obtain a copolymer polyester film (sample) with a thickness of 25 μm.

[Example 4]
Chips of a polyester composition containing 25% by mass of copolymer polyester (a1-1), 50% by mass of copolymer polyester (a1-3) and 25% by mass of homopolyester (a2-2) were fed into a main vented twin-screw extruder set at 270° C. The chips were extruded from a die and rapidly solidified on a cooling roll whose surface temperature was set at 25° C. using an electrostatic application adhesion method to obtain an unstretched sheet.
The unstretched sheet thus obtained was then stretched 3.0 times in the machine direction (MD) at 90°C, introduced into a tenter, and then stretched 3.0 times in the width direction (TD) at 90°C, after which it was heat-treated at 160°C for 15 seconds to obtain a copolymer polyester film (sample) having a thickness of 50 μm.

[Comparative Example 1]
Chips of a polyester composition containing 85% by mass of copolymer polyester (a1-2) and 15% by mass of homopolyester (a2-3) were fed into a main vented twin-screw extruder set at 270°C.
The extrusion was performed through a die, and the extrusion was rapidly cooled and solidified on a cooling roll having a surface temperature set at 25° C. using an electrostatic application adhesion method, to obtain an unstretched sheet.

The resulting unstretched sheet was then stretched 3.3 times in the longitudinal direction (MD) at 90°C, introduced into a tenter, and then stretched 3.7 times in the transverse direction (TD) at 100°C, after which it was heat-treated at 190°C for 10 seconds to obtain a copolymer polyester film (sample) with a thickness of 75 μm.

[Comparative Example 2]
Chips of a polyester composition containing 92% by mass of homopolyester (a2-1) and 8% by mass of homopolyester (a2-3) were fed into a main vented twin-screw extruder set at 280°C.
The extrusion was performed through a die, and the extrusion was rapidly cooled and solidified on a cooling roll having a surface temperature set at 25° C. using an electrostatic application adhesion method, to obtain an unstretched sheet.

The resulting unstretched sheet was then stretched 3.4 times in the longitudinal direction (MD) at 90°C, introduced into a tenter, and then stretched 4.5 times in the transverse direction (TD) at 135°C, after which it was heat-treated at 223°C for 10 seconds to obtain a polyester film (sample) with a thickness of 50 μm.

[Comparative Example 3]
In Comparative Example 2, the same procedure was followed except that the film was not stretched, to obtain an unstretched polyester film (sample) having a thickness of 200 μm.

[Comparative Example 4]
For the intermediate layer, the copolymer polyester (a1-4) was fed into a main vented twin-screw extruder set at 280°C.
For the surface layer, chips of a polyester composition containing 50% by mass of homopolyester (a2-1) and 50% by mass of copolymer polyester (a1-2) were fed into a sub-vented twin-screw extruder set at 280°C.
The polymer from the main extruder was extruded from a die in a two-kind, three-layer structure (surface layer/intermediate layer/surface layer) such that the polymer from the main extruder formed an intermediate layer and the polymer from the sub-extruder formed a surface layer. The extruded polymer was then rapidly cooled and solidified on a cooling roll whose surface temperature was set at 30°C using an electrostatic application adhesion method, to obtain an unstretched sheet.
The unstretched sheet was then stretched 3.5 times in the machine direction (MD) at 85° C., introduced into a tenter, stretched 4.4 times in the width direction (TD) at 100° C., and then heat-treated at 200° C. for 10 seconds to obtain a copolymer polyester film (sample) having a thickness of 38 μm. In Table 1, the crystalline melting enthalpy ΔHm, cold crystallization temperature (Tcc), and glass transition temperature (Tg) are values for the intermediate layer.

[Comparative Example 5]
Chips of a polyester composition containing 10% by mass of copolymer polyester (a1-1), 30% by mass of copolymer polyester (a1-5), and 60% by mass of copolymer polyester (a1-6) were fed into a main vented twin-screw extruder set at 270°C.
The extrusion was performed through a die, and the extrusion was rapidly cooled and solidified on a cooling roll having a surface temperature set at 25° C. using an electrostatic application adhesion method, to obtain an unstretched sheet (sample) having a thickness of 200 μm.

[Reference Examples 1 to 4]
The following film samples were also evaluated as reference examples.
Unstretched PVC: Diaplus: GR379
ONY (oriented nylon film): Santonil manufactured by Mitsubishi Chemical Corporation OPP (oriented polypropylene film): Pylen P2161 manufactured by Toyobo Co., Ltd.
CPP (unstretched polypropylene film): Artply, manufactured by Diaplus Co., Ltd.

※ジカルボン酸成分、及びアルコール成分におけるｍｏｌ％は、共重合ポリエステルフィルム（共重合ポリエステル層（Ａ１））に含まれる全てのポリエステル（Ａ）におけるジカルボン酸成分、及びアルコール成分それぞれに対する割合である。

*The mol % of the dicarboxylic acid component and the alcohol component are the proportions relative to the dicarboxylic acid component and the alcohol component, respectively, in the entire polyester (A) contained in the copolymer polyester film (copolymer polyester layer (A1)).

From the above examples and the results of tests conducted by the inventors, it has been found that a copolymer polyester film having a copolymer polyester layer (A1) containing a copolymer polyester (a1), wherein the copolymer polyester (a1) is a copolymer containing terephthalic acid (X1), a dicarboxylic acid component (X), and an alcohol component (Y2) other than ethylene glycol (Y1), the dicarboxylic acid component (X) contains a dicarboxylic acid component (X2) having 4 to 10 carbon atoms, and the other alcohol component (Y2) contains two or more types, has a difference between the cold crystallization temperature (Tcc) and the glass transition temperature (Tg) of more than 60°C, and therefore has excellent flexibility at room temperature, and is not only flexible, but also has elongation and strength, and further has heat resistance sufficient for practical use.

The copolymer polyester film of the present invention can be used for battery packaging materials, surface protection films, dicing tapes, adhesive tapes, image display components such as flexible displays, wearable terminals, bioelectrode substrates, biosensor substrates and other bio-related components, for electronic component manufacturing, for example, green sheet molding used in the manufacturing of ceramic laminated components, and for optical component manufacturing, for example, polarizers constituting polarizing plates. In particular, it is suitable for stretching in a laminated configuration with different materials, particularly for applications involving a process of stretching the film by stretching at room temperature or near room temperature.

Claims (45)

A copolymer polyester film having a copolymer polyester layer (A1) containing a copolymer polyester (a1),
The copolymer polyester (a1) is a copolymer containing terephthalic acid (X1), a dicarboxylic acid component (X2) having 4 to 10 carbon atoms, and an alcohol component (Y2) other than ethylene glycol (Y1),
the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in all the dicarboxylic acid components in the polyester (A) contained in the copolymerized polyester layer (A1) is 3 to 25 mol %,
the proportion of the other alcohol component (Y2) in the alcohol components in all the polyesters (A) contained in the copolymerized polyester layer (A1) is 15 to 55 mol %,
the other alcohol component (Y2) contains an aliphatic diol or an alicyclic diol,
a polyester layer (B1) and a polyester layer (B2) are provided on both the front and back sides of the copolymer polyester layer (A1),
The copolymer polyester film has a difference between the cold crystallization temperature (Tcc) and the glass transition temperature (Tg) of the copolymer polyester layer (A1) exceeding 60°C. The copolymer polyester film according to claim 1 , further comprising two or more other alcohol components (Y2). 3. The copolymer polyester film according to claim 1, wherein the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in all the dicarboxylic acid components in the polyester (A) contained in the copolymer polyester layer (A1) is 3 to 12 mol %. The copolymer polyester film according to any one of claims 1 to 3 , wherein the other alcohol component (Y2) comprises an aliphatic diol . The copolymer polyester film according to any one of claims 1 to 4, wherein the other alcohol component (Y2) comprises an aliphatic diol having 4 to 8 carbon atoms. The copolymer polyester film according to any one of claims 1 to 5 , which has a tensile elongation at break of 295% or more at 25°C measured under conditions of a speed of 200 mm/min and a chuck distance of 50 mm . The copolymer polyester film according to any one of claims 1 to 6 , which has a storage modulus of 2500 MPa or less at 25°C and a storage modulus of 10 MPa or more at 120°C, measured at a vibration frequency of 10 Hz . The copolymer polyester film according to any one of claims 1 to 7 , wherein the dicarboxylic acid component (X2) having 4 to 10 carbon atoms includes an aliphatic dicarboxylic acid. The copolymer polyester film according to any one of claims 1 to 8 , wherein the dicarboxylic acid component (X2) having 4 to 10 carbon atoms comprises at least one selected from the group consisting of adipic acid, sebacic acid and isophthalic acid . The copolymer polyester film according to any one of claims 1 to 9 , wherein the other alcohol component (Y2) comprises 1,4-butanediol. The copolymer polyester film according to any one of claims 1 to 10 , wherein the other alcohol component (Y2) comprises 1,4-butanediol and 1,6-hexanediol. The copolymer polyester film according to any one of claims 1 to 11, wherein the copolymer polyester layer (A1) further contains a polyester (a2) which is a polyester other than the copolymer polyester ( a1 ) and contains terephthalic acid as a dicarboxylic acid component and ethylene glycol as an alcohol component. The copolymer polyester film according to claim 12, wherein the polyester (a2) comprises a homopolyester. A copolymer polyester film having a copolymer polyester layer (A1) containing a copolymer polyester (a1),
The copolymer polyester (a1) is a copolymer containing terephthalic acid (X1), a dicarboxylic acid component (X2) having 4 to 10 carbon atoms, and an alcohol component (Y2) other than ethylene glycol (Y1),
the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in all the dicarboxylic acid components in the polyester (A) contained in the copolymerized polyester layer (A1) is 3 to 25 mol %,
the proportion of the other alcohol component (Y2) in the alcohol components in all the polyesters (A) contained in the copolymerized polyester layer (A1) is 15 to 55 mol %,
the other alcohol component (Y2) contains an aliphatic diol or an alicyclic diol,
A laminated film comprising a copolymerized polyester film having a difference between its cold crystallization temperature (Tcc) and glass transition temperature (Tg) exceeding 60°C, and a functional layer provided on at least one surface of the copolymerized polyester film. The laminate film according to claim 14, further comprising two or more types of other alcohol components (Y2). The laminate film according to claim 14 or 15, wherein the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in all the dicarboxylic acid components in the polyester (A) contained in the copolymerized polyester layer (A1) is 3 to 12 mol %. The laminate film according to any one of claims 14 to 16, wherein the other alcohol component (Y2) includes an aliphatic diol. The laminate film according to any one of claims 14 to 17, wherein the other alcohol component (Y2) includes an aliphatic diol having 4 to 8 carbon atoms. The laminate film according to any one of claims 14 to 18, wherein the dicarboxylic acid component (X2) having 4 to 10 carbon atoms includes an aliphatic dicarboxylic acid. The laminate film according to any one of claims 14 to 19, wherein the dicarboxylic acid component (X2) having 4 to 10 carbon atoms includes at least one selected from the group consisting of adipic acid, sebacic acid, and isophthalic acid . The laminate film according to any one of claims 14 to 20, wherein the copolymer polyester layer (A1) further contains a homopolyester. The laminate film according to any one of claims 14 to 21 , wherein the functional layer is a resin layer containing a resin containing a vinyl alcohol structural unit. The laminated film according to any one of claims 14 to 22 , wherein the functional layer constitutes a green sheet. The laminate film according to claim 14 , wherein the functional layer constitutes a polarizer. The laminate film according to any one of claims 14 to 21 , wherein the functional layer is an adhesive layer. The laminated film according to claim 25 , comprising a conductive material in the adhesive layer. The laminate film according to any one of claims 14 to 21 , wherein the functional layer is a conductive layer. The copolymer polyester film according to any one of claims 1 to 13 , which is used for an adhesive tape, a surface protection film, a dicing tape for semiconductors, or for manufacturing electronic parts. The laminate film according to any one of claims 14 to 27 , which is used for an adhesive tape, a surface protection film, a dicing tape for semiconductors, or for manufacturing electronic parts. A copolymer polyester film for use in a wearable terminal, a bioelectrode substrate, a biosensor substrate, or for use in the manufacture of an optical component, the copolymer polyester film having a copolymer polyester layer (A1) containing a copolymer polyester (a1),
The copolymer polyester (a1) is a copolymer containing terephthalic acid (X1), a dicarboxylic acid component (X2) having 4 to 10 carbon atoms, and an alcohol component (Y2) other than ethylene glycol (Y1),
the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in all the dicarboxylic acid components in the polyester (A) contained in the copolymerized polyester layer (A1) is 3 to 25 mol %,
the proportion of the other alcohol component (Y2) in the alcohol components in all the polyesters (A) contained in the copolymerized polyester layer (A1) is 15 to 55 mol %,
the other alcohol component (Y2) contains an aliphatic diol or an alicyclic diol,
A copolymer polyester film having a difference between its cold crystallization temperature (Tcc) and glass transition temperature (Tg) of more than 60°C. The copolymer polyester film according to claim 30, further comprising two or more other alcohol components (Y2). The copolymer polyester film according to claim 30 or 31, wherein the proportion of the dicarboxylic acid component (X2) having 4 to 10 carbon atoms in all the dicarboxylic acid components in the polyester (A) contained in the copolymer polyester layer ( A1 ) is 3 to 12 mol %. The copolymer polyester film according to any one of claims 30 to 32 , wherein the other alcohol component (Y2) comprises an aliphatic diol . The copolymer polyester film according to any one of claims 30 to 33, wherein the other alcohol component (Y2) comprises an aliphatic diol having 4 to 8 carbon atoms. The copolymer polyester film according to any one of claims 30 to 34 , which has a tensile elongation at break of 295% or more at 25°C measured under conditions of a speed of 200 mm/min and a chuck distance of 50 mm . The copolymer polyester film according to any one of claims 30 to 35 , which has a storage modulus of 2500 MPa or less at 25°C and a storage modulus of 10 MPa or more at 120°C, measured at a vibration frequency of 10 Hz . The copolymer polyester film according to any one of claims 30 to 36 , wherein the dicarboxylic acid component (X2) having 4 to 10 carbon atoms includes an aliphatic dicarboxylic acid. The copolymer polyester film according to any one of claims 30 to 37 , wherein the dicarboxylic acid component (X2) having 4 to 10 carbon atoms comprises at least one selected from the group consisting of adipic acid, sebacic acid, and isophthalic acid . The copolymer polyester film according to any one of claims 30 to 38 , wherein the other alcohol component (Y2) comprises 1,4-butanediol. The copolymer polyester film according to any one of claims 30 to 39 , wherein the other alcohol component (Y2) comprises 1,4-butanediol and 1,6-hexanediol. The copolymer polyester film according to any one of claims 30 to 40 , wherein the copolymer polyester layer (A1) further contains a polyester (a2) which is a polyester other than the copolymer polyester ( a1 ) and contains terephthalic acid as a dicarboxylic acid component and ethylene glycol as an alcohol component. The copolymer polyester film according to claim 41 , wherein the polyester (a2) comprises a homopolyester. The copolymer polyester film according to any one of claims 30 to 42 , comprising a polyester layer (B1) and a polyester layer (B2) on both sides of the copolymer polyester layer (A1). A laminated film comprising the copolymer polyester film according to any one of claims 30 to 43 and a functional layer provided on at least one surface of the copolymer polyester film. The laminate film according to claim 44 , wherein the functional layer constitutes a polarizer.