TWI813769B - Copolyester film - Google Patents

Abstract

The present invention proposes a copolymerized polyester film, which is softer and more flexible, but also has elongation, strength and heat resistance. It is characterized in that: it contains copolymerized polyester A. As the copolyester layer (I layer) of the main component resin, and the above-mentioned copolyester A is a copolymer of terephthalic acid and "other dicarboxylic acid components" and ethylene glycol and "other alcohol components", in this In the copolymer polyester, the ratio of "other dicarboxylic acid components" to the dicarboxylic acid component is 5 mol% or more and 20 mol% or less, and the ratio of "other alcohol components" to the alcohol component is 1 mol% Above but less than 25 mol%, the storage elastic modulus at 25°C is below 2500 MPa, and the storage elastic modulus at 120°C is above 10 MPa.

Description

copolyester film

The present invention relates to a copolymerized polyester film provided with a copolymerized polyester layer containing copolymerized polyester as a main component resin.

Polyethylene terephthalate (PET) film, which is a representative polyester film, especially biaxially stretched PET film, is used as an industrial material due to its excellent transparency, mechanical strength, heat resistance, flexibility, etc. , optical materials, electronic parts materials, battery packaging materials and other fields.

Regarding this type of polyester film, for example, Patent Document 1 proposes a softened polyester film that exhibits softness that conventional polyester films do not have and has excellent moldability at relatively low temperatures and low pressures. The softened polyester film is characterized by: the elastic modulus E' of the film is less than 20 MPa at 120°C and less than 5 MPa at 180°C, the film haze is less than 1.0%, and contains 29 to 32 moles. It contains 1,4-cyclohexanedimethanol units as diol components and does not contain isophthalic acid units as dicarboxylic acid components.

Furthermore, Patent Document 2 proposes a developing sheet for thermal transfer, which is formed by laminating a developing layer on at least a single area of a polyester film, and the developing layer contains a copolymer with a copolymerization rate of 5 to 30 mol%. Copolyester layer. Furthermore, Patent Document 3 proposes a polyester film for metal plate bonding and molding processing, which is characterized in that it is a biaxially aligned film containing copolymerized polyester, and the copolymerized polyester contains an average particle diameter of 0.1 to 2.5 μm. , a lubricant with a pore volume of 0.05 to 2.5 ml/g, a specific surface area of 50 to 600 m ² /g and a compression resistance of 1 to 100 MPa of 0.05 to 5.0% by weight, and the inherent viscosity of the biaxial alignment film is 0.50～0.80 dl/g, the glass transition point is above 70℃, the melting point is 210～250℃, and the coarse particles of the above lubricant with a particle size of 20 μm or above in the biaxial alignment film only contain at most 10 particles/mm ² .

In addition, Patent Document 4 proposes a biaxially stretched polyester film for molding, which is characterized in that it contains a copolyester containing 1 to 20 mol% of an aliphatic dicarboxylic acid component based on the total acid component. In an atmosphere of ℃, the film strength F ₁₀₀ at 100% elongation is 0.5 to 5 kg/mm ² , and the thickness unevenness of the film is less than 40%. Furthermore, Patent Document 5 proposes a laminated polyester film, which is characterized in that at least a single area of a polyester (A) layer containing polyester (A) as the main component is laminated with polyester (B). It is a polyester (B) layer as the main component, and the elastic modulus of the laminated film in an atmosphere of 23°C is 20 to 1000 MPa, and the elastic modulus in an atmosphere of 120°C is 10 to 200 MPa, and there is essentially no alignment. .

In recent years, as image display devices, computers (wearable computers) that have been miniaturized into a size that can be worn on the body due to miniaturization and high performance of mobile terminals have attracted much attention. Electronic devices (wearable terminals) used in wearable computers are ideally equipped with items carried by the human body such as watches (Patent Document 6).

In addition, as the next generation of image display devices, flexible displays that can be bent freely have attracted much attention. Organic electroluminescence (organic EL) displays are mainly used in flexible displays. Considering the use of thinner glass substrates or plastic substrates in flexible displays, in addition to the optical properties or durability required for previous planar display panels, the polyester films used in components for these image display devices, It is also required that even if a bending test is performed, no bending, etc. will occur. [Prior technical literature] [Patent Document]

Patent Document 1: Japanese Patent Application Publication No. 2014-169371 Patent Document 2: Japanese Patent Application Publication No. 04-086293 Patent document 3: Japanese Patent Application Publication No. 2000-001552 Patent Document 4: Japanese Patent Application Publication No. 03-067629 Patent Document 5: International Publication No. 09/078304 Patent Document 6: Japanese Patent Application Publication No. 2014-134903

[Problem to be solved by the invention]

As mentioned above, if the use of a polyester film for wearable terminals, flexible displays, etc. is considered, it is necessary to develop a polyester film that is not only soft but also more flexible than polyester films that have been generally used. In this way, it also has elongation and strength. In addition, heat resistance that does not shrink when heated is also required.

Therefore, the object of the present invention is to provide a new copolymerized polyester film that is softer and more flexible than the polyester films commonly used in the past, and yet has elongation, strength and heat resistance. [Technical means to solve problems]

The present invention proposes a copolymerized polyester film, which is characterized in that it is provided with a copolymerized polyester layer (I layer) containing copolymerized polyester A as a main component resin, and The above-mentioned copolyester A is a copolymer of terephthalic acid and "other dicarboxylic acid components" and ethylene glycol and "other alcohol components". In this copolymerized polyester, "other dicarboxylic acid components" are in the dicarboxylic acid The proportion of "other alcohol components" in the alcohol component is more than 5 mol% and less than 20 mol%. The proportion of "other alcohol components" in the alcohol component is more than 1 mol% and less than 25 mol%. The storage elastic modulus at 25°C is below 2500 MPa, and the storage elastic modulus at 120°C is above 10 MPa.

Furthermore, the present invention proposes a copolymerized polyester film, which is characterized in that it is provided with a copolymerized polyester layer (I layer) containing one or more types of polyester, and In all polyesters contained in the copolymerized polyester layer (layer I), the ratio of the total content of "other dicarboxylic acid components" to the total content of dicarboxylic acid components is 5 mol% or more and 20 mol% Below, the ratio of the total content of "other alcohol components" to the total content of alcohol components is 1 mol% or more and less than 25 mol%, The storage elastic modulus at 25°C is below 2500 MPa, and the storage elastic modulus at 120°C is above 10 MPa. [Effects of the invention]

The copolyester film proposed by the present invention has excellent softness at normal temperature. It is not only soft but also more flexible. However, it also has elongation and strength, and thus has sufficient heat resistance for practical use. Therefore, the copolyester film proposed by the present invention can be preferably used as a packaging material for batteries, a member for image display, especially a structural member of a flexible display or a wearable terminal.

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

＜This copolyester film＞ A copolyester film (referred to as "this copolyester film") according to an embodiment of the present invention is a single-layer or laminated film having a copolyester layer (layer I) containing copolyester A as a main component resin.

The copolyester film can be a non-stretched film (sheet) or a stretched film. Among them, a stretched film stretched in a uniaxial direction or a biaxial direction is preferred. Among them, a biaxially stretched film is preferred in terms of balance of mechanical properties and excellent flatness. If the copolyester film is such a stretched film, the storage elastic modulus at 120° C. tends to be 10 MPa or more.

＜Copolyester layer (I layer)＞ The copolymerized polyester layer (layer I) is a layer containing copolymerized polyester A as a main component resin.

Here, the above-mentioned "main component resin" means the resin with the largest content among the resins constituting the copolymerized polyester layer (I layer). The main component resin may account for more than 30% by mass of the resin constituting the copolyester layer (layer I), preferably more than 50% by mass, and more preferably more than 80% by mass (including 100% by mass). %).

The resin constituting the copolyester layer (layer I) may be only copolyester A, or may include resin B other than copolyester A. In this case, the resin B is preferably a resin that is compatible with the copolyester A. The following describes the case where the copolyester layer (layer I) includes copolyester A and resin B that is compatible with it.

(Copolyester A) Copolyester A is preferably a copolymer of terephthalic acid and other dicarboxylic acid components and ethylene glycol and other alcohol components.

Copolyester A may be crystalline or amorphous. In addition, in the present invention, the so-called crystalline polyester resin refers to a polyester resin generally having a crystalline melting peak temperature (melting point), and more specifically, it refers to a differential scanning calorimetry based on JIS K7121 (1987). The polyester resin has a melting point observed in measurement (DSC) and contains a so-called semi-crystalline state. On the contrary, a thermoplastic resin whose melting point is not observed in DSC is called "amorphous". The so-called crystalline polyester refers to polyester that generally has a crystalline melting peak temperature (melting point). More specifically, it refers to a polyester whose melting point is observed in differential scanning calorimetry (DSC) based on JIS K7121 (1987) and which contains a so-called semi-crystalline state. On the contrary, a thermoplastic resin whose melting point is not observed in DSC is called "amorphous".

Examples of the "other dicarboxylic acid components" include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, polyfunctional acids, and the like. Furthermore, "other dicarboxylic acid components" may be used in combination of two or more types. By using two or more types together in this way, it may be possible to not only soften the copolymerized polyester film more effectively, but also maintain the crystal structure and have heat resistance. Among them, from the viewpoint of easily softening the copolyester film, the "other dicarboxylic acid components" are preferably aromatic compounds such as isophthalic acid, 2,6-naphthalene dicarboxylic acid, and biphenyl dicarboxylic acid. Dicarboxylic acids; aliphatic dicarboxylic acids such as adipic acid, sebacic acid, dodecanedioic acid, eicosanedioic acid and their derivatives; 1,4-cyclohexanedicarboxylic acid, 1,2 -Alicyclic dicarboxylic acids such as cyclopentanedicarboxylic acid and cyclooctanedicarboxylic acid; or dimer acid. Among them, those containing aliphatic dicarboxylic acid or dimer acid are preferred. Among aliphatic dicarboxylic acids, from the viewpoint of further lowering the glass transition temperature, aliphatic dicarboxylic acids having a carbon number of 20 to 80 are preferred, and among these, aliphatic dicarboxylic acids having a carbon number of 30 or more or 60 or less are more preferred. Carboxylic acid, particularly preferably an aliphatic dicarboxylic acid having a carbon number of 36 or more or 48 or less.

As the dimer acid, a dicarboxylic acid containing a dimer of an unsaturated fatty acid and having a carbon number of 18 or more in the unsaturated fatty acid is preferred. Examples of such dimer acids include the use of different or identical ones selected from the group consisting of oleic acid, elaidic acid, cetylenic acid, erucic acid, brazoleic acid, linoleic acid, and sublinolenic acid. It is formed by dimerization of unsaturated fatty acids. Furthermore, those obtained by hydrogenation after such dimerization can also be used. Furthermore, the above-mentioned dimer acid may also contain an aromatic ring or an alicyclic monocyclic ring or an alicyclic polycyclic ring. Among such dimer acids, from the viewpoint of further lowering the glass transition temperature, a dimer acid having a carbon number of 20 to 80 is preferred, and a dimer acid having a carbon number of 26 or more or 60 or less is more preferred, and furthermore, A dimer acid having a carbon number of 30 or more or 50 or less is preferred.

As mentioned above, "other dicarboxylic acid components" can be selected arbitrarily. Among them, it is preferable to select one or more types from aromatic dicarboxylic acids, and one or more types from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and dimer acids, and to use these together. Among them, the one containing isophthalic acid, an aliphatic dicarboxylic acid and two or more dimer acids is particularly preferred, and the one containing isophthalic acid, an aliphatic dicarboxylic acid having a carbon number of 20 to 80, and a dimer acid is particularly preferred. More than 2 types of polyacid. If aromatic dicarboxylic acid is used as the "other dicarboxylic acid component", the film tends to be softened while maintaining strength and heat resistance. On the other hand, if aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, or dimer acid is selected as the "other dicarboxylic acid component", the elongation (elongation at break) can be maintained at a smaller content ratio. Among them, the use of dimer acid is most effective in softening the film. Therefore, by combining and using "other dicarboxylic acid components" as described above, a film that has a good balance of strength, heat resistance, elongation, and flexibility can be produced.

In copolyester A, the ratio of "other dicarboxylic acid components" to the total of dicarboxylic acid components, that is, terephthalic acid and "other dicarboxylic acid components" is preferably 5 to 20 mol%, where More preferably, it is 8 mol% or more or 18 mol% or less, and further more preferably, it is 10 mol% or more or 15 mol% or less. Here, when two or more "other dicarboxylic acid components" are used together, it means the total amount of these. If the ratio of "other dicarboxylic acid components" is within the above range, the copolyester film will have good elongation, strength and heat resistance, and will tend to be effectively softened.

Examples of the above "other alcohol components (diol components)" include: 1,4-butanediol, 1,6-hexanediol, diethylene glycol, 1,3-propanediol, neopentyl glycol, 1, 4-Cyclohexane dimethanol, bisphenol and their derivatives, etc. Among these, diethylene glycol is preferred from the viewpoint of flexibility, and 1,4-butanediol is preferred from the viewpoint of heat resistance and strength. Furthermore, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, part of the ethylene glycol is usually modified to become diethylene glycol and introduced into the polyester skeleton. This diethylene glycol is called by-product diethylene glycol. This by-product varies depending on the method of polycondensation (ester exchange method, direct polycondensation), etc., but is about 1 to 5 mol% in ethylene glycol. In the present invention, diethylene glycol thus produced from ethylene glycol is also treated as a copolymer component and is included in "other alcohol components".

In copolyester A, the ratio of "other alcohol components (diol components)" to the total of alcohol components (diol components), that is, ethylene glycol and "other alcohol components" is preferably 1 mol% or more And less than 25 mol%, more preferably 2 mol% or more or 20 mol% or less, and still more preferably 3 mol% or more or 18 mol% or less. Here, when two or more "other alcohol components" are used together, it means the total amount of these. If the ratio of "other alcohol components" is within the above range, the copolyester film will have good elongation, strength and heat resistance, and will tend to be effectively softened. Furthermore, "other alcohol components" may be used in combination of two or more types. By using two or more types together, the copolymerized polyester film may be softened more effectively.

Moreover, it is preferable to use three or more types together of "other dicarboxylic acid components" and "other alcohol components" in total. By using a plurality of copolymer components in combination, the film tends to be softened at a smaller content ratio. Furthermore, if there are too many types of copolymer components, it may be difficult to stabilize the characteristics of the film. Therefore, the total number of "other dicarboxylic acid components" and "other alcohol components" is preferably 3 to 5 types, and 3 types are more preferred. Or 4 kinds.

A particularly preferred copolyester A among the above is a crystalline copolyester Aa, which is composed of terephthalic acid, isophthalic acid and an aliphatic dicarboxylic acid or dimer acid and ethylene glycol and diethylene glycol. copolymer, and the proportion of isophthalic acid, aliphatic dicarboxylic acid or dimer acid in the dicarboxylic acid component constituting the copolyester is 5 mol% or more and 20 mol% or less, and diethylene glycol is The proportion of the alcohol component constituting the copolyester is 1 mol% or more and less than 25 mol%. In general, if the ratio of copolymerized components is increased in order to reduce the elastic modulus of copolymerized polyester, the crystallinity will be reduced, and if the ratio is further increased, the copolymerized polyester will become amorphous. Although the above-mentioned copolymerized polyester Aa has a high ratio of copolymerized components and can achieve a low elastic modulus, it maintains crystallinity and can therefore be heat-fixed by heat treatment after stretching. As a result, copolymer polyester Aa is flexible, but has good elongation and strength, and can further suppress thermal shrinkage.

(Resin B) As mentioned above, the copolyester layer (layer I) may be a layer including copolyester A and resin B that is compatible with it. Furthermore, in the present invention, "miscibility" means a state in which two or more mixed resins are completely mixed at the molecular level. At this time, the amorphous region mixed at the molecular level can be regarded as a single phase, and micro-Brownian motion is also generated at a single temperature. Therefore, when two or more resins are miscible, the melting point or glass transition temperature of the mixed resin of the two or more resins is single, and the main dispersion peak is also single. Therefore, conversely, the so-called resin that is compatible with copolyester A can also be defined as a resin that can change the melting point or glass transition temperature of copolyester A when mixed with copolyester A. In addition, the glass transition temperature at this time is the loss when temperature dispersion measurement of dynamic viscoelasticity (Measurement of dynamic viscoelasticity by JIS K7244 method) is performed under the conditions of strain 0.1%, frequency 10 Hz, and heating rate 3°C/min. The temperature of the main dispersion peak of tangent (tanδ).

When the copolyester layer (layer I) is a layer including copolyester A and resin B, resin B is preferably compatible with copolyester A and has a melting point of 270°C or lower, or is amorphous, Resin with glass transition temperature of 30~120℃. By selecting this resin B, the glass transition temperature of the copolymerized polyester layer (layer I) can be increased and the heat resistance can be improved. By selecting polyester such as polyethylene terephthalate (PET) as the resin B, dimensional stability and heat resistance can be imparted.

Furthermore, from the viewpoint of having both flexibility and heat resistance, the resin B contains one or more polyesters, and the polyester (including one or more polyesters) contains a dicarboxylic acid. The ingredients include terephthalic acid and "other dicarboxylic acid components" and ethylene glycol and "other alcohol components" as alcohol components. The total content of "other dicarboxylic acid components" is relative to the total content of dicarboxylic acid components (in When two or more types of polyesters are included, the ratio (total of dicarboxylic acid components contained in each polyester) is preferably 5 mol% or more and 20 mol% or less, and more preferably 8 mol% or more or 18 mol% or less, and more preferably 10 mol% or more or 15 mol% or less, the total content of "other alcohol components" relative to the total content of alcohol components (when two or more types of polyester are included, each is The ratio of the total alcohol components contained in the polyester) is preferably 1 mol% or more and less than 25 mol%, more preferably 2 mol% or more or 20 mol% or less, and still more preferably 3 mol% or more Or less than 18 mol%.

Furthermore, the copolyester layer (layer I) may also be a layer including copolyester A and resin D that is incompatible with it. Examples of the resin D include polyolefin, polystyrene, acrylic resin, urethane resin, and the like.

In the copolyester layer (layer I), the mass ratio of copolyester A to resin B is preferably 98:2 to 50:50, more preferably 95:5 to 60:40, and even more preferably 90 :10~65:35.

Furthermore, it is considered that if the component ratio of the entire polyester contained in the copolymerized polyester layer (I layer) is the same as that of the copolymerized polyester A, the same resin as the case containing the copolymerized polyester A as the main component resin can be obtained. The effect. Therefore, when the copolymerized polyester layer (I layer) contains one or more types of polyester, if the total component amount of all polyesters contained in the copolymerized polyester layer (I layer) is "other The total content of "dicarboxylic acid components" accounts for 5 mol% or more and less than 20 mol% of the total content of dicarboxylic acid components, and the total content of "other alcohol components" accounts for a percentage of the total content of alcohol components If the ratio is 1 mol% or more and less than 25 mol%, the same effect as when copolymerized polyester A is included as the main component resin can be obtained. At this time, the preferred range of the ratio of the total content of "other dicarboxylic acid components" to the total content of dicarboxylic acid components is the same as the ratio of "other dicarboxylic acid components" in the copolymerized polyester A to the dicarboxylic acid component The preferred range of the ratio is the same. In addition, the preferable range of the ratio of the total content of "other alcohol components" to the total content of alcohol components is the same as the preferable range of the ratio of "other alcohol components" to the alcohol component in copolyester A. .

＜Situation of layered construction＞ As mentioned above, this copolyester film may be a laminated film including a copolyester layer (layer I) and other layers.

For example, there is a laminated film having a structure in which a polyester layer (II layer) containing polyester C as a main component resin is laminated on both the front and back sides of a copolymerized polyester layer (I layer). At this time, when the copolyester A is crystalline, the polyester C is preferably a polyester having a higher melting point than the melting point of the copolyester A. When the copolyester A is amorphous, The polyester C is preferably a polyester having a melting point at a higher temperature than the glass transition point of the copolyester A.

If this type of laminated film has a structure in which a polyester layer (II layer) containing polyester C as a main component resin is laminated, it is called polyester layer (II layer)/copolymerized polyester layer (I layer)/ The polyester layer (II layer) is laminated by laminating the raw resin composition by co-extrusion, etc. and then stretched. Compared with the case of a single layer including the copolymerized polyester layer (I layer), it can be performed at a higher temperature. It is heat-fixed, so it can be softened to a level that cannot be achieved by a single layer of the copolyester layer (I layer), and can improve heat resistance and further prevent thermal shrinkage. Specifically, the storage elastic modulus at 25°C of the present copolymerized polyester film can be set to 300 to 2500 MPa, and preferably set to 500 MPa or more or 2000 MPa or less.

In the above laminated film, the thickness of each layer of the polyester layer (layer II) is preferably 1 to 20% of the thickness of the copolyester layer (layer I). If the thickness of each layer of the polyester layer (II layer) is 1% or more of the thickness of the copolymerized polyester layer (I layer), film production can be carried out without seriously impairing productivity. If it is 20% or less, all the thickness can be fully ensured. The required softness is therefore preferred. From this point of view, the thickness of each layer of the polyester layer (layer II) is preferably 1 to 20% of the thickness of the copolymerized polyester layer (layer I), more preferably 3% or more or 15% or less, and more preferably The best is more than 5% or less than 12%. Furthermore, the thickness of the polyester layer (II layer) existing on both sides of the front and back sides of the copolymerized polyester layer (I layer) may be different on the front side and the back side, or may be the same.

When copolyester A is crystalline, polyester C is preferably a polyester with a melting point 10 to 100°C higher than the melting point of copolyester A, and more preferably 20°C or more or 90°C or less. Among them, it is more preferable that it is 40°C or more or 70°C or less. On the other hand, when copolyester A is amorphous, polyester C preferably has a glass transition point that is 120 to 120°C higher than that of copolyester A. Polyester with a melting point of 260°C is more preferably 140°C or more or 230°C or less, and further preferably 160°C or more or 200°C or less. Furthermore, the polyester C, which is the main component of the polyester layer (II layer) present on both sides of the front and back surfaces of the copolymerized polyester layer (I layer), may be different from the front surface and the back surface, or may be the same. Among them, it is preferable that the melting points of the polyester C on the front side and the back side are not much different. Specifically, the difference in the melting points of the polyester layers (layer II) present on both sides of the front and back surfaces is preferably 80°C or less, more preferably 60°C or less, and still more preferably 40°C or less. If the polyester C in the polyester layer (layer II) existing on both sides of the front and back of the copolyester layer A is the same, co-extrusion of two types of three layers can be achieved, so this aspect is also preferable.

As the polyester C, for example, a homopolyester or a copolyester containing terephthalic acid as a dicarboxylic acid component and ethylene glycol as an alcohol component can be preferably used. However, it is not limited to this.

When polyester C is a copolyester, examples of dicarboxylic acid components other than terephthalic acid include aromatic dicarboxylic acid, alicyclic dicarboxylic acid, aliphatic dicarboxylic acid, and polyfunctional acid. wait. In polyester C, the ratio of "dicarboxylic acid components other than terephthalic acid" to the dicarboxylic acid component is preferably 1 to 30 mol%, and more preferably 5 mol% or more or 25 mol%. below, and more preferably 10 mol% or more or 20 mol% or less.

When polyester C is a copolyester, alcohol components other than ethylene glycol include: 1,4-butanediol, 1,6-hexanediol, diethylene glycol, 1,3- Propylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, bisphenol and their derivatives, etc. In polyester C, the ratio of "alcohol components other than ethylene glycol" in the alcohol component is preferably 1 to 100 mol%, more preferably 5 mol% or more or 95 mol% or less, and further preferably Preferably, it is 10 mol% or more or 90 mol% or less.

＜Thickness of this copolyester film＞ The thickness of this copolyester film is not particularly limited, and an appropriate thickness can be selected according to the purpose. Among these, from the viewpoint of further utilizing the characteristics of the copolyester film, the total thickness of the film is preferably more than 20 μm. The plastic strength of the film can be said to be proportional to the cube of the thickness. However, even if the copolyester film has a thickness exceeding 20 μm, it still has the characteristics of poor plasticity and flexibility, and can further enjoy the benefits of the present invention. From this point of view, the total thickness of the copolyester film is preferably more than 20 μm, more preferably 23 μm or more, and still more preferably 30 μm or more. On the other hand, the upper limit of the total thickness of the copolyester film is not particularly limited. It is preferably 1000 μm or less, more preferably 500 μm or less, still more preferably 250 μm or less, and still more preferably 100 μm or less.

＜Physical properties of this copolyester film＞ The copolyester film preferably has a storage elastic modulus of 2500 MPa or less at 25°C. By setting the storage elastic modulus at 25°C, that is, normal temperature, to 2500 MPa or less, for example, a wearable terminal can fully follow the skin. From this point of view, the storage elastic modulus of the present copolymerized polyester film at 25° C. is preferably 2,500 MPa or less, more preferably 2,000 MPa or less, and still more preferably 1,200 MPa or less. From a rational viewpoint in the process, the storage elastic modulus at 25° C. is preferably 300 MPa or more, more preferably 500 MPa or more, and further more preferably 700 MPa or more. In addition, the storage elastic modulus at 25°C is a value obtained by the measurement method described in the Examples described below.

In the present copolymerized polyester film, in order to make the storage elastic modulus at 25° C. fall within the above range, this can be achieved, for example, by adjusting the type and content of the copolymerized component of copolymerized polyester A. Moreover, as mentioned above, it can also be adjusted by laminating a polyester layer (II layer) containing polyester C as a main component resin on both front and back sides of the copolymerized polyester layer (I layer). A laminated film composed of it. Furthermore, it can also be adjusted by the stretching conditions when producing the copolyester film of the present invention and the subsequent heat fixing conditions. However, it is not limited to these methods.

In addition, the copolyester film preferably has a storage elastic modulus at 120°C of 10 MPa or more. By setting the storage elastic modulus at high temperature to 10 MPa or more, it can have sufficient heat resistance and suppress the occurrence of wrinkles during processing. From this point of view, the storage elastic modulus of the present copolymerized polyester film at 120° C. is preferably 10 MPa or more, more preferably 30 MPa or more, and still more preferably 50 MPa or more. From the viewpoint of suppressing heat required for processing, the storage elastic modulus of this copolyester film at 120°C is preferably 500 MPa or less, more preferably 400 MPa or less, and further more preferably 300 MPa or less. . In addition, the storage elastic modulus at 120°C is a value obtained by the measurement method described in the Examples described below. In the present copolymerized polyester film, the method for adjusting the storage elastic modulus at 120°C to the above range may be the same method as the method described above as the method for adjusting the storage elastic modulus at 25°C. Among them, the method of adjusting the stretching conditions and subsequent heat fixing conditions is particularly effective. However, it is not limited to this method.

The copolyester film preferably has a loss tangent (tanδ) of 0.02 or more at 25°C. By setting the loss tangent at 25°C, which is normal temperature, to be 0.02 or more, for example, when wearing a wearable terminal, it can fully follow the skin. From this point of view, the loss tangent of the copolyester film at 25° C. is preferably 0.05 or more, more preferably 0.08 or more, and still more preferably 0.10 or more. Furthermore, from a rational viewpoint in the step, the loss tangent (tanδ) at 25° C. is preferably 1.5 or less, more preferably 1.0 or less, and even more preferably 0.5 or less.

In the present copolymerized polyester film, the method for adjusting the loss tangent at 25° C. to the above range can be the same method as the method described above as a method for adjusting the storage elastic modulus at 25° C. Among them, the method of adjusting by adjusting the type and content of the copolymerized component of copolyester A is particularly effective. However, it is not limited to this method.

When the copolymer polyester A is crystalline, the crystallization melting enthalpy ΔHm of the present copolyester film is preferably 3.0 J/g or more, more preferably 5.0 J/g or more, and even more preferably 7.0 J/g or more. . ΔHm is an index of crystallinity. By setting it to 3.0 J/g or more, sufficient heat resistance can be obtained and thermal shrinkage can be suppressed.

The "flexibility (plasticity)" of this copolymer polyester film was measured by the deflection measurement method described in the Examples described below, that is, the length of the vertical direction decrease is (a), and the horizontal direction protrusion length is (a). In the case of b), the ratio of (a) to (b) ((a)/(b)) is preferably 0.3 or more, more preferably 0.5 or more, and still more preferably 1.0 or more. It is suggested that by making the above (a)/(b) 0.3 or more, the film has sufficient flexibility. On the other hand, the upper limit of the above-mentioned (a)/(b) is not particularly limited. From a rational point of view in the process, it is preferably 15.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less. .

In this copolyester film, in order to adjust (a)/(b) to the above range, the key is to first adjust the thickness of the film. Secondly, for the same film thickness, the type of copolymer component of copolyester A can be adjusted. Achieved with content. However, it is not limited to this method. From this point of view, the copolymerized component of copolyester A is preferably an aliphatic dicarboxylic acid or dimer acid, and its content is preferably 5 mol% or more and 20 mol% or less. On the other hand, the above-mentioned "other alcohol component" is preferably diethylene glycol, and its content is preferably 1 mol% or more and less than 25 mol%.

＜Manufacturing method of this copolyester film＞ As an example of the manufacturing method of this copolyester film, the case where this copolyester film is a biaxially stretched film is demonstrated. However, it is not limited to the manufacturing method described here.

It can be produced as follows: first, feed raw materials such as polyester chips to a melt extrusion device by a known method, heat it to above the melting point of each polymer, extrudate the molten polymer from the mold, and place it in a rotating cooling cylinder. The above is cooled and solidified at a temperature below the glass transition point of the polymer to obtain an unaligned sheet that is essentially amorphous. Secondly, the non-aligned sheet is unidirectionally extended through a roller or tenter stretching machine. At this time, the stretching temperature is usually 25 to 120°C, preferably 35 to 100°C, and the stretching ratio is usually 2.5 to 7 times, preferably 2.8 to 6 times. Secondly, extend in a direction orthogonal to the extension direction of the first stage. At this time, the stretching temperature is usually 50 to 140°C, and the stretching ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. Then, the copolymer polyester film as a biaxial alignment film can be obtained by performing heat fixing treatment at a temperature of 130 to 270°C under tension or under relaxation within 30%. Furthermore, in the above-mentioned stretching, a method of unidirectional stretching in two or more stages may also be used.

In the case of a single layer including a copolyester layer (layer I), the above-mentioned heat fixing treatment (also referred to as "heat treatment") is preferably performed at a temperature 10 to 70°C lower than the melting point of copolyester A.

When the copolymerized polyester film has a laminated structure of a copolymerized polyester layer (layer I) and a polyester layer (layer II), the copolymerized polyester layer (layer I) and the polyester layer (layer II) are co-extruded. Finally, as mentioned above, it is sufficient to perform stretching and heat fixing processes as an integrated film. The heat setting treatment at this time is preferably performed by heating to a temperature lower than the melting point of polyester C. Furthermore, when the copolymerized polyester A is crystalline, it is preferable to perform heat setting treatment at a temperature higher than the melting point of the copolymerized polyester A. By performing heat fixation treatment at this temperature, it can be softened to a level that cannot be achieved by a single layer of the copolyester layer (layer I). The reason for this is that by heat-setting at a temperature lower than the melting point of polyester C, the extension orientation of the surface layer is fixed, so the elongation, strength, and heat resistance (heat shrinkage) become good. On the other hand, by Thermal fixation is carried out at a temperature higher than the melting point of copolyester A, which relaxes the extension orientation or strain of the middle layer, so that a more flexible film can be made.

＜Use of this copolyester film＞ As mentioned above, this copolymerized polyester film has the characteristics of being excellent in flexibility at normal temperature and not only being soft but also having almost no plasticity. On the other hand, it can exhibit sufficient heat resistance for practical use despite this. Therefore, it can be suitably used as, for example, battery packaging materials, surface protective films, image display members, particularly structural members of flexible displays, wearable terminals, and the like. In addition, the uses of this copolyester film are not limited to the above, and can be used, for example, in various packaging materials, building materials, stationery, automobile components, and other structural components.

＜Explanation of statements, etc.＞ In the present invention, even when it is called a "film", it also includes a "sheet", and even when it is called a "sheet", it also includes a "film". In addition, when it is expressed as a "panel" such as an image display panel, a protective panel, etc., it includes a board, a sheet, and a film.

In the present invention, when it is described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "more than X and less than Y", and also includes "preferably greater than X". ” or “preferably less than Y” means. In addition, when it is described as "more than X" (X is an arbitrary number), unless otherwise specified, it includes the meaning of "preferably greater than In this case, unless otherwise specified, it also includes the meaning of "preferably less than Y". [Example]

Next, the present invention will be further described in detail through examples. However, the present invention is not limited to the Examples described below.

＜Evaluation method＞ Hereinafter, various physical properties and the like are measured and evaluated in the following manner.

(1)Storage elastic modulus E', tangent loss tanδ Based on JIS K 7244, using the dynamic viscoelasticity measuring device DVA-200 manufactured by IT Meter. and Control, Inc., the width direction (TD) of the copolyester film (sample) was measured with a vibration frequency of 10 Hz, a strain of 0.1%, The temperature rise rate is 1°C/min from -100°C to 200°C. Based on the obtained data, the storage elastic modulus E' at 25°C and 120°C and the tangent loss tanδ at 25°C are obtained.

(2) Crystallization melting enthalpy ΔHm Based on JIS K7141-2 (2006), differential scanning calorimeter (DSC) measurement of the measurement sample was performed. After raising the temperature from 30°C to 280°C at 10°C/min, hold it for 1 minute, then lowering the temperature from 280°C to 30°C at 10°C/min, hold it for 1 minute, and then raise the temperature from 30°C to 280°C at 10°C/min. ℃. At this time, the crystallization melting enthalpy (ΔHm) is calculated based on the crystallization melting peak area during the reheating process. In addition, in the case of a single layer, the copolyester film is used as the measurement sample, and in the case of lamination, the intermediate layer is used as the measurement sample.

(3)Young’s modulus The copolyester films (samples) obtained in the Examples and Comparative Examples were tested with a tensile testing machine (Intesco Model 2001 manufactured by Intesco Co., Ltd.) at a temperature of 23° C. and a humidity of 50% RH in a room adjusted to 10% The strain rate / minute of a copolyester film (sample) stretched with a length of 300 mm and a width of 20 mm is calculated by the following formula using the initial straight line part of the tensile stress-strain curve. E=Δσ/Δε (In the above formula, E is Young's modulus (GPa), Δσ is the stress difference between the original average cross-sectional area (GPa) between two points of the straight line, and Δε is the strain difference/initial length between the same two points)

(4) Tensile breaking strength The copolyester films (samples) obtained in Examples and Comparative Examples were adjusted to a temperature of 23°C and a humidity of 50% using a tensile testing machine (Intesco Model 2001 manufactured by Intesco Co., Ltd.). In the room of RH, place the copolyester film (sample) with a width of 15 mm in the testing machine so that the distance between the clamps is 50 mm, and apply a strain rate of 200 mm/min in the length direction (MD) or width direction ( TD), and the tensile breaking strength was determined by the following formula. Tensile breaking strength (MPa) = F/A where, in the above formula, F is the load (N) applied when breaking, and A is the original cross-sectional area of the test piece (mm ² ).

(5) Tensile elongation at break The same test as the above-mentioned tensile breaking strength was performed, and the tensile breaking elongation of the copolyester films (samples) obtained in Examples and Comparative Examples was determined by the following formula. Tensile elongation at break (%) = 100×(L-L0)/L0 Among them, in the above formula, L is the gauge length at break (mm), and L0 is the original gauge length (mm).

(6) Heating shrinkage The copolyester films (samples) obtained in the Examples and Comparative Examples were placed in an oven maintained at 120°C for 5 minutes in a tension-free state, and the lengths of the samples before and after were measured. The film was calculated by the following formula The respective heating shrinkage rates in the length direction (MD) and width direction (TD). Heating shrinkage (%) = {(L0-L1)/L0}×100 (In the above formula, L0 is the sample length before heat treatment, L1 is the sample length after heat treatment) Five points were measured in each of the length direction (MD) and width direction (TD) of the film, and the average value was calculated.

(7) Evaluation of flexibility (plasticity) (flexure measurement method) Samples were prepared as follows: After leaving the copolyester films (samples) obtained in Examples and Comparative Examples for 24 hours in an atmosphere of 23°C and 50% RH, they were cut into sizes of 150 mm in length and 50 mm in width. . As shown in Figure 1, the copolyester film (sample) is placed on the table in an environment of 23°C in such a manner that it protrudes 50 mm from the edge of the table, and the copolyester film (sample) on the table ) and fix it by placing a 200 g weight on it, so that the front end side of the sample protruding from the edge of the table is deflected downward by its own weight. After 3 minutes, measure the length (a) of the front end of the sample that protrudes from the table edge and flexes vertically downward and droops, and the length of the front end that protrudes from the table edge in the horizontal direction (b). Then, calculate the ratio ((a)/(b)) of the length (a) that bends and sag relative to the length (b) that protrudes in the horizontal direction. If it is 0.30 or more, it is evaluated as "passed". If it is not 0.30, the evaluation is "unqualified".

(raw material) The following raw materials were used in Examples and Comparative Examples.

Copolyester 1 ("Co-PS1"): The acid component contains 88 mol% of terephthalic acid, 7 mol% of hydrogenated dimer acid with a carbon number of 36 and 5 mol% of isophthalic acid, and the glycol component contains ethyl alcohol. Crystalline copolyester with 90 mol% glycol and 10 mol% diethylene glycol. The melting point is 208°C and the intrinsic viscosity is 0.68 dl/g.

Copolyester 2 ("Co-PS2"): The acid component contains 88 mol% of terephthalic acid and 12 mol% of hydrogenated dimer acid with a carbon number of 36, and the glycol component contains 67 mol% of ethylene glycol and 1, Crystalline copolyester with 33 mol% of 4-butanediol (less than 0.1 mol% of by-product diethylene glycol). The melting point is 200°C and the intrinsic viscosity is 0.72dl/g.

Copolyester 3 ("Co-PS3"): The acid component contains 78 mol% of terephthalic acid and 22 mol% of isophthalic acid, and the glycol component contains 98 mol% of ethylene glycol and the by-product diethylene glycol 2 mol% crystalline copolyester. The melting point is 198°C and the intrinsic viscosity is 0.70 dl/g.

Polyester ("PET"): polyethylene terephthalate (by-product diethylene glycol: 2 mol%). The melting point is 250°C and the intrinsic viscosity is 0.64 dl/g.

[Example 1] As the surface layer and the middle layer, the fragments of copolyester 1 (PS1 in total) are fed into an extruder with a vent set at 280°C, and are extruded from the nozzle of the extruder through a gear pump and filter. , use the electrostatic application bonding method to perform rapid cooling and solidification on a cooling roll with the surface temperature set to 30°C to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched 3.3 times at 50°C in the longitudinal direction (MD), and then introduced into a tenter, and then stretched 4.2 times at 80°C in the width direction (TD), and then stretched at 200°C. Heat treatment was performed for 10 seconds, and the film was relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolyester film (sample) with a thickness of 25 μm that essentially comprised a single layer.

[Example 2] As an intermediate layer, pieces of copolyester 1 (co-PS1) were fed into a twin-screw extruder with main vents set at 280°C. Moreover, as a surface layer, polyester (PET) pieces were sent to a twin-screw extruder with a vent set to 280°C. Through the gear pump and filter, the polymer from the main extruder becomes the middle layer, and the polymer from the sub-extruder becomes the surface layer. Two types of three-layer (surface layer/middle layer/surface layer) are used for coexistence. It was extruded from a nozzle, and the electrostatic bonding method was used to perform rapid cooling and solidification on a cooling roll with a surface temperature set to 30° C. to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched 3.2 times in the longitudinal direction (MD) at 80°C, and then introduced into a tenter, and then stretched 4.0 times in the width direction (TD) at 100°C, and then stretched at 200°C. Heat treatment was carried out for 10 seconds and relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolymer with a thickness of 25 μm consisting of a thickness of 1 μm (surface layer)/23 μm (middle layer)/1 μm (surface layer). Ester film (sample).

[Examples 3 to 5] A biaxially stretched copolyester film (sample) was obtained in the same manner as in Example 2, except that the conditions were changed to those shown in Table 1. Furthermore, in the table, for example, "Total PS1/PET=80/20" in Example 3 means that 80 parts by mass of PS1 and 20 parts by mass of PET are mixed, and the mass ratio is expressed similarly in other examples.

[Comparative example 1] The polyester (PET) fragments are fed into an extruder with a vent set at 280°C, and are extruded from the nozzle of the extruder through a gear pump and filter. Use electrostatic application to seal the surface. Rapid cooling and solidification are performed on a cooling roll with a temperature set to 30°C to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched 3.5 times in the longitudinal direction (MD) at 86°C, and then introduced into the tenter, and then stretched 4.3 times in the width direction (TD) at 110°C, and then stretched at 235°C. Heat treatment was carried out for 10 seconds, and the film was relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolyester film (sample) with a thickness of 50 μm.

[Comparative example 2] A total of 85 parts by mass of PS3 fragments and 15 parts by mass of PET fragments were mixed and fed into an extruder with a vent set at 280°C, through a gear pump, a filter, and from the nozzle of the extruder. After extrusion, the electrostatic application bonding method was used to perform rapid cooling and solidification on a cooling roll with the surface temperature set to 30°C to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched 3.4 times in the length direction (MD) at 80°C, and then introduced into the tenter, and then stretched 3.9 times in the width direction (TD) at 145°C, and then stretched at 186°C. Heat treatment was carried out for 10 seconds, and the film was relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolyester film (sample) with a thickness of 50 μm.

[Comparative example 3] The fragments of copolyester 2 (co-polyester 2) are fed into an extruder with a vent set at 280°C. They are extruded from the nozzle of the extruder through a gear pump and filter, and the electrostatic sealing method is used. Rapid cooling and solidification were performed on a cooling roll with a surface temperature set to 30° C. to obtain an unstretched copolyester film (sample) with a thickness of 200 μm.

[Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative example 1 Comparative example 2 Comparative example 3 Surface layer (II layer) Total PS1 PET PET PET PET - - - Middle layer (I layer) Total PS1 Total PS1 Total PS1/PET＝80/20 Total PS1/Total PS2=80/20 Total PS1/Total PS2=50/50 PET Total PS3/PET＝85/15 Total PS2 Other dicarboxylic acid ingredients [mol%] 12 12 9.6 12 12 0 18.7 12 Other alcohol ingredients [mol%] 10 10 8.4 14.6 21.5 2 2 33 Layer composition (thickness ratio) [-] 4/17/4 1/23/1 1/23/1 1/23/1 1/23/1 - - - thickness [μm] 25 25 25 25 25 50 50 200 Extension ratio MD [times] 3.3 3.2 3.2 3.2 3.2 3.5 3.4 - TD [times] 4.2 4.0 4.0 4.0 4.0 4.3 3.9 - extension temperature MD [℃] 50 80 80 80 80 86 80 - TD [℃] 80 100 100 100 100 110 145 - Heat treatment temperature [℃] 200 200 200 200 200 235 186 - Store elastic modulus 25℃ [MPa] 2100 1600 2400 1400 1100 4800 3800 320 120℃ [MPa] 55 140 160 150 150 1300 66 5.3 tanδ 25℃ [-] 0.09 0.11 0.06 0.13 0.15 0.01 0.01 0.50 ⊿Hm* [J/q] 17.4 7.7 26.7 16.1 14.4 33.3 13.2 8.9 Young's modulus MD [GPa] 1.7 1.4 2.2 1.1 0.8 4.7 4.1 0.4 TD [GPa] 1.8 1.3 2.3 1.1 0.8 5.1 4.4 - Breaking strength MD [MPa] 106 45 82 40 40 244 154 13 TD [MPa] 135 46 116 43 40 273 168 - Elongation at break MD [%] 204 115 146 110 108 162 220 1229 TD [%] 152 130 142 105 98 136 204 - Heating shrinkage (120℃×5 min) MD [%] 1.9 2.0 1.7 1.6 1.4 0.8 2.1 0.8 TD [%] 0.2 -0.1 1.0 1.1 1.0 -0.2 0.4 0.7 Flexibility (plasticity) (a) [mm] 43 42 41 46 44 12 14 3 (b) [mm] 25 18 18 12 13 47 48 49 (a)/(b) [-] 1.72 2.33 2.28 3.83 3.38 0.26 0.29 0.06 *In the case of stacking layers, it is the middle layer

According to the above-mentioned Examples and the test results conducted by the inventors so far, it is known that for a copolyester film having a copolyester layer (layer I) containing the above-mentioned copolyester A as the main component resin, by storing at 25°C The elastic modulus is less than 2500 MPa, and it has excellent softness at room temperature. It is not only soft but also more flexible. However, it also has elongation and strength. Furthermore, by setting the storage elastic modulus at 120°C to 10 MPa or more, it is possible to obtain practically sufficient heat resistance.

As in Examples 2 to 5, it was confirmed that when the main component resin of the intermediate layer is crystalline copolymerized polyester, it is confirmed that the polyester as the main component resin of the surface layer has a melting point higher than the melting point of the copolymerized polyester. In polyester, compared with the case of a single layer consisting only of the above-mentioned intermediate layer, the heat treatment (heat setting) temperature after stretching can be further increased, and the heat shrinkage can be further suppressed. Furthermore, when the main component resin of the intermediate layer is an amorphous copolymerized polyester, it is considered that if the polyester as the main component resin of the surface layer is a polyester with a melting point higher than the glass transition point of the above-mentioned copolymerized polyester, , compared with the case of a single layer composed only of the above-mentioned intermediate layer, the heat treatment (heat fixing) temperature after stretching can be further increased, so the thermal shrinkage can be further suppressed.

FIG. 1 is a diagram schematically showing a method of measuring deflection performed in Examples.

Claims (17)

A copolymerized polyester film, characterized in that it is provided with a copolymerized polyester layer (I layer) containing copolymerized polyester A as a main component resin, and the above-mentioned copolymerized polyester A is composed of terephthalic acid and "other dicarboxylic acid components" "A copolymer with ethylene glycol and "other alcohol components". The above-mentioned "other dicarboxylic acid components" include aliphatic dicarboxylic acid or dimer acid. In this copolymer, "other dicarboxylic acid components" are in two The proportion of the carboxylic acid component in the alcohol component is greater than 5 mol% and less than 20 mol%, and the proportion of "other alcohol components" in the alcohol component is more than 1 mol% and less than 25 mol%. The above copolymer polyester film is stored at 25°C The elastic modulus is below 2500MPa, and the storage elastic modulus at 120°C is above 10MPa. The copolyester film of claim 1, wherein the copolyester layer (layer I) is a layer including the copolyester A and a resin B that is compatible with it. For example, the copolyester film of claim 2, wherein the above-mentioned resin B contains one or more types of polyester, and the polyester contains terephthalic acid and "other dicarboxylic acid components" and ethylene glycol and "other The ratio of the total content of "alcohol components" and "other dicarboxylic acid components" to the total content of dicarboxylic acid components is 5 mol% or more and less than 20 mol%, and the ratio of the total content of "other alcohol components" to the total content of alcohol components The ratio is 1 mol% or more and less than 25 mol%. A copolymerized polyester film, characterized in that it contains one or more than two kinds of polyesters. For the copolymerized polyester layer (layer I), among all the polyesters contained in the copolymerized polyester layer (layer I), the total content of "other dicarboxylic acid components" accounts for the total content of the dicarboxylic acid components The ratio of the total content of "other alcohol components" is more than 5 mol% and less than 20 mol%, and the ratio of the total content of "other alcohol components" to the total content of alcohol components is more than 1 mol% and less than 25 mol%. The above "other dicarboxylic acid components" are for Dicarboxylic acid components other than phthalic acid, the above-mentioned "other alcohol components" are alcohol components other than ethylene glycol, the above-mentioned "other dicarboxylic acid components" include aliphatic dicarboxylic acids or dimer acids, and the above-mentioned copolyester film The storage elastic modulus at 25℃ is less than 2500MPa, and the storage elastic modulus at 120℃ is more than 10MPa. The copolyester film of any one of claims 1 to 4, wherein the "other dicarboxylic acid component" includes isophthalic acid, and aliphatic dicarboxylic acid or dimer acid. The copolyester film of any one of claims 1 to 4, wherein the "other dicarboxylic acid component" includes isophthalic acid, and aliphatic dicarboxylic acid or dimer acid with a carbon number of 20 to 80. The copolyester film according to any one of claims 1 to 4, wherein the "other dicarboxylic acid components" include isophthalic acid and dimer acid. The copolyester film according to any one of claims 1 to 4, wherein the "other alcohol component" includes diethylene glycol. The copolyester film according to any one of claims 1 to 4, wherein the copolyester A is a dicarboxylic acid component containing terephthalic acid, isophthalic acid and dimer acid and a dicarboxylic acid component containing ethylene glycol and diethylene glycol. For copolymers of diol alcohol components, the total ratio of isophthalic acid and dimer acid in the dicarboxylic acid component is greater than 5 mol% and less than 20 mol%, and the ratio of diethylene glycol in the alcohol component is 1 mol% or more and 50 mol% or less, and the above-mentioned copolyester A is a crystalline copolyester. The copolyester film of any one of claims 1 to 4, wherein the dimer acid is a dicarboxylic acid containing a dimer of unsaturated fatty acid and the number of carbon atoms of the unsaturated fatty acid is 20 to 80. The copolyester film according to any one of claims 1 to 4, wherein the dimer acid is a hydrogenated dimer acid obtained by dimerizing different or identical unsaturated fatty acids and then hydrogenating them. The copolyester film according to any one of claims 1 to 4, which has a polyester layer (II layer) containing polyester C as the main component resin laminated on both sides of the front and back sides of the copolyester layer (I layer). When the copolyester A is crystalline, the polyester C is a polyester with a higher melting point than the copolyester A. When the copolyester A is amorphous, , the polyester C is a polyester having a melting point at a temperature higher than the glass transition point of the copolyester A. For example, the copolyester film of claim 12, wherein the thickness of each layer of the polyester layer (layer II) is 1 to 20% of the thickness of the copolyester layer (layer I). For example, the copolyester film of any one of claims 1 to 4 has a loss tangent (tanδ) at 25°C of 0.02 or more. The copolyester film of any one of claims 1 to 4, wherein the total thickness of the film exceeds 20 μm. A surface protection film using the copolyester film according to any one of claims 1 to 15. An optical member using the copolyester film according to any one of claims 1 to 15.

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