JP7192869B2 - Copolyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a copolymer polyester film having a copolymer polyester layer containing a copolymer polyester as a main component resin.

Polyethylene terephthalate (PET) film, which is a typical polyester film, especially biaxially stretched PET film, is excellent in transparency, mechanical strength, heat resistance, flexibility, etc. It is used in various fields such as packaging materials.

Regarding this type of polyester film, for example, in Patent Document 1, as a softened polyester film that expresses softness not found in conventional polyester films and has excellent moldability under relatively low temperature and low pressure, the elastic modulus of the film E ' is 20 MPa or less at 120° C. and 5 MPa or less at 180° C., has a film haze of 1.0% or less, and contains 29 to 32 mol % of 1,4-cyclohexanedimethanol units as a diol component. , proposed a softened polyester film characterized by not containing an isophthalic acid unit as a dicarboxylic acid constituent.

Further, Patent Document 2 proposes an image-receiving sheet for thermal transfer, which is obtained by laminating an image-receiving layer comprising a copolymerized polyester layer having a copolymerization rate of 5 to 30 mol % on at least one side of a polyester film.
Furthermore, in Patent Document 3, the average particle size is 0.1 to 2.5 μm, the pore volume is 0.05 to 2.5 ml/g, the specific surface area is 50 to 600 m ² /g, and the compression resistance is 1 to 100 MPa. A biaxially oriented film made of a copolymer polyester containing 0.05 to 5.0% by weight of a lubricant, the biaxially oriented film having an intrinsic viscosity of 0.50 to 0.80 dl/g and a glass transition point of 70° C. or higher, a melting point of 210 to 250° C., and the biaxially oriented film contains at most 10 particles/mm ² of coarse particles of the lubricant having a particle size of 20 μm or more. A polyester film for molding has been proposed.

In addition, in Patent Document 4, it is made of a copolymer polyester containing 1 to 20 mol % of an aliphatic dicarboxylic acid component relative to the total acid component, and the film strength F ₁₀₀ at 100% elongation in an atmosphere of 150 ° C. is 0.00. A biaxially oriented polyester film for molding has been proposed, characterized by having a weight of 5 to 5 kg/mm ² and a thickness variation of the film of 40% or less.
Further, in Patent Document 5, a laminated film in which a polyester (B) layer containing polyester (B) as a main component is laminated on at least one side of a polyester (A) layer containing polyester (A) as a main component, A laminated polyester film has been proposed in which the laminated film has an elastic modulus of 20 to 1000 MPa in an atmosphere of 23° C., an elastic modulus of 10 to 200 MPa in an atmosphere of 120° C., and is substantially non-oriented. there is

2. Description of the Related Art In recent years, as an image display device, attention has been paid to a computer (wearable computer) that is small enough to be worn on the body due to the miniaturization and high performance of mobile terminals.
Ideally, an electronic device (wearable terminal) used in a wearable computer should be attached to a personal item such as a wristwatch (Patent Document 6).

In addition, as a next-generation image display device, a flexible display that can be freely bent is attracting attention. 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 must have optical properties and durability in addition to those required for conventional flat display panels. It is required that no breakage occurs even after bending test.

JP 2014-169371 A JP-A-04-086293 JP-A-2000-001552 JP-A-03-067629 International Publication No. 09/078304 JP 2014-134903 A

As mentioned above, when considering the use of polyester film for wearable terminals and flexible displays, it is not only flexible but also more flexible than polyester films that have been commonly used in the past. There was a need to develop a polyester film that had elongation and strength. In addition, it was necessary to have heat resistance so that it would not shrink when heated.

Therefore, the object of the present invention is to provide a new copolymerized polyester film that is more flexible and supple than polyester films that have been generally used in the past, and yet has both elongation, strength and heat resistance. to provide.

The present invention provides a copolymer polyester film comprising a copolymer polyester layer (layer I) containing a copolymer polyester A as a main component resin,
The copolymer polyester A is a copolymer of terephthalic acid and "other dicarboxylic acid components" and ethylene glycol and "other alcohol components". The proportion of "acid component" is 5 mol% or more and 20 mol% or less, and the proportion of "other alcohol components" in the alcohol component is 1 mol% or more and less than 25 mol%,
A copolymer polyester film is proposed 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.

The present invention also provides a copolymer polyester film comprising a copolymer polyester layer (I layer) containing one or more polyesters,
In all the polyester contained in the copolymer polyester layer (I layer), 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% or less, and the alcohol component The ratio of the total content of "other alcohol components" to the total content is 1 mol% or more and less than 25 mol%,
A copolymer polyester film is proposed 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.

The copolyester film proposed by the present invention has excellent flexibility at room temperature, is not only flexible but also more supple, yet has elongation and strength, and is practically sufficient. heat resistance. Therefore, the copolymer polyester film proposed by the present invention can be suitably used, for example, as a component for battery packaging materials, image display members, particularly flexible displays and wearable terminals.

FIG. 2 is a diagram schematically showing a method of measuring deflection performed in Examples.

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

<This copolymer polyester film>
A copolymerized polyester film (referred to as "the present copolymerized polyester film") according to an example of the embodiment of the present invention is a single layer having a copolymerized polyester layer (I layer) containing copolymerized polyester A as a main component resin. Or it is a laminated film.

The copolymer polyester film may be a non-stretched film (sheet) or a stretched film. Among them, stretched films uniaxially or biaxially stretched are preferred. Among them, a biaxially stretched film is preferable from the viewpoint of excellent balance of mechanical properties and flatness. If the present copolymer polyester film is such a stretched film, it tends to be easy to make the storage elastic modulus at 120° C. 10 MPa or more.

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

Here, the above-mentioned "main component resin" means the resin having the highest content ratio among the resins constituting the copolyester layer (I layer). The main component resin may account for 30% by mass or more, particularly 50% by mass or more, and 80% by mass or more (including 100% by mass) of the resins constituting the copolyester layer (I layer).

The copolyester layer (layer I) may consist of the copolyester A only, or may contain a resin B other than the copolyester A.
At this time, the resin B is preferably a resin compatible with the copolymer polyester A.
The case where the copolyester layer (layer I) contains the copolyester A and the resin B compatible therewith will be described later.

(Copolyester A)
The copolymer polyester A is preferably a copolymer polyester which is 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 the present invention, the crystalline polyester resin generally refers to a polyester resin that is said to have a crystalline melting peak temperature (melting point). It includes polyester resins whose melting point is observed in scanning calorimetry (DSC) and is in a so-called semi-crystalline state. Conversely, a thermoplastic resin for which no melting point is observed in DSC is called "amorphous." A crystalline polyester generally refers to a polyester having a crystalline melting peak temperature (melting point). More specifically, it includes a polyester whose melting point is observed in differential scanning calorimetry (DSC) according to JIS K7121 (1987) and is in a so-called semi-crystalline state.
Conversely, a thermoplastic resin for which no melting point is observed in DSC is called "amorphous."

Examples of the "other dicarboxylic acid components" include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, and polyfunctional acids. Two or more kinds of "other dicarboxylic acid components" may be used in combination. By using two or more of them in combination, not only can the copolymerized polyester film be more effectively softened, but also the crystal structure can be maintained, and heat resistance can be obtained in some cases.
Among them, from the viewpoint of facilitating the softening of the present copolymer polyester film, "other dicarboxylic acid components" include aromatic dicarboxylic acids such as isophthalic acid, 2,6-naphthalene dicarboxylic acid and diphenyldicarboxylic acid, adipic acid, and sebacine. acids, aliphatic dicarboxylic acids such as dodecanedioic acid, eicoic acid and their derivatives, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid, cyclooctanedicarboxylic acid, or Dimer acid is preferred. Among them, it is preferable to contain an aliphatic dicarboxylic acid or a dimer acid.
Among the aliphatic dicarboxylic acids, aliphatic dicarboxylic acids having 20 to 80 carbon atoms, preferably 30 or more or 60 or less, especially 36 or more or 48 or less, are particularly preferable from the viewpoint of further lowering the glass transition temperature.

As the dimer acid, a dicarboxylic acid composed of a dimer of an unsaturated fatty acid and having 18 or more carbon atoms in the unsaturated fatty acid is preferable. Examples of such dimer acids include those dimerized with different or identical unsaturated fatty acids selected from oleic acid, elaidic acid, cetoleic acid, erucic acid, brassic acid, linoleic acid, linolenic acid, etc. can be mentioned. Furthermore, hydrogenated products after such dimerization can also be used. The dimer acid may contain an aromatic ring, an alicyclic monocyclic ring, or an alicyclic polycyclic ring.
Among such dimer acids, dimer acids having 20 to 80 carbon atoms, preferably 26 or more or 60 or less, especially 30 or more or 50 or less, are preferable from the viewpoint of further lowering the glass transition temperature.

As described above, "another dicarboxylic acid component" can be arbitrarily selected. Among them, it is preferable to select one or more kinds from aromatic dicarboxylic acids and select one or more kinds from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and dimer acids and use them together. Among them, it is particularly preferable to contain two or more of isophthalic acid, aliphatic dicarboxylic acid and dimer acid, and more particularly two or more of isophthalic acid, aliphatic dicarboxylic acid having 20 to 80 carbon atoms and dimer acid. is particularly preferred.
When an aromatic dicarboxylic acid is used as "another dicarboxylic acid component", there is a tendency that the film can be softened while maintaining strength and heat resistance. On the other hand, when selected from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and dimer acids as "other dicarboxylic acid components", the film can be formed at a smaller content ratio while maintaining the elongation (breaking elongation). Softening tends to be possible, and among them, the use of dimer acid is the most effective. Therefore, by combining and using "another dicarboxylic acid component" as described above, it is possible to obtain a film that satisfactorily combines strength, heat resistance, elongation and flexibility.

In the copolymer polyester A, the ratio of the "other dicarboxylic acid component" to the total of the dicarboxylic acid component, that is, the terephthalic acid and the "other dicarboxylic acid component" is preferably 5 to 20 mol%, especially 8 mol% or more. Alternatively, it is 18 mol % or less, more preferably 10 mol % or more or 15 mol % or less. Here, when two or more of the "other dicarboxylic acid components" are used in combination, the total amount thereof is meant.
When the ratio of the "other dicarboxylic acid component" is within the above range, the copolymer polyester film tends to be effectively softened while having good elongation, strength and heat resistance.

Examples of the above-mentioned "other alcohol components (diol components)" include 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, bisphenol and their Derivatives etc. can be mentioned. Among them, diethylene glycol is preferable from the viewpoint of flexibility, and 1,4-butanediol is preferable from the viewpoint of heat resistance and strength.
Generally, when polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, part of the ethylene glycol is modified into diethylene glycol and introduced into the polyester skeleton. This diethylene glycol is called by-product diethylene glycol, and the amount of the by-product is about 1 to 5 mol % of ethylene glycol, depending on the polycondensation method (ester exchange method, direct polycondensation) and the like. In the present invention, such diethylene glycol by-produced from ethylene glycol is treated as a copolymerization component and included in "other alcohol components".

In the copolymer polyester A, the alcohol component (diol component), that is, the ratio of the "other alcohol component (diol component)" to the total of ethylene glycol and "other alcohol component" is 1 mol% or more and less than 25 mol%. It is preferably 2 mol % or more or 20 mol % or less, and more preferably 3 mol % or more or 18 mol % or less. Here, when two or more types of "other alcohol components" are used in combination, the total amount thereof is meant.
When the proportion of the "other alcohol component" is within the above range, the copolymer polyester film tends to be effectively softened while having good elongation, strength and heat resistance.
In addition, "another alcohol component" may use 2 or more types together. By using two or more kinds together, the copolymer polyester film can be softened more effectively in some cases.

In addition, it is preferable to use three or more of "other dicarboxylic acid components" and "other alcohol components" in total. By using a plurality of copolymer components in combination, there is a tendency that the film can be softened with a smaller content ratio. In addition, if there are too many types of copolymer components, it may be difficult to stabilize the properties of the film. It is preferable that it is a seed|species, and it is especially preferable that it is 3 types or 4 types.

Copolyester A, which is particularly preferred among the above, is a copolymer of terephthalic acid, isophthalic acid, aliphatic dicarboxylic acid or dimer acid, and ethylene glycol and diethylene glycol, and is isophthalic acid in the dicarboxylic acid component constituting the copolymer polyester. A crystalline copolyester in which the proportion of an acid, an aliphatic dicarboxylic acid, or a dimer acid is 5 mol% or more and 20 mol% or less, and the proportion of diethylene glycol in the alcohol component constituting the copolyester is 1 mol% or more and less than 25 mol%. Aa can be mentioned.
Generally, copolyesters become less crystalline when the ratio of the copolymer components is increased in order to lower the elastic modulus, and become amorphous when the ratio is further increased. The copolymer polyester Aa has a high ratio of the copolymer component and can achieve a low elastic modulus, but maintains crystallinity, so that it can be heat-set by heat treatment after stretching. As a result, the copolyester Aa is flexible, yet has good elongation and strength, and can suppress heat shrinkage.

(Resin B)
As described above, the copolyester layer (layer I) may be a layer containing copolyester A and resin B compatible therewith.
In the present invention, the term "compatible" means a state in which two or more resins are completely mixed at the molecular level. At this time, the amorphous regions mixed at the molecular level can be regarded as a single phase, and the micro-Brownian motion also occurs at a single temperature. Therefore, when two or more resins are compatible, the mixed resin of the two or more resins has a single melting point or a single glass transition temperature, and also has a single principal dispersion peak. Therefore, conversely, a resin that is compatible with copolyester A is defined as a resin that can change the melting point or glass transition temperature of copolyester A when mixed with copolyester A. can also
The glass transition temperature at this time is, for example, a strain of 0.1%, a frequency of 10 Hz, a temperature dispersion measurement of dynamic viscoelasticity under the conditions of a heating rate of 3 ° C./min (Dynamic viscoelasticity measurement of JIS K7244 method ) is the peak temperature of the principal dispersion of the loss tangent (tan δ).

When the copolymer polyester layer (I layer) is a layer containing the copolymer polyester A and the resin B, the resin B is a resin compatible with the copolymer polyester A and has a melting point of 270 ° C. or less, or a non- A resin that is crystalline and has a glass transition temperature of 30 to 120° C. is preferred. By selecting such resin B, the glass transition temperature of the copolyester layer (layer I) can be increased, and the heat resistance can be improved. By selecting a polyester such as polyethylene terephthalate (PET) as the resin B, dimensional stability and heat resistance can be imparted.

Further, from the viewpoint of achieving both flexibility and heat resistance, the resin B contains one or more polyesters, and the polyester (including one or more polyesters) is terephthalic acid, which is a dicarboxylic acid component. and "other dicarboxylic acid components", and the alcohol component ethylene glycol and "other alcohol components", the total content of dicarboxylic acid components (when containing two or more polyesters, the dicarboxylic acid contained in each polyester The ratio of the total content of "other dicarboxylic acid components" to the total of acid components) is 5 mol% or more and 20 mol% or less, more preferably 8 mol% or more or 18 mol% or less, and more preferably 10 mol% or more or 15 mol% or less. Yes, the ratio of the total content of "other alcohol components" to the total content of alcohol components (the total of alcohol components contained in each polyester when two or more polyesters are included) is 1 mol% or more and less than 25 mol%, especially It is preferably 2 mol % or more or 20 mol % or less, and more preferably 3 mol % or more or 18 mol % or less.

The copolyester layer (I layer) may be a layer containing copolyester A and resin D incompatible therewith. Examples of resin D include polyolefin, polystyrene, acrylic resin, and urethane resin.

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

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

<In the case of laminated structure>
The present copolyester film may be a laminated film comprising a copolyester layer (I layer) and other layers, as described above.

For example, a laminated film having a configuration in which a polyester layer (II layer) containing polyester C as a main component resin is laminated on both front and back sides of a copolymer polyester layer (I layer) can be mentioned.
At this time, when the copolyester A is crystalline, the polyester C is preferably a polyester having a melting point higher than that of the copolyester A. When the copolyester A is amorphous, A polyester having a melting point higher than the glass transition point of copolyester A is preferred.

If it is a laminated film having a configuration in which a polyester layer (II layer) containing polyester C as a main component resin is laminated, polyester layer (II layer) / copolymer polyester layer (I layer) / polyester The raw material resin composition is laminated by coextrusion or the like so as to form a layer (II layer), stretched, and then heat-set at a higher temperature than in the case of a single copolyester layer (I layer). Therefore, it is possible to soften to a level that cannot be achieved with a single copolymer polyester layer (I layer), to increase heat resistance, and to further prevent heat shrinkage.
Specifically, the storage elastic modulus of the present copolymer polyester film at 25° C. can be 300 to 2500 MPa, especially 500 MPa or more or 2000 MPa or less.

In the laminated film, the thickness of each layer of the polyester layer (layer II) is preferably 1 to 20% of the thickness of the copolymer polyester layer (layer I).
If the thickness of each layer of the polyester layer (II layer) is 1% or more of the thickness of the copolymer polyester layer (I layer), film formation is possible without greatly impairing productivity, and if it is 20% or less, it is required. It is preferable because it can ensure sufficient flexibility to be used.
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 copolymer polyester layer (layer I), especially 3% or more or 15% or less, especially 5% or more. Alternatively, it is more preferably 12% or less.
In addition, the thickness of the polyester layer (II layer) existing on both the front and back sides of the copolymer polyester layer (I layer) may be different on the front and back, or may be the same.

When the copolymer polyester A is crystalline, the polyester C has a melting point higher than the melting point of the copolymer polyester A by 10 to 100° C., especially 20° C. or more or 90° C. or less, especially 40° C. or more or 70° C. or less. On the other hand, when the copolymer polyester A is amorphous, the glass transition point of the copolymer polyester A is 120 to 260 ° C. higher, especially 140 ° C. or higher or 230 ° C. or lower. A polyester having a melting point higher than 160° C. or lower than 200° C. is preferred.
The polyester C, which is the main component of the polyester layer (II layer) present on both the front and back sides of the copolymer polyester layer (I layer), may be different or the same on the front and back sides. Above all, it is preferable that the melting points of the polyester C on the front and back sides are not significantly different. Specifically, the difference in melting points between the polyester layers (layer II) present on both the front and back sides is preferably 80° C. or less, preferably 60° C. or less, and more preferably 40° C. or less.
When the polyester layer (II layer) present on both the front and back sides of the copolymerized polyester layer A has the same polyester C, co-extrusion molding of two kinds and three layers is possible, and this aspect is also preferable.

As polyester C, 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, it is not limited to this.

When the polyester C is a copolymerized polyester, dicarboxylic acid components other than terephthalic acid include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, and polyfunctional acids.
In the polyester C, the ratio of the "dicarboxylic acid component other than terephthalic acid" to the dicarboxylic acid component is preferably 1 to 30 mol%, especially 5 mol% or more or 25 mol% or less, and among them 10 mol% or more or 20 mol% or less. is more preferable.

When the polyester C is a copolymerized polyester, alcohol components other than ethylene glycol include 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, neopentyl glycol, and 1,4-cyclohexane. Examples include dimethanol, bisphenol and derivatives thereof.
In Polyester C, the ratio of "alcohol components other than ethylene glycol" to the alcohol components is preferably 1 to 100 mol%, especially 5 mol% or more or 95 mol% or less, and among them 10 mol% or more or 90 mol% or less. is more preferred.

<Thickness of the present 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.
Above all, it is preferable that the total thickness of the film exceeds 20 μm from the viewpoint of exhibiting the characteristics of the present copolymerized polyester film more effectively.
It is said that the stiffness of a film is proportional to the cube of its thickness. However, the present copolyester film is characterized by being weak in stiffness and supple even though it has a thickness of more than 20 μm, and can further enjoy the benefits of the present invention.
From this point of view, the total thickness of the present copolymer polyester film is preferably more than 20 μm, more preferably 23 μm or more, more preferably 30 μm or more.
On the other hand, the upper limit of the total thickness of the copolymer polyester film is not particularly limited. It is preferably 1000 μm or less, more preferably 500 μm or less, more preferably 250 μm or less, and more preferably 100 μm or less.

<Physical properties of the present copolymer polyester film>
The copolymer polyester film preferably has a storage elastic modulus at 25° C. of 2500 MPa or less.
When the storage elastic modulus is 2500 MPa or less at 25° C., that is, normal temperature, for example, when a wearable terminal is worn, it can sufficiently follow the skin.
From this point of view, the copolyester film preferably has a storage modulus at 25° C. of 2500 MPa or less, more preferably 2000 MPa or less, and more preferably 1200 MPa or less.
The storage elastic modulus at 25° C. is preferably 300 MPa or more, more preferably 500 MPa or more, and more preferably 700 MPa or more, from the viewpoint of handleability in the process.
The storage elastic modulus at 25°C is a value obtained by the measuring method described in Examples below.

In the present copolymerized polyester film, the 25° C. storage elastic modulus within the above range can be achieved, for example, by adjusting the type and content of the copolymerization component of the copolymerized polyester A.
Further, as described above, a laminated film having a configuration in which a polyester layer (II layer) containing polyester C as a main component resin is laminated on both front and back sides of a copolymer polyester layer (I layer). , can be adjusted.
Furthermore, it can also be adjusted by the stretching conditions when producing the copolymer polyester film of the present invention and the subsequent heat setting conditions.
However, it is not limited to these methods.

Moreover, the present copolymer polyester film preferably has a storage elastic modulus at 120° C. of 10 MPa or more.
When the storage elastic modulus at high temperatures is 10 MPa or more, the material has sufficient heat resistance and can suppress the occurrence of wrinkles during processing.
From this point of view, the copolyester film preferably has a storage modulus at 120° C. of 10 MPa or more, more preferably 30 MPa or more, and more preferably 50 MPa or more.
The copolyester film preferably has a storage modulus of 500 MPa or less at 120° C., more preferably 400 MPa or less, more preferably 300 MPa or less, from the viewpoint of suppressing the amount of heat required during processing.
The storage elastic modulus at 120°C is a value obtained by the measuring method described in Examples below.
In the present copolymer polyester film, the method for adjusting the storage modulus at 120°C within the above range includes the same method as the method for adjusting the storage modulus at 25°C. Among these, the method of adjusting the stretching conditions and subsequent heat setting conditions is particularly effective. However, it is not limited to this method.

The copolymer polyester film preferably has a loss tangent (tan δ) at 25° C. of 0.02 or more.
With a loss tangent of 0.02 or more at 25° C., that is, at room temperature, for example, when a wearable terminal is worn, it can sufficiently follow the skin.
From this point of view, the copolymer polyester film preferably has a loss tangent at 25° C. of 0.05 or more, more preferably 0.08 or more, and more preferably 0.10 or more.
The loss tangent (tan δ) at 25° C. is preferably 1.5 or less, more preferably 1.0 or less, more preferably 0.5 or less, from the viewpoint of handleability in the process.

In the present copolymer polyester film, the method for adjusting the loss tangent at 25°C within the above range includes the same method as the method for adjusting the storage elastic modulus at 25°C. Among these, the method of adjusting the type and content of the copolymerization component of the copolymerized polyester A is particularly effective. However, it is not limited to this method.

In the present copolymer polyester film, when the copolymer polyester A is crystalline, the crystal melting enthalpy ΔHm is preferably 3.0 J/g or more, especially 5.0 J/g or more, especially 7.0 J/g or more. is more preferable. ΔHm is an index of crystallinity, and when it is 3.0 J/g or more, sufficient heat resistance can be obtained and heat shrinkage can be suppressed.

This copolymer polyester film has a "flexibility" measured by the deflection measurement method described in Examples below, that is, the length that is lowered in the vertical direction (a), and the length that is protruded in the horizontal direction. When the width is (b), the ratio of (a) to (b) ((a)/(b)) is preferably 0.3 or more, especially 0.5 or more, especially 1 0.0 or more is more preferable.
When (a)/(b) is 0.3 or more, it is suggested that the film has sufficient flexibility.
On the other hand, the upper limit of (a)/(b) is not particularly limited, but from the viewpoint of handling in the process, it is preferably 15.0 or less, especially 10.0 or less, and especially 6.0 or less. is more preferred.

In order to adjust (a)/(b) in the above range in the present copolymer polyester film, it is important to first adjust the thickness of the film. It can be achieved by adjusting the type and content of the copolymer component of A. However, it is not limited to this method.
From this point of view, it is preferable that the "other dicarboxylic acid component" of the copolymerization component of the copolymer polyester A is an aliphatic dicarboxylic acid or a dimer acid, and the content thereof is 5 mol% or more and 20 mol% or less. preferable. On the other hand, the "other alcohol component" is preferably diethylene glycol, and its content is preferably 1 mol % or more and less than 25 mol %.

<Method for producing the present copolymer polyester film>
As an example of the method for producing the present copolymer polyester film, the case where the present copolymer polyester film is a biaxially stretched film will be described. However, it is not limited to the manufacturing method described here.

First, by a known method, raw materials such as polyester chips are supplied to a melt extruder, heated to the melting point of each polymer or higher, the molten polymer is extruded from a die, and cooled to a temperature below the glass transition point of the polymer on a rotating cooling drum. By cooling and solidifying so as to obtain a substantially amorphous non-oriented sheet.
Next, the unoriented sheet is stretched in one direction by a roll or tenter type 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.
Next, the film is stretched in a direction orthogonal to the stretching 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.
Subsequently, heat setting treatment is performed at a temperature of 130 to 270° C. under tension or under relaxation of 30% or less to obtain the present copolyester film as a biaxially oriented film.
In addition, in the above stretching, a method of stretching in one direction in two or more stages can also be employed.

The heat setting treatment (also referred to as “heat treatment”) is preferably performed at a temperature lower than the melting point of the copolymer polyester A by 10 to 70° C. when the copolymer polyester layer (I layer) is a single layer.

When the present copolymer polyester film has a laminated structure of a copolymer polyester layer (I layer) and a polyester layer (II layer), the copolymer polyester layer (I layer) and the polyester layer (II layer) are coextruded, As described above, stretching and heat setting may be performed 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 the polyester C. Furthermore, when the copolyester A is crystalline, it is preferable to heat-set at a temperature higher than the melting point of the copolyester A. The heat setting treatment at such a temperature enables softening to a level that cannot be achieved with a single layer of the copolyester layer (I layer).
This is because the stretching orientation of the surface layer is fixed by heat setting at a temperature lower than the melting point of the polyester C, so that the elongation, strength and heat resistance (heat shrinkability) are good, while the copolymer polyester A By heat-setting at a temperature higher than the melting point of , stretch orientation and distortion of the intermediate layer are relaxed, so that a more flexible film can be obtained.

<Uses of this copolymerized polyester film>
As described above, the copolymer polyester film has excellent flexibility at room temperature, and is not only flexible, but also has almost no stiffness. can be demonstrated. Therefore, it can be suitably used, for example, as a constituent member for battery packaging materials, surface protection films, image display members, particularly flexible displays, wearable terminals, and the like.
The uses of the copolymer polyester film are not limited to those described above, and can be used, for example, as various packaging materials, building materials, stationery, automobile members, other structural members, and the like.

<Explanation of terms, etc.>
In the present invention, the term "film" includes the "sheet", and the term "sheet" includes the "film".
In addition, the expression "panel" such as an image display panel, a protective panel, etc. includes a plate, a sheet and a film.

In the present invention, when described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, "X or more and Y or less" and "preferably larger than X" or "preferably Y It also includes the meaning of "less than".
In addition, when described as "X or more" (X is an arbitrary number), it includes the meaning of "preferably greater than X" unless otherwise specified, and is described as "Y or less" (Y is an arbitrary number). If not otherwise specified, it also includes the meaning of "preferably smaller than Y".

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, various physical properties were measured and evaluated as follows.

(1) Storage modulus E′, tangent loss tan δ
Based on JIS K 7244, using a dynamic viscoelasticity measuring device DVA-200 manufactured by IT Keisoku Co., Ltd., the width direction (TD) of the copolymer polyester film (sample) was measured at a vibration frequency of 10 Hz and a strain of 0.1%. , measured from -100°C to 200°C at a heating rate of 1°C/min, and from the obtained data, the storage modulus E' at 25°C and 120°C and the tangent loss tan δ at 25°C were obtained.

(2) Crystal melting enthalpy ΔHm
Based on JIS K7141-2 (2006), differential scanning calorimeter (DSC) measurement of the measurement sample was performed. The temperature was raised from 30°C to 280°C at a rate of 10°C/min, held for 1 minute, then lowered from 280°C to 30°C at a rate of 10°C/min, held for 1 minute, and further from 30°C to 280°C at 10°C. /min. At this time, the crystal melting enthalpy (ΔHm) was calculated from the crystal melting peak area in the reheating process.
In the case of a single layer, a copolymer polyester film was used as a measurement sample, and in the case of a laminate, an intermediate layer was used as a measurement sample.

(3) Young's modulus For the copolymer polyester films (samples) obtained in Examples and Comparative Examples, a tensile tester (Intesco Model 2001, manufactured by Intesco Co., Ltd.) was used at a temperature of 23 ° C. and a humidity of 50% RH. In a controlled room, a copolymer polyester film (sample) of 300 mm length and 20 mm width was pulled at a strain rate of 10%/min.
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 on the straight line, and Δε is the strain difference/initial length between the same two points)

(4) Tensile breaking strength The copolymer polyester films (samples) obtained in Examples and Comparative Examples were tested using a tensile tester (manufactured by Intesco Co., Ltd., Intesco Model 2001) at a temperature of 23 ° C. and a humidity of 50% RH. In a room adjusted to , set a copolymer polyester film (sample) with a width of 15 mm on the tester so that the chuck distance is 50 mm, and at a strain rate of 200 mm / min, the longitudinal direction (MD) or width direction of the film (TD), and the tensile strength at break was determined by the following formula.
Tensile breaking strength (MPa) = F/A
However, 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.

(5) Tensile elongation at break The same test as for the tensile strength at break was performed, and the tensile elongation at break of the copolymer polyester films (samples) obtained in Examples and Comparative Examples was determined by the following formula.
Tensile elongation at break (%) = 100 x (L - L0) / L0
However, in the above formula, L is the gauge length (mm) at breakage, and L0 is the original gauge length (mm).

(6) Heat Shrinkage Copolyester films (samples) obtained in Examples and Comparative Examples were left untensioned in an oven maintained at 120°C for 5 minutes, and the length of the sample was measured before and after that. Then, the heat shrinkage rate in each of the longitudinal direction (MD) and width direction (TD) of the film was calculated by 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 5 points each in the machine direction (MD) and the width direction (TD) of the film, and an average value was obtained for each.

(7) Evaluation of suppleness (flexibility) (deflection measurement method)
Samples Samples were prepared by leaving the copolymer polyester films (samples) obtained in Examples and Comparative Examples in an atmosphere of 23° C. and 50% RH for 24 hours, and then cutting them into a size of 150 mm long and 50 mm wide.
As shown in FIG. 1, a copolymer polyester film (sample) is placed on a desk in an environment of 23 ° C. so that it protrudes 50 mm from the edge of the desk, and the copolymer polyester film on the desk is A weight of 200 g was placed and fixed on the film (sample), and the tip side of the sample protruding from the edge of the desk was bent downward by its own weight. After 3 minutes, measure the length (a) that the tip of the sample protruding from the edge of the desk bends vertically and hangs down, and the length (b) that the tip protrudes horizontally from the edge of the desk. did.
Then, the ratio ((a)/(b)) of the bent length (a) to the horizontally protruding length (b) was calculated. If it was less than 30, it was evaluated as "failed".

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

Copolyester 1 (“co-PS1”): Acid component consists of 88 mol % of terephthalic acid, 7 mol % of hydrogenated dimer acid having 36 carbon atoms and 5 mol % of isophthalic acid, and diol components consist of 90 mol % of ethylene glycol and diethylene glycol. A crystalline copolyester consisting of 10 mol %. Melting point 208°C, intrinsic viscosity 0.68 dl/g.

Copolyester 2 (“co-PS2”): acid component consisting of 88 mol % terephthalic acid and 12 mol % hydrogenated dimer acid having 36 carbon atoms, and diol component consisting of 67 mol % ethylene glycol and 33 mol % 1,4-butanediol A crystalline copolyester containing mol % (less than 0.1 mol % of by-product diethylene glycol). Melting point 200°C, intrinsic viscosity 0.72 dl/g.

Copolyester 3 (“Co-PS3”): A crystalline copolyester containing 78 mol % terephthalic acid and 22 mol % isophthalic acid as the acid component, and 98 mol % ethylene glycol and 2 mol % by-product diethylene glycol as the diol component. Melting point 198°C, intrinsic viscosity 0.70 dl/g.

Polyester (“PET”): polyethylene terephthalate (by-product diethylene glycol: 2 mol %). Melting point 250°C, intrinsic viscosity 0.64 dl/g.

[Example 1]
Copolyester 1 (co-PS1) chips were fed into a vented extruder set at 280° C. for the surface layer and intermediate layer, extruded from the die of the extruder via a gear pump and a filter, and then subjected to an electrostatic contact method. The sheet was rapidly cooled and solidified on a cooling roll whose surface temperature was set to 30° C. to obtain an unstretched sheet.
Next, the obtained unstretched sheet is stretched 3.3 times at 50 ° C. in the longitudinal direction (MD), guided to a tenter, and then stretched 4.2 times at 80 ° C. in the width direction (TD). The film was heat-treated at 200° C. for 10 seconds and relaxed 10% in the width direction (TD) to obtain a 25 μm-thick biaxially stretched copolymer polyester film (sample) consisting essentially of a single layer.

[Example 2]
As an intermediate layer, Copolyester 1 (Co-PS1) chips were fed into the main vented twin-screw extruder set at 280°C.
As a surface layer, polyester (PET) chips were fed into a sub-vented twin-screw extruder set at 280°C.
Through a gear pump and a filter, the polymer from the main extruder becomes the intermediate layer, and the polymer from the sub-extruder becomes the surface layer. An unstretched sheet was obtained by extruding and solidifying rapidly on a cooling roll whose surface temperature was set to 30° C. using an electrostatic contact method.
Next, the obtained unstretched sheet is stretched 3.2 times at 80 ° C. in the longitudinal direction (MD), guided to a tenter, and then stretched 4.0 times at 100 ° C. in the width direction (TD). Heat treated at 200° C. for 10 seconds, relaxed 10% in the width direction (TD), and having a thickness of 1 μm (surface layer) / 23 μm (intermediate layer) / 1 μm (surface layer) Biaxially stretched copolymer polyester with a thickness of 25 μm A film (sample) was obtained.

[Examples 3 to 5]
A biaxially stretched copolymer polyester film (sample) was obtained in the same manner as in Example 2, except that the conditions were changed as shown in Table 1.
In the table, for example, "co-PS1/PET = 80/20" in Example 3 means that 80 parts by mass of co-PS1 and 20 parts by mass of PET were mixed. also indicates a mass ratio.

[Comparative Example 1]
A polyester (PET) chip is fed into a vented extruder set at 280°C, extruded from the nozzle of the extruder via a gear pump and a filter, and cooled with the surface temperature set to 30°C using an electrostatic contact method. It was solidified by rapid cooling on a roll to obtain an unstretched sheet.
Next, the obtained unstretched sheet is stretched 3.5 times at 86 ° C. in the longitudinal direction (MD), guided to a tenter, and then stretched 4.3 times at 110 ° C. in the width direction (TD). It was heat-treated at 235° C. for 10 seconds and relaxed 10% in the width direction (TD) to obtain a biaxially stretched copolymer polyester film (sample) with a thickness of 50 μm.

[Comparative Example 2]
A mixture of 85 parts by mass of co-PS3 chips and 15 parts by mass of PET chips was fed into a vented extruder set at 280° C., extruded from the nozzle of the extruder through a gear pump and a filter, and electrostatically applied. A contact method was used to rapidly cool and solidify on a cooling roll whose surface temperature was set to 30° C. to obtain an unstretched sheet.
Next, the obtained unstretched sheet is stretched 3.4 times at 80 ° C. in the longitudinal direction (MD), guided to a tenter, and then stretched 3.9 times at 145 ° C. in the width direction (TD). It was heat-treated at 186° C. for 10 seconds and relaxed 10% in the width direction (TD) to obtain a 50 μm-thick biaxially stretched copolymer polyester film (sample).

[Comparative Example 3]
Copolyester 2 (co-PS2) chips were fed into a vented extruder set at 280°C, extruded from the nozzle of the extruder via a gear pump and a filter, and the surface temperature was reduced to 30°C using an electrostatic contact method. was rapidly solidified on a cooling roll set to 200 μm to obtain an unstretched copolymer polyester film (sample) having a thickness of 200 μm.

From the above examples and the results of tests conducted by the inventors so far, it was found that a copolymer polyester film having a copolymer polyester layer (I layer) containing the copolymer polyester A as a main component resin was When the storage modulus is 2500 MPa or less, it is excellent in flexibility at room temperature, is not only flexible but also more supple, and can have elongation and strength. Moreover, it was found that practically sufficient heat resistance can be obtained when the storage elastic modulus at 120° C. is 10 MPa or more.

When the main component resin of the intermediate layer is a crystalline copolyester as in Examples 2 to 5, the polyester as the main component resin of the surface layer is a polyester having a melting point higher than that of the copolyester. It was confirmed that the heat treatment (heat setting) temperature after stretching can be made higher than in the case of a single layer consisting only of the intermediate layer, and the heat shrinkability can be further suppressed.
In addition, when the main component resin of the intermediate layer is an amorphous copolyester, if the polyester as the main component resin of the surface layer has a melting point higher than the glass transition point of the copolyester, Compared to the case of a single layer consisting only of the intermediate layer, the heat treatment (heat setting) temperature after stretching can be made higher, so it is thought that the heat shrinkability can be further suppressed.

Claims (15)

A copolymerized polyester film comprising a copolymerized polyester layer (I layer) containing a copolymerized polyester A as a main component resin,
The copolymer polyester A is a copolymer of terephthalic acid and "other dicarboxylic acid components" and ethylene glycol and "other alcohol components",
The "other dicarboxylic acid component" contains an aliphatic dicarboxylic acid or a dimer acid,
In the copolymer polyester, the ratio of "other dicarboxylic acid components" to the dicarboxylic acid components is more than 5 mol% and 20 mol% or less, and the ratio of "other alcohol components" to the alcohol components is 1 mol% or more and less than 25 mol%. can be,
A copolymer polyester film having a storage modulus of 2500 MPa or less at 25°C and a storage modulus of 10 MPa or more at 120°C. 2. The copolymer polyester film according to claim 1, wherein the copolymer polyester layer (I layer) is a layer containing the copolymer polyester A and a resin B compatible therewith. The resin B contains one or more polyesters, and in the polyester, 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% or less. 3. The copolymer polyester film according to claim 2 , wherein 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 %. A copolymer polyester film comprising a copolymer polyester layer (I layer) containing one or more polyesters,
In the total polyester contained in the copolymer polyester layer (layer I), the ratio of the total content of "other dicarboxylic acid components" to the total content of dicarboxylic acid components is more than 5 mol% and 20 mol% or less, and the alcohol component The ratio of the total content of "other alcohol components" to the total content of is 1 mol% or more and less than 25 mol%, the "other dicarboxylic acid component" is a dicarboxylic acid component other than terephthalic acid, and the "other "Alcohol component of" is an alcohol component other than ethylene glycol,
The "other dicarboxylic acid component" contains an aliphatic dicarboxylic acid or a dimer acid,
A copolymer polyester film having a storage modulus of 2500 MPa or less at 25°C and a storage modulus of 10 MPa or more at 120°C. 5. The copolymer polyester film according to any one of claims 1 to 4, excluding a film containing a copolymer polyester layer (layer I) containing a crystal nucleating agent. 6. The copolymer polyester film according to any one of claims 1 to 5 , wherein the "other dicarboxylic acid component" contains isophthalic acid and aliphatic dicarboxylic acid or dimer acid. 6. The combination according to any one of claims 1 to 5 , wherein the "other dicarboxylic acid component" includes isophthalic acid and an aliphatic dicarboxylic acid having 20 to 80 carbon atoms or a dimer acid. Polymerized polyester film. 6. The copolymer polyester film according to any one of claims 1 to 5, wherein the "other dicarboxylic acid component" contains isophthalic acid and dimer acid. 9. The copolymer polyester film according to any one of claims 1 to 8 , wherein the "other alcohol component" contains diethylene glycol. It has a structure in which a polyester layer (II layer) containing polyester C as a main component resin is laminated on both front and back sides of a copolymer polyester layer (I layer),
The polyester C is a polyester having a melting point higher than the melting point of the copolymer polyester A when the copolymer polyester A is crystalline, and the glass of the copolymer polyester A when the copolymer polyester A is amorphous. 10. The copolyester film according to any one of claims 1 to 9 , wherein the polyester has a melting point higher than the transition point. 11. The copolymer polyester film according to claim 10 , wherein each layer thickness of the polyester layer (II layer) is 1 to 20% of the thickness of the copolymer polyester layer (I layer). The copolymer polyester film according to any one of claims 1 to 11 , wherein the loss tangent (tan δ) at 25°C is 0.02 or more. Copolyester film according to any one of claims 1 to 12 , characterized in that the total thickness of the film exceeds 20 µm. A surface protective film using the copolymer polyester film according to any one of claims 1 to 13 . An optical member using the copolymer polyester film according to any one of claims 1 to 13 .

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