WO2020054576A1

WO2020054576A1 - Copolymerized polyester film

Info

Publication number: WO2020054576A1
Application number: PCT/JP2019/035003
Authority: WO
Inventors: 鈴木　智博; 博以西河
Original assignee: 三菱ケミカル株式会社
Priority date: 2018-09-13
Filing date: 2019-09-05
Publication date: 2020-03-19
Also published as: KR20210057011A; CN112654664B; JP7192869B2; CN112654664A; TWI813769B; TW202024171A; JPWO2020054576A1

Abstract

As a novel copolymerized polyester film that is softer and more flexible, while having adequate elongation, strength and heat resistance at the same time, the present invention proposes a copolymerized polyester film which is provided with a copolymerized polyester layer (layer I) that contains a copolymerized polyester A as a main component resin, and which is characterized in that: the copolymerized polyester A is a copolymer of terephthalic acid and "another dicarboxylic acid component" and ethylene glycol and "another alcohol component"; the ratio of the "another dicarboxylic acid component" in the dicarboxylic acid components in the copolymerized polyester is from 5 mol% to 20 mol% (inclusive); the ratio of the "another alcohol component" in the alcohol components in the copolymerized polyester is 1 mol% or more but less than 25 mol%; the storage elastic modulus at 25°C is 2,500 MPa or less; and the storage elastic modulus at 120°C is 10 MPa or more.

Description

Copolyester film

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

Polyethylene terephthalate (PET) films, which are typical polyester films, especially biaxially stretched PET films are excellent in transparency, mechanical strength, heat resistance, flexibility, etc., and are therefore used as industrial materials, optical materials, electronic component materials, and batteries. It is used in various fields such as packaging materials.

With respect to this type of polyester film, for example, Patent Document 1 discloses a softened polyester film that exhibits softness not found in conventional polyester films and has excellent moldability at relatively low temperature and low pressure. Is less than or equal to 20 MPa at 120 ° C. and less than or equal to 5 MPa at 180 ° C., has a film haze of less than or equal to 1.0%, and contains 29 to 32 mol% of 1,4-cyclohexanedimethanol unit as a diol component. A softened polyester film characterized by not containing an isophthalic acid unit as a dicarboxylic acid component has been proposed.

Patent Document 2 proposes an image receiving sheet for thermal transfer in which an image receiving layer composed of a copolymerized polyester layer having a copolymerization ratio of 5 to 30 mol% is laminated on at least one surface of a polyester film.
Further, 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 comprising a copolymerized polyester containing 0.05 to 5.0% by weight of a lubricant, wherein the biaxially oriented film has 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 ~ 250 ° C., also laminated metal plate, characterized in that the coarse particles having a particle size 20μm or more of the above lubricants of the biaxially oriented film in does not contain at most 10 / mm ² A polyester film for forming has been proposed.

In addition, in Patent Document 4, made of copolyester containing 1 ~ 20 mol% of an aliphatic dicarboxylic acid component to the total acid component, an atmosphere of 0.99 ° C., at 100% elongation film strength _{F 100} is 0. There has been proposed a biaxially stretched polyester film for molding, which has a thickness of 5 to 5 kg / mm ² and a thickness unevenness of the film of 40% or less.
Patent Document 5 discloses a laminated film in which a polyester (B) layer mainly composed of polyester (B) is laminated on at least one surface of a polyester (A) layer mainly composed of polyester (A), A laminated polyester film has been proposed, characterized in that the laminated film has an elastic modulus in a 23 ° C. atmosphere of 20 to 1000 MPa, an elastic modulus in a 120 ° C. atmosphere of 10 to 200 MPa, and is substantially non-oriented. I have.

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

In addition, a flexible display that can be freely bent has attracted attention as a next-generation image display device. As the flexible display, an organic electroluminescence (organic EL) display is mainly used.
Since thin glass substrates and plastic substrates are used for flexible displays, the polyester film used for these image display device members needs to have the optical properties and durability required for conventional flat display panels, in addition to the required optical characteristics and durability. It is required that no bending or the like occurs even in a bending test.

JP 2014-169371 A JP-A-04-086293 JP 2000-001552 A JP 03-0667629 A International Publication No. WO09 / 078304 JP 2014-134903 A

As mentioned above, considering the use of polyester films for wearable terminals and flexible displays, it is not only more flexible but also more pliable than polyester films commonly used in the past, and yet, It was necessary to develop a polyester film having elongation and strength. Further, heat resistance that does not shrink when heated is also required.

Therefore, an object of the present invention is to provide a new copolyester film that is more flexible and more pliable than conventional generally used polyester films, yet has both elongation, strength and heat resistance. To provide.

The present invention is a copolymerized polyester film provided with a copolymerized polyester layer (I layer) containing copolymerized polyester A as a main component resin,
The copolymerized polyester A is a copolymer of terephthalic acid and “other dicarboxylic acid components”, ethylene glycol and “other alcohol components”, and “other dicarboxylic acid components” in the dicarboxylic acid component in the copolymerized polyester. The ratio of the “acid component” is 5 mol% or more and 20 mol% or less, and the ratio of the “other alcohol component” in the alcohol component is 1 mol% or more and less than 25 mol%,
The present invention proposes a copolymer polyester film having a storage elastic modulus at 25 ° C of 2500 MPa or less and a storage elastic modulus at 120 ° C of 10 MPa or more.

The present invention also relates to a copolymerized polyester film provided with a copolymerized polyester layer (I layer) containing one or more polyesters,
In all the polyesters contained in the copolymerized polyester layer (I layer), the ratio of the total content of the “other dicarboxylic acid components” to the total content of the 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%,
The present invention proposes a copolymer polyester film having a storage elastic modulus at 25 ° C of 2500 MPa or less and a storage elastic modulus at 120 ° C of 10 MPa or more.

The copolymerized polyester film proposed by the present invention is excellent in flexibility at room temperature, is not only flexible, but also more pliable, yet has elongation and strength, and is practically sufficient High heat resistance. Therefore, the copolymerized polyester film proposed by the present invention can be suitably used as, for example, a packaging material for a battery, a member for image display, particularly a component such as a flexible display or a wearable terminal.

It is the figure which showed typically the method of the deflection measurement method performed in the Example.

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

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

The present copolymerized polyester film may 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 preferable. Among them, a biaxially stretched film is preferable in terms of excellent balance of mechanical properties and excellent flatness. When the present copolymerized polyester film is such a stretched film, the storage elastic modulus at 120 ° C. tends to be easily set to 10 MPa or more.

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

Here, the “main component resin” means a resin having the highest content ratio among the resins constituting the copolymerized polyester layer (I layer). The main component resin may account for 30% by mass or more, particularly 50% by mass or more, and especially 80% by mass or more (including 100% by mass) of the resin constituting the copolymerized polyester layer (I layer).

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

(Copolymer polyester 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.

The copolyester A may be crystalline or amorphous.
In the present invention, the crystalline polyester resin generally refers to a polyester resin having a crystal melting peak temperature (melting point), and more specifically, a differential resin made in accordance with JIS K7121 (1987). A polyester resin whose melting point is observed in scanning calorimetry (DSC) includes a so-called semi-crystalline state. Conversely, a thermoplastic resin whose melting point is not observed in DSC is referred to as “amorphous”. A crystalline polyester generally refers to a polyester having a crystal melting peak temperature (melting point). More specifically, it includes a polyester whose melting point is observed in differential scanning calorimetry (DSC) performed according to JIS K7121 (1987), and includes a so-called semi-crystalline state.
Conversely, a thermoplastic resin whose melting point is not observed in DSC is referred to as “amorphous”.

Examples of the “other dicarboxylic acid component” include aromatic dicarboxylic acids, alicyclic dicarboxylic acids, aliphatic dicarboxylic acids, and polyfunctional acids. In addition, you may use together 2 or more types of "other dicarboxylic acid components." By using two or more kinds in combination as described above, not only can the copolymerized polyester film be more effectively softened, but also the crystal structure can be maintained and heat resistance may be obtained.
Among them, from the viewpoint of facilitating the softening of the copolymerized polyester film, the "other dicarboxylic acid components" include aromatic dicarboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, adipic acid, and sebacine. Aliphatic dicarboxylic acids such as acids, dodecane diacids, eico acids and derivatives thereof, alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid, cyclooctanedicarboxylic acid, or Dimer acid is preferred. Especially, it is preferable to contain an aliphatic dicarboxylic acid or a dimer acid.
Among aliphatic dicarboxylic acids, from the viewpoint of further lowering the glass transition temperature, aliphatic dicarboxylic acids having 20 to 80 carbon atoms, particularly 30 or more and 60 or less, and among them, 36 or 48 or less are particularly preferable.

The dimer acid is preferably a dicarboxylic acid composed of a dimer of an unsaturated fatty acid, wherein the unsaturated fatty acid has 18 or more carbon atoms. Examples of such dimer acids include oleic acid, elaidic acid, setreic acid, erucic acid, brassic acid, linoleic acid, those dimerized using different or identical unsaturated fatty acids selected from linolenic acid, and the like. Can be mentioned. Further, those obtained by hydrogenation 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, from the viewpoint of further reducing the glass transition temperature, dimer acids having 20 to 80 carbon atoms, particularly 26 or more or 60 or less, and among them, 30 or more or 50 or less are preferable.

As described above, the “other dicarboxylic acid component” can be arbitrarily selected. Above all, it is preferable to select one or more from aromatic dicarboxylic acids and select and use one or more from aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and dimer acids. Among them, it is particularly preferable to include two or more of isophthalic acid, aliphatic dicarboxylic acid and dimer acid, and particularly, two or more of isophthalic acid, aliphatic dicarboxylic acid having 20 to 80 carbon atoms and dimer acid. It is particularly preferred to include
When an aromatic dicarboxylic acid is used as the “other dicarboxylic acid component”, the film tends to be flexible while maintaining strength and heat resistance. On the other hand, when an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid, or a dimer acid is used as the “other dicarboxylic acid component”, the film can be formed at a smaller content while maintaining the elongation (elongation at break). It tends to be soft, and among them, the use of dimer acid is most effective. Therefore, a film having good strength, heat resistance, elongation, and flexibility can be obtained by combining and using "other dicarboxylic acid components" as described above.

In the copolyester A, the proportion of the dicarboxylic acid component, that is, “other dicarboxylic acid component” in the total of terephthalic acid and “other dicarboxylic acid component” is preferably 5 to 20 mol%, and more preferably 8 mol% or more. Alternatively, the content is more preferably 18 mol% or less, among which 10 mol% or more or 15 mol% or less. When two or more other “dicarboxylic acid components” are used in combination, the total amount thereof is meant.
When the proportion of the “other dicarboxylic acid component” is within the above range, the copolymerized polyester film tends to be effectively softened while having good elongation, strength and heat resistance.

Examples of the “other alcohol component (diol component)” include 1,4-butanediol, 1,6-hexanediol, diethylene glycol, trimethylene glycol, neopentyl glycol, 1,4-cyclohexane dimethanol, bisphenol, and the like. Derivatives and the like 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.
In general, when a polyester is produced (polycondensed) using ethylene glycol as one of the raw materials, a part of the ethylene glycol is modified into diethylene glycol and introduced into the polyester skeleton. This diethylene glycol is referred to as by-product diethylene glycol. The amount of by-product varies depending on the type of polycondensation (ester exchange method, direct polycondensation) and the like, but is about 1 to 5 mol% of ethylene glycol. In the present invention, diethylene glycol by-produced from ethylene glycol as described above is also treated as a copolymer component, and is included in “other alcohol components”.

In the copolyester A, the proportion of the alcohol component (diol component), that is, the “other alcohol component (diol component)” in the total of ethylene glycol and the “other alcohol component” is 1 mol% or more and less than 25 mol%. More preferably, it is 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 “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 copolymerized polyester film tends to be effectively softened while having good elongation, strength and heat resistance.
In addition, you may use 2 or more types of "other alcohol components" together. By using two or more kinds together, the copolyester film may be more effectively softened in some cases.

In addition, it is preferable that the “other dicarboxylic acid component” and the “other alcohol component” are used in total and used in combination of three or more. By using a plurality of copolymer components in combination, the film tends to be softened with a smaller content ratio. If the type of the copolymer component is too large, it may be difficult to stabilize the properties of the film. Therefore, the “other dicarboxylic acid component” and the “other alcohol component” are 3 to 5 in total. It is preferably a species, and more preferably three or four species.

Among the above-mentioned particularly preferred copolymer polyester A, terephthalic acid, isophthalic acid and aliphatic dicarboxylic acid or dimer acid, and a copolymer of ethylene glycol and diethylene glycol, isophthalic acid in the dicarboxylic acid component constituting the copolymerized polyester The ratio of the acid, aliphatic dicarboxylic acid or dimer acid is 5 mol% or more and 20 mol% or less, and the ratio of diethylene glycol in the alcohol component constituting the copolymer polyester is 1 mol% or more and less than 25 mol%, Aa can be mentioned.
Usually, the crystallinity of the copolymerized polyester decreases when the proportion of the copolymer component is increased in order to decrease the elastic modulus, and becomes amorphous when the proportion is further increased. Although the copolymerized polyester Aa has a high copolymerization component ratio and can realize a low elastic modulus, it maintains the crystallinity, and thus can be heat-set by heat treatment after stretching. As a result, the copolymerized polyester Aa is flexible, and yet has good elongation and strength, and can further suppress heat shrinkage.

(Resin B)
As described above, the copolymerized polyester layer (I layer) may be a layer containing a copolymerized polyester A and a resin B compatible therewith.
In the present invention, "compatible" means a state where two or more kinds of mixed resins are completely mixed at a molecular level. At this time, the amorphous region mixed at the molecular level can be regarded as a single phase, and micro-Brownian motion also occurs at a single temperature. Therefore, when two or more kinds of resins are compatible with each other, the mixed resin of the two or more kinds of resins has a single melting point or a single glass transition temperature, and a single main dispersion peak. Therefore, conversely, a resin compatible with the copolyester A is defined as a resin capable of changing the melting point or the glass transition temperature of the copolyester A when mixed with the copolyester A. You can also.
In this case, the glass transition temperature is, for example, a temperature dispersion measurement of dynamic viscoelasticity under conditions of 0.1% strain, 10 Hz frequency, and a heating rate of 3 ° C./min (dynamic viscoelasticity measurement according to JIS K7244 method). ) Is the peak temperature of the main dispersion of the loss tangent (tan δ).

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

In addition, 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 "another dicarboxylic acid component", an alcohol component such as ethylene glycol and "another alcohol component", and a total content of the dicarboxylic acid component (when two or more polyesters are contained, the dicarboxylic acid contained in each polyester is included). The ratio of the total content of "other dicarboxylic acid components" to the total content of the other dicarboxylic acid components is from 5 mol% to 20 mol%, preferably from 8 mol% to 18 mol%, more preferably from 10 mol% to 15 mol%. Yes, the total content of alcohol components (two or more When containing tellurium, the ratio of the total content of the "other alcohol components" to the total of the alcohol components contained in each polyester is 1 mol% or more and less than 25 mol%, preferably 2 mol% or more or 20 mol% or less, more preferably Is preferably 3 mol% or more or 18 mol% or less.

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

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

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 effect as in the case where the copolymerized polyester A is contained as the main component resin is obtained. It is thought that it is possible.
Therefore, when the copolymerized polyester layer (I layer) contains one or more polyesters, the content of the dicarboxylic acid component in the total amount of the components of all the polyesters contained in the copolymerized polyester layer (I layer) is included. The ratio of the total content of "other dicarboxylic acid components" to the total amount is 5 mol% to 20 mol%, and the ratio of the total content of "other alcohol components" to the total content of alcohol components is 1 mol%. When the content is at least 25 mol%, the same effect as in the case where the copolyester A is contained 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 component” to the total content of the dicarboxylic acid component is the ratio of the “other dicarboxylic acid component” to the dicarboxylic acid component in the copolymerized polyester A. Is the same as the preferred range. 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 component in the copolymerized polyester A. It is.

<In the case of a laminated structure>
As described above, the present copolymerized polyester film may be a laminated film including a copolymerized polyester layer (I layer) and another layer.

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 sides of the copolymerized polyester layer (I layer).
At this time, the polyester C is preferably a polyester having a melting point higher than the melting point of the copolyester A when the copolyester A is crystalline, and when the copolyester A is amorphous, It is preferable that the polyester has a melting point at a temperature higher than the glass transition point of the copolymerized polyester A.

In the case of a laminated film having a configuration in which such a polyester layer (II layer) containing polyester C as a main component resin is laminated, polyester layer (II layer) / copolyester layer (I layer) / polyester Laminating the raw resin composition by co-extrusion or the like so as to form a layer (II layer), stretching, and heat-setting at a higher temperature than in the case of a single layer of a copolymerized polyester layer (I layer). Therefore, it can be softened to a level that cannot be achieved with a single layer of the copolyester layer (I layer), can increase heat resistance, and can further prevent heat shrinkage.
Specifically, the storage elastic modulus at 25 ° C. of the copolymerized polyester film can be 300 to 2500 MPa, especially 500 MPa or more and 2000 MPa or less.

In the laminated film, the thickness of each polyester layer (II layer) is preferably 1 to 20% of the thickness of the copolymerized polyester layer (I layer).
If the thickness of each polyester layer (II layer) is 1% or more of the thickness of the copolymerized polyester layer (I layer), film formation can be performed without significantly impairing productivity. This is preferable because sufficient flexibility can be ensured.
From this viewpoint, the thickness of each layer of the polyester layer (II layer) is preferably 1 to 20% of the thickness of the copolymerized polyester layer (I layer), more preferably 3% or more, or 15% or less, and especially 5% or more. Alternatively, it is more preferably 12% or less.
In addition, the thickness of the polyester layer (II layer) present on both sides of the copolymerized polyester layer (I layer) may be different on the front and back, or may be the same.

Polyester C has a melting point that is 10 to 100 ° C. higher than the melting point of copolyester A, particularly 20 ° C. or higher, or 90 ° C. or lower, especially 40 ° C. or higher or 70 ° C. or lower, when copolyester A is crystalline. In the case where the copolyester A is amorphous, the copolyester A is preferably 120 to 260 ° C. higher than the glass transition point of the copolyester A, more preferably 140 ° C. or higher or 230 ° C. or lower. It is preferable that the polyester has a high melting point of 160 ° C. or more or 200 ° C. or less.
In addition, the polyester C which is a main component of the polyester layer (II layer) existing on both sides of the copolymerized polyester layer (I layer) may be different on the front and back or may be the same. Above all, it is preferable that the melting points of the front and back polyesters C do not greatly differ. Specifically, the difference between the melting points of the polyester layers (II layers) present on both the front and back sides is preferably 80 ° C or less, more preferably 60 ° C or less, and particularly preferably 40 ° C or less.
If the polyester C in the polyester layer (II layer) present on both the front and back sides of the copolymer polyester layer A is the same, coextrusion molding of two or three layers becomes possible, so this embodiment 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 suitably used. However, it is not limited to this.

When the polyester C is a copolymerized polyester, examples of the dicarboxylic acid component 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%, more preferably 5 mol% or more or 25 mol% or less, among which 10 mol% or more or 20 mol% or less. Is more preferred.

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 the polyester C, the ratio of the “alcohol component other than ethylene glycol” to the alcohol component is preferably 1 to 100 mol%, more preferably 5 mol% or more, or 95 mol% or less, among which 10 mol% or more, or 90 mol% or less. Is more preferred.

<Thickness of the copolymerized polyester film>
The thickness of the present copolymerized polyester film is not particularly limited, and an appropriate thickness can be selected depending on the use.
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.
It is said that the stiffness of the film is proportional to the cube of the thickness. However, even if the present copolymerized polyester film has a thickness of more than 20 μm, it has the characteristic of being weak and flexible, and can further enjoy the benefits of the present invention.
From such a viewpoint, the total thickness of the present copolyester film is preferably more than 20 μm, more preferably 23 μm or more, and particularly preferably 30 μm or more.
On the other hand, the upper limit of the total thickness of the present copolymerized polyester film is not particularly limited. The thickness is preferably 1000 μm or less, more preferably 500 μm or less, particularly 250 μm or less, and particularly preferably 100 μm or less.

<Physical properties of the copolymerized 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 at 25 ° C., that is, at room temperature, is 2500 MPa or less, for example, when the wearable terminal is worn, it can sufficiently follow the skin.
From this viewpoint, the present copolymerized polyester film preferably has a storage modulus at 25 ° C. of 2500 MPa or less, more preferably 2000 MPa or less, and even more preferably 1200 MPa or less.
The storage elastic modulus at 25 ° C. is preferably 300 MPa or more, and more preferably 500 MPa or more, and particularly preferably 700 MPa or more, from the viewpoint of handling properties in the process.
The storage elastic modulus at 25 ° C. is a value obtained by a measurement method described in Examples described later.

In the present copolymerized polyester film, the storage elastic modulus at 25 ° C. can be set in the above range, for example, by adjusting the type and content of the copolymerized 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 sides of the copolymerized polyester layer (I layer). , Can be adjusted.
Furthermore, it can also be adjusted by the stretching conditions when producing the copolymerized polyester film of the present invention and the subsequent heat setting conditions.
However, it is not limited to these methods.

The copolymer polyester film preferably has a storage elastic modulus at 120 ° C. of 10 MPa or more.
When the storage elastic modulus at a high temperature is 10 MPa or more, sufficient heat resistance can be obtained, and generation of wrinkles during processing can be suppressed.
From this viewpoint, the present copolymerized polyester film preferably has a storage elastic modulus at 120 ° C. of 10 MPa or more, more preferably 30 MPa or more, and particularly preferably 50 MPa or more.
The copolymer polyester film preferably has a storage elastic modulus at 120 ° C. of 500 MPa or less, more preferably 400 MPa or less, and particularly preferably 300 MPa or less, from the viewpoint of suppressing the amount of heat required during processing.
In addition, the storage elastic modulus at 120 ° C. is a value obtained by a measurement method described in Examples described later.
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 as the method described above as the method for adjusting the storage elastic modulus at 25 ° C. Among these, the method of adjusting the stretching conditions and the subsequent heat setting conditions is particularly effective. However, it is not limited to this method.

This copolymerized polyester film preferably has a loss tangent (tan δ) at 25 ° C. of 0.02 or more.
When the loss tangent at 25 ° C., that is, at room temperature, is 0.02 or more, for example, when the wearable terminal is worn, it can sufficiently follow the skin.
From this viewpoint, the present copolyester film preferably has a loss tangent at 25 ° C. of 0.05 or more, more preferably 0.08 or more, and even 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, and even more preferably 0.5 or less, from the viewpoint of handling properties in the process.

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

When the copolymer polyester A is crystalline, the copolymer polyester film preferably has a crystal melting enthalpy ΔHm of 3.0 J / g or more, more preferably 5.0 J / g or more, and among them, 7.0 J / g or more. Is more preferred. 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 copolymerized polyester film has a “flexibility” (strength) measured by a deflection measurement method described in Examples described later, that is, a length lowered vertically (a) and a length protruded horizontally. When the value is (b), the value of the ratio of (a) to (b) ((a) / (b)) is preferably 0.3 or more, more preferably 0.5 or more, and more preferably 1 or more. More preferably, it is not less than 0.0.
When the ratio (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 is preferably 15.0 or less, more preferably 10.0 or less, and especially 6.0 or less, from the viewpoint of handling properties in the process. Is more preferred.

In order to adjust (a) / (b) to the above-mentioned range in the present copolymerized 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 copolymerization component of A. However, it is not limited to this method.
From this viewpoint, the copolymer component of the copolymer polyester A is preferably such that the “other dicarboxylic acid component” 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%.

<Production method of the present copolymerized polyester film>
As an example of a method for producing the present copolymerized polyester film, a case where the present copolymerized 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, a raw material, for example, a polyester chip is supplied to a melt extruder, heated to a temperature equal to or higher than the melting point of each polymer, and extruded from a die. It is sufficient to solidify by cooling to obtain a non-oriented sheet in a substantially amorphous state.
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 step. 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 is performed at a temperature of 130 to 270 ° C. under tension or relaxation within 30% to obtain the present copolymerized polyester film as a biaxially oriented film.
In the above-mentioned stretching, a method in which stretching in one direction is performed in two or more stages may be adopted.

(4) When the heat-setting treatment (also referred to as “heat treatment”) is a single layer of the copolyester layer (I layer), it is preferably performed at a temperature lower by 10 to 70 ° C. than the melting point of copolyester A.

When the present copolyester film has a laminated structure of a copolyester layer (I layer) and a polyester layer (II layer), the copolyester layer (I layer) and the polyester layer (II layer) are co-extruded, As described above, stretching and heat setting may be performed as an integral film.
In this case, the heat setting 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 perform a heat-setting treatment at a temperature higher than the melting point of the copolyester A. By performing the heat setting treatment at such a temperature, it is possible to soften to a level that cannot be achieved with a single layer of the copolymerized polyester layer (I layer).
This is because, by heat-setting at a temperature lower than the melting point of the polyester C, the stretch orientation of the surface layer is fixed, so that the elongation, strength and heat resistance (heat shrinkability) are improved, while the copolymer polyester A This is because, by heat-setting at a temperature higher than the melting point of the intermediate layer, stretching orientation and distortion of the intermediate layer are alleviated, so that a more flexible film can be obtained.

<Uses of this copolymerized polyester film>
As described above, the present copolymerized polyester film is excellent in flexibility at normal temperature, and is not only flexible, but also characterized by having almost no stiffness, but still having sufficient heat resistance for practical use. Can be demonstrated. Therefore, it can be suitably used, for example, as a constituent member of a battery packaging material, a surface protection film, an image display member, particularly a flexible display, a wearable terminal, or the like.
The application of the present copolymerized polyester film is not limited to the above, and for example, it can be used for various packaging materials, building materials, stationery, automobile members, and other structural members.

<Explanation of terms>
In the present invention, the term “film” includes a “sheet”, and the term “sheet” includes a “film”.
Further, when expressed as a "panel" such as an image display panel or a protection panel, it includes a plate, a sheet, and a film.

In the present invention, when "X to Y" (X and Y are arbitrary numbers) is described, "preferably larger than X" or "preferably Y" together with "X or more and Y or less" unless otherwise specified. The meaning of "smaller" is also included.
Further, when described as “X or more” (X is an arbitrary number), the meaning of “preferably larger than X” is included unless otherwise specified, and described as “Y or less” (Y is an arbitrary number). In this case, the meaning of “preferably smaller than Y” is also included unless otherwise specified.

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

<Evaluation method>
Hereinafter, the measurement and evaluation of various physical properties and the like were performed 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 Measurement Control Co., Ltd., in the width direction (TD) of the copolymerized polyester film (sample), vibration frequency 10 Hz, strain 0.1%. The temperature was measured from -100 ° C. to 200 ° C. at a rate of 1 ° C./min. From the obtained data, the storage elastic 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), the measurement sample was measured by a differential scanning calorimeter (DSC). The temperature is raised from 30 ° C. to 280 ° C. at 10 ° C./min, held for 1 minute, then lowered from 280 ° C. to 30 ° C. at 10 ° C./min, held for 1 minute, and further 10 ° C. from 30 ° C. to 280 ° C. / Min again. 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 copolyester film was used as a measurement sample, and in the case of a lamination, an intermediate layer was used as a measurement sample.

(3) Young's modulus The copolymerized polyester film (sample) obtained in each of Examples and Comparative Examples was adjusted to a temperature of 23 ° C and a humidity of 50% RH using a tensile tester (Intesco Model 2001, manufactured by Intesco Corporation). In a conditioned room, a copolymerized polyester film (sample) having a length of 300 mm and a width of 20 mm was pulled at a strain rate of 10% / min, and was calculated by the following equation using a straight line portion at the beginning of a tensile stress-strain curve.
E = Δσ / Δε
(In the above equation, E is Young's modulus (GPa), Δσ is a stress difference (GPa) due to the original average cross-sectional area between two points of a straight line, and Δε is a strain difference / initial length between the same two points.)

(4) Tensile breaking strength For the copolymerized polyester film (sample) obtained in Examples and Comparative Examples, a tensile tester (manufactured by Intesco Corporation, Intesco Model 2001) was used at a temperature of 23 ° C. and a humidity of 50% RH. In a controlled room, a copolyester film (sample) having a width of 15 mm is set in a tester so that the distance between the chucks is 50 mm, and at a strain rate of 200 mm / min, a longitudinal direction (MD) or a width direction of the film is set. (TD), and the tensile breaking strength was determined by the following equation.
Tensile breaking strength (MPa) = F / A
In the above equation, F is the load (N) at the time of breaking, and A is the original cross-sectional area (mm ² ) of the test piece.

(5) Tensile rupture elongation The same test as the above-described tensile rupture strength was performed, and the tensile rupture elongation was determined by the following formula for the copolymerized polyester films (samples) obtained in Examples and Comparative Examples.
Tensile elongation at break (%) = 100 × (L−L0) / L0
Here, in the above formula, L is the distance between gauge points at break (mm), and L0 is the original distance between gauge points (mm).

(6) Heat shrinkage rate The copolymerized polyester films (samples) obtained in Examples and Comparative Examples were allowed to stand for 5 minutes in an oven maintained at 120 ° C. under no tension, and the lengths of the samples before and after the measurement were measured. The heat shrinkage in each of the longitudinal direction (MD) and the width direction (TD) of the film was calculated by the following equation.
Heat shrinkage (%) = {(L0−L1) / L0} × 100
(In the above formula, L0 is the sample length before the heat treatment, and L1 is the sample length after the heat treatment.)
Five points were measured in the longitudinal direction (MD) and in the width direction (TD) of the film, and an average value was obtained for each of the five points.

(7) Evaluation of flexibility (stiffness) (deflection measurement method)
A sample was prepared by leaving the copolymerized polyester films (samples) obtained in the examples and comparative examples at 23 ° C. and a 50% RH atmosphere for 24 hours, and then cutting them out to a size of 150 mm in length and 50 mm in width.
As shown in FIG. 1, a copolyester film (sample) is placed on a desk in an environment of 23 ° C. so as to protrude 50 mm outside from the end of the desk, and the copolyester on the desk is placed on the desk. A 200 g weight was placed and fixed on the film (sample), and the tip side of the sample protruding from the end of the desk was bent downward by its own weight. Three minutes later, the length (a) of the tip of the sample protruding from the edge of the desk and sagging vertically and hanging down, and the length (b) of the tip protruding horizontally from the edge of the desk are measured. did.
Then, the ratio ((a) / (b)) of the length (a) flexing and hanging down to the length (b) protruding in the horizontal direction is calculated. If it was less than 30, it was evaluated as "fail".

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

Copolyester 1 ("CoPS1"): the acid component is composed of 88 mol% of terephthalic acid, 7 mol% of hydrogenated dimer acid having 36 carbon atoms and 5 mol% of isophthalic acid, and the diol component is composed 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"): the acid component is composed of 88 mol% of terephthalic acid and 12 mol% of hydrogenated dimer acid having 36 carbon atoms, and the diol components are 67 mol% of ethylene glycol and 1,4-butanediol 33. A crystalline copolyester composed of mol% (by-product diethylene glycol of less than 0.1 mol%). Melting point 200 ° C, intrinsic viscosity 0.72 dl / g.

Copolyester 3 (“CoPS3”): a crystalline copolyester in which the acid component is composed of 78 mol% of terephthalic acid and 22 mol% of isophthalic acid, and the diol component is composed of 98 mol% of ethylene glycol and 2 mol% of by-product diethylene glycol. 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]
As a surface layer and an intermediate layer, chips of copolymerized polyester 1 (co-PS1) are fed into a vented extruder set at 280 ° C., extruded from a die of the extruder via a gear pump and a filter, and subjected to an electrostatic application contact method. The mixture was quenched and solidified on a cooling roll having a surface temperature set to 30 ° C. to obtain an unstretched sheet.
Next, after stretching the obtained unstretched sheet 3.3 times at 50 ° C. in the longitudinal direction (MD), it is guided to a tenter, and then stretched 4.2 times at 80 ° C. in the width direction (TD). A heat treatment was performed at 200 ° C. for 10 seconds, and the film was relaxed by 10% in the width direction (TD) to obtain a 25 μm-thick biaxially stretched copolyester film (sample) substantially consisting of a single layer.

[Example 2]
As an intermediate layer, a copolyester 1 (co-PS1) chip was fed into a main vented twin-screw extruder set at 280 ° C.
As the 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, co-extrude in two and three layers (surface layer / intermediate layer / surface layer) so that the polymer from the main extruder becomes the middle layer and the polymer from the sub-extruder becomes the surface layer. The sheet was extruded and quenched and solidified on a cooling roll having a surface temperature set to 30 ° C. using an electrostatic contact method to obtain an unstretched sheet.
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 by 10% in the width direction (TD), and biaxially stretched copolyester having a thickness of 1 μm (surface layer) / 23 μm (intermediate layer) / 1 μm (surface layer) and a thickness of 25 μm A film (sample) was obtained.

[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 as shown in Table 1.
In the table, for example, “PS1 / PET = 80/20” in Example 3 means that 80 parts by weight of PS1 and 20 parts by weight of PET were mixed. Also indicates the mass ratio.

[Comparative Example 1]
A polyester (PET) chip is fed into a vented extruder set at 280 ° C., extruded from a die of the extruder via a gear pump and a filter, and cooled at a surface temperature set at 30 ° C. using an electrostatic application contact method. It was quenched and solidified 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). A heat treatment was performed at 235 ° C. for 10 seconds, and the film was relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolymerized polyester film (sample) having a thickness of 50 μm.

[Comparative Example 2]
A mixture of 85 parts by mass of PS3 chips and 15 parts by mass of PET chips is fed into a vented extruder set at 280 ° C., extruded from a die of the extruder via a gear pump and a filter, and subjected to electrostatic application. Using an adhesion method, the mixture was quenched and solidified on a cooling roll having a surface temperature set at 30 ° C. to obtain an unstretched sheet.
Next, the obtained unstretched sheet is stretched 3.4 times in the longitudinal direction (MD) at 80 ° C., then guided to a tenter, and then stretched 3.9 times in the width direction (TD) at 145 ° C. Heat treatment was performed at 186 ° C. for 10 seconds, and the film was relaxed by 10% in the width direction (TD) to obtain a biaxially stretched copolymerized polyester film (sample) having a thickness of 50 μm.

[Comparative Example 3]
The copolyester 2 (co-PS2) chips are fed into a vented extruder set at 280 ° C., extruded from a die of the extruder via a gear pump and a filter, and the surface temperature is set to 30 ° C. using an electrostatic application contact method. Quenched and solidified on a cooling roll set as described above to obtain an unstretched copolymerized polyester film (sample) having a thickness of 200 μm.

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

When the main component resin of the intermediate layer is a crystalline copolymer polyester 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 the melting point of the copolymer polyester. If so, it was confirmed that the heat treatment (heat setting) temperature after stretching can be further increased and the heat shrinkage can be further suppressed as compared with the case of a single layer consisting of only the intermediate layer.
When the main component resin of the intermediate layer is an amorphous copolymerized polyester, if the polyester as the main component resin of the surface layer is a polyester having a melting point higher than the glass transition point of the copolymerized polyester, It is considered that the heat treatment (thermal fixation) temperature after stretching can be higher than in the case of a single layer consisting of only the intermediate layer, so that the heat shrinkability can be further suppressed.

Claims

A copolymer polyester film having a copolymer polyester layer (I layer) containing copolymer polyester A as a main component resin,
The copolymerized polyester A is a copolymer of terephthalic acid and “other dicarboxylic acid components”, ethylene glycol and “other alcohol components”, and “other dicarboxylic acid components” in the dicarboxylic acid component in the copolymerized polyester. The ratio of the “acid component” is 5 mol% or more and 20 mol% or less, and the ratio of the “other alcohol component” in the alcohol component is 1 mol% or more and less than 25 mol%,
A copolymer polyester film having a storage elastic modulus at 25 ° C. of 2500 MPa or less and a storage elastic modulus at 120 ° C. of 10 MPa or more.
The copolyester film according to claim 1, wherein the copolyester layer (I layer) is a layer containing the copolyester A and a resin B compatible therewith.
The resin B contains one or more polyesters, and the polyester has a ratio of a total content of “other dicarboxylic acid components” to a total content of dicarboxylic acid components of 5 mol% or more and 20 mol% or less. The copolymer polyester film according to claim 1, wherein a ratio of a total content of “other alcohol components” to a total content of alcohol components is 1 mol% or more and less than 25 mol%.
A copolymerized polyester film comprising a copolymerized polyester layer (I layer) containing one or more polyesters,
In all the polyesters contained in the copolymerized polyester layer (I layer), the ratio of the total content of the “other dicarboxylic acid components” to the total content of the 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 having a storage elastic modulus at 25 ° C. of 2500 MPa or less and a storage elastic modulus at 120 ° C. of 10 MPa or more.
(5) The copolyester film according to any one of (1) to (4), wherein the “other dicarboxylic acid component” contains an aliphatic dicarboxylic acid or a dimer acid.
The copolyester film according to any one of claims 1 to 5, wherein the “other dicarboxylic acid component” contains two or more of isophthalic acid, aliphatic dicarboxylic acid, and dimer acid. .
6. The method according to claim 1, wherein the “other dicarboxylic acid component” contains two or more of isophthalic acid, an aliphatic dicarboxylic acid having 20 to 80 carbon atoms, and dimer acid. The polyester film according to 1.
8. The copolymerized polyester film according to claim 1, wherein the “other alcohol component” contains diethylene glycol.
It has 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 the copolymerized polyester layer (I layer),
The polyester C is a polyester having a melting point higher than the melting point of the copolyester A when the copolyester A is crystalline, and a glass of the copolyester A when the copolyester A is amorphous. The copolymerized polyester film according to any one of claims 1 to 8, which is a polyester having a melting point higher than the transition point.
10. The copolyester film according to claim 9, wherein the thickness of each polyester layer (II layer) is 1 to 20% of the thickness of the copolyester layer (I layer).
The copolymerized polyester film according to any one of claims 1 to 10, wherein a loss tangent (tan δ) at 25 ° C is 0.02 or more.
12. The copolymerized polyester film according to claim 1, wherein the total thickness of the film exceeds 20 μm.
A surface protective film using the copolymerized polyester film according to any one of claims 1 to 12.
An optical member using the copolymerized polyester film according to any one of claims 1 to 12.